Saturday, January 13, 2018

2017 in review: Advances in marine mammal paleontology

Well, we’re here again! 2017 was a pretty slow year for this blog, and as I’ve gotten more heavily involved in teaching and museum work I’ve had less free time. Whatever free time I do have ends up being diverted to research and artwork – which I admit I enjoy a tad more. Nevertheless, I’ve got some ideas for future posts, and will attempt to get some of them done. Owing to my decrease in spare time, this year I have elected to just copy the abstracts rather than write out summaries of each article. There are certain articles I have less good things to say about than others, so perhaps it’s best this way.

An iniid fossil (Cetacea, Odontoceti) is reported based on a periotic found in the Codore Formation (late Miocene to middle Pliocene) of northwestern Venezuela. The marine sediments where the Codore dolphin was collected have yielded another cetacean and a diverse elasmobranch fauna. Cladistic analysis indicates a close relationship between the Codore dolphin and the extant Amazon River dolphin (Inia geoffrensis); key characteristics include a large cochlear portion that is dorsoventrally compressed and the extremely small size of the posterior process. High-resolution micro-computed tomography scans were used for the description and analysis of the bony labyrinth endocast. Geometric morphometric analysis of the bony labyrinth endocast places the Codore dolphin as intermediate between the La Plata dolphin (Pontoporia blainvillei) and Inia geoffrensis (principal component 1), but distinctive from both extant species (principal component 2). Comparisons of the depositional environment with cladistically informed reconstructions and inferences based on cochlear and vestibular anatomy suggest that the Codore dolphin had the flexibility to enter marine, brackish, and fluvial environments as some extant cetaceans do today (e.g., Pontoporia blainvillei).

Assessment of archaeocete vertebral function is vital for understanding the land-to-sea transition of cetaceans. Models of swimming evolution propose that some early cetaceans utilized undulation, which would have required significant lumbar flexibility compared to their artiodactyl ancestors. To assess archaeocete lumbar mobility, 14 linear and three angular measurements were collected from lumbar vertebrae of modern dorsostable and dorsomobile mammals. Principal component analyses successfully differentiate dorsostable mammals from dorsomobile mammals based on centrum length, neural spine length and angulation of transverse processes. Lumbar vertebrae of basal archaeocetes (pakicetids, ambulocetids and remingtonocetids) plot among dorsostable mammals, while those of more derived archaeocetes (protocetids and basilosaurids) plot among dorsomobile mammals. This supports the hypothesis that archaeocetes exhibited a trend of increasing lumbar mobility as they adapted to aquatic life. Notably, two modern cetaceans possess lumbar vertebrae that plot among dorsostable mammals. This is consistent with the observation that many modern cetaceans limit vertebral motion to the caudal vertebrae anterior to the fluke. In sum, these results suggest that the lumbar region of cetaceans underwent an increase in mobility during the transition from foot-powered swimming to undulation, followed by a subsequent decrease in mobility as cetaceans began to swim via caudal oscillation.

In 1941, Abel established Balaena belgica based on a series of fused cervical vertebrae and citing other cranial fragments from the late Neogene of the Antwerp harbor (northern Belgium). Later, Plisnier-Ladame & Quinet (1969) added a neurocranium and other skeletal remains from the same area to this species. Recently, the neurocranium was re-assigned to the genus Eubalaena thanks to newer phylogenetic analyses. Here, a new description is provided of materials previously assigned to “Balaena” belgica together with taxonomic revisions. Our work suggests that the cervical complex originally designated as the type of “Balaena” belgica is too poorly preserved to be used as such and is assigned to Balaenidae gen. et sp. indet., thus making “Balaena” belgica a nomen dubium. In addition to the neurocranium, the other remains consist in a fragment of maxilla assigned to Balaenidae gen. et sp. indet. and in a humerus assigned to Eubalaena sp. Discovered in the Kruisschans Sands Member of the Lillo Formation (3.2–2.8 Ma, Piacenzian, Late Pliocene), the neurocranium is designated as the holotype of the new species Eubalaena ianitrix. Our phylogenetic analysis supports a sister-group relationship of Eubalaena ianitrix and Eubalaena glacialis, and helps constraining the ages of origin for balaenid clades. Ecological and phylogenetic data suggest that Eubalaena ianitrix may represent the direct ancestor of Eubalaena glacialis, the latter having evolved through phyletic transformation including body size increase during the temperature decline of the Late Pliocene.

Many odontocete groups have developed enlarged facial crests, although these crests differ in topography, composition and function. The most elaborate crests occur in the South Asian river dolphin (Platanista gangetica), in which they rise dorsally as delicate, pneumatized wings anterior of the facial bones. Their position wrapping around the melon suggests their involvement in sound propagation for echolocation. To better understand the origin of crests in this lineage, we examined facial crests among fossil and living Platanistoidea, including a new taxon, Dilophodelphis fordycei, nov. gen. and sp., described herein, from the Early Miocene Astoria Formation of Oregon, USA. We measured the physical extent and thickness of platanistoid crests, categorized their relative position and used computed tomography scans to examine their internal morphology and relative bone density. Integrating these traits in a phylogenetic context, we determined that the onset of crest elaboration or enlargement and the evolution of crest pneumatization among the platanistoids were separate events, with crest enlargement beginning in the Oligocene. However, we find no evidence for pneumatization until possibly the Early Miocene, although certainly by the Middle Miocene. Such an evolutionary context, including data from the fossil record, should inform modelling efforts that seek to understand the diversity of sound generation morphology in Odontoceti. 

The walrus (Odobenus rosmarus) is a large tusked molluskivore that inhabits the Arctic and is the sole living member of the family Odobenidae. In contrast to the modern walrus, extinct walruses lived in temperate and even subtropical climates as far south as Baja California and Japan in the Pacific, and Florida and Morocco in the Atlantic. Multispecies walrus assemblages are now documented from several localities in the North Pacific, the center of origin for the family. The genus Valenictus is a toothless dense-boned walrus reported from several localities in southern California and Baja California. An isolated astragalus from lower Pliocene (5.33–4.89 Ma, Zanclean correlative) sediments of the Purisima Formation of northern California (Santa Cruz County, California) matches the highly derived morphology of Valenictus chulavistensis, and is identifiable as Valenictus sp. This specimen is the first record of Valenictus from the Purisima Formation and the first from northern California.

Toothed whales (Odontoceti) are adapted for catching prey underwater and possess some of the most derived feeding specializations of all mammals, including the loss of milk teeth (monophyodonty), high tooth count (polydonty), and the loss of discrete tooth classes (homodonty). Many extant odontocetes possess some combination of short, broad rostra, reduced tooth counts, fleshy lips, and enlarged hyoid bones—all adaptations for suction feeding upon fishes and squid. We report a new fossil odontocete from the Oligocene (approx. 30 Ma) of South Carolina (Inermorostrum xenops, gen. et sp. nov.) that possesses adaptations for suction feeding: toothlessness and a shortened rostrum (brevirostry). Enlarged foramina on the rostrum suggest the presence of enlarged lips or perhaps vibrissae. Phylogenetic analysis firmly places Inermorostrum within the Xenorophidae, an early diverging odontocete clade typified by long-snouted, heterodont dolphins. Inermorostrum is the earliest obligate suction feeder within the Odontoceti, a feeding mode that independently evolved several times within the clade. Analysis of macroevolutionary trends in rostral shape indicate stabilizing selection around an optimum rostral shape over the course of odontocete evolution, and a post-Eocene explosion in feeding morphology, heralding the diversity of feeding behaviour among modern Odontoceti.

We report five new specimens of xenorophid dolphins from North and South Carolina. Four of the specimens represent the xenorophid Albertocetus meffordorum, previously only known from the holotype skull. The other is a fragmentary petrosal from the upper Oligocene Belgrade Formation that we refer to Echovenator sp, indicating at least two xenorophids from that unit. Two of the Albertocetus meffordorum specimens are from the lower Oligocene Ashley Formation: 1) a partial skeleton with neurocranium, fragmentary mandible, ribs, vertebrae, and chevrons, and 2) an isolated braincase. The partial vertebral column indicates that Albertocetus retained the ancestral morphology and locomotory capabilities of basilosaurid archaeocetes, toothed mysticetes, and physeteroids, and caudal vertebrae that are as wide as tall suggest that the caudal peduncle, which occurs in all extant Cetacea, was either wide or lacking. CT data from the isolated braincase were used to generate a digital endocast of the cranial cavity. The estimated EQ of this specimen is relatively high for an Oligocene odontocete, and other aspects of the brain, such as its anteroposterior length and relative size of the temporal lobe, are intermediate in morphology between those of extant cetaceans and terrestrial artiodactyls. Ethmoturbinals are also preserved, and are similar in morphology and number to those described for the Miocene odontocete Squalodon. These fossils extend the temporal range of Albertocetus meffordorum into the early Oligocene, its geographic range into South Carolina, and expand our paleobiological understanding of the Xenorophidae.

The Eomysticetidae is an extinct family of early-diverging baleen whales. They are baleen-bearing filter feeders, but some have vestigial teeth. A limited fossil record indicates an acme during the Oligocene and probable worldwide distribution (South Carolina, USA, Japan, New Zealand), but little further regarding distribution and the timing of their origin and extinction. Newly discovered Oligo-Miocene specimens from New Zealand elucidate the biochronology and biogeography of the Eomysticetidae. First, a new specimen of the eomysticetid Waharoa from the upper Otekaike Limestone represents the youngest reliably dated eomysticetid worldwide (upper Waitakian, earliest Miocene). The fossil demonstrates that eomysticetids survived into the earliest Miocene. Second, a specimen from the lower Otekaike Limestone (Duntroonian, late Oligocene) shares unique craniomandibular features with the eomysticetid Yamatocetus, a genus hitherto reported only from Japan, indicating cosmopolitan or antitropical distribution for eomysticetids. Incomplete specimens such as these may elucidate biogeography, faunal change and other aspects of cetacean paleobiology.

Balaenidae (right and bowhead whales) are a key group in understanding baleen whale evolution, because they are the oldest surviving lineage of crown Mysticeti, with a fossil record that dates back 20 million years. However, this record is mostly Pliocene and younger, with most of the Miocene history of the clade remaining practically unknown. The earliest recognized balaenid is the early Miocene Morenocetus parvus Cabrera, 1926 from Argentina. M. parvus was originally briefly described from two incomplete crania, a mandible and some cervical vertebrae collected from the lower Miocene Gaiman Formation of Patagonia. Since then it has not been revised, thus remaining a frequently cited yet enigmatic fossil cetacean with great potential for shedding light on the early history of crown Mysticeti. Here we provide a detailed morphological description of this taxon and revisit its phylogenetic position. The phylogenetic analysis recovered the middle Miocene Peripolocetus as the earliest diverging balaenid, and Morenocetus as the sister taxon of all other balaenids. The analysis of cranial and periotic morphology of Morenocetus suggest that some of the specialized morphological traits of modern balaenids were acquired by the early Miocene and have remained essentially unchanged up to the present. Throughout balaenid evolution, morphological changes in skull arching and ventral displacement of the orbits appear to be coupled and functionally linked to mitigating a reduction of the field of vision. The body length of Morenocetus and other extinct balaenids was estimated and the evolution of body size in Balaenidae was reconstructed. Optimization of body length on our phylogeny of Balaenidae suggests that the primitive condition was a relatively small body length represented by Morenocetus, and that gigantism has been acquired independently at least twice (in Balaena mysticetus and Eubalaena spp.), with the earliest occurrence of this trait in the late Miocene–early Pliocene as represented by Eubalaena shinshuensis.

We report on bite marks incising fossil mammal bones collected from upper Miocene deposits of the Pisco Formation exposed at Aguada de Lomas (southern Peru) and attributed to the giant megatooth shark Carcharocles megalodon. The bitten material includes skull remains referred to small-sized baleen whales as well as fragmentary cetacean and pinniped postcrania. These occurrences, the first in their kind from the Southern Hemisphere, significantly expand the still scarce record of bite marks for C. megalodon; moreover, for the first time a prey (or scavenging item) of C. megalodon is identified at the species level (as Piscobalaena nana, a diminutive member of the extinct mysticete family Cetotheriidae). Due to the fragmentary nature of the studied material, the exact origin of the detected marks (i.e., by scavenging or by active predation) cannot be ascertained. Nevertheless, relying on actualistic observations and size-based considerations, we propose that diminutive mysticetes (e.g., cetotheriids) were some of the target prey of adult C. megalodon, at least along the coast of present-day Peru. C. megalodon is thus here interpreted as an apex predator whose trophic spectrum was focused on relatively small-sized prey. Lastly, we propose a link between the recent collapse of various lineages of diminutive mysticetes (observed around 3 Ma) and the extinction of C. megalodon (occurring around the end of the Pliocene).

Among odontocetes, members of the family Kogiidae (pygmy and dwarf sperm whales) are known as smallsized and in many respects enigmatic relatives of the great sperm whale Physeter macrocephalus. Most of the still scanty fossil record of Kogiidae is represented by isolated skulls and ear bones from Neogene deposits of the Northern Hemisphere, with the significant exception of Scaphokogia, a highly autapomorphic genus from late Miocene deposits of the Pisco Formation exposed along the southerncoast of Peru. Here we report on a new fossil kogiid from Aguada de Lomas, a site where the late Miocene beds of the Pisco Formation are exposed. This specimen consists of an almost complete cranium representing a new taxon of Kogiidae: Koristocetus pescei gen. et sp. nov. Koristocetus mainly differs from extant Kogia spp. by displaying a larger temporal fossa and well-individualized dental alveoli on the upper jaws. Coupled with a relatively elongated rostrum, these characters suggest that Koristocetus retained some degree of raptorial feeding abilities, contrasting with the strong suction feeding specialization seen in Recent kogiids. Our phylogenetic analysis recognizes Koristocetus as the earliest branching member of the subfamily Kogiinae. Interestingly, Koristocetus shared the southern coast of present-day Peru with members of the genus Scaphokogia, whose unique convex rostrum and unusual neurocranial morphology seemingly indicate a peculiar foraging specialization that has still to be understood. In conclusion, Koristocetus evokes a long history of high diversity, morphological disparity, and sympatric habits in fossil kogiids, thus suggesting that our comprehension of the evolutionary history of pygmy and dwarf sperm whales is still far from being exhaustive.

Studies dedicated to palaeoenvironments and taphonomy have made wide use of rare earth elements (REE) contents of fossil bones as proxies. However, the complex diagenetic history of individual specimens combined with intra-bone REE fractionation and the uncertain timing of REE uptake generally prevents the robust interpretation of REE patterns. In this case study we show that combining REE analysis with, on the one hand, histology and microstructural observations and, on the other hand, additional analyses of other trace elements, allows deciphering at least three distinct trace element uptake stages, as well as one leaching event. More than 35 trace elements (including the REE) are analysed using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) within compact rostrum bones of the Miocene-Pliocene beaked whale Globicetus hiberus from deep-sea deposits and a comparable extant specimen (Blainville's beaked whale Mesoplodon densirostris). Comparison of the extinct and the extant bones allows a better quantification of the diagenetic trace element content. This study highlights the crucial role played by diagenetic minerals such as the Fe-Mn oxyhydroxides in the uptake and release of trace elements (Co, Ni, Ti, V, Zr, Hf and Nb) and REE by bones, in response to changes of the diagenetic fluid redox conditions over time. Such changes of the geochemical environment help constraining the post-mortem history of the bone and its interaction with diagenetic fluids. We conclude that the unique interpretation of geochemical proxies within individual fossil bones requires a thorough investigation of each individual specimen.

Thalassocnus is a sloth (Mammalia, Tardigrada) adapted to an aquatic lifestyle. It was first described from the Neogene deposits of the Pisco Formation of Peru, from where most of the specimens come. The genus is represented by five species ranging from the late Miocene to the late Pliocene, occupying successive stratigraphic levels. Morpho-functional studies of the cranial and postcranial skeleton of Thalassocnus have demonstrated the progressive adaptation of these sloths to a marine environment, establishing gradual differences from from the geologically oldest to the youngest species of the genus. The first records of Thalassocnus outside the Pisco Formation have been referred to the Neogene Bahía Inglesa Formation, in northern Chile, where older species were recovered. In this paper, we describe materials from two new Pliocene localities in Chile: the Coquimbo and the Horcón formations, in northern and central Chile, respectively. The Coquimbo Formation material was collected from the Lomas del Sauce locality and consists of a partial skeleton of a single individual. Detailed comparisons of the elements with diagnostic features enabled the referral of this specimen to T. carolomartini. The material from the Horcón Formation was collected from the Playa La Luna locality and consists of an isolated phalanx, which is attributed to one of the species of Thalassocnus younger than T. natans. Thus, we present the first record of younger species of Thalassocnus in Chile and the southernmost occurrence of the genus.

Background: Prophoca and Leptophoca represent the oldest known genera of phocine seals, dating from the latest early to middle Miocene. Originally, Prophoca rousseaui and Prophoca proxima were described based on fragmentary remains from the Miocene of Belgium. However, several researchers contested the union of Prophoca rousseaui and Prophoca proxima into one genus, without providing evidence. The stratigraphic context of Prophoca remained poorly constrained due to the lack of precise data associated with the original specimens collected in the area of Antwerp (north of Belgium).
Methods: Prophoca and Leptophoca are redescribed and their phylogenetic position
among Phocidae is reassessed using PAUP. Dinoflagellate biostratigraphy has been carried out on sediment samples associated with specimens from Prophoca and Leptophoca to elucidate their approximate ages.
Results: Whereas the species Prophoca rousseaui is redescribed, Prophoca proxima is
considered synonymous to Leptophoca lenis, with the proposal of a new combination
Leptophoca proxima (Van Beneden, 1877). Sediment samples from specimens of both
taxa have been dated to the late Langhian–early Serravallian (middle Miocene).
Following a reinvestigation of Leptophoca amphiatlantica, characters from the
original diagnosis are questioned and the specimens of Leptophoca amphiatlantica
are considered Leptophoca cf. L. proxima. In a phylogenetic analysis, Prophoca
rousseaui and Leptophoca proxima constitute early branching stem-phocines.
Discussion: Leptophoca proxima from the North Sea Basin is younger than the oldest
known find of Leptophoca proxima from North America, which does not contradict
the hypothesis that Phocinae originated along the east coast of North America
during the late early Miocene, followed by dispersal to Europe shortly after.
Morphological features of the appendicular skeleton indicate that Prophoca rousseaui
and Leptophoca proxima have archaic locomotory modes, retaining a more prominent use of the fore flipper for aquatic propulsion than extant Phocidae.

Background: Discovered on the southern margin of the North Sea Basin, “Phoca” vitulinoides represents one of the best-known extinct species of Phocidae. However, little attention has been given to the species ever since its original 19th century description. Newly discovered material, including the most complete specimen of fossil Phocidae from the North Sea Basin, prompted the redescription of the species. Also, the type material of “Phoca” vitulinoides is lost.
Methods: “Phoca” vitulinoides is redescribed. Its phylogenetic position among Phocinae is assessed through phylogenetic analysis. Dinoflagellate cyst biostratigraphy is used to determine and reassess the geological age of the species. Myological descriptions of extant taxa are used to infer muscle attachments, and basic comparative anatomy of the gross morphology and biomechanics are applied to reconstruct locomotion.
Results: Detailed redescription of “Phoca” vitulinoides indicates relatively little affinities with the genus Phoca, but rather asks for the establishment of a new genus: Nanophoca gen. nov. Hence, “Phoca” vitulinoides is recombined into Nanophoca vitulinoides. This reassignment is confirmed by the phylogenetic analysis, grouping the genus Nanophoca and other extinct phocine taxa as stem phocines. Biostratigraphy and lithostratigraphy expand the known stratigraphic range of N. vitulinoides from the late Langhian to the late Serravallian. The osteological anatomy of N. vitulinoides indicates a relatively strong development of muscles used for fore flipper propulsion and increased flexibility for the
hind flipper.
Discussion: The extended stratigraphic range of N. vitulinoides into the middle Miocene confirms relatively early diversification of Phocinae in the North Atlantic. Morphological features on the fore- and hindlimb of the species point toward an increased use of the fore flipper and greater flexibility of the hind flipper as compared to extant Phocinae, clearly indicating less derived locomotor strategies in this Miocene phocine species. Estimations of the overall body size indicate that N. vitulinoides is much smaller than Pusa, the smallest extant genus of Phocinae (and Phocidae), and than most extinct phocines.

The sequence stratigraphic framework and a summary of the fossil fauna of the upper Miocene portion of the Pisco Formation exposed along the western side of the Ica River (southern Peru) is presented through a new geological map encompassing an area of about 200 km2 and detailed chronostratigraphic analyses. Extensive field mapping and sedimentological study of outcrop sections have shown that the Pisco Formation is a cyclical sediment unit composed of at least three fining-upward, unconformity-bounded depositional sequences, designated P0, P1, and P2 from oldest to youngest. In the study area, these sequences progressively onlap a composite basal unconformity from southwest to northeast. Integration of biostratigraphic and tephrochronologic age determinations constrains the ages of the three Pisco sequences within the study area. Based on the age of surrounding sediments, a conservative estimate of the age of P0 suggests deposition of these strata between 17.99 ± 0.10 Ma and 9.00 ± 0.02 Ma, whereas diatom biostratigraphy and calculated 40Ar/39Ar ages converge to indicate that strata of the P1 sequence were deposited sometime between 9.5 Ma and 8.9 Ma and that those of the P2 sequence are younger than 8.5 Ma and older than 6.71 ± 0.02 Ma. Our survey for both vertebrate and macro-invertebrate remains in the three sequences confirms the outstanding paleontological value of the Pisco Formation and contributes to depict regional faunal shifts in the fossil assemblage.

Tuscany has a rich Pliocene record of marine megafauna (MM), including mysticetes, odontocetes, sirenians and seals among the mammals, and six orders of sharks among the elasmobranchs. This is reviewed with respect to paleogeography and sequence-stratigraphy in six different basins. Conditions at the ancient seafloor are explored by means of sedimentary facies analysis, taphonomy and multivariate techniques applied to a large quantitative dataset of benthic molluscs. MM is rare or absent in most basins during the Zanclean, except in one basin, and most abundant in Piacenzian deposits in all six basins. MM occurs preferentially in fine-grained, shelfal highstand-deposits of small-scale depositional sequences, or at condensed horizons of the maximum flooding interval. It is rare in shallow marine paleonvironments and nearly absent in bathyal paleosettings. Paleogeographic and paleoecological evidence and a comparison with modern patterns of marine upwelling suggest that a wedge of nutrient-rich waters sustained in the offshore during the Pliocene a high biomass of primary producers and a community of apex consumers and mesopredators, similarly to the modern northwestern Mediterranean Sea, with a species-richness higher than the modern and a more complex trophic structure. The highest MM diversity coincides with the mid-Piacenzian warm period, suggesting that facies control does not obscure a link between climate and diversity. We underline however that not all marine environments were suitable for marine mammal preservation. Buoyant carcasses were preferentially dismembered and destroyed in high-energy shallow waters, with the possible exception of delta front deposits, where sudden sediment input occasionally buried pristine carcasses. We hypothesise that carcasses sunken on the seafloor below the shelf break underwent destruction through the activity of a whale-fall biota of modern type, specialised in the consumption of decomposing tissues, both soft and mineralised. A taphonomic window was left between storm wave base and the shelf break. Here water pressure is high enough to prevent the formation of decomposing gases and the resurfacing of carcasses, while the lack of a specialised whale-fall biota slows down bone degradation with respect to deeper settings. Sedimentation rate was high enough to cover skeletal material before its complete destruction. An estimate of paleobathymetries based on multivariate techniques suggests that the preferential depth for the inclusion of MM in the fossil record was 30–300 m. The results are compared with major Mesozoic and Cenozoic MM records worldwide. Available evidence suggests that the late Neogene radiation of large whales, true ecosystem engineers, and their size increase, triggered the radiation of a bone-eating fauna that hampered, and hampers, MM preservation in the deep sea. Stratigraphic paleobiology and an ecosystem-level approach deliver useful insights to the nature of the fossil record.

Fossil sirenian specimens collected in 1964 by the late R. J. G. Savage's expeditions in north-central Libya are described. They come from early middle Eocene (lower Lutetian, 47.8–43.6 Ma) deposits at the locality of Bu el Haderait and represent a new genus and species, Libysiren sickenbergi. This animal is the largest known protosirenid, and the largest Eocene sirenian known to date (condylobasal length >420 mm). Its dental formula was apparently, with five premolar loci as in all other Eocene sirenians, but the teeth are mostly not preserved. Its postcranial skeleton is unknown except for the atlas, a thoracic vertebra, and rib fragments. Stable isotopes indicate a mostly seagrass diet and a habitat of fully marine salinity. The Protosirenidae presently comprise the genera Protosiren, Ashokia, and Libysiren, with their interrelationships unresolved. Together, they are most parsimoniously regarded as a paraphyletic group basal to both Trichechidae and Dugongidae. However, as more of their morphology and diversity are revealed, they may prove to be more closely allied to the former and may shed crucial light on the still-mysterious origins of the trichechids (manatees).

Extant baleen whales (Cetacea, Mysticeti) are a disparate and species-rich group, but little is known about their fossil record in the northernmost Atlantic Ocean, a region that supports considerable extant cetacean diversity. Iceland's geographical setting, dividing North Atlantic and Arctic waters, renders it ideally situated to shed light on cetacean evolution in this region. However, as a volcanic island, Iceland exhibits very little marine sedimentary exposure, and fossil whales from Iceland older than the late Pleistocene are virtually unknown. Here, we present the first fossil whale found in situ from the Pliocene Tjörnes Formation (c. 4.5 Ma), Iceland's only substantial marine sedimentary outcrop. The specimen is diagnosed as a partial skull from a large right whale (Mysticeti, Balaenidae). This discovery highlights the Tjörnes Formation as a potentially productive fossil vertebrate locality. Additionally, this find indicates that right whales (Eubalaena) and bowhead whales (Balaena) were sympatric, with broadly overlapping latitudinal ranges in the Pliocene, in contrast to the modern latitudinal separation of their living counterparts.

As the largest known vertebrates of all time, mysticetes depend on keratinous sieves called baleen to capture enough small prey to sustain their enormous size [ 1 ]. The origins of baleen are controversial: one hypothesis suggests that teeth were lost during a suction-feeding stage of mysticete evolution and that baleen evolved thereafter [ 2–4 ], whereas another suggests that baleen evolved before teeth were lost [ 5 ]. Here we report a new species of toothed mysticete, Coronodon havensteini, from the Oligocene of South Carolina that is transitional between raptorial archaeocete whales and modern mysticetes. Although the morphology and wear on its anterior teeth indicate that it captured large prey, its broad, imbricated, multi-cusped lower molars frame narrow slots that were likely used for filter feeding. Coronodon havensteini is a basal, if not the most basal, mysticete, and our analysis suggests that it is representative of an initial stage of mysticete evolution in which teeth were functional analogs to baleen. In later lineages, the diastema between teeth increased—in some cases, markedly so [ 6 ]—and may mark a stage at which the balance of the oral fissure shifted from mostly teeth to mostly baleen. When placed in a phylogenetic context, our new taxon indicates that filter feeding was preceded by raptorial feeding and that suction feeding evolved separately within a clade removed from modern baleen whales.

Richard Dehm and colleagues of the Bayerische Staatssammlung für Paläontologie und Geologie in Munich made an important collection of early-to-middle Eocene mammals at Ganda Kas in Pakistan during the winter of 1955/56. The genera and species Ichthyolestes pinfoldi and Gandakasia potens were named from this collection. Both are now recognized as early and primitive archaeocete cetaceans. In addition, Dehm’s group collected 16 complete or partial astragali of archaeocetes that were misidentified as artiodactyls. These bring the total number of archaeocete astragali known from Ganda Kas to 28. They separate clearly into four species distinguished by size: from smallest to largest Ichthyolestes pinfoldi Dehm and Oettingen-Spielberg, Pakicetus attocki (West), Gandakasia potens Dehm and Oettingen-Spielberg, and Ambulocetus natans Thewissen et al. Ganda Kas artiodactyls are smaller and rare in comparison. Ichthyolestes and Pakicetus are pakicetid archaeocetes, Gandakasia is presently indeterminate to family, and Ambulocetus is an ambulocetid. Tooth size and astragalus size are highly correlated, corroborating reference of astragali to the first three archaeocete taxa based on teeth. Multivariate morphometric comparison (Auto3Dgm) shows that pakicetid astragali overlap almost completely in shape with those of early artiodactyls. Middle Eocene protocetid astragali are divergent from both. Retention of an astragalus indistinguishable from that of artiodactyls shows that pakicetids are closely related to artiodactyls phylogenetically, but does not make Ichthyolestes and Pakicetus terrestrial or cursorial. Other skeletal elements and bone microstructure indicate that pakicetids were semiaquatic like later protocetids. Tropical riverine and marginal marine facies of the Kuldana Formation are likely habitats for initial stages of the transition from terrestrial artiodactyls to semiaquatic and fully aquatic archaeocetes.

The late Miocene Pisco Formation of Peru is an outstanding example of richness and high-quality preservation of fossil marine vertebrates. In order to reconstruct the fossilization path, we present new textural, mineralogical and Sr-isotope data of diagenetic minerals formed in correspondence of fossil specimens such as marine vertebrates and mollusks. These fossil specimens were found at Cerro los Quesos, in the Ica Desert, within the diatomaceous strata of the Pisco Formation. Dolomite, gypsum, anhydrite and Mn minerals are the main phases found, while the calcium carbonate originally forming the mollusk valves is replaced by gypsum. An early formation of dolomite and of Mn minerals, triggered by the modifications of the geochemical environment due to organic matter degradation, is suggested by the textural relationships and is confirmed by the Sr isotopic ratio of dolomite, which agrees with that of seawater at the time of sedimentation. Instead, gypsum Sr isotopic ratios indicate a pre-Miocene seawater-derived brine circulating within the sedimentary sequence as a source for Sr. Oxidation of diagenetic sulfide causing a lowering of the pH of porewater is proposed as an explanation for Ca-carbonate dissolution. The diagenetic chemical environment was, nevertheless, favorable to bone preservation.

On the basis of an assigned specimen (USNM 526604, from the Plum Point Member of the Calvert Formation, Early Miocene, Maryland, U.S.A.), Araeodelphis natator Kellogg, 1957, is referred to the Platanistidae. A phylogenetic analysis identifies A. natator as the most stemward member of the family. By contrast, the extant river dolphin, Platanista gangetica (Platanistidae), is one of the most specialized odontocetes. Araeodelphis natator exhibits the following unique combination of characters: overall skull length (condylobasal length) estimated at about 50 cm; rostrum twice the length of the facial region; rostrum wider than deep throughout its entire length; approximately 50 teeth in each quadrant of rostrum; mesorostral canal closed dorsally through anterior half of rostrum by apposition of contralateral premaxillae; cranium with elevated orbits directed anterolaterally; maxillary crest (supraorbital process of frontal and overlapping maxilla) modestly thickened laterally and elevated above midline of skull; non-pneumatized supraorbital eminences; lobe of the pterygoid air-sac sinus occupying orbital surface of frontal; zygomatic process compressed transversely; no postglenoid process; and glenoid facet faces medially. Araeodelphis provides new data about the definition and phylogenetic relationships of platanistids with other platanistoids, confirming the sister-group relationship with the extinct squalodelphinids and the ancestral platanistid skull morphology preceding the platanistine-pomatodelphinine split.

The Carmel Church Quarry fossil site in central Virginia has yielded thousands of vertebrate fossils over more than two decades of excavations conducted by the Virginia Museum of Natural History. The exposure of marine sediment here includes a highly fossiliferous bone bed within the Calvert Formation. Unlike most fossil finds from this formation along the Potomac River, the majority of fossils collected are from in situ deposits. The exposed section at Carmel Church includes Paleocene to Pliocene sediment, with vertebrate fossils also having been recovered from the Eocene Nanjemoy Formation. Common fossil finds within the Calvert Formation are typically isolated shark teeth, especially of Isurus (mako sharks) and Carcharhinus (requiem sharks). However, many large teeth of Carcharocles megalodon have been found as well. The ancient shallow sea ecosystem also supported a diversity of bony fish, reptiles, birds, and marine mammals. Carmel Church is the type locality for the mysticete (baleen) whale, Eobalaenoptera harrisoni, and has produced numerous other cetacean taxa. In addition, 28 species of diatoms have been identified from the site, further correlating the fossiliferous zone of the Calvert Formation to Bed 15 of other localities. The Carmel Church site also has one of the richest land mammal faunas of the Calvert Formation, particularly for the upper section, including fossil horses, tapirs, and peccaries. Despite intense excavations over many years, the site is still producing a large volume of fossil material, allowing participants the opportunity to help contribute to new discoveries from this fascinating locality.

Baja California Sur has an import­ant Cenozoic marine fossil record which includes diverse but poorly known Oligocene cetaceans from Mexico. Here we review the cetacean fossil record including new observa­tions from materials that elucidate the evolution of the Neoceti in the Pacific basin. Fossils were collected from outcrops of the El Cien For­mation (Oligocene-Early Miocene) and from San Gregorio Formation (Late Oligocene). The specimens be­long to the paleontological collection of Museo de Historia Natural de la Universidad Autónoma de Baja Cali­fornia Sur. An estimated 26 unnamed species include toothed cetaceans: possible “archaeocetes” (?Kekeno­dontidae); archaic Odontoceti; and the basal group Aetiocetidae, toothed mysticetes (Mysticeti). Toothless mys­ticetes (Chaeomysticeti) include the basal group Eomysticetidae, and ba­laenopterids-like forms. The Oligo­cene cetaceans from Baja California Sur, Mexico are diverse and represent the most southern such assemblages known from North America.

The origin of baleen whales (Mysticeti), the largest animals on Earth, is closely tied to their signature filter-feeding strategy. Unlike their modern relatives, archaic whales possessed a well-developed, heterodont adult dentition. How these teeth were used, and what role their function and subsequent loss played in the emergence of filter feeding, is an enduring mystery. In particular, it has been suggested that elaborate tooth crowns may have enabled stem mysticetes to filter with their postcanine teeth in a manner analogous to living crabeater and leopard seals, thereby facilitating the transition to baleen-assisted filtering. Here we show that the teeth of archaic mysticetes are as sharp as those of terrestrial carnivorans, raptorial pinnipeds and archaeocetes, and thus were capable of capturing and processing prey. By contrast, the postcanine teeth of leopard and crabeater seals are markedly blunter, and clearly unsuited to raptorial feeding. Our results suggest that mysticetes never passed through a tooth-based filtration phase, and that the use of teeth and baleen in early whales was not functionally connected. Continued selection for tooth sharpness in archaic mysticetes is best explained by a feeding strategy that included both biting and suction, similar to that of most living pinnipeds and, probably, early toothed whales (Odontoceti).

The family Eschrichtiidae is presently only represented by Eschrichtius robustus, a relict species from the North Pacific. Because of the scarcity of fossil records of the Eschrichtiidae, their evolutionary history is not well understood. A finely preserved mysticete skeleton was recovered from the Lower Pleistocene (1.77–1.95 Ma) of Tokyo, Japan, in 1961. The fossil consists of a cranium, mandibles, cervical, thoracic, lumbar and caudal vertebrae, chevrons, ribs, and forelimb bones, including scapula, humerus, radius, ulna and digit bones. Here, we describe and diagnose this fossil as a new species of the Eschrichtiidae, Eschrichtius akishimaensis sp. nov. This is the first fossil species of the genus Eschrichtius and suggests that at least two lineages represented by the modern species of Eschrichtius and the new species described here survived as late as the Early Pleistocene. This expands our knowledge of the paleodiversity of the eschrichtiids.

[No abstract] Despite extensive knowledge about the distribution of pachyosteosclerosis (increased bone volume and density) among some modern groups of marine mammals, this aquatic adaptation is not well known in Phocidae (true seals). Pachyosteosclerotic bones reduce buoyancy and permit easier submergence for some marine mammals. Pachyostosis and osteosclerosis are two vastly different bone adaptations, which have co-occurred independently (termed pachyosteosclerosis). Pachyostosis describes the thickening of bone in cross-sectional area, whereas osteosclerosis is the replacement of cancellous bone with compact bone. Osteosclerosis, pachyostosis, and bone lightening consecutively occurred to various degrees as adaptations of marine mammals to different environmental niches and lifestyles.

Although combined molecular and morphological analyses point to a late middle Eocene (38–39 million years ago) origin for the clade Neoceti (Odontoceti, echolocating toothed whales plus Mysticeti, baleen whales, and relatives), the oldest known mysticete fossil dates from the latest Eocene (about 34 million years ago) of Antarctica [1, 2]. Considering that the latter is not the most stemward mysticete in recent phylogenies and that Oligocene toothed mysticetes display a broad morphological disparity most likely corresponding to contrasted ecological niches, the origin of mysticetes from a basilosaurid ancestor and its drivers are currently poorly understood [1, 3–8]. Based on an articulated cetacean skeleton from the early late Eocene (Priabonian, around 36.4 million years ago) of the Pisco Basin, Peru, we describe a new archaic tooth-bearing mysticete, Mystacodon selenensis gen. et sp. nov. Being the geologically oldest neocete (crown group cetacean) and the earliest mysticete to branch off described so far, the new taxon is interpreted as morphologically intermediate between basilosaurids and later toothed mysticetes, providing thus crucial information about the anatomy of the skull, forelimb, and innominate at these critical initial stages of mysticete evolution. Major changes in the morphology of the oral apparatus (including tooth wear) and flipper compared to basilosaurids suggest that suction and possibly benthic feeding represented key, early ecological traits accompanying the emergence of modern filter-feeding baleen whales’ ancestors.

A key step in the evolutionary history of Odontoceti (echolocating toothed cetaceans) is the transition from the ancestral heterodont condition – characterized by the presence of double-rooted cheek teeth bearing accessory denticles – to the homodont dentition displayed by most extant odontocete species. During the last few decades, new finds and the reassessment of specimens in collections revealed an increased morphological disparity amongst the Oligo–Miocene heterodont odontocetes. Based on a partly articulated skeleton from late Early Miocene (Burdigalian, 18.8–18.0 Ma) beds of the Chilcatay Formation (Pisco Basin, Peru), we describe a new genus and species of heterodont odontocete, Inticetus vertizi, in the new family Inticetidae. This large dolphin is characterized by, amongst other things, a long and robust rostrum bearing at least 18 teeth per quadrant; the absence of procumbent anterior teeth; many large, broad-based accessory denticles in double-rooted posterior cheek teeth; a reduced ornament of dental crowns; the styliform process of the jugal being markedly robust; a large fovea epitubaria on the periotic, with a correspondingly voluminous accessory ossicle of the tympanic bulla; and a shortened tuberculum of the malleus. Phylogenetic analyses (with and without molecular constraint; with and without down-weighting of homoplastic characters) yielded contrasting results, with Inticetus falling either as a stem Odontoceti or as an early branching member of a large Platanistoidea clade. With its large size, robust rostrum and unusual dental morphology, and the absence of conspicuous tooth wear, Inticetus increases the morphological and ecological disparity of Late Oligocene–Early Miocene heterodont odontocetes. Finally, this new taxon calls for caution when attempting to identify isolated cetacean cheek teeth, even at the suborder level.

In this paper we describe Brujadelphis ankylorostris gen. nov., sp. nov., a new delphinidan (Cetacea, Odontoceti, Delphinida), based on a well-preserved skull with ear bones, associated mandibles, most of the teeth in situ and a fragment of the atlas, from the late middle to early late Miocene (Serravallian to early Tortonian) of the Pisco Formation, Pisco Basin, Peru. The new taxon differs from all other delphinidans in the following unique combination of character states: partial ankylosis of the thickened premaxillae above the mesorostral groove; presence of premaxillary eminences; premaxilla does not contact nasal; inflated nasals with a transversely convex dorsal surface; presence of an internasal fossa; and a longitudinal crest on the vertex formed by transversely pinched frontals. Our cladistic analyses of a supermatrix that includes molecular and morphological data identifies B. ankylorostris as an inioid (Iniidae + Pontoporiidae) that is more closely related to Inia than to Pontoporia. This result persists even if a molecular scaffold based on published Bayesian analyses is used. The inclusion of a large sample (12 taxa) of ‘kentriodontids’ allows us to confirm the paraphyly of this group of archaic Miocene delphinidans but contradicts the prevailing views in placing all of these taxa outside of Delphinoidea (Delphinidae + Monodontidae + Phocoenidae). In our unconstrained analysis ‘kentriodontids’ are split into five separate clades that occur along the stem of Inioidea + Delphinoidea. Based on our most parsimonious trees, we discuss published calibration points for molecular divergence estimates within Odontoceti and propose one new point: 18 Ma for an unnamed clade including Delphinida + Ziphiidae.

Cynthiacetus peruvianus Martínez-Cáceres & Muizon, 2011 is a Dorudon-like basilosaurid (Cetacea, Basilosauridae), being one of the largest members of the family. The holotype of this species is a sub-complete skeleton, which comes from the late Eocene (Priabonian) of the Otuma Formation on the southern coast of Peru. A thorough description of this specimen is presented here. Cynthiacetus peruvianus differs from the other species of the genus (C. maxwelli) in having fewer accessory cusps on the distal and mesial edges of p3 and p4. Its skull shows the general pattern of the basilosaurid skull, which is relatively monotonous across the whole family, but it is much larger than those of Dorudon and Zygorhiza, and slightly smaller and distinctly more slender than that of Basilosaurus. The most characteristic features of C. peruvianus stand on the postcranial skeleton: it presents large vertebrarterial foramina on the cervical vertebrae; it lacks a ventral expansion of the transverse processes of C3-C5; it presents the greatest number of thoracic vertebrae (20) observed in cetaceans; and its first thoracics have an almost vertical neural spine. The second part of the monograph is devoted to evolutionary trends and phylogenetic relationships of Archaeocetes with a special focus on Basilosauridae. Some of the major trends considered concern, the rostrum morphology, the asymmetry of the rostrum, the supraorbital region, the neurocranium, the pelvic girdle and hind limb, and the chevrons. A parsimony analysis confirms the monophyly of the Basilosauridae, which are supported by four unambiguous synapomorphies: the presence of well-defined embrasure pits between the upper incisors, a narrow palate anterior to P4, a cleft on the mesial edge of the lower molars, and more than 13 thoracic vertebrae. In contrast with previous hypotheses, in which Saghacetus was the sister taxon of the Pelagiceti, the results of our analysis reveal this taxon as the most basal basilosaurid. In all the analyses performed Cynthiacetus forms a clade with Dorudon and Basilosaurus, being almost constantly the sister taxon of Basilosaurus.

Baleen is a comb-like structure that enables mysticete whales to bulk feed on vast quantities of small prey, and ultimately allowed them to become the largest animals on Earth. Because baleen rarely fossilises, extremely little is known about its evolution, structure and function outside the living families. Here we describe, for the first time, the exceptionally preserved baleen apparatus of an entirely extinct mysticete morphotype: the Late Miocene cetotheriid, Piscobalaena nana, from the Pisco Formation of Peru. The baleen plates of P. nana are closely spaced and built around relatively dense, fine tubules, as in the enigmatic pygmy right whale, Caperea marginata. Phosphatisation of the intertubular horn, but not the tubules themselves, suggests in vivo intertubular calcification. The size of the rack matches the distribution of nutrient foramina on the palate, and implies the presence of an unusually large subrostral gap. Overall, the baleen morphology of Piscobalaena likely reflects the interacting effects of size, function and phylogeny, and reveals a previously unknown degree of complexity in modern mysticete feeding evolution.

Cetotheriidae are an iconic, nearly extinct family of baleen whales (Mysticeti) with a highly distinct cranial morphology. Their origins remain a mystery, with even the most archaic species showing a variety of characteristic features. Here, we describe a new species of archaic cetotheriid, Tiucetus rosae, from the Miocene of Peru. The new material represents the first mysticete from the poorly explored lowest portion of the highly fossiliferous Pisco Formation (allomember P0), and appears to form part of a more archaic assemblage than observed at the well-known localities of Cerro Colorado, Cerro los Quesos, Sud-Sacaco and Aguada de Lomas. Tiucetus resembles basal plicogulans (crown Mysticeti excluding right whales), such as Diorocetus and Parietobalaena, but shares with cetotheriids a distinct morphology of the auditory region, including the presence of an enlarged paroccipital concavity. The distinctive morphology of Tiucetus firmly places Cetotheriidae in the context of the poorly understood ‘cetotheres’ sensu lato, and helps to resolve basal relationships within crown Mysticeti.

Desmostylus and Paleoparadoxia are extinct marine mammals belonging to the order Desmostylia that existed in the period between the late Oligocene and middle Miocene. All occurrences of their fossils are limited to marine strata along the coasts of the North Pacific Ocean. Although these two genera have similar body form, their paleoecologies including habitat preferences are thought to be different because their cranial structures are distinctive as well as they have been known separately in different localities. We estimated the depositional depths of their fossil occurrences on the basis of the associated mollusks and benthic foraminiferal assemblages from 45 desmostylian localities. Only data on complete or partial skeletal specimens were considered in order to exclude cases of reworking and pre-burial drift of carcasses that would confound our inference.
Our results indicate that the depositional environment of Desmostylus specimens was restricted to the inner sublittoral zone shallower than 30 m in depth whereas that of Paleoparadoxia specimens ranged from the inner sublittoral (0–50 m) to upper bathyal zone (between 150 and 400 and 500 m). This finding indicates that Desmostylus lived in nearshore water while Paleoparadoxia foraged in a relatively deep, offshore water. The depositional segregation of these two genera most likely reflects their different habitat preferences.

Desmostylia is a clade of marine mammals belonging to either Tethytheria or Perissodactyla. Rich fossil records of Desmostylia were found in the Oligocene to Miocene strata of the Northern Pacific Rim, especially in the northwestern region, which includes the Japanese archipelago. Fossils in many shapes and forms, including whole or partial skeletons, skulls, teeth, and fragmentary bones have been discovered from this region. Despite the prevalent availability of fossil records, detailed taxonomic identification based on fragmentary postcranial materials has been difficult owing to to our limited knowledge of the postcranial diagnostic features of many desmostylian taxa. In this study, I propose the utilization of diagnostic characters found in the humerus to identify desmostylian genus. These characters can be used to identify isolated desmostylian humeri at the genus level, contributing to a better understanding of the stratigraphic and geographic distributions of each genus.

The late Palaeogene represents a crucial time in cetacean evolution that witnessed the origin of modern baleen and toothed whales (Neoceti) from their “archaeocete” ancestors. So far, this fundamental transition has been discussed mainly in terms of cranial morphology, whereas descriptions of postcranial material remain rare. Here, we report a small cetacean humerus from the Nichinan Group (lower Oligocene to lower Miocene),
Kushima City, Miyazaki Prefecture, southern Kyushu, Japan. Our specimen resembles archaeocete humeri in being proximodistally elongate and in retaining a distinct deltoid ridge, but shares with neocetes the defining feature of an immobilised elbow joint. It resembles most Oligocene odontocetes in its small size and in lacking a notch marking the position of the distal epiphysis, and is furthermore similar to the enigmatic Microzeuglodon in having a transversely compressed shaft. A morphometric analysis based on five linear measurements, however, fails to cluster our specimen with any other known group of cetaceans, indicating that it is not easily referable to either basal mysticetes or odontocetes. Therefore, we here classify it as Neoceti incertae sedis.

Mysticeti (baleen whales) and Odontoceti (toothed whales) today greatly differ in their hearing abilities: Mysticeti are presumed to be sensitive to infrasonic noises [ 1–3 ], whereas Odontoceti are sensitive to ultrasonic sounds [ 4–6 ]. Two competing hypotheses exist regarding the attainment of hearing abilities in modern whales: ancestral low-frequency sensitivity [ 7–13 ] or ancestral high-frequency sensitivity [ 14, 15 ]. The significance of these evolutionary scenarios is limited by the undersampling of both early-diverging cetaceans (archaeocetes) and terrestrial hoofed relatives of cetaceans (non-cetacean artiodactyls). Here, we document for the first time the bony labyrinth, the hollow cavity housing the hearing organ, of two species of protocetid whales from Lutetian deposits (ca. 46–43 Ma) of Kpogamé, Togo. These archaeocete cetaceans, which are transitional between terrestrial and aquatic forms, prove to be a key for determining the hearing abilities of early whales. We propose a new evolutionary picture for the early stages of this history, based on qualitative and quantitative studies of the cochlear morphology of an unparalleled sample of extant and extinct land artiodactyls and cetaceans. Contrary to the hypothesis that archaeocetes have been more sensitive to high-frequency sounds than their terrestrial ancestors [ 15 ], we demonstrate that early cetaceans presented a cochlear functional pattern close to that of their terrestrial relatives, and that specialization for infrasonic or ultrasonic hearing in Mysticeti or Odontoceti, respectively, instead only occurred in fully aquatic whales, after the emergence of Neoceti (Mysticeti+Odontoceti).

Extant cetaceans are fully aquatic mammals with deep modifications of their sensory organs, notably of the sound perception pathway. Early diverging cetaceans, known as archaeocetes, show a diversity of morphologies of the petrotympanic complex and middle ear ossicles, documenting a variety of sound transmission mechanisms from a mostly terrestrial configuration to a fully aquatic layout. Protocetids are a paraphyletic assemblage of semi-aquatic archaeocetes known from the Eocene. The auditory region of these ‘transitional’ forms is only partly known. The middle Eocene locality of Kpogamé, Togo (46–43 Ma) has yielded abundant material of protocetid whales documenting the auditory region, including isolated bullae, one petrosal and a skull fragment preserving the petrotympanic complex. Detailed study of this material leads us to reassess the original taxonomic attribution of this material, first attributed to Togocetus traversei, and to recognize three different protocetid taxa on the basis of bullar and petrosal remains: ?Carolinacetus sp., Togocetus traversei and Protocetidae indeterminate (morphotype γ). Associating isolated petrosals or bullae with dental remains solely based on size criteria can be misleading and we show here that there is no correlation between the size of tympanic bulla and size of dental remains in protocetids. CT-scan investigation of the in situ petrotympanic complex reveals that Protocetidae retained a complete tympanic ring similar to that of terrestrial artiodactyls and that the involucrum could probably articulate with the medial side of the ventral surface of the petrosal. This bulla/petrosal articulation is absent in fully aquatic cetaceans. Finally, the close phylogenetic relationships between protocetids from Kpogamé and North American protocetids suggest successive dispersals of these non-fully aquatic archaeocetes from African coasts to North America.

The pygmy right whale, Caperea marginata, is the least understood extant baleen whale (Cetacea, Mysticeti). Knowledge on its basic anatomy, ecology, and fossil record is limited, even though its singular position outside both balaenids (right whales) and balaenopteroids (rorquals + grey whales) gives Caperea a pivotal role in mysticete evolution. Recent investigations of the cetacean cochlea have provided new insights into sensory capabilities and phylogeny. Here, we extend this advance to Caperea by describing, for the first time, the inner ear of this enigmatic species. The cochlea is large and appears to be sensitive to low-frequency sounds, but its hearing limit is relatively high. The presence of a well-developed tympanal recess links Caperea with cetotheriids and balaenopteroids, rather than balaenids, contrary to the traditional morphological view of a close Caperea-balaenid relationship. Nevertheless, a broader sample of the cetotheriid Herpetocetus demonstrates that the presence of a tympanal recess can be variable at the specific and possibly even the intraspecific level.

Living baleen whales (mysticetes) produce and hear the lowest-frequency (infrasonic) sounds among mammals. There is currently debate over whether the ancestor of crown cetaceans (Neoceti) was able to detect low frequencies. However, the lack of information on the most archaic fossil mysticetes has prevented us from determining the earliest evolution of their extreme acoustic biology. Here, we report the first anatomical analyses and frequency range estimation of the inner ear in Oligocene (34–23 Ma) fossils of archaic toothed mysticetes from Australia and the USA. The cochlear anatomy of these small fossil mysticetes resembles basilosaurid archaeocetes, but is also similar to that of today's baleen whales, indicating that even the earliest mysticetes detected low-frequency sounds, and lacked ultrasonic hearing and echolocation. This suggests that, in contrast to recent research, the plesiomorphic hearing condition for Neoceti was low frequency, which was retained by toothed mysticetes, and the high-frequency hearing of odontocetes is derived. Therefore, the low-frequency hearing of baleen whales has remained relatively unchanged over the last approximately 34 Myr, being present before the evolution of other signature mysticete traits, including filter feeding, baleen and giant body size.

Baleen whales, or mysticetes, include the largest vertebrates to have ever evolved. Their gigantism, evolutionary success, and ecological diversity have been linked to filter feeding. Mysticetes filter feed using elaborate keratinous baleen plates, which grow from the palate and allow them to strain large quantities of prey out of the water. While the earliest mysticetes retained the adult, mineralized teeth present in ancestral whales, all species of living baleen whales lack teeth and instead possess baleen. The mechanism by which this evolutionary transformation took place remains unknown. We present four independent, but non-exclusive hypotheses for the origin of baleen. We evaluate the support for these hypotheses based on separate lines of evidence, including paleontological, molecular, and ontogenetic data. We suggest that the origin of baleen is decoupled from the loss of teeth, with a separate morphological and genetic basis. Moreover, we outline how new fossils and phylogenetic analyses may resolve current debates about morphological transformations in tooth loss and baleen origin across the phylogeny of stem and crown Mysticeti. Additional insights will likely arise from more detailed examination of developmental and biomechanical data, with sufficient ontogenetic and phylogenetic sampling.

Background. The family Pontoporiidae (Cetacea, Odontoceti, Inioidea) is currentlyrepresented in our oceans by just one species of diminutive dolphin (Pontoporia blainvillei, franciscana). Although P. blainvillei is limited to coastal waters of the SouthAtlantic along Brazil, Uruguay and Argentina, multiple Miocene and Pliocene fossilsindicate the past presence of members of the family in the South Atlantic, South Paciifcand North Atlantic oceans. Our comprehension of the origin and diversity of this cladeand of the relationships of its members with other inioids is hampered by the fact thatpart of the described fossil specimens, especially from the North Atlantic realm, are cranial fragments often associated to limited stratigraphic information. Methods. Based on an almost complete fossil cranium of pontoporiid from the Westerschelde estuary, The Netherlands, whose preservation allows for detailed morphological observations, we describe a new genus and species. The latter is compared to other pontoporiids, as well as a few non-pontoporiid inioids. A phylogenetic analysis is performed to investigate the relationship of S. vandokkumi with the best-known extinct and extant inioids. Palynological analysis of the sediment associated to the holotype is used to assess its geological age. Results and discussion. The new genus and species Scaldiporia vandokkumi is
characterized among others by greatly thickened premaxillary eminences reaching the level of the antorbital notch. Palynologically dated from the late Tortonian-earliest Zanclean (7.6-5 Ma, Late Miocene_earliest Pliocene), this new pontoporiid confirmsthe surprising past diversity of marine inioids in the North Atlantic area. Finally the   content of the pontoporiid subfamily Brachydelphininae is briefly discussed.

The Pleistocene sea lion Proterozetes ulysses belongs to a monophyletic group of North Pacific otariids that includes the living genera Eumetopias and Zalophus. Mandibles of Proterozetes from the Port Orford Formation of Oregon are described and found to be intermediate in morphology and size to the other North Pacific otariids, most resembling Eumetopias. Among other characters, the presence of an oblong lingual prominence on the anterior lingual surface of the mandible links the taxon to Eumetopias, which commonly expresses the same feature. Uniquely among North Pacific otariids, Proterozetes possesses a p1 alveolus distinctly smaller than that of the p2. The presence of a distinct but morphologically intermediate taxon in the eastern North Pacific during the Pleistocene establishes it as a time of increased otariid diversity, in contrast to a suggested decline in other marine mammal clades. The timing of sea lion diversification along the west coast of North America appears to follow diversification in Japan, reinforcing the possibility of an eastward dispersal trend in the North Pacific after the end-Pliocene.

The early pinnipedimorph Enaliarctos was a marine-adapted carnivore with dental and locomotor features intermediate between terrestrial arctoids and living pinnipeds. New specimens of Enaliarctos are described from Oligocene and Miocene deposits on the Pacific coast of North America, and include the oldest enaliarctine mandible (Yaquina Formation, 30.6–27.4 Ma), the first enaliarctine from Northern California (Skooner Gulch Formation, 23.8–22 Ma), and the stratigraphically youngest fossil of the genus (Astoria Formation, 17.3–16.6 Ma). The wide biogeographic and temporal range of Enaliarctos provided the potential for interaction or competition with plotopterid birds, odontocete whales, and crown pinnipeds such as early odobenids, early otariids, and desmatophocids. The expansion of the known ranges of Enaliarctos species and the description of additional morphology, particularly of the mandible and lower dentition, provides insight into the origins of pinniped diversity and their possible interactions with other early Neogene coastal marine organisms.

The Family Phocidae includes four subfamilies (Phocinae, Monachinae, Cystophorinae, and Devinophocinae) consisting of mediumto large-sized mammals that possess distinctive adaptations to semi-aquatic life. In the Miocene of the Chesapeake Group, only two subfamilies of the Family Phocidae were identified: Phocinae and Monachinae. Leptophoca, a representative of the subfamily Phocinae, appears on the eastern shore of the North Atlantic around 16 million years ago. Recently, two new monachine species, the larger Terranectes magnus (n. gen., n. sp.) and the medium-sized T. parvus (n. sp.), were recorded in the Upper Miocene of the Chesapeake Group in the Eastover Formation (7.0–6.0 Ma) and St. Marys Formation (10.0-8.0 Ma). These two distinct subfamilies of seals indicate a well-marked divergence between phocines and monachines, much earlier than 18 million years ago, as previously suggested. The Eastover Formation was deposited in a shallow embayment that covered southern Maryland, the coastal plain of Virginia, and the northeastern corner of North Carolina. The geologically older St. Marys Formation represents a tide-influenced coastal environment, with low-salinity estuaries. There was a sharp temperature decrease in the Late Miocene, indicated by a shift to a cooler-water fish fauna during St. Marys time. The Eastover Formation reflects warmer waters with relatively strong currents, significant shoals, barriers, and varied depths. Fossil evidence of earlier seals suggests that phocids originated in the North Atlantic and otarioids in the North Pacific. True seals diverged from ancient Carnivora in the early Oligocene (or earlier) in the Paratethyan / Mediterranean Basins, spread widely during the Middle Miocene and crossed westward across the Atlantic Ocean, before dispersing in the eastern United States by the Early Pliocene.

Two large sperm whale teeth were found offshore from Breskens in the Westerschelde estuary. Comparison shows they share features with the teeth of the stem physteroid Zygophyseter, described from the Late Miocene of southern Italy. Both teeth are however significantly larger than the teeth of the Zygophyseter type material, yet still somewhat smaller than the teeth of the giant raptorial sperm whale Livyatan melvillei, and confirm the presence of so far undescribed giant macroraptorial sperm whales in the Late Miocene of The Netherlands.

A new small probable Oligocene dolphin from Ecuador represents a new genus and species, Urkudelphis chawpipacha. The new taxon is known from a single juvenile skull and earbones; it differs from other archaic dolphins in features including widely exposed frontals at the vertex, a dorsally wide open vomer at the mesorostral groove, and a strongly projected and pointed lateral tuberosity of the periotic. Phylogenetic analysis places it toward the base of the largely-extinct clade Platanistoidea. The fossil is one of a few records of tropical fossil dolphins.

[no abstract] Balaenoptera, including the world’s largest animal—the blue whale (Balaenoptera musculus)—is the most diverse genus of baleen whale (Cetacea, Mysticeti). There are at least seven extant species (B. musculus, B. physalus, B. borealis, B. brydei/edeni complex, B. omurai, B. acutorostrata, and B. bonaerensis); the number of recognized species varies between different taxonomic schemes (e.g., Rice, 1998; Wilson and Mittermeier, 2014). Of note, B. omurai was only recently discovered and named (Wada et al., 2003), highlighting the limited understanding of diversity, phylogenetic relationships, and evolution of extant Balaenoptera. Some fossil species of Balaenoptera have been named, for example, B. siberi Pilleri, 1989, and B. bertae Boessenecker, 2013a (also see Dem_er_e, 1986, and Dem_er_e et al., 2005, for a review of balaenopterids), but it remains unknown whether there are any ancestor-descendant relationships between fossil and living Balaenoptera. Given its phylogenetic position, the extinct species Balaenoptera bertae may represent an ancestral minke whale (e.g., Marx and Fordyce, 2015:fig. 2; also see Tsai and Fordyce, 2015a, for recognizing ancestral species), and B. siberi is deeply nested within the genus Balaenoptera (Marx and Fordyce, 2015; Boessenecker and Fordyce, 2016). However, the phylogenetic relationships among extinct and extant Balaenopteridae remain uncertain in published cladistic analyses (e.g., Marx and Fordyce, 2015; Boessenecker and Fordyce, 2016).

The pygmy right whale, Caperea marginata, is the most enigmatic living whale. Little is known about its ecology and behaviour, but unusual specialisations of visual pigments [1] , mitochondrial tRNAs [2] , and postcranial anatomy [3] suggest a lifestyle different from that of other extant whales. Geographically, Caperea represents the only major baleen whale lineage entirely restricted to the Southern Ocean. Caperea-like fossils, the oldest of which date to the Late Miocene, are exceedingly rare and likewise limited to the Southern Hemisphere [4] , despite a more substantial history of fossil sampling north of the equator. Two new Pleistocene fossils now provide unexpected evidence of a brief and relatively recent period in geological history when Caperea occurred in the Northern Hemisphere ( Figure 1 A,B).

Locating breeding sites is definitely a key to understanding the ecological requirements and maintaining the sustainability of populations/species. Here I re-examined published specimens of an extinct baleen whale, Parietobalaena yamaokai, from the lower part of Itahashi Formation (16.1–15.6 Ma, Middle Miocene) in Shobara, Hiroshima, Japan. A critical and previously unnoticed feature, the open suture between the supraoccipital and exoccipital, in one specimen indicates the preservation of a very young individual–under six months old and even close to a new-born calf. Given the occurrence of a new-born whale and relatively abundant assemblage of Parietobalaena yamaokai, I propose a previously hidden and unknown breeding ground for the extinct baleen whale, P. yamaokai, in the Middle Miocene of Shobara (16.1–15.6 Ma), Hiroshima. Discovery of paleo-breeding sites of extinct populations/species should further help us to understand biological extinctions from a long-term perspective as conservation paleobiology aims to offer new insights into policy making for conserving endangered populations/species.

A new taxon of stem otariid, Eotaria citrica sp. nov., is described from the upper Burdigalian to lower Langhian “Topanga” formation of Orange County, California.The new species is described from mandibular and dental remains that show a unique combination of plesiomorphic and derived characters. Specifically, it is characterized by having trenchant and prominent paraconid cusps in p3–m1, lingual cingula of p2–4 with faint crenulations, premolars and molars with vestigial metaconid, bilobed root of m2 and a genial tuberosity located under p3. Furthermore, additional material of the contemporaneous Eotaria crypta is described, providing new information on the morphology of this taxon. Both species of Eotaria represent the earliest stem otariids, reinforcing the hypothesis that the group originated in the north Eastern Pacific Region. At present, the “Topanga” Fm. pinniped fauna includes Eotaria citrica, Eotaria crypta, the desmatophocid Allodesmus sp., the odobenids Neotherium sp., Pelagiarctos sp. and includes the oldest records of crown pinnipeds in California. Overall this pinniped fauna is similar to the nearly contemporaneous Sharktooth Hill bonebed. However, unambiguous records of Eotaria are still missing from Sharktooth Hill. This absence may be due to taphonomic or paleoenvironmental factors. The new “Topanga” record presented here was integrated into an overview of the late Oligocene through early Pleistocene pinniped faunas of Southern California. The results show an overall increase in body size over time until the Pleistocene.
Furthermore, desmatophocids were the largest pinnipeds during the middle Miocene, but were extinct by the beginning of the late Miocene. Odobenids diversified and became the dominant pinnipeds in late Miocene through Pleistocene assemblages, usually approaching or exceeding 3 m in body length,
while otariids remained as the smallest taxa. This pattern contrasts with modern assemblages, in which the phocid Mirounga angustirostris is the largest pinniped taxon in the region, odobenids are extinct and medium and small size ranges are occupied by otariids or other phocids.

Odontocetes first appear in the fossil record during the early Oligocene and soon after show a near-worldwide distribution. However, little is still known of their early diversity, especially in the North Pacific Region. A new taxon of stem odontocete with heterodont dentition, Olympicetus avitus, gen. et sp. nov., is described herein from the upper Oligocene Pysht Formation in Washington State, U.S.A. The material consists of two partial skulls belonging to a juvenile and a neonate and includes part of the dentition and a tympanic bulla. Olympicetus shares many similarities with the Oligocene odontocetes Simocetus rayi and Ashleycetus planicapitis but displays a combination of characters that distinguish it from these and other coeval taxa. A phylogenetic analysis shows Olympicetus in a polytomy with Xenorophidae, a clade of early high-frequency-hearing odontocetes mainly known from the western Atlantic. Furthermore, Olympicetus displays characters that can be considered as structural proxies for echolocation, such as having premaxillary sac fossae and the maxilla expanded over the frontal. In addition to Olympicetus, other marine tetrapods from the Pysht Formation include marine birds, desmostylians, pinnipeds, and early mysticetes, giving us a unique insight into late Oligocene marine tetrapod faunas of the North Pacific.

The early Oligocene (Rupelian) sirenian Halitherium schinzii Kaup, 1838, which represents the type species of the genus Halitherium Kaup, 1838, is revised herein based on a morphological re-evaluation of skeletal material originally assigned to this taxon. This study provides new and comprehensive information on the cranial and postcranial anatomy and allows the distinction of two sympatric species. Following a recent approach on the invalidity and subsequent rejection of H. schinzii Kaup, 1838, Kaupitherium gruelli new genus new species is established on the basis of a nearly complete holotype. The second taxon resembles K. gruelli n. sp. in a number of skeletal features, such as reduced nasals and absence of the canines, but can be clearly distinguished mainly by the post-canine dental formula and the supraoccipital morphology. The diagnostic skullcap of a species formerly synonymized under “H. schinzii” is re-validated as the holotype of K. bronni (Krauss, 1858). On the basis of paleoecological implications, a hypothesis is established to explain the overlapping stratigraphic and biogeographic occurrences (i.e., sympatry of both taxa). A diagnosis and up-to-date synonymy complement the taxonomical information. The revision of “H. schinzii” provides new data on the past sirenian diversity and forms the basis for a taxonomic and systematic re-evaluation of species originally grouped in the genus “Halitherium.”