Somniosus gonzalezi

Credit: Skye McDavid.

*Somniosus gonzalezi* is an extinct species of sleeper shark that lived in western Washington during the Early Oligocene.

## History

*S. gonzlezi* is named after Gerardo González-Barba of the Universidad Autónoma de Baja California Sur due to his work on fossil sharks and being the first to recognize the teeth as a new species of *Somniosus*. The species was previously called ?*S.* sp. by Kiel et al. (2010).

## Description

It is known from five teeth (USNM 559335-559339) that were found while preparing a cetacean skull in "insoluble phosphatic residue" after an acid bath. 559335, a complete lower right anterolateral from the mesial half of the dentition, is the holotype; 559336, a complete lower anterolateral tooth from the mesial half of the dentition, 559337, a lower left anteroposterior tooth from the from the distal half of the dentition but missing most of the distal root and infindibulum lingual groove, and 559338, a complete upper left anterolateral tooth, are all paratypes. USNM 559339, an incomplete upper tooth associated with the holo- and paratypes, is referred.

It differs from *S. microcephalus* and *S. pacificus* by having lower teeth (mesial half) with a straight mesial crown cutting edge, a distobasally-sloped distal heel, a broad and convex distal tooth border, a continuing crowwn to base of root, a distolingual foramen that is very small, a wide distolingual facet, a mesolabial crown base that is projected basally and lobate, a mesolabial crown base that is apically smoothly convex between the apron and medial edge and a distolabial foramen that is slightly enlarged. In the upper teeth, the root width is greater than the height, the root is weakly bilobate, the lingual groove is narrow and the basal notch is shallow. Other characters distinguished from *S. pacificus* are a short and broad tringular cusp, a moderately well-developed and bifid uvula, a deep axial trough, a smaller infindibulum and a narrower lingual groove. The same of *S. microcephalus* includes a lower cusp angle, a 39-46% distal extension cusp apex of the heel length and smaller mesolingual and mesolabial foramina.

## Paleoecology

*S. gonzalezi* was discovered from the Pysht Formation, the uppermost unit from the Early Miocene and the majority hailing from the Early Oligocene. From the lower formation, a grade of basal cetaceans are known. It is from here that *S. gonzalezi* was discovered from the ?late Early Oligocene, or of an older age. LACM 5412 is the type locality, concretions as float sitting on beach terrace at the western mouth of the Murdock Creek along the Strait of Juan de Fuca, Clallam County, Washington shoreline. Tooth row positions may indicate that these teteh are from one individual or rather several individuals or similar size that may have been shed by scavenging on the mysticete. However, the mysticete lacked tooth marks on the skull characteristic of feeding, though Kiel et al. (2010) associates some associated postcranial scratches with scavenging done by small sharks. Fossil birds from the same locality with similar scratrches reported by Mayr et al. (2015) may have been made by similar sources.

## References

* https://www.researchgate.net/publication/308522069\_New\_fossil\_species\_of\_Somniosus\_and\_Rhinoscymnus\_Squaliformes\_Somniosidae\_deep\_water\_sharks\_from\_Oligocene\_rocks\_of\_western\_Washington\_State\_USA
* https://en.wikipedia.org/wiki/Somniosus\_gonzalezi