[PaleoMammalogy • 2024] Ontocetus posti • New Species of Ontocetus (Pinnipedia: Odobenidae) from the Lower Pleistocene of the North Atlantic shows similar Feeding Adaptation independent to the extant walrus (Odobenus rosmarus)

Ontocetus posti

Boisville​, Chatar & Kohno, 2024

 

DOI: 10.7717/peerj.17666

  x.com/NarimaneChatar

Abstract 

Ontocetus is one of the most notable extinct odobenines owing to its global distribution in the Northern Hemisphere. Originating in the Late Miocene of the western North Pacific, this lineage quickly spread to the Atlantic Ocean during the Pliocene, with notable occurrences in England, Belgium, The Netherlands, Morocco and the eastern seaboard of the United States. Reassessment of a pair of mandibles from the Lower Pleistocene of Norwich (United Kingdom) and a mandible from the Upper Pliocene of Antwerp (Belgium) that were referred to as Ontocetus emmonsi reveals existences of features of both Ontocetus and Odobenus. The presence of four post-canine teeth, a lower canine larger than the cheek-teeth and a lower incisor confirms the assignment to Ontocetus; simultaneously, characteristics such as a fused and short mandibular symphysis, a well-curved mandibular arch and thin septa between teeth align with traits usually found in Odobenus. Based on a combination of these characters, we describe Ontocetus posti, sp. nov. Its mandibular anatomy suggests, a better adaptation to suction-feeding than what was previously described in the genus suggesting that Ontocetus posti sp. nov. likely occupied a similar ecological niche to the extant walrus Odobenus rosmarus. Originating from the North Pacific Ocean, Ontocetus most likely dispersed via the Central American Seaway. Although initially discovered in the Lower Pliocene deposits of the western North Atlantic, Ontocetus also left its imprint in the North Sea basin and Moroccan Plio-Pleistocene deposits. The closure of the Isthmus of Panama during the Mio-Pliocene boundary significantly impacted the contemporary climate, inducing global cooling. This event constrained Ontocetus posti in the North Sea basin leaving the taxon unable to endure the abrupt climate changes of the Early Pleistocene, ultimately going extinct before the arrival of the extant counterpart, Odobenus rosmarus.

Systematic paleontology

Mammalia Linnaeus, 1758

Carnivora Bowdich, 1821

Pinnipedia Illiger, 1811

Odobenidae Allen, 1880

Odobeninae Mitchell, 1968

Odobenini Deméré, 1994b

Genus Ontocetus Leidy, 1859

Type species: Ontocetus emmonsi Leidy, 1859; Yorktown Formation, North Carolina, Pliocene

Ontocetus posti sp. nov.

A species of Ontocetus that exhibits mosaic characters including some shared traits with the genus Odobenus. These diagnostic features of Ontocetus comprise a lower canine markedly larger (at least 20% larger than cheekteeth) from the cheek toothrow, presence of the lower first premolar (p1), specifically at least four lower postcanine teeth that are consisted of p1–p4, a broad and short edentulous mandibular terminus exhibiting two lower incisors (i2, i3), an elevated and slanted anterior margin, the relative size of the mandible (reaching almost 30 cm in horizontal length), a high, thin, and posterolaterally projected coronoid process, as well as a short distance between the dorsal margin and coronoid process (less than 8% of the total length of the mandible).

This species also shares certain characteristics with Odobenus, such as the fusion of the mandibular symphysis, a mandibular symphysis oval in shape and shorter in proportion to the total length of the mandible (less than 50%), a horizontal ramus with a well-curved lateral occlusal outline (also occurs in the referred mandible of Dusignathus seftoni) that accounts for the shortening of the rostrum. Additionally, a shorter space between the canine and the cheek teeth can be observed (less than 10% of the total length of the dental row), as well as between the thin cheek tooth alveoli themselves. Other shared traits encompass an underdeveloped angular process, and a flat, less developed mandibular condyle.

Etymology: The species is named in honor of Mr. Klaas Post, curator of Vertebrate Paleontology at Natuurhistorisch Museum Rotterdam, in recognition of his extensive contributions to geology and paleontology in the North Sea district, and as a token of appreciation for his continuous support, encouragement, and invaluable assistance provided to all of us throughout this study.

Holotype mandibles of Ontocetus posti. adult female, NMR 7472, cast of NWHCM 1996.1.

 Scale bar equals 5 cm. The hatched parts correspond to broken surfaces. Pictures taken and figures drawn by M. Boisville.

Hypothesized sequence of cranial, mandibular, and dental character transformations during odobenine evolution toward the suction-feeding specialization. Cranial, mandibular and dental characters from Deméré (1994b) and Boessenecker & Churchill (2013). Scale bar equals 10 cm. The restored mandible of Ontocetus posti sp. nov. based on NWHCM 1996.1. The shaded areas correspond to the missing parts of the specimens.

Reconstructions redrawn from R.W. Boessenecker illustrations by N. Chatar.

Mathieu Boisville​, Narimane Chatar and Naoki Kohno. 2024. New Species of Ontocetus (Pinnipedia: Odobenidae) from the Lower Pleistocene of the North Atlantic shows similar Feeding Adaptation independent to the extant walrus (Odobenus rosmarus). PeerJ. 12:e17666. DOI: doi.org/10.7717/peerj.17666

  x.com/NarimaneChatar/status/1823388564291477814

[PaleoMammalogy • 2024] Valenictus sheperdi • Tusked Walruses (Carnivora: Odobenidae) from the Miocene–Pliocene Purisima Formation of Santa Cruz, California (U.S.A.): A New Species of the Toothless Walrus Valenictus and the Oldest Records of Odobeninae and Odobenini

Valenictus sheperdi

R. Boessenecker, Poust, S. Boessenecker & Churchill. 2024

DOI: 10.1080/02724634.2023.2296567 

 coastalpaleo.blogspot.com 

 

ABSTRACT

Currently limited to cold climates near the Arctic circle, living walruses are the sole survivors of a previously much more diverse clade that occupied coastal waters throughout the northern hemisphere during the Mio–Pliocene. Though pinniped faunas have the highest diversity of walruses in the Miocene, the Purisima Formation of California records a moderately diverse assemblage of four walrus species. We report new specimens of tusked walruses (Odobeninae) including the oldest known members of Odobeninae, and Odobenini, and fossils of the specialized toothless odobenine walrus Valenictus Mitchell, 1961. Among these is the new species Valenictus sheperdi sp. nov., represented by a complete skull and referred post-crania from lower Pliocene strata within the Purisima Formation (5.33–4.89 Ma). Additionally, we report a geochronologically younger skull of Valenictus chulavistensis Deméré, 1994 from further up section (4.89–3.59 Ma). Expanded phylogenetic analysis recovers Odobeninae including Ontocetus Leidy, 1859 as the earliest diverging lineage in the Odobenini, and places a monophyletic Valenictus as the sister taxon to Pliopedia, Kellogg, 1921 which is included in a phylogeny for the first time; Odobenus is sister to the Valenictus + Pliopedia clade. Discovery of an isolated metacarpal near the base of the formation provides the oldest known well-dated evidence of odobenines. A diverse assemblage of molluskivores characterized the Neogene eastern North Pacific and their extinction around the Pliocene–Pleistocene boundary coincided with tectonically driven paleogeographic changes on the Pacific coast. The loss of temperate walruses may have provided opportunities for both new molluskivores and the otariid and phocid pinnipeds that make up present North Pacific pinniped communities.

New life restoration of the extinct "toothless" walrus Valenictus sheperdi - cruising along in an early kelp forest along the shoreline of northern California during the early Pliocene epoch.

 Illustration by Robert Boessenecker 

Robert W. Boessenecker, Ashley W. Poust, Sarah J. Boessenecker and Morgan Churchill. 2024. Tusked Walruses (Carnivora: Odobenidae) from the Miocene–Pliocene Purisima Formation of Santa Cruz, California (U.S.A.): A New Species of the Toothless Walrus Valenictus and the Oldest Records of Odobeninae and Odobenini. Journal of Vertebrate Paleontology. e2296567. DOI: 10.1080/02724634.2023.2296567

  twitter.com/CoastalPaleo/status/1751966430021767187

Valenictus sheperdi and friends: Miocene-Pliocene tusked walruses from the Purisima Formation in Santa Cruz, California

 coastalpaleo.blogspot.com/2024/02/valenictus-sheperdi-and-friends-miocene.html

[Mammalogy • 2023] An evolutionarily distinct Ringed Seal in the Ilulissat Icefjord, Greenland

Kangia ringed seals Pusa hispida hispida in the Ilulissat Icefjord system, West Greenland 

(c) Pelage of Kangia (left) and typical Arctic ringed seals (right).

in Rosing-Asvid, Löytynoja, Momigliano, Hansen, ... et Olsen, 2023.

DOI: 10.1111/mec.17163

 All photographs by Greenland Institute of Natural Resources.

 

Abstract

The Earth's polar regions are low rates of inter- and intraspecific diversification. An extreme mammalian example is the Arctic ringed seal (Pusa hispida hispida), which is assumed to be panmictic across its circumpolar Arctic range. Yet, local Inuit communities in Greenland and Canada recognize several regional variants; a finding supported by scientific studies of body size variation. It is however unclear whether this phenotypic variation reflects plasticity, morphs or distinct ecotypes. Here, we combine genomic, biologging and survey data, to document the existence of a unique ringed seal ecotype in the Ilulissat Icefjord (locally ‘Kangia’), Greenland; a UNESCO World Heritage site, which is home to the most productive marine-terminating glacier in the Arctic. Genomic analyses reveal a divergence of Kangia ringed seals from other Arctic ringed seals about 240 kya, followed by secondary contact since the Last Glacial Maximum. Despite ongoing gene flow, multiple genomic regions appear under strong selection in Kangia ringed seals, including candidate genes associated with pelage coloration, growth and osmoregulation, potentially explaining the Kangia seal's phenotypic and behavioural uniqueness. The description of ‘hidden’ diversity and adaptations in yet another Arctic species merits a reassessment of the evolutionary processes that have shaped Arctic diversity and the traditional view of this region as an evolutionary freezer. Our study highlights the value of indigenous knowledge in guiding science and calls for efforts to identify distinct populations or ecotypes to understand how these might respond differently to environmental change.

Keywords: arctic, diversity, indigenous knowledge, local adaptation, marine mammal

Unusual population of ringed seals in the Ilulissat Icefjord system, West Greenland.
 (a) Kangia ringed seals hauling out on sea ice.
(b) The dynamic Ilulissat Icefjord system. (c) Pelage of Kangia (left) and typical Arctic ringed seals (right).
 (d) Kangia ringed seal instrumented with a satellite tag (image edited to remove person in background. Original image provided in (d). (e) Typical Arctic ringed seal instrumented with a satellite tag (movement data not shown).

 All photographs by Greenland Institute of Natural Resources.

CONCLUSION: 

The discovery of a distinct ringed seal ecotype in the Ilulissat Icefjord adds to a growing list of Arctic marine species with newly detected genetic and/or phenotypic diversity (Bringloe et al., 2020; Jacobsen et al., 2022; Laidre et al., 2022; Madsen et al., 2016; Mathiesen et al., 2017; Tempestini et al., 2020). The Arctic environment is highly dynamic, with marine systems characterized by long- and short-term fluctuations in glacial extent and run-off, marine-freshwater clines, sea-level changes and isostatic rebound. These processes might facilitate both regional and local speciation, perhaps down to the scale of individual fjord systems or larger marine-terminating glacier fronts. Thus, while our study is the first to demonstrate the existence of a distinct Kangia ringed seal ecotype in the Ilulissat Icefjord, similar intraspecific diversity and differentiation may exist elsewhere in both ringed seals and other Arctic marine species. Across the Arctic, marine-terminating glaciers, deep fjord systems and polynyas sustain high biological productivity and provide important foraging and resting habitats for marine organisms (Heide-Jørgensen et al., 2016; Lydersen et al., 2014; Meire et al., 2017). These areas may have constituted important high-latitude refugia and even micro-evolutionary speciation factories through glacial and interglacial periods, potentially supporting uniquely adapted populations of otherwise wide-spread and seemingly panmictic Arctic marine organisms. Some local populations may not easily respond to climate change by simply tracking their habitat northward, whereas others may harbour the adaptive potential providing species-level resistance to current climate warming. Our findings highlight the need for dedicated scientific efforts and thorough sampling to record and understand regional and local drivers of intraspecific diversity in the Arctic to provide information for nature management.

Aqqalu Rosing-Asvid, Ari Löytynoja, Paolo Momigliano, Rikke Guldborg Hansen, Camilla Hjorth Scharff-Olsen, Mia Valtonen, Juhana Kammonen, Rune Dietz, Frank Farsø Rigét, Steve H. Ferguson, Christian Lydersen, Kit M. Kovacs, David M. Holland, Jukka Jernvall, Petri Auvinen and Morten Tange Olsen. 2023. An evolutionarily distinct Ringed Seal in the Ilulissat Icefjord. Molecular Ecology. DOI: 10.1111/mec.17163

  phys.org/news/2023-10-west-greenland.html

[PaleoMammalogy • 2023] Fossil Brains provide Evidence of Underwater Feeding in early Seals

 

Potamotherium valletoni (Geoffroy, 1833)

in Lyras, Werdelin, B. G. M. van der Geer & A. A. E. van der Geer, 2023. 

DOI: 10.1038/s42003-023-05135-z

  twitter.com/IslandEvolution

reconstruction by Gabriel Ugueto twitter.com/SerpenIllus

Abstract

Pinnipeds (seals and related species) use their whiskers to explore their environment and locate their prey. Today they live mostly in marine habitats and are adapted for a highly specialised amphibious lifestyle with their flippers for locomotion and a hydrodynamically streamlined body. The earliest pinnipeds, however, lived on land and in freshwater habitats, much like mustelids today. Here we reconstruct the underwater foraging behaviour of one of these earliest pinnipeds (Potamotherium), focusing in particular on how it used its whiskers (vibrissae). For this purpose, we analyse the coronal gyrus of the brain of 7 fossil and 31 extant carnivorans. This region receives somatosensory input from the head. Our results show that the reliance on whiskers in modern pinnipeds is an ancestral feature that favoured survival of stem pinnipeds in marine habitats. This study provides insights into an impressive ecological transition in carnivoran evolution: from terrestrial to amphibious marine species. Adaptations for underwater foraging were crucial for this transition.

The phylogenetic position and brain of the early pinniped Potamotherium compared to other carnivorans.

reconstruction of Potamotherium valletoni

by Gabriel Ugueto

George A. Lyras, Lars Werdelin, Bartholomeus G. M. van der Geer and Alexandra A. E. van der Geer. 2023. Fossil Brains provide Evidence of Underwater Feeding in early Seals. Communications Biology. 6: 747.  DOI: 10.1038/s42003-023-05135-z

   twitter.com/IslandEvolution/status/1692190745384411212

  twitter.com/SerpenIllus/status/1692198189762248731

[PaleoMammalogy • 2020] Eomonachus belegaerensis • First Monk Seal from the Southern Hemisphere rewrites the Evolutionary History of True Seals

Eomonachus belegaerensis

Rule, Adams, Marx, Evans, Tennyson, Scofield & Fitzgerald, 2020

 DOI: 10.1098/rspb.2020.2318 

twitter.com/Te_Papa 

Illustration by Jaime Bran / Museum of New Zealand Te Papa. 

Abstract

Living true seals (phocids) are the most widely dispersed semi-aquatic marine mammals, and comprise geographically separate northern (phocine) and southern (monachine) groups. Both are thought to have evolved in the North Atlantic, with only two monachine lineages—elephant seals and lobodontins—subsequently crossing the equator. The third and most basal monachine tribe, the monk seals, have hitherto been interpreted as exclusively northern and (sub)tropical throughout their entire history. Here, we describe a new species of extinct monk seal from the Pliocene of New Zealand, the first of its kind from the Southern Hemisphere, based on one of the best-preserved and richest samples of seal fossils worldwide. This unanticipated discovery reveals that all three monachine tribes once coexisted south of the equator, and forces a profound revision of their evolutionary history: rather than primarily diversifying in the North Atlantic, monachines largely evolved in the Southern Hemisphere, and from this southern cradle later reinvaded the north. Our results suggest that true seals crossed the equator over eight times in their history. Overall, they more than double the age of the north–south dichotomy characterizing living true seals and confirms a surprisingly recent major change in southern phocid diversity.

Keywords: Monachini, biogeography, Taranaki, phylogeny, Monachinae, fossil

Eomonachus belegaerensis

Illustration by Jaime Bran /

 Museum of New Zealand Te Papa. 

James P. Rule, Justin W. Adams, Felix G. Marx, Alistair R. Evans, Alan J. D. Tennyson, R. Paul Scofield and Erich M. G. Fitzgerald. 2020. First Monk Seal from the Southern Hemisphere rewrites the Evolutionary History of True Seals. Proceedings of the Royal Society. DOI: 10.1098/rspb.2020.2318

 twitter.com/Te_Papa/status/1326315106968350720

The new species is named Eomonachus belegaerensis, (meaning 'dawn monk seal from Belegaer') after the sea of Belegaer, which lies west of Middle Earth in J.R.R. Tolkien's Lord of the Rings.

New fossil seal species rewrites history

eurekalert.org/pub_releases/2020-11/mu-nfs110920.php

[Ichthyology / Behaviour • 2019] Cryptic Habitat Use of White Sharks Carcharodon carcharias in Kelp Forest revealed by Animal-borne Video

a white shark Carcharodon carcharias 
encountering Cape fur seals Arctocephalus pusillus pusillus in kelp canopy. 

in Jewell, Gleiss, Jorgensen, et al., 2019.

  DOI: 10.1098/rsbl.2019.0085 

  twitter.com/RSocPublishing 

Abstract

Traditional forms of marine wildlife research are often restricted to coarse telemetry or surface-based observations, limiting information on fine-scale behaviours such as predator–prey events and interactions with habitat features. We use contemporary animal-attached cameras with motion sensing dataloggers, to reveal novel behaviours by white sharks, Carcharodon carcharias, within areas of kelp forest in South Africa. All white sharks tagged in this study spent time adjacent to kelp forests, with several moving throughout densely kelp-covered areas, navigating through channels and pushing directly through stipes and fronds. We found that activity and turning rates significantly increased within kelp forest. Over 28 h of video data revealed that white shark encounters with Cape fur seals, Arctocephalus pusillus pusillus, occurred exclusively within kelp forests, with seals displaying predator evasion behaviour during those encounters. Uniquely, we reveal the use of kelp forest habitat by white sharks, previously assumed inaccessible to these large predators.

Keywords: biologging, animal-borne video and environmental data collection systems (AVEDs), foraging, camera tags

Figure 2. Still-picture frames of a white shark encountering Cape fur seals in kelp canopy. (a) AVED footage of a white shark (Shark 5) encountering Cape fur seals. (b) The seals respond to the shark's presence by hunkering to the sea floor and blowing bubble streams as the shark passes overhead or swimming further into the kelp. (c) The shark swims through the bubbles, (d) then through kelp. (e) The shark pursues the seals, making contact with dense kelp fronds at several points and pushing through them. (f) At least three Cape fur seals (indicated by red arrows) are seen taking refuge in the canopy area of the kelp forest fronds and successfully avoiding the white shark.

Oliver J. D. Jewell , Adrian C. Gleiss , Salvador J. Jorgensen , Samantha Andrzejaczek , Jerry H. Moxley , Stephen J. Beatty , Martin Wikelski , Barbara A. Block  and Taylor K. Chapple. 2019. Cryptic Habitat Use of White Sharks in Kelp Forest revealed by Animal-borne Video.  Biology Letters.  DOI: 10.1098/rsbl.2019.0085  

 twitter.com/RSocPublishing/status/1120035760223203329

Shark's-Eye-View Video Captures Epic Seal Chase Through Kelp Forest shar.es/amT4vE via @LiveScience

[Mammalogy • 2019] Otaria flavescens (Shaw, 1800) • Solving A Long-standing Nomenclatorial Controversy: Designation of A Neotype for the Southern Sea Lion

Otaria flavescens (Shaw, 1800)

in Lucero, Rodríguez, Teta, et al., 2019.

  DOI:  10.11646/zootaxa.4555.2.13

During almost two centuries, two available specific epithets have competed for the southern sea lions of the genus Otaria Péron, 1816 (Fig. 1), which is classically regarded as monotypic (but see below). The species distributes more or less continuously along the Atlantic coast from southern Brazil south to Cape Horn and along the Pacific from northern Peru to the west South American Pacific coast . While some researchers have argued that the correct name for this species is Phoca flavescens Shaw, 1800 (e.g., Cabrera, 1940, Rice, 1977; Rodriguez & Bastida, 1993; Teta et al., 2018), others have used P. byronia de Blainville, 1820 (e.g., Allen, 1905; Hamilton, 1934; King, 1978, Oliva, 1988; Berta & Churchill, 2012). This controversy originates from the fact that the diagnosis of the type of flavescens, the oldest epithet and as such the one that has priority, would not match the phenotypic features of the genus Otaria. This view, which favors the usage of byronia for populations of southern sea lions, was strongly defended by Oliva (1988:768), who argued that “…(1) the total length of the holotype [of flavescens]; (2) the size of the external ear; and (3) the color and length of the specimen’s fur do not correspond to any developmental stage of the species.” However, Rodríguez and Bastida (1993:378) discussed these same features reaching a very different conclusion, by indicating that “Shaw’s holotype, collected in the Strait of Magellan, could only have been a newborn pup of Otaria or Arctocephalus australis; its body size (circa 62 cm) could correspond to either species, but the uniform yellowish color is found exclusively in some molted pups of the Southern sea lion. Ear length, though not matching well with the described body length, lies within the recorded range of Otaria, but outside that for Arctocephalus australis.”

Sergio Lucero, Sara M. Rodríguez, Pablo Teta, Guillermo Cassini and Guillermo D'Elía. 2019.  Solving A Long-standing Nomenclatorial Controversy: Designation of A Neotype for the Southern Sea Lion Otaria flavescens (Shaw, 1800). Zootaxa. 4555(2); 296–300. DOI:  10.11646/zootaxa.4555.2.13

[PaleoMammalogy • 2018] Nanodobenus arandai • A Dwarf Walrus from the Miocene of Baja California Sur, Mexico

Nanodobenus arandai 

Velez-Juarbe & Salinas-Márquez, 2018

 DOI: 10.1098/rsos.180423 

twitter.com/VelezJuarbeJ

Abstract

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.

KEYWORDS: Odobenidae, marine mammals, eastern Pacific, Miocene

Systematic palaeontology

Pinnipedia Illiger, 1811

Odobenidae Allen, 1880

Nanodobenus arandai, gen. et sp. nov.

Etymology. The name derives from the combination of ‘nano’, from the Latin ‘nanus’ which translates to dwarf, in reference to the small size of the specimen and estimated body size, combined with Odobenus, the genus of extant walrus, Odobenus rosmarus (Linnaeus, 1758), and the occasionally used suffix in odobenids (e.g. Archaeodobenus). The specific epithet honours Dr Francisco Aranda-Manteca (UABC) in recognition of his mentorship to the junior author and contributions to the knowledge of extinct marine vertebrates of Baja California and Baja California Sur.

Holotype. UABC FCM 0072, nearly complete left mandible, including p2–4. Collected by T. McMillan, c. 1987.

Type locality. Arroyo La Chiva (=Arroyo Tiburón [12–14]), Asunción, Baja California Sur, Mexico (figure 1).

Figure 2. Mandible and lower dentition of Nanodobenus arandai gen. et sp. nov. (UABC FCM 0072).

Mandible in lateral (a), medial (b) and occlusal (c) views. Lower dentition in labial (d), lingual (e) and occlusal (f) views. 

Abbreviations: c, lower canine; di, digastric insertion; gt, genial tuberosity; hyd, hypoconid; lc, lingual cingulum; p1–4, lower premolars 1–4; m1–2, lower molars 1–2; maf, masseteric fossa; mf, mental foramina; mnf, mandibular foramen; ms, mandibular sumphysis; pad, paraconid; prd, protoconid; wf, wear facet.

Figure 4. Time-calibrated strict consensus tree of Odobenidae and body size distribution.

Species range from [Velez-Juarbe, 2017; Boessenecker & Churchill, 2018; Boessenecher et al., 2018]; body size estimates from table 3 and outlines modified from Berta et al. [2018] and Lydersen [2018]. Numbers in nodes represent posterior probability (in bold) and bootstrap values.

Jorge Velez-Juarbe and Fernando M. Salinas-Márquez. 2018. A Dwarf Walrus from the Miocene of Baja California Sur, Mexico. Royal Society Open Science. DOI: 10.1098/rsos.180423

twitter.com/VelezJuarbeJ/status/1027207623593078784

[PaleoMammalogy • 2018] The Origin and Evolutionary Biology of Pinnipeds: Seals, Sea Lions, and Walruses

The Origin and Evolutionary Biology of Pinnipeds

Berta, Churchill & Boessenecker, 2018.

DOI:  10.1146/annurev-earth-082517-010009 

@CoastalPaleo

Abstract 

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.

Keywords Pinnipedia, Otariidae, Odobenidae, Phocidae, Desmatophocidae, paleobiology 

Figure 1 Time-calibrated phylogeny of pinnipeds, showing relationships among major clades.

Figure 2 Major localities for fossil pinnipeds.

Figure 3 Life restorations of fossil pinnipeds and a close relative. 
(a) Enaliarctos mealsi (total length 1.4–1.5 m); illustrated by M. Parrish. (b) Pithanotaria starri (total length 1.26 m); illustrated by R. Boessenecker. (c) Allodesmus kernensis (total length 2.2 m); illustrated by C. Buell. (d ) Dusignathus seftoni (skull length up to 40 cm) and Valenictus chulavistensis (skull length 40 cm); illustrated by W. Stout. (e) Puijila darwini (total length just over 1 m); illustrated by C. Buell. (f) Pelagiarctos sp. (ca. 2.7 m); illustrated by R. Boessenecker.

@CoastalPaleo

Annalisa Berta, Morgan Churchill and Robert 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. DOI:  10.1146/annurev-earth-082517-010009

 twitter.com/CoastalPaleo/status/978251979582566400

[PaleoMammalogy • 2015] Archaeodobenus akamatsui • A New Late Miocene Odobenid (Mammalia: Carnivora) from Hokkaido, Japan Suggests Rapid Diversification of Basal Miocene Odobenids

Archaeodobenus akamatsui

 Tanaka & Kohno, 2015

Fig 13. The role of eustasy in early late Miocene odobenid diversification in Hokkaido, Japan.DOI: 10.1371/journal.pone.0131856

Abstract

The modern walrus, Odobenus rosmarus, is specialized and only extant member of the family Odobenidae. They were much more diversified in the past, and at least 16 genera and 20 species of fossil walruses have been known. Although their diversity increased in the late Miocene and Pliocene (around 8–2 Million years ago), older records are poorly known. A new genus and species of archaic odobenid, Archaeodobenus akamatsui, gen. et sp. nov. from the late Miocene (ca. 10.0–9.5 Ma) top of the Ichibangawa Formation, Hokkaido, northern Japan, suggests rapid diversification of basal Miocene walruses. Archaeodobenus akamatsui is the contemporaneous Pseudotaria muramotoi from the same formation, but they are distinguishable from each other in size and shape of the occipital condyle, foramen magnum and mastoid process of the cranium, and other postcranial features. Based on our phylogenetic analysis, A. akamatsui might have split from P. muramotoi at the late Miocene in the western North Pacific. This rapid diversification of the archaic odobenids occurred with a combination of marine regression and transgression, which provided geological isolation among the common ancestors of extinct odobenids.

Systematic paleontology

MAMMALIA Linnaeus, 1758

CARNIVORA Bowdich, 1821

ODOBENIDAE Allen, 1880

Archaeodobenus gen. nov.

urn:lsid:zoobank.org:act:F509D05A-CE42-4​72F-9311-83405695F5F6

Type species: Archaeodobenus akamatsui sp. nov. 

Etymology: The generic name, Archaeodobenus, is named in Greek archaios meaning ancient, and the type genus name of the family Odobenidae.

Distribution: Known from the late Miocene (ca. 10.0–9.5 Ma), Japan.

Archaeodobenus akamatsui sp. nov.

Etymology: The species is named in honor of Dr. Morio Akamatsu, a curator emeritus of the Hokkaido Museum, for his longstanding contributions to geology and paleontology of Hokkaido, and in gratitude for his encouragement and assistance to both of us throughout this study.

Archaeodobenus akamatsui

 Tanaka & Kohno, 2015

Fig 13. The role of eustasy in early late Miocene odobenid diversification in Hokkaido, Japan.

DOI: 10.1371/journal.pone.0131856

Conclusions: 

Archaeodobenus akamatsui gen. et sp. nov. represents the second taxon of the archaic odobenids from the early late Miocene (ca. 10.0–9.5 Ma) Ichibangawa Formation, Hokkaido, northern Japan. The same formation has also produced the archaic odobenid Pseudotaria muramotoi Kohno, 2006. These two odobenids are distinguishable from another in size and shape of the occipital condyle, foramen magnum and mastoid process of the cranium, and some postcranial features. Phylogenetic analysis reveals that A. akamatsui has two synapomorphies that unites the new species with later diverging odobenids (i.e., Imagotaria downsi, Pontolis magnus, the “dusignathines” and the Odobeninae). Therefore, two closely similar odobenids having relatively ancestral characters (P. muramotoi) and relatively derived characters (A. akamatsui) both lived in the same area during the same age. Perhaps the coexistence of two morphologically similar archaic odobenids as represented by A. akamatsui and P. muramotoi in the early late Miocene suggest their rapid speciations by geographical and reproductive isolation during a regressive phase and subsequent transgressions.

Yoshihiro Tanaka and Naoki Kohno. 2015. A New Late Miocene Odobenid (Mammalia: Carnivora) from Hokkaido, Japan Suggests Rapid Diversification of Basal Miocene Odobenids. PLoS ONE.   DOI: 10.1371/journal.pone.0131856

Ancient Walrus Relative Had No Tusks: IFLScience.com/plants-and-animals/ancient-walrus-relative-bared-no-tusks

No Tusks: Ancient Walrus Cousin Looked More Like a Sea Lion https://shar.es/1tGEZk via @LiveScience

Ancient Walrus Cousin Looked More Like a Sea Lion:
News.Discovery.com/animals/ancient-walrus-looked-more-like-a-sea-lion-150806.htm

http://carnivoraforum.com/topic/10349703/1/