Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy

Abstract

General comparisons of the manual elements of megaraptorid theropods are conducted with the aim to enlarge the morphological dataset of phylogenetically useful features within Tetanurae. Distinctive features of Megaraptor are concentrated along the medial side of the manus, with metacarpal I and its corresponding digit being considerably elongated. Manual ungual of digit I is characteristically enlarged in megaraptorids, but it is also transversely compressed resulting in a sharp ventral edge. We recognize two derived characters shared by megaraptorans and coelurosaurs (i.e., proximal end of metacarpal I without a deep and wide groove continuous with the semilunar carpal, and metacarpals I and II long and slender), and one derived trait similar to derived tyrannosauroids (i.e., metacarpal III length <0.75 length of metacarpal II). However, after comparing carpal, metacarpal and phalangeal morphologies, it becomes evident that megaraptorids retained most of the manual features present in Allosaurus. Moreover, Megaraptor and Australovenator are devoid of several manual features that the basal tyrannosauroid Guanlong shares with more derived coelurosaurs (e.g., Deinonychus), thus countering our own previous hypothesis that Megaraptora is well nested within Tyrannosauroidea.

Skeletal completeness of the non‐avian theropod dinosaur fossil record

“…, ; Novas et al . ). Continued finds in relatively unexplored areas of South America and Australasia are likely to boost its currently poor skeletal record.…”

The oldest ceratosaurian (Dinosauria: Theropoda), from the Lower Jurassic of Italy, sheds light on the evolution of the three-fingered hand of birds

“…The right humerus of Saltriovenator appears almost straight also in lateral and medial view, being just slightly bent in its distal third. Likely, the missing adductor crest was as slightly curved as the distal epiphysis, giving the whole bone a only moderately sigmoid shape, as in most Neoceratosauria (Tykoski & Rowe, 2004), and in some large-sized basal tetanuran taxa, such as Poekilopleuron (Allain & Chure, 2002; C. Dal Sasso & S. Maganuco, 2004, personal observation on plastotype MNHN 1897-2), Acrocanthosaurus, Szechuanosaurus (Gao, 1993), and Xuanhanosaurus (Novas, Aranciaga Rolando & Agnolín, 2016). It is also similar to Dilophosaurus (Welles, 1984), although in the latter the diaphysis is more slender and a little more bowed, with an arch which is continuous from the dorsal lamina to the entepicondylar crest (C. Dal Sasso, 2004, personal observation on UCMP 37302).…”

New theropod remains and implications for megaraptorid diversity in the Winton Formation (lower Upper Cretaceous), Queensland, Australia

“…These are: Rapator ornitholestoides, known only from a metacarpal I [2][3][4]; Walgettosuchus woodwardi, represented by a partial caudal vertebra [2,3]; Kakuru kujani, restricted to an incomplete tibia [3,[5][6][7]; Timimus hermani, known only from a femur [3,[8][9][10][11][12]; and Ozraptor subotaii, a distal tibia [3,6,[13][14][15][16][17][18][19][20]. The only exception is Australovenator wintonensis, represented by a partial skeleton [4,[21][22][23][24][25][26], which was initially classified as an indeterminate allosauroid but has since been universally allied with Megaraptor and its kin within Megaraptoridae [10,27,28]. Some general characteristics possessed by Megaraptoridae include: elongated three-digit hands with two enlarged recurved unguals on digits I and II and a much smaller digit III ungual [22,25,28], robust forearms [25,28], small blade-like teeth [9,23,[29][30]…”

“…The only exception is Australovenator wintonensis, represented by a partial skeleton [4,[21][22][23][24][25][26], which was initially classified as an indeterminate allosauroid but has since been universally allied with Megaraptor and its kin within Megaraptoridae [10,27,28]. Some general characteristics possessed by Megaraptoridae include: elongated three-digit hands with two enlarged recurved unguals on digits I and II and a much smaller digit III ungual [22,25,28], robust forearms [25,28], small blade-like teeth [9,23,[29][30][31][32][33]; proportionally large feet compared to hind limb length and relatively gracile hindlimbs built for running [24,26]; and heavily pneumatized bones [29]. The completeness of the Australovenator type specimen has been fundamental to our current understanding of megaraptorid anatomy and phylogenetic hypotheses, and provided robust comparative data that have permitted the assignment of numerous isolated theropod specimens from the mid-Cretaceous of New South Wales [34,35] and Victoria [1,9] to Megaraptora (or its subclade Megaraptoridae), and validated an earlier report of a Megaraptor-like theropod from Victoria, based on an ulna [36].…”

“…The spatio-temporal range of Megaraptora (and Megaraptoridae) is becoming ever better understood as a result of numerous discoveries made within the last 2 decades. The South American record is the most extensive, diverse and abundant, with six taxa named to date: Aoniraptor libertatem [37], Orkoraptor burkei [33], Megaraptor namunhuaiquii [32,38,39], Murusraptor barrosaensis [30,40,41], Aerosteon riocoloradensis [28], and Tratayenia rosalesi [42]. Numerous fragmentary specimens have also been reported from South America (see supplementary table 7 in [1]), which include the oldest (Albian [43]) and the youngest (Campanian [44]).…”