Explaining Haplocheirus

Newly added to the Why Evolution is True Youtube channel is a video from the National Science Foundation, explaining why Haplocheirus sollers, a basal alvarezsaur from Jurassic China, was such an important discovery last year.



In addition to piles and piles of good documentaries on the varying facets of evolution, the WEIT channel also hosts the dino docs T. rex: Warrior or Wimp, What Killed the Dinosaurs, Mystery of the Jurassic, and The Four-Winged Dinosaur.

Dave Hone on Linhenykus

University College of Dublin has posted a short video with resident paleontologist Dave Hone of Archosaur Musings fame, discussing the new alvarezsaur, Linhenykus.



From the few times I've seen him on video, Hone seems pretty comfortable with being on camera. Maybe one day he'll have the clout to helm a documentary series himself, and all of our gripes with media and pop culture handling of paleontology will melt away...

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.

Hello, Haplocheirus

Illustration by Portia Sloan, courtesy George Washington University

There is a whole lot of dinosaur news going on right now. Predictably, the dinosaur feather color story has made the biggest splash in the general media. But there have also been two new species described in the last week or so.

Here's that new alvarezsaur I posted about last week. It's called Haplocheirus sollers, a basal member of the group, and the only one known from the Jurassic period. The discovery of Haplocheirus is one of those lovely instances when scientists make a prediction about evolution and it pans out. Many features of Haplocheirus are transitional between the later, more specialized alvarezsaurids and their common theropod ancestor. And it was found exactly where an early member of the group should be expected - in Jurassic rock dating to when theropods were diversifying into their myriad Cretaceous forms.

The hand in particular is remarkable. When I was in high school, the cool program we all loved messing with in art class allowed us to morph two faces together, an effect used to great artistic success in Michael Jackson's "Black and White" video. Take a look at the theropod hand comparisons used by Jonah Choiniere, lead author of the Nature paper describing the find, in his latest guest post at Archosaur Musings. It's like he took the hands of Allosaurus and Shuvuuia and morphed them, and ended up with Haplocheirus. Maybe not exactly, but close. Haplo looks a lot like a generic theropod, showing that the things that made its later descendants look so birdish really were examples of convergent evolution - separate lines that arrive at similar bodily features because the pressures of natural selection happened to favor them. The deeply keeled sternums of alvarezsaurs and birds allow for powerful arm muscles - muscles that evolved for digging and flying, respectively. Imagine I'm writing "cool" several hundred times, so I don't have to do it.

Another new species is a tyrannosaur unearthed in New Mexico, Bistahieversor sealeyi. I'll post on this one tomorrow.

The Mysterious, Intriguing, Utterly Cool Alvarezsaurs

Yesterday at Archosaur Musings, Dave Hone made a brief post about what he thinks is going to be one of the dinosaur clades to receive some major light this year: the Alvarezsaurs. Today, guest-blogger Jonah Choiniere continues the alvarezsaur love with a history of the study of this strange group. Hone promises a major post tomorrow which will accompany a paper to be published in science, a paper announcing a new Jurassic alvarezsaur from China described by Coiniere.

Personally, I'd be thrilled if 2010 is as good to the alvarezsaurs as 2009 was to the tyrannosaurs. The alvarezsaurs are very birdlike group of small theropods, members of the maniraptors, found in Europe, Asia and the Americas. But, as maniraptors go, they actually aren't very closely related to birds. And the basal (more "primitive") members of the group are actually less birdlike. This means that the birdlike features the alvarezsaurs would evolve, especially the deep, keeled breastbone, were examples of convergent evolution, separately evolved for their own purposes. The reason birds have such a deep breastbone is that it's needed for the attachment of the flight muscles.

The forelimbs of alvarezsaurs, on the other hand, are not exactly winglike. They are short, strong, with a pronounced first claw. This claw was so favored that some of the alvarezsaurs, such as Mononykus, have evolved only one finger. Some, like mongolia's Shuvuuia, have drastically reduced second and third digits, which were likely useless in life. This feature, plus what seems to have been a flexible snout, has led to the widely accepted view that this group of dinosaurs were specially adapted to an insectivorous niche, using their powerful little arms to dig into termite mounds, probing for yummy little morsels with their snouts. More color added to our picture of dinosaur lives.


Mononykus reconstruction at AMNH, photo from wikipedia user Ivan Akira.