Juravenator starki

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Juravenator starki is a new small theropod dinosaur from the late Jurassic—the specimen is exceptionally well-preserved, and retains fossilized imprints of its skin. The surprising thing about it is that its anatomy puts it smack in the middle of a large clade of coelurosaurs, members of which are known to have feathers…and its skin is bare and scaly. What it suggests is that feather evolution was complicated (no surprise there, actually), and that some lineages secondarily lost their feathery covering, or that there were seasonal or age-related or regional variations in feather expression.

More pictures are below the fold—this really is a very pretty specimen.

Here's the skull in UV light and in reconstruction:

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a, Specimen photographed under ultraviolet light. b, As reconstructed (shaded areas show missing portions). Abbreviations: an, angular; aofe, antorbital fenestra; d, dentary; en, external naris; f, frontal; itfe, infratemporal fenestra; j, jugal; l, lacrimal; m, maxilla; mfe, maxillary fenestra; n, nasal; or, orbit; p, parietal; pm, premaxilla; po, postorbital; qj, quadratojugal; sq, squamosal; sa, surangular.

The whole specimen—it's wonderfully well preserved. The integument impressions are preserved along portions of the hind limb and tail.

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a, Specimen photographed under normal light. b, The presence of 'hair-like' cervical ribs (inset 1) is synapomorphic of Compsognathidae. The proximally high manual claws that taper abruptly at their midpoint (inset 2) and bow-like zygapophyses of mid-caudal vertebrae (inset 3) are regarded as autapomorphies of Juravenator starki. The serrated premaxillary teeth (inset 4) also distinguish this taxon from most other basal coelurosaurs. Abbreviations: ca, calcaneus; co, coracoid; cv, cervical vertebrae; dv, dorsal vertebrae; fe, femur; fi, fibula; ha, haemal arches; hu, humerus; il, ilium; mI, metacarpal I; mII, metacarpal II; ra, radius; sc, scapula; st, soft tissue; ti, tibia; ul, ulna; I-IV, pedal digits I-IV; V, metatarsal V.

Here's where Juravenator fits into the grand scheme of things. As you can see, it's bracketed by lineages where feathers are known, yet the preserved portions of this animal have no feathers at all.

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The eight most parsimonious trees (length 497, consistency index 0.45, retention index 0.65) for 28 theropod taxa, including Juravenator starki and 189 variables, are shown. In spite of lacking feathers in the preserved integumentary portions, Juravenator starki is grouped together with coelurosaur clades known for having feathery coverings. Plumulaceous and/or pennaceous feathers have been discovered in taxa assigned to Tyrannosauroidea (namely Dilong; in this cladogram, tyrannosauroids are represented by the more advanced Tyrannosaurus and Albertosaurus), Compsognathidae (namely Sinosauropteryx), Alvarezsauridae (namely Shuvuuia), Oviraptorosauria (namely Caudipteryx), Dromaeosauridae (namely Microraptor and Sinornithosaurus) and Aves (namely Archaeopteryx and Confuciusornis).

Göhlich UB, Chiappe LM (2006) A new carnivorous dinosaur from the Late Jurassic Solnhofen archipelago. Nature 440:329-332.

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a, b, Cranial reconstruction in left lateral (a; shaded area indicates the unpreserved portion) and dorsal (b) views. adc, anterodorsal concavity; al, anterior lamina; an, angular; aof, antorbital fenestra; d, dentary; dg, dentary groove; emf, external mandibular fenestra; en, external naris; if,…
tags: evolutionary biology, convergent evolution, paleontology, taxonomy, zoology, basal birds, theropods, dinosaurs, ornithology, birds, Alvarezsauroidea, Haplocheirus sollers, Maniraptora, Archaeopteryx, researchblogging.org,peer-reviewed research, peer-reviewed paper A Newly Discovered Basal…
I'm not going to say much about this since Ed Yong has an excellent write-up, but a new feathered dinosaur has been discovered, called Tianyulong. As you can see in this image of the fossil, it was bristling with a fuzz of thin fibers — proto-feathers. (Click for larger image)a, Main slab of the…
Quiz time! What's wrong with this paragraph? Sometimes life takes a creative leap that's almost miraculous. Nobody knows how this happens, and it can never be predicted. You'd never know, looking at a reptile's round, hard, shiny scales, that they could genetically morph into feathers.…

Note that its neck is arched as if it's trying to avoid drowning in a flood.

If you doubt this is possible, how is it there are PYGMIES + DWARFS??

(.)(.)

LOL!!! WOOT!

I do not really see what is so surprising about finding scales on the tail and hindlimbs. Most birds have scales on their feet and Scansoriopteryx heilmanni had scales on the tail as well as feathers on other regions of the body. I don't see why the absence of feathers on parts of the body for which featherlessness was probably common should indicate that the entire body had scales. Feathers also have a tendency to fall off when the animal dies or just preserve very poorly, the problem of falling off does not apply so much to scales, so it is not surprising either that impressions of scales may be preserved but no feathers are preserved.

The National Geograhic News article on this says that the skin was preserved around the tail and hind limbs. What are the possibilities that this animal had feathers on other parts of its body? Ornamental feathers, maybe.

This is from the Solnhofen, the fine-grained limestone that preserved feathers in archaeopteryx. If skin (keratinous scales) impressions were preserved presumably at least some feather detail would be preserved too.

This new fossil doesn't even Google yet. It's nice to see Barvaria still has some suprises. I used to do stone lithography (printmaking) on Stolnhofen stones and fantasized about grinding the surface down to reveal a new critter.

Bavaria, sorry Bavarians.

"This is from the Solnhofen, the fine-grained limestone that preserved feathers in archaeopteryx. If skin (keratinous scales) impressions were preserved presumably at least some feather detail would be preserved too."

This is a false assumption. None of the Archaeopteryx specimens shows body feathers, but only show the larger, and much harder to decay before preservation, remiges and rectrices (wing and tal feathers). Light downy type feathers do not preserve well in that environment, and the scales are found where one would might expect to find them in a small feathered dinosaur, as on the tail, and back legs. There are other regions that can also have scales on birds and might be preserved as well...

There is simply nothing about this that contradicts the cladograms...

By Lagomortis@com… (not verified) on 15 Mar 2006 #permalink

It's a Miracle! You have to look at the skull under UV light, right? So, God devised a creature to spread the word of his love to maknkind, knowing how long it would be before Man even invented the BlackLight!

-jcr

By John C. Randolph (not verified) on 15 Mar 2006 #permalink

Lagomortis wrote:

"This is a false assumption. None of the Archaeopteryx specimens shows body feathers, but only show the larger, and much harder to decay before preservation, remiges and rectrices (wing and tal feathers). Light downy type feathers do not preserve well in that environment, and the scales are found where one would might expect to find them in a small feathered dinosaur, as on the tail, and back legs. There are other regions that can also have scales on birds and might be preserved as well..."

Three specimens of Archaeopteryx to date show body feathers, not just remiges or retrices. The Berlin and London specimens, the first two known and described, are both known to clearly preserved feathers along the lower leg, but not as far as the ankle, and the Berlin also shows breast feathers and feathers around the arch of the neck. The "Maxberg" specimen, which is currently missing but for which casts are available worldwide, shows several large feathers preserved alongside the dislocated leg, while the remainder are attached to the separate arms, suggesting the leg supported large feathers of its own. Lastly, feathers around the hips and dorsal region of the body are present in the newest, Thermopolis specimen.

The Solnhofen Limestone (sometimes in the States the Solnhofen Formation) is fine enough to preserve the microscopic aktinofibrils of a pterosaur wing, and the barbs of an "avian" feather, though certainly the same preservation may not be present in each and every specimen, as the rules around preservation are relative to hundreds of factors that give us rare snapshots of occassional "survivors." Finer ash and sandstones, as in Liaoning, preserve finer details of the integument, but are less useful in preserving bone, sadly. Nonetheless, as Mike Hanson indicated, birds have scales and feathers on the same body parts, and a fossil dromaeosaurid, known colloquially as "Dave" (aka, NGMC 91, or alternatively Sinornithosaurus sp.) has been preserved with scales around the feet as well as bone filamentous and downy-type feathers on the legs, body, arms, tail and head.

The new find, also nicknamed "Borsti", is nothing special in this regard, but shows tubuculate structures on the tail. Confer the living scale-tailed squirrels, Anomaluridae, or even opposums, beavers and rats. Squamation and pennation are hardly mutually exclusive, as much as squamation and fur-bearing are not in living mammals.

By Jaime Headden (not verified) on 15 Mar 2006 #permalink

Maybe it had mange, like that coyote/chupacabra that showed up last year.

Jaime...

First, the second paragraph really has nothing to do with what I said. I did not say it was impossible, just that light-downy type feathers do not well in that environment, and that has shown to be the case. Also, the "Dave" bit means nothing because Comps from those type sediments show feathers rather well.

The first paragraph seems to be implying that downy type feathers are being found on Archaeopteryx, when you know, and I do, the back leg feathers mentioned are more along the lines of reduced hindlimb remiges as seen M. gui, so are not applicable to what I meant as body feathers, and especially does not refer to the downy-type feathers seen on other comps relative to this new find.

It seems near impossible to determine the origin of the feathers near the hips in Thermopolis, which could be retrices from the base of the tail spread out randomly as the animal assumes its road-kill position. The length of the feathers in question indicates to me they are most likely not body coverying, and they certainly do not fit a down-type feather description. Do you have better pictures than I (mine are only the ones from the paperr) that shows the point of origin of these feathers clearly?

The only thing you said that may give evidence to feathers of the type mentioned on an Archaeopteryx specimen is the Berlin. I heard mention when it was first found there were feathers in the neck region, but work to remove the matrix was said to have removed much of these elements. The elements left that you refer to are hardly obvious feathers. Do you have some pictures that show these elements clearly to be feathers? They marks always looked rather ambiguous to me on my cast.

How is it we haven't heard a bunch of caterwauling from the anti-evolutionists on this yet? If you know of any, gimme a link so i can go harass them. :)

How is it we haven't heard a bunch of caterwauling from the anti-evolutionists on this yet? If you know of any, gimme a link so i can go harass them. :)

In my experience it usually takes them about two working days to get on the same page with a response to this kind of thing. Finely honed bullshit doesn't grow on trees, you know.

Expect something Monday.

By george cauldron (not verified) on 16 Mar 2006 #permalink