It's also been a big year for marine mammal paleontology. The toothed baleen whale Llanocetus has finally been described after a 30 year wait (Fordyce and Marx, 2018, below), a major milestone in baleen whaleontology. Two other major long-neglected fossils have been finally written up as well: Allodesmus demerei (written up by yours truly and Morgan Churchill), collected even earlier than Llanocetus (1984) and languishing unstudied at the Burke Museum, and Titanotaria, otherwise known as the walrus "Waldo", collected in 1993 from the Capistrano Formation in Orange County (fun fact: this specimen would have been the core specimen for a prospective Ph.D. thesis had I gone to San Diego State University, but that did not work out and I ended up studying eomysticetids at U. Otago in NZ instead, which worked out just fine). Some great fine-scale taphonomic/diagenetic work has been done on fossil cetaceans (Decree et al., Gioncada et al.) and an enormous pile of ziphiid skulls from really, really far south (Kerguelen islands) is reported by Lambert et al. A bunch of new mysticetes are named (Gol'din, Peredo and Pyenson, Peredo et al., Solis-Anorve et al., Tanaka et al.) meaning I have a LOT of coding to do to update my matrix! A large number of papers this year are published by students, and a flurry of papers from Leonard Dewaele (U. Ghent) and Carlos Peredo (George Mason U.) have come from the final stages of their respective doctoral programs (congratulations gentlemen). It's also been a fantastic year for pinnipeds: 1 out of 5 papers were on pinnipeds! (10 total, out of 50 papers) We're undergoing a bit of a pinniped renaissance at present; the last time so many well-formulated papers on fossil pinnipeds were being published was the early 1990s. Any way, without further adieu, here are the abstracts of all newly published articles from 2018.
Disclaimer: as always, I leave out papers published initially in late 2017 but with formal publication dates in 2018, because they were already covered last year. No, I do not have the time to update the publication dates on all of these, and you should feel ashamed for asking. Go look it up yourself! I guarantee that there are inconsistencies in the citation format, so if you find one, congratulations! I don't care. The entire point of this is to provide younger researchers with a comprehensive source of new publications. With that last point in mind, if I have forgotten anything, please leave a comment or send me a email, twitter, or facebook message informing me - unless of course it deals with modern species only (in which case it's not paleontological, although morphological and probably very evolutionary informative) or if it was first published in 2017 (see above).
Notably NOT included here are a bunch of extended conference abstracts on largely Italian fossils by a veritable battalion of Italian student paleontologists published in the new journal "Fossilia". I'm interpreting these as conference proceedings for now as full-length papers are not yet in evidence. However, if you're interested in what these students have worked on, take a look here: https://www.fossiliajournal.com/volumes/volume-1
Albright, L.B., A.E. Sanders, and J.H. Geisler. 2018. An
unexpectedly derived odontocete from the Ashley Formation (upper Rupelian) of
South Carolina, U.S.A. Journal of Vertebrate Paleontology. Online Early.
https://www.tandfonline.com/doi/abs/10.1080/02724634.2018.1482555?journalCode=ujvp20
Fossil whale material from the Oligocene-aged marine beds
underlying the region around Charleston, South Carolina, has provided an
unparalleled view of post-archaeocete cetacean evolution. Both the
Chattian-aged Chandler Bridge Formation and the underlying Rupelian-aged Ashley
Formation have yielded dozens of specimens, many yet-to-be described, that
document an explosive evolutionary radiation at this time, particularly in
odontocetes, but in early mysticetes as well. Specimens include early
odontocetes, such as Ashleycetus planicapitis, Xenorophus sloanii,
and Agorophius pygmaeus; the earliest baleen-bearing mysticetes, such as
Eomysticetus whitmorei and E. carolinensis; and even
multiple species of archaeocete-like toothed mysticetes, such as the recently
described Coronodon havensteini. Herein, we describe yet another species
of odontocete from the Ashley Formation, but one that is surprisingly derived
relative to contemporary species noted above that maintain a pronounced
intertemporal constriction, with broad exposure of the parietals across the
skull roof. In contrast to those taxa, Ediscetus osbornei, gen. et sp.
nov., shows an unexpectedly advanced degree of ‘telescoping’ whereby there is
no exposure of the parietals across the vertex of the skull and only minimally
exposed ‘parietal triangles’ at the lateral margins of the nearly lost
intertemporal constriction. Phylogenetic analyses of a supermatrix of
morphological and molecular data place E. osbornei slightly outside the
odontocete crown group, with the presence of double-rooted teeth and a deep
maxillary cleft, among other features, supporting this position. The holotype
also has a well-developed articular ridge on the petrosal, typically considered
a platanistoid synapomorphy, indicating that this character shows more
homoplasy than generally realized.
Berta, A., M. Churchill, and R.W. Boessenecker. 2018. The
origin and evolutionary biology of pinnipeds: seals, sea lions, and walruses.
Annual Review of Earth and Planetary Sciences 46:203-228.
The oldest definitive pinniped fossils date
from approximately 30.6–23 million years ago (Ma) in the North Pacific.
Pinniped monophyly is consistently supported; the group shares a common
ancestry with arctoid carnivorans, either ursids or musteloids. Crown pinnipeds
comprise the Otariidae (fur seals and sea lions), Odobenidae (walruses), and
Phocidae (seals), with paraphyletic “enaliarctines” falling outside the crown
group. The position of extinct Desmatophocidae is debated; they are considered
to be closely related to both otariids and odobenids or, alternatively, to
phocids. Both otariids and odobenids are known from the North Pacific,
diverging approximately 19 Ma, with phocids originating in the North Atlantic
or Paratethys region 19–14 Ma. Our understanding of pinniped paleobiology has
been enriched by studies that incorporate anatomical and behavioral data into a
phylogenetic framework. There is now evidence for sexual dimorphism in the
earliest pinnipeds, heralding polygynous breeding systems, followed by increased
body sizes, diving capabilities, and diverse feeding strategies in later-diverging
phocid and otarioid lineages.
Bianucci, G., A. Collareta, G. Bosio, et. al. 2018. Taphonomy
and palaeoecology of the lower Miocene marine vertebrate assemblage of Ullujaya
(Chilcatay Formation, East Pisco Basin, Southern Peru). Palaeogeography,
Palaeoclimatology, Palaeoecology
Bianucci, G., G. Bosio, E. Malinverno, et al. 2018. A new
large squalodelphinid (Cetacea, Odontoceti) from Peru sheds light on the early
Miocene platanistoid disparity and ecology. Royal Society Open Science
5:172302.
https://royalsocietypublishing.org/doi/full/10.1098/rsos.172302
The South Asian river dolphin (Platanista gangetica)
is the only extant survivor of the large clade Platanistoidea, having a
well-diversified fossil record from the Late Oligocene to the Middle Miocene.
Based on a partial skeleton collected from the Chilcatay Formation (Chilcatay
Fm; southern coast of Peru), we report here a new squalodelphinid genus and
species, Macrosqualodelphis ukupachai. A volcanic ash layer, sampled
near the fossil, yielded the 40Ar/39Ar age of
18.78 ± 0.08 Ma (Burdigalian, Early Miocene). The phylogenetic analysis places Macrosqualodelphis
as the earliest branching squalodelphinid. Combined with several cranial and
dental features, the large body size (estimated body length of 3.5 m) of this
odontocete suggests that it consumed larger prey than the other members of its
family. Together with Huaridelphis raimondii and Notocetus
vanbenedeni, both also found in the Chilcatay Fm, this new squalodelphinid
further demonstrates the peculiar local diversity of the family along the
southeastern Pacific coast, possibly related to their partition into different
dietary niches. At a wider geographical scale, the morphological and ecological
diversity of squalodelphinids confirms the major role played by platanistoids
during the Early Miocene radiation of crown odontocetes.
Boessenecker, R.W. 2018. Problematic archaic whale Phococetus (Cetacea: Odontoceti) from
the Lee Creek Mine, North Carolina, USA, with comments on geochronology of the
Pungo River Formation. Pal Z. Online early.
Heterodont cetaceans are abundant in Eocene, Oligocene, and
early to middle Miocene deposits worldwide. Taxonomic practice in the 19th and
early 20th centuries led to the establishment of a multitude of names based on
isolated teeth. Some of these taxa, such as Phococetus vasconum from
the lower Miocene (Burdigalian) of France, have been alternatively interpreted
as archaeocetes, odontocetes, and mysticetes. Isolated teeth resembling Phococetus
vasconum from the Pungo River Formation in the Lee Creek Mine (Beaufort
County, North Carolina, USA) also share features with the enigmatic early Miocene
odontocete Inticetus vertizi, suggesting that Phococetus may
represent a large heterodont odontocete.
Boessenecker, R.W. and M. Churchill. 2018. The last of the
desmatophocid seals: a new species of Allodesmus
from the upper Miocene of Washington, USA, and a revision of the taxonomy of
Desmatophocidae. Zoological Journal of the Linnean Society 184:1:211-235.
The family Desmatophocidae represents an early radiation of
extinct pinnipeds that peaked in diversity during the middle Miocene. Although
represented by abundant well-preserved fossils, the taxonomy and evolutionary
relationships of this family remain poorly known. Late Miocene desmatophocids
have been recorded, although none have been formally described, preventing a
thorough appraisal of their decline and extinction. We report the discovery of
a new species, Allodesmus demerei sp. nov., represented
by a partial skeleton with cranium, mandibles, and axial skeleton, from the
upper Miocene Montesano Formation of Washington, prompting reinterpretation of
desmatophocid taxonomy, phylogeny, and extinction. Phylogenetic analysis (95
characters, 26 taxa) found strong support for monophyletic Desmatophocidae and Allodesmus.
Desmatophocidae was found as sister to Phocidae with poor support. Allodesmus
demerei was placed within the Allodesmus as the sister taxon to Allodesmus
kernensis. The geochronologically young age (10.5–9.1 Mya) of Al.
demerei establishes this species as the last of the desmatophocid seals.
The middle Miocene peak in desmatophocid diversity coincides with the middle
Miocene climatic optimum, suggesting that declining sea surface temperature
played a role in their decline and extinction. Walruses diversified and
increased in body size during the mid- to late Miocene as desmatophocids
declined, suggesting some form of ecological displacement.
Boessenecker, R.W. and J.H. Geisler. 2018. New records of the archaic dolphin Agorophius
(Mammalia: Cetacea) from the upper Oligocene Chandler Bridge Formation of South
Carolina, USA. PeerJ 6:e5290.
The stem odontocete Agorophius pygmaeus (Ashley
Formation, lower Oligocene, South Carolina; 29.0–26.57 Ma) has been a critical
point of comparison for studies of early neocete evolution owing to its early
discovery as well as its transitional anatomy relative to archaeocete whales
and modern odontocetes. Some time during the late nineteenth century the
holotype skull went missing and has never been relocated; supplementary
reference specimens have since been recently referred to the species from the
Ashley Formation and the overlying Chandler Bridge Formation (upper Oligocene;
24.7–23.5). New crania referable to Agorophius sp. are identifiable to the
genus based on several features of the intertemporal region. Furthermore, all
published specimens from the Chandler Bridge Formation consistently share
larger absolute size and a proportionally shorter exposure of the parietal in
the skull roof than specimens from the Ashley Formation (including the
holotype). Furthermore, these specimens include well-preserved ethmoid labyrinths
and cribriform plates, indicating that Agorophius primitively retained a
strong olfactory sense. These new crania suggest that at least two species of Agorophius
are present in the Oligocene of South Carolina, revealing a somewhat more
complicated taxonomic perspective.
Boessenecker, S.J., R.W. Boessenecker, and J.H. Geisler.
2018. Youngest record of the extinct walrus Ontocetus
emmonsi from the Early Pleistocene of
South Carolina and a review of North Atlantic walrus biochronology. Acta
Palaeontologica Polonica 63:279-286.
The extinct North Atlantic walrus Ontocetus emmonsi
is widely reported from Pliocene marine deposits in the eastern USA (New
Jersey, Florida), Belgium, Netherlands, Great Britain, and Morocco. Ontocetus
was slightly larger than the modern walrus Odobenus rosmarus, may
have had wider climatic tolerances (subtropical), and likely originated in the
western North Pacific before dispersing through the Arctic. Owing to
geochronologic uncertainties in the North Atlantic Plio-Pleistocene walrus
record, it is unclear whether Ontocetus and Odobenus
overlapped in time and thus may have competed, or whether the two were
temporally separate invasions of the North Atlantic. A new specimen of Ontocetus
emmonsi (CCNHM-1144) from the Austin Sand Pit (Ridgeville, South Carolina,
USA) is a complete, well-preserved left tusk that is proximally inflated and
oval in cross-section, relatively short (maximum length: 369 mm) and markedly
curved (radius of arc of curvature 197 mm). Globular dentine is present,
confirming assignment to Odobenini; proportions and curvature identify
the specimen as Ontocetus emmonsi rather than Odobenus.
Hitherto unstudied deposits in the Austin Sand Pit lack calcareous macro and
microinvertebrates, but vertebrate biochronology provides some temporal
resolution. The co-occurrence of a giant beaver (Castoroides sp.) and
a snaggletooth shark (Hemipristis serra) indicate an age of 1.1–1.8 Ma
(Early Pleistocene) and correlation with the Lower Pleistocene Waccamaw
Formation. The vertebrate assemblage is named the Ridgeville Local Fauna. The
composition of the marine mammal assemblage from the Austin Sand Pit is
intermediate between that of the lower Pliocene Yorktown Formation (North
Carolina, USA) and the modern North Atlantic fauna. This record reported here
is the youngest of Ontocetus emmonsi from the Atlantic Coastal Plain.
A review of North Atlantic Plio-Pleistocene walrus records reveals no overlap
between extinct Ontocetus and extant Odobenus—suggesting
independent dispersal to the North Atlantic and a lack of competition.
Churchill, M., J.H. Geisler, B.L. Beatty, and A. Goswami.
2018. Evolution of cranial telescoping in echolocating whales (Cetacea:
Odontoceti). Evolution 72:1092-1108.
https://onlinelibrary.wiley.com/doi/abs/10.1111/evo.13480
Odontocete (echolocating whale) skulls exhibit extreme
posterior displacement and overlapping of facial bones, here referred to as
retrograde cranial telescoping. To examine retrograde cranial telescoping across
40 million years of whale evolution, we collected 3D scans of whale skulls
spanning odontocete evolution. We used a sliding semilandmark morphometric
approach with Procrustes superimposition and PCA to capture and describe the
morphological variation present in the facial region, followed by Ancestral
Character State Reconstruction (ACSR) and evolutionary model fitting on
significant components to determine how retrograde cranial telescoping evolved.
The first PC score explains the majority of variation associated with telescoping
and reflects the posterior migration of the external nares and premaxilla
alongside expansion of the maxilla and frontal. The earliest diverging fossil
odontocetes were found to exhibit a lesser degree of cranial telescoping than
later diverging but contemporary whale taxa. Major shifts in PC scores and
centroid size are identified at the base of Odontoceti, and early burst and
punctuated equilibrium models best fit the evolution of retrograde telescoping.
This indicates that the Oligocene was a period of unusually high diversity and
evolution in whale skull morphology, with little subsequent evolution in
telescoping.
Decree, S., D. Herwartz, J. Mercadier, et al. 2018. The
post-mortem history of a bone revealed by its trace element signature: the case
of a fossil whale rostrum. Chemical Gelology 477:137-150.
https://www.sciencedirect.com/science/article/abs/pii/S0009254117307027?via%3Dihub
Dewaele, L., O. Lambert, and S. Louwye. 2018. A late
surviving Pliocene seal from high latitudes of the North Atlantic realm: the
latest monachine seal on the southern margin of the North Sea. PeerJ 6:e7534.
The family of true seals, the Phocidae, is subdivided into
two subfamilies: the southern Monachinae, and the northern Phocinae, following
the subfamilies’ current distribution: extant Monachinae are largely restricted
to the (sub-)Antarctic and the eastern Pacific, with historical distributions
of the monk seals of the genus Monachus in the Caribbean, the
Mediterranean and around Hawaii; and Phocinae to the northern temperate and Arctic
zones. However, the fossil record shows that Monachinae were common in the
North Atlantic realm during the late Miocene and early Pliocene. Until now,
only one late Pliocene record is known from the Mediterranean, Pliophoca
etrusca from Tuscany, Italy, but none from farther north in the North
Atlantic.
Dewaele, L., O. Lambert, M. Laurin, et al. 2018. Generalized
osteosclerotic condition in the skeleton of Nanophoca vitulinoides, a dwarf
seal from the Miocene of Belgium. Journal of Mammalian Evolution. Online Early.
In the fossil record, it has been shown that various clades
of secondarily aquatic tetrapods experienced an initial densification of their
bones in the early stages of their evolution, and developed spongier and
lighter bones only later in their evolution, with the acquisition of more
efficient swimming modes. Although the inner bone structure of most secondarily
aquatic tetrapods has already been studied, no research hitherto focused on
true seals, or Phocidae. However, preliminary observations previously made on a
Miocene species, Nanophoca vitulinoides, suggested that this taxon
showed pronounced specialization of bone structure as compared to other seals.
This feature justifies a specific comparative study, which is the purpose of
this article. Microanatomical analysis of bones of N. vitulinoides
shows compactness values nearing 100%, which is much higher than in other
semi-aquatic mammals, pinnipeds included. Osteohistological analyses show
virtually complete remodeling of the medullary territory by Haversian
substitution. Extreme bone compactness locally resulted from an imbalance,
towards reconstruction, of this process. Cortical regions were less intensely
remodeled. In a number of specimens, the cortex shows clear growth marks as
seasonal lines of arrested growth. The results suggest that, despite the
extreme compactness of long bones of N. vitulinoides and the small
size of this taxon, the growth rate of the cortex, and that of the bones in
general, did not differ strongly from that of other, larger phocids. Extreme
skeletal compaction and densification must have increased body density in Nanophoca.
Consequently, speed, acceleration, and maneuverability must have been low, and
this taxon was most likely a near-shore bottom-dwelling seal. Consequently,
dietary preferences were most likely oriented towards benthic food sources.
Dewaele, L., O. Lambert, and S. Louwye. 2018. A critical
revision of the fossil record, stratigraphy and diversity of the Neogene seal
genus Monotherium (Carnivora,
Phocidae). Royal Society Open Science 5:e171669.
Historically, Monotherium had been one of the few
genera of extinct Phocidae (true seals) that served as a wastebin taxon. Consequently,
it did neither aid in understanding phylogenetic relationships of extinct
Phocidae, nor in understanding seal diversity in deep time. This urged the
reassessment of the genus. Before our review, Monotherium included five
different species: Monotherium aberratum, Monotherium affine, and
Monotherium delognii from Belgium; Monotherium gaudini from
Italy; and Monotherium? wymani from the east coast USA. In this
work we redescribe the fossil record of the genus, retaining the type species M.
delognii. Monotherium aberratum and M. affine are reassigned
to the new phocine genus Frisiphoca. Monotherium gaudini is
renamed and considered a stem-monachine (Noriphoca gaudini). The
holotype of the monachine M.? wymani requires further study
pending the discovery of new fossil material that could be attributed to the
same taxon. Reinvestigating the stratigraphic context reveals that N.
gaudini most likely represents one of the two oldest named phocid seals, or
even the oldest, dated to the late Oligocene–earliest Miocene. Our results
allow questioning the widespread idea that Phocidae originated in the western
Atlantic and better appreciate their palaeobiogeography during the late
Oligocene–Miocene interval in the North Atlantic realm.
Dewaele, L., C.M. Peredo, P. Meyvisch, and S. Louwye. 2018.
Diversity of late Neogene Monachinae (Carnivora, Phocidae) from the North
Atlantic, with a description of two new species. Royal Society Open Science
5:172437.
While the diversity of ‘southern seals’, or Monachinae, in
the North Atlantic realm is currently limited to the Mediterranean monk seal, Monachus
monachus, their diversity was much higher during the late Miocene and Pliocene.
Although the fossil record of Monachinae from the North Atlantic is mainly
composed of isolated specimens, many taxa have been erected on the basis of
fragmentary and incomparable specimens. The humerus is commonly considered the
most diagnostic postcranial bone. The research presented in this study limits
the selection of type specimens for different fossil Monachinae to humeri and
questions fossil taxa that have other types of bones as type specimens, such as
for Terranectes parvus. In addition, it is essential that the humeri
selected as type specimens are (almost) complete. This questions the validity
of partial humeri selected as type specimens, such as for Terranectes magnus.
This study revises Callophoca obscura, Homiphoca capensis and Pliophoca
etrusca, all purportedly known from the Lee Creek Mine, Aurora, North
Carolina, in addition to their respective type localities in Belgium, South
Africa and Italy, respectively. C. obscura is retained as a
monachine seal taxon that lived both on the east coast of North America and in
the North Sea Basin. However, H. capensis from North America cannot be
identified beyond the genus level, and specimens previously assigned to Pl.
etrusca from North America clearly belong to different taxa. Indeed, we
also present new material and describe two new genera of late Miocene and
Pliocene Monachinae from the east coast of North America: Auroraphoca
atlantica nov. gen. et nov. sp., and Virginiaphoca magurai nov. gen.
et nov. sp. This suggests less faunal interchange of late Neogene Monachinae
between the east and west coasts of the North Atlantic than previously
expected.
Domning, D.P. 2018. Fossil sirenians (Mammalia) of the
Miocene Chesapeake Group, Eastern United States. [in Godfrey, S.J., ed., The
Geology and Vertebrate Paleontology of Calvert Cliffs, Maryland, USA] Smithsonian
Contributions to Paleobiology 100:241-266.
The extensive
Miocene vertebrate fauna collected from the Chesapeake
Group in
New Jersey, Delaware, Maryland, Virginia, and North Carolina includes
relatively rare sirenians of the family Dugongidae. They are most abundant in
the early to middle Miocene Calvert and equivalent formations and in the
Calvert Cliffs and nearby exposures in southern Maryland, as well as in the Lee
Creek phosphate mine in North Carolina. These Calvert-correlative deposits have
yielded evidence of at least three sirenian taxa: the halitheriine dugongid Metaxytherium
crataegense (=M. calvertense), the dugongine dugongid Nanosiren sp.,
and another dugongine, aff. Corystosiren sp. A possible fourth
unidentified form may also be a dugongine. The stratigraphically higher St. Marys
Formation contains remains that (in view of their late Miocene age) may be referable
to Metaxytherium floridanum, but those so far collected are too
fragmentary to be distinguished morphologically from M. crataegense.
Fordyce, R.E., and F.G. Marx. 2018. Gigantism precedes
filter feeding in baleen whale evolution. Current Biology 28:1670-1676.
Baleen whales (Mysticeti) are
the largest animals on Earth, thanks to their ability to filter feed huge
volumes of small prey from seawater.
Mysticetes appeared during the Late Eocene, but evidence of their early
evolution remains both sparse and controversial [1, 2], with several models
competing to explain the origin of baleen-based bulk feeding [3–6]. Here, we
describe a virtually complete skull of Llanocetus denticrenatus, the
second-oldest (ca. 34 Ma) mysticete known. The new material represents the same
individual as the type and only specimen, a fragmentary mandible. Phylogenetic
analysis groups Llanocetus with the oldest mysticete, Mystacodon selenensis [2],
into the basal family Llanocetidae. Llanocetus is gigantic (body length _8 m)
compared to other early mysticetes [7–9]. The broad rostrum has sharp, widely
spaced teeth with marked dental abrasion and attrition, suggesting biting and
occlusal shearing. As in extant mysticetes, the palate bears many sulci,
commonly interpreted as osteological correlates of baleen [3]. Unexpectedly,
these sulci converge on the upper alveoli, suggesting a peridental blood supply to well-developed gums, rather than
to inter-alveolar racks of baleen. We interpret Llanocetus as a raptorial or
suction feeder, revealing that whales evolved gigantism well before the
emergence of filter feeding. Rather than driving the origin of mysticetes,
baleen and filtering most likely only arose after an initial phase of
suction-assisted raptorial feeding [2, 4, 5]. This scenario differs strikingly from
that proposed for odontocetes, whose defining adaptation—echolocation—was
present even in their earliest representatives [10].
Galatius, A., Olsen, M.T., M.E. Steeman, et a. 2018. Raising
your voice: evolution of narrow-band high-frequency signals in toothed whales
(Odontoceti). Biological Journal of the Linnean Society. Online early.
Cetaceans use sound for communication, navigation and
finding prey. Most extant odontocetes produce broadband (BB) biosonar clicks
covering frequency ranges from tens of kilohertz to 150–170 kHz. In contrast,
the biosonar clicks of some odontocetes are unique, being narrow in bandwidth
with high centroid frequency (NBHF), peak frequencies being at 125–140 kHz and
bandwidths of 11–20 kHz. Thirteen species within four families (Phocoenidae,
Pontoporiidae, Kogiidae, Delphinidae) are known to produce these signals,
implying convergent evolution under strong selective drivers. Several
hypotheses have been proposed, including acoustic crypsis to escape predation
by killer whales, but none has provided comprehensive explanation of the timing
of NBHF evolution and the pressures driving sound production to such extremes.
Using molecular phylogenetics and the cochlea anatomy of extinct and extant
taxa, we demonstrate that early NBHF adaptations occurred at least 10 Mya, and
possibly up to 18 Mya, indicating that killer whales cannot have been the sole
driving force of NBHF signals, but that now extinct odontocetes may have
provided similar pressures. Using palaeoclimate modelling, we further
demonstrate that the upper advantageous spectral window for NBHF signals at
around 130 kHz has persisted throughout most of the global sea area since the
mid-Miocene, covering all known instances of NBHF evolution.
Gilbert, K.N., L.C. Ivany, and M.D. Uhen. 2018/ Living fast
and dying young: life history and ecology of a Neogene sperm whale. Journal of
Vertebrate Paleontology 38:e1439038.
Physeteroidea (sperm whales) attained great diversity during
the Miocene and early Pliocene, and the phosphatic sands of the U.S. Atlantic
Coastal Plain have produced thousands of specimens. Although postcranial and
cranial materials are rare, teeth are remarkably common and have the potential
to provide valuable insight into the lives of these animals. We examine a suite
of Physeteroidea indet. teeth from the Lee Creek Mine to better constrain the
life history and ecology of this extinct group. Wear facets indicate that these
animals, unlike modern sperm whales, had both maxillary and mandibular teeth,
suggesting a raptorial feeding ecology more akin to killer whales. A
relationship between tooth diameter and body size established for modern
odontocetes suggests that these animals as adults were also about the size of
modern killer whales. Because physeteroid teeth grow continuously over ontogeny
and are not replaced, counts of accretionary growth layer groups can be used to
ascertain the age of an animal at death. Tallies of growth increments from 10
teeth, including some of the largest available, reveal that life spans only
rarely exceeded 20 years, significantly shorter than the 65+ years typical
of modern sperm whales or orcas. Despite their large size, these odontocetes
experienced a ‘fast’ life history, more like beluga whales today. We suggest
that the rapid growth and short life span exhibited by the Lee Creek
physeteroids are, like the modern beluga, evolutionary responses to high
predation pressure imposed by large co-occurring predatory taxa, particularly
including Carcharocles megalodon or other large macroraptorial
physeteorids.
Gioncada, A., K. Gariboldi, A. Collareta et al. 2018. Looking
for the key to preservation of fossil marine vertebrates in the Pisco Formation
of Peru: new insights from a small dolphin skeleton. Andean Geology 45:379-398.
The upper Neogene Pisco Formation of Peru is known worldwide
as one of the most significant Cenozoic marine vertebrate
Konservatt-Lagerstätten, even featuring cetacean specimens that retain remains
of soft tissues or stomach contents. Previous works showed that biomediated
precipitation of dolomite concretions around large-sized decaying carcasses was
one of the most relevant processes responsible for exceptional fossil
preservation. In turn, little is known about the modes of fossilization of
well-preserved small-sized vertebrates, which are rather common in the Pisco
Formation, but mostly do not exhibit dolomite concretions. We report on a
cetacean specimen, identified as belonging to the extinct short-snouted, small
dolphin species Brachydelphis mazeasi (Pontoporiidae), preserved within a late
Miocene sandy deposit at the site of Pampa Corre Viento. This specimen consists
of a moderately disarticulated partial skeleton exhibiting well-mineralized
bones; it is not enclosed within a dolomite concretion, being however delimited
by an evident dark boundary in the host sediment. Scanning electron microscopy
and microanalytical investigations identify Mn-oxides and apatite as early
diagenetic minerals around the skeleton. We argue that a rapid burial of the
specimen was pivotal for the preservation of the bones, and allowed the early
establishment of anoxic processes for degradation of organic matter. Coupled
with availability of P in porewater, the reducing conditions and the lowered pH
allowed precipitation of Ca-phosphate while increasing Mn solubility close to
the pontoporiid carcass. Mn-oxides precipitated at the redox boundary, the
latter defining the outer edge of the volume of sediment affected by altered
chemical conditions due to the decaying processes. The permeability of the
sediment and the small size of the carcass were possible factors unfavorable to
extensive sulfate reduction, thus preventing the formation of a dolomite
concretion and allowing bone phosphatization. This record emphasizes the role
of conditions favorable to bone mineralization in absence of an isolating
carbonate concretion, in cases of high quality preservation of small-sized
vertebrates observed in the Pisco Formation. The observation of patterns in the
distribution of diagenetic minerals in the sediment enclosing vertebrate
remains without, or with limited carbonate concretions provides insights into
early taphonomic processes.
Godfrey, S.J., M. Ellwood, S. Groff, and M.S. Verdin. 2018. Carcharocles-bitten odontocete caudal
vertebrae from the coastal Eastern United States. Acta Palaeontologica Polonica
63:463-468.
https://www.app.pan.pl/article/item/app004952018.html
A description and analysis is given of three Neogene
odontocete caudal vertebrae that were bitten by the extinct megatooth sharks Carcharocles
megalodon or Carcharocles chubutensis. The peduncular caudal
vertebrae show bilateral gouge marks consistent with having been actively
bitten and wedged between adjacent teeth of C. megalodon or C.
chubutensis. None of the vertebrae show signs of healing. The occurrence
of bite marks on distal caudals suggests active predation (vs. scavenging) in
order to immobilize even relatively small prey prior to consumption.
Gol’din, P. 2018. New Paratethyan dwarf baleen whales mark
the origin of cetotheres. PeerJ 6:e5800.
https://peerj.com/articles/5800/
Family Cetotheriidae sensu stricto and several closely
related taxa comprise the Cetotherioidea and represent a lineage of Neogene
baleen whales that includes the smallest edentulous baleen whales in Earth
history. Most of known cetotheriids came from the Late Miocene to Quaternary,
and the earliest records from the latest Middle Miocene. The Paratethys region
shows a great diversity of Middle to Late Miocene cetotheriids. That includes
nominative taxon of the family, Cetotherium rathkii, and this suggests
that the earliest cetotheriids may have lived in that region. Here, Ciuciulea
davidi, a new genus and species from the Middle Miocene of southeastern
Europe, is described as the chronologically earliest and earliest diverging
member of Cetotheriidae. Also, a new specimen of Otradnocetus, a basal
Cetotherioidea sensu Gol’din & Steeman, 2015 is identified from the Late
Miocene deposits of Caucasus and compared with Otradnocetus virodovi
from the Middle Miocene of the same region. Ciuciulea davidi is a
dwarf whale displaying primitive traits: posterior ends of facial bones forming
a single transverse line, a narrow occipital shield, and a relatively long
interparietal region. Meanwhile, it shares some cetotheriid apomorphies:
posteriorly telescoped wedge-shaped facial bones and an ovoid tympanic bulla
with shallow lateral and medial furrows, a short anterior lobe and a short
sigmoid process. Phylogenetic analysis suggests that Parietobalaena
and Otradnocetus are branches diverging before the clade Cetotheriidae
+ Neobalaenidae. This is confirmed by the stepwise evolution of the anatomy of
the squamosal, mandible, and ear bones across these groups. The re-described
juvenile specimen of Otradnocetus differs from O. virodovi in
the more primitive anatomy of the mandible and the autapomorphic anatomy of the
humerus. Records of the earliest cetotheriids and related taxa in the
Paratethys support the idea that this could be the region where Cetotheriidae
evolved before their worldwide dispersal and radiation.
Gol’din, P., and P. Radovic. 2018. A middle Miocene baleen
whale from Bele Vode in Belgrade, Serbia. Rivista Italiana di Paleontologia e
Stratigrafia 124:127-138.
There was a fauna of baleen whales (Cetacea: Mysticeti) in
the Central Paratethys, a Miocene water body which covered the area of present-day
Central Europe. Most of the fossil baleen whales from the Central Paratethys
have been found in strata assigned to the regional Badenian age and comprise
endemic forms, known only from this region. Here a new description is provided
for a fragmentary skeleton of a whale found in Belgrade, Serbia, and its age
context and biological aspects are discussed. This specimen, consisting of a
fragmentary horizontal ramus of the mandible and eight caudal vertebrae, is
tentatively identified as ?Parietobalaena sp., a globally known
Miocene taxon, with related forms having been recorded earlier from the Eastern
Paratethys. An early Sarmatian age (i.e., about 12.7-12.4 Ma) is proposed for
the specimen. Based on epiphyseal fusion of caudal vertebrae, the specimen’s age
is identified as a subadult, with a body length of around 2.5 m and an
estimated adult body length around 3-3.5 m, which is extremely small for baleen
whales. This find represents one of the latest records of baleen whales in the
Central Paratethys and one of the latest published records of Parietobalaena-like
taxa in the world.
Hernandez-Cisneros, E. 2018. A new group of late Oligocene
mysticetes from Mexico. Palaeontologia Electronica 21:7A:1-30.
The Oligocene cetacean fossil record from Mexico represents
an important element to understand the cetacean evolutionary history in the
Pacific Basin. However, our knowledge of these fossils is poor, as the
specimens have not yet been properly described. Nonetheless, recent
observations on Oligocene fossils from the state of Baja California Sur offer
new ideas with regard to the cetacean taxonomic composition and suggest a high
diversity of mysticete fossils with several forms of toothless mysticetes.
Consequently, a new group of extinct mysticetes from the late Oligocene
(Chattian) of Mexico is described based on two different specimens (partial
skulls), which share a phenetically similar periotic bone. These fossils were
collected from the marine units of the San Juan Member (30 to 23 Ma) of the El
Cien Formation in Baja California Sur. Furthermore, this new group of archaic
mysticetes is distinct to eomysticetid-like animals, Mauicetus, Horopeta,
and Whakakai mainly in the periotic morphology specifically in: a longer
and anteroposteriorly flattened compound posterior process of the periotic, and
a periotic (pars cochlearis, anterior process and body of the periotic) with an
ovoid shape in lateral and medial views. Phylogenetic analysis suggests a closer
relation to Sitsqwayk and eomysticetes than to Horopeta +
Whakakai and crown Mysticeti. Oligocene cetaceans from Mexico are still
poorly known in terms of their paleoecology and phyletic relationship. This
work represents the first description of Oligocene mysticetes from Baja
California Sur and shows the potential to further understanding of the
biogeographic history of mysticetes in the Eastern Pacific.
Hocking, D.P., F.G. Marx, R. Sattler, et al. 2018. Clawed
forelimbs allow northern seals to eat like their ancient ancestors. Royal
Society Open Science 5:172393.
Streamlined flippers are often considered the defining
feature of seals and sea lions, whose very name ‘pinniped’ comes from the Latin
pinna and pedis, meaning ‘fin-footed’. Yet not all pinniped limbs
are alike. Whereas otariids (fur seals and sea lions) possess stiff streamlined
forelimb flippers, phocine seals (northern true seals) have retained a webbed
yet mobile paw bearing sharp claws. Here, we show that captive and wild phocines
routinely use these claws to secure prey during processing, enabling seals to
tear large fish by stretching them between their teeth and forelimbs. ‘Hold and
tear’ processing relies on the primitive forelimb anatomy displayed by
phocines, which is also found in the early fossil pinniped Enaliarctos.
Phocine forelimb anatomy and behaviour therefore provide a glimpse into how the
earliest seals likely fed, and indicate what behaviours may have assisted
pinnipeds along their journey from terrestrial to aquatic feeding.
Ichishima, H., H. Furusawam M. Tachibana, and M. Kimura.
2018. First monodontid cetacean (Odontoceti, Delphinoidea) from the early
Pliocene of the northwestern Pacific Ocean. Papers in Palaeontology. Online early.
Monodontids are among the most enigmatic cetaceans due to
their scarcity in the fossil record. Previously, except for fragmentary
materials, only three skulls were known from the pre‐Pleistocene;
these came from the east coast of the Pacific and both east and west coasts of
the Atlantic. Haborodelphis japonicus, a new early Pliocene monodontid
cetacean from the north‐west Pacific, significantly
expands the palaeobiogeographical extent of the ancestral monodontids. The new
taxon differs from all other monodontids in the following character states: the
robust postorbital process for the skull size; the short rostrum relative to
the whole skull length; the anterior dorsal infraorbital foramina posterior to
the level of the antorbital notch; the premaxillary foramen on the level of the
antorbital notch; the dorsally gently convex premaxillary sac fossa; the
palatines wedged into the maxillae anteriorly on the midline; and the presence
of the clearly excavated posteromedial sulcus. Monodontids were almost
certainly adapted to warmer waters than their living counterparts Delphinapterus
leucas and Monodon monoceros, both of which are confined to the high
latitudes of the northern hemisphere. However, closer inspection (based mainly
on fossil invertebrates) of the palaeoenvironments from which the monodontid
fossils were produced, reveals that they may have preferred cooler conditions
than previously thought. Due to the short climatic fluctuation cycles during
the Pliocene in the northern hemisphere, and the increase of heterogeneity and
regionality of the coastal environments, the dating of layers within a
formation is critical for understanding palaeoenvironment in terms of the sea
surface temperatures.
Kimura, T., and K. Ishihara. 2018. A fossil phocoenid periotic from Nagasakibana, Chiba, Japan. Bulletin of the Gunma Museum of Natural History 22:73-77.
http://www.gmnh.pref.gunma.jp/research_no22
We describe a fossil odontocete periotic from the Nagasakihana, Cyoshi, Chiba Prefecture Japan. The specimen was found as a pebble on the beach and no matrix was preserved. At the area from which the specimen was found, there are conglomerates representing the lowest part of the Naarai Formation (corresponding to planktonic foraminiferal zone PL1:latest Miocene - early Pliocene) and many fossils have been recovered from the Naarai Formation. But, at the same area, Kato (2017) reported several fossils from the unnamed Holocene deposit which is exposed a few meters below the coastal line. Therefore, the age of the present specimen remains unclear (possibly latest Miocene - early Pliocene or Holocene). The periotic displays a combination of the following morphological characters and diagnosed as genus Neophocaena: anterior bullar facet is not present; parabullary ridge is present but not so laterally developed as typically seen in the Delphinidae; outline of anterior process is quadrangular in lateral view; anterior process is directed slight medially; aperture for vestibular aqueduct opens dorsally as slit; dorsal tuberosity is not so developed; foramen sigulare is separated by spiral cribriform tract by high crest; periotic body is relatively narrow in comparison with the width of pars cochlearis. Since the present specimen has a much wider transverse crest in comparison with that of N. phocaenoides, here we report the present specimen as
Neophocaena sp.
Kimura, T., and K. Ishihara. 2018. A fossil phocoenid periotic from Nagasakibana, Chiba, Japan. Bulletin of the Gunma Museum of Natural History 22:73-77.
http://www.gmnh.pref.gunma.jp/research_no22
We describe a fossil odontocete periotic from the Nagasakihana, Cyoshi, Chiba Prefecture Japan. The specimen was found as a pebble on the beach and no matrix was preserved. At the area from which the specimen was found, there are conglomerates representing the lowest part of the Naarai Formation (corresponding to planktonic foraminiferal zone PL1:latest Miocene - early Pliocene) and many fossils have been recovered from the Naarai Formation. But, at the same area, Kato (2017) reported several fossils from the unnamed Holocene deposit which is exposed a few meters below the coastal line. Therefore, the age of the present specimen remains unclear (possibly latest Miocene - early Pliocene or Holocene). The periotic displays a combination of the following morphological characters and diagnosed as genus Neophocaena: anterior bullar facet is not present; parabullary ridge is present but not so laterally developed as typically seen in the Delphinidae; outline of anterior process is quadrangular in lateral view; anterior process is directed slight medially; aperture for vestibular aqueduct opens dorsally as slit; dorsal tuberosity is not so developed; foramen sigulare is separated by spiral cribriform tract by high crest; periotic body is relatively narrow in comparison with the width of pars cochlearis. Since the present specimen has a much wider transverse crest in comparison with that of N. phocaenoides, here we report the present specimen as
Neophocaena sp.
Lambert, O., C. Auclair, C. Cauxeiro, et al. 2018. A close
relative of the Amazon river dolphin in marine deposits: a new Iniidae from the
late Miocene of Angola. PeerJ 6:e5556.
Lambert O., C. de Muizon, G. Duhamel, and J. Van der Plicht.
2018. Neogene and Quaternary fossil remains of beaked whales (Cetacea,
Odontoceti, Ziphiidae) from deep-sea deposits off Crozet and Kerguelen islands,
Southern Ocean. Geodiversitas 40:135-160.
Magallanes, I., J.F. Parham, G-P. Santos, and J.
Velez-Juarbe. 2018. A new tuskless walrus from the Miocene of Orange County,
California, with comments on the diversity and taxonomy of odobenids. PeerJ
6:e5708.
Marx , F.G., T. Park, E.M.G. Fitzgerald, and A.R. Evans.
2018. A Miocene pygmy right whale fossil from Australia. PeerJ 6:e5025.
Neobalaenines are an enigmatic group of baleen whales
represented today by a single living species: the pygmy right whale, Caperea
marginata, found only in the Southern Hemisphere. Molecular divergence
estimates date the origin of pygmy right whales to 22–26 Ma, yet so far there
are only three confirmed fossil occurrences. Here, we describe an isolated
periotic from the latest Miocene of Victoria (Australia). The new fossil shows
all the hallmarks of Caperea, making it the second-oldest described
neobalaenine, and the oldest record of the genus. Overall, the new specimen
resembles C. marginata in its external morphology and details of the
cochlea, but is more archaic in it having a hypertrophied suprameatal area and
a greater number of cochlear turns. The presence of Caperea in
Australian waters during the Late Miocene matches the distribution of the
living species, and supports a southern origin for pygmy right whales.
Matsui, K., Y. Kimura, M. Nagata et al. 2018. A
long-forgotten ‘dinosaur’ bone from a museum cabinet, uncovered to be a Japan’s
iconic extinct mammal, Paleoparadoxia (Desmostylia, Mammalia). Royal Society
Open Science 5:e172441.
Here, we report a new ‘discovery’ of a desmostylian fossil
in the geological collection at a national university in Japan. This fossil was
unearthed over 60 years ago and donated to the university. Owing to the original
hand-written note kept with the fossil in combination with interview
investigation, we were able to reach two equally possible fossil sites in the
town of Tsuchiyu Onsen, Fukushima. Through the interviews, we learned that the
fossil was discovered during construction of a debris flow barrier and that it
was recognized as a ‘dinosaur’ bone among the locals and displayed in the
Village Hall before/until the town experienced a fire disaster in 1954. As
scientific findings, the fossil was identified to be a right femur of Paleoparadoxia
(Desmostylia), which shows well-preserved muscle scars on the surface. The age
was estimated to be 15.9 Ma or younger in zircon-dating. This study shows an
excellent case that historical and scientific significances could be extracted
from long-forgotten uncatalogued specimens as long as the original information
is retained with the specimens.
McCurry, M.R. and N.D. Pyenson. 2018. Hyperlongirostry and
kinematic disparity in extinct toothed whales. Paleobiology. Online early.
https://www.cambridge.org/core/journals/paleobiology/article/hyperlongirostry-and-kinematic-disparity-in-extinct-toothed-whales/5B68F5FAD697EB11FDE6298106509722
Toothed cetacean (Odontoceti) lineages in the Miocene and
Pliocene evolved rostra that are proportionally more elongate than any other
aquatic mammal or reptile, living or extinct. Their similarities in cranial
proportions to billfish may suggest a convergent feeding style, where the
rostrum is swept through the water to hit and stun prey. Here we calculated
second moment of area from rostral cross sections of these fossil odontocete
taxa, as well as from extant ecological analogues, to infer variation in
feeding behavior. Our results show that the extremely long rostra of extinct
toothed whales vary considerably in functionally relevant measures of shape and
likely exhibited a diversity of feeding behaviors, ranging from those similar
to modern odontocetes to those convergent with billfish. Eustatic sea-level and
temperature maxima of the Miocene likely led to changes in prey characteristics
or abundance that enabled the repeated evolution of this extreme morphotype,
which later went extinct during late Pliocene climatic deterioration.
Nelson, M.D. and M.D. Uhen. 2018. First occurrence of a
squalodelphinid (Cetacea, Odontoceti) from the early Miocene of Washington
state. Journal of Vertebrate Paleontology 38:e1428197.
Here, we present a new indeterminate
squalodelphinid from the early Miocene of Washington State. The Oligocene and
Miocene formations of Washington State possess a rich, yet underreported record
of fossil cetaceans. Specimen UWBM 87105 is the posterior third of the skull,
with portions of the premaxillae, maxillae, nasals, frontals, lacrimals, and
palatine. No associated periotic or ectotympanic bone has been preserved. In
addition, undiagnostic rib fragments and vertebrae are present. This specimen represents
a small odontocete that is characterized by a dramatically thickened
supraorbital process. This feature is a synapomorphy of the taxon
Squalodelphinidae C Platanistidae (Muizon, 1987). In the Platanistidae, such as
in Platanista, this supraorbital process is so exaggerated as to be a
supraorbital crest, whereas in the Squalodelphinidae the thickening is not so extreme.
Due to the relatively minor thickening of the supraorbital process in UWBM
87105, we place it within the Squalodelphinidae. The Squalodelphinidae are also
known for having mildly asymmetrical skulls (Muizon, 1987), although this is
not considered a synapomorphy because such asymmetry is common within
Odontoceti. Specimen UWBM 87105 is valuable in that it extends the known geographic
range of the Squalodelphinidae and offers insight into the diversity of the
Platanistoidea during the early Miocene.
Peredo, C.M., N.D. Pyenson, C.D. Marshall, and M.D. Uhen.
2018. Tooth loss precedes the origin of baleen in whales. Current Biology
28:1-9.
Whales use baleen, a novel integumentary structure, to
filter feed; filter feeding itself evolved at least five times in tetrapod
history but demonstrably only once in mammals [1]. Living baleen
whales (mysticetes) are born without teeth, but paleontological and
embryological evidence demonstrate that they evolved from toothed ancestors
that lacked baleen entirely [2]. The mechanisms driving the
origin of filter feeding in tetrapods remain obscure. Here we report Maiabalaena
nesbittae gen. et sp. nov., a new fossil whale from early Oligocene rocks
of Washington State, USA, lacking evidence of both teeth and baleen. The holotype
possesses a nearly complete skull with ear bones, both mandibles, and
associated postcrania. Phylogenetic analysis shows Maiabalaena as
crownward of all toothed mysticetes, demonstrating that tooth loss preceded the
evolution of baleen. The functional transition from teeth to baleen in
mysticetes has remained enigmatic because baleen decays rapidly and leaves
osteological correlates with unclear homology; the oldest direct
evidence for fossil baleen is ∼25 million
years younger [3] than the oldest stem mysticetes (∼36 Ma). Previous hypotheses for
the origin of baleen [4, 5] are
inconsistent with the morphology and phylogenetic position of Maiabalaena.
The absence of both teeth and baleen in Maiabalaena is consistent with
recent evidence that the evolutionary loss of teeth and origin of baleen are
decoupled evolutionary transformations, each with a separate morphological and
genetic basis [2, 6]. Understanding these
macroevolutionary patterns in baleen whales is akin to other macroevolutionary
transformations in tetrapods such as scales to feathers in birds.
Peredo, C.M., J.S. Peredo, and N.D. Pyenson. 2018. Convergence
on dental simplification in the evolution of whales. Paleobiology 44:434-443.
The fossil record of mammal dentition provides crucial
insight into key ecological and functional transitions throughout mammalian
evolutionary history. For cetaceans, both extant clades differ markedly from
their stem ancestors; neither retains the differentiated dentition or the
tribosphenic molars characteristic of Mammalia. We used quantitative measures
of dental complexity across fossil and living cetaceans to identify a trend
toward dental simplicity through the Neogene. Both extant cetacean clades
depart from the ancestral mammalian condition and concurrently converge upon a
reduced and simplified dentition; modern mysticetes all have become entirely
edentulous (at birth), and living odontocetes possess teeth as single-rooted,
conical pegs. These two parallel trends accompany major shifts in feeding
strategy (i.e., filter feeding in mysticetes and echolocation in odontocetes),
suggesting that these evolutionary innovations for prey acquisition are
enabling factors for the loss of prey processing and subsequent convergence on
dental simplification.
Peredo, C.M. and N.D. Pyenson. 2018. Salishicetus meadi, a new
aetiocetid from the late Oligocene of Washington state and implications for
feeding transitions in early mysticete evolution.
https://royalsocietypublishing.org/doi/10.1098/rsos.172336
Living baleen whales, or Mysticeti, lack teeth and instead
feed using keratinous baleen plates to sieve prey-laden water. This feeding
strategy is profoundly different from that of their toothed ancestors, which
processed prey using the differentiated dentition characteristic of mammals.
The fossil record of mysticetes reveals stem members that include extinct taxa
with dentition, illuminating the morphological states that preceded the loss of
teeth and the subsequent origin of baleen. The relationships among stem
mysticetes, including putative clades such as Mammalodontidae and Aetiocetidae,
remain debatable. Aetiocetids are among the more species-rich clade of stem
mysticetes, and known only from fossil localities along the North Pacific
coastline. Here, we report a new aetiocetid, Salishicetus meadi gen. et
sp. nov, from the late Oligocene of Washington State, USA. Salishicetus
preserves a near-complete lower dentition with extensive occlusal wear,
indicating that it processed prey using shearing cheek teeth in the same way as
its stem cetacean ancestors. Using a matrix with all known species of
aetiocetids, we recover a monophyletic Aetiocetidae, crownward of a basal clade
of Mammalodontidae. The description of Salishicetus resolves
phylogenetic relationships among aetiocetids, which provides a basis for
reconstructing ancestral feeding morphology along the stem leading to crown
Mysticeti.
Peredo, C.M., M.D. Uhen, and M.D. Nelson. 2018. A new
kentriodontid (Cetacea: Odontoceti) from the early Miocene Astoria Formation
and a revision of the stem delphinidin family Kentriodontidae. Journal of
Vertebrate Paleontology 38:e1411357.
https://www.tandfonline.com/doi/full/10.1080/02724634.2017.1411357
The Family Kentriodontidae is a diverse and abundant group
of odontocetes from the late Oligocene and Miocene around the globe. Despite
nearly a century of research on the group, the relationships across the family
have remained poorly understood. Several recent studies have suggested that the
family is polyphyletic and in need of major taxonomic revision. A new fossil
stem delphinidan from the early Miocene of Washington State is described as Wimahl
chinookensis, gen. et sp. nov., and is assigned to a revised
Kentriodontidae. Wimahl chinookensis represents one of the oldest
kentriodontids and is the northernmost kentriodontid described from the Pacific
Ocean, extending their range in the eastern Pacific from central California up
to Washington State. Its phylogenetic position relative to other stem
delphinidans suggests that it is sister to Kampholophos serrulus from
the middle Miocene Monterey Formation of California. Additional phylogenetic
results guide the revision of stem delphinidans and new diagnosis and
delimitation of the Family Kentriodontidae
Rahmat, S., F. Muniz, A. Toscano, et al. 2018. First
European record of Homiphoca (Phocidae: Monachinae: Lobodontini) and its
bearing on the paleobiogeography of the genus. Historical Biology. Online
Early.
https://www.tandfonline.com/doi/full/10.1080/08912963.2018.1507030
Marine mammal fossils (except pinnipeds) have commonly been
found in Pliocene marine siliciclastic layers of the Neogene Guadalquivir Basin
in Southwest Spain. A few Neogene phocid innominate bones are known from the
Western Paratethys and Western Atlantic. Here we describe a new innominate bone
from the early Pliocene (5.3–3.6 Ma) of the Western Paratethys (Spain),
which is typical of the subfamily Monachinae, and has a flattened ilium similar
to representatives of the tribe Lobodontini, particularly Leptonychotes
weddellii. Comparison with other fossil monachine innominates from North
America, South America and South Africa reveals that this specimen represents
the genus Homiphoca, but species classification remains premature. This
is the first European record of the genus Homiphoca and has
paleobiogeographic implications, questioning the geological age of the
Varswater Formation ‘E’ Quarry, Langebaanweg, Cape Province of South Africa.
This discovery from the eastern North Atlantic further implies a more regular
transatlantic gene flow in Miocene and Pliocene times than today. We argue that
during the Messinian-Zanclean crisis, monachines became isolated and retreated
southward to lower latitudes, possibly due to climatic deterioration (during
glacial stages) and competition from the cold-adapted phocines from the north.
Ramasammy, B., O. Lambert, A. Collareta, et al. 2018.
Description of the skeleton of the fossil beaked whale Messapicetus gregarius: searching potential proxies for deep-diving
abilities. Fossil Record 21:11-32.
Ziphiidae (beaked whales) are a successful family of medium-
to large-sized toothed whales. Their extant members perform regular deep dives
beyond the photic zone to forage for cephalopods and fish. Conversely, extinct
long-snouted stem ziphiids are interpreted as epipelagic predators. However,
some aspects of this hypothesis remain unclear due to the lack of clear
morphological proxies for recognizing regular deep divers. We compared the
forelimb, neck, and pterygoid sinus system of the fossil ziphiid Messapicetus
gregarius with those of other odontocetes to evaluate the potential of
these body regions as proxies to assess deep-diving specialization. The
reconstructed musculature of the neck and forelimb of M. gregarius
was also compared with that of other odontocetes. We also quantified variation
in the proportions of the forelimb and the hamular fossa of the pterygoid sinus
(HF) using 16 linear measurements. The degree of association between diving
behaviour in extant odontocetes and these measurements was evaluated with and
without phylogenetic correction. Reconstruction of the neck musculature
suggests that M. gregarius possessed a neck more flexible than most
extant ziphiids due to the lower degree of fusion of the cervical vertebrae and
the large insertions for the M. longus colli and Mm. intertransversarii
ventrales cervicis. While neck rigidity might be related to deep diving,
differences in neck flexibility among extant ziphiids indicate a more complex
functional interpretation. The relationship between forelimb morphology and
diving behaviour was not significant, both with and without phylogenetic
correction, suggesting that it cannot be used to assess deep-diving abilities
with the parameters considered here. Measurements of the HF revealed successful
to evaluate deep-diving abilities in odontocetes, with an enlargement of this
structure in deep divers. Considering other evidence that suggests an
epipelagic behaviour, we propose different scenarios to explain the observation
of an enlarged HF in M. gregarius: (1) this species may have fed at
different depths; (2) it performed deep dives to avoid potential predators; or
(3) the enlarged HF and deep-diving habitat correspond to an ancestral
condition, with M. gregarius returning to a more epipelagic
habitat.
Ritsche, I.S., J.M. Fahlke, F. Wieder, et al. 2018. Relationships
of cochlear coiling shape and hearing frequencies in cetaceans, and the
occurrence of infrasonic hearing in Miocene Mysticeti. Fossil Record 21:33-45.
Baleen whales (Mysticeti) are known to use low frequencies
(LF; 200Hz and below) and infrasound (<20hz able="" are="" communication.="" dontoceti="" for="" hearing="" limits="" lowest="" of="" produce="" the="" to="" toothed="" ultrasound="" whales="" which="">20kHz), reach low frequencies. Researchers have tried to
understand the evolution of LF and infrasonic hearing in mysticetes by linking
the shape of the inner ear cochlea or individual cochlear measurements to known
hearing frequencies and making inferences to extinct species. Using
landmark-based shape analysis of complete cochlear coiling, we show that
cochlear coiling shape correlates with LF and high-frequency (HF; >10kHz)
hearing limits in cetaceans. Very LF ( ≤ 50Hz) and infrasonic hearing are
associated with, for example, a protruding second turn, a descending apex, and
a high number of turns. Correlations between cochlear and cranial variables and
cochlear and cranial shape indicate that low LF hearing limits are furthermore
connected to longer cochleae and relatively larger cranial widths. Very LF
hearing in Mysticeti appeared in the middle Miocene, and mysticete infrasonic
hearing had evolved by the late Miocene. Complete cochlear coiling is suitable
for estimating hearing limits in cetaceans, closely approximated by cochlear
length times number of cochlear turns.
Solis-Anorve, A., G. Gonzalez-Barba, and R. Hernandez-Rivera.
Description of a new toothed mysticete from the late Oligocene of San Juan de
la Costa, B.C.S., Mexico. Journal of South American Earth Sciences 89:337-346.
https://www.sciencedirect.com/science/article/pii/S0895981118303882
This paper describes a toothed mysticete that belongs to a
basal family found in Oligocene sedimentary rocks deposited in the North Pacific
Ocean. The material that is described here belongs in the Chattian stage of the
Oligocene, and it was collected near Arroyo El Saladito from the San Juan
Member in the El Cien Formation, Baja California Sur, México. The sedimentary
environment of this area has been interpreted to be a continental platform with
nutrient-rich waters combined with anoxic conditions. Therefore, the specimens
that have been found in the phosphorite layers lived in an environment of shallow
coastal waters. The material described is a dentary fragment, a skull and
fragments of the teeth. The new taxon is located within the Superfamily
Aetiocetoidea due to the presence of functional teeth, which have a slightly
globose shape with eight slightly triangular apices. Niparajacetus
palmadentis presents a morphology that contrasts with other toothed
whales. For example, it shows an elongated and wide skull in the posterior
region with a triangular shape, and its estimated total length is 3.2–3.5 m.
Tanaka, Y. M. and Watanabe. 2018. Geologically old and
ontogenetically young Herpetocetus sp. from the late Miocene of Japan. Journal
of Vertebrate Paleontology. Online Early.
An ontogenetically young fossil baleen whale from the lower
part of the Horokaoshirarika Formation of Hokkaido, Japan, includes a partial
skull, periotics, bullae, mandible, vertebrae, and a scapula. It is identified
as Herpetocetus sp. because it exhibits a postglenoid process of the
squamosal more transversely compressed than in Nannocetus, a deep and
anteroposteriorly long fossa on the dorsal surface of the squamosal between the
zygomatic process and the lateral wall of the brain case, and a prominent
squamosal flange of the periotic. The Hokkaido specimen differs from currently
described Herpetocetus species in having a large hiatus fallopii, and an
angle at the anteromedial edge of the pars cochlearis, just medial to the
hiatus fallopii. Because the lower part of the Horokaoshirarika Formation is
late Miocene in age (approximately 7.7 to 6.8 Ma), the Hokkaido Herpetocetus
specimen is the only record of Miocene Herpetocetinae from the western Pacific.
Previously, Miocene Herpetocetinae were reported from the eastern North Pacific
and western Atlantic. Accordingly, this new record of Herpetocetus from
the upper Miocene of the western North Pacific suggests an earlier origin for
both the genus and the subfamily.
Tanaka, Y., H. Furusawa, and L.G. Barnes. 2018. Fossil
herpetocetine baleen whales (Cetacea, Mysticeti, Cetotheriidae) from the lower
Pliocene Horokaoshirarika Formation at Numata, Hokkaido, Northern Japan.
Paleontological Research 22:295-306.
Two mandibles of fossil mysticetes from the early Pliocene,
upper part of the Horokaoshirarika Formation at Numata Town, Hokkaido, Japan,
belong to the archaic, extinct cetotheriid baleen whale, Herpetocetinae gen. et
sp. indet. by having an elongated angular process projecting posteriorly beyond
the mandibular condyle. The new materials of the Herpetocetinae represent their
northernmost occurrence in the North Pacific.
Tanaka, Y., T. Ando, and H. Sawamura. 2018. A new species of
middle Miocene baleen whale from the Nupinai Group, Hikatagawa Formation of
Hokkaido, Japan. PeerJ 6:e4934
Tonomori, W., H. Sawamura, T. Sato, and N. Kohno. 2018. A
new Miocene pinniped Allodesmus (Mammalia:
Carnivora) from Hokkaido, northern Japan. Royal Society Open Science 5:172440.
A nearly complete pinniped skeleton from the middle Miocene
Okoppezawa Formation (ca 16.3–13.9 Ma), Hokkaido, northern Japan, is
described as the holotype of Allodesmus uraiporensis sp. nov. The new
species is distinguishable from other species of the genus by having the
palatine fissure (incisive foramen) that is located anterior to the canine, an
anteriorly located supraorbital process of the frontal, and by having the
calcaneum with a developed peroneal tubercle. Our phylogenetic analysis
suggests that the subfamily Allodesminae are represented by two genera, Atopotarus
and Allodesmus, and the latter genus is represented by at least six
species; Al. kernensis, Al. sinanoensis, Al.
naorai, Al. packardi, Al. demerei and Al. uraiporensis
sp. nov. Allodesmus uraiporensis sp. nov. is one of the oldest and the
northernmost record of the genus in the western North Pacific, and it suggests
that the diversification of the genus in the western North Pacific was
synchronous to the time of their diversification in the eastern North Pacific.
Tsai, C.H. and R.E. Fordyce. 2018. A new archaic baleen
whale Toihapautea waitaiki (early Late Oligocene, New
Zealand) and the origins of crown Mysticeti. Royal Society Open Science
5:172453.
A new genus and species of extinct baleen whale †Toipahautea
waitaki (Late Oligocene, New Zealand) is based on a skull and associated
bones, from the lower Kokoamu Greensand, about 27.5 Ma (local upper Whaingaroan
Stage, early Chattian). The upper jaw includes a thin, elongate and apparently
toothless maxilla, with evidence of arterial supply for baleen. Open sutures
with the premaxilla suggest a flexible (kinetic) upper jaw. The blowhole is
well forward. The mandible is bowed laterally and slightly dorsally; unlike the
Eomysticetidae, there are no mandibular alveoli, and the coronoid process is
tapered and curved laterally. Jaw structure is consistent with baleen-assisted
gulp-feeding. The age of early Chattian makes †Toipahautea a
very early, if not the oldest named, toothless and baleen-bearing mysticete,
suggesting that the full transition from toothed to baleen-bearing probably
occurred in the Early Oligocene. Late Oligocene mysticetes vary considerably in
jaw form and kinesis, tooth form and function, and development of baleen,
implying a wide range of raptorial, suctorial and filter-feeding behaviour.
More study may elucidate the function of jaws, teeth and baleen in terms of opportunist/generalist
feeding, as in modern gray whales, versus specialized feeding. We here propose
that early mysticetes, when transitioned from toothed to baleen-bearing, were
generalists and opportunists instead of specializing in any forms of feeding strategies.
In addition, two different phylogenetic analyses placed †Toipahautea
either in a polytomy including crown Mysticeti, or immediately basal to the
crown, and above †Eomysticetidae in both cases. Because the †Toipahautea
waitaki holotype is an immature individual, it may plot more basally in
phylogeny than its true position.
Velez-Juarbe, J. 2018. New data on the early odobenid Neotherium Kellogg, 1931, and other
pinniped remains from the Sharktooth Hill Bonebed, California. Journal of Vertebrate
Paleontology. Online Early.
Velez-Juarbe, J. and F.M. Salinas-Marquez. 2018. A dwarf
walrus from the Miocene of Baja California Sur, Mexico. Royal Society Open
Science 5:180423.
Here, we describe the odobenid Nanodobenus arandai
gen. et sp. nov., based on a nearly complete left mandible from the mid to late
Miocene Tortugas Formation in Baja California Sur. Nanodobenus is
distinguished among odobenids by displaying a unique combination of
plesiomorphic and derived characters, such as narrow mandibular symphysis,
well-developed genial tuberosity, bilobed canine and p2 roots, bulbous
post-canine teeth with the paraconid, protoconid and hypoconid, and smooth
lingual cingula. Moreover, it is characterized by its small adult body length,
which is estimated at about 1.65 m. Throughout the Miocene–Pliocene odobenids
are characterized by an increase in body size, especially after the extinction
of desmatophocids in the late Miocene. The small size of Nanodobenus
departs from this trend, demonstrating that there was greater size disparity
among odobenids in the mid–late Miocene than previously thought. It is
hypothesized that Nanodobenus occupied a niche that was later on
occupied by similar-sized otariids, such as Thalassoleon mexicanus,
which occurs sympatrically with large odobenids in the overlying Almejas Formation.
Viglino, M., M.R. Buono, R.E. Fordyce, et al. 2018. Anatomy
and phylogeny of the large shark-toothed dolphin Phoberodon arctirostris
Cabrera, 1926 (Cetacea: Odontoceti) from the early Miocene of Patagonia
(Argentina). Zoological Journal of the Linnean Society. Online early.
https://academic.oup.com/zoolinnean/advance-article-abstract/doi/10.1093/zoolinnean/zly053/5086400?redirectedFrom=fulltext
The early Miocene of Patagonia (Argentina) provides one of
the best-known records of odontocetes for an age interval with scarce fossils.
Most of these taxa are historically old and briefly described, which has
contributed, in part, to their controversial taxonomic position. The
shark-toothed dolphin Phoberodon arctirostris was described almost 100
years ago and suggested as a member of Platanistoidea and Squalodontidae. However,
it has not been analysed recently and has never been included in a phylogenetic
analysis. Recent fieldwork in the early Miocene sediments in Patagonia yielded
a new specimen referred to this species, allowing for its modern and detailed
description and the first phylogenetic analyses. Analyses recovered P. arctirostris
as a stem Odontoceti or an early-diverging platanistoid, more closely related
to an unnamed Oligocene specimen from New Zealand and not in a clade with Squalodon
calvertensis (i.e. Squalodontidae). The reconstructed body length of P.
arctirostris indicates that it is one of the largest stem Odontoceti. Our
results suggest that during the early Miocene of Patagonia, archaic odontocete
forms (i.e. P. arctirostris) cohabited with archaic and more crownward
platanistoids (i.e. Aondelphis talen and Notocetus vanbenedeni),
helping to characterize the early Miocene cetacean communities of Patagonia.
Viglino, M., M.R. Buono, C.S. Gutstein, et al. 2018. A new
dolphin from the early Miocene of Patagonia, Argentina: insights into the
evolution of Platanistoidea in the southern hemisphere. Acta Palaeontologica
Polonica 63:261-277.
https://www.app.pan.pl/article/item/app004412017.html
The contents of the superfamily Platanistoidea, an
early-diverging lineage comprising extinct species and a single extant representative
of South Asian river dolphin (Platanista gangetica), remain
controversial. We describe here a partial skull and associated tympano-periotic
bones identified as a new genus and species, Aondelphis talen gen. et
sp. nov., collected in the lower levels of the Gaiman Formation (early
Miocene), in Patagonia (Chubut Province, Argentina). Aondelphis is the
first Patagonian platanistoid species named in almost a century. Phylogenetic
analyses suggest Aondelphis talen gen. et sp. nov. and a taxon from New
Zealand (cf. Papahu ZMT-73) are basal Platanistoidea sensu lato.
Unambiguous synapomorphies related to the ear bones allowed us to determine its
phylogenetic position. Aondelphis talen markedly differs from the
other well-known early Miocene Patagonian platanistoid Notocetus,
suggesting the coexistence of at least two different morphotypes that may have
occupied different ecological niches at that time. The putative close
relationship with a species from New Zealand indicates there was a rapid
diversification and widespread distribution of the group in the Southern
Hemisphere during the early Miocene. The description of new species and
revision of historical records of Patagonian platanistoids can help shedding
light on cetacean assemblages of the Patagonian sea during this epoch.
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