The last few weeks have been pretty exciting for people interested in theropod dinosaurs…. but then, you could say this about most weeks: new theropods are constantly being published.
Last week saw the publication of the weird, functionally two-fingered, short-footed maniraptoran Balaur bondoc from the latest Cretaceous of the Haţeg Basin in Romania (Csiki et al. 2010) [left foot of Balaur shown here, from BBC News]. When Balaur was alive, the Hateg region was an island, so this was another of those weird, island-dwelling dinosaurs we’ve often hoped would exist. I have a vested personal interest, given that its discovery has implications for work I’ve published on Haţeg maniraptorans (Naish & Dyke 2004).
Seeing publication today (in Nature) is the remarkable new Spanish carcharodontosaurian allosauroid Concavenator corcovatus Ortega et al., 2010 from the Barremian Calizas de La Huérguina Formation of Las Hoyas [life restoration above by R. Martín]. The Calizas de La Huérguina Formation is well known as a rich Lagerstätte (a place where fossils are exquisitely preserved, often including soft tissues traces). It has yielded several early bird fossils, the multi-toothed ostrich dinosaur Pelecanimimus, and many other neat fossils.
Concavenator is represented by a near-complete, articulated skeleton (about 6 m long) and is in excellent shape. As usual with new dinosaurs, it’s already much-discussed all over the blogosphere (Ed Yong’s take at NERS here).
Two things in particular make this animal really interesting.
Allosauroids with proto-feathered arms?
The big deal about Concavenator – the one thing that probably near-guaranteed its publication in Nature – is that it preserves a row of small bumps on its ulna that look very similar to the ulnar papillae (or quill knobs) present on bird ulnae [see image below, borrowed from NERS]. In birds, these bumps anchor the ‘roots’ of the remiges, the large, vaned feathers that form the main surface of the wing. We’ve already known for a while that these structures aren’t unique to birds, as they’re present in at least some dromaeosaurs (Turner et al. 2007).
The structures in Concavenator are well-defined and arranged in a definite line, and Ortega et al. (2010) conclude that these are most likely homologous with quill knobs: rather than possessing true feathers, the epidermal structures that grew from these knobs in Concavenator may have been short, stiff filaments. Could this mean that feather homologues first evolved in the neotetanuran common ancestor (the theropod that gave rise to both coelurosaurs and allosauroids), or is this more evidence indicating that quill-like structures were present throughout Dinosauria? As you’ll know, the possibility that the integumentary structures of theropods are homologous with the quills of some ornithischians, and even with the pycnofibers of pterosaurs, has been mentioned several times.
However, I admit to being slightly sceptical. Firstly, the bumps of Concavenator are way up on the lateral side of the ulna, not down close to (or on) the bone’s posterior border as they are in birds (and dromaeosaurs). Secondly, the bumps in Concavenator seem to be irregularly spaced, whereas true quill knobs tend to be spaced quite evenly. Ok, a ‘prototype’ stage may well have existed at some point, so differences like this are certainly not ‘killer’ points.
Thirdly, animals sometimes have weird, irregularly spaced tubercles arranged in lines on various of their bones, typically located on intermuscular lines (they presumably represent partially ossified attachment sites for tendinous sheets or similar structures): I’ve seen them on mammal bones and on a theropod tibia (specimen MIWG.5137, illustrated in Text-Fig. 9.29 of Naish et al. (2001)). In view of the differences apparent between the structures of Concavenator and true quill knobs, and the fact that a plausible alternative explanation exists, I hope you understand my scepticism. You may well argue that interpretation of these structures as prototype versions of quill knobs is more parsimonious. Maybe it is.
Poor, neglected Becklespinax
The second really interesting thing about Concavenator concerns the neural spines on its dorsal vertebrae. Naturally, we tend to find things particularly interesting when they overlap with our own special interests. One of the dinosaurs I worked on for my PhD was Becklespinax altispinax, a mid-sized theropod from the Hastings Group rocks of East Sussex, southern England. It’s always been a bit of an enigma, and I discussed it at reasonable length in this Tet Zoo article from 2007 [Becklespinax holotype shown here, as illustrated by Richard Owen in the 1850s]. I’ve suggested that Becklespinax might be an allosauroid; if it is close to (or even congeneric with) Concavenator (read on), this identification would be correct, but it would also mean that, within Allosauroidea, Becklespinax is a carcharodontosaur, not a sinraptorid as I’ve proposed.
Of the three articulated Becklespinax vertebrae, the two more posterior ones (which I identified as the 10th and 11th vertebrae) have taller spines than the first. And note that these are posterior dorsal vertebrae (Naish 2006, Naish & Martill 2007), not anterior dorsals as has been generally assumed.
In my 2006 thesis, and in a paper that reported some of the results of this work (Naish & Martill 2007), I suggested that Becklespinax might have looked really stupid: that it might have had a tall ‘sail’ restricted only to the posterior part of the back and sacral region. My reconstruction (which was included in Naish & Martill (2007), and was used online in the 2007 Tet Zoo article) shows this possibility [it's B in the adjacent image]. An alternative idea is that Becklespinax had a continuous sail, in which case the short first neural spine must represent breakage [A, in adjacent image].
What interests me in particular about Concavenator it that it essentially vindicates my stupid suggestion: in this theropod, the 11th and 12th dorsal vertebrae have really tall neural spines, five times taller than the centra. The spine of the 10th vertebra is shorter, but it’s still taller than the preceding 9 dorsals. While I assumed – I would say quite reasonably – that Becklespinax had tall sacral neural spines, Concavenator has really short ones that don’t even make it over the dorsal edge of the ilium. So, Concavenator had a short, tall sail (or hump) that rose abruptly from the posterior part of the back, and was restricted to this part of the back alone. As is obvious from Raul Martín’s excellent life restoration [used at very top], it would have made the animal look like it had a dorsal fin [image below - from NERS - shows Ortega and colleagues working on the spectacular Concavenator holotype].
While I identified the tall-spined vertebrae of Becklespinax as vertebrae 10 and 11, I could easily be off by a position or two, so identification of the three Becklespinax vertebrae as vertebrae 10-12 works fine too. We don’t know anything about the sacral vertebrae of Becklespinax, but it’s obviously like Concavenator in having tall neural spines on those posterior dorsal vertebrae, and in having a neural spine preceding the two tall ones that was also tall, but not as tall. Ortega et al. (2010) noted that Concavenator is unique in having elongate neural spines on just two of its dorsal vertebrae, but they didn’t discuss the possibility that Becklespinax might have a similar condition, nor did they acknowledge my reconstruction where Becklespinax was given a short, tall sail in the posterior dorsal region (Naish & Martill 2007). This should have been mentioned and cited in their paper, but I can live with it. This sort of thing has happened before.
Becklespinax and Concavenator are further alike in lacking pneumatic fossae on the centra of their dorsal vertebrae, and they seem to be similar in size, too (the centra of Becklespinax are between 75 and 84 mm long, and the tallest neural spine is 350 mm tall; judging by the scale bars, the measurements are about the same in Concavenator). They’re also fairly close stratigraphically and geographically; indeed, the possibility that the Calizas de La Huérguina Formation and Wealden Supergroup might share certain faunal elements has been suggested on a number of occasions.
Given that Concavenator and Becklespinax are so similar, we have to wonder if they’re the same animal. Given that Becklespinax is only represented by three dorsal vertebrae (some other material was mentioned during the 1850s, but it seems to be lost), it’s not possible to be absolutely confident about this, even if they are identical in the anatomy of their posterior dorsal vertebrae (and note that the configuration of neural arch laminae and fossae – well known in Becklespinax because these areas are totally exposed (Naish 2006, in press) – isn’t yet clear for Concavenator).
I would say that circumstantial evidence counts against them being the same species: Becklespinax is (most likely) from the Valanginian, whereas Concavenator is from the Barremian, and is hence about 10 million years younger [the stratigraphy of the Wealden Supergroup, shown above, should help give you some perspective on where the Valanginian and Barremian are with respect to each other]. Dinosaur species don’t, as a rule, seem to have lasted for more than a couple of million years. Genera, on the other hand, do seem to have durations of 10 million years (or more) in cases*, so it does remain plausible that Concavenator is, after all, a species of Becklespinax. They may differ in that the neural spine apices of Becklespinax are transversely thick and robust (this is, in fact, one of its potentially diagnostic features), but I can’t tell from the paper whether Concavenator exhibits this condition too.
* Remember, of course, that the boundaries of genera are essentially arbitrary and artificial.
All in all, Concavenator is a remarkable fossil, and I’m not in any way downplaying its importance or quality. Congratulations to Francisco Ortega and colleagues on this fabulous discovery, and in publishing a paper that brings it to global attention.
I have one more thing to say: what were the tall neural spines for? Ortega et al. (2010) conclude that we just can’t say, though they note that thermoregulatory, display or energy storage functions have all been suggested. I tend to prefer the display option, but only by analogy with the extant tall-spined reptiles that everyone seems to ignore whenever they talk about tall neural spines. Sure, maybe these structures were partially buried in fat or muscle, but the implication from some that they simply must have been like this, and that the existence of ‘dorsal sails’ is a total no-no (Bailey 1997) ignores the fact that all tetrapods aren’t mammals. There are living reptiles with dorsal sails: I really must get photos of sail-backed chameleon neural spines some time [adjacent photo shows body of Meller's chameleon Chamaeleo melleri - best I can do at short notice. Photo by Adrian Pingstone, from wikipedia].
Ironically, I was going to talk about another paper on Cretaceous fossils that was also published today, but it’ll have to wait. And a particularly significant book was also published today. More on that later, too.
For previous articles on allosauroids and other Mesozoic theropods, see…
- Of Becklespinax and Valdoraptor
- My most favouritest dinosaurs: ceratosaurids
- Early abelisaurs and fan-crested and stretch-jawed hadrosaurs
- An American tyrant in London
- 100 years of Tyrannosaurus rex
- Oh no, not another new Wealden theropod!
- The aquatic Majungasaurus, or not
- Limusaurus: awesome and wonderful, with or without the hands
- Tyrant dinosaurs were not a Northern Hemisphere speciality: they also colonised Australia!
Refs – –
Bailey, J. B. 1997. Neural spine elongation in dinosaurs: sailbacks or buffalo-backs? Journal of Paleontology 71, 1124-1146.
Csiki, Z., Vremir, M., Brusatte, S. L. & Norell, M. A. 2010. An aberrant island-dwelling theropod dinosaur from the Late Cretaceous of Romania. Proceedings of the National Academy of Sciences 107, 15357-15361.
Naish, D. 2006. The osteology and affinities of Eotyrannus lengi and other Lower Cretaceous theropod dinosaurs from England. Unpublished Ph.D. Thesis, University of Portsmouth.
– . & Dyke, G. J. 2004. Heptasteornis was no ornithomimid, troodontid, dromaeosaurid or owl: the first alvarezsaurid (Dinosauria: Theropoda) from Europe. Neues Jahrbuch für Geologie und Paläontologie, Monatshefte 2004, 385-401.
– ., Hutt, S. & Martill, D. M. 2001. Saurischian dinosaurs 2: Theropods. In Martill, D. M. & Naish, D. (eds) Dinosaurs of the Isle of Wight. The Palaeontological Association (London), pp. 242-309.
Naish, D., & Martill, D. (2007). Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia Journal of the Geological Society, 164 (3), 493-510 DOI: 10.1144/0016-76492006-032
– . In press. Pneumaticity, the early years: Wealden Supergroup dinosaurs and
the hypothesis of saurischian pneumaticity. In Moody, R. T. J., Buffetaut, E., Naish, D. & Martill, D. M. (eds) Dinosaurs and Other Extinct Saurians: A Historical Perspective. Geological Society, London, Special Publications 343, 227-234.
Ortega, F., Escaso, F. & Sanz, J. L. 2010. A bizarre, humped Carcharodontosauria (Theropoda) from the Lower Cretaceous of Spain. Nature 467, 203-206.
Turner, A. H., Makovicky, P. J. & Norell, M. A. 2007. Feather quill knobs in the dinosaur Velociraptor. Science 317, 1721.