Thursday, March 19, 2009
Brontosaurus is on it's way back.
At least, if the SV-POWers that be have anything to say about it.
Vague, tantalizing comments here.
[Image: Apatosaurus excelsus by ДиБгд from Wikipedia, modified by N.Tamura and M.Martyniuk, public domain.]
Wednesday, March 18, 2009
Just when you thought the picture of feather evolution was getting clearer... enter Tianyulong, the feathered heterodontosaurid.
You heard me. Read about the new find at Ed Young's blog.
So what does it all mean? I doubt there'll be any consensus, but the authors do a pretty good job of showing that, like the feathers of Sinosauropteryx and Beipiaosaurus, these structures are hollow and not collagen. So were all dinosaurs (or ornithodirans as a whole, dinosaurs + pterosaurs) feathered, and many lost feathers and re-grew scales? The distribution is now making it look like all these structures (ceratopsian quills, ptero-fuzz, feather,s protofeathers and now ornithischian fibres) are homologous--that is, they all derive from a common, ancestral structure. However, I think it's more likely that these started out at bristle-like quills, and evolved into softer, more fuzzy pelts in a few lineages independently, the small, active ones that would be pre-disposed to adapting these inherited quills.
But what do I know? I'll keep you posted on what ideas start getting inevitably tossed around.
Tuesday, March 17, 2009
Ok, so this isn't really news, but I thought it would be an interesting topic for the Goss to review: Coelurosaur ghost lineages. Rumors abound of coelurosaurs creeping their way back out of the Late Jurassic and Cretaceous where they belong, and into the murky shadows of the Early Jurassic or even Triassic. Nobody has ever gotten a glimpse of such specters, but little bits of evidence that can't be explained away so easily keep poking little, irritating holes in our picture of how the lineage that lead to birds came about. Spooky!
You all know coelurosaurs: those little (ok, not so little) carnivorous (but not all of them, or maybe even most) dinosaurs (in all likelihood). The first coelurosaurs were discovered in the Late Jurassic Solnhoffen and Morrison formations, familiar little critter like Compsognathus, Coelurus, Ornitholestes, and Archaeopteryx (thanks to phylogenetic nomenclature, birds are classified as coelurosaurs too), all found during the 19th Century. In the 20th Century, coelurosaur discoveries exploded. Turns out, coelurosaurs really flourished in the Cretaceous, with the dromaeosaurids ("raptors"), troodontids, oviraptorosaurs, ornithomimosaurs, therizinosaurs, alvarezsaurs, and tyrannosaurs pretty much monopolizing the theropod game. Despite the diversity of fossils and number of specimens, however, the evolution of these dinosaurs is a bit murky. We have a generally good idea of how they were all related on a large scale (Tyrannosaurs and coelurids are the most primitive, followed by ornithomimids, alvarezsaurids, therizinosaurids, oviraptorosaurs, deinonychosaurs and birds). The problem is the timing.
The most advanced coelurosaur lineage is Avialae, the birds, and their close relatives the deinonychosaurs. These groups reached their apeces in the Cretaceous, but we know they were around in the Late Jurassic thanks to Archaeopteryx. So how could avialan birds, which are more advanced than the deinonychosaurs, have been around before the deinonychosaurs?
So ghost lineages exist, and we still have a very poor record, if any, of the other coelurosaur groups over this time span. But in general, the ghosts seem to be appeased. Or are they?
Enter Eshanosaurus. When described in 2001, the scientists were baffled. This specimen, a long lower jaw and teeth, looked for all the world like a therizinosaurid. Not a therizinosaur in general mind, but a member of the advanced clade Therizinosauridae, more advanced than primitive, Early Cretaceous therizinosaurs like Falcarius. This would not be very surprising if it hadn't been for one thing: the bone hailed from the Early Jurassic, 60 million years before the previous, earliest known therizinosaur. Uh oh.
The Eshanosaurus jaw was found beneath a bonebed of the prosauropod Lufengosaurus. Mystery solved, you may say. Prosauropods and therizinosaurs have famously been confused in the past. Their skulls and dentition tend to be similar. Jim Kirkland thought so, and in a 2001 review said one aspect of the teeth, a mid-line ridge, screamed prosauropod. But he hadn't seen the specimen himself, and was going from a bit of unpublished goss (in scientific circles, when you use goss in an official, published paper it's called "personal correspondence", or pers. cor.). The authors of Eshanosaurus themselves, Zhao and Xu, had thought of the prosauropod thing, and tried every method to test that hypothesis, but could only rule it out.
Now for more pers. cor. The debate raged on for years, and still nobody has published a real rebuttal to the idea that Eshanosaurus is a ridiculously early therizinosaur. In fact, according to comments posted on Darren Naish's blog, Xu is sticking by his identification, and so are Richard Butler and Paul Barrett (the later a bona-fide prosauropod expert). Barrett has seen the specimen personally, and says it's no prosauropod. It's a therizinosaur.
Could it be, that therizinosaur existed throughout the entire Jurassic and even into the Late Triassic, and left no fossils (that we've found anyway)? That seems to be the case. Talk about a ghost lineage.
Incidentally, that same comments section discusses Larry Witmer's (2001, 2002) assessment of the infamous Triassic "bird" Protoavis. Likely a chimera made of a jumble of bones from all kinds of animals, Witmer seems adamant that, at the very least, the braincase of Protoavis is too coelurosaurian to ignore. And Witmer's opinion is nothing to be sneezed at, he's only the guru of dinosaur skull anatomy. Well, if therizinosaurs lived in the Early Jurassic, a Late Triassic coelurosaur doesn't seem so far fetched after all.
[Image: Lawrence Witmer, photo copyright Rick Fatica for Ohio Today, 2003. From here.]
In conclusion, it looks like there's no good reason to think Eshanosaurus is not a coelurosaur, ghost lineages or no, and lots of good reasons to think it probably is unless other evidence proves otherwise. But what does all this mean for dinosaur evolution as a whole? If coelurosaurs, or even maniraptorans were stomping around the Late Triassic, shortly after dinosaurs first appeared, it would seem dinosaurs radiated much, much more quickly than anybody had thought, unless they have their own ghost lineage back into the mid-Triassic. Either that, or Steven Czerkas (2002) was right about Scansoriopteryx and it's mysteriously closed acetabulum (the hole in the hip for which an open state has always been a key characteristic of all dinosaurs). Maybe coeulurosaurs brached off of the dinosaurian tree much earlier than our cladograms would like us to think. Only more fossils will tell.
- Czerkas, S.A., and Yuan, C. (2002). "An arboreal maniraptoran from northeast China." Pp. 63-95 in Czerkas, S.J. (Ed.), Feathered Dinosaurs and the Origin of Flight. The Dinosaur Museum Journal 1. The Dinosaur Museum, Blanding, U.S.A.
- Witmer, L.M. (2001). "The role of Protoavis in the debate on avian origins"; pp. 537-548 in Gauthier, J., and Gall, L.F. (eds.), New Perspectives on the Origin and Evolution of Birds. Yale University Press, New Haven.
- Witmer, L.M. (2002). "The debate on avian ancestry: phylogeny, function, and fossils"; pp. 1-29 in Chiappe, L.M., and Witmer, L.M. (eds.), Mesozoic Birds: Above the Heads of Dinosaurs. University of California Press, Berkeley.- Xu, X., Zhao, X. and Clark, J.M. (2001). "A new therizinosaur from the Lower Jurassic Lower Lufeng Formation of Yunnan, China." Journal of Vertebrate Paleontology, 21(3): 477–483.
From the DML:
"As exciting as this week has already been with new dinosaur stories (e.g., Hesperonychus), I just want to put everyone on alert to keep an eyeball on Nature starting Wednesday afternoon for a breaking new dinosaur story, and believe me, you won't see it coming...!"
"Isn't this supposed to be coming out a little later? I recall the end of the embargo being set for the 19th."
Deinocheirus? Lori? Amphicoelias? Feathered brachiosaur? Stay tuned for coverage of this cryptic new goss as it unfolds!
Monday, March 16, 2009
Go out in the woods of North America today, and what animals are you likely to see? Small birds, squirrels, groundhogs, raccoons, opossums, foxes? The largest animals you'll see, if you're lucky, are dear or bears.
Not so in the forests and marshes of the Late Cretaceous. In ecosystems like the Dinosaur Park Formation of Alberta, the most common dinosaur species have all been large to quite large. Tyrannosaurs, ceratopsians, hadrosaurs, etc. Until today, the smallest known species in the formation was Saurornitholestes, weighing in at 25lbs. Not exactly a small carnivore in the same way a raccoon is. This is doubly suspicious, as in other dinosaur fauna, such as the Late Cretaceous formations of Mongolia, many small carnivores are known, bridging the gap between mammals and Velociraptor-sized carnivores.
So, is the size gap in North America real, or due to preservation bias? After all, smaller animals fossilize less frequently than large ones. Well, the discovery of a new, small carnivore from Dinosaur Park seems to settle it. Small carnivores were indeed present, and in fact seem to have been pretty common.
Hesperonychus ("western claw") was not only the smallest North American carnivore, it's the only known, and latest known, North American microraptorian (microraptorians are, of course, that group of mainly Asian dromaeosaurs that seem to have retained very small size through their evolution, and were previously only known from the Early Cretaceous. Bambiraptor, briefly considered a NA microraptorian, is probably a juvenile Saurornitholestes instead).
(Picture above copyright Nick Longrich).
Anyway, Hesperonychus isn't technically a "new" find, but joins the fables list of new species "discovered" in museum collections. Nick Longrich explains the story of how he found a suspiciously microraptorian pubic bone sticking out of a piece of rock collected in 1982 in the video here. Additionally, a heap of tiny finger and toe bones, and claws smaller than a Loonie, have turned up over the years in the Dinosaur Park Formation. These probably belong to Hesperonychus, and show that it was pretty common compared to other, smallish carnivores. Given how infrequently small bones fossilize, it may be safe to say it was as common a feature of NA forests as the ubiquitous squirrels are today.
So, we have some nice, tiny dinosaurs in North America at last (the later Albertonykus was also quite small, tough an insectivore rather than carnivore). The real question is why haven't we found any even smaller ones? Hesperonychus is still larger than the largest carnivorous mammals it lived with. The traditional view is that dinosaurs kept the mammals from getting large through competition, but were the mammals also keeping the dinosaurs from getting smaller? The plot thickens...
Wednesday, March 11, 2009
Just popping in to report on the ongoing saga of the new Deinocheirus specimen(s?).
For those who haven't been keeping up, rumors of one or more new finds from this age-old dino mystery have been swirling for a few months now. While a new find was whispered of over a year ago, the real action didn't start until Michael Ryan posted on his blog regarding Phil Currie's re-discovery of the original quarry where the infamous "terrible hands" and their adjoining titanic arms were first found in the late 1960s. He ended the short post with the tantalizing statement that they'd found more of the skeleton.
[Reconstruction of Deinocheirus as an ornithomimid by Wikipedia illustrator and DinoForum member known as FunkMonk, some rights reserved. More on this image below]
As a child of the '80s, and thanks to any number of old dinosaur books for kids, Deinocheirus stands out at THE mystery dinosaur. Gigantic, clawed arms of a predatory dinosaur larger than anything else like them by an order of magnitude. What kind of creature could these possibly have belonged to? The imagination runs wild.
Thanks to phylogenetic studies done in the 1990s and 2000s, most paleontologists have concluded that it was probably a gigantic ornithomid, or "ostrich dinosaur," though just what a 40ft ornithomimid would look like and what kind of specialised adaptations it must have had remain a mystery.
Well, a mystery to most. I brought up Ryan's blog post at DinoForum last November to fish for clues. And boy did I get them. Several people posted tortured cries of "wait for the paper." I can't imagine the Machiavellian pleasure people must take in knowing the answer to such a compelling and long-standing mystery and not being able to talk about it. They must feel like the creators of Lost.
Most people couldn't resist posting more clues, or teaser answers to questions in that thread. T. Mike Keesey of Dinosauricon fame knows what it is. Is it a giant ornithomid, or something more? Says Keesey: "Oh, it's more." Keesey also dropped the bomb that the find in the original quarry was NOT the one he was thinking of. More than one Deinocheirus? A new member of the deinocheirid family? Something else? Somebody knows what it is. Somebody knows. Ok, now I'm just sounding like the creepy ginger guy from Watchmen. Anyway, more rumors from those in the know suggested that, while Currie and Ryan's site had turned up new remains, they weren't much. The other new find, however, seemed to be something much more complete.
By the end of January, Scott Hartman weighed in... by laughing at us poor blind plebs. Openly mocking our futile attempts at solving the puzzle. Yup, creators of Lost all right.
But, today, another solid clue, perhaps the most solid yet. Not a clue: an answer.
FunkMonk (mentioned above, sorry, don't know your real name dude) had posted a thread for critiques of his artwork a while back, also at DinoForum. Now the subject of his Deinocheirus has come up again. Scott Hartman reckoned a giant ornithomimid should be more graviportal (with heavy and stout limbs, unlike the lithe form of small, fast ornithomimds). But, it was an old thread, and the picture was done before rumors of the new find(s), and Keesey's implication that it might not be an ornithomimid. Funk didn't want to put more effort into a drawing that might be completely off base. Well, someone came along and put that one to rest.
"It's an ornithomimid."
Stay tuned, gosshounds, as the saga continues to unfold!
[Photo: cast of the currently-known Deinocheirus specimen from Wikipedia, some rights reserved.]
Wednesday, March 4, 2009
Everybody and your mom (their mother?) is blogging about "The Squatter" finally getting published. This is the amazing trace fossil in St. George, Utah that shows not only the footprints of a dilophosaur-sized theropod, but a nearly complete lower-body impression. This is not where the dinosaur walked, but where it sat down to take a breather from constantly chasing things and roaring its fool head off (if every CGI dinosaur show on Discovery is to be believed). (They're not).
The impression includes the pubic boot it sat on, feet/metatarsals, tail, and--most importantly--hands. The hands prints were left side-on, offering the final piece of conclusive proof that theropods did not "pronate" the hands. They could not point palm down like dribbling a basketball, but like a bird wing, were locked with palms facing each other, like holding a basketball. This is something paleontology types have known for a long time based on anatomical studies but it's nice to have behavioral proof. Also nice to have it confirmed in such a primitive species, since many of said anatomical studies were based on more advanced, more bird-like species. Years ago when rumors of this find first hit the tubes, it was said to preserve feathers as well, but that's probably just a bunch of plant material it was sitting on. It's unlikely such a primitive dinosaur would have had feathers (they appear to be restricted to advanced coelurosaurs and birds).
So why does this fossil need saving? Well, it already narrowly avoided being intentionally destroyed in order to build the rear wall of the St. George Dinosaur Discovery Site Museum (ironic, eh?). Now the museum has built a section around the fossil in order to help preserve it from erosion, but it's still weathering ever so slowly, and the museum is too underfunded to really go to the lengths they need to preserve it over the long-term.
That's where we come in. This whole story was brought to by Sarah Spears, former employee of the museum, has put out a call for donations at her blog Gombessa Girl (which also has a more in-depth discussion of the specimen and its predicament).
So, dino fans, you can help save the Squatter by visiting http://www.dinosite.org and becoming a member, joining their Adopt-A-Track program, or buying some swag from the gift shop (which has some pretty cool casts of the dino tracks for sale).
Oh, and for you research-hungry gosshounds, the paper describing the Squatter is online for absolutely free at PLoS ONE, including CC licensed images like the awesome reconstruction here, by awesome wildlife artist Kyoht Luterman.
As many of you will know, up until the advent of modern birds (Aves), most flying dinosaurs had teeth. Real teeth, as in little things covered in enamel and set into sockets in the jaw. Alas, however, all the toothed birds went extinct at the end of the Mesozoic, leaving only the boring old toothless birds to survive to the present day.
But some Cenozoic birds still were able to occupy niches left by toothed Mesozoic seabirds, and by a quirk of evolution developed "pseudoteeth" to suit this task. This group, the pelagornithids, were also among the largest flying birds that ever lived. Relatives of pelicans and boobies, these superficially albatross-like birds could grow up to 6 m in wingspan (that's 20ft for the seppos). And they were pretty recent, with the last species dying out only three million years ago or so.
The "teeth" of pelagornithids were actually sharp, saw-like serrations of the beak. This week, National Geographic announced the discovery of the most complete pelagornithid skull known. It's crazy cool looking, as you can see by the photo in the link. This specimen is from about the middle of the pseudo-toothed bird era, and lived about ten million years ago (the earliest records are from 58 million years ago, showing that these birds started filling in for their toothed forebears shortly after the big extinction). The article doesn't mention if this represents a new species, so stay tuned for more pseudo-toothed goss.
Image from Wikipedia of Osteodontorins by NTamura, licensed under Creative Commons Attribution 3.0 Unported.