Introducing Notatesseraeraptor frickensis.

Notatesseraeraptor frickensis at the Sauriermuseum Frick. (From Wikimedia Commons)

Over the last two decades our knowledge of the fossil record of early theropod dinosaurs has greatly improved. However, there are different hypotheses about their relationships. Theropods are relatively abundant in post-Carnian Triassic faunas, including the European Liliensternus, the South American Zupaysaurus, and the North American Coelophysis. Those taxons represent the earliest major radiation of Neotheropoda. Two primitive branches of this clade are the Coelophysoidea and the Dilophosauridae. More recent studies suggest that at least some members of the ‘traditional Coelophsoidea’ are more closely related to the tetanurans and that the Dilophosauridae may represent a second clade of early non-averostran neotheropods. Notatesseraeraptor frickensis gen. et sp, from the Late Triassic of Switzerland, provides new clues about the relationships of the early theropods.

The new specimen belong to an immature individual of length 2.6–3.0 m, and it was collected in 2006 from Gruhalde clay pit in Frick (Aargau, Switzerland), a place well known for its abundant, articulated Plateosaurus material. The genus name derives from the Latin “nota” meaning feature and “tesserae”, a word used to describe glass, or other material used in the construction of a mosaic, in reference to the interesting mixture of characters found in the fossil.

Skeletal anatomy of N. frickensis gen. et sp. nov. From Zahner and Brinkmann, 2019.

The new specimen was described based on a cranium (SMF 09-2) and partial postcranial skeleton (SMF 06-1). The cranium is proportionally long and low as is commonly found in traditional coelophysoid-grade neotheropods. But in contrast to coelophysids, the premaxillary tooth crowns of N. frickensis are all strongly recurved, laterally compressed and bear fine serrations. The postcranial skeleton includes two articulated forelimbs, 13 dorsal, four sacral and four proximal caudal vertebrae; cervical, dorsal and sacral ribs; chevrons; gastralia; and even stomach contents ( a well-preserved maxilla of the rhynchocephalian Clevosaurus). The preserved postcranial elements share most of their morphological similarities with ‘Syntarsus’ kayentakatae. N. frickensis has plesiomorphically long forelimbs. The radius is about three-quarters of the length of the humerus. The manus is composed of four digits, whereas the fourth is reduced to a very slim metacarpal. The shape of the ilium are similar to those found in Coelophysis.  

The phylogenetic analyses, with emphasis on early neotheropods, suggests that Notatesseraeraptor is a basal member of Dilophosauridae, a clade that comprises Dilophosaurus, and Cryolophosaurus.

 

References:

Marion Zahner; Winand Brinkmann (2019). “A Triassic averostran-line theropod from Switzerland and the early evolution of dinosaurs”. Nature Ecology & Evolution. doi:10.1038/s41559-019-0941-z

Martín D. Ezcurra, and Federico L. Agnolín (2017). Gondwanan perspectives: Theropod dinosaurs from western Gondwana. A brief historical overview on the research of Mesozoic theropods in Gondwana. Ameghiniana 54: 483–487. https://doi.org/10.5710/102.054.0501