Linhenykus, the Mighty Monodactyl

A year ago today at Archosaur Musings, Dave Hone wrote about the alvarezsaurs in anticipation of the description of Haplocheirus being published. He wrote, "It’s going to be a big year for alvarezsaurs in China if all the papers come through in time." They didn't quite manage to all come through in time. A couple months after Haplocheirus, Xixianykus was described. Then, all went quiet on the alvarezsaur front as the ceratopsians dominated the rest of 2010.

Now, with the announced description of Linhenykus, fanciers of the still-obscure group of theropods can break out the cigars and celebrate. As described in PNAS by a team of scientists led by Xu Xing, Late Cretaceous Linhenykus is unique among the alvarezsaurs for possessing a single finger - no reduced nubbins, no hints at additional fingers simply missing from the remains. The reduction in forelimbs and loss of digits, along with keeled sternums perfect for anchoring robust muscles, have led to the popularity of a hypothesized "termite digger" lifestyle among them.


Linhenykus monodactylus by Julius Csotonyi, from the University College of London press release.

Evolution is a tricky thing, and Linhenykus is a good reminder of the falsehood of easy, linear models. If you take a look at Linhenykus and see its single finger, you might come to the conclusion that it represents the peak of alvarezsaur evolution, the storyline of which is the reduction and loss of digits. But that's not the case. When compared to all other members of the family, Linhenykus lands in the middle, an offshoot whose loss of fingers occured separately from later forms.

One thing that's interesting about the alvarezsaurs is that they're one family that almost always is depicted as feathered. Having only been around for the last two decades, they were at times thought to be true birds. Even so, they fit well within the maniraptoran family of theropods; a cladogram put forth by Lindsay Zanno in 2009 has them nestled between forms that are known to be feathered, the therizinosaurs and the oviraptorosaurs.

Will alvarezsaurs ever achieve the mass-popularity of their maniraptoran kin? I personally love them, but I'm not sure that the words "diminutive, possibly insectivorous theropod" really get most folks juiced up. But the questions they pose are juicy ones indeed, and anyone who enjoys setting their mind to such puzzles will probably be occupied with these little guys for a long time.

Endemism in the Time of Chasmosaurs

After tossing about ideas for the title of this blog for a while, I settled on a twist on the title of Gabriel Garcia Marquez's Love in the Time of Cholera. I then had to decide between dinosaurs with a nice hard "C" at the beginning of their generic name. There were some good ones. I ultimately chose "chasmosaurs" because I've always liked the name, and I liked that it wasn't a single dinosaur, but rather a whole tribe of ceratopsids, always one of my favorite groups. In contrast to their centrosaurine relatives, the chasmosaurine ceratopsids are distingushed by larger brow horns and frills.

Today, a team of scientists led by Dr. Scott Sampson has published a paper in PLoS One, revealing two new members of the chasmosaurine line: Kosmoceratops richardsoni and Utahceratops gettyi. They were denizens of the southern part of Laramidia, a small continent formed by the sea that clove North America in twain during the Late Cretaceous. Kosmoceratops sported especially odd headgear: long, sideways-pointing brow horns and swept-forward spikes lining the top of its frill.


Utahceratops and Kosmoceratops with a map of Laramidia. Copyright Lukas Panzarin, provided by the University of Utah.

As you would expect from research led by Dr. Sampson, the paper concerns itself with larger issues of dinosaur ecology. The authors present a convincing scenario of two coexisting lines of chasmosaurs, one in the north and one in the south, separated by an as-yet unknown barrier.

Laramidia was a strange place. There was a narrow strip of land crammed between the sea mentioned earlier and a great mountain range containing the future Sierra Nevadas (the Rockies were only just beginning to form). Most of the North American late cretaceous dinosaurs we know are from this ribbon of low-lying land on Laramidia, a veritable dinosaurian paradise. This is the big, exciting question the paper asks. Why was there such a stunning diversity of dinosaurs in such a small area? I'm looking forward to more discoveries, and more reconstructions by Lukas Panzarin. Dude's got skills.

More:
The Open Source Paleontologist (the blog of paper co-author Andrew Farke)
DinoChick Blogs
Dinosaur Tracking
Discovery News
University of Utah press release

Come On Shake Your Body Baby, Do the Concavenator

That's a Miami Sound Machine reference. I usually footnote the odd references in my post titles, but I feel like this post will be much more fun if you have that song in your head. If you're having trouble summoning the tune - or if you sadly aren't familiar with the aural wizardry of the Sound Machine - here's the video. If anyone would be able to deal with the burden of three extra syllables being added to a song, Gloria Estefan would be the woman. Play it and read.



I am a little late to the Concavenator party, but I'm usually late to social functions in off-line life, so it's not stressing me too much. In case you haven't heard yet, Concavenator is a very cool, weird early Cretaceous theropod from Spain. Described in Nature by Francisco Ortega, Fernando Escaso, and José L. Sanz, it's the second strange theropod described in the last few weeks, and like Balaur, it's going to be the subject of debate for a while. Judging by its presence on the blogosphere and the conversation surrounding it on the Dinosaur Mailing List, it's making a much bigger splash than the island-dwelling dromaeosaur did.

The reason for this is probably its hump. Its hump and its possibly feathered forelimbs. Mostly though, the hump. People seem to love the hump.

Concavenator corcovatus by Raúl Martin. From the Nature paper.

Concavenator possessed elongated neural spines - those are the vertical protrusions on top of its vertebrae - right above the hips. This isn't the sort of sail that Spinosaurus would have had on its back; rather, it's more like a "fin," tying nicely into the fact that Concavenator was a carcharodontosaurid (that's seven syllables, if you weren't counting), the "shark tooth" relatives of Allosaurus who grew to enormous sizes in the Cretaceous before being replaced by giant tyrannosaurs and mid-size abelisaurs. It would have made for an odd-looking theropod, but at this point, ornamentation like this isn't shocking.

The really big news here is that Concavenator may have had quills or feathers on its arms. There is a line of bumps on its ulna - one of its longer arm bones - which look like the anchors for long flight feathers in modern birds, so the authors of the paper describing Concavenator propose that it had some sort of feathers or quills on its arms. This adds evidence to the idea that feathery, quilly, downy, filamentous body covering may have been a more basic trait of the dinosaurs than imagined. The image of dinosaurs as scaly beasts has been dead for a long time, of course, with multiple discoveries of skin and feather impressions. Ornithischians with quill-like features have been found, and the theropod clade known as the coleurosaurs include many feathered examples, and eventually spawned the modern birds. But carcharodontosaurids like Concavenator are carnosaurs (that's five hard C's, if you weren't counting), the sister clade to the coleurosaurs. It suggests that even earlier theropods could grow this kind of integument. So, too, may have the earliest dinosaurs. It's an open question, but daring paleoartists have some plausible grounding for clothing all sorts of dinosaurs in quills and feathery garments.

Dissenting voices have arisen in the days since the paper was published, proposing that the bumps may better be explained as being the line where muscle attached to the bone. It will just take more analysis, and hopefully some new, similar, dinosaurs to be found. I absolutely relish good back-and-forths like this in paleontology; while the argument itself may not be settled soon, I always come out of it with some new knowledge about evolution or anatomy.

Just don't get too used to saying Concavenator. It looks like this beast has already been named, from an earlier discovery of those hump-forming vertebrae. That name is Becklespinax.

More on Concavenator, er... Becklespinax:

Not Exactly Rocket Science
Dinosaur Tracking
Science Today
Theropoda (english speakers will want to use Google translate)
More on the quill knobs: Dots in Deep Time, Tetrapod Zoology.
More on Becklespinax: Tetrapod Zoology also covers this in detail; the Theropod Database Blog's first and second posts.
Artistic reconstructions: Brett Booth, Tricia Arnold, Camila Alli Chair, Nobu Tamura

Bună ziua, Balaur bondoc

Balaur bondoc, by Mick Ellison. From the PNAS paper.

I love the smell of lifted embargos in the morning. Yesterday, the web exploded to life with news of a new dromaeosaur from the Haţeg Basin in Romania, newly described in the Proceedings of the National Academy of Sciences. Remember the fuss Dr. Grant made over the Velociraptor's single sickle-claw at the beginning of Jurassic Park? Well, Balaur bondoc (the "stocky dragon") had two of them. Suck on those, Telmatosaurus and Magyarosaurus.

This is a significant discovery, helping paleontologists flesh out the menagerie of strange island dinosaurs from the European archipelago during the late Cretaceous. Balaur is the first good fossil of a predatory dinosaur from the time, and provides additional insight into the unique ways animals evolve on islands, where they are isolated from their mainland brethren and have to compete for food in different ways.

Because of limits on space, and therefore food, islands often cause populations of large herbivores to reduce in size over time. About a century ago, Franz Baron Nopsca believed this to be the explanation for the herbivorous dinosaurs discovered in Transylvania, an hypothesis that took a while to gain traction, but which is now widely accepted (I wrote about the Baron and his island dwarf ideas last spring). What was eating those smaller sauropods and dantier ornithopods? One of their harrassers would have been Balaur, a scaled-up relative of Velociraptor.

One part of the island rule holds that as herbivores reduce in size to better manage scarce food sources, predators grow to take advantage of the easier prey. Balaur is only a bit larger than Velociraptor (which in reality was a fraction of the size othe JP version, leading Dan Telfer to joke that he'd punt one out of the way if it tried anything with him). But it's a lot more robust than the lithe Mongolian dromaeosaur.

Its unique features don't end with its stockiness: Balaur possessed the above-mentioned twin sickle-claws, four functional toes on its feet as opposed to the typical three for theropods, and a two-fingered hand. This was clearly a predator adapted for a unique lifestyle. Those two claws on its feet have been proposed as its main weapons - as coauthor Steven Brussatte says, "Compared to Velociraptor, Balaur was probably more of a kickboxer than a sprinter, and it might have been able to take down larger animals than itself, as many carnivores do today." The skull of Balaur has yet to be found. I'd love to see if it had additional unique features which may have been of use in taking down prey.

The authors, led by Zoltán Csiki of Bucharest University, write that Balaur's close kinship to the Mongolian Velociraptor suggests that there must have been some connection between the islands and the mainland, an idea that has been hard to state firmly until now. Those herbivorous dwarf dinosaurs of Haţeg are more primitive than their late Cretaceous relatives, suggesting that they had been isolated from their mainland families since the Jurassic. Not so with Balaur. This is an animal descended from advanced dromaeosaurs of the late Cretaceous, so it must have arrived later.

This leads to my big, possibly stupid question, which I'll nonetheless pose here. What if Balaur isn't an example of the island rule after all? Dromaeosaurs are (for the most part) small, nimble predators who may have been able to travel between the island and the mainland more easily than the herbivores. Its unique features may have been of use on the mainland, and it may have been able to access the islands by swimming. Hoping for more skeletons of an interesting new dinosaur like Balaur is a lot to ask, but I'll be interested to see where else they might turn up. Preferably with a nice, complete skull. Csiki promises functional analyses to come in this interview, which will help shed light on how this two-finger, four-toed, robustly built dude hunted.

This is the kind of new species that's easy to get excited about. It represents new and interesting variations on the classic dromaeosaur body plan. It's in a geographically interesting place. Its relation to other dromaeosaurs is significant. And it's got one heck of a cool sounding name, conjuring a positively Tolkienian mood. Balaur bondoc sounds like some dark memory from the depths of elvenlore. Anytime you're compelled to say both the genus and species name, you know you've got a keeper.

More coverage of Balaur bondoc:

Not Exactly Rocket Science
Discovery
More From Discovery: Jennifer Viegas interviews Zoltán Csiki
Nat Geo
Science Daily
DinoGoss
Dinosaur Tracking
Wired (including very cool illo of Velociraptor)
HuffPo
BBC
The Dragon's Tales
Everything Dinosaur

PS. Bună ziua = "Good day" in Romanian.