Tyrant dinosaurs - properly called tyrannosauroids - are most usually associated with the Late Cretaceous of North America. Of course, if you know anything about dinosaurs you'll also know that many tyrants were Asian. So, the most familiar tyrants - the big, short-armed kinds like Tyrannosaurus, Tarbosaurus, Albertosaurus and Daspletosaurus (all of which belong to the best-known tyrant clade, Tyrannosauridae) - were all animals of Laurasia, the northern landmass that split up during the Cretaceous to form North America and Eurasia [image above provided by Roger Benson; read on for explanation].
The history and diversity of early, non-tyrannosaurid tyrants is still poorly known, but in recent years a number of such forms have been discovered in Europe and Asia. Eotyrannus lengi (named in 2001) is from the Lower Cretaceous of southern England; little Aviatyrannis jurassica (named in 2003) is from the Upper Jurassic of Portugal; small, feathered Dilong paradoxus (named in 2004) is from the Lower Cretaceous of Liaoning Province in China; crested Guanlong wucaii (named in 2006) is from the Upper Jurassic of the Junggar Basin in China; Stokesosaurus langhami (named in 2008) is from the Upper Jurassic of southern England; Xiongguanlong baimoensis (named in 2009) is from the Lower Cretaceous of Gansu in China; Raptorex kriegsteini (also named in 2009) is inferred to be from the Lower Cretaceous of somewhere in north-eastern China*; and Sinotyrannus kazuoensis (also named in 2009) is also from the Lower Cretaceous of Liaoning Province [adjacent image shows life restoration of Raptorex by Nobu Tamura, from wikipedia].
* There is some scepticism about the claim that Raptorex came from Liaoning Province, as it was recovered from a commercial source.
Proceratosaurus bradleyi [shown here, image © NHM] from the Middle Jurassic of England has also been recently identified as an early tyrannosauroid closely related to Guanlong (Rauhut et al. 2010). The name Proceratosauridae can be used for the Proceratosaurus + Guanlong clade (I'm pleased to say that I found Proceratosaurus to be a tyrannosauroid in my 2006 Ph.D. thesis... though shame I still haven't published).
The presence of Proceratosaurus in the Jurassic of England, Aviatyrannis in the Jurassic of Portugal, Stokesosaurus in the Jurassic of the USA and England, and Guanlong in the Jurassic of China indicates that tyrants were distributed across Laurasia by the Late Jurassic.
This distribution raises an interesting question: seeing as tyrants were living across Laurasia during the Jurassic, why didn't they colonise the southern continents? During the Cretaceous, several dinosaur groups (such as macronarian sauropods and allosauroid theropods) occurred in North America and Eurasia in the north, and in South America, Africa and Australia in the south. This pattern indicates that these groups were able to colonise both the northern (Laurasian) and southern (Gondwanan) landmasses during the Jurassic, prior to their Cretaceous separation. So, the deep Jurassic origin of tyrants means that we should predict their presence on the Gondwanan continents.
Today sees the publication of a paper by Roger Benson and colleagues on the first Australian tyrant dinosaur (Benson et al. 2010). Thanks to this find, we now know that tyrants did, indeed, get deep into the south. The specimen is, unfortunately, not a complete skeleton or even a partial one: it's a single, 30-cm-long pubic bone, currently known only by its catalogue number, NMV P186046 [shown here, image provided by Roger Benson]. It's from the famous Dinosaur Cove site in Victoria, and its detailed anatomy demonstrates its tyrannosauroid identity. Additional clues show whereabouts the specimen lies within the tyrannosauroid radiation.
The pubic boot - the projecting, foot-shaped bony mass present at the lower end of the bone - is narrow from side to side. This means that the bone belongs to a coelurosaurian theropod (other theropods have broader pubic boots). Among coelurosaurs, a particularly large pubic boot (like that present in NMV P186046) is seen in tyrannosauroids, as is a prominent, flange-like ridge (the pubic tubercle) at the upper end of the bone. Other characteristic tyrannosauroid features are present on the bone too. The proposed tyrannosauroid identification of the specimen is therefore pretty secure: no other group of theropods possesses this combination of unusual features.
NMV P186046 is Aptian in age (that is, it's from the late part of the Early Cretaceous), so it's somewhat younger than all of the Jurassic tyrants, and also younger than the non-tyrannosaurids Dilong, Eotyrannus, Sinotyrannus and Raptorex. Interestingly, its anatomy suggests that it was more closely related to tyrannosaurids than were any other currently known tyrants (the pubic flange, for example, is present in tyrannosaurid tyrants, but not in Raptorex or other non-tyrannosaurid tyrants). It can therefore be inferred that any characters shared by Raptorex and Tyrannosauridae (see Sereno et al. 2009) were also present in the Victorian tyrant: it would have had relatively short arms and hands (in contrast to Eotyrannus and some other early tyrants), and it would have had robust jaws and generally been tyrannosaurid-like in overall proportions (Benson et al. 2010) [cladogram below from Benson et al. (2010)].
Is it possible that the specimen isn't really a tyrant, but an Australasian 'tyrant mimic'? When making identifications based on partial specimens, we've been wrong before, sometimes very wrong. In the absence of better remains, this possibility will remain, but it should be clear that it's nothing more than a speculation: at the moment, a tyrannosauroid identity for NMV P186046 is as robust as it could be. The conclusion must be that 'mid-sized', Raptorex-like tyrant dinosaurs (total length = about 3 m) invaded the southern continents, and inhabited Australia as well as Asia during the Early Cretaceous.
As usual, this discovery raises new, interesting questions. Tyrants became successful, gigantic arch-predators in the north, yet we have no evidence that this happened in the south. Is this because other big theropods (like megalosauroids and/or allosauroids) held sway in the south, therefore preventing the evolution of giant size in southern tyrants? Or is it that only tyrannosaurid tyrants had the requisite anatomical or behavioural features that 'allowed' gigantism? Did this lineage of mid-sized southern tyrants die out long before the close of the Cretaceous, or are there more finds to come? We can't pretend to know that much about the Cretaceous fossil record of Australia, let alone that of Antarctica or much of Africa, so could mid-sized or even gigantic southern non-tyrannosaurid tyrants await discovery, either in Australia, or in Africa, India, Antarctica or elsewhere in Gondwana?
In fact, while NMV P186046 is the first Gondwanan theropod that we can confidently identify as a tyrant, there are at least a few other southern continent taxa that might, just might, belong to this group too. Santanaraptor placidus and Mirischia asymmetrica, both from the Santana Formation of Brazil, have been suggested to be non-tyrannosaurid tyrants (Holtz 2004, Naish 2006). To be honest, they don't really look like they might be part of the same clade as Raptorex, NMV P186046 and Tyrannosauridae, so were additional tyrannosauroid lineages present in Gondwana during the Jurassic and Cretaceous?
And, one more thing - - it's well known these days that Dinosaur Cove was located pretty close to the Cretaceous South Pole [adjacent palaeomap from wikipedia]. Therefore, it was affected by seasonal darkness and cool or cold weather. The dinosaurs and other animals that lived here must have coped with these conditions. What does the presence of a mid-sized tyrant dinosaur in the Dinosaur Cove fauna tell us about tyrannosauroid physiology, behaviour and ecology? We don't know, obviously, but it's going to be fun to speculate.
As usual, things have turned out to be more interesting that we might previously have guessed. I leave you with the vision of a short-armed, cold-adapted tyrant dinosaur, chasing an ornithopod through the chilly air of an Australian winter...
For previous articles on tyrannosauroids and other coelurosaurian theropods see...
- Oh no, not another new Wealden theropod!
- 100 years of Tyrannosaurus rex
- Long and Schouten's Feathered Dinosaurs, a review
- The Crystal Palace monsters, armoured tyrannosaurs and lurking sauropods: a look back at 'Dinosaurs - A Historical Perspective' (part I)
- An American tyrant in London
- Of Becklespinax and Valdoraptor
- Feathers and filaments of non-avian dinosaurs, part I
- Feathers and filaments of dinosaurs, part II
Refs - -
Benson, R. B. J., Barrett, P. M., Rich, T. H. & Vickers-Rich, P. 2010. A southern tyrant reptile. Science 327, 1613.
Holtz, T. R. 2004. Tyrannosauroidea. In Weishampel, D. B., Dodson, P. & Osmólska, H. (eds) The Dinosauria, Second Edition. University of California Press (Berkeley), pp. 111-136.
Naish, D. 2006. The osteology and affinities of Eotyrannus lengi and other Lower Cretaceus theropod dinosaurs from England. Unpubished Ph.D. thesis, University of Portsmouth.
Rauhut, O. W. M., Milner, A. C. & Moore-Fay, S. 2010. Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi (Woodward, 1910) from the Middle Jurassic of England. Zoological Journal of the Linnean Society 158, 155-195.
Sereno, P. C., Tan, L., Brusatte, S. L., Kriegstein, H. J., Zhao, X. & Cloward, K. 2009. Tyrannosaurid skeletal design first evolved at small body size. Sciencexpress 10.1126/science.1177428
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Gotta say, this is pretty awesome.
Now wait a second. I thought Mirischia was a compsognathid?
It was, but new data can do that to a taxon :) (and, it might still be a compsognathid: it's a very incomplete taxon that's fairly labile in analyses).
Darren Naish wrote:
"Or is it that only tyrannosaurid tyrants had the requisite anatomical or behavioural features that 'allowed' gigantism?"
I don't think so. First, Brusatte et al. (2010) suggest that Sinotyrannus was really basal. In fact, it has proceratosaurid synapomophies of Rauhut et al. (published in 2010, not 2009), but this morphology can be plesiomorphic for Tyrannosauroidea. Second, theropods generally seem to be adapted in getting bigger.
Ref.
Brusatte, S.L., Chure, D.J., Benson, R.B.J. & Xu, X. (2010). "The osteology of Shaochilong maortuensis, a carcharodontosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Asia". Zootaxa 2334: 1â46.
If there were Tyrannosaurs in Oz they were probably venomous, poisonous and way more aggressive than a regular T.Rex.
Four dinosaur posts in a row? What are you, making up for the babirusafest?
All together now!
Tie me dinosaur down, sport,
Tie me dinosaur down!
Can you see what it is yet?
Awesome.
Also awesome that you have broken your habit of not blogging about the latest news. :-)
What's the name of this new Tyrannosaur?
I whole-heartedly concur with David MarjanoviÄ.
If I'm not wrong, we haven't discovered any dinosaurs from the end of the Cretaceous in Australia, right? And this Aussie tyrant is older than Leaellynasaura, Timimus and Australovenator, which also hail from Dinosaur Cove and elsewhere in Victoria, but are Albian.
Very interesting news.
Earlier this year, my parents did a week of volunteer dinosaur digging in Victoria - but at Dinosaur Dreaming, not Dinosaur Cove. Dad (who had a copy of your book in his luggage, btw) found the February 1 Bone of the Day as credited on the official blog, but I'm sure he would have loved to have found a tyrannosauroid!
(Meanwhile, I took beach photographs.)
This is awesome! Tyrannosaurs are some of my favorites. While we're on that topic, Darren, I'm curious. What are your thoughts on Carr's suggestion that Guanlong is actually a sister taxon to Monolophosaurus?
Hey, I remember asking that a looooong time ago. A relatively recent redescription of Monolophosaurus' skull addresses that question. Short answer: Not related.
I'm curious how the pubis differs from the contemporaneous supposedly ornithomimosaur pubis NMV P186058 mentioned by Currie et al. (1996). I wouldn't be surprised if this supposed tyrannosauroid pubis turns out to be from another kind of non-maniraptoran coelurosaur, as it's hard enough to tell when we have entire skeletons like Guanlong. Also, minor nitpick- as far as I know Proceratosauridae did not exist prior to Rauhut et al.'s study.
What's the latest word on the affinities of Rapator?
It didn't get one, probably* because it's too fragmentary to be compared to other fragments of anything but the same bone.
* Haven't read the paper.
Rapator continues to be a coelurosaurian MCI without any severely diagnostic features that groups it with much more than a generaluized, basal, potentially arctometatarsalian coelurosaur, although it still has the closest physical similarity to Ornitholestes.
Greetings,
The critter (probably a tyrannosauroid, but since it is a single pubis the possibility of convergence does exist) does NOT have a name: thank Benson, Barrett, Rich & Vickers-Rich for having the courage to wait for more material!!
Also, I now have a cast of Rapator, and in light of the new Neovenatoridae discoveries I think it is quite likely a neovenatorid. (Heck, there is the non-zero chance it is the senior synonym of Australovenator!)
How tyrannosaurs reached Australia without be present in the very rich sites of Argentina? There's another examples of Gondwanan Cretaceous groups coming from Laurasia (birds, dromeosaurians, alvarezsaurids, eusuchians, etc).
I do feel a bit skeptical about this find, seeing as there have been some claims that the fossils from the Dinosaur Cove site (particularly in the book Dinosaurs of Darkness), that Australia was the ancestor of almost everything Laurasian, including oviraptorosaurs, ceratopsians, placentals, etc. But when one thinks about it, if tyrannosauroids were present in Laurasia in the Late Jurassic, when the continents were together, then they would most likely be in Gondwanaland. And while it does seem a bit odd that the taxon they find is supposed to be one of the closest non-tyrannosaurid relatives of the Tyrannosauridae, the idea isn't really unheard of. I mean the closest relatives of the South American marsupials are in Australia, after all.
>I'm curious how the pubis differs from the contemporaneous supposedly ornithomimosaur pubis NMV P186058 mentioned by Currie et al. (1996). I wouldn't be surprised if this supposed tyrannosauroid pubis turns out to be from another kind of non-maniraptoran coelurosaur, as it's hard enough to tell when we have entire skeletons like Guanlong.
---------------------------
We didn't have much space to discuss these sorts of things in the paper. But I can clarify the anatomical information here.
I agree with those who think we should be cautious when referring isolated elements to narrow clades. In fact, most of the Dinosaur Cove stuff I looked at is impossible to assign to any particular clade. However, in this case there are a couple of features that link the pubis, not just to tyrannosauroids, but to a derived clade within tyrannosauroids. It is very distinct from ornithomimosaurs (see the online supplement of the article).
The pubic boot is large - sure, you get this in some more basal theropods, but all of these have transversely broad, massive, pubic boots; the transversely narow boot is a unique, unreversed coelurosaurian synapomorphy. The pubic boot is smaller than in tyrannosaurids, but Phil Currie showed in 2003 that the boot size is positively allometric. So in fact, the boot is relatively gigantic for such a small animal. It also has a prominent anterior expansion, which narrows down the possibilities.
The morphology of the pubic tubercle is more distinctive. It isn't just prominent. It is prominent, and it forms a curving flange with a large rugose area on its lateral surface. Other clades elaborate the pubic tubercle, but none of them looks at all like this (other than dromaeosaurids, which lack the rugosity, and are totally different anyway).
These features, together with the overall morphology (straight shaft, narrow pubic apron, orientation of the ischial facet) all add up to give a striking resemblance to tyrannosaurids. In fact, they are basically identical. That's why we figured the two side by side in the paper. And to show that this is unique similarity we figured a lot of other theropod pubes in the supplement. The australian pubis is actually much closer to a tyrannosaurid pubis than is that of Guanlong, or even Raptorex. This is why we drew the phylogenetic conclusion that it was a close relative of tyrannosaurids.
We went to a lot of effort to back up our claim. In my opinion, the anatomical observations are not something that can be argued with. However, as Darren and Tom rightly pointed out, there is one reasonable alternative explanation. What if a hitherto unknown dinosaur clade with a pubis literally identical to that of small derived tyrannosauroids lived in the mid Cretaceous of Australia? This is possible. But in the absence of evidence it certainly shouldn't be our first recourse.
Roger
For those interested in a preliminary test of both the new Australian pubis and _Rapator_, I entered them in my large phylogenetic analysis of Theropoda.
The only known specimen of _Rapator_, interpreted as a McI, results inside Megaraptora, so, I agree with Tom's interpretation.
The Australian pubis results a close relative of the "Tyrannosauridae + _Appalachiosaurus_" node, so, I agree with Roger (and collegues) hypothesis. The analysis includes all the features and taxa cited in that study.
I may be wrong, but these, in my opinion, are the most plausible interpretations for both specimens, PENDING NEW DATA.
In an article on the Dinosaur Cove fauna in Scientific American back in 1993, Rich et al mention "a close relative of the familiar Allosaurus" some six and a half feet tall. "This 'pygmy', presumably a juvenile, is the latest-surviving allosaur that has been found."
Where does this animal fit into the current story?
Probably, they mentioned the Australian "Allosaurus", based solely on an astragalus, now re-interpreted as a relative of the neovenatorid allosauroid Australovenator.
How will it be named? My humble sugestions:
Exotyrannus "Outsider Tyrant"
Teletyrannus "Distant Tyrant"
Antipodotyrannus "Antipode's tyrant"
Antipodanax "Antipode's princeps/king"
Australianax "Australian king"
Ozrex "Australian king"
What's the position of the Australian Nanantius in Enantiornithes cladogram? The faunistic correlation between Chinese and Australian Early Cretaceous tyrannosauroids and enantiornithes could represent the same pattern.
As stated elsewhere by others, the specimen lacks autapomorphies, so cannot be used as holotype for the formal erection of a new genus/species name.
If new specimens with diagnostic features will be found, I suggest using "Ozraptorex" ;-)
Nanantius is an enantiornithine of uncertain position: based solely on a tibiotarsus, and considering that enantiornithine phylogeny lacks a consensus (see in the last JVP, O'Connor et al discussion on this topic), we cannot say nothing more than "Enantiornithes".
Of course it can -- the in the ICZN doesn't have any rules about this. But it shouldn't be, because that would risk resulting in a nomen dubium or a junior synonym of something else.
I'm gonna surprise everyone and say that the morphological data seems overwhelming in favor of a deeply nested tyrannosauroid that is practically a tyrannosaurid (depending on where you want to draw the line with whose definition in the cladistic sense, which some of you don't follow).
The biogeographic sense is puzzling me, but the Early Jurassic positing of a divergence timing suggests that, with seeming Late Jurassic ornithomimosaur, troodontid, and dromaeosaurid divergences, and an Early Cretaceous divergence at most for oviraptorosaurs, that the jump in time of divergence across the Jurassic seems staggeringly long for what is also apparently limited morphological change.
Early alvarezsaurs like Haplocheirus are remarkably similar to "compsognath" grade basal coelurosaurs, and these two include a feature common to and potentially derivative of basal tyrannosauroids: An elongated, and extensive postpubic process of the "foot." Hesitatingly, the "foot" of the pubis in tyrannosaurids proper are tirangular in aspect when viewed distally ... but in this specimen, the boot is parallel-sided in aspect, rather quadrangular and much unlike that of even some purported English "compsognaths" like Aristosuchus.
So the curious-minded here would like to know: What is the relative value of the pubic morphology when only the projection anteriorly is noted, but the ventral aspect or a functional consideration for the projection are also of concern? Kent Sanders has projected an argument that the large pubic boot, being allometric as noted above by Benson, aids in sitting and resting in tyrannosaurids, so should be smaller in smaller animals, and this is why it is shorter if not absent in such smaller taxa. so here, the question also becomes, is this feature convergent to function with a clear allometric sugnal involved, and if so (as it is the case), does this downgrade the importance of the boot in assignment?
This is to say nothing of the proximal flange, though, which is pretty solid-seeming.
Gobiconodon was found in Early Cretaceous Asia, Spain, North America and Morocco, so, a dispersion of Laurasian elements from Asia, through Europe to Africa is not impossible, with Africa as a "gate" to Gondwana. Nevertheless there was some ecologic filter between Northern and Southern Gondwana. [North: Northern South America, including NE Brazil (Santana and Itapecuru formations) and Northern Africa; South: Argentina, Southern Africa, ANtarctica, Australia and Indomadagascar]
This "filter" originated slightly different faunistic provinces in North and South Gondwana. Until now, there was no found Spinosaurid in Argentine, for example, while they were common in Northeastern Brazil. Australosphenidans and advanced Notosuchians became nested in South. Some of these Southern elements only reach North in some stage of Last Cretaceous, and reached Europe from Africa (abelisaurids, titanosaurs, ziphodont crocs, madtsoiids). Southern province broke apart with split of Africa, and of Indo-Madagascar.
Echoing Anonymous' post (#16) - I find this extremely hard to accept, especially in light of the identifications made of several other isolated bones in Victoria: the identification of a possible oviraptorosaur from a surangular and a vertebra, the naming of Serendipaceratops arthurcclarkei from a single ulna, the naming of Timimus hermani from two femora... to me, convergence seems a more likely explanation for the similarity of this specimen to tyrannosauroids.
What's the timing for Australia's breakoff from the other continents? Could basal tyrannosauroids have gotten down there before it broke off, or would that require an extensive ghost lineage?
Zach, Australia didn't break away from other continents. They broke away from us! (Boom-boom!) And there was still two-way traffic (in marsupials and snakes) between Australia and South America up to, and probably after the K-P boundary, so no ghost lineages are required in the early K.
I'm confused (which is nothing new for me), South America is not the key so much as the Gondwana and Laurasia break up (and when it occurred) its self. It's odd considering how derived the specimen appears to be. There seems to be a lot of 'advanced' forms just waiting their chance while more primitive taxa hold fort. This seems particularly true for theropods. Then throughout much of the Cretaceous you get adaptations and a continual shifting of the guard, so to speak, but little else. Something doesn't ring true.
Of course, my lack of knowledge concerning exact dates and things like land-bridges might be a key.
@24, J.S. Lopes, if the pubis has any possible indication of a having come from a long-tailed Australian leaping biped, Tyrannosauroo might be a good name.
(It'd be great label for a an Aussie beer too.)
A speculation: Why are Australian, N American & E Asian dinos similar while S American & African dinos differ? Because IMO they were linked via the Indonesian archipelago (shown incorrectly on top map IMO, the 'tail' should be hanging far southerly) and has since been distorted sideways due to lateral compression from Australia/Papua collision. After Australia separated from Antarctica, it piled into the archipelago, allowing flora/fauna transfers along coasts of E Asia & N America via Beringea.
Definitely after. Australia stayed connected to Antarctica till the middle Eocene, and there's no evidence of metatherians in South America in the Cretaceous.
I think you're simply getting misled by the terms "advanced" and "primitive"...
I'm not saying there's nothing here which requires an explanation, but, still, you exaggerate both facts.
You're wrong based on paleomagnetic data.
Congrats to Roger and co. on an exciting discovery. I find their interpretations entirely reasonable. If somebody was to find an isolated hyperextensible pedal ungual, it would be referred to a deinonychosaur without any debate. Sure, a more complete specimen may reveal that the claw belongs to an aberrant oviraptorosaur, but convergence shouldn't be the null hypothesis when unique, diagnostic characters are present. Tyrannosauroid pubes have several unique characters, and the Benson et al. note, although short, made all of the reasonable comparasions and drew the most defensible conclusion. An Australian tyrannosauroid makes sense biogeographically. Laurasian-only tyrannosauroids were becoming an anomaly in an Early-mid Cretaceous world full of cosmopolitan taxa (neovenatorids, sauropods, ornithopods). I predict that further southern tyrannosauroids will be found soon, which will corroborate Benson et al.'s conclusions.
I admit to having been surprised, over the last few years, to see just how ancient and wide-ranging tyrannosauroids have become.
Steve,
Until recently, it was still assumed that despite being a ceratosaur, the noasaurid Noasaurus leali had a hyperextensible second toe. The phalanx/ungual association is now invalidated with the proposal that the ungual is manual, but the phalanx may continue to be pedal. The development of a large ventroposterior "heel" to the phalanx, the massively asymmetrical articular surface, and the apparently higher radius of rotation around the distal articulation still implies it's form is deinonychosaur. This is in addition to the finding of Late Cretaceous deinonychosaurs in South America.
The problem with the Oz "despot" is that is appears to be nested within a group of near-tyrannosaurid taxa, which renders a deep ghost lineage to all non-tyrannosaurids to the Early Jurassic, just as the Oz "lystrosaur" implies a massvbely deep lineage extension for dicynodonts.
Thanks Jaime, your last paragraph (post #39) was more or less what I was getting at, only from a different angle.
I'd love to see it given a traditional Australian name; perhaps in the tradition of the crocodilian Baru, Burrunjor rex? (sadly, the name is overly co-opted by sensationalist cryptozoologists* to describe a large theropod apparently running around the outback. The zero evidence kind of works against it..)
* as opposed to more moderate ones, like Darren, who advocate a critical examination looking at the evidence.
Finback:
'Demon Dinosaur of Doom'?
Or how about 'Mad Max'? This is an Australian member of an essentially American family; it's rather small in stature but bloodthirsty; it has affinities to tyrant dinosaurs... Sounds like a description of Mel Gibson to me.
Jaime A. Headden wrote: "The problem with the Oz "despot" is that is appears to be nested within a group of near-tyrannosaurid taxa, which renders a deep ghost lineage to all non-tyrannosaurids to the Early Jurassic, just as the Oz "lystrosaur" implies a massvbely deep lineage extension for dicynodonts."
Why?
The Australian tyrannosauroid does not imply these deep ghost lineages: it could be a derived Laurasian lineage that crossed the Thethys along the insular arches between Laurasia and Gondwana in the Early Cretaceous, and then radiated mainly into East Gondwana. I fear most of you underestimate the importance of these biogeographic models and consider the Gondwana fossil record only from a "Patagonian point" of view. Rember that most of the African, Indian and Australian frossil record of Cretaceous theropods is yet unknown, and the well known faunas from Patagonia cannot be used as "standard for Gondwana" only because we know almost only them.
As showed in the neovenatorid paper, we have to reject the old simplicistic view of the biogeography of Cretaceous terrestrial vertebrates as a dogmatic Laurasia-Gondwana dichotomy.
In my opinion, theropods were more able to swim than usually depicted, so, they were able to colonise the system of islands present in the emerging Alpine-Himalayan region linking Laurasia and Gondwana.
Andrea,
Not that I disagree, but so far, the concept of a intromittent land bridge of islands stepping-stone the path to Oz from Laurasia is unsupported. It is possible, sure, but virtually all other taxa on the continent so far seem to be relictual of former contacts or transients during more immediately intromittent contacts (like Antarctica).
Correct me if I'm wrong, of course.
Were there more taxa that implied a direct contact with Laurasian taxa that cannot be found in Antarctica or South America or Africa & India/Madagascar and their potentially closer Laurasian contacts, I would speculate this idea would be better received by glorified sceptics like myself.
You mention the neovenatorid lineage, which had an established and more recent association in Gondwana during its breakup. This doesn't invalidate my questioning about the ghost lineage linking this fossil to tyrannosauroids, but it is ill-supported as such fossils are unknown. I would therefore be more sceptical on the basis of the absense of data than assume the data is merely absent, but the conclusion correct despite it.
Consider this:
Genusaurus is an Early Cretaceous abelisauroid from Europe that has been linked by Carrano and Sampson (2008) to Late Cretaceous noasaurids from Gondwana (in my opinion, it may be closer to Carnotaurines). It shows that an Early Cretaceous theropod from an Hemisphere may be linked to a Late Cretaceous lineage from the other Hemisphere. It's the same situation of the Australian pubis, but inverted geographically. Nobody considers it a bizarre hypothesis.
Given the presence of abelisauroids in Early Cretaceous of Europe (Genusaurus) linked to Late Cretaceous taxa from Gondwana, why the presence of an Early Cretaceous tyrannosauroid in Australia linked to Late Cretaceous taxa from Laurasia should be so unexpected?
I agree that more data are needed, but I see no real objections to the tyrannosauroid status of that specimen. Is assuming it's a new Gondwanan lineage convergent in pubis morphology with tyrannosauroids more parsimonious than accepting a more intense faunal interchange between Laurasia and, at least, East Gondwana?
Andrea,
I, too, see no difficulty putting the tyrannosauroid clade (generally) into Australia. As I stated, it is possible to walk a taxon over there from the conventional land bridges. But currently, no data supports this as there are no comparative intervening fossils which tell us otherwise.
On another point, the cross-over of Australian taxa ("abelisauroid," "allosauroid," and some interesting ornithischian subgroups which I won't detail for particular reasons) do seem to cross over from South America (we lack the Antarctica fossils to directly link them, but the SA-Oz link seems relatively secure in other taxa, as well), which provides a strong biogeographic connection that so far doesn't seem to be contradicted (until now, and that's if we think the new fossil indicates a less-probable direclt OZ/Laurasia link).
I figured I'd respond to this separately, to cut down on my posts' size:
Andrea wrote:
Genusaurus is an Early Cretaceous abelisauroid from Europe that has been linked by Carrano and Sampson (2008) to Late Cretaceous noasaurids from Gondwana (in my opinion, it may be closer to Carnotaurines). It shows that an Early Cretaceous theropod from an Hemisphere may be linked to a Late Cretaceous lineage from the other Hemisphere. It's the same situation of the Australian pubis, but inverted geographically. Nobody considers it a bizarre hypothesis.
I have my opinions on Genusaurus, and a whole group of abelisauroids, that would have been a nice paper to write were it not for my utter lack of time to do so.
We find a swath of abelisauroids that are Jurassic or potentially even Cretaceous relics of cross-overs and nascent contacts with other continents in Africa, forming land bridges up inyo Europe. These taxa apparently used Africa and Indo-Madagascar as points of interest, tourists from South America or wherever, but got caught in Africa and decided to try a European invasion a la Hannibal when the opportunity presented itself. We do not find other Laurasian cross-overs in this time, from North america or eastern Asia (proper), crossing over to Europe into Africa into South america and all the way down into Antarctica and then into Australia, just to leave a relic that would have had to start its journey in the Early Jurassic. It's possible this is true, and the time of fauna in abelisauroids (such as a link between Quilmessaurus and Genusaurus, the various noasaurs across Gondwana, and the "elaphrosaurs" that come dangerously closs to crossing into Europe by proximity.
Similarly, when we get carcharodontosaurs and "neovenatorids" making this same connection, they do so without making jumps into other Laurasian continents. The biogeography is fairly consistent with a Africa/Europe link in the Late Jurassic/Early Cretaceous, suggesting that the European taxa of these groups are the invaders, rather than the invadees. This should even be true of Acrocanthosaurus, if it's anything like a carcharodontosaur/neovenatorer -- yet it only implies a link to North America during a time when there were less definitive contacts between Gondwana and Laurasia save for the Arica/Europe link, and then a Europe/NA link; we can get a tyrannosaur transfer, but the data does not indicate such taxa exist yet, implying that the taxa were not present (as we know them).
I should note that I have nothing to say about whether this is a tyrannosauroid or not; the data makes the question intriguing and I am certainly intrigued. The paper was a fine piece of work in making its case, and it does so morphologically. Solving the biogeographic puzzle is the big job here, I think, and something that some readers (like Steve Brusatte) have shown some interest in.
Maybe 237ma there was a Triassic link, since lost?
http://www.scotese.com/newpage8.htm
Intresting article, though it would be hard to explain how a tyrant that was closer to the ancestry of tyrannosaurs of Asia and Western N. America got from the land of Oz to those places (unless it had sprouted wings and got there. Or more realistically it could be another large, southern raptor, or even a abelisaur, that evolved tyrannosaur-like hip).
BTW, since you [Darren] made a whole series of baiburasas, ever thought of doing a series on Tyrannosauriods? Or even coelurosaurs in general?
Lost very soon after. In the Late Triassic, Thailand already had the same fauna as the rest of Pangaea, meaning that the whole thing had already collided with it.
Found a good picture of Antarctic tectonic splits with geologic data (without the mercator equatorial bias):
http://www.nap.edu/books/12168/xhtml/images/p20014a96g127001.jpg
Sorry, should have included the book link:Antarctica, A Keystone in a Changing World
http://www.nap.edu/openbook.php?record_id=12168&page=127
Well, indirectly. It shows the age of the oceanic crust around Antarctica. (Continental crust is shown in black, basalt outflows in brown.)
It confirms what I've been saying, as far as I can see.