When I wrote about the new sauropod Futalognkosaurus dukei last October, I noted that the authors of the paper describing the animal also included a brief summary of the other animals found nearby. Remains of crocodiles, fish, and pterosaurs provided some clues as to the paleoecology of the area about 90 million years ago, but one of the big surprises was a big honkin' claw from Megaraptor. At first the remains of Megaraptor were thought to represent a coelurosaur, but the complete hand has shown that it is probably either a spinosaurid or carcharodontosaurid. A recent study of the hand, lower arm, and shoulder blade has revealed that Megaraptor probably had surprisingly strong arms for ripping into its meals, although whether it caught prey with its claws or just used them to process carcasses is unknown. Ultimately, however, the skull and other parts of the postcranial skeleton will be needed to figure out more about the relationships and habits of this terrifying dinosaur.
*Pictured above; The hand of Megaraptor. From Calvo et al 2007.
Megaraptor is significant for another reason, as well. A new study published in the Proceedings of the Royal Society B describes the ulna of an as-yet-unnamed theropod from Australia the authors say may have been closely related to Megaraptor. The new forearm bone is about 20 million years older than the South American fossil (Megaraptor being the youngest spinosaurid known to date), but if it does indeed belong to something related to Megaraptor, it may have the potential to rearrange our view of global geography during the Cretaceous. According to most maps I have seen, by the Cretaceous Africa and South America had separated from each other and Australia was still connected to Antarctica with no apparent connection to South America. If the new study is correct then the breakup of these continents or the dispersal of animals over them may be more complex than previously thought.
The sole piece of evidence that the paper rests on is a left ulna from the new theropod, the lower arm bone showing similarities with spinosauroid dinosaurs. Although the authors of the paper boldly state "This ulna represents the first Australian non-avian theropod with unquestionable affinities to taxa from other Gondwanan landmasses," in the abstract, more of the skeleton (and more of Megaraptor) will have to be investigated before such a hypothesis can be verified. The general lack of fossil material and hazy phylogenetic position of Megaraptor make it difficult to determine the evolutionary relationship of the new theropod, much less it's biogeographical relationship to other dinosaurs. It may be a spinosaurid or it may be a carcharodontosaurid; more research is required to find out.
If we follow the phylogenetic tree provided in the new paper, however, the Australian theropod is contemporaneous with the spinosaurids Suchomimus (Africa) and Irritator (South America) on the one hand and the carcharodontosaurids Acrocanthrosaurus (North America) and Tyrannotitan (South America) on the other. Depending on how the family trees might be rearranged when the relationship of Megaraptor and the Australian theropod are known, their evolution and biogeography could certainly change. If Megaraptor and the new theropod turn out to be carcharodontosaurids, for instance, their early geographical history becomes more complicated, involving Europe, North America, and South America, but at present it seems likely that both of the theropods discussed in the paper are some type of spinosaurid.
Still, there is some difficulty in reconciling ancient geography with a relationship between the Australian theropod and Megaraptor. South America was not directly connected with Australia during the Cretaceous and it is doubtful that the spinosaurids swam between the two continents. If South America was connected to Antarctica (with Australia still being connected to Antarctica during this time), however, it is possible that intermediates between the earlier Australian theropod and Megaraptor are waiting to be found in Antarctica. Being that Megaraptor is younger than the Australian fossil, however, there is a question of which direction the dispersal went and from where it started. Indeed, just about any scenario contains plenty of problems that have yet to be resolved.
The new paper is interesting in that is proposes a number of hypotheses that will require further testing. For those looking for research ideas, this means that we need to find more of the skeleton of the Australian theropod, of Megaraptor, of spinosaurids or carcharodontosaurids in the Cretaceous rocks of Antarctica, other Gondwanan-type dinosaurs in the Cretaceous formations of Australia, and more fully resolve the relationships of spinosaurids. While the hypotheses presented in the paper are a bit tenuous and certainly are provisional, good questions are raised and I certainly hope that in the coming years more information is accumulated to confirm or refute some of these predictions.
Elsewhere;
References;
Calvo, J. O., Porfiri, J. D., Gonzalez-Riga, B. J. & Kellner, A. W.A. (2007). "A new Cretaceous terrestrial ecosystem from Gondwana with the description of a new sauropod dinosaur." Anais da Academia Brasileira de Ciencias 79(3): pp. 529-541.
Porfiri, J.D.; Dos Santos, D.; Calvo, J.O.(2007) "New Information on Megaraptor namunhuaiquii (Theropoda: Tetanurae), Patagonia: Considerations on Paleoecological Aspects." Arquivos do Museu Nacional, Rio de Janeiro, 65 (4), pp.545-550
Smith, N.D., Makovicky, P.J., Agnolin, F.L., Ezcurra, M.D., Pais, D.F., Salisbury, S.W. (2008). A Megaraptor-like theropod (Dinosauria: Tetanurae) in Australia: support for faunal exchange across eastern and western Gondwana in the Mid-Cretaceous. Proceedings of the Royal Society B: Biological Sciences, -1(-1), -1--1. DOI: 10.1098/rspb.2008.0504
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Hmmm...one thing makes a great deal of sense, if this relationship between Megaraptor and the Australian theropod is well-supported.
That would be the nature of the Australian theropod Rapator, which was recently reclassified as a humongous alvarezsaurid. Considering the diversity of alvarezsaurs in South America in the Cretaceous, a connection between the two continents make Rapator's assignment to that group more feasible. It would be incredible if Antarctica served as an interchange-route between the two continents through the early parts of the Cretaceous.
I'm mainly interested in the separation of South America from Antarctica which produced the antarctic circumpolar current and thus a huge climactic change in the southern hemisphere.
Admittedly, I was apprehensive about agreeing with the conclusions proposed by Smith et al. until I read over the supplemental material.
You'll find this paper has been made available by the authors at this URL:
http://www.uq.edu.au/dinosaurs/documents/Smith_et_al_2008.pdf
The supplemental material provided here:
http://journals.royalsociety.org/content/e237r183381362u7/#Supplemental
The Australian fossil record for dinosaur is incredibly scant, and even at the level of scantness it's at, the Aussies are usually very quick to point to some fragmentary creature and claim it rewrites history.
Remember, they had history's first ceratopsian (based on a single ulna), history's first ornithomimid (probably a coelophysid), and the earliest placental mammals (probably stem-group mammals--tribosphenic molars evolved multiple times). Rapator is known from virtually nothing, and correct me if I'm wrong, but aren't ulnas pretty conservative among theropods?
Timimus is a coelophysid? Really?
The fragmentary nature of the Mesozoic faunas of Australia is a sad thing. The only reasonably complete dinosaurs that come to mind are Minmi, Muttaburrasaurus, and the Aussie basal ornithopod jumble (Laellynasaura, Atlascopcosaurus, etc.) Seeing how the ornithopods of South America match up with the ornithopods of Australia might be a great way to strengthen this proposed biogeographic relationship.
Minmi comes off as very odd, regardless of whether it's a nodosaurid, ankylosaurid, or basal to the two families. It and Antarctopelta are alone as representatives of Gondwanan ankylosaurs, unless there's someone I'm forgetting. With Minmi alone, it seems clear that at least one predominately Laurasian group worked its way down to Australia by the EK. Whatever the heck happened, Australia, as always, seems just plain weird.
Rapator seems to bounce around a lot. Wikipedia cites a source that dropped it in the "basal coelurosaur" region of the theropod tree with Nqwebasaurus. Granted, that's based on what can be determined from a single finger bone...
Adam-
New Zealand has a thus far unidentifable Ankylosaur/Nodosaurid of some type, but its even more fragmented than most Aussie stuff... I'm covering it in a post on my blog in about a week hopefully (I covered half of NZs known dinos in the latest [21] boneyard though this armoured guy is in the still to come half).
Zach-
I've been doing a lot of reading on Aussie/Kiwi Dinos as of late for my Kiwi Dino series (and upcoming Aussie dinos series), and to say it's the Aussie's blowing their stuff out of proportion is completely unfair.
Serendipaceratops (the single ulna ceratopsid) was identified and hailed by Dale Russell, who is of course not an Aussie. Frankly it IS next to identical to Leptoceratops, which AT moment would make it the oldest known ceratopsian. It's a statement of fact. Not blowing it out of proportion.
Regardless of whether Serendipaceratops is a ceratopsian or some other sort of ornithischian, it is definitely NOT the oldest! Yinlong is from the Middle/Late Jurassic boundary.
Traumador, I've seen the ulnars of Serendipi and Lepto together (there was an Aussie dino exhibit up here a few years back) and while the resemblence is very strong, there are some basic differences in overall shape and proportion. I'm just not convinced that Serendipi is a ceratopsian. I'd be more willing to say "marginocephalian."
And Dr. Holtz is right, Yinlong is older, and what's more, Yinlong suggests that ceratopsids originated in China, not Australia!
Okay to start off with I need to applogize for the structuing of my (quickly written) comment.
What I was addressing specifically was Zach's statement
" the Aussies are usually very quick to point to some fragmentary creature and claim it rewrites history"
I'm sure you meant it in a different context Zach, but in that exact wording it can be taken slightly wrong to people down here in the southren hemisphere, as again it is just as often outsiders who make these claims about their fossils as them...
I pointed out Serendip due to the fossils history, not the animals palaeobiology.
Dale Russell is not Australian, and it was he who made the ceratopsian connection with the bone. The Australians had been thinking it was theropod till that time.
As for my statement about Serendip being the oldest... First off I've never heard of Yinlong till now myself (very exciting to learn about). My statements were based off what I've been reading. Apart from John Long's Dinosaurs of Australia and New Zealand (written in 1998, which I'm pretty sure was before Yinlong was found, yes?) there isn't much talk about Serendip in ANY context to other ceratopsians or Dinos elsewhere other than to simply compare it to other neoceratopsids. In other words their much more preoccupied with whether figuring out WHAT it is, than claiming its the oldest (especially since it turns out it is not).
I wasn't saying the Serendip WAS definately the oldest, and thus no others would be found. What I was saying is that at the time the Aussie's made the claim it was the oldest, at that time the evidence pointed at it being so. I've only seen it in SCIENTIFIC lit as being claimed to be the oldest in the John Long book (again 98), and he expressed his DISCOMFORT with this notion there!!!
Popular Aussie and Kiwi books on the other hand do make the claim about Serendip... but how often does anybody's popular dino books not make dumb claims about the local animals or outdated ideas?
Again I wrote it quick, but my previous point was trying to say not to make possibly insulting generalizations about countries or people.
Zach,
Actually, while the evidence of an Asian origin for Ceratopsia is pretty strong, Ceratopsidae is pretty securely a uniquely North American radiation.
Ack! Darn it, that's what I meant, Tom! Hahaha...I was actually thinking to myself "is there a clade name for the animals that aren't Neoceratopsians besides "Ceratopsia?" :-)