Megaraptora

Evolution and origin

The origins of megaraptorans have recently been determined. Studies by paleontologists Phil Bell, Steve Salisbury et al. of a newly discovered, as-yet-unnamed megaraptorid (referred to by the public media as "Lightning Claw," and possibly synonymous with Rapator) from opal fields southwest of Lightning Ridge, Australia, dating back 110 million years ago reveals that megaraptorans likely evolved in Australia, then spread to the rest of Gondwana in an episode of evolutionary radiation. The specimen also allowed for alternative phylogenitic testing as to the placement of megaraptorans as either tyrannosauroids or carcharodontosaurids.

Classification

Megaraptora has historically been a group with highly controversial relationships.

Early phylogenetic studies of the group's relationships conducted by Benson, Carrano and Brusatte in 2010 and Carrano, Benson and Sampson in 2012 recovered the group as a branch of the allosauroids (specifically within the family Neovenatoridae), part of a large group of theropods that also includes the metriacanthosaurids, carcharodontosaurids, and allosaurids. This would make megaraptorans the last surviving allosauroids; at least a few megaraptorans, including Orkoraptor, lived near the end of the Mesozoic era, dating to the late Santonian stage of the late Cretaceous period, about 84 million years ago. Another study published later in 2010 found the Australian theropod Rapator to be a megaraptoran extremely similar to Australovenator.

On the other hand, Novas et al. published a study in 2012 which, while confirming that Neovenator was closely related to carcharodontosaurids, also found Megaraptor and its relatives to be coelurosaurs closely related to tyrannosaurids. Study of the skull anatomy of a juvenile specimen of Megaraptor also suggested to Novas and his colleagues that it was a tyrannosauroid. Analysis of the theropod Gualicho published by Apesteguía and colleagues in 2016 recovered megaraptorans as either allosauroids or basal coelurosaurs, and depended on whether Gualicho's anatomy was plugged into Carrion's analysis or Novas' analysis. This suggested that the controversial placement of megaraptorans was more of a consequence of incomplete analyses than to their actual anatomy.

Later in 2016, Novas and colleagues published a study of megaraptoran hand anatomy, in an attempt to help settle the question of their classification. They found that megaraptorans lacked most of the key features in the hands of derived coelurosaurs including Guanlong and Deinonychus. Instead, their hands retain a number of primitive characteristics seen in basal tetanurans such as Allosaurus. Nevertheless, there are still a number of traits that support megaraptorans as members of the Coelurosauria.

The cladogram below follows Coria & Currie (2016), based on the Carrano et al. (2012) dataset.