Mahakala (dinosaur)

''Mahakala'' ( from संस्कृतम् (''Sanskrit''), named for Mahakala, one of eight protector deities ( dharmapalas) in Tibetan Buddhism) is a genus of halszkaraptorine theropod dinosaur from the Campanian-age (about 80 million years ago) Upper Cretaceous Djadokhta Formation of Ömnögovi, Mongolia. It is based on a partial skeleton found in the Gobi Desert. ''Mahakala'' was a small dromaeosaurid, and its skeleton shows features that are also found in early troodontids and avialans. Despite its late appearance, it is among the most basal dromaeosaurids. Its small size, and the small size of other basal deinonychosaurians, suggests that small size appeared before flight capability in birds.

Description

''Mahakala'' was a small dromaeosaurid, measuring long and weighing . The holotype specimen, IGM 100/1033, consists of a partial skeleton including skull bones, vertebrae, limb bones, and portions of the pelvis and shoulder girdle. Although this individual was small, comparable in size to ''Archaeopteryx'', '' Caudipteryx'', and ''Mei'', it was close to adulthood. This genus can be distinguished from other paravians (dromaeosaurids, troodontids, and birds) by details of the ulna, thighbone, ilium, and tail vertebrae. Like ''Archaeopteryx'' and derived dromaeosaurids, but unlike basal troodontids and other dromaeosaurids, the middle (third) metatarsal was not compressed, suggesting that the uncompressed version was the basal version. It had a typical dromaeosaurid form of the second toe, with an expanded claw.

Classification

A phylogenetic analysis performed by Turner and colleagues, who described the specimen, found ''Mahakala'' to be the most basal known dromaeosaurid. Their results, along with the small size of other theropods found at the base of paravian lineages, suggest that small size was not an innovation of early birds, but a common trait of early paravians; small size would have preceded flight and would not have been a special avian autapomorphy as the result of a size squeeze. Like birds, troodontids and dromaeosaurids were not small throughout their evolutionary history, and showed size increases among several different lineages. ''Mahakala'' has a combination of characteristics found among basal troodontids and birds, but lacks some that are present in more derived dromaeosaurids. A study in 2017 found that ''Mahakala'' was a member of the enigmatic, basal subfamily Halszkaraptorinae.

The cladogram below is based on the phylogenetic analysis conducted in 2017 by Cau et al. using updated data from the Theropod Working Group in their description of ''Halszkaraptor''.

Paleoecology and paleobiology

The paleoenvironment of the Djadokhta Formation is interpreted as having a semiarid climate, with sand dune and alluvial settings. The semiarid steppe landscape was drained by intermittent streams and was sometimes affected by dust and sandstorms, and moisture was seasonal. Animals present included terrestrial turtles and crocodilians, lizards, mammals, and a variety of dinosaurs; aquatic animals like fish were not present. The majority of the fauna was small to medium-sized. Small coelurosaurians are the most diverse dinosaurs, including fellow dromaeosaurid ''Velociraptor'', troodontids ''Byronosaurus'' and '' Saurornithoides'', oviraptorids ''Citipati'', '' Khaan'', and '' Oviraptor'', and alvarezsaurids '' Kol'' and ''Shuvuuia''; other dinosaurs present included ceratopsians '' Protoceratops'' and '' Udanoceratops'', the hadrosaur '' Plesiohadros'', and the ankylosaurid '' Pinacosaurus''. Like other dromaeosaurids, ''Mahakala'' would have been a small active predaceous carnivore.

See also

* Timeline of dromaeosaurid research

References

External links

HTML version of "A Basal Dromaeosaurid and Size Evolution Preceding Avian Flight"

{{Portal bar, Dinosaurs, Cretaceous

Late Cretaceous dinosaurs of Asia
Djadochta fauna
Dromaeosaurs
Fossil taxa described in 2007
Taxa named by Mark Norell