A new megalosaurid theropod dinosaur from the late Middle Jurassic (Callovian) of north-western Germany: Implications for theropod evolution and faunal turnover in the Jurassic

Abstract

Fragmentary remains of a large, robustly built theropod dinosaur were recovered from the marine middle Callovian Ornatenton Formation of northeastern Northrhine-Westphalia, Germany. The specimen includes a premaxilla, maxilla, lacrimal, postorbital, dentary, several caudal vertebrae, ribs, fibulae, astragalus, and partial calcaneum. It is here described as a new species of megalosauroid, Wiehenvenator albati n. gen. n. sp., diagnosed by a strongly reduced maxillary antorbital fossa on the base of the ascending process of the maxilla, a very short anterior ramus of the lacrimal with an additional pneumatic depression anteroventral to the lacrimal fenestra, a transversely expanded orbital facet in the postorbital, and a laterally flexed proximal end of the ascending process of the astragalus. Phylogenetic analysis recovers Wiehenvenator as a megalosaurine megalosaurid, sister taxon to the Late Jurassic genus Torvosaurus. It thus adds to the considerable diversity of megalosauroids in the Middle Jurassic. A time-calibrated phylogeny of theropods indicates a rapid radiation of averostran theropods between the Toarcian and the Bathonian. This radiation was probably triggered by the Pliensbachian-Toarcian extinction event, which might have been more important for theropod evolution than the Triassic-Jurassic extinction. The fossil record indicates a faunal turnover from megalosauroid dominated Middle Jurassic to allosauroid / coelurosaur dominated Late Jurassic faunas. However, differences in the Middle and Late Jurassic theropod fossil records both in respect to geographic distribution of localities, as well as sampled environments make this inference problematic, at least in respect to allosauroids. An analysis of environmental preferences of allosauroids and megalosauroids indicates that the former preferred inland environments, whereas the latter are more common in nearshore environments.

Megalosauripus transjuranicus ichnosp. nov. A new Late Jurassic theropod ichnotaxon from NW Switzerland and implications for tridactyl dinosaur ichnology and ichnotaxomy

“…The osteological convergence and substantial overlap in phalangeal proportions of the theropod foot would not allow a lower level distinction among different theropod taxa [122,123]. …”

The tracks of giant theropods (Jurabrontes curtedulensisichnogen. & ichnosp. nov.) from the Late Jurassic of NW Switzerland: palaeoecological & palaeogeographical implications

“…A new large megalosaurid, Wiehenvenator albati, has recently been described (Rauhut et al 2016) from the Callovian (late Middle Jurassic) of Germany. Despite its older age, with an estimated body length of 9 m, it may be a good candidate for tracks of the size reported herein.…”

A hypertrophied ungual phalanx from the lower Barremian of Spain: Implications for the diversity and palaeoecology of Spinosauridae (Theropoda) in Iberia

“…However, later phylogenetic analyses by other authors place Chilantaisaurus within Allosauroidea, more specifically within the clade of neovenatorid carcharodontosaurians as the sister taxon of megaraptorans (Carrano et al, 2012;Rauhut et al, 2016). Unlike Spinosauridae, the ungual claw of Chilantaisaurus is clearly more laterally compressed (see Benson and Xu, 2008: fig.…”

“…The anatomical nomenclature of theropod unguals follows Charig and Milner (1997) and Agnolin and Chiarelli (2010). The phylogenetic framework for Tetanurae followed in this work is based on the results obtained by Rauhut et al, (2016) who performed a phylogenetic analysis on a revised version of the datamatrix of Carrano et al (2012).…”