Wednesday, 14 October 2015

The Anatomical Antiquity Of Avian Flight

There is debate over whether early birds and
their close theropod relatives could fly
There is great debate surrounding the topic of whether the first birds could fly or not. They certainly had feathers, long limbs and light, compact bodies required for flight. Yet they were descended from theropod dinosaurs which were almost certainly terrestrial.

Some theropod species, such as Microraptor, may have been able to fly, but there is little evidence to support this beyond their similarity to and close evolutionary affinities with avians. Equally such forms may have simply been gliders, utilising feathers to increase gliding distance between trees. Whether flight evolved in dinosaurs or birds is therefore contentious.

If it evolved in dinosaurs then the first birds would have been airworthy also, but if it evolved first in avians then it becomes more difficult to tell whether the early birds were able to fly. A recent study, however, shows that the early birds were capable of powered flight. Yet there is more to flight than simple feathers and bones. A complex array of ligaments and tendons is required to animate the frame in such a way that flight becomes possible. To determine whether early birds had the requisite anatomy for flight a group of researchers, led by Dr. Luis Chiappe from Natural History Museum of Spain, compared the anatomy of an early avian to that of modern birds.
The 125 million year old fossil and its reconstruction

The researchers used an exceptionally well preserved, 125 million year old wing from Las Hoyas in Spain. The specimen contained enough detail for the arrangement of the tendons, bones and muscles to be reconstructed.

By comparing the reconstructed anatomy to that of modern flying birds, the researchers found similarities.

'The anatomical match between the muscle network preserved in the fossil and those that characterise the wings of living birds strongly indicates that some of the earliest birds were capable of aerodynamic prowess like many present-day birds,' said Chiappe. 'It is very surprising that despite being skeletally quite different from their modern counterparts, these primitive birds show striking similarities in their soft anatomy,' continues Guillermo Navalón, a doctoral candidate at the University of Bristol and lead author of the study.

This is intriguing as it shows that the anatomical constraints on flight may not be as stringent as previously thought. If a different skeletal architecture with the same musculature can result in flight, it opens up the possibility that avian-like theropods may also have taken to the air in active fashion.