Paleontologists have described the largest megaraptor about 10 meters long

(ORDO NEWS) — Paleontologists have described a new carnivorous dinosaur from the megaraptor group, fossils of which have been found in Argentine deposits ranging in age from 72.1 to 66 million years. The dinosaur was named Maip macrothorax.

It reached 9-10 meters in length, which makes it the largest representative of megaraptors. This discovery confirms the assumption that the evolution of megaraptors followed the path of increasing body size. The study was published in the journal Scientific Reports.

Megaraptors (Megaraptora) – a group of predatory dinosaurs that lived in the Cretaceous period in Australia, Asia and South America. Compared to other large theropods, megaraptors had long and powerful forelimbs with large claws.

The family ties of this group have long been controversial among paleontologists. Recently, there is more and more evidence that megaraptors belong to the coelurosaurs (Coelurosauria) – a group that combines dinosaurs such as tyrannosaurs, velociraptors and birds.

A new representative of megaraptors was described by paleontologists from Argentina and Japan, led by Alexis M. Aranciaga Rolando from the Bernardino Rivadavia Museum of Natural Sciences. Dinosaur fossils have been found in deposits of the Argentine Chorrillo Formation, which range in age from 72.1 to 66 million years (Maastrichtian).

Paleontologists have described the largest megaraptor about 10 meters long 2
Thorax of Maip macrothorax (B) and location of its bones during excavation (C)

Scientists have named the new megaraptor Maip macrothorax. The generic name is given in honor of the evil spirit from Tehuelche mythology, which was represented as “the shadow of death that killed with a cold wind.” And the name of the species is translated as “large chest” – the width of its chest cavity reached 120 centimeters.

M. macrothorax turned out to be the largest known megaraptor: its length was estimated at 9–10 meters. Another feature was that many of the vertebrae and ribs had a characteristic striation, which scientists interpreted as places of attachment of ligaments.

The researchers hypothesized that these ligaments could provide advanced respiratory movements of the ribs (a similar pattern is seen in tyrannosaurids).

Scientists conducted a phylogenetic analysis that showed that megaraptors are a sister group to tyrannosauroids. South American megaraptors, according to the data obtained, form two monophyletic clades: A and B, with the second clade being nested within the first.

Many representatives of clade A reached a length of six meters or more, and the length of representatives of the advanced clade B, in which the new species appeared, exceeded eight meters. This means that in the course of evolution, the size of megaraptors increased, as previously assumed.

It is noteworthy that the increase in the size of megaraptors coincides with the disappearance of carcharodontosaurids – large predatory dinosaurs.

Apparently, in Laramidia (western North America), carcharodontosaurids were replaced by tyrannosaurids, and in South America by megaraptors, as well as abelisaurids, including carnotaurus known for its horns.

Paleontologists have described the largest megaraptor about 10 meters long 3
A, time distribution of megaraptors and carcharodontosaurids; B, results of phylogenetic analysis; C is a graph showing the increase in the average body size of megaraptors

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