Baby dinosaurs, that is.

Based on a fossil from India scientists from Michigan have described a 67 million year old snake found curled up in a sauropod nest. The 3.5 meter long serpent, which has been named Sanajeh inidcus, swirls around the eggs in the nest and points its fossilized skull towards the remains of a 50 cm long sauropod hatchling. The question is; was the snake really hunting for sauropod youngsters when it was surprised and buried by a mudslide (or an ashfall or something to that effect)? Or did the corpse of a snake that had died elsewhere wash into the nest by accident during a local flood? The scientists who describe Sanajeh think it died on the spot while hunting. They base this on the way its body curls into a lifelike position with its head on top of its body and on the very fine preservation of the eggs and skeletons.

This is an excellent example of the importance of taphonomy - the study of what has happened to a fossil specimen between the time of death and the time of fossilization. Taphonomy is absolutely necessary for palaeontologists to consider, when they want to derive clues about how the animal looked, lived, and died. Was the animal buried in its natural environment or was it moved after death? Was the animal buried quickly or did it dry in the sun for a week first? Did it rot and twist into a position its body could never have taken when it was alive? Were the bones scattered and crushed by scavengers or by geological processes? And so on..

I’ll recommend Ed Young’s breakdown of the finding of Sanajeh at his blog Not Exactly Rocket Science. He also describes the interesting history of how it took 17 years from excavation until the importance of the fossil was understood.

So... what do you think? Please leave me a comment.

A review of what is rapidly becoming one of my favorite dinosaurs.

_{Anchiornis color reconstruction painted by Michael DiGiorgio, Yale}

This late Jurassic theropod from China is named Anchiornis huxleyi, meaning “Huxley’s near-bird”, in commemoration of late biologist and comparative anatomist Thomas Henry Huxley (1825-1895). He was a close friend of Charles Darwin and the first scientist to notice and describe the pervasive skeletal similarity between Archaeopteryx and the small theropod Compsognathus - both of which were found in 150 million year old limestone deposits of Solnhofen, Germany. 

It was back in December 2008 that I first read about Anchiornis on palaeontologist Dave Hone’s blog (link). Back then it seemed from the morphology of the preserved bones that this was the closest relative of Archaeopteryx yet found - just slightly more ‘dinosaurian’ and around 10 million years older than Archie (hence the name “near-bird” or “almost bird”). At this point only one fossil had been prepared and described: A fairly complete specimen, but it was missing the head and had no traces of feathers. David Hone wrote that several new, far more complete specimens had been uncovered as they were preparing this first description. More on these critters would follow in 2009 and 2010, he promised.

September 2009 the shocking news broke: Not only did the new fossils preserve the plumage of the animals in wonderful detail; since complete skeletons were now available, the family relations of Anchiornis could be determined with much higher certainty. And surprisingly it turned out instead to be the oldest and basalmost troodontid ever found. Derived troodonts from the late cretaceous were 1-2 meters high, long legged theropods with binocular vision, large brains (for a dinosaur), and a body shape somewhat intermediary between dromaeosaurs and ornithomimosaurs. Chinese Jinfengopteryx from the early Cretaceous had already demonstrated that basal troodonts were small and just as feathered as Microraptor and Archaeopteryx. And from “Lori”, the as-of-yet undescribed troodontid from the Morrison Formation, we also knew that the troodontid lineage extended back into the Jurassic. Still, this was quite a find, showing just how ‘Archaeopteryx-like’ basal deinonychosaurs were. And Anchiornis had even more in store for us..

_{Picture composite by Andrea Cau}

The feathers preserved in the new fossils included a fluffy mane of plumaceous feathers around the head (the coloured painting by Michael DiGiorgioin the top of this post actually leaves too much of the snout bare!) as well as a thin layer along the neck and body, and another fluffy ball at the base of the tail. The distal tail, the arms and the hindlegs preserved long pennaceous flight-feathers, much like those seen in the basal dromaeosaur Microraptor. This is important. The hindleg-feathers that earned Microraptor its reputation as “the four winged dinosaur” are also seen in the ambiguous paravian hindleg-fossil known as Pedopenna and now in Anchiornis as well. In the oldest photo of the Berlin Archaeopteryx specimen the impressions of long feathers are also discernable on the hindlegs. Sadly they were lost as the 19th century preparators dug into the fossil to expose the leg bones. But as basal members of all three paravian lineages (troodonts, dromaeosaurs and avialians) have thus been found with long hind leg feathers, it is clear that they must have served some sort of purpose. The best guesses so far are display, stabilization and steering during gliding and perhaps controlled deceleration during landing. These interpretations are not mutually exclusive and may all be right.

If you find the concept of ‘wings’ on the hind legs strange and unrealistic, you should see these pigeons that have been bred to grow pennaceous rather than plumaceous feathers on their legs: link, link.

The picture below shows the reconstructed Anchiornis with full plumage. (The feather colors were still hypothetical at this point).

_{Anchiornis plumage reconstruction from Xu et al. 2009}

So what’s new with Anchiornis in 2010? Feather colors!

The 2008 discovery that fossil plumage preserved as dark carbon films are due to the preservation of melanosomes has opened up for the brand new science of dinosaur color reconstruction(*). Lately a joined team of scientists from China, England and Denmark carefully extracted 29 small flakes from various parts of the plumage on this Anchiornis specimen and examined the preserved melanosomes under a Scanning Electron Microscope. From this analysis they were able to present in early February 2010 the first ever full body(**) color reconstruction of a Mesozoic dinosaur: Most of the body of Anchiornis was apparently grey with dark and red spots. The ‘mane’ or ‘mohawk’ was reddish-brown while the rest of the head was grey with red patches on the cheeks. The pennaceous feathers on the arms and legs alternated sharply between black and white and so did the burst of feathers at the base of the tail.

CG reconstruction of Anchiornis by National Geographic. You can also see a rotating animation here. I assume that this CG model is based on the painting at the top of this post, because once again they’ve made the snout too naked.

That’s all for now. I hope you’ve enjoyed this review of the spectacular Anchiornis huxleyi.

 _{( * ) Melanosomes are in fact only one of the color pigments in feathers. I hope to cover this in my next blog post.}

_{( ** ) Except that the specimen they examined had no tail, so we still don’t know the colors of its tail feathers. Interestingly the tails of both Sinosauropteryx and Jinfengopteryx show alternating dark and bright bands. So phylogenetic bracketing would suggests that the tail of Anchiornis was striped as well.}

Links to selected pages about Anchionis and its feathers:

David Hones’ first description in 2008

The surprice in 2009

Followups in The Guardian and Wired

And now, in 2010:

GrrlScientist’s detailed take on the colors of Anchiornis

Ed Young’s summary at ‘Not Exactly Rocket Science’

And Carl Zimmer perspective in The New York Times

So... what do you think? Please leave me a comment.