Chaoyangopteridae is a clade of pterosaurs (family in taxonomical terms, but we shall not use them for the sake of cladistics, being more accurate) that lived in the Lower Cretaceous, with most known taxa from the Barremian and Aptian stages, but extending into the Albian (more discussion on that below). It is within Azhdarchoidea, a clade that also includes azhdarchids, tapejarids and thalassodromedids. As a whole, this is not a very well studied clade, so this project focuses on displaying the most information about them as possible.

(On the left, the most "well known" genus, Lacusovagus. Courtesy to Mark Witton, whose image is pratically public domain now)

Anatomy and paleoecology

Chaoyangopteridae Is known mostly from asian fossils, but Lacusovagus and some african remains suggests they were widespread on Gondwannan landmasses as well; this could be an indicator of some faunal exchange between Asia and Gondwanna in the Jurassic and Lower Cretaceous, as forms like stegosaurs and volaticothere mammals also indicate, but it is probably more likely that chaoyangopterids, alongside other pterosaurs like tapejarids and dsungaripterids, simply made use of their flight capacities to disperse across these landmasses. Chaoyangopterids occur mostly on lagerstätten fossil sites, including the Jiufotang Formation, the Yixian Formation (both part of Liaoning) and, in the case of Lacusovagus, the Crato Formation (information of where the african remains were obtained is very apreciated). This kind of environments formed around bodies of water with poor conditions for decomposing bacteria, either by hypoxia cycles or extreme salt content. In the case of the Liaoning formations, the present environment would have been a volcanic lake, sorrounded by lush forests according to the preserved vegetation and polen; the Crato Formation would have been an arid/dry tropical biome sorrounding a saline lagoon. These formations are rich in pterosaur fossils, besides chaoyangopterids, much like Cenozoic lagerstätten are rich in bird fauna, and it may be possible to evaluate the ecological roles of these animals by comparing the suggested lifestyles with the environment.


Chaoyangopterids have proportionally short wings (on the right another picture of Lacusovagus; note how the wing finger is as long as the arm, while in most pterosaurs its longer), and the metacarpals are quite long, the front limb as a whole having the same proportions as the ones of your average ungulate. This feature is shared with other azhdarchoids, specially azhdarchids and tapejarids; as a whole, Azhdarchoidea seems to have specialised to a more terrestrial existence, both in terms of prefered habitats (as they mostly occur inland) and on terms of lifestyle, the long limbs indicating that they had an efficient terrestrial locomotion. It is known pterosaurs were efficient fliers, having evolved the most complex wings of the animal Kingdom and an also complex nervous system for flight control, but the exact flight capacities of azhdarchoids are unknown. Having proportionally shorter wings than in most pterosaurs, and having shoulder joints in a lower position than in other pterosaurs, thus allowing generally not a lot of wing musculature on the chest, it is considered that these pterosaurs did indeed spent most of their time on the ground, usually taking off for defense reasons or to cover large distances. Modern ground dweeling birds like Galliformes however aren't good models, because as mentioned before azhdarchoid wing musculature wasn't as developed as in other pterosaurs - dsungaripteroids, for instance, spent most of their time on the ground and yet had strong wing musculature, following the Galliforme model more closely - most likely these animals made more use of soaring flight. Take off would be easy, as pterosaurs used a catapult like motion of the forelimbs instead of wasting their time running like birds do; once aloft some wing beats would be enough to elevate it on the air, and depending of the duration of the flight the animal would either glide down or take advantage of the winds and thermals to stay in the air. Pterosaurs, specially azhdarchoids, would have used a lot of anaerobic respiration, as the long necks would create a "dead air" space; the initial launch, in particular, would have had used a lot of energy very quickly, something that would be very difficult if oxygen was required. To compensate, pterosaurs had a very complex air sac pulmonary system, much like birds; this also allowed them to develop a pneumatic skeleton. An animal like Lacusovagus would have been as heavy as 20 kg, similar in weight to a modern Darwin's Rhea.


Chaoyangopterids had long, toothless jaws. The lack of teeth is in fact ancestral to azhdarchoids, although whereas they had or not a rhamphoteca like modern birds is debatable. Unlike tapejarids and thalassodromedids (the later showing no specialazations towards a specific lifestyle), chaoyangopterids had long necks, much like azhdarchids; thus, it has been suggested they filled a similar ecological niche, feeding on small animals that they captured on the ground using their long rostrum. In addition, their toes and fingers are quite short, suggesting they usually didn't wade, and their claws are small and blunt, unsuitable to tree climbing like in tapejarids. Thus, much like their larger cousins, chaoyangopterids had a mostly terrestrial existence, preying on small animals in a stork like manner and taking off when requiring too. However, chaoyangopterids were appearently more diverse in terms of lifetyles than azhdarchids; whereas only one or two azhdarchid genera occur in a specific fossil site, only in Liaoning there's about 5 chaoyangopterid genera. One of the most notable examples of chaoyangopterid specialzation is the head; while the basic form (a long, toothless rostrum more or less straight) is present, the size and shape of the nasoanteorbital frenestrae varies quite much. In fact, this variation of nasoanteorbital fresnestrae sizes makes Chaoyangopteridae unique; in most pterosaurs, the size and shape of the nasoanteorbital frenestrae varies little. In istyodactylids, for instance, the nasoanteorbital fresnestrae is quite large and deep, occupying most of the rostrum, while in pteranodontians it is quite small and more and less circular in shape. In azhdarchoids, it is typically quite large; notably, in neoazhdarchoids (the clade composed of thalassodromedids, chaoyangopterids and azhdarchids), it is not only quite deep, but it extends above the eye, something that doesn't happen in other pterodactyloids. Chaoyangopterids presumably have this design as ancestral to the clade, but in several genera the nasoanteorbital fresnestrae decreased dramatically in size and depth. The most extreme example must be Eopteranodon, whose nasoanteorbital fresnestrae is proportionally as small as that of pteranodontians.
Shenzhoupterus as drawn by Ville Sinkkonen. Note the large nasoanteorbital fresnestrae that extends above the eye, as well as the proportionally short wings
Eopteranodon as drawn by Mike Hanson. Note the small nasoanteorbital frenestrae and the overall similarity with pteranodontian skulls.
Jidapterus as drawn by Mike Hanson. Note the reduced (but still deep) nasoanteorbital frenestrae, and the slightly curved jaws, remaniscient of tapejarid ones.
The exact reason why the nasoanteorbital fresnestrae varies so wildy in size within Pterodactyloidea is unknown - indeed, why it is so big in several forms isn't unknown either - but there seems to be a correlation between its size and the environment and presumed habits of the animal. It is possible that, much like modern toucans and hornbills, neoazhdarchoids made use of their huge rostrums as display devices (the skin covering the nasoanteorbital fresnestrae could in particular had been quite colourfull), and indeed thalassodromedids and azhdarchids seem to have roamed open environments, where extravagant heads would have been used to impress mates and scare off rivals; at least one chaoyangopterid, Lacusovagus, did occured in what is presumed to have been a dry environment, and its nasoanteorbital frenestrae are typical for a neoazhdarchoid. By contrast, forest dweeling species are usually more secretive, ence perhaps why Liaoning's chaoyangopterids tend to have small nasoanteorbital frenestrae; incidently, a similar pattern occurs with tapejarids, with South America's forms having flamboyant head crests and chinese ones having smaller and less spectacular ones. The shape of the nasoanteorbital frenestrae however may also play a part in the animal's lifestyle; as pictured above, the chaoyangopterids Eopteranodon and Jidapterus, while both having reduced nasoanteorbital frenestrae, have very differently shaped ones and differently shaped rostrums. While chaoyangopterid bite forces haven't been measured yet, both shapes imply a stronger bite force than in animals like Shenzhoupterus, and thus the three genera, while occupying roughly the same distribution area, could had been looking for different food stuffs. Its unknown whereas chaoyangopterids were hypercarnivorous (much like modern storks) or if they were omnivorous (presumably like the related tapejarids), and if omnivory was present maybe that would explain why the diversity of genera was high in Liaoning.

Much like other pterosaurs, chaoyangopterids would have layed soft shelled eggs and buried them, much like in modern non-avian sauropsids. Parental care is unknown, and most likely was unexistent, as chaoyangopterids much like other pterosaurs could possibly have been volant since birth. The young would have used their energy primarily to search for food instead of growing up as in other precocial tetrapods, and thus growing would have occured quite slowly, taking several years to reach the maximum size. This means they would have occupied several niches across their lifetime, and in the case of chaoyangopterids the mystery of how the Liaoning species avoided competition becomes more intense, as only with age they would become more specialised.

From prosperity to demise

Chaoyangopterids first appeared in the Barremian staage of the Cretaceous, in which the diversification of pterodactyloids reached its maximum. In fact, Azhdarchoidea first appears in this age (Doratorhynchus, AFAIK, turned out to be something else), with the first tapejarids dating more or less from this era as well. Chaoyangopteridae, reached its apex during the Aptian and Albian stages of the Lower Cretaceous, before gradually disappearing until vanishing completly from the face of the Earth by the Cenomanian. Its worth to note that all chaoyangopterid remains (again, with the possible exception of the african remains) come from lagerstätten fossil sites, as do many pterosaur fossils, indicating perhaps that their hollow bones with thin walls were too fragile to be preserved - indeed, there's very few chaoyangopterid fossils even when there are 6 known genera plus an unnamed one - and in fact there might be several unknown genera, and the longevity of the group as well as its diversity could had been longer. However, while its almost a certainty that there are chaoyangopterids that haven't been discovered yet, its unlikely they would have lasted long into the Late Cretaceous; by the Turonian, several extinction events caused the demise of many large animal groups, and pterosaurs seem to have been among them. Its by the Turonian that the azhdarchid pterosaurs, which appeared more or less as far back as the Albian/Aptian, became more pronounced, while other azhdarchoid pterosaurs seem to have gone extinct or at least weren't as common. Filling roughly similar ecological niches to those of chaoyangopterids, azhdarchids were less specialised and presumably more adaptable, which is perhaps why they outlived them, and even if chaoyangopterids survived beyond the numerous crisis of the Turonian the now more diverse azhdarchids would have outcompeted the remaining species. The disappearence of the other azhdarchoids, tapejarids and thalassodromedids, is less clear, though the later, occupying a similar niche to that of azhdarchids and chaoyangopterids, most likely got outcompeted as well.

Chaoyangopteridae, as a whole, is a mysterious group, the fact that their bones are mostly restricted to lagerstätten fossil sites (unknown after the Lower Cretaceous) certainly not helping with the date of their death, nor the lack of biomechanical studies on the part of scientists helping with their lifestyle, but their mystery makes them a very interesting group, and I hope that this wonderfull clade isn't ignored for much longer.