May 5, 2015

Yi qi Is Neat but Might Not Have Been the Black Screaming Dino-Dragon of Death

A couple of weeks ago I hatched a plan to write about all the neat new dinosaur-themed studies that had just appeared in print; I began by penning my thoughts on the Brontosaurus issue.

By Darren Naish

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American

A couple of weeks ago I hatched a plan to write about all the neat new dinosaur-themed studies that had just appeared in print; I began by penning my thoughts on the Brontosaurus issue. But that then turned into a whole article all its own. So I set to work on an article devoted to the neat theropod-themed discoveries that had just been announced. And then Yi qi was published. These plans for 2015 aren’t going well at all.

Yi qi (quite rightly) received enormous global coverage in the news media and blogosphere. It’s a pigeon-sized scansoriopterygid known only from a single, seemingly adult, specimen from the Callovian or Oxfordian (Middle-Upper Jurassic boundary) Tiaojishan Formation of Hebei Province, China. And what’s the big deal about it? I think that should be obvious. Read on.

What, exactly, is a scansoriopterygid? Scansoriopterygids are small maniraptoran theropods, notable for their elongate third fingers and for a peculiar pelvis where the pubis is directed forwards and downwards, is proportionally short and lacks an expanded ventral end. The scansoriopterygid skull is short-faced and robust, the anterior end of the lower jaw is slightly downturned, and the teeth are procumbent. This skull (which superficially recalls that of some insectivorous bats) is quite similar to that of early oviraptorosaurs (like Caudipteryx) and some birds (like Sapeornis), suggesting that this shape was ancestral for Pennaraptora (the oviraptorosaur + paravian clade within Maniraptora). Scansoriopterygids have been covered on Tet Zoo before, by the way: see links below.

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Like all maniraptorans, scansoriopterygids are fully feathered, but it seems that they don’t possess vaned, pennaceous feathers like those present in oviraptorosaurs, birds, dromaeosaurids and so on. Instead, they have filamentous, branching, brush-like structures of various sorts. Long, strap-like tail structures (feathers?) are present in at least some members of the group. And Yi qi is another Mesozoic fossil dinosaur that seemingly preserves melanosomes in its integumentary structures. Xu et al. (2005) note the presence of several distinct shapes and sizes among them: there are apparently eumelanosomes (the semi-spherical kind often associated with greys and blacks) in the integumentary fibres, and phaeomelanosomes (associated with reddish and yellowish hues) in the skin associated with the forelimb. As everybody knows, there is now doubt attached to the idea that the melanosomes identified in fossil dinosaurs really do give us a reliable guide to colour in life. Maybe Yi qi was black with reddish arm skin… maybe it wasn’t.

Because of their weirdness, there’s been some minor effort to get scansoriopterygids placed outside of Theropoda in the archosaur tree (Czerkas & Yuan 2002, Czerkas & Feduccia 2014). However, this view comes from people aiming to bolster the ‘birds are not dinosaurs’ movement and relies predominantly on the ignoring of most of the data we have. Several more conventional analyses have included these animals (e.g., Zhang et al. 2002, Senter 2007, Godefroit et al. 2014, O’Connor & Sullivan 2014). The possibility that they might be early members of the oviraptorosaur lineage has been put forward (Paul 2010, O’Connor & Sullivan 2014) and is supported by details of tail and hand form. It’s a pretty appealing idea, but the hypothesis supported by Xu et al. (2015) is that these dinosaurs are part of Paraves, the pennaraptoran clade that includes birds, dromaeosaurids and troodontids. Things may change in future.

Anyway, the thing that makes Yi qi so remarkable is its presence of a novel, rod-like forelimb component, termed the styliform element (Xu et al. 2015). This structure (there is one on each forelimb, extending from the wrist) seems to be associated with patagia (skin membranes): Xu et al. (2015) suggest that these membranes spanned the spaces between its manual digits as well as those between its forelimb and body. The rod-like element – which is seemingly slightly curved anteriorly at its distal end – is unique within Dinosauria, but strongly recalls the cartilaginous ‘spreaders’ that emerge from the wrists or elbows of various modern gliding rodents (we recently looked at these in the article on anomalures, or scaly-tail gliders). The fossil does not consist of the front half of the animal only (as implied by photos of the fossil); bones from the hindlimb are preserved too. The foot is proportionally short and fuzz is preserved adjacent to the metatarsus and other parts of the hindlimb (Xu et al. 2015, supplementary information) – this is another fuzzy-footed Jurassic theropod. One specimen of Epidendrosaurus (another scansoriopterygid) has scaly skin preserved on part of its metatarsus (Czerkas & Feduccia 2014), though exactly how this was placed on the foot is uncertain.

Judging by the several reconstructions present online, Yi qi has mostly been imagined as a sort of ‘bat-winged’ theropod; a dragon-like beast that glided or even flapped its way through the air. This dragon-like nature has resulted in this sort of thing…

And given both that the story of theropod flight evolution is predominantly one involving feathers, and that there’s no prior evidence for membranous forelimbs in a theropod (though read on), this all seems insanely radical.

Yi qi (which is apparently pronounced yee chee) is the shortest binomial name yet published for any dinosaur. In fact, it’s one of the shortest binomial names yet published for anything, vying with the bat Ia io for the prize of shortest of all. Could the one known specimen be a fake or composite of some kind? No – the authors checked and checked again, and went to some trouble to be confident in their identifications. Claims that the specimen might be an Archaeoraptor-style chimaera, or that the authors screwed up on the identification of the bones concerned, are highly disrespectful to the abilities of the scientists involved, unlikely to be correct given the data on hand, and disregard the extensive amount of work that Xu Xing and colleagues so obviously did (Xu et al. 2015). Yi qi really does have great big long spines projecting from its wrists.

By the way, the skeletal reconstructions we’re seeing in the articles on Yi qi (Padian 2015, Xu et al. 2015) are remarkably similar to those produced in recent years by Jaime Headden. Are they really original or are we seeing uncredited use of someone else’s art here?

Membranous-winged scansoriopterygids were predicted in 2008. Moving on, there are several neat things that I think should be discussed here (scarcely none of which have been mentioned in existing online discussions of this find). The first one is that the concept of a scansoriopterygid with gliding membranes is (while radical and shocking) not novel if you’ve been paying attention.

Exactly such a creature was predicted by my colleague Andrea Cau (and illustrated by excellent palaeoartist Lukas Pankarin) way back in October 2008 after the publication of Epidexipteryx* (Zhang et al. 2008). Like Yi qi and other scansoriopterygids, Epidexipteryx lacks vaned feathers yet has a hyper-long digit that looks suitable – Andrea proposed – for the support of a patagial membrane. Yi qi is, therefore, yet another of those fossil animals predicted to exist prior to its discovery. SpecBio fans might like to know that C. M. Kosemen took this suggestion and ran with it, but that’s a story for another time.

* I was a reviewer for this paper and got the authors to change their planned use of Epidendrosauridae to Scansoriopterygidae. They thought that Scansoriopterygidae was unavailable due to the fact that its type genus – Scansoriopteryx – is considered a junior synonym of Epidendrosaurus. But that’s not how it works.

Patagia might not mean ‘bat wings’. So, Yi qi is a small theropod with patagia. Radical, right? Well, not so fast. What’s been mostly overlooked in discussions of Yi qi is that pennaraptoran maniraptorans already have patagia. Look at the (perhaps familiar) pictures of nightjar wings below and observe all the ‘webbing’ that surrounds the fingers and arm. A membrane called the propatagium spans the space between the wrist and shoulder, and membranes run along the trailing (or posterior, or postaxial) edges of the hand and ulna too.

We’ve already seen that scansoriopterygids are seemingly nested within Pennaraptora, and there are already signs that these skin webs are widespread in this group (a propatagium has previously been identified in Epidendrosaurus, and in other non-bird pennaraptorans). Could it be, therefore, that Yi qi simply had enlarged versions of the membranes seen in other pennaraptorans, and that its membranes were feathered as they are in other pennaraptorans? If this were so, Yi qi wouldn’t be the ‘bat-winged’ beast depicted widely in reconstructions. It wouldn’t be so radical. The big stumbling block with this idea are the naked, sheet-like skin patches preserved around both the styliform elements and the long third digits of Yi qi: these really look like unfeathered bits of naked membrane, and maybe they are (Xu et al. 2015). Xu et al. (2015) also note that these patches have an unusual wrinkled texture, not typical of skin that would have been covered in filaments or feathers. But maybe they’re naked and wrinkled for taphonomic reasons. Decomposing animals often slough hair, feathers or other integumentary structures as they rot, thereby ending up with naked patches.

For now, this ‘non-bat-winged’ model is certainly speculative, but it’s less radical than the bat-winged model. This will be resolved when a better specimen turns up. Xu et al. (2015) do discuss the presence of patagial membranes in birds, by the way, but it’s in the supplementary information, not the main paper.

Styliform elements as battle spines. Are those styliform elements really associated with membranes? I mean – could they be associated with some other function? As just mentioned, Xu et al. (2015) support the possible role of these elements in membrane support by pointing to patches of sheet-like tissue preserved in close association. But – pending the description of additional specimens – those sheet-like tissue fragments aren’t extensive enough to convincingly reveal the presence of true, extensive patagia: as discussed above, they might show that small patagia like those already known for birds and other pennaraptorans were present.

Furthermore, such tissue fragments might have been displaced from elsewhere nearby (remember: squashed fossilised animals are not freshly dead corpses: they’re flattened, messy things where at least some of the soft tissue has been moved around relative to its original position). Having said all that, Xu et al.’s (2015) ideas about patagium presence and extent is certainly reasonable and they may well be right. I don’t mean to imply that they’re not.

But… I’m reminded of the assorted carpal and manual spurs and spines present in various birds and other animals. Could Yi qi‘s styliform elements actually be battle spines or something? Xu et al. (2015, supplementary information) state that “we are aware of no case in which a long, unjointed bony or cartilaginous rod extending from a limb joint has evolved in any vertebrate without being associated with an aerodynamic membrane, and plausible alternative functions for such a structure are difficult to conceive”.

But but but there are long, unjointed bony or cartilaginous rods that extend from limb joints and aren’t associated with aerodynamic membranes in certain animals. There are large, conical or dagger-like carpal spines in various birds (like screamers, jacanas and lapwings) – in cases they do extend from wrist bones, not just from the carpometacarpus – and there are also several frog groups that possess large, dagger-like carpal spines.

Notably though, even the biggest of these structures are much, much shorter than the styliform processes of Yi qi. If Yi qi is imagined with ‘battle spines’ of this sort, it must have possessed the most unwieldy and ridiculously over-sized structures of this sort to ever evolve. Nevertheless, I was intrigued enough by this possibility to have a go at drawing it. Having done so, I conclude that they’re probably more ridiculous than membrane-supporting spines. Furthermore, use of the spines in membrane support is bolstered by the presence of an also ridiculously long digit III, and perhaps by the fact that brachial soft tissue in Yi qi extends at least as far as the spine’s distal end (Xu et al. 2015). Nevertheless, super-giant, dumb-looking battle spines are, one might argue, not definitely more ridiculous than giant rods used in the support of gliding membranes.

What to conclude then? Xu et al. (2015) came up with thoroughly reasonable ideas on this remarkable fossil, and their (Cau-predicted!) idea that we’ve discovered ‘bat-winged maniraptorans’ looks sensible based on the one fossil we have, however radical. But there’s room for doubt, and the presence of more ‘conventional’ patagia is also a real possibility, as is – more remotely – the ridiculous idea that those styliform elements were giant ‘battle spines’.

However, the idea that seems promoted in most artwork produced so far is that this animal was some sort of screaming bat-winged mini-dragon. It’s difficult to pinpoint where the mistakes have been made, but my suspicion is that Yi qi would have looked more like other maniraptorans, and less dragony overall [adjacent image by Emily Willoughby].

Once again, Mesozoic dinosaurs surprise and intrigue us with their diversity. However it’s interpreted, Yi qi shows that lots of weirdness and evolutionary innovation was occurring in the lineage that also includes birds. It shouldn’t be lost on you that Yi qi and other scansoriopterygids look to have been experimenting with flight and climbing, despite being well outside the bird clade itself. What does this mean for the distribution of gliding, flying and climbing behaviour within Pennaraptora, and within Maniraptora as a whole? We’ll come back to those subjects very soon – there’s much that needs to be said.

For previous Tet Zoo articles on scansoriopterygids, Mesozoic maniraptorans and other issues related to those discussed here, see…

UPDATE: I’ve just discovered that John Conway has also done a novel reconstruction of Yi qi that – like Emily’s image above – does a good job of making it look more like an actual animal, less like an angry screaming nightmare dragon. See it here.

Refs – -

Czerkas, S. A. & Feduccia, A. 2014. Jurassic archosaur is a non-dinosaurian bird. Journal of Ornithology 155, 841-851.

- . & Yuan, C. 2002. An arboreal maniraptoran from northeast China. In Czerkas, S. J. (ed) Feathered Dinosaurs and the Origin of Flight. The Dinosaur Museum (Blanding, Utah), pp. 63-95.

Godefroit, P., Cau, A., Hu, D.-Y., Escuilli?, F., Wu, W. & Dyke, G. 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature 498, 359-362.

O’Connor, J. K. & Sullivan, C. 2014. Reinterpretation of the Early Cretaceous maniraptoran (Dinosauria: Theropoda) Zhongornis haoae as a scansoriopterygid-like non-avian, and morphological resemblances between scansoriopterygids and basal oviraptorosaurs. Vertebrata PalAsiatica 52, 3-30.

Padian, K. 2015. Dinosaur up in the air. Nature doi: 10.1038/nature14392

Paul, G. S. 2010. Dinosaurs: A Field Guide. A & C Black, London.

Senter, P. 2007. A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda). Journal of Systematic Palaeontology 5, 429-463.

Xu, X., Zheng, X., Sullivan, C., Wang, X., Xing, L., Wang, Y., Zhang, X., O’Connor, J. K., Zhang, F. & Pan, Y. 2015. A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings. Nature doi:10.1038/nature14423

Zhang, F., Zhou, Z., Xu, X. & Wang, X. 2002. A juvenile coelurosaurian theropod from China indicates arboreal habits. Naturwissenschaften 89, 394-398.

- ., Zhou, Z., Xu, X., Wang, X. & Sullivan, C. 2008. A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers. Nature 455, 1105-1108.