Recently a new carnivorous theropod dinosaur has been unearthed in the Tiaojishan Formation of Hebei Province, China. This formation, near Beijing, is famous for its primitive bird fossils from the Jurassic Period. Without fail, it has yet again turned up a unique and amazing specimen, described in the May 7 issue of the journal Nature . The dinosaur, named Yi qi (meaning “strange wing”) by a team led by Xing Xu of Linyi University in Shandong, China, was discovered by a local farmer. Yi is part of the quite literally small dinosaur family Scansoriopterygidae and is one of only three species in the family. All members in this group are about the size of a pigeon or smaller. The Yi fossil, assumed to be an adult, appears to be the largest of the three species. Although incomplete and quite fragmented, the remains of this fossil are astoundingly well preserved and reveal a unique morphological feature.
The fossil find includes not only lush plumage but also remnants of a membrane believed to have stretched across the animal’s side to form a primitive wing. Yi is especially unusual because of a mysterious bone that attached somewhere on the wrist of the dinosaur (the exact positioning is unclear), projecting outward as though it were a finger. Scientists first tested the composition of the structure, and showed that it and other bones of the fossil were made up of the same material. This proved that this appendage was in fact bone and not cartilage or some other substance in the skeleton. This bone, and others of similar shapes, are referred to as “styliform” bones. Paleontologists believe that this kind of bone, together with a membrane stretching over the bone, formed a primitive wing. Many interpretations have been made suggesting how this bone might have been arranged in the hand or wrist of Yi.
Considering that the fossil is the only one of its kind, and that the skeleton was disarticulated (not in the correct anatomical position), it is difficult to say exactly where the bone connected and faced. Yet another difficulty that arose in interpreting the bone is the fact that one end is sharpened and the other is squared off. The squared off end, although clearly the end that attached to the wrist, does not appear to have been very mobile during use by the animal. On top of that, if the bone could move, it might have impeded flight by getting in the way of the main body. This lead paleontologists to believe that Yi was also not a strong flier— if at all—and was more likely a glider. Despite this, Yi might still have flown, because of structural similarities to modern animals. Modern analogs (organisms that act or function similarly to things in the past) to the proposed wing structures of Yi are likely flying squirrels and bats rather than birds. Flying squirrels do in fact have a styliform bone very similar to that in Yi, giving scientists more reason to believe that Yi was a glider and not a flier. Nevertheless, the elongated fingers and styliform bone resemble the outspread hand of a bat, which flies and does not glide. Yi especially resembles pterosaurs (extinct flying reptiles), which share the extreme elongation of a single digit (pterosaurs did not have a styliform bone), providing a good example of convergent evolution (unrelated organisms evolving a similar feature).
Yi is not only intriguing because of this strange styliform protrusion in its wrist, but also for its heavily feathered body. It is not surprising that yet another feathered dinosaur has been found in China, because that region is the origin of many such theropods. Most of this animal’s body appears to have been covered in feathers aside from the membranous wings and head.
Because the rear of the animal, including its tail, is not well preserved, feather structures along these parts of the body are unknown. We do know that from what remains of the fossil, the dinosaur did not have primary (or “pennae”) feathers (the long ones used in flying). The feathers of Yi closely resemble those of many other kinds of theropods, although they are most similar to those of raptors (related to the famous Oviraptor). Using advanced technology involving an electron microscope, the fossil’s feathers were examined for structures at the point of attachment. This analysis showed remnants of melanosomes—tiny holes in the skin of the dinosaur. Although seemingly dull and insignificant to the lay person, to scientists they could open up a world of understanding regarding dinosaur color and anatomy.
Yi qi is certainly an interesting new find among the paleontological community, but until more specimens are found, much of its anatomy and natural history will remain unknown. It is highly probable that this theropod performed some kind of aerial locomotion, but whether that was full blown flight or just simple gliding is not yet confirmed. Our present understanding of its flying mechanism is leaning toward gliding, with the evidence of little mobility in the long styliform bone and the fact that flapping would obstruct full locomotion. It might never be known which form of movement it took, especially as an ancestor of modern birds, but paleontologists always hope that another fossil will be found and the mysteries unraveled.