Long-time readers might have noticed that I tend not to cover new dinosaur stories here at Tet Zoo. Partly this is because I like to be novel: I can’t help but feel slightly disappointed when the subject I’m blogging about gets covered on a hundred other blogs and news-sites. It’s also partly because dinosaurs get way too much coverage as it is: my aim here is to reflect tetrapod diversity as a whole, and not to focus on the attention-grabbing taxa alone. And I’ve done dinosaurs quite a lot already. So, sorry Aardonyx, Tawa, the proposal of venomosity in dromaeosaurs, and all those million other recent dinosaur stories that made the newswires.
Having said all that, I’m always prepared to make exceptions. New theropods – particularly bird-like coelurosaurs (like dromaeosaurs) and big non-coelurosaurian tetanurans (like allosauroids) – make the news all the time, but ornithischians consistently draw the short straw. Nobody seems to care, no matter how remarkable the animal. Well, here’s my effort to try and redress the balance a little. The latest issue of Journal of Vertebrate Paleontology includes Fabio Dalla Vecchia’s long-awaited paper on the remarkable European hadrosaur Tethyshadros insularis [image above shows Fabio to scale with Lukas Panzarin's reconstruction of Tethyshadros insularis. Fabio is holding a toy Safari Ltd. Corythosaurus].
Discovered in the Campanian-Maastrichtian Liburnian Formation of Trieste Province, Italy, Tethyshadros inhabited a Cuba-sized island that was at the northern end of what’s known as the Adriatic-Dinarian Carbonate Platform (ADCP) [see adjacent palaeo-map, courtesy F. M. Dalla Vecchia]. In keeping with its (presumed) island endemism, Tethyshadros was small for a hadrosaur – about 3.6 m long – and this suggests that, like some of the other dinosaurs reported from the ADCP, it was an island dwarf (Dalla Vecchia 2009). The holotype specimen [shown below, from Dalla Vecchia (2009)] is spectacularly complete (missing only part of the snout), and indeed it’s one of the most complete large dinosaurs ever discovered in Europe. A few additional Tethyshadros specimens are known and include a partial skeleton, an isolated skull and various additional isolated bones or limbs (Dalla Vecchia 2009).
Tethyshadros is already moderately familiar if you follow the dinosaur literature, having been discussed at length in a popular book – Cristiano Dal Sasso’s Dinosaurs of Italy (reviewed here on Tet Zoo) – and figured in the technical literature (Dal Sasso 2003). It was previously known by its nickname, ‘Antonio’. I think that Tethyshadros is a weird, and very newsworthy, beast; in part because it represents a really interesting divergence from typical hadrosaur morphology. Rather than being ‘just’ a dwarf, island-dwelling version of its larger mainland relatives, Tethyshadros was a weird, long-legged cursorial form with a bizarre spiky beak.
In keeping with what appears to be a rather basal position within the hadrosauroid clade (Dalla Vecchia 2009) (throughout this article, I’ll be using ‘hadrosaur’ as a vernacular term for both Hadrosauridae, and for Hadrosauroidea), Tethyshadros has a rather conservative skull morphology. But the skull is peculiar in being proportionally large and long, and in having a particularly large infratemporal fenestra. Many iguanodontians have serrated edges to their premaxillae, with the serrations being formed by distinct bony denticles. This suggests that, in life, the rhamphothecal covering to the premaxillae was serrated too, and you’ll note that some artists have depicted their iguanodontians with beaks of this form. Tethyshadros takes the serrated edges to an extreme: the premaxillary denticles are long, forward-pointing spikes. Enlarged in life by the beak tissue, these would have looked bizarre indeed [adjacent reconstruction by Davide Bonnadonna, used with permission]. Did they help Tethyshadros to bite at specific food items? Were they for grooming? For display? The mind boggles.
The animal’s hand is also weird. There are only three digits (fingers I and V are entirely absent) – giving Tethyshadros the most ‘reduced’ hand of any iguanodontian – and the three remaining metacarpals are long, slender, and closely appressed. This is a very ‘cursorial-looking’ hand. Tetrapods specialised for cursoriality tend to have absent or reduced lateral digits; reduced, ‘lightweight’ distal limb segments; interlocked or fused hand and foot elements; and a subunguligrade or unguligrade stance (unguligrady = condition where the animal bears all weight on its unguals; subunguligrady = similar, but with some weight borne on the penultimate phalanges as well). And in fact, there are indications elsewhere in the Tethyshadros skeleton that this was a specialised cursor: in the hindlimb, the tibia is longer than the femur (the hadrosaur femur is normally longer than, or subequal to, the tibia).
And the tail is also peculiar: a long proximal portion lacks chevrons, the vertebral centra themselves are rather long, and the distal caudals are rod-like. The most proximal chevrons are long and rod-like, the more distal ones have expanded ventral ends, and those near the tail-tip are shaped like an inverted ‘T’. These vertebral and chevron features imply that the caudofemoral muscles – the main retractors of the hindlimb – were particularly big and powerful in Tethyshadros, and again here is an indication that this animal was a specialised cursor [reconstruction below from from Dalla Vecchia (2009), by Marco Auditore].
Like so many groups of animals where all the species are often assumed to be very ‘samey’, hadrosaurs actually exhibit quite a lot of variation in postcranial proportions, and many clades exhibit specialisations that imply diverse lifestyles. For example, brachylophosaurs have particularly long forelimbs and hence may have fed at higher levels than other clades, while parasaurolophs had especially stout limbs and large limb girdles, and may have been denizens of deep forests that literally had to muscle their way through thick vegetation. So, as Brett-Surman & Wagner (2007) emphasised, it’s misleading to think that ‘all hadrosaurs were alike’.
Seen within this context, Tethyshadros is perhaps not such a big deal: it’s a slight variation on the plan, being a small-bodied, gracile-limbed taxon with a peculiar snout and modified hand. Nevertheless, here, at last, is one of those weird, divergent, island-endemic dinosaurs we’ve always hoped we would find, and I hope you’ll agree with me that it’s a very special beast indeed.
For previous Tet Zoo articles on ornithischians see…
- Early abelisaurs and fan-crested and stretch-jawed hadrosaurs
- Where the scelidosaurs and iguanodontians roam
- Udanoceratops tschizhovi, the basics
- No-one talks about Anchiceratops, boo hoo
- Zuniceratops and the early acquisition and alleged dimorphism of ceratopsian brow horns
- A very alternative view of horned dinosaur anatomy
- Ceratopsian dinosaurs: cheeky or beaky?
- Greek-nosed first-horned face and the ‘bagaceratopids’
Next: we break-up for Christmas!
Refs – -
Brett-Surman, M. K. & Wagner, J. R. 2007. Discussion of character analysis of the appendicular anatomy in Campanian and Maastrichtian North American hadrosaurids – variation and ontogeny. In Carpenter, K. (ed) Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Indiana University Press (Bloomington & Indianapolis), pp. 135-169.
Dal Sasso, C. 2003. Dinosaurs of Italy. C. R. Palevol 2, 45-66.
Dalla Vecchia, F. M. 2009. Tethyshadros insularis, a new hadrosauroid dinosaur (Ornithischia) from the Upper Cretaceous of Italy. Journal of Vertebrate Paleontology 29, 1100-1116.