Tetrapod Zoology

Ankylosaur week, day 5: Edmontonia

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Welcome to day 5 of ankylosaur week. This time, we look at Panoplosaurus‘ sister-taxon Edmontonia. Edmontonia was a large (6-7 m long) Campanian-Maastrichtian nodosaurid that lived right across North America…

Two species are presently recognised. The type species, E. longiceps, named by Charles M. Sternberg in 1928 for a specimen from the Horseshoe Canyon Formation of Alberta, is today known from multiple units of both the USA and Alberta [adjacent image shows the Drumheller Edmontonia model].

The second species, E. rugosidens, was first described in 1930 by Charles Gilmore for a specimen discovered by George Sternberg in the Upper Two Medicine Formation of Montana. This species has also proved widespread, being known from various Campanian units of Wyoming, Texas and Alberta. E. longiceps and E. rugosidens differ in skull shape, with E. longiceps having a narrower palate and a smaller boss behind the eye than E. rugosidens. Bakker (1988) argued that E. rugosidens was distinct enough from E. longiceps in its shorter snout and expanded postorbital region to warrant its own ‘wide-bossed edmontoniine’ subgenus, Chassternbergia (named in honour of Charles Sternberg, obviously. Shades of Florentino Ameghino there*). He also suggested that Chassternbergia specimens from the Judith River Formation might represent a new species or subspecies of this subgenus. Two authors later regarded Chassternbergia as a distinct genus (Olshevsky 1991, Ford 2000), but it has otherwise been thought that E. rugosidens should remain with E. longiceps in Edmontonia.

* The Argentinean palaeontologist Florentino Ameghino enjoyed naming fossil mammals after colleagues, and gave us such wonders as Asmithwoodwardia, Thomashuxleya, Oldfieldthomasia, Ricardolydekkeria, Ricardowenia, Ernestokokenia, Edvardcopeia, Edvardotrouessartia, Henricofilholia, Carolozittelia, Othnielmarshia and Henricosbornia.

Death of Denversaurus

i-d792d5e64aa136ff397b139038582aa1-Bakker's iconic image, stolen from flickr.jpg

Bakker (1988) also named a new edmontoniine genus and species, Denversaurus schlessmani, for a specimen from the Hell Creek Formation of South Dakota, originally described by Carpenter & Breithaupt (1986) as Edmontonia sp. This animal would have lived alongside Triceratops and Tyrannosaurus, but its position low down in the Hell Creek Formation led Carpenter & Breithaupt (1986) to argue that, while nodosaurids persisted into the Maastrichtian, they apparently disappeared before the end-Maastrichtian event (they didn’t base this contention on this specimen alone however, as there are other Maastrichtian nodosaurids). Bakker regarded D. schlessmani as distinct because, compared to other edmontoniines, its orbits were located further posteriorly and the underside of the occipital region was broader. Alas, these putative differences are almost certainly the result of the distortion that the skull had undergone: Carpenter (1990) argued that the diagnosis provided for this species relied on how the skull was reconstructed, and furthermore that the reconstruction was not necessarily accurate anyway [adjacent image is Bakker's iconic 1986 charging Edmontonia. The snout is too short for that genus actually].

Exactly what we’re meant to do with D. schlessmani today seems uncertain: everyone agrees that it can’t be reliably diagnosed as a distinct species, and should be regarded as part of Edmontonia, but various Hell Creek and Lance Formation specimens are listed by Vickaryous et al. (2004) as representing an ‘unnamed Edmontonia species’. Edmontonia specimens from the Aguja Formation of Texas and the Upper Matanuka Formation of Alaska are also regarded as representing an ‘unnamed Edmontonia species’, but I suspect what’s meant here is that we lack remains good enough to diagnose and name these species (Agaju Formation material has more recently been referred to E. longiceps). A third Edmontonia species, E. australis, was named by Ford (2000) for cervical scutes from the Maastrichtian Kirtland Formation of New Mexico. These scutes differ in shape and in the position of their dorsal keels from those of other Edmontonia specimens, but the species has since been listed as a nomen dubium (Vickaryous et al. 2004).

Palates, sinuses and cheeks (again)

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In the long-muzzled skull of Edmontonia, the orbits are located far back and are surrounded by bony bosses. These may have protected the eye during combat, but the position of the orbits might also imply that Edmontonia had a particularly extensive field of vision. I can’t say any more on this subject, because it’s totally unstudied (so far as I know). Edmontonia is also interesting in having a particularly extensive osseous secondary palate (OSP). Some ankylosaurids also had one of these, but because it’s absent in both basal ankylosaurids and basal nodosaurids it must have evolved convergently. Edmontonia also resembles OSP-bearing ankylosaurids in possessing sinuses on the lateral sides of its internal nasal cavity, dorsal to the tooth row. Furthermore, the internal nasal cavity was subdivided by a vertical plate of bone, and a bony keel along the palate (formed by fused vomers) would seem to have divided the mouth cavity and decreased the space available for food (Vickaryous et al. 2004, Vickaryous 2006). We now know that Edmontonia was like Panoplosaurus in having a special ‘cheek scute’, and CT scans show that this wasn’t fused to either of the jaws but must have been ‘floating’ in soft tissue (Vickaryous 2006). All of these features suggest that Edmontonia was doing quite complex things during eating. The OSP and nasal sinuses might have evolved to reinforce the skull (acting as a structural brace); the divided nasal chamber shows that paired streams of air were transmitted during respiration; and the presence of cheeks suggests that food was retained in the mouth while complex chewing was practised [in the adjacent CT-scan, the subdivided nasal chamber is clearly visible, as are cross-sections through the cheek plates. In the image below, the paranasal sinuses are visible below the lateral sides of the nasal chamber, just dorsal to the cheek plates. The deep keel on the palate is also visible. Images kindly provided by Matt Vickaryous and used with permission: for further explanations of these scans see Vickaryous et al. 2004 and Vickaryous 2006].

i-2bf5bf0faab28efb9bd85f2efc336a51-Edmontonia section CT section 2.jpg

Edmontonia‘s most remarkable features were the elongate spikes on the neck and shoulders, the two most anterior of which pointed forwards and sideways. One of the longest spikes had a forked tip, but specimens differ in how pronounced this fork was and it might have been sexually dimorphic. The fact that Edmontonia ranged far and wide across Campanian and Maastrichtian North America suggests that it was an ecological generalist, able to make a living in diverse habitats and to feed on numerous types of plants. These dinosaurs would have had to watch out for giant tyrannosaurids – the dominant predators in their ecosystems – but again I must protest against the textbook wisdom that these dinosaurs squatted on the ground in the vain hope that the lurking 5-ton theropod would get bored and wander off. That is definitely a crap idea.

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And – more tomorrow! Credit to puuikibeach for the above.

PS – happy Valentine’s Day!

Refs – –

Bakker, R. T. 1988. Review of the Late Cretaceous nodosauroid Dinosauria. Denversaurus schlessmani, a new armor-plated dinosaur from the latest Cretaceous of South Dakota, the last survivor of the nodosaurians, with comments on the stegosaur-nodosaur relationships. Hunteria 1 (3), 1-23.

Carpenter, K. 1990. Ankylosaur systematics: example using Panoplosaurus and Edmontonia (Ankylosauria: Nodosauridae). In Carpenter, K. & Currie, P. J. (eds) Dinosaur Systematics: Approaches and Perspectives. Cambridge University Press, Cambridge, pp. 281-298.

– . & Breithaupt, B. 1986. Latest Cretaceous occurrence of nodosaurid ankylosaurs (Dinosauria, Ornithischia) in western North America and the gradual extinction of the dinosaurs. Journal of Vertebrate Paleontology 6, 251-257.

Ford, T. L. 2000. A review of ankylosaur osteoderms from New Mexico and a preliminary review of ankylosaur armor. New Mexico of Natural History & Science Bulletin 17, 157-176.

Olshevsky, G. 1991. A Revision of the Parainfraclass Archosauria Cope, 1869, Excluding the Advanced Crocodylia. Publications Requiring Research, San Diego.

Vickaryous, M. K., Maryanska, T. & Weishampel, D. B. 2004. In Weishampel, D. B., Dodson, P. & Osmólska, H. (eds) The Dinosauria, Second Edition. University of California Press (Berkeley), pp. 363-392.

– . 2006. New information of the cranial anatomy of Edmontonia rugosidens Gilmore, a Late Cretaceous nodosaurid dinosaur from Dinosaur Provincial Park, Alberta. Journal of Vertebrate Paleontology 26, 1011-1013.

Comments

  1. #1 Emile
    February 14, 2008

    The Argentinean palaeontologist Florentino Ameghino enjoyed naming fossil mammals after colleagues, and gave us such wonders as…

    Gaah! And they’re all valid?

    I must protest against the textbook wisdom that these dinosaurs squatted on the ground in the vain hope that the lurking 5-ton theropod would get bored and wander off.

    Edmontonia, at least, looks equipped for sudden sideways lunges with those large shoulder spikes, if not Bakker’s “runaway steamroller” approach.

  2. #2 David Marjanovi?
    February 14, 2008

    Gaah! And they’re all valid?

    AFAIK most or all of them are, and the tradition has been continued: Florentinoameghinia, Ricardoestesia*, Josephoartigasia

    * Not to be confused with Estesia and Restes.

  3. #3 John Conway
    February 14, 2008

    5-ton theropods may have got bored of get their shins bashed with great big spikey-things, however.

  4. #4 Darren Naish
    February 14, 2008

    What great big spikey-things? Have you looked at Edmontonia‘s tail lately? Anyway, even for tail-clubbed ankylosaurids the idea that they sat still and gamefully hoped that the predator would come without whacking range is stupid.

    And – nod to Scott Hartman’s ‘Armor – what armor?’ pic :)

  5. #5 Lars Dietz
    February 14, 2008

    “Gaah! And they’re all valid?”

    Nomenclaturally, yes. I’m not sure if all of them are still being used as generic names, as Ameghino was something of an overzealous splitter (like many 19th century paleontologists) and many of his names have been sunken into synonymy. Simpson later named a genus Florentinoameghinia in his honor.

  6. #6 Lars Dietz
    February 14, 2008

    Sorry, David’s comment hadn’t appeared yet when I wrote mine.

  7. #7 Nick
    February 14, 2008

    What great big spikey-things? Have you looked at Edmontonia’s tail lately?

    Um, I think John might have been referring to the shoulders…

  8. #8 Zach Miller
    February 14, 2008

    Ah, my favorite nodosaur! Great post, Darren.

    My geckos take an interesting stance when they feel threatened and/or try to be dominant. They puff their bodies up, stand as tall as possible, and stand their tails up in the air, moving the tail left and right. Sometimes they will bob their bodies up and down, too. This is something I can see ankylosaurs doing, although I’m sure the analogue is a little far-flung, phylogenetically.

  9. #9 Hai~Ren
    February 14, 2008

    Hurrah for all this ankylosaurian goodness! I’ve always been extremely fascinated by ankylosaurs, but it always seems to me that they’re so difficult to reconstruct and restore accurately, especially if only partial remains and disarticulated bits of scutes and spikes are known.

    Edmontonia is my favourite nodosaurid; I find it quite surprising that even though Edmontonia and Sauropelta are apparently the most completely known nodosaurids, both of these never featured at all in the dinosaur books I used to read as a little child, which were instead full of ankylosaurids, with the nodosaurids represented by less complete taxa such as Nodosaurus and Silvisaurus, or even non-nodosaurids like ?Acanthopholis, Hylaeosaurus, and Polacanthus. Even the supposedly pretty complete Panoplosaurus didn’t get a proper reconstruction in the books that bothered to include it.

    Will you be covering Nodosaurus itself? I find it very intriguing that most restorations leave it devoid of any spikes at all, even though it apparently did possess them (haven’t seen any reconstructions that reflect this though).

  10. #10 Nathan Myers
    February 14, 2008

    Zach: Your geckos must have learned it somewhere.

  11. #11 David Marjanovi?
    February 14, 2008

    This is something I can see ankylosaurs doing

    I can’t, because — already having vertical legs — they already stood as tall as possible.

    Sorry, David’s comment hadn’t appeared yet when I wrote mine.

    Yours contains information that I didn’t even know! :-)

  12. #12 Christopher Taylor
    February 14, 2008

    Ameghino was something of an overzealous splitter

    If you want a good example of Ameghino’s occassionally somewhat… slipshod approach to palaeontology, go to http://www.palaeos.org/Palaeoapterodytes_ictus and read on his description of the ‘wingless’ fossil penguin Palaeoapterodytes, named for a humerus with the unique condition of having the distal end atrophied and lost. When Lambrecht later re-examined the specimen, he decided that rather than being atrophied, the distal end had simply broken off.

  13. #13 Lars Dietz
    February 15, 2008

    “Yours contains information that I didn’t even know! :-)”
    I actually don’t know that much about South American fossil mammals. Probably much less than you do.

    Oh yes, Palaeoapterodytes. Certainly one of Ameghino’s strangest errors. However, his work was usually better than that. When it came to South American mammals, he got the phylogeny mostly right when it came to their relation with each other. He often was completely wrong when he tried to derive non-South American forms from them, which is why many notongulates have such confusing names as Notohippus, Archaeohyrax or Notopithecus. Same with stratigraphy. He got the sequence of the fossil-bearing strata mostly right but he far overestimated their relative age. So I think Simpson was right that Ameghino’s main faults were his obsession with a South American origin of all major mammal groups and overzealous splitting. If you want to see an example of the latter, look at the synonymy of Henricosbornia lophodonta at http://www.paleocene-mammals.de/pal4.htm. These synonyms were distributed by Ameghino in 4 families and 3 orders, but he did recognize they were related to each other. And I should better be quiet now, as I’ve never even seen Ameghino’s major works, only some shorter publications that are online, and I am basing this essentially on what others (especially Simpson) wrote about him.
    Browsing through the lists of Paleocene mammals at that site, I saw that there are genera called Paulacoutoia, Carolopaulacoutoia, and Carolocoutoia, named in the Ameghinian tradition and all valid.
    Oh yes, I know: ankylosaurs!

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