There are dwarf, island-dwelling, cursorial, tridactyl hadrosaurs now: didn't you get the memo?

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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].

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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).

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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.

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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].

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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...

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.

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Hey now, its not my fault there aren't any Triassic ornithischian dinosaurs from North America! Still, Tethyhadros is super cool, and very worthy of mention.

Okay, okay, THIS hadrosaur is pretty awesome. :-)

One wonders, if duckbills had not gone extinct, would they have eventually become ungulate-like runners?

Very short lumbar ribs: rib cage looks almost mammalian. I assume that in a hadrosaur the shortening of the rib cage gives more space for gut, and doesn't reflect anything like the presence of a diaphragm?

By Allen Hazen (not verified) on 22 Dec 2009 #permalink

Would saying "all hadrosaurs were alike" be more like saying "all mammals are alike", "all ungulates are alike", or "all antelope are alike"? We like to imagine mammals are adorably diverse, but how do we really compare?

Darren: You could fend off the demands for current dinosaur coverage by doing a quarterly "archosaur roundup" with a sentence or paragraph for each surprising archaic development in the past quarter, and a link to the most useful other-blog entry. It might cut off arbitrarily a month before the roundup publication date. For people who follow the other blogs, it would be a nice high-level reminder of the level of activity in the field. For those of us who can't follow everything else, your roundup might be the only place we run across some news items. Roundup postings would be link magnets.

By Nathan Myers (not verified) on 22 Dec 2009 #permalink

"...wierd, divergent, island-endemic" Careful what you´re saying, old bean!

By Spike Ekins (not verified) on 22 Dec 2009 #permalink

@#4: I know, Mike. I just try to forget. Booze does not help.

@#3: Many ornithischians have short lumbar ribs. I take this to indicate a large gut volume.

When I see that beak in the reconstruction, one of my first thoughts is "the better to kill his prey?" (could Tethyshadros have been experimenting with omnivory or carnivory?)

thanks for sharing a novel hadrosaur.

By Anthony Docimo (not verified) on 22 Dec 2009 #permalink

Man. That skeletal restoration hints at a musculus caudifemoralis longus the size of the ribcage!!! That beast must have been crazily cursorial.

dinosaurs get way too much coverage as it is

You mean all the others get too little coverage.

Dinosaurs can never get too much coverage.

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.

Craniocentrism is one of my (numerous) pet peeves. :-)

Very short lumbar ribs: rib cage looks almost mammalian.

More so than in saurischians, yes, but still long ribs are found a very short distance in front of the pelvic girdle.

By David MarjanoviÄ (not verified) on 22 Dec 2009 #permalink

Feet of a mountain goat and mouth of a beaver!?

While you have an obvious facility in generating interesting zoological prose, I must say that your extinct dino pieces are the best, even if they are uncommon. Thanks for bringing Tethyshadros to the fore -- I had neglected it with all the other interesting stuff. The premaxilla is most striking -- does the predentary offer a similarly decorated counterfit ? Which iguanodontians have comparable structures; is it in an ancestral feature of the clade?

Earlier this month I had a chance to see a remarkable collection of Caecilians -- I thought of your blog then. Some new species are likely to be described in the next year or so. The owner was working with some English scientists so perhaps they are people whom you know.

I suppose the long front half of the tail would give extra attachment area for leg muscles, but my thoughts were of a specialist digestive area. Unusual digestive features at the back end as well as the front.

And did this thing breath with a diaphragm? Wasn't there a primitive dinosaur found recently with evidence of thoracic air-sacs? Does this mean ornithiscians split off before the bird-like breathing system (front sacs too, allowing flow through the lungs during both in and out phases, rather than just rear allowing no more than one-way) evolved? Or did ornithiscians drop all that and go back to a mammalian style â and if so, why?

Went to the NHM London last week. Nothing on evolution of human uprightness, nothing on evolution of flight (not in the human or dinosaur birds anyway - I forgot to go to the Darwin Centre.) Clear the decks!

By strangetruther (not verified) on 23 Dec 2009 #permalink

A brand new, weird hadrosauroid, and you've even got a pretty skeletal of it. This IS exciting!

>>the proposal of venomosity in dromaeosaurs

Really? And is this a sound proposal? If so, I think dromaeosaurs just beat out Megalania for "scariest predator of all time"...

By William Miller (not verified) on 24 Dec 2009 #permalink

Terrestrial cursoriality without vertebral flexibility? What other terrestrial cursors, showing derived femoral retraction mind, also exhibit vertebral rigidity to this level? Not only was the dorsal series bound with ossified tendons, but the proximal half of the tail was, the caudal number reduced with elongation of the centra indicating relative movement of each vertebral segement to the tail was reduced, and the overall effectiveness of the mediolateral flexibility of the tail reduced compared to most any other hadrosaur reduced. Comparatively, a very short pes with short femur/long tibia contradict each other (the former is a graviportal feature, the latter a cursorial one).

By Jaime A. Headden (not verified) on 25 Dec 2009 #permalink

Jaime: do you know what you are talking about? I fear not. Rigidity of the vertebral column is common (normal in fact) in large cursorial ungulates.

By Daniella Perea (not verified) on 25 Dec 2009 #permalink
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.

Craniocentrism is one of my (numerous) pet peeves. :-)

I've also complained of this numerous times myself on the DML and on my blog. I also have a short paper in review regarding the relevance of the postcrania within `hadrosaur` phylogeny. ~:|

Apologies to the authors, but the 'venomous sinornithosaur' hypothesis is incredibly weak; the paper includes assorted erroneous, speculative and illogical claims, and deserves some heavy criticism. In short, we can't reject the proposal, but we can't support it either. I'll provide the details some time soonish.

Daniella (#19), I do think I know what I'm talking about. "Large" ungulates typically stop being cursorial at the wildebeest size range, and in this point, and smaller, the spine is not only dorsally flexible, but laterally so (especially in the lumbars, but not the thoracics) despite the common occurence of the tendon sheet underlying the skin (more prominent in smaller ungulates, like chevrotains etc. The level of vertebral flexibility depends mostly on the gait used to "run," and in at least "large" ungulates bounding (requiring dorsoventral lumbar flexion) and the ability to turn at speed (esp. while bounding) requires lateral flexion. Large nonungulate mammals (which we should know Tethyshadros is not) exhibit even more vertebral flexibility in the spine (e.g., see various cats and dogs). Relatively fixed lumbars occur in some gaits (such as trotting) but not in others (galloping).

A few years back, Dalla Vecchia and I talked about "Antonio" (as the public specimen of a new taxon) and its apparent cursorial features, but these are limited to the limb bones for the most part, and there are other possible explanations even when the limb features that do NOT typically occur in cursors are excluded (see the short pes, mentioned earlier).

Also note that I did not say it wasn't cursorial, but that there are difficulties with the argument for cursoriality (these are not the same thing, but I am sure it's easy to confuse these two).

By Jaime A. Headden (not verified) on 25 Dec 2009 #permalink

Jaime: I'm sorry, but you are just not correct and I do not understand the various points you make in your response above (why bring in small ungulates, and carnivores etc?/ Not relevant to topic of discussion). Many ungulates have been and are cursorial at "larger than wildebeest" size, examples include eland, horses, bison, entelodonts, camels, giraffids and many others. It is true that many smaller artiodactyls have very flexible spines, useful in bounding gaits and saltation etc, but large artiodactyls in particular are well known for exhibiting stiffened columns. That's why they exhibit such a "jerky", loping gait. So, a somewhat restricted amount of vertebral mobility is fine for cursors.

How this applies to the new hadrosaur? Those tendons don't mean that the spine was rigid, recent studies have shown that ornithischians tendons probably did not make backs and tails stiff as once assumed. But a reasonable amount of vertebral stiffness is fine for a cursor, and might if anything help support the cursorial model.

By Daniella Perea (not verified) on 26 Dec 2009 #permalink

As I wrote in my first post, the tendons are only part of the issue. And what studies actually show they did not restrict movement? To my understanding, the comparability of ossified tendons to the degree seen in ornithischians is unparalleled in living vertebrates. But that digresses. I noted that the vertebral centra of the tail are elongated while also reduced in number, and as noted by Darren and in the paper, the chevrons are distally expanded and form a "skid," which is likely coincident with the lack of movement each imply. This makes the tail less apparently flexible than, say, that of larger hadrosaurs. The neural spines of hadrosaurs are quite tall, which restricts dorsal movement; and as with virtually all hadrosaurs the zygapophyses are close together at the midline, rather than angled broadly or outward, which restricts latertal movement.

My bad on "wildebeest"-sized animals there: I did intend to imply a horse-levle, but I figured wildebeests are more constrained on their size than the various horses, so picked a large ungualte (you were also vague on what your "large ungulate" size was). The point is that at high speeds, for cursoriality, vertebral flexion is required, unless by "high speed" we mean faster than a walk (similarly vague, as crocs lack cursorial features and can gallop, and display a large amount of vertebral flexibility to do so). High speed requires to some degree the ability to turn "at speed," which is evidenced in counterbalancing tails (with flexibility at the base [see cats, but also dromaeosaurs, which show basally short centra, short, broad and rounded zygapophyseal processes, etc.]) or with specific adaptations in the fore or high feet that allow recovery (horses and arctometatarsalian theropods).

For a good test of how flexible is "flexible," let's look at deer: In a full run, bounding gait, deer lumbars flex along the column to about 20 or so degrees. Compare directly with hadrosaur spines. Then find ANY tall spined, tendon-encrusted vertebral series that can flex 20 or so degrees in the sagittal plane.

Incidentally, it is not that I disgree that this taxon is cursorial, but that the elongation of the limbs are cursorial _alone_ (even if there is another feature that accompanies it, just one, it must withstand the vertebral movement and study of gait -- and I do not think we are there yet). Perhaps we can also reject my argument by finding and demonstrating an animal that can demonstrably run (on four legs) with a fixed spine.

By Jaime A. Headden (not verified) on 26 Dec 2009 #permalink

Jaime, my apologies I do not want to sound rude - but I just cannot understand the way you write (English is not my first language, I admit). Are you saying that cursorial animals can have stiffened vertebral columns or not? I cannot work this out from your comment.

I will make again the same response: that a 'stiff' spine is in fact fully compatible with cursoriality, and that this condition is seen in many mammalian cursors. If you need examples you should learn about artiodactyl anatomy. In fact Darren covered this subject in one of the mesonychians articles - http://scienceblogs.com/tetrapodzoology/2009/08/mesonychians_part_iv.php.

By Daniella Perea (not verified) on 27 Dec 2009 #permalink

This is no gripe directed at any one person, if it is a gripe at all but why does 'political' correctness (however dubious the origin of the term may be) extend to the scientific world? Are we 'speciesist' if we find animals that are wonderfully able to eat other animals to be more dynamic and exiting? I know I do, am I guilty? I could always watch boxing or particularly violent movies to get my entertainment but I don't like them. I would prefer to watch a Martial Eagle bring down a bustard or imagine Mapusaurus chomping into it's Sauropod dinner.

Give me more carnivore blogs, I say. Panthera Atrox is perhaps closer to a jaguar than a lion, yep, that's interesting. Magericyon anceps is named and is even more wonderfully able to eat fresh meat than most other Amphicyonids. Species assigned to Liodon are referred to an ever more diverse genus in Prognathodon. I even heard that the Philippine Eagle might actually be closer to snake eagles, I'd like to hear more about that. Oh well - 'redneck' rant over.

Having said all that, Tethyshadros really is an interesting beastie...I wonder what ate it?

Of course I meant to type "exciting" (frown).

It's a shame how such an awesome discovery is completely obscured by some closet "BAnD"its screaming out about some imaginary venom glands in an already-known dinosaur.

By C. M. Koseman (not verified) on 28 Dec 2009 #permalink

Darren:

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

Any damn fool can make headlines by writing about breaking news items. But precious few are those who can write authoritative yet accessible syntheses of the most stupefyingly diverse zoological subjects while still keeping up with new discoveries and immidiately putting those in their proper context. Your particular blogosphere talent is to somehow manage to pull off that trick, time and time again. That's also why your blog posts keep attracting so many brilliant and insightful comments. And, occasionally, comments that point out petty, trivial matters such as this:

(missing only part of the snout)

You mean 'part of the tail', don't you?

Thanks much Dartian :) But, no, I did mean 'part of the snout': part of the premaxilla and maxilla are absent in the holotype (though this is not obvious from the images used above). The tail comprises 33 vertebrae and seems to be complete.

The tail comprises 33 vertebrae and seems to be complete.

Not according to Fabio Dalla Vecchia (2009), who writes in the paper, on page 1102, that

The tail is incomplete distally because the tip was not excavated and remained in the site.

and, on page 1107, that

The whole distal segment of the tail (at least 10 vertebrae, probably more) remained in situ.

Apart from that, I stand corrected; illustrations in the original paper clearly show that parts of the skull are indeed missing.