New dinosaur (Theropoda, stem -Averostra) from the earliest Jurassic of the La Quinta formation, Venezuelan Andes

Abstract

Dinosaur skeletal remains are almost unknown from northern South America. One of the few exceptions comes from a small outcrop in the northernmost extension of the Andes, along the western border of Venezuela, where strata of the La Quinta Formation have yielded the ornithischian Laquintasaura venezuelae and other dinosaur remains. Here, we report isolated bones (ischium and tibia) of a small new theropod, Tachiraptor admirabilis gen. et sp. nov., which differs from all previously known members of the group by an unique suite of features of its tibial articulations. Comparative/phylogenetic studies place the new form as the sister taxon to Averostra, a theropod group that is known primarily from the Middle Jurassic onwards. A new U–Pb zircon date (isotope dilution thermal-ionization mass spectrometry; ID-TIMS method) from the bone bed matrix suggests an earliest Jurassic maximum age for the La Quinta Formation. A dispersal–vicariance analysis suggests that such a stratigraphic gap is more likely to be filled by new records from north and central Pangaea than from southern areas. Indeed, our data show that the sampled summer-wet equatorial belt, which yielded the new taxon, played a pivotal role in theropod evolution across the Triassic–Jurassic boundary.

Postcranial anatomy ofLesothosaurus diagnosticus(Dinosauria: Ornithischia) from the Lower Jurassic of southern Africa: implications for basal ornithischian taxonomy and systematics

“…In anterior view, the distal end of the tibia is transversely expanded and the malleoli are separated by a small, shallow depression. The posterior surface of the distal expansion is convex, with the outer malleolus extending further distally than the inner malleolus, which is similar to the condition in Scelidosaurus harrisonii (NHMUK PV R1111), Jeholosaurus shangyuanensis (Han et al, 2012) and some neotheropods such as Tachiraptor admirabilis (Langer et al, 2014). The inner malleolus of Lesothosaurus diagnosticus is anteroposteriorly thicker and slightly more rounded than the outer malleolus, giving the tibia a triangular outline in distal end view as in Eocursor parvus (Butler, 2010).…”

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

“…Likewise, in theropods, the most common Late Triassic clade are the coelophysoids (e.g., Rauhut and Hungerbühler, 2000;Nesbitt and Ezcurra, 2015), which are also still diverse in the Early Jurassic (see Ezcurra, 2012;You et al, 2014;Martill et al, 2016). The sister taxon to Coelophysoidea, the lineage leading towards Averostra, must have originated at the same time; its probably oldest known representative being the Norian Zupaysaurus (Ezcurra, 2012;Langer et al, 2014). The stem lineage of Averostra might have included yet another distinct clade, the dilophosaurids (Smith et al, 2007;Ezcurra, 2012;Holtz, 2012;Langer et al, 2014), the monophyly of which is debated (see Brusatte et al, 2010aBrusatte et al, , 2010b.…”

“…The sister taxon to Coelophysoidea, the lineage leading towards Averostra, must have originated at the same time; its probably oldest known representative being the Norian Zupaysaurus (Ezcurra, 2012;Langer et al, 2014). The stem lineage of Averostra might have included yet another distinct clade, the dilophosaurids (Smith et al, 2007;Ezcurra, 2012;Holtz, 2012;Langer et al, 2014), the monophyly of which is debated (see Brusatte et al, 2010aBrusatte et al, , 2010b. If these taxa indeed form a clade, all of the constituent taxa are known from Lower Jurassic rocks, but the stratigraphic position of the immediate outgroup taxon of Averostra, Tachiraptor, at the base of the Jurassic indicates that the origin of this clade also reaches back to the Triassic (Figure 26; Langer et al, 2014).…”

The theropod dinosaurElaphrosaurus bambergiJanensch, 1920, from the Late Jurassic of Tendaguru, Tanzania

“…Recently, Langer et al . () reported fragmentary remains of Tachiraptor from the Hettangian of Venezuela, which probably represent the oldest known averostran. Allain et al .…”