As promised here is the guest post on the new feathered dinosaur by my colleague Corwin Sullivan
In recent years there’s been no shortage of feathered theropod fossils, avian and non-avian, from the People’s Republic of China. Almost all of them come from the Lower Cretaceous Yixian Formation of western Liaoning Province, historically a part of Manchuria. The exquisitely preserved Yixian fossils, which include everything from plants to insects to mammals in addition to the famous feathered wonders, give us an astonishingly clear window into an Early Cretaceous ecosystem.
However, it must be said that dinosaurs of a feather do not always flock entirely together. The profusion of specimens from the Yixian Formation has tended to overshadow the small number of highly intriguing feathered theropods that have been collected at another locality, Daohugou in eastern Inner Mongolia. The Daohugou beds are practically across the provincial border from the Yixian of western Liaoning, and are similar to the Yixian in many respects: both are lacustrine deposits that have yielded a mixture of plants, invertebrates, non-dinosaurian vertebrates such as salamanders and pterosaurs, and feathered dinosaurs. However, the Daohugou beds are substantially older, being Middle to Upper Jurassic rather than Lower Cretaceous.
For years the only two feather-sporting Daohugou taxa were Pedopenna, known only from a single partial leg, and an intriguing but also incompletely known creature called Epidendrosaurus. (Scansoriopteryx, a putative third, is quite probably a synonym of Epidendrosaurus.) Epidendrosaurus was a kind of dinosaurian aye-aye, a small, possibly arboreal maniraptoran with an elongated third manual digit. It is apparently close to the origin of birds, emerging just basal to Archaeopteryx in phylogenetic analyses. This is particularly satisfying because the Daohugou fossils also slightly precede Archaeopteryx in age, being at least a few million years older than the Solnhofen beds.
Now Epidendrosaurus has a close cousin from the same locality, as Professor Zhang Fucheng of the IVPP and a few coauthors – including, clinging barnacle-like to the end of the authorship list, yours truly – report in a Nature paper that came out earlier today. (The citation is given below, and the paper is here, but full access requires a personal or institutional subscription.) The new animal, Epidexipteryx hui, is apparently not a second aye-aye but rather something more like an undersized vampire peacock. I should hasten to nip misinterpretations in the bud by insisting that I am not promoting any wild hypothesis of blood-drinking, or even necessarily carnivory. But it does have big, protruding teeth at the front of the mouth.
Epidexipteryx also has what we call in the paper elongate tail feathers (ETFs), making the tail into a showy frond that is in remarkably good shape after more than 150 million years. What is particularly exciting about this, for those of us interested in the evolution of feathers, is that the rest of the body of Epidexipteryx seems to have been covered only by short, rather fuzzy protofeathers of a kind that are now familiar from several maniraptorans more or less remote from the origin of birds. Protofeathers of this kind might well have provided insulation, and perhaps a bit of either camouflage or visual flair depending on their colouration. But they weren’t going to get Epidexipteryx into the air, so the taxon was evidently neither a flier nor a glider.
The ETFs on the tail, however, are downright ostentatious. They come in two pairs, and are of prodigious length in proportion to the animal’s skeleton. In life they would have been prominent, conspicuous, and probably a bit physically awkward to drag around, suggesting that they functioned purely as a visual signal. The mind leaps instantly to sexual selection, and torrid scenes of colourful tails swaying back and forth before the beady eyes of mesmerised females, but of course there are other possibilities. For example, the ETFs could have been a battle flag brandished at territorial rivals, rather than a gaudy ornament wielded to impress potential lovers. The sexual explanation is far from improbable, but at present we cannot even determine whether the holotype and only specimen of Epidexipteryx was male or female. Taking cues from extant birds, it is somewhat more likely that any sexual signals were sent primarily by males.
Epidexipteryx and Epidendrosaurus seem to be sister taxa, forming a clade called Scansoriopterygidae that lies immediately basal to Archaeopteryx. This might just indicate that display feathers preceded the evolution of flight feathers in avian evolution, a conclusion that would have implications well beyond the scope of this blog post. However, there’s no question that the pattern of early feather evolution was exceedingly complex. The dromaeosaur Microraptor, after all, was almost certainly capable of getting airborne even if palaeontologists disagree about its exact flight (or gliding) posture and capabilities. Did Microraptor evolve its aerial abilities independently of Archaeopteryx and other birds? Or was access to the air part of the common inheritance of avialans and dromaeosaurs, a possibility that would imply secondary losses in some members of each group? Is it even possible that avialans might turn out to roost phylogenetically within dromaeosaurs, so that volancy could be primitive for the former and a subset of the latter? At the moment the first alternative strikes me as most intuitively plausible, but the evidence is not yet conclusive. Nevertheless, we now have Epidexipteryx, the vampire peacock of Daohugou – and a basal avialan in the hand, as they say (well, they don’t really, but they should), is worth two in the outcrop.
Zhang, F., Zhou, Z., Xu, X., Wang, X. and Sullivan, C. 2008. A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers. Nature 455: 1105-1108.
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