fossils

Little dragons of the Jurassic: The wukongopterids

3986b46bb4f35aa1ff4d42167a12e0fc

Vasika
Udurawane

Lead Writer
The Jurassic skies were once ruled by tiny dragons. These furry-bodied fliers are wonders in paleontology, true 21st-Century milestones that changed what we thought we knew about the flying reptiles. Soar through the forests of the Mid Jurassic as Earth Archives teams up with Pteros to bring you the weird and wonderful wukongopterids!

In their own worlds, they were diverse, bizarre and probably showy and colorful with huge crests topping their slim heads. They lived among the trees, pursuing small prey on narrow wings. For more than 161 million years, these strange fliers were buried throughout the Northern Hemisphere until their discovery in the 21st Century. They belong to the wider group of pterosaurs, the warm-blooded winged reptiles that dominated the Mesozoic skies. As a group all their own, the pterosaurs were highly successful and beautiful creatures. There were giraffe-sized terrestrial stalkers, albatross-like fishermen, night hunters reminiscent of a bat and some that seem to have come from the pages of a fantasy novel. This final group contains among the most dragon-like of pterosaurs. They are classified as the Wukongopteridae.


The wukongopterids are limited to the Jurassic Period, a time when dinosaurs had finally mushroomed into titans and for a long time, the world was hot and fertile. Two mega-continents existed, one in the north and one in the south. Fossils of wukongopterids have been found only on what once made up the Northern Hemisphere or Laurasia. These days, the remnants of Laurasia’s unique past are preserved in Asia, North America and Europe. Among the earliest wukongopterid discoveries hails from China, now regarded as a paradise for paleontologists. As a group, these creatures embody what the field of paleontology is like these days. It is a force that is more popular and powerful than ever thanks to social media and regular collaborations between the top scientists and the top artists. Cutting-edge technology, like computer modeling and scans have enabled researchers to peer deeper into the rock and even online researchers are making a name for themselves thanks to open-access papers. Plus, newer bone beds have been named and continue to push boundaries for the study as a whole.


One of these new and popular fossil locations is the Tiaojishan Formation. The Tiaojishan is from China’s Liaoning Province, an area famous for impressively preserved fossils. Many of the Liaoning beds preserve temperate forests of ginkgo, fern and benettite plants bordering a volcanic region of what was then eastern China. The Tiaojishan dates back to the mid-Jurassic, roughly 161 million years ago and was full of some of the earliest feathered dinosaurs, early mammals, insects, reptiles and pterosaurs. The first wukongopterid discovery was named Wukongopterus lii, and was scientifically described in 2009. The small flying animal had a wingspan of 73 centimeters, and was named by a team consisting of known pterosaur worker Alexander Kellner and Chinese paleontologist Wang Xiaolin and colleagues. This small pterosaur gets its name from the folkloric Monkey King, a popular fixture in Chinese mythology. At the time, it was not really thought of as an important find. In terms of its body, it did resemble a little medieval dragon but was soon forgotten by the general public. The fossil was nearly complete and somewhat crushed, missing parts of the skull. Another named Changchengopterus was discovered from the same rocks. It was a small juvenile with a wingspan only 47.5 centimeters across. We do not know how big it would have grown. For a while, little Changchengopterus was classified in a completely different family. Only later was it included in its proper group.


Things would change the following year though with the discovery of Darwinopterus. Here was the star player that the wukongopterids were begging for. The type specimen was nearly totally complete, allowing for better research than the preceding two. To make things even better, the new animal was named in honor of Charles Darwin himself. It also gained fame because it was seen to have a number of very peculiar traits that set it apart from all other pterosaurs known at the time. For one, it belongs to a much bigger group of pterosaurs called non-pterodactyloids. All wukongopterids belong to this huge order of primitive, small and sometimes long-tailed flying reptiles. The other group is the pterodactyloids, which includes some of the largest and most spectacular, albeit tailless pterosaurs. The non-pterodactyloids had their heyday in the Jurassic, when a variety of forms existed. The family died out when the period ended, and from then on the air belonged to the pterodactyloids.


Darwinopterus actually contained features of both families in one body. It had the long tail of other non-pterodactyloids, as well as the long neck vertebrae of the advanced pterodactyloids. Its skull bore the most tell-tale of these features. Between the nasal opening and the eye opening of most primitive pterosaurs, there is a hole in the skull called the antorbital fenestra. In Darwinopterus however, there is only one opening in front of the eyes. Furthermore, its skull was long and large in proportion to its body, a rather pterodactyloid feature. Darwinopterus was instantly hailed as a transitional fossil, a sort of missing link that lay between the two pterosaur families. By this definition one might expect the features to flow smoothly between primitive and advanced forms. However, there is something different going on.


Darwinopterus is a good example of modular (or mosaic) evolution, in which both basal and advanced body parts can exist in the same body and evolve at different rates instead of following a smooth and general road. This system of evolution has been ascribed to numerous other organisms, and evidence for this comes quite exclusively from paleontology. The full name of the type species is, by no accident, Darwinopterus modularis, named after this modular evolution. For a long time, it was paraded in the media as some vicious aerial killer, wings outstretched as it lunged for a hapless feathered dinosaur much smaller than itself. Darwinopterus modularis did indeed have spike-like teeth but it had the wrong kind of body to allow this kind of predatory prowess. It weighed just 300 grams, as big as some crows. Its wingspan was around 85 centimeters across or so. This was hardly impressive even for a Jurassic pterosaur. Then there is the size of its supposed prey. Most of the contemporary feathered dinosaurs, like crow-sized Anchiornis and Xiaotingia were far too large and heavy for the delicate flying reptile to tackle. A good fight with one of them could seriously damage one of these lightly-built flyers, potentially killing it in the process.


As pterosaur researcher Mark Witton adds, it was completely unlike modern aerial pursuit predators like the spectral bat. This bat is a very large active hunter that uses a combination of large toe claws and powerful jaws to grab and kill its prey. Even modern birds of prey are very robust, with powerful talons, skulls and wing muscles that enable an active raptorial lifestyle. The slim Darwinopterus modularis was certainly not of this ilk, so very soon a lifestyle of catching insects was prescribed, with the spiky teeth used to grab rather soft and tiny prey.


Soon, two more species were discovered, all in the Tiaojishan. They were all separated on the basis of their teeth and some other, finer characteristics. The species D. linglongtaensis was found in the same year while D. robustodens was discovered one year later, in 2011. All three of them were coexisting in relative peace at the time due to acute niche partitioning. Not only was Darwinopterus robustodens one of the larger species, with a body the size of a robin but it also had very strong and rather thickly-constructed teeth. This animal was built for crushing hard prey, possibly the shells of beetles.


The second species also had a very strongly built snout and jaws, with short teeth that could be used to take on small and hard-shelled victims like the other species. Even Wukongopterus and Changchengopterus were found in the same beds and the different wukongopterid varieties probably coexisted. They differed in diet and even in looks, with some being smaller and lighter while others were larger and more heavily built. In life, of course, there would have been differences in color and habits, none of which have been preserved in the fossil record. The wukongopterids are not the only pterosaurs from this time and place, though. Several of these flying reptiles seem to have been living here, many of them small and living on insect prey. One of these, Jeholopterus, might even have been nocturnal. It had huge eyes for better sight, and thickly furred wings to muffle its approach against the night air.


Between the years 2010 and 2011, roughly 30 to 40 specimens of Darwinopterus were discovered. The remarkable number of fossils allows for very in-depth studies of the animal. For one, these remains suggest that sexual dimorphism occurred in the animal. Differences between sexes have been discovered in the big and famous pterodactyloid Pteranodon, with the males being twice as big as the females and sporting huge bony crests. Darwinopterus’ dimorphism was somewhat less dramatic than that of Pteranodon. The stupendous number of fossils show us that some individuals had narrower hips while others had the wider hips needed for laying eggs. Also, Darwinopterus did have a bony keel along the top of its head to support a crest of skin rather than just a bony display organ. Some specimens had a weaker keel than others, suggesting that these might have been females.


One particular female specimen was nicknamed Mrs. T and stuck in her pelvis was something extraordinary. It was a fossilized egg, and in general pterosaur eggs are a rare treasure. Studies of both her and her egg showed that it was soft-shelled unlike the hard eggs of the contemporary dinosaurs. Her eggs were also very small in comparison to her body. Small, soft-shelled eggs are found in many of today’s reptiles, therefore contradicting the image of the pterosaur mother brooding a well-constructed nest. Perhaps they were precocial, able to fly and take care of themselves soon after hatching. This indicates a possibly slow growth for young pterosaurs, spending more energy on flying and finding food than actually growing. For a while, it was accepted.


As the years went by, further studies of Mrs. T revealed something else that would soon upset even this theory. For one, Kevin Padian reassigned her from Darwinopterus to the contemporary Kunpengopterus. This even smaller and slimmer wukongopterid was found with remains of soft tissue, thus allowing us to properly reconstruct the animal’s crest. These days, Mrs. T is thought to belong to this genus, a rather surprising turn that was confirmed in an additional study by Kellner, Wang and others last year. There was not just one egg but two, suggesting that the pterosaur had two oviducts. Were the young of Kunpengopterus truly precocial or altricial, being helpless like those of many modern birds? Studies of the pterosaur Rhamphorhynchus by Edina Prondavi in 2012 indicate that its babies at least, were flightless until they reached some sort of maturity, during which they grew quickly before slowing down as adulthood approached. Whether or not baby pterosaurs required parental care is a matter of debate, and for Kunpengopterus, no more can be said till more evidence is uncovered.


The wukongopterid story though, is far from complete. One of the last of their family was named and scientifically described in 2013, based on a large skull of 33 centimeters. At this size, it was one of the biggest-known Jurassic pterosaur skulls and while it was not very complete the owner of the skull soon revealed its true identity. It was the largest of all wukongopterids, an animal with a 1.2-meter wingspan. This still did not make for a big Jurassic pterosaur though. It’s not just its size that makes Cuspicephalus interesting. This creature was discovered hundreds of miles away from its kin, in the Kimmeridge Clay Formation of England. The classification of this pterosaur as a wukongopterid last year came as somewhat of a shock. Somewhat after its discovery it was classified as just another pterodactyloid, which made sense at the time. During the closing stages of the Jurassic, the advanced pterosaurs had burst onto the scene and were living all over, with excellent fossils of these creatures being found in Germany’s famous Solnhofen Limestone Formation. For centuries both the Solnhofen and the Kimmeridge have revealed marine animals from the Late Jurassic, somewhere between 155 and 145 million years ago. They varied from small fish and shelled creatures to gigantic marine reptiles as big as a killer whale. This is much later than any of the Chinese specimens, and Cuspicephalus was indeed probably lost among the coastal landscapes of Jurassic Europe. At the time, the continent consisted of a series of large and small islands lying in the ancient Tethys Ocean which separated the northern and southern continents.


Clearly these weird dragonish pterosaurs were doing something, or they would not survive for so long and have such a wide range across the Northern Hemisphere. For now, Cuspicephalus has been reconstructed as a typical member of its family. It has a long and narrow head and a soft tissue crest. Its tail is long, and bears multiple vanes of skin, while mixing both pterodactyloid and non-pterodactyloid features. It was just another great wonder in a family of incredible little creatures.


With just a few species, the wukongopterids are far from being the biggest pterosaur family. They were small flyers in the same range as medium-sized birds today and managed to coexist with one another and with a whole range of other pterosaurs. Their time was limited and their stature was small, yet these little dragons of the Jurassic have left their mark on how we see the evolution of some of the most magnificent creatures ever to take to the air.

Image Credit: Julio Lacerda

3986b46bb4f35aa1ff4d42167a12e0fc

Vasika
Udurawane

Lead Writer


http://sulc.us/oziwi
http://www.eartharchives.org/articles/little-dragons-of-the-jurassic-the-wukongopoterids/