New pterosaurs, and especially new well preserved pterosaurs, are rarely found. As I’ve mentioned in the past, pterosaurs exhibit significant skeletal pneumaticity, meaning their bones are often filled with air. This is common in skulls of animals (like the sinuses in your own head), and is especially prevalent in pterosaurs. For this reason, pterosaur skulls are often crushed, making their brain cases hard to study. This is why the new pterosaur Allkaruen koi found in Argentina and described in PeerJ by Codorniú et al. is so important.
Brain cases are useful in understanding extinct animals, because they let us see the general structure of the brain, which can teach us about which regions were well defined. As different regions of the brain are responsible for different behaviours or senses, we can then make inferences about the capabilities of these animals when alive. If the portion of the brain related to smell is particularly well developed, the animal probably relied on smell significantly, which can indicate that it was a keen predator or scavenger. The same things can be said for areas relighted to eyesight, flight, etc. This is where the new pterosaur comes in.
Allkaruen comes from the Early/Middle Jurassic of Argentina, a time in which pterosaur fossils are rare. It sits just outside of the Monofenestrata, the group including the transitional pterosaurs (wukongopterids) and more derived pterodactyloids. The specimen is very fragmentary, but it has an exceptionally 3D preserved braincase, allowing for Codorniú et al. to study the evolution of the pterosaur braincase through CT scanning, since primitive non-pterodactyloid braincases, and derived pterodactyloid cases have been studied before. Now we have a braincase from one of these animals in between.
The braincase of Allkaruen shows some features in common with basal “rhamphorhynchoids” or non-pterodactyloids, while some are shared with derived pterodactyloids. Additionally, it has some unique features that appear to be transitional features between the two groups. The interesting part of this mosaic of features, is that it is a different pattern than in what is seen in other parts of the body in the evolution of basal non-pterodactyloids into wukongopterids and pterodactyloids. The discovery of the transitional Darwinopterus showed us that pterosaurs exhibited modular evolution with different parts of the skeleton evolving at different times. The first stage includes changes in the skull, neck and ribs, while the second stage shows changes to the wing and feet. The fact that the braincase shows a mosaic of features means that although pterosaurs seem to have evolve different regions of the body in phases, not all “modules” of the body follow this trend. The other significance of this find is the age. Pterodactyloids didn’t evolve until the Late Jurassic, but Allkaruen is from the Early-Middle Jurassic, meaning at least some features of the pterodactyloid brain and skull had already started to evolve at this point. Since pterosaur fossils from this time are so rare, we had no reason to expect them so early in pterosaur evolution.
Slowly but surely more pterosaur fossils are being found, teaching us more and more about pterosaur diversity and evolution. As more specimens are found, we are starting to better understand how pterosaurs evolved. Now all we need are some better Triassic fossils to figure out exactly where pterosaurs came from! For now, however, new specimens such as Allkaruen are great for us pterosaur workers to help understand their evolution.