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 3.1.5.3,
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.
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.
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.”