| Atopotarus | |
|---|---|
 | |
| Fossil cast of the holotype skeleton ofAtopotarus courseni at theNatural History Museum of Los Angeles County | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Clade: | Pinnipedia |
| Family: | †Desmatophocidae |
| Genus: | †Atopotarus Downs, 1956 |
| Species | |
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Atopotarus is anextinctgenus ofpinniped from the middleMiocene known from one specimen (holotype LACM 1376) fromLos Angeles County, California. It belongs to the extinct familyDesmatophocidae, an early lineage of seal-like pinnipeds from the NorthPacific.[1]
It is amonotypic genus, with the only known species beingAtopotarus courseni, or commonly referred to as 'Coursen's Strange Seal.' The species name'courseni' is attributed to the Coursen family that discovered the fossil in 1952 on theirPalos Verdes residence.[2] It is currently on display at theNatural History Museum of Los Angeles County.[3]
The specimen was discovered in the rocks of theAltamira Shale of theMonterey Formation.[4]
The only specimen ofAtopotarus is an incomplete articulated skeleton preserved in a slab of rock, with material from the skull to part of the spine, ending before the pelvis. It includes the skull, most teeth, jaws,cervical vertebrae, ribs, somedorsal vertebrae, and elements of the forelimbs, with outlines of thecarpals andmetacarpals.[2]
As with other members of its family,Atopotarus possessed largeorbits, which would indicate that they relied heavily on eyesight for hunting, and may have been deep divers.[5]
BothAtopotarus and moderneared seals share similarly long and well developed neck structures, which is used to allow flexible movements for hunting prey underwater and swimming. It also possessed unusually strongcanines and thick jaws, indicating a strong bite force.[2]
While no modern descendants of this genus exist today, they may have been most ecologically similar toelephant seals, due to similarities in eye size that indicate deep-diving hunting strategies.[5]
Atopotarus can be distinguished from other desmatophocids based on differences in the skull and teeth. Notable differences in the skull include an elongated cranium with large crests, lack of a pre-narial shelf, and the elongatedmastoid process, where neck muscles attach and blood vessels flow through, which protrudes ventral to level of the postglenoid process. Differences in the teeth include double rootedpremolars as opposed to the single rooted premolars of related genera, smaller canines, and the lack of a secondmolar.[4]
Atopotarus courseni has been sometimes considered to be a species withinAllodesmus, but most recentphylogenetic analysis retains it as a separate genus and asister taxon toAllodesmus.[1]