Steve Sweetman and I have just published a paper on a new maniraptoran theropod dinosaur from the Lower Cretaceous Wealden Supergroup of East Sussex, England (Naish & Sweetman 2011).
As you might know if you’re a regular reader, much of my technical work has been devoted to Wealden theropods and I publish papers on them fairly regularly (recent articles: Benson et al. (2009), Naish (2010); see links below). I still have yet to publish one of my most significant contributions – the monographic description of the tyrannosauroid Eotyrannus lengi (the follow-up to the rushed and preliminary Hutt et al. (2001) paper) – but let’s not talk about that. A large, state-of-the-art revision of Wealden theropods was submitted earlier this year and has been through review and accepted for publication.
I make no secret of the fact that many of the fossils I publish on are extremely fragmentary, in many cases being single bones. Identifications made on the basis of single bones can very occasionally be horribly, horribly wrong (one personal example: a cervical vertebra that I identified as oviraptorosaurian (Naish & Martill 2002) now seems to be from an abelisauroid), but they can often be made with confidence if the material is good enough, and if it preserves the required informative bits of anatomy.
A new Wealden fauna
Such is the case with the new specimen. It’s a single cervical vertebra, discovered by local collector Dave Brockhurst at Ashdown Brickworks near Bexhill [adjacent photo shows me at the site, 2006]. Unlike most of the familiar Wealden dinosaur fossils, it isn’t from the Wealden Group of the Isle of Wight, but from the rather older Hastings Group, and specifically from the Wadhurst Clay Formation [for help with the stratigraphic terms and their relations to one another, see the diagram below]. This unit dates to the early part of the Valanginian in the Early Cretaceous and hence is about 12 million years older than the Isle of Wight’s dinosaur-bearing Wessex Formation.
Those who care about Wealden stratigraphy and Lower Cretaceous fossils will note that we’re now using the term ‘Hastings Group’, rather than ‘Hastings Beds Group’, for this unit. Theropod remains are rather rare in the Hastings Group. Becklespinax and Valdoraptor come from Hastings Group units as do a number of baryonychine teeth (so does another of ‘my’ dinosaurs: weirdo sauropod Xenoposeidon), but all other Hastings Group theropod fossils are scrappy, indeterminate bits and pieces.
The Ashdown Brickworks locality is a new one for dinosaurs and other Cretaceous animals (at least so far as the technical published literature is concerned), and one of the things Steve and I do in our paper is draw attention to the diverse fauna recovered from the site. In addition to hybodont sharks and various other fishes, there are several (new) salamanders and anurans, assorted lizards (including skinks and an aigialosaur), and the remains of turtles, crocodilians, a plesiosaur, an ornithocheiroid pterosaur, thyreophorans, iguanodonts and theropods, including Baryonyx and an allosauroid (Naish & Sweetman 2011). That’s a very representative selection of Wealden vertebrates. Incidentally, I have big projects in the works on Wealden plesiosaurs and crocodilians and will be discussing them at length at some point in the near future.
The Ashdown maniraptoran
Anyway, the big deal about the Ashdown maniraptoran [shown here, in all views] is its size. It’s tiny – the whole vertebra has a total length of 7.1 mm – and the absence of any discernible neurocentral suture indicates that the animal the vertebra belonged to was skeletally mature. An adult.
Before discussing size further, let me note that the maniraptoran identification is pretty sound. On first seeing the vertebra, I was struck by the X-like shape of the neural arch (as seen in dorsal view), the large hypapophysis (a prominent keel located on the midline of the ventral surface) and the presence of fossae on the sides of the neural arch. It looked immediately like a maniraptoran cervical vertebra, especially that of an oviraptorosaur. This was confirmed by other details, like the shapes of the articular surfaces, the positions of the parapophyses, the shapes of the zygapophyses and so on. The presence of a rather large hypapophysis, combined with the position of the parapophyses (low down on the centrum), shows that the Ashdown maniraptoran vertebra is a posterior cervical: that is, a vertebra from near the base of the neck.
Having identified the specimen as from a maniraptoran, can we go further? The X-like shape of the neural arch gives the vertebra an oviraptorosaur-like appearance, and various other features are consistent with such an identification. Meanwhile, the proportionally large neural canal makes it bird-like. As we argue in the paper, however, the proportionally large neural canal seen in birds may be a size-related feature rather than a specific character of Avialae. For now, it seems most prudent to identify the specimen as Maniraptora indet., though I do suspect that it’s from an oviraptorosaur or oviraptorosaur-like taxon. Before committing to anything in print, Steve and I showed the specimen to a few other theropod specialists, and I’m pleased to say that they agreed with our determination in entirety.
Small, but how small?
So, what about the size of this animal? We’re careful throughout the article (Naish & Sweetman 2011) to note that determining total length from just a single bone is highly speculative. Nevertheless, it seems wrong not to at least provide a rough estimate. We used two techniques to provide a rough estimate of size; neither is particularly reliable and one is almost wholly intuitive.
The intuitive method involved duplicating modified digital versions of the vertebra to make an ‘articulated’ neck (the digital vertebrae were modified since vertebrae within a neck are not all the same length). Said neck was then positioned within the silhouette of a generic, oviraptorosaur-like maniraptoran. This is definitely more art than science and I’m sure that it will make some people vomit with rage. It relies on the massive assumption that the silhouette is correct to begin with. I expect to be pelted with fruit, hit in the stomach etc. when next I go on the street (sigh, after the giant tortoise incident I sure am owed a good beating). Anyway, whatever, the resulting scaled silhouette was about 45 cm long.
A second technique also involved that reconstructed neck, but this time we worked out how neck length compared to total skeletal length (TSL). I’m going to use ‘TSL’ here in order to make it clear that the lengths being discussed don’t involve tail plumage. Neck length is not that variable across non-neornithine maniraptorans. In the oviraptorosaur Caudipteryx the neck accounts for c. 24% of TSL while it’s c. 20% of TSL in short-tailed birds like Confuciusornis and c. 16% of TSL in the long-tailed bird Archaeopteryx (the paper erroneously states that neck length is c. 47% of TSL in Archaeopteryx: this is completely wrong and I’m currently trying to get it fixed). If proportioned like Caudipteryx, the Ashdown maniraptoran could have been c. 33 cm in TSL. 40 cm is about right if it was built like a short-tailed bird, and c. 50 cm is right if it was proportioned like Archaeopteryx. Because I’m leaning slightly toward the oviraptorosaur identification, c. 33 cm is looking most likely, but a ballpark of 33-50 cm is the range we’re looking at.
And that’s pretty interesting, because it makes the Ashdown maniraptoran one of the smallest Mesozoic dinosaurs reported so far. Excluding Epidendrosaurus (c. 16 cm TSL) and Epidexipteryx (c. 25 cm TSL) – for both are regarded as juveniles or subadults – the smallest non-avialian theropod is currently Anchiornis, with a TSL of between 34 and 40 cm (depending on whose estimate you follow). A few other small non-avialian theropods were between 40 and 50 cm: Parvicursor, Mahakala, Mei and Jinfengopteryx are among them (and, no, Compsognathus isn’t one of them any more). Some of these mini-theropods are shown here, with Pioneer Dork for scale [by Matt Martyniuk, from wikipedia]. The point I’m making here is that the Ashdown maniraptoran may well be one of the smallest non-avialian theropods we know of, possibly even the smallest. Please note the many, many caveats, however.
On a similar note, this fossil is a bit of a joke when you remember that such localities as Liaoning in China are revealing 100% complete, fully articulated, fully feathered maniraptoran skeletons. However, while these fossils are, clearly, awesome, the fact that they’re so awesome doesn’t mean that we shouldn’t be putting crappy fossils on record too. And we live in hope that more substantial remains of our tiny Ashdown maniraptoran will be found one day.
And it isn’t lost on me that this is, like, the fourth paper I’ve published that involves analysis of a single vertebra: Ashdown maniraptoran (Naish & Sweetman 2011), Xenoposeidon (Taylor & Naish 2007), ‘Angloposeidon’ (Naish et al. 2004) and Thecocoelurus (Naish & Martill 2002) [in composite below, images very much not to scale]. Yikes. I might get a reputation.
Because Naish & Sweetman (2011) has been online for a while (as an in-press manuscript*), it’s been covered by a few bloggers already: there’s brief coverage at Beasts Evolved (though ignore the fact that the specimen is said to be from the Isle of Wight), Palaeoblog and Theropoda.
* Grumble grumble. I so hate the fact that journals put in-press/unpublished manuscripts online.
For previous Tet Zoo articles on Wealden theropods and other Wealden dinosaurs, see…
- The world’s most amazing sauropod (Xenoposeidon)
- Of Becklespinax and Valdoraptor
- Where the scelidosaurs and iguanodontians roam
- Oh no, not another new Wealden theropod!
- My dinosaur colouring book # 2 (Wessex Formation dinosaurs)
- Concavenator: an incredible allosauroid with a weird sail (or hump)… and proto-feathers?
- The explosion of Iguanodon at Scientific American
- Goodbye super-inclusive Iguanodon, hello Mantellisaurus, Owenodon, Dakotadon, Dollodon, Barilium, Kukufeldia, Hypselospinus, Sellacoxa, Proplanicoxa etc. etc.
Refs – -
Benson, R. B. J., Brusatte, S. L., Hutt, S. & Naish, D. 2009. A new large basal tetanuran (Dinosauria: Theropoda) from the Wessex Formation (Barremian) of the Isle of Wight, England. Journal of Vertebrate Paleontology 29, 612-615.
Hutt, S., Naish, D., Martill, D. M., Barker, M. J. & Newbery, P. 2001. A preliminary account of a new tyrannosauroid theropod from the Wessex Formation (Early Cretaceous) of southern England. Cretaceous Research 22, 227-242.
Naish, D. 2010. 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, pp. 229-236.
- . & 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.
- ., Martill, D. M., Cooper, D. & Stevens, K. A. 2004. Europe’s largest dinosaur? A giant brachiosaurid cervical vertebra from the Wessex Formation (Early Cretaceous) of southern England. Cretaceous Research 25, 787-795.
Naish, D., & Sweetman, S. C. (2011). A tiny maniraptoran dinosaur in the Lower Cretaceous Hastings Group: evidence from a new vertebrate-bearing locality in south-east England. Cretaceous Research, 32, 464-471 : 10.1016/j.cretres.2011.03.001
Taylor, M. P. & Naish, D. 2007. An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England. Palaeontology 50, 1547-1564.