Thursday, January 28, 2010

Haplocheirus, the (or one of the?) Jurassic alvarezsaur(s)

Above: Illustration of Haplocheirus, from Stone 2010 (intro article published in Science)

Those coelurosaur ghost lineages just keep getting filled in lately. Today sees the publication of Haplocheirus sollers, the first Jurassic alverezsaur. Unlike its later brethren, this doesn't look very alvarezsaurian at first glance, more like you're typical generic coelurosaur. As Tom Holtz said o the DML, this is the first alvarezsaur that "looks normal"!

However, telltale signs (such as downward-flared basipterygoid processes on the skull) and a phylogenetic analysis shows that this is the earliest and most primitive member of the group. It comes from the Late Jurassic of China, and falls out as a basal maniraptoran, which jibes with the placement of alvarezsaurs in many recent studies, not avialan or ornithomimosaur as previously suspected by some. Interestingly, the teeth are heterodont, which seems to me to give weight to the reent hypothesis that all maniraptorans are ancestrally omnivorous. It's also the largest nkown alvarezsaurid known from good material, indicating that these guys may have started out fairly big and later shrunk to the diminutive sizes seen in the likes of Parvicursor.

But, is this really the earliest alvarezsaur on the radar? Some goss fans may have heard of a supposed alvarezsaur from the Tiaojishan Formation, preserved with feathers, mentioned at last year's SVP. That ain't this, though it would be from roughly the same time period (about 60 Ma ago). Depending on how similar the two species are, we might be looking at a ghost lineage that goes even further back than before, rther than being clipped to the mid-Jurassic. Time will tell.

Wednesday, January 27, 2010

The White Stripes

Back in August, I posted about a study by Vinther and colleagues looking at fossil bird feathers in an attempt to not only determine color patterns in life, but the actual colors constituting those patterns. That study looked only at Cenozoic birds, but tantalizingly, Vinther and co. promised follow-ups looking at Mesozoic birds and other feathered or proto-feathered dinosaurs.

Well, somebody has beat them to it (though, interestingly, Vinther has responded with skepticism to this newest study which has beat him to the punch though appears to use similar methods, as reported by Ed Young). Specifically, Zhang and colleagues have an online-first paper out in Nature today reporting the presence of melanosomes (pigmentation-bearing cell bits) for the first time in protofeathers. The team looked at Sinosauropteryx, Sinornithosaurus and Confuciusornis, and found pigment in all of them.

This is interesting for a few reasons, not the least of which that children's books can now officially limit their audiences imaginations by saying "no, little Billy, dinosaurs weren't whatever color you can dream of, this one here for example was black with shades of red and white patches thrown in." Firstly, this whole color-patterns-in-dinos thing was (as far as I know) first officially brought up by Nick Longrich at SVP 2002. Longrich pointed out that the thing everybody noticed about Sinosauropteryx (the stripey tail) was not an artifact of preservation, as the describers suggested, but reflected color, in the same way that prehistoric insects and fish fossils can show patterns. Based on Longrich's conclusions, I did the painting of Sinosauropteryx shown above, and this has proven largely correct (I lightened the color a bit to seem lighter browning orange, but the original was pretty close if I may say so!).

Unfortunately, being a Nature publication, this announcement comes with high prestige and itty bitty page count. The authors here promise more detailed follow-ups with more specific color patterns, and presumably Vinther et al. are also still working on their studies. Vinther's objection, which I mentioned above, is that as they had pointed out, really deciphering fossil animal colors requires a thorough understanding of how different pigment structures create color in modern birds, which is barely understood. So new discoveries with modern animals could overturn some or all of this. But, for now, all good paleoartists will reconstruct Sinosauropteryx as red-brown with a striped tail, and if Longrich was right about the rest, a bit of counter-shading.

Interestingly, the Sinosaur the new study uses is an undescribed specimen. In some news reports like this one, it is stated that Sinosauropteryx had only a feather fringe along the back, implying a partly scaly body. Now, other specimens have shown evidence of feathers on at least the lateral torso, but could this new one show evidence of a more Juravenator-type scalation on the legs and tail base (as I also restored above)? We'll see...