Analysis of a beautifully preserved lower jawbone found in the southern Pyrenees of Spain has led to a new species of Late Cretaceous hadrosauroid dinosaur being erected. Named Fylax (F. thyrakolasus), it is the youngest non-hadrosaurid hadrosauroid described to date. This dinosaur was one of the very last of all the non-avian dinosaurs to have existed and a phylogenetic assessment places Fylax as the sister taxon of Tethyshadros which is known from north-eastern Italy and was formally named and described in 2009.

Views of the lower jawbone of Fylax thyrakolasus
Dentary of the hadrosauroid dinosaur Fylax thyrakolasus gen. et sp. nov. (IPS-36338, holotype) from the uppermost Maastrichtian Figuerola Formation. Views of the specimen in posterior (A1), medial (A2), dorsal (A4), anterior (A5), lateral (A6), and ventral (A7) views. A detailed lingual view of the tooth crowns appears in A3. Picture credit: Prieto-Márquez and Carrera Farias.

Described from a Dentary

Described from a left dentary (lower jawbone), found in Lleida Province in Spain, the researchers from The Autonomous University of Barcelona (Universitat Autònoma de Barcelona), identified several unique characteristics that enabled them to erect a new taxon. The genus name is derived from the Greek thýra which means door or gate and kólasi which means hell. This translates as the “keeper of the gates of hell” a reference to the proximity of the fossil dentary to the layers of rock that mark the end Cretaceous mass extinction event that saw the demise of the non-avian dinosaurs.

Based on analysis of more complete hadrosaurid fossil remains, Fylax is estimated to have been between 3.5 to 4 metres in length and it is the stratigraphically youngest non-hadrosaurid hadrosauroid known to date.

Fylax thyrakolasus drawing
A life reconstruction of the recently described hadrosauroid from the uppermost Maastrichtian strata of the Figuerola Formation in the southern Pyrenees of Spain. The dinosaur, one of the very last to exist, has been named Fylax thyrakolasus. Note scale bar = 1 metre.

An Asian Origin for Hadrosauroids

Although not the focus of their study, subsequent analysis and mapping of the geographical distribution of ornithopod fossil remains led the researchers to support the hypothesis of an Asian origin for hadrosauroids, which then subsequently dispersed to the eastern North American landmass of Appalachia. They suggest that the European archipelago that existed during the Late Cretaceous could have facilitated the westward dispersal of hadrosaurid outgroups from Asia to Appalachia.

Mapping the distribution of hadrosaurid dispersal in the Late Cretaceous.
A time calibrated cladogram showing global distribution of hadrosaurs and their close relatives. Pie charts indicate the likelihood of ancestral areas. This study suggests an Asian origin for hadrosauroids and subsequent dispersal to Appalachia, where Hadrosauridae probably evolved, from here once dispersed into Laramidia the Lambeosaurinae and Saurolophinae subfamilies evolved. The European archipelago probably provided a series of island stepping stones permitting the dispersal of hadrosaurids from Asia into North America. Picture credit: Prieto-Márquez and Carrera Farias.

The scientific paper: “A new late-surviving early diverging Ibero-Armorican duck-billed dinosaur and the role of the Late Cretaceous European Archipelago in hadrosauroid biogeography” by Prieto-Márquez, A. and Carrera Farias published in Acta Palaeontologica Polonica.

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