Algunos científicos llaman a Liaoning "La Pompeya del Mesozoico", pero a su manera, Liaoning es aún más notable. Erupciones volcánicas repetidas crearon un pastel de capas de yacimientos de fósiles que abarcan millones de años . Hasta 2002, se han identificado más de 60 especies de plantas, unas 90 especies de vertebrados, y alrededor de 300 especies de invertebrados. Los paleontólogos se maravillaron con el hallazgo de fósiles de dinosaurios con el contenido del estómago identificable, donde se patentizaba huesos de lagartos y mamíferos, y tambien con fósiles de aves que contienen semillas de plantas.
FAUNA de la FORMACIÓN YIXIAN
Near background From left to right:
1.- A pair of Psittacosaurus (Ornithischia): Beaked, primitive relative of ceratopsians. A new psittacosaur specimen from the Yixian formation has been described in Germany. It's been found with preserved external integument . This is so far the first ornithischian with what seems unequivocally dermal long quill-like structures lining up a good part of the top of the tail. The quills (90 to 100 in this specimen) were 1 to 2 mm thick and possibly hollow, some of them reaching nearly 20 or 30 cm long and look well flexible, falling over the tail like a fountain. The rest of the skin is naked and covered with typical ceratopsian scaly skin ( a mosaic of larger non-overlapping round scutes surrounded by many small ones). This time there were not feathers or protofeathers as in the well known theropods, but I'm not discounting that one day we'll see furry ornithischian juveniles since the adults had these tail quills! For me this shows that quill-like skin structures were probably endemic (as a way of insulation) in all groups of dinosaurs and a main characteristic of the Dinosauria. The muscle and fat are preserved in a carbonized layer surrounding the whole body (a fact that makes the fossil look remarkably similar to any mammal from the Messel deposits in Germany 50 million years later) showing precisely how muscle and other soft tissues were preserved in the Yixiang deposits (contra Ruben et al) and further demonstrating that accusing theropod feathers or skin structures of being traces of dried muscular tissue (collagen fibers) is baloney. The silhouetted carcass shows that the animal might have been somewhat stocky. Other psittacosaur specimens with gut contents (including bones and stones) have been found giving credence to the idea that indeed psittacosaurs were probably 'fat porcupine mimics'. We may also like to speculate that the quills were venomous as a way of defence. But we may never know. There's still a lot of work to be done to help us have a completely accurate picture of this new landmark discovery and further investigation may change our view of it in the future.
2.- A couple of displaying "BPM 1 3-13" (Cryptovolans) newly described by Mark Norell and still unnamed dromaeosaur specimen that looks very much like Microraptor. What is striking about these new ones is that the tip of the tail feathers are up to 20 cm long, adding extraordinary length to a tail that was already long. I depicted them here as rather ornamental, spectacular display structures but their usefulness is anybody's guess. They may also have served as rudders for balancing the short body and long limbs when on top of the trees as they jump from branch to branch .
The(corrected) Chinese Revolution Part 2.
With the discovery of perfectly preserved specimens of Microraptor gui and its long metatarsal feathers, a reappraisal of the genus Cryptovolans was very much needed.
The evidence was there from the start (seeing now the fossil it's even clearer): Cryptovolans clearly did show those tarsal feathers from the very beginning and may be nothing more than just another version of Microraptor!
I personally think that Microraptor and Cryptovolans are one and the same(skeletal differences are minimal). Accordingly, I have corrected and added the spectacular fans of leg feathers to the two displaying animals on background (right), giving them also a different dimension: Feathers not just for flight, but (very importantly) for display too.
Far background: A couple of Beipiaosaurus feed from some trees while a plethora of birds and pterosaurs dominate the skies of the nearby lagoon.
Foreground (right side): a couple of Sinosauropteryx approach the scene.
Two male Confuciusornis sanctus in full display. The picture of bird evolution that is coming our of the Yixian today is extremely complex. Confuciusornis was beaked and toothless and had rather typical small bird body with an avian pygostile (males had two long feathers attached to it) but powerful arm-wings that show fully functional three clawed fingers with little sign of becoming a fully digit-fused modern avian wing. But recently, new specimens of birds -like the recently described Jeholornis that were contemporaries of Confuciusornis- show that other groups were instead still toothed and with long bony tails, but the forelimbs and hand bones started showing signs of fusion on a trend to become a more advanced, typical bird wing,. Much more than Confuciusornis' wing itself but keeping a more 'primitive' lower part of the body and head! The contemporary picture of bird evolution is still hotly debated. Investigating what group of birds is the one that gave rise to all the contemporary descendants we know today is becoming a complex puzzle... an amazing mosaic of evolution possibilities still to be clarified.