Mahakala

Mahakala is a dromaeosaurid dinosaur from the Upper Cretaceous of 80 million years ago. 
It is based on a partial skeleton found in the Gobi Desert, Mongolia. 
"Mahakala" was a small dromaeosaur, about 70 centimeters long (28 in). Its skeleton shows some features which are also found in early troodontids and avialans. However, its short forearms rule it out of the Alialae.
Despite its late appearance, its structure is that of a basal dromaeosaur. Its small size, and the small size of other basal deinonychosauria, suggests that small size came before flight in birds.
Description.
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 (dromaeosaurs, troodonts, and birds) by details of the ulna, thighbone, ilium, and tail vertebrae.
It had a typical dromaeosaurid form of the second toe, with an expanded claw. "Mahakala" also had very short forelimbs compared to other Dromaeosaurs.
Classification.
A phylogenetic analysis performed by Turner and colleagues, who described the specimen, found "Mahakala" to be the most basal known dromaeosaur. 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.
In evolution, small size would have come before flight. Like birds, troodonts and dromaeosaurs did not keep small size throughout their evolutionary history. They had several separate size increases among different lineages. 
"Mahakala" also shows a combination of characteristics found among basal troodonts and birds, and is missing some that are present in more derived (specialised) dromaeosaurs.
Paleoecology and paleobiology.
The paleoenvironment had a semiarid climate, with sand dunes and alluvium (loose stuff). The semiarid steppe landscape was drained by streams after rain, and was affected by dust and sandstorms. Rainfall was low, and 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", troodonts "Byronosaurus" and "Saurornithoides", oviraptors "Citipati", "Khaan", and "Oviraptor", and alvarezsaurs "Mononykus" and "Shuvuuia"; other dinosaurs present included the ceratopsian "Protoceratops" and the ankylosaur "Pinacosaurus". Like other dromaeosaurs, "Mahakala" would have been a small, active, predaceous carnivore.