Osodobenus

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Osodobenus
Temporal range:
Ma
↓
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Order:
Carnivora
Family:
Odobenidae
Genus:
Osodobenus

Biewer et al., 2020
Type species
Osodobenus eodon
Biewer et al., 2020

Osodobenus is an extinct genus of walrus from the Miocene to Pliocene of California. Osodobenus may have been the first tusked walrus and shows several adaptations that suggest it was a suction feeder, possibly even a benthic feeder like modern species. Three skulls are known showing pronounced sexual dimorphism, with the female lacking the same tusks as the male. Only a single species, Osodobenus eodon, is currently recognized.

Discovery and naming

Osodobenus is known from three specimens including an adult male, adult female and a juvenile specimen preserving skulls and some postcranial material. All the material was collected from the Late Miocene to Early Pliocene (Messinian to Zanclean) Capistrano Formation, Orange County, California alongside the remains of several other early odobenids. In 2020, Biewer and colleagues published a detailed description of the material, establishing Osodobenus as a new genus while also erecting two new species of Pontolis.[1]

The genus name of Osodobenus is a combination of the genus name for the modern

species name eodon translates to "dawn tooth" or "dawn tusk", a reference to this animal's key role in the evolution of walrus tusks.[1]

Description

Osodobenus likely had whiskers like the modern walrus.

Compared to other basal odobenids, the rostrum of Osodobenus is short and robust, bulging notably around the canines and with a forward-projecting

sexually dimorphic. The teeth of Osodobenus show a somewhat transitional form between the less specialised odobenids with a tooth specialisation score of 0.4 and lower and the more derived and specialised members of the group (score >0.5). This indicates that odobenids rapidly specialised during the late Tortonian to early Messinian of the Miocene, which included the development of tusks in later taxa. This again corresponds to what is observed in Osodobenus, whose canines form an intermediate form between what has previously been considered tusked and tuskless. Biewer and colleagues argue that the continuous nature of tusk growth in an evolutionary context makes a rigid separation futile and that Osodobenus represents the first walrus with canines that could be considered tusks.[1]

Phylogeny

Osodobenus was recovered as a sister taxon to the

Neodobenia[2] in both parsimony phylogenetic analysis and Bayesian analyses, which makes it the basalmost walrus with canines that can be considered tusks. The following phylogenetic tree was recovered by the study of Biewer et al. (2020).[1]

Paleobiology

Although the presence of tusks is sexually dimorphic in Osodobenus, it is suggested that feeding likewise played a part in the evolution of these enlarged canine teeth. Osodobenus and other tusked odobenids share an enlarged

sirenians in foraging. Another trait that suggests that Osodobenus may habe been a benthic feeder is the anatomy of the palate, which indicates that this genus much like extant walrus was a specialised suction feeder. Biewer and his colleagues note that these traits alone are not enough to fully establish Osodobenus as a benthic feeder, but argue that its feeding behavior may have been similar regardless. As some more derived odobenids lack these adaptations, it is possible that this ecology was evolved independently from crown walrus.[1]

Fossils of Osodobenus were discovered in the Californian Capistrano Formation, which also yielded the fossils of the walrus Pontolis magnus, Pontolis kohnoi and Titanotaria orangensis.

Crocodylians and sabertoothed salmons are also known to have inhabited the waters of the Capistrano Formation.[5]

References

  1. ^
    S2CID 228814992
    .
  2. S2CID 233708113
    .
  3. ^ "Paleontologists uncover three new species of extinct walruses in Orange County". EurekAlert!. American Association for the Advancement of Science (AAAS). 16 November 2020. Retrieved 14 April 2022.
  4. ^ Hayden, Tyler. "Walruses: On the Tusk of Greatness". Natural History Museum of LA County. Retrieved 14 April 2022.
  5. doi:10.5070/P9341033797
    .
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