In the Cretaceous, they were the rulers: giant flying dinosaurs hunting for prey over the seas and the land. For example, the Quetzalcoatlus living in the area of today's North America had a wing span of 11 to 13 meters, fossil finds prove. Other species were smaller, but still the size of the largest birds alive today. "Pterosaur species with spans of 2.50 to 3 meters were common in the late Cretaceous, today accounting for around 70 percent of all fossil finds in some localities, " explain Elizabeth Martin-Silverstone of the University of Southampton and her colleagues. "Conspicuously absent, however, are fossils of smaller pterodactyls with less than two meters wing span." Therefore, paleontologists discuss for some time, whether this is because these small pterosaurs at that time hardly occurred, or if these smaller species were simply preserved much less often. Because the bones of the pterosaurs were hollow and can therefore be easily crushed in the ground and destroyed.
"An exciting and important find"
The discovery of a first small pterosaur could now provide an answer to this question. The bones of the fossil were found on Hornby Island in British Columbia. A fossil collector had hit the bone and then handed it over to the Royal British Columbia Museum. There Martin-Silverstone and her colleagues have now examined the ten bones - including a complete humerus and some vertebrae - in more detail. According to their anatomical features, paleontologists assign the fossil to the Azhdarchoidea, a late-Cretaceous group of short-tailed pterosaurs. From the length of the humerus, the scientists conclude that this dinosaur may only have had a wingspan of about 1.50 meters. He is one of the smallest ever found pterosaurs. "This specimen was not just a juvenile of a larger species, but seems to belong to a naturally small species, " says co-author Mark Witton of the University of Portsmouth. "Because of his bone structure and the fusion of his vertebrae, we could see that this animal was almost fully grown despite its small size."
The discovery of such a small pterosaur shows for the first time that this group of animals also had small species in the late Cretaceous, as the researchers explain. "This specimen is by no means the prettiest or most complete pterodactyl known, but it's an exciting and significant find, " says Witton. Because the fossil speaks against the theory that the birds had already replaced the small pterosaurs at that time and displaced. Instead, the apparent absence of the smaller species could have a very different cause: "The hollow bones of pterosaurs are very poorly conserved even in large species, " explains Martin-Silverstone. "A small pterosaur would therefore probably only rarely be preserved." The rarity of smaller pterosaur fossils is therefore a consequence of this low durability of fragile bones over the millions of years. This may also explain why there have been virtually no finds of gullaurs of the great pterosaurs - their bones were too fine to survive.
- Elizabeth Martin-Silverstone (University of Southampton, UK) et al., Royal Society Open Science, doi: 10.1098 / rsos.160333