A story of cheeks, beaks, feathers, bizarre theropod dinosaurs, and truly, truly amazing fossils....
Yesterday I made a special visit to the University of Portsmouth's School of Earth and Environmental Sciences in order to attend a talk by, and meet, Professor Altangerel Perle, the famous Mongolian palaeontologist and finder of awesome Cretaceous dinosaur fossils. From the 1970s onwards, Perle has personally excavated and described such incredible fossils as the fighting Velociraptor and Protoceratops, the alvarezsaurid Mononykus, the unusual giant dromaeosaurid Achillobator, and the therizinosauroids Erlikosaurus* and Segnosaurus. We spoke about Deinocheirus (no new fossils as of yet), I showed him a new taxon of Brazilian theropod and, I am ashamed to say, I even asked him about the Mongolian death worm. He had heard of it, but seemed pretty confident that it was mythical. Perle (this is not pronounced 'pearl' as I had imagined, but more like 'per-lay') can speak English (and Russian) but requires assistance these days, in part because of a stroke he suffered within recent years. He was accompanied by Batbayar, a Mongolian helper and translator, and by two representatives of the Scientific Exploration Society (SES), the group whom Perle has led into the Mongolian wilds in quest of fossils, flora and fauna. We were invited to come along with them on their next Mongolian expedition. I'd love to, of course, if only I had a spare few thousand pounds.
* Erlikosaurus was later spelt Erlicosaurus in several publications. The former spelling, however, is older (Barsbold & Perle 1980) and thus has priority.
All of this was memorable enough. However... Perle brought along some fossils with him. Real fossils. The ACTUAL HOLOTYPES of the therizinosauroids Erlikosaurus andrewsi and Segnosaurus galbinensis. Oh. My. God. I could not believe it. As you can see from the accompanying photos, we spent a lot of time examining, holding (carefully!!) and manipulating (very carefully!!) these stunning, three-dimensional remains ('we' = me, Richard Hing, Mark Witton and [much later in the day] Graeme Elliott). In the adjacent image, I'm holding the jaw of Segnosaurus, with Perle and Batbayar behind me (Perle is on the left). In the photo at the top of the page, Mark and Graeme are - carefully - getting the jaw of Erlikosaurus into articulation. To see and hold specimens that you 'know' from the literature is, for me, tremendously emotional, almost disturbingly so. It's like meeting a famous person that you admire or idolize. From a more nerdy point of view, finally you have the chance to check the tiny details that you've always been curious about, or see for yourself the bits and pieces that people have argued about or interpreted differently.
Therizinosauroids are far better known nowadays that they were in the late 1970s when Perle first discovered them, of course. In recent years we've seen the description of the small basal form Beipiaosaurus from the Yixian Formation of Liaoning Province, of Alxasaurus from the Bayin-Gobi Formation, and of the North American taxa Nothronychus from the Moreno Hill Formation of New Mexico and Falcarius from the Cedar Mountain Formation of Utah*. Several new Asian taxa, including Erliansaurus and Neimongosaurus from the Iren Dabasu Formation, have also been described. These specimens and others have added considerably to our understanding of therizinosauroid anatomy and evolution. Therizinosauroids were of uncertain affinity during the 1970s and 80s but new work and new data has shown that they are not close relatives of ornithischians or plateosaurs as formerly proposed, but are in fact highly peculiar maniraptoran theropods close to oviraptorosaurs [adjacent image of Jim Kirkland and Falcarius skeleton from here].
* On the subject of American therizinosauroids, Perle told me that John Ostrom had once showed him a manual phalanx from the Morrison Formation that seemed to be from one of these dinosaurs. I can't recall reading about such a record, but given that the Cedar Mountain Formation (source of Falcarius) overlies the Morrison Formation in places, I wonder if the provenance data was accurate.
Therizinosauroids were long-necked, and their elongate cervical vertebrae share a number of unusual features with the cervical vertebrae of oviraptorosaurs. They had long arms with powerfully muscled humeri and long, tridactyl hands sporting long, laterally compressed and weakly curved claws. In the biggest member of the group, Therizinosaurus, some of the hand claws were over 60 cm long, and don't forget that this is the length of the bony claw; not of its attached keratin sheath. The pelvis is wide, with the anterior parts of the iliac blades flaring outwards to support a massive gut, and the pubic bones are rotated backwards, and not projecting forwards as is typical for saurischian dinosaurs. Their feet are remarkably short and stocky and highly unusual in that the first digit - the hallux - was enlarged and fully in contact with the ground, making the foot functionally tetradactyl (and thus unlike the bird-like functionally tridactyl foot of other theropods). Their hindlimb proportions (where the tibia is nearly equal in length to the femur) also indicate that they were poor runners. The tail was short (though read on), with the nearly complete tail of Neimongosaurus consisting of just 23 vertebrae.
Overall then we have a picture of a remarkably odd group of long-necked, broad-bellied, short-tailed, stocky-legged dinosaurs with long hand claws, and short, tetradactyl feet. Combined, these features suggest that they were relatively slow moving, and probably herbivorous, relying on hindgut fermentation. This idea is supported by skull anatomy, as we'll see in a moment. Falcarius was superficially different from later therizinosauroids in having a vertical pubis and in being long-tailed and with a more typical functionally tridactyl foot (Kirkland et al. 2005). Overall it would have looked more gracile than later, more specialized therizinosauroid taxa. Incidentally, Falcarius is of special relevance to me as it was initially claimed to be the same animal as Thecocoelurus, an enigmatic theropod from the Isle of Wight that Dave Martill and I interpreted as an oviraptorosaur (Naish & Martill 2002). The two are not the same by the way, nor is Thecocoelurus a therizinosauroid.
Therizinosauroids were generally known as segnosaurs in the older literature, and an unfortunate complication for the group's taxonomy is that Clark et al.'s (2004) phylogenetic definition for the group defines it as 'the least inclusive clade containing Therizinosaurus and Beipiaosaurus' (p. 153). If this definition is followed, then Falcarius is not a member of Therizinosauroidea, nor are any other taxa more basal than Beipiaosaurus (a Lower Jurassic lower jaw, named Eshanosaurus deguchiianus, has been regarded as the oldest known therizinosauroid but is more likely a misidentified plateosaur mandible).
The Erlikosaurus skull that I and Graeme are posing with in the adjacent photo is one of the best therizinosauroid specimens of them all (I don't normally put my arm round Graeme, but it was a special occasion). Its preservation is just amazing and, while broken in places, even the thinnest-boned bits of the skull are complete or nearly so. First described, in Russian, by Perle (1981), it was later redescribed in full detail by Clark et al. (1994). The nostrils are huge and the sharp-edged toothless premaxillae form a broad, rounded beak that would almost certainly have been covered in beak tissue in life. Clark et al. (1994, p. 6) described bony denticulations along the beak margin near the midline, similar to those present in oviraptorosaurus. There are tiny projections in this region, but I couldn't convince myself that they were real denticulations and not the result of breakage. Teeth line the maxillae; the teeth are lanceolate, transversely compressed and with serrated crown edges.
The lower jaws form a U-like shape when articulated and teeth extend much further rostrally than they do in the cranium, with only those parts of the dentaries on either side of the symphysis being edentulous. Atypically for a theropod, the teeth in both the upper and lower jaws are inset medially and low ridges run parallel to the tooth rows on the outside surfaces of the jaws. Paul (1984) argued that these inset tooth rows and lateral horizontal ridges demonstrated the presence of cheeks flanking the sides of the mouth. In recent years Larry Witmer and colleagues have argued that these features don't necessarily indicate the presence of cheeks, but might instead show that dinosaurs equipped with these features had beak tissue lining the sides of their jaws, in which case (1) they looked tremendously freaky and (2) were unable to retain food in their mouths [adjacent image of cheekless Leptoceratops from here]. The notion of cheeked therizinosauroids hasn't been discussed in the literature since Paul's 1984 paper, in part because new data confirms that therizinosauroids are coelurosaurian theropods, a clade in which cheeks have otherwise been unsuspected. However, Greg Paul has pointed out (though not in print so far as I know) that cheeks are sometimes present in birds, specifically in Californian condors Gymnogyps californianus [image below from here]. Therizinosauroids may therefore have possessed both cheeks and a beak, though this remains speculative.
The toothless beak, lanceolate teeth and possible evidence for cheeks all agrees with evidence from the postcranial skeleton that therizinosauroids were predominantly herbivorous, perhaps supplementing their diet with fungi and animal material on occasion. It has been suggested that these dinosaurs caught fish, dug up ants and termites or harvested wasp nests, but none of these ideas are supported by morphological details.
Perle also brought along the holotype lower jaws of Segnosaurus galbinensis, part of GIN 100/80: a specimen that includes fore- and hindlimb bones, fragmentary vertebrae and a pelvis (Perle 1979). This animal is bigger and altogether different from Erlikosaurus in having a lower tooth count, differently shaped teeth, a far more strongly decurved lower jaw tip and other differences. Furthermore, a little bit more of Segnosaurus is known than usually reported, as Perle brought along a fragment that I've never seen reported in the literature: a Segnosaurus basioccipital. Essentially identical to the basioccipital of Erlikosaurus, it was nevertheless substantially larger.
Based on their position within coelurosaur phylogeny - they are surrounded by oviraptorosaurs, birds and deinonychosaurs (all of which are known to possess indisputable vaned feathers on their limbs and tails) - we would predict that therizinosauroids were feathered. Little Beipiaosaurus preserves filamentous integumentary structures on its body and limbs but isn't well-preserved enough to confirm that remiges and rectrices were present, though - again, based on related taxa - they probably were. The presence of a pygostyle-like structure in Beipiaosaurus (Xu et al. 2003) strongly suggests that it sported a rectricial fan of feathers, as did members of various other maniraptoran clades. Does this mean that we should imagine all therizinosauroids as feathered, even the giants like Therizinosaurus? In the absence of evidence to the contrary I would say yes, no matter how outlandish the concept of a feathered behemoth weighing several tons might seem to be. It is possible though that such big forms retained, say, remiges and rectrices (plausibly used for visual display), but lost the integumentary covering on the body [in the adjacent image, Mark holds court while a throng of enthralled students, and palaeobotanist Bob Loveridge, look on. Yes, that's Mark Witton, the pterosaur worker].
But would there really have been selective pressures encouraging the loss of a feathery integument in therizinosauroids? While people generally imagine the Mesozoic world to have been a thermally stable hothouse where big insulated animals would have faced meltdown, we're actually not sure that this was true and in fact some studies indicate otherwise. Particularly intriguing is that Cretaceous continental interiors such as those of Mongolia may not have been that warm, and apparently subjected to cold winters with strong winds (Barron & Washington 1982, Sloan & Barron 1990, Sellwood et al. 1994).
Clearly, these perpetually interesting bizarre dinosaurs leave us with a lot of unanswered questions. It was a great day, a great honour to meet Prof. Perle, and we had a great time in getting to see such truly extraordinary fossils.
Refs - -
Barron, E. J. & Washington, W. M. 1982. Cretaceous climate: a comparison of atmospheric simulations with the geological record. Palaeogeography, Palaeoclimatology, Palaeoecology 40, 103-133.
Barsbold, R. & Perle, A. 1980. Segnosauria, a new infraorder of carnivorous dinosaurs. Acta Palaeontologica Polonica 25, 187-195.
Clark, J. M., Perle, A. & Norell, M. A. 1994. The skull of Erlicosaurus andrewsi, a Late Cretaceous "segnosaur" (Theropoda: Therizinosauridae) from Mongolia. American Museum Novitates 3115, 1-39.
- ., Maryanska, T. & Barsbold, R. 2004. Therizinosauroidea. In Weishampel, D. B., Dodson, P. & Osmolska, H. (eds) The Dinosauria, Second Edition. University of California Press (Berkeley), pp. 151-164.
Kirkland, J. I., Zanno, L. E., Sampson, S. D., Clark, J. M. & DeBlieux, D. D. 2005. A primitive therizinosauroid dinosaur from the Early Cretaceous of Utah. Nature 435, 84-87.
Naish, D. & Martill, D. M. 2002. A reappraisal of Thecocoelurus daviesi (Dinosauria: Theropoda) from the Early Cretaceous of the Isle of Wight. Proceedings of the Geologists' Association 113, 23-30.
Paul, G. S. 1984. The segnosaurian dinosaurs: relics of the prosauropod-ornithischian transition? Journal of Vertebrate Paleontology 4, 507-515.
Perle, A. 1979. Segnosauridae - a new family of theropods from the Late Cretaceous of Mongolia. Sovmestnaya Sovetsko-Mongol'skaya Paleontologicheskaya Ekspiditsiya, Trudy 8, 45-55 [in Russian].
- . 1981. A new segnosaurid from the Upper Cretaceous of Mongolia. Sovmestnaya Sovetsko-Mongol'skaya Paleontologicheskaya Ekspiditsiya, Trudy 8, 50-59 [in Russian].
Sellwood, B. W., Price, G. D. & Valdes, P. J. 1994. Cooler estimates of Cretaceous temperatures. Nature 370, 453-455.
Sloan, L. C. & Barron, E. J. 1990. Equable climates during Earth history. Geology 18, 489-492.
Xu, X., Cheng, C., Wang, X. & Chang, C. 2003. Pygostyle-like structure from Beipiaosaurus (Theropoda, Therizinosauroidea) from the Lower Cretaceous Yixian Formation of Liaoning, China. Acta Geologica Sinica 77, 294-298.
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Hi Darren:
Well I am extremely envious, but had a question about one credit you gave Dr. Perle. My understanding is that the fighting dinosaur specimens were found by the Polish-Mongolian expeditions. Was he a member of that?
Bruce
Very Cool, and it looks like you had a good time. Learning and fun - it don't get no better than that!
Okay, so granted that these were herbivores, but the inane question for the day is...where did they fit into the ecology? Browsers? grazers? Can we even piece together something of the paleoecology of the Cretaceous or is it doomed to fail?
Thecocoelurus isn't a therizinosaur? Since when!
Who said it was?
On the subject of Therizinosaurus having feathers, perhaps it had them for the cold winter, and moulted in the spring, leaving only short or no feathers on its body area in the warmer months?
You lucky %#&*!@%$ ;)
Don't suppose Perle (who I've always thought of as per-lee; guess we were both wrong) brought Segnosaurus postcrania along? Those vertebrae, forelimb elements and femora are pretty elusive.
Hi Mickey. Nope, no postcrania. By 'elusive' I presume you mean that (most of) the material has yet to be adequately figured, not that it's hard to find in the collections of the Mongolian Academy of Sciences...
a Lower Jurassic lower jaw, named Eshanosaurus deguchiianus, has been regarded as the oldest known therizinosauroid but is more likely a misidentified plateosaur mandible.
I know we've been through this before, but just for the
record ...
Yes it has been suggested in print that Eshanosaurus is a prosauropod rather than a therizinosaur; but AFAIK only ever as a pers. comm., with the bare minimum of justification: "it has been noted that the teeth in Zhao and Xu's jaw have a medial ridge, which is present on at least some prosauropod teeth, but is completely unknown in therizinosauroid teeth" (Kirkland and Wolfe 2001:412).
The reidentification may or may not be right, and it's certainly tempting given the much better fit with stratigraphy if that identification is accepted. But Xu Xing still thinks it's a therizinosaur; and Richard Butler, who's also seen the material, also leans towards a therizinosauroid identity.
So even though it's been pointed out (ahem, Taylor 2005) that the reidentification greatly reduces the ghost lineages for Therizinosauroidea, Maniraptora, Coelurosauria and even Avetheropoda, this is not an open and shut case.
Hello Mr. Naish.
Sometimes I've read this blog though I am not so good at English.
It is very interesting the topic on dinosaur's beak and cheek.
Ah the great fleshy oral connective tissue debate.
The cheekiness, or lack thereof it all!
Non-avian dinosaurs are quite fustrating in this respect.As an illustrator on another thread list stated,That hadrosaurid mummy 'Leonardo' is so fustrating because it provides detailed preservation of everything _but_ the face!
Personally, I like the concept of dinosaurian herbivores
without cheeks, the weirder the better.
Ah well, I'm not THAT jealous now. And yes, I only meant the published information is limited. I certainly hope the material is still available. So many holotypes are turning up at least partially missing nowadays.
Great summary of my favorite dinosaur group. You are blessed to have held the original specimens themselves.
On the cheek issue...Paul Barrett pointed out to me that at least one ankylosaur skull has been found with osteoderms laying alongside the teeth. The obvious interpretation is that the osteoderms were embedded in the skin of the cheeks. And if those jaw characters go with cheeks in ankylosaurs, then there's no reason to think they didn't do the same in all the other ornithischians.
The "Beaks, Cheeks, or Freaks" (seriously, that was the title of the talk) thing has never been rebutted in print, probably because it's never appeared in print. And that talk was a good while ago--five or six years at least. I can't help wondering if the authors thought better of it.
That Eshanosaurus sure is a pain in the ass. People keep going and looking at it and then assaulting us with their informed opinions! That's just not how paleontology works!
Thanks Matt. The ankylosaur with the big bone covering its cheek region is Panoplosaurus - I use a photo of the key specimen in my dinosaur talks. Of course Barrett and Upchurch have just (in the Chinshakiangosaurus paper) restated the case for cheeks in sauropodomorphs, and this provides indirect support for the concept of cheeks in some theropods. As Paul Barrett has noted in this talks, all of this means that we need a less, err, rigorous interpretation of the extant phylogenetic bracket concept at times. Essentially, the bracket can be violated by novelty.
All of this means that we need a less, err, rigorous interpretation of the extant phylogenetic bracket concept at times. Essentially, the bracket can be violated by novelty.
Say it ain't so! You mean evolution involves freaking' homoplasy?
You beat me to to the punch in mentioning the new Chinshakiangosaurus paper. For those who've not seen it, the reference is:
The abstract, and the PDF for those with access, is at
http://dx.doi.org/10.1017/S0016756806003062
The cheek osteoderm of Panoplosaurus has been known for a long time. It's mentioned in The Field Guide to the Dinosaurs from 1983. Phylogenetic bracketing should be used like the parsimony principle: to decide between hypotheses that explain the data equally well.
Come on! English has the worst orthography of any language that uses an alphabet or syllabary.* So, never assume that anything is pronounced like in English. He isn't Perl or Perlii. If you know what Spanish is like, its use of the Latin alphabet is much more representative.
* Seriously. It's worse than Irish (which, I'm told, "does at least follow rules"), worse than Tibetan, worse than Mongolian-in-the-Mongolian-script, worse than French (where you have plenty of ways of spelling a given sound, but only one way of pronouncing any written word, except for the exceptions), and worse than German (where sometimes vowel length is indicated in one of several different ways, sometimes vowel shortness is indicated, and sometimes neither is indicated so you have to either know the word by heart or use complicated rules to reconstruct it... never mind the clumsiness of sch and a ton more small weirdnesses).
Darren Naish: officially, a bastard ;)
Coolness.
A couple of items: Sereno, like Paul, advocated for cheeked segnosaurs, but this was at an SVP back in the the before time, in the long long ago (1989), when he still supported a "phytodinosaurian" arrangement.
More recently, though, a contribution by Sereno to therizinosaur studies relevant to the discussion: in his "Taxon Search" project, he defines Therizinosauria as "The most inclusive clade containing Therizinosaurus cheloniformis Maleev 1954 but not Ornithomimus edmontonicus Sternberg 1933, Tyrannosaurus rex Osborn 1905, Shuvuuia deserti Chiappe et al. 1998, Oviraptor philoceratops Osborn 1924, Troodon formosus Leidy 1856." So Falcarius would be a therizinosaur, but not a therizinosauroid. At present, the therizinosauroids would be the stump-footed therizinosaurs.
(He claims that Russell 1997 is the source of the name Therizinosauria, but I'll have to double check that Barsbold didn't coin that name in the 1980s...).
Glad to hear that Perle is up and about.
As for a Morrison therizinosaur or close relative: a non-crazy idea, given the YPM 1996 and 1997 vertebrae described by Pete Makovicky (1997. JVP 17:755-757).
In the most recent Journal of Vertebrate Paleontology (26(4):1011-1013), Vickaryous reports the presence of buccal osteoderms in a specimen (AMNH 5381) of Edmontonia as well:
"Unique to the articulated skulls AMNH 5381 and the holotype of Panoplosaurus mirus (NMC 2759) are flat, ovoid osteoderms nested lateral to the tooth rows, between the buccal emargination (dorsally) and the lateral border of the mandible (ventrally). CT scans of AMNH 5381 demonstrate that these buccal ossifications do not fuse to either the mandible or the maxilla. No osteoderms matching the ovoid morphology described above been identified in TMP 98.98.01 or TMP 2000.12.158."
Essentially, the bracket can be violated by novelty.
Violated. I like that.
NATURE: Cheeks! Feathers! Endothermy! Arboreality! Electroreceptors! Poison glands! [down on its knees, belting it out rock-star style] Freakin' BAAAAAAAAATS!!!
EPB: [shudder] I feel so violated.
Thecocoelurus isn't a therizinosaur? Since when!
Posted by: Simon M. Clabby | February 21, 2007 05:06 PM
Who said it was?
Posted by: Darren Naish | February 21, 2007 05:40 PM
Kirkland, Zanno, DeBlieux, Smith and Sampson, 2004. A new, basal-most therizinosauroid (Theropoda: Maniraptora) from Utah demonstrates a Pan-Laurasian distribution for Early Cretaceous therizinosauroids. JVP 24(3).
At least according to http://staff.washington.edu/eoraptor/Therizinosauroidea.htm
David: stop being so bloody European :)
Simon: Kirkland et al. redeemed themselves in the Falcarius paper by not even mentioning Thecocoelurus. Having put material of the two taxa literally side by side, I can confirm that there is (presently) no reason to think that Thecocoelurus is a therizinosauroid. More to come on this issue when Naish & Martill (in press) appears.
Thanks to everyone else for assorted musings.
I knew I forgot something in my linguistics rant: the name Segnosauria. What has happened to it? Has nobody given it a phylogenetic definition? It would be the obvious choice for everything closer to Segnosaurus than to Oviraptor (and whatever else). The-ri-zi-no-sau-ro-i-de-a... what a mouthful.
Also, what has happened to the original usage of Therizinosauroidea? The paper that coined that name used it for Alxasauridae (monotypic) + Therizinosauridae, and the paper that includes the phylogenetic definition seems quite arbitrary at choosing Beipiaosaurus as an anchor.
Tracy Ford has an interesting imterpretation regarding the osteoderms lining the jaws of *Panoplosaurus* at his
website.
http://www.dinohunter.info/
A quicker view for the lazy.
http://www.fossil.org.cn/Museum/images/Panoplosaurus41242.jpg
I believe the term "segnosaurinae" is still used to describe a few Mongolian taxa (Elrikosaurus, Alxasaurus, Segnosaurus), although they are within a greater Therizinosauridae. I'm not sure if Falcarius sits within the Therizinosauridae or is an outgroup to it. The big guy, Therizinosaurus, currently resides in his own subfamily, the Therizinosaurinae.
Of course, the last time I read anything about the entire family was "The Complete Dinosaur" back in the early 90's. Does anybody have a good overview paper of the entire family and its phylogeny? Has something like that even been published?
Great post. Perle is going to be here next week, which should be fun.
As a follow-up to Mike's post, Paul Barrett and I examined Eshanosaurus last time we were in Beijing. Both of us agreed with Xu Xing's therizinosaur identification - Paul certainly doesn't think it's a prosauropod (and he's the sauropodomorph expert, not me).
Thanks Richard: that is the most significant and useful pers. comm. yet produced on controversial Eshanosaurus (and for some reason I had never bothered to ask Paul what his opinion of the taxon is).
Richard, that is some GREAT information. (Okay, I personally don't like it, with all that it implies about divergence dates, but it is great that a sauropodomorph worker got a chance to evaluate it.)
Zach, the most recent overview of the therizinosaurs was Clark, Maryanska & Barsbold's chapter in the second edition of The Dinosauria (2004, U Cal Press).
With regards to Eshanosaurus, I think people should take the lesson of Shuvosaurus/Chatterjeea more to heart. I'm not suggesting Eshanosaurus is some sort of aberrant pseudosuchian, but with such limited material, homoplasy can really bite you in the posterior. OK, so maybe its no sauropodomorph we've ever seen, but calling it a therizinosaur (in fact one that would be more derived than Falcarius) could be a bit premature. Why couldn't it be an aberrant basal theropod? Of course we really need more material to be sure of anything.
Tom Holtz- Did Sereno ever support Phytodinosauria, even in 1989? I know he supported prosauropod segnosaurs, but that's not quite the same.
Zach Miller- There is no reason to separate Segnosaurus, Erlikosaurus and Alxasaurus from Therizinosaurus. Indeed, several characters suggest Therizinosaurus is more closely related to Segnosaurus and Erlikosaurus than the latter are to Alxasaurus.
Randy Irmis- Did Shuvosaurus actually teach us a lesson? Even though it turned out to be a crurotarsan once we could compare it to Effigia, there was no reason besides subjective personal incredulity to synonymize it with Chatterjeea before that. I tend to view the question of how/why you get to an answer as being more important than whether the answer is correct. The same could be said for Revueltosaurus as a crurotarsan or Rahonavis as a dromaeosaurid. The people who say Early Jurassic = sauropodomorph may end up being right, but not for the right reason. I fully expect Eshanosaurus to not be a therizinosaur, but since when should my intuition count as science?
Maybe not in 1989, but in 1984. Back in the Dreamtime. Before he started using phylogenetic nomenclature. When I was two years old (and I think you too).
Of course homoplasy is an issue, and of course Eshanosaurus might with more material turn out to be an aberrant basal theropod, sauropodomorph, ornithischian or even something else: my point (incompletely made in my previous post) is that having seen the specimen, I believe that there is nothing in the available character evidence to contradict Zhao, Xu & Clark's therizinosaur identification. We must take the therizinosaur identification seriously, rather than just dismissing it on stratigraphic grounds.
Mickey: Okay, by '89 (in the post-Gauthier 1986 years) Sereno did not support sauropodomorphs + ornithischians; but as David pointed out he did back in 1984.
To my knowledge he never used the "Phytodinosauria" label, even if he accepted the hypothesis.
Repy to Mickey: I think that Shuvosaurus, Revueltosaurus, and other examples have taught us a lesson - to be sceptical of claims of "the earliest" that are based on very limited material. At least with Shuvosaurus, Long & Murry (1995) did make an argument for its possible synonymy with Chatterjeea. Also, all of these taxa had some characters that were shared with their hypothosized clades, but lacked complete character combinations found in the rest of the members of the group. I fully recognize that this isn't necessarily problematic (most taxa have unique combos of character states), but it should make one skeptical when there is limited material and it constitutes an extremely long range extension.
Richard: I completely agree that stratigraphic evidence alone cannot be used to refute the assignment of a taxon to a particular clade - and that we can't reject a therizinosaur assignment for Eshanosaurus just because we don't like the idea. I would only point out that there are tons of examples where dental characters are more misleading than informative with regards to phylogenetic position (Exhibit A: Revueltosaurus). It is conspicuous that 8 of the 11 characters Xu et al. (2001) use to assign Eshanosaurus to the Therizinosauroidea are tooth characters. A great example is Azendohsaurus and the Madagascar material described by Flynn et al (1999); these were based on dentaries and maxillae, and turn out to be nowhere close to sauropodomorphs, even though the character evidence was completely concordant with a sauropodomorph placement until more material was found.
Relevant to the Eshanosaurus flap is the fact that Larry Witmer has seen the Protoavis material and although he does not think it's a bird, he thinks the braincase is definitely from a coelurosaur (Witmer 2001, 2002). If he's right, Coelurosauria originated in the Triassic, which would extend the ghost lineages for ceratosaurs (if closer to Tetanurae than to coelophysoids), spinosauroids, and allosauroids, at least, and possibly some coelurosaurian lineages depending on who the Protoavis braincase actually belongs to.
Two thoughts follow: Larry Witmer has advocated one or two things that I disagree with, but in general he is the most careful researcher I know. If he says there's a Triassic coelurosaur out there, shouldn't we take him seriously? And if coelurosaurs were around in the Triassic, then an Early Jurassic therizinosaur is not as hard to swallow.
Yeah, yeah, scrappy material, homoplasy, yadda yadda. I'm just sayin'.
-----------
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.
Isn't all the skull and neck material from a drepanosaurid? (An avicephalan, for the sake of the irony!)
Isn't all the skull and neck material from a drepanosaurid?
I think the idea that the cervicals are from a drepanosaurid is plausible, and widely if unofficially accepted. But I hadn't heard that advanced for the braincase.
Here's what Witmer (2001:542-3) had to say:
"The braincase is, in general, that of a small coelurosaur. Indeed, Currie and Zhao (1993:2244) regarded the braincase of the Cretaceous maniraptoran Troodon formosus to be 'amazingly similar' to that of TTU P 9200 [Protoavis]. In fact, many of the bird-like characters pointed to by Chatterjee (1991, 1998)--such as the large auricular fossa, cranial pneumatic recesses, the metotic strut, and the occipitally opening vagal canal--are all widely distributed among coelurosaurs....Regardless of whether or not it is a bird, perhaps the clearest significance of Protoavis is that it shows that there were taxa with coelurosaur apomorphies even older than the Early Jurassic Lufeng therizinosaur (Zhao and Xu 1998), and perhaps even that the divergence of Coelurosauria from other theropods took place before the Early Norian."
Note that he says "taxa with coelurosaur apomorphies" here instead of pulling the trigger and calling it a coelurosaur. However, in reading his 2002 paper I got the impression that he thinks it is a coelurosaur.
As I've been turning all this over in my head, I've been finding it more and more plausible. The Early and Middle Jurassic record is pretty sucky. At least some of these things might have been lurking around. It's a thought-provoking possibility, at least.
Larry Witmer has said on a few occasions that there are some indications that most of the key divergences in dinosaur evolution 'happened on one afternoon in the Late Triassic' (I used this back at him at SVP 1999 when Chatterjee brought out his Maleri 'pachycephalosaur domes'). In part I suppose this is based on the idea that some of the Protoavis material is coelurosaurian. Phil Currie is also on record as saying that the Protoavis braincase material is strikingly coelurosaur-like.
I've mentioned on occasion (e.g., in Dinosaurs of the Isle of Wight) that there are maniraptoran-like teeth known from units as old as the Bathonian, though given rampant homoplasy and the lack of reliability inherent to tooth-based identifications I don't expect this to be widely accepted. Having said that, the stratigraphic position of archaeopterygids still shows that maniraptorans and other 'Cretaceous' coelurosaur clades had appeared prior to the Late Jurassic, in which case we still have looooong ghost lineages and not enough fossils. Bring on those Lower and Middle Jurassic lagerstatte!
Zach, the most recent overview of the therizinosaurs was Clark, Maryanska & Barsbold's chapter in the second edition of The Dinosauria (2004, U Cal Press).
Well, then I'll have to at least read that section at Barnes & Nobel. I've never been a fan of "overview" books. They always seem too textbooky for my tastes. I prefer symposiums.
There are "dromaeosaurine" teeth in Guimarota (Kimmeridgian)... and taxa with such teeth are at present only known within (part of?) Dromaeosaurinae... "Velociraptorine" teeth are also present, but those are plesiomorphic for dromaeosaurids sensu lato.
1 Lagerstätte, 2 Lagerstätten. Regular (...well... one of the many regular ways to make a plural in German, that is).
God, I sound like an idiot in these posts. Has that much changed in three years? Seriously, I said Darren was "blessed" to have held the original specimens.
/facepalm
Darren, do you have any citation for the Maleri pachycephalosaur material?