Rafael Delcourt & Orlando Nelson Grillo (2018)
Tyrannosauroids from the Southern Hemisphere: Implications for biogeography, evolution, and taxonomy.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
Highlights
New ideas about the evolution and biogeography of the group Tyrannosauroidea are discussed based on phylogenetic analyses.
Tyrannosaurs were widespread in Laurasia and Gondwana since the Middle Jurassic.
We propose two new taxonomic groups to describe the evolution of tyrannosaurs: Pantyrannosauroidea and Eutyrannosauroidea.
Abstract
Tyrannosauroidea is a well-studied group of carnivorous dinosaurs known mainly from the Late Cretaceous of the Northern Hemisphere. Specimens from Australia (Timimus hermani and the articulated pubes NMV P186046) and Brazil (Santanaraptor placidus) have been referred to this clade, but their phylogenetic placement is unresolved. Here, we investigated the phylogenetic positions of these Southern Hemisphere specimens within the theropods and among tyrannosauroids using three different phylogenetic datasets: the first covered all major theropod clades, the second was focused on non-Maniraptoriformes Tetanurae, and the third was focused on Tyrannosauroidea. It was found that Santanaraptor and Timimus were tyrannosauroids of a type that was more derived than Dilong paradoxus and more basal than Xiongguanlong baimoensis. However, the pubes NMV P186046 may have phylogenetic relationships among Coelurosauria, probably within Tyrannosauroidea. The resultant topologies, which were associated with temporal and geographical distributions of basal non-proceratosaurid tyrannosauroids, suggest a worldwide cosmopolitan distribution for this clade (named Pantyrannosauria), at least from the Bajocian-Callovian. Our analyses also support a Late Cretaceous monophyletic clade of gigantic animals that occurred exclusively in the Northern Hemisphere (named Eutyrannosauria).