A new carcharodontosaurian theropod dinosaur occupies apex predator niche in the early Late Cretaceous of Uzbekistan

Abstract

Carcharodontosauria is a group of medium to large-sized predatory theropods, distributed worldwide during the Cretaceous. These theropods were probably the apex predators of Asiamerica in the early Late Cretaceous prior to the ascent of tyrannosaurids, although few Laurasian species are known from this time due to a poor rock record. Here, we describe Ulughbegsaurus uzbekistanensis gen. et sp. nov. from the early Late Cretaceous (Turonian) of Central Asia, which represents the first record of a Late Cretaceous carcharodontosaurian from the region. This new taxon is represented by a large, isolated maxilla from the Bissekty Formation of the Kyzylkum Desert, the Republic of Uzbekistan, a formation yielding a rich and diverse assemblage of dinosaurs and other vertebrates from fragmentary remains. Comparison of the maxilla with that of other allosauroids indicates Ulughbegsaurus was 7.5–8 m in body length and greater than 1000 kg in body mass, suggesting it was the previously unrecognized apex predator of the Bissekty ecosystem while smaller known tryannosauroids and dromaeosaurids were probable mesopredators. The discovery of Ulughbegsaurus records the geologically latest stratigraphic co-occurrence of carcharodontosaurid and tyrannosauroid dinosaurs from Laurasia, and evidence indicates carcharodontosaurians remained the dominant predators relative to tyrannosauroids, at least in Asia, as late as the Turonian.

A giant dromaeosaurid theropod from the Upper Cretaceous (Turonian) Bissekty Formation of Uzbekistan and the status of Ulughbegsaurus uzbekistanensis

“…Thirdly, Tanaka et al (2021) cited the presence of fused, slightly rugose interdental plates in Ulughbegsaurus uzbekistanensis. The absence of distinct interdental plates is not restricted to most but not all allosauroids (Currie, 1995) but is shared by abelisaurids (Lamanna et al 2002;Sampson & Witmer, 2007), the megalosauroid Torvosaurus spp.…”

“…We could not identify a single feature that unambiguously supports referral of Ulughbegsaurus uzbekistanensis to neovenatorid carcharodontosaurians. Three of the purported synapomorphies cited by Tanaka et al (2021) are also shared by dromaeosaurids. In addition, some features like the sub-vertical contact between the premaxilla and maxilla and the smooth junction between the ventral margin of the antorbital fossa and the lateral surface of the maxilla ventral to this margin (Powers et al 2022) are present in both Ulughbegsaurus uzbekistanensis and some dromaeosaurids such as Utahraptor ostrommaysi (Fig.…”

“…3c,d). Tanaka et al (2021) presented a phylogenetic analysis that included only allosauroids and tyrannosauroids and excluded all other non-avian theropod clades. This selective taxon sampling assumed relationships a priori and did not allow a comprehensive assessment.…”

“…Dromaeosaurids such as Achillobator giganticus from the Late Cretaceous (Cenomanian-Santonian) Bayn Shire Formation of Mongolia (Perle et al 1999;Turner et al 2012) and Utahraptor ostrommaysi from the Lower Cretaceous (Barremian-Aptian) Upper Yellow Cat Member of the Cedar Mountain Formation of Utah (Kirkland et al 1993) attained linear dimensions comparable to those of other large theropods. Indeed, Tanaka et al (2021) even made reference to ZIN PH 11/16 discussed here. Tanaka et al (2021) referred the two fragments of maxillae described by Sues & Averianov (2014) to Ulughbegsaurus uzbekistanensis, even though there is no anatomical similarity or overlap between the three specimens.…”

“…In addition, there are two form taxa for distinctive small theropod teeth, Richardoestesia americana and Paronychodon asiaticus (Sues & Averianov, 2013;Averianov & Sues, 2019). Recently, Tanaka et al (2021) described what they considered a neovenatorid carcharodontosaurian, Ulughbegsaurus uzbekistanensis, which will be further discussed in this paper.…”