SVP23 – A new thalattosaur from Oregon

Metz et al. 2015
reports several new associated and likely conspecific bits and pieces of a new thalattosaur from the Middle Triassic of  Oregon.

From the abstract:
“Thalattosauria is a clade of secondarily aquatic Triassic reptiles generally found as
isolated skeletons from localities in Europe, China, and North America. In North America, four genera of thalattosaurs have been described from two formations: the Hosselkus Limestone of California (Carnian) and the Sulphur Mountain Formation of British Columbia (Lower to Middle Triassic). In 2011, a new thalattosaur locality was discovered from the Late Triassic (Carnian) Brisbois Member of the Vester Formation in central Oregon. This formation records deposition in a nearshore environment in the forearc region of the Izee Terrane. The material consists of one large block of highly concentrated, three-dimensionally preserved, disarticulated skeletons of five or more individuals. Preparation to date has revealed partial crania, including complete braincases, as well as numerous axial and appendicular elements from individuals of varying size.

Preliminary examination of the most complete skull, University of Oregon Museum of Natural and Cultural History F64236, reveals a unique combination of characters including a strong degree of rostral ventral deflection, frontals that are excluded from the orbital margin, nasals separated by a long anterior projection of the frontal, a small degree of contribution by the jugal to the ventral margin of the orbit, the absence of an upper temporal fenestra and diastema, and a peg-like homodont dentition. Based on the morphological similarity of several multiple-sized elements, we interpret that this material represents the first ontogenetic series of any known thalattosaur. The new Oregon material represents the largest thalattosaur species yet found in North America, and is both the oldest vertebrate remains and the first occurrence of a thalattosaur from Oregon. Finally, the quality of preservation, particularly of poorly-known cranial elements, contributes important new morphological data about thalattosaurs for resolving phylogenetic relationships within the clade as a whole.”

Photos of Eric Metz
and his SVP poster have appeared online here and here. From the images and description F64236 (Fig. 1) is a sister to Clarazia (Peyer 1936, Rieppel 1987, Figs. 2, 3) with a more deeply downturned premaxilla.

Figure 1. Oregon thalattosaur skull parts.

Figure 1. Oregon thalattosaur skull parts. Middle Triassic 238-228 mya. Gray elements are restored.

According to Metz
“The specimen had a downturned snout, which it likely used to break apart reefs made of mollusks and sponges. Adults would have measured 3 meters in length.” Like similar thalattosaurs, rather large vomer teeth were present.

Figure 2. The Thalattosauria and outgroups (Wumengosaurus and Stereosternum) to scale.

Figure 2. The Thalattosauria and outgroups (Wumengosaurus and Stereosternum) to scale. Note the heretical and verified inclusion of Vancleavea here. The new specimen would be as large as the largest of these.

Clarazia was a much smaller thalattosaur and more primitive with a straighter snout.

Figure 4. Clarazia, a thalattosaur sister to the new Oregon specimens.

Figure 3. Clarazia, a thalattosaur sister to the new Oregon specimens.

 

References
Metz E, Druckenmiler PS, and Carr G 2015. A new thalattosaur from the Vester Formation (Carnian) of central Oregon. Journal of Vertebrate Paleontology abstracts 2015.
Peyer B 1936. Die Triasfauna der Tessiner Kalkalpen. X.  Clarazia schinzi nov. gen. nov. spec. Abhandlungen der Schweizerischen Pala¨ontologischen Gesellschaft, 57, 1–61.
Rieppel O 1987. Clarazia and Hescheleria; a reinvestigation of two problematic reptiles from the Middle Triassic of Monte San Giorgio (Switzerland). Palaeontographica, A, 195, 101–129.

wiki/Thalattosaur

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One thought on “SVP23 – A new thalattosaur from Oregon

  1. Nice to see this! Just about all of Oregon is accreted terrain covered with pretty recent volcanics [and the western third covered with vegetation as well], so there are few Mesozoic vertebrate fossils of any kind, and fewer still that are worth study.

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