Tetrapod Zoology

Ankylosaur week, day 2: Tarchia

i-17b0eb69d5f2350c57eb090aa0560f77-Tarchia M. Shiraishi.jpg

Welcome to day 2 of the ‘ankylosaur week’ series – for the background on this go see day 1 on Hungarosaurus. Before talking about today’s ankylosaur, here’s a quick ‘everything you wanted to know about ankylosaurs but were afraid to ask’. Ankylosaurs were ornithischian dinosaurs from the Jurassic and Cretaceous, they have a highly modified skull where the sutures are closed, the external openings are mostly or entirely closed, the dorsal surface is covered with thick bony layers and bony bosses, and the small teeth are inset from the jaw margins. Horns often project from the cheek and rear margin of the skull. Within the group, snout shape varies from long and narrow to short and very broad. All ankylosaurs were quadrupeds (obligate bipedality has been suggested for one taxon, but this is almost certainly wrong); their limbs are typically short and strongly muscled. An average ankylosaur was probably 4-5 m long, but there were giants twice as size, as well as dwarfs of only 2-3 m long or less.

Their hips are broad, sometimes incredibly so, and some of them would have been extraordinarily broad, flat-backed animals. All of these features indicate that ankylosaurs were herbivorous (insect-eating has been suggested in the past, as has a marine seaweed-eating lifestyle), and gut contents from an Australian taxon confirm this. Tooth and jaw morphology indicates that ankylosaurs mostly fed by orthal pulping (simple vertical mashing of plant material), but complex jaw movements may have been present in some taxa (Rybczynski & Vickaryous 2001). Various details indicate that cheeks were probably present. Complex air passages show that ankylosaurid ankylosaurs in particular were doing something odd with inspired air, but we aren’t quite sure what this was, and thick skulls and a mobile joint in the braincase suggest to some workers that head-butting was practised by at least some species.

i-5fb412835deacdb5c516b6ebbf2d126f-ankylosaurs WA text guide 340 px.jpg

Rows of armour lined the ankylosaur neck, body and tail: articulated armour is rare, but often seems to have consisted of plate-like scutes that were arranged in half-circles around the dorsal surface of the neck, and a covering of keeled plates and/or spikes across the back, hips and tail. A large fused plate covered the hip region in some taxa, one poorly known ankylosaur even had a ‘belly plate’, and scutes protected the limbs in at least some forms. The armour appears to have been absent in juveniles. Ankylosaurid ankylosaurs possessed a tail club formed from large osteoderms connected to a handle-like structure formed by fused caudal vertebrae. The old idea that ankylosaurs were ‘passive defenders’ which just sat like tortoises and waited for predators to go away seems extraordinarily unlikely given the evolution of big shoulder spikes, laterally projecting tail plates, and tail clubs. However, armour may have been important in intraspecific combat and display as much as in predator avoidance. Some time I’ll elaborate on the crazy idea that tail-clubbed ankylosaurs were mimics of iguanodontian ornithopods.

i-e7e27e3a97ffd1b6f585a492befc720b-Sole scelidosaur 11-2-2008.jpg

Ankylosaurs are thyreophorans, and share a list of characters with stegosaurs, the plated dinosaurs. A recent claim that Scelidosaurus [shown in adjacent image] from Lower Jurassic England is closer to ankylosaurs than stegosaurs are, and that the Ankylosauria + Scelidosaurus clade be named Ankylosauromorpha (Carpenter 2001), has proved less well supported than the idea that stegosaurs and ankylosaurs – grouped together as Eurypoda – form a clade (Butler et al. 2008). Since the 1970s, ankylosaurs have been classified in two groups: Nodosauridae and Ankylosauridae (Coombs 1978). Some recent work indicates that a group of taxa that share pelvic shields and long shoulder spines that bear posterior grooves deserve to be separated as Polacanthidae (this isn’t a new name: Polacanthidae was first named in 1911).

Huh – that went on for much longer than I’d planned. To business…

i-f4f812305855365c45009f9f169b42b1-Tarchia skull wikipedia.jpg

Reaching about 8 m in length, Tarchia gigantea from the Maastrichtian Nemegt Formation of Mongolia is the largest of Asian ankylosaurid ankylosaurs, and also the last. The Tarchia image used at the top of the article was produced by Mineo Shiraishi and is used with permission (© M. Shiraishi, all rights reserved). Mineo’s gallery of excellent dinosaur reconstructions can be found here. A club-tailed, broad-skulled form, Tarchia is probably a basal member of the ankylosaurid clade Ankylosaurinae. It has been suggested that the Asian ankylosaurids Tarchia and Saichania are close relatives of the North American Nodocephalosaurus (Sullivan 1999), as all three share bulbous, polygonal, symmetrically arranged bony lumps on their nasals and frontals [Tarchia skull shown here borrowed from wikipedia].

The 40-cm-long skull was not only covered in bony bumps, but also decorated with large, flattened triangular spines which projected sideways from its cheeks. Ankylosaurids could have used these in fights with members of their own species, perhaps butting one another on the side of the head. Tarchia also has backwardly curved horns on the posterior corners of its skull. Originally named in 1956 as a new species of the North American genus Dyoplosaurus (itself now regarded as synonymous with Euoplocephalus), Tarchia was named as a distinct genus in 1977 when Teresa Maryanska recognised a second species (T. kielanae). Though Maryanska’s idea about the generic distinctness of Tarchia is regarded as correct, T. kielanae is mostly regarded as a synonym of T. gigantea.

More ankylosaurian action tomorrow!

Refs – -

Butler, R. J., Upchurch, P. & Norman D. B. 2008. The phylogeny of the ornithischian dinosaurs. Journal of Systematic Palaeontology 6, 1-40.

Carpenter, K. 2001. Phylogenetic analysis of the Ankylosauria. In Carpenter, K. (ed) The Armored Dinosaurs. Indiana University Press (Bloomington and Indianapolis), pp. 455-483.

Coombs, W. P. 1978. The families of the ornithischian dinosaur order Ankylosauria. Palaeontology 21, 143-170.

Rybczynski, N. & Vickaryous, M. K. 2001. Evidence of complex jaw movement in the Late Cretaceous ankylosaurid Euoplocephalus tutus (Dinosauria: Thyreophora). In Carpenter, K. (ed) The Armored Dinosaurs. Indiana University Press (Bloomington and Indianapolis), pp. 299-317.

Sullivan, R. M. 1999. Nodocephalosaurus kirtlandensis, gen. et sp. nov., a new ankylosaurid dinosaur (Ornithischia: Ankylosauria) from the Upper Cretaceous Kirtland Formation (Upper Campanian), San Juan Basin, New Mexico. Journal of Vertebrate Paleontology 19, 126-139.

Comments

  1. #1 John Conway
    February 11, 2008

    Whoa, it’s huge! How much do you think that thing weighed?

  2. #2 David Marjanovi?
    February 11, 2008

    Their hips are broad, sometimes incredibly so, and some of them would have been extraordinarily broad, flat-backed animals.

    How much of this could be due to diagenetic exaggeration? I’m thinking of GSP’s illustration of a completely flat-backed Euoplocephalus.

    The armour appears to have been cartilaginous in juveniles.

    No, absent — dermal bone isn’t preformed in cartilage.

  3. #3 Darren Naish
    February 11, 2008

    Oh yeah, I knew that :)

    And, yes, the flat-backedness of (e.g.) Cutler’s Euoplocephalus is probably due in part to compression, but this depends on who you ask. Even so, they would still have been very broad-bodied.

  4. #4 Nick
    February 11, 2008

    The top surface of the 40-cm-long skull was covered in large, bumpy armour plates

    I thought it had been determined that the “armor” on the skull was really due to remodeling of the bone surface, and not separate ossifications.

  5. #5 Brad McFeeters
    February 11, 2008

    “obligate bipedality has been suggested for one taxon, but this is almost certainly wrong”

    …which taxon was this? I’d like to read this ref, just for the entertainment value.

  6. #6 Darren Naish
    February 11, 2008

    Is cranial armour really ‘armour’ (viz, is it composed of dermal scutes, or is it formed from remodelled skull surface?). Nick is right, the paper he probably has in mind is…

    Vickaryous, M. K., Russell, A. P. & Currie, P. J. 2001. Cranial ornamentation of ankylosaurs (Ornithischia: Thyreophora): reappraisal of developmental hypotheses. In Carpenter, K. (ed) The Armored Dinosaurs. Indiana University Press (Bloomington and Indianapolis), pp. 318-340.

    Note from the wording in the first paragraph that I had all of this in mind when writing. However, when I was paraphrasing Sullivan (1999), I forgot about it, plus of course he was writing before Vickaryous et al. had been published.

    What’s the ‘bipedal’ ankylosaur? It’s Cryptosaurus eumerus. See…

    Galton, P. M. 1983. Armored dinosaurs (Ornithischia: Ankylosauria) from the Middle and Upper Jurassic of Europe. Palaeontographica Abteilung A 182, 1-25.

    Finally – sad to say, the reconstruction of Tarchia shown at top is a bit oversize. If Tarchia has a skull 43 cm long, compare the head length to that of the human silhouette.

  7. #7 Zach Miller
    February 11, 2008

    Ah, good to see coverage of a dinosaur group that never gets any. I’ve read (somewhere–my mind is a blank) that Nodosauridae may be a paraphyletic group, although it certainly looks like they have some relationship with polacanthids, what with the scuted backs and lack of tail club…

  8. #8 ALEFRISK
    February 11, 2008

    Wow i didn’t know Tarchia…? I’m imagineing this fantastic animal avoids a Tarbosaurus such an Ankylosaurs probably safegarded itself against a Tyrannosaurus…amazing!

    I’m sorry for my english but I’m italian :)

  9. #9 Nick Gardner
    February 11, 2008

    I’ve read (somewhere–my mind is a blank) that Nodosauridae may be a paraphyletic group, although it certainly looks like they have some relationship with polacanthids, what with the scuted backs and lack of tail club…

    Both of those are plesiomorphic characters. :P

  10. #10 Alec T
    February 11, 2008

    What part of ankylosaur morphology would even suggest a seaweed eating lifestyle?

  11. #11 John Scanlon, FCD
    February 11, 2008

    A number of ankylosaur skeletons have been found in marine deposits, so obviously they were fully aquatic, unable to support themselves on land, and doomed by their degenerate dentition to munching on soft vegetation or gulping jellyfish. The heavy armour was clearly only ballast to allow them to move around on the bottom or hide in kelp beds from predators while holding sufficient air in the lungs to keep their cold-blooded reptilian physiology ticking over. How am I doing?

  12. #12 Lars Dietz
    February 12, 2008

    John Scanlon: You’re doing quite well, although you obviously forgot that they used the ends of their tails for anchoring in the mud. This must be true because it was published. The reference is:
    Wilfarth, M., 1949, Die Lebensweise der Dinosaurier, E. Schweizerbart, Stuttgart.
    The book proposes similarly creative interpretations of the lifestyles of all major dinosaur groups, all based on the idea that the moon was closer to Earth in the Mesozoic, so the tides were higher and all the dinosaurs must have lived in tidal areas.

  13. #13 Thomas R. Holtz, Jr.
    February 12, 2008

    To defend tyrant honor, PIN 3142/250 (a Tarchia specimen) has a tyrannosaurid (presumably Tarbosaurus) tooth puncture wound (healed) in its skull. So tyrants did on occasion try to munch even an enormous ankylosaurid like this.

  14. #14 Zach Miller
    February 13, 2008

    I’ve read (somewhere–my mind is a blank) that Nodosauridae may be a paraphyletic group, although it certainly looks like they have some relationship with polacanthids, what with the scuted backs and lack of tail club…

    Both of those are plesiomorphic characters. :P

    *smacks forehead*

  15. #15 David Marjanovi?
    February 26, 2008

    Not that I could tell why, but this article is currently the most active ScienceBlogs post!!!

    Congratulations, Darren!

  16. #16 kid bitzer
    February 26, 2008

    your first illustration is *proof positive* that humans and dinosaurs were contemporary–in the garden of eden!
    i mean–there they are. in the same picture!
    the only mystery is how they found a photo-booth big enough for both of them to crawl in.

  17. #17 JC Otis
    January 27, 2011

    Hi Professor Naish
    I discovered a dinosaur graveyard in my front drive way while doing some improvements, there appears to be a number of young (10)?, mid sized(6) and at least one adult. I believe they are Ankylosaurs because of the shapes of the dermal plates and clubs on thier tails. I was wondering what I should do with them?

  18. #18 David Marjanović
    January 28, 2011

    JC Otis, one adult ankylosaur is about the size of a driveway…

    Do you mean you found a pile of skeletons? And in what kind of rock?

  19. #19 JC Otis
    January 29, 2011

    Yes a pile all mixed together and the ground is dirt, rocks?/fossils? and thick muck two feet down with more of the fossils? thats why I quit digging didnt want to make it any worse.

  20. #20 David Marjanović
    January 30, 2011

    Dirt? Earth? Whatever is in that cannot be old.

    Could you upload photos somewhere? Or could you send me some by e-mail? (scholar.google.com knows my e-mail address.)

    Stones and bones are usually very easy to tell apart by things like shape and texture.

  21. #21 JC Otis
    February 13, 2011

    I have tried to email pictures of the rocks or fossils to both of you and I havn,t heard from anyone and I cant hold off on the land improvements much longer so please …..!let me know if you even recieved my pictures so I can do something!

  22. #22 Darren Naish
    February 14, 2011

    Hi – I received your photos, sorry.. haven’t had time to respond. The objects you’ve discovered are not fossils: they are indeed stones. All of them.

  23. #23 David Marjanović
    February 14, 2011

    Hi – I received your photos, sorry.. haven’t had time to respond. The objects you’ve discovered are not fossils: they are indeed stones. All of them.

    I second every word of this.

    They’re just rounded pebbles; it requires a lot of imagination to “see” bones or teeth in them. They’re not even all the same kind of rock; and all are rock, not bone or tooth enamel. Check out the broken surfaces in particular: bones are porous inside, denser toward the outside and spongy or outright hollow toward the center; your finds are massive rock.

    Contrary to what many people seem to believe, fossils do not literally turn into stone. Rather, minerals from the groundwater crystallize in their pores, filling all the hollow spaces and making the fossil much heavier, but the original material is still there.

    An exception are cases when the original material is dissolved in acidic groundwater and the resulting hollow shapes (which can, BTW, persist!) are filled in by minerals that crystallize from later groundwater. However, this process exactly preserves the original shapes; your finds aren’t shaped closely enough like bones or teeth by far.

    That you found them in the modern soil is a further giveaway. Soil doesn’t stay soil over tens of millions of years; it’s either washed away or turns into rock (or coal or something).

  24. #24 JC Otis
    February 14, 2011

    Thank you for checking them out I wasnt really sure but didnt want to take any chances of destroying a piece of the earth’s history, off to work I go!

  25. #25 andrew ferguson
    February 20, 2011

    Some things don’t add up. Tarchia means ‘big brain’ or something like that. Yet it’s skull was only about 16cm long, much smaller than the largest Ankylosaurus skull, which is about 25 inches. Yet Ankylosaurus is now regarded as being only about 20 feet long and 5 1/2 feet high. Tarchia, with its much smaller skull, was about 25+ feet long and 8 feet high. None of the illustrations i have seen of tarchia have the skull in proportion to its body. It should look like a pin head but all heads are drawn at about 2 1/2 to 3 feet long, includng the one at the top of this article.

    Additionally, Ankylosaurus is considered to have been the largest of the ankylosaurs, yet Tarchia is much larger than any ankylosaurus skeleton (or portion thereof) yet found.

  26. #26 andrew ferguson
    February 20, 2011

    that should be 16 inches, not 16cm for Tarchia’s skull length.

  27. #27 David Marjanović
    February 21, 2011

    Thank you for checking them out I wasnt really sure but didnt want to take any chances of destroying a piece of the earth’s history, off to work I go!

    Glad to have helped. :-)

  28. #28 JC Otis
    February 27, 2011

    Hey I dug down deeper into the drive way and found fossil skin and actual bone shaped fossils they are black and very smooth and cold to the touch, I can say this much because I have a degree in medical science and know what an ulna or femur, ribs and vertebrae look like,which these do. I did some research on north america and this whole area was a sea during the late cretaceous and I think your right about the hollow pores filled in by mineral’s because they are heavy.

  29. #29 David Marjanović
    February 27, 2011

    OK, please send me pictures of those.

    But if you’re still digging in, you know, earth, in dirt, then they can’t be bones that are old enough to have become black.

    By “fossil skin”, do you mean impressions or a black halo around bones?