They already resembled birds, were still unable to fly: The Cretaceous Oviraptorosauria are considered close relatives of real birds. A newly discovered species of these dinosaurs is now shedding light on how they were able to spread across much of Asia and North America. Unlike other Oviraptorosauria, the new species Oksoko avarsan only had two fingers instead of three. This deviation indicates a great adaptability of this group of dinosaurs. Apparently, specialized species could evolve and populate many different habitats.
Oviraptorosauria lived in Asia and North America in the Cretaceous 130 to 66 million years ago. The small to medium-sized dinosaurs moved on two legs and already had plumage and a beak that usually no longer had teeth. Like today’s birds, they laid eggs and hatched them. The group of Oviraptorosauria is divided into four subgroups, of which the oviraptorids, which only occur in Asia, are the most diverse and so far best investigated. Oksoko avarsan, which is now being introduced for the first time, is one of them.
Adaptation to different ways of life
A team led by Gregory Funston from the University of Edinburgh describes the new species using several complete skeletons that were found in the Gobi Desert in Mongolia. Some of them have been legally excavated by research teams, while others have been confiscated by illegal traffickers. The exceptionally well-preserved fossils show that Oksoko avarsan only had two functional fingers per hand, while all related species known to date have three fingers. According to the researchers, the two fingers of Oksoko avarsan were strongly built and relatively immobile. They were therefore hardly suitable for grasping or holding onto prey. According to Funston and colleagues, this suggests that the species was plant-based. The jaw structure with a toothless, parrot-like beak also supports this thesis.
The researchers can only speculate for what exactly the reduction to just two fingers was beneficial. Perhaps they were cheaper for building nests or cleaning plumage. In any case, they mark a clear difference to other oviraptorids. The researchers conclude that these dinosaurs were able to adapt to different lifestyles and diets. This thesis was already established earlier on the basis of the body size and the shape of the skull and lower jaw of different species. The forelimbs have not yet been examined in this regard. The great adaptability enabled the Oviraptoriden to occupy different ecological niches. On the one hand, they could open up new areas and, on the other hand, coexist in the same habitat. According to the researchers, this explains the great diversity of species of the genus and its wide distribution.
Sociable young animals
One of the remarkable finds suggests that Oksoko avarsan lived a sociable way of life. So four individuals were close to each other at one site. Their posture suggests that they curled up in this position to sleep – and not only after their death, for example due to geological events, were pushed so close together. Researchers had previously suspected that oviraptorids lived in groups. The find now described is the first direct evidence of this. Living together presumably offered the animals advantages in foraging for food and protection against predators. Using bone analyzes, the research team was able to show that three of the individuals were young animals around the age of one year. Their bone structure indicated rapid growth and the skull bone was not yet closed. According to the analyzes, another individual was almost fully grown and at least five years old, as growth plates revealed.
“Oksoko avarsan is interesting because the skeletons are very complete and the way they lie together shows that young animals lived together in groups,” says Gregory Funston. “But more importantly, the two-fingered hand prompted us to study how the hand and front limb changed during the evolution of oviraptors. That has not been investigated before. Our results provide an important piece of the puzzle to the question of why oviraptors were so diverse before the dinosaurs became extinct. “
Source: Gregory F. Funston (University of Edingburgh) et al., Royal Society Open Science, doi: 10.1098 / rsos.201184