Ankylosaurids, even more than their
nodosaurid cousins, epitomize the idea of "dinosaurian tanks." They
wide animals, covered in armor, and often had large bony clubs at the end of their
tails. Unlike nodosaurids, most ankylosaurids did not have
large spikes or spines, but
rather concentrated on scutes and ossicles (essentially little scutes).
Ankylosauridae may include two main groups. A subset of long-skulled basal ankylosaurids may form a group called Shamosaurinae, with the more derived ankylosaurids as ankylosaurines. Ankylosaurines had short, wide skulls and large tail clubs composed of two lateral enlarged dermal bones and a terminal dermal bone. Tail clubs may have been limited to ankylosaurines. Both types are known to have had convoluted sinus passages in their skulls, possibly for a variety of reasons including improving the sense of smell, making loud sounds, and warming the air inhaled. They also had large pyramid-shaped "horns" the the top and bottom corners of the back of the skull. Ankylosaurids with clubbed tails had stiffened tails and less armor along the tail than their clubless counterparts. The club could not move up or down too far, and its lateral movement was also limited, but not to the same degree; nevertheless, it was at a good height to injure theropod metatarsals through simple blunt trauma.
Good ankylosaurid remains first show up in late Early Cretaceous Asia with Shamosaurus, and the group apparently quickly spread to North America (Cedarpelta) near the EK-LK boundary, along with other groups with an Asian-European start like hadrosaurids, tyrannosaurids, therizinosaurians, and ceratopsians. Also like these groups, while becoming well-established in the northern continents, the ankylosaurids do not appear to have made big inroads into Gondwanaland (although occasional reports from South America, Antarctica, Africa, and India show nodosaurids dispersed there, but were never particularly common); it may be that the Gondwana continents had spread too far from the northern continents by the middle of the Cretaceous that dispersal between the two great zones couldn't occur. This may have broken down by the end of the Cretaceous; see the relative success of hadrosaurids in South America.
|Taxon or Taxa:||Time/Place:||Comments:|
|Minmi paravertebra Molnar, 1980||Aptian-Albian (EK) of Queensland, Australia||This small ankylosaurian was first thought to be a nodosaurid, but is too generalized. It has unusual structures along its spine, called paravertebrae, whose function and purpose are still unclear; they may have strengthened the back and allowed for faster locomotion than other ankylosaurians. It is known from the partial type specimen and a nearly complete skeleton referred to M. sp.; the armor of the latter shows large scutes on the neck and flanking the shoulders and hips, with additional plate-like scutes on the tail (uncertain orientation). Possible gut contents show short lengths of vegetation not ground by gastroliths.|
|Cedarpelta bilbeyhallorum Carpenter, Kirkland, Burge, and Bird, 2001||late Aptian-early Cenomanian (EK-LK) of Utah||This was a large basal ankylosaurid. It is based on a partial skull and known from partial remains from several individuals from the upper Cedar Mountain Formation. The skull horns were not as large as later ankylosaurids displayed, and the snout was unusually narrow and had premaxillary teeth. Earlier reports had called this creature "Bilbeyhallorum". It could be a shamosaurine.|
|Chuanqilong chaoyangensis Han F., Zheng W., Hu D., Xu X., and Barrett, 2014||early Aptian (EK) of China||From the Jiufotang Formation, and thus a bit younger than similar Liaoningosaurus, Chuanqilong is known from the practically complete skeleton of a partially grown individual, with the underside of the skeleton exposed. Proportionally, the upper arms are long. The jaws are unusual for ornithischians in that the joint is at about the same level as the tooth row; usually the jaw joint is lower in herbivorous dinosaurs, which is interpreted as an adaptation for distributing force.|
|Liaoningosaurus paradoxus Xu, Wang, and You, 2001||early Aptian (EK) of China||Liaoningosaurus is based on the almost-complete remains of a juvenile ankylosaurian from the Yixian Formation. It is incredibly small (femora are 2.8 cm long, for example; body length maybe 34 cm, or a little over a foot) and includes an interesting and unprecedented shell-like bony plate shielding the abdomen.|
|Gobisaurus domoculus Vickaryous, Russell, Currie, and Zhao, 2001||Aptian-?Albian (EK) of China||Based on a nearly complete specimen, found in 1959 or 1960 (inspiring a specific name roughly meaning "overlooked," recalling the "neglected marvelous lizard" Thescelosaurus), Gobisaurus is described as close to Shamosaurus.|
|Shamosaurus scutatus Tumanova, 1983||Barremian-early Aptian (EK) of Mongolia||Shamosaurus is a basal ankylosaurid known from remains pertaining to several individuals, including a good skull with a narrow beak and small horns like Cedarpelta. It is usually assumed to have had a tail club, but this part of its anatomy has never been discovered (indeed, apparently nobody has ever really gotten around to describing the referred postcranial material).|
|Taxon or Taxa:||Time/Place:||Comments:|
|Bissektipelta archibaldi Parish, Jolyon, and Barrett, 2004 (originally Amtosaurus archibaldi Averianov, 2002)||late Turonian-?Coniacian (LK) of Uzbekistan||First assigned to Amtosaurus, here considered a synonym of Talarurus, this new species is known from a braincase. As far as I know, it is Uzbekistan's first named ankylosaurian.|
|Taxon or Taxa:||Time/Place:||Comments:|
|Zhongyuansaurus luoyangensis Xu L., Lu J., Zhang X., Jia S., Hu W., Zhang J., Wu Y., and Ji Q., 2007||early LK of China||Zhongyuansaurus is known from at least skull, forelimb, and pelvic material, and is distinguished by characters including a skull length/width ratio of 1.4:1, a flat roof of the skull, a straight ischium, and where muscle attachments are located on the humerus. It was described as a nodosaurid, but appears to be a basal ankylosaurid instead.|
|Crichtonsaurus: Dong, 2002||C. bohlini (type) Dong, 2002||Cenomanian-Turonian (LK) of China||As yet obscure, Crichtonsaurus is
based on a partial jaw with referred postcrania including verts, shoulder
girdle, humerus, femur, and armor, and is named for Michael Crichton, author of Jurassic Park.
A nice ankylosaurid-type skull (with big
squamosal horns) has also been referred to it.
C. benxiensis is known from a nearly complete skull (longer than wide) and partial skeleton, probably from the same individual. It is larger than C. bohlini, and that, along with some of the characteristics used to differentiate the two (fused or unfused scapula and coracoid) suggest to me at least that there are some growth-related things at work here. It may instead represent a different genus
|C. benxiensis Lü J., Ji Q., Gao Y. and Li Z., 2007|
|Euoplocephalus tutus Lambe, 1910 (originally Stereocephalus tutus Lambe, 1902)||late middle-early late Campanian (LK) of Alberta||Since the 1970s or so, Euoplocephalus
has been considered to be the best-known ankylosaurid, with more than
forty specimens to its credit. How it got to be so well-known is a
bit of a dirty secret: it absorbed all of the other Dinosaur
Park/Horseshoe Canyon Formation ankylosaurids, including Anodontosaurus, Dyoplosaurus, and Scolosaurus. This would not be such
a problem if it also weren't for the fact that Euoplocephalus is
based on a beat-up partial skull and a half ring of cervical armor. As is usual, the other names involved are only marginally comparable. Anodontosaurus
is based on another beat-up skull and cervical half-ring, with some more
pieces-parts, Dyoplosaurus is based on a hind end and tail with
even less of a skull, and Scolosaurus dispenses with the skull
altogether and is based on a very good articulated torso. Thus, it
should not be surprising that Euoplocephalus was ripe for a
reassessment in light of new advances in Dinosaur Park Formation
stratigraphy. It and its cohort genera were
modest-sized ankylosaurines, smaller than Tarchia
Reviewing this, I have my answer as to why Euoplocephalus was never restored in old illustrations instead of Dyoplosaurus and Scolosaurus: it wasn't well-known during the initial time the other genera were separated. Traditionally, Scolosaurus was depicted with two rows of large dorsal spines, reaching maximum size over the hips, and two large spikes on the tail club, while Dyoplosaurus was depicted with two rows of more subdued dorsal spines, no club spikes, and a modest club.
Euoplocephalus was the first ankylosaurian known to have armored eyelids, although others are now known to have had them, too (Pawpawsaurus).
Although cerapods are best known for complex jaw action, Euoplocephalus seems to have come up with its own method of chewing.
|Anodontosaurus lambei Sternberg, 1929||late Campanian-middle Maastrichtian (LK) of Alberta||Anodontosaurus is based on a partial skull and other fossils from the Horseshoe Canyon Formation. The name refers to a supposed absence of teeth. The tail club was wider than long, with pointed osteoderms (not quite the true spiked club, but noticeable). There were small nodes at the base of the horns, and small scutes between the large scutes of the first cervical ring.|
|Ankylosaurus magniventris Brown, 1908||late Maastrichtian (LK) of Montana, Wyoming, and Alberta||Ankylosaurus was a rare, large (c.
6-7 m long) Lancian ankylosaurine with very prominent "horns". It is known from
three substantial specimens including good skulls, but oddly has never
received much attention. It is traditionally depicted with a regular
checkerboard of oval scutes over the back and a fringe of short lateral
conical spikes, an embellishment based on Edmontonia
(you see, it was only in the '70s that ankylosaurians were separated into
nodosaurids and ankylosaurids, so in older restorations it is not uncommon
to see "Palaeoscincus" wandering about with a fat tail
club and armor based on Edmontonia; Edmontonia, more often
than not called Palaeoscincus,
being the only ankylosaurian besides Scolosaurus with
decent in-situ armor remains known at that point, became every
artist's favorite ankylosaurid model).
Anyway, Ankylosaurus armor is sometimes compared to Euoplocephalus (Scolosaurus) but isn't all that similar; in particular, the animal had some very large scutes.
|Scolosaurus cutleri Nopcsa, 1928 (?including Oohkotokia horneri Penkalski 2013)||early late Campanian (LK) of Alberta, late Campanian (LK) of Montana?||Scolosaurus is based on a good
postcranial skeleton with in situ armor. It came to be
restored as having a tail club with two large spikes, whch was based on a
misinterpretation of the type specimen: the distal half of the tail is not
preserved, and about the last thing on the remaining half is a pair of
midline spikes, which became the classic (albeit imaginary) spiked
Oohkotokia is probably the same as Scolosaurus. If it is, Scolosaurus receives several other specimens, which add a skull and club to the picture and establish it as operating the Two Medicine Formation franchise of Euoplocephalus-ish North American ankylosaurids. Oohkotokia is based on a partial skull, a few vertebrae, and armor, found with the remains of at least one other animal, a nodosaurid. A few other specimens have been referred, which include two more skulls, a ring of cervical armor, and a tail plus tail club.
Scolosaurus primarily differs from the other members of Euoplocephalus Anonymous by details of the armor; the most obvious, if you were to walk up to one in the street, are the long backswept squamosal horns, small nodes at the bases of the horns behind the eyes (also in Anodontosaurus), cervical armor with a combination of flat circular midline scutes and lateral scutes with tall keels, and a roughly circular tail club.
|Ziapelta sanjuanensis Arbour, Burns, Sullivan, Lucas, Cantrell, Fry, and Suazo, 2014||late Campanian (LK) of New Mexico||Ziapelta is based on a skull, partial cervical rings, and other pieces of armor. The squamosal horns are large and curve slightly forward; on the type skull, they actually look something like big round ears in profile. The osteoderm over the nasal area is also quite prominent. Unlike the roughly contemporaneous Nodocephalosaurus, Ziapelta appears to be more closely related to North American ankylosaurids from the Alberta–Montana region.|
|Dyoplosaurus acutosquameus Parks, 1924||late middle Campanian (LK) of Alberta||As you may have gathered from the discussion above at Euoplocephalus, Dyoplosaurus is one of several genera long thought to be synonymous with it. It differs in a number of details from Euoplocephalus as it has come to be understood, and has been restored as its own genus. It is most notable for its gracile tail club, longer than wide.|
|Talarurus plicatospineus Maleev, 1952 (including Syrmosaurus disparoserratus Maleev, 1952 [Maleevus Tumanova, 1987] and ?Amtosaurus magnus (N.D.) Kurzanov and Tumanova, 1978)||?Santonian (LK) of Mongolia||Talarurus was an ankylosaurine with some similarities to Euoplocephalus, but with a weakly developed tail club. Remains from at least five individuals are known, not including the partial skulls that contemporaneous Maleevus and Amtosaurus are based on, here considered conspecific with T. plicatospineus (although some researchers have in the past considered Amtosaurus to have been a hadrosaurid, or even too indeterminate for assignment beyond Ornithischia incertae sedis). It has been suggested that it lived like a dinosaurian hippo.|
|Tsagantegia longicranialis Tumanova, 1994||?Santonian (LK) of Mongolia||Tsagantegia may be a shamosaurine or a basal ankylosaurine. It had a long, very flat, smooth skull and small horns, but a wider snout that Shamosaurus or Cedarpelta.|
|Nodocephalosaurus kirtlandensis Sullivan, 1999||middle late Campanian (LK) of New Mexico||This ankylosaurid, based on a partial skull, may be close to the roughly contemporaneous Saichania and Tarchia. It is mostly interesting at this point as an example of the incompletely-known New Mexican late Cretaceous fauna.|
|Pinacosaurus: Gilmore, 1933 (including Heishansaurus)||P. grangeri (type) Gilmore, 1933 (including Heishansaurus pachycephalus Bohlin, 1953)||late Campanian (LK) of Mongolia and China||Pinacosaurus is one of the best-known ankylosaurians, with over fifteen specimens referred to it, and is also one of the few ankylosaurians for which juvenile remains are known. In one case, several juveniles were found huddled together, and had apparently died in a sandstorm. Juvenile ankylosaurian skulls are particularly useful because it's not easy to tell where the major bones are underneath all the armor in adults, and patterns of bone location are useful in determining relationships. The sometimes-pachycephalosaurid Heishanosaurus pachycephalus is a synonym.|
|P. mephistocephalus Godefroit, Pereda-Suberbiola, Li, and Dong, 1999||late Campanian (LK) of China||The second species is based on a subadult skeleton and skull with distinctively demonic horns (prompting the species name). It may represent a genus distinct from Pinacosaurus.|
|Saichania chulsanensis Maryanska, 1977 (?Shanxia, Tianzhenosaurus)||?mid Campanian (LK) of Mongolia||This ankylosaurine had unusual crescent-shaped armor plates around the neck, and armor on the belly region, a rare find. Its arms were very short and massive, leading to a very low-slung animal. It's probably the senior synonym of Shanxia and Tianzhenosaurus.|
|Tarchia kielanae Maryanska, 1977 (including Minotaurasaurus ramachandrani C.A. Miles and C.J. Miles, 2009)||early Maastrichtian (LK) of Mongolia||Tarchia is the largest known Mongolian ankylosaurine, at over eight meters in length. It had a large head, relatively tall for an ankylosaurid. The type exhibits partially-healed skull injuries, both internal and external, suggestive of a tyrannosaurid attack. It may have been a close relative of Saichania. Remains from several individuals are known.|
|Taxon or Taxa:||Time/Place:||Comments:|
|Ahshislepelta minor Burns and Sullivan, 2011||middle late Campanian (LK) of New Mexico||Ahshislepelta is a small ankylosaurine based mostly on part of the anterior torso (partial shoulder girdle and left arm), along with vertebral fragments and armor.|
|"Dyoplosaurus" giganteus (N.D.) Maleev, 1956||early Maastrichtian (LK) of Mongolia||This species is generally considered a senior synonym of Tarchia kielanae, but the type material appears to be indeterminate. It is based on caudal verts, metatarsals, phalanges, a tail club, and other bits of armor.|
|"Palaeoscincus" asper (N.D.) Lambe, 1902||late middle or early late Campanian (LK) of Alberta||"P." asper is a tooth taxon usually assigned to Euoplocephalus, but all bets are off with Euoplocephalus receiving an Iguanodon-like taxonomic dissection.|
|Shanxia tianzhenensis Barrett, You, Upchurch, and Burton, 1998 (?Saichania, Tianzhenosaurus)||?Campanian (LK) of China||Shanxia is known from a partial skull, six cervicals, three dorsals, four caudals, a humerus, part of an ilium, a complete and a partial femur, and a scute. It may be the same as Tianzhenosaurus and/or Saichania.|
|Tianzhenosaurus youngi Pang and Cheng, 1998 (?Saichania, Shanxia)||?Campanian (LK) of China||Tianzhenosaurus is known from a skull, which is much wider than tall and shows long, slender squamosal horns. Priority is somewhat uncertain, but it may not matter, because they could both be the same as Saichania.|
|Zaraapelta nomadis Arbour, Currie, and Badamgarav, 2014||early Maastrichtian (LK) of Mongolia||Zaraapelta is based on a mostly complete and heavily ornamented skull of a Tarchia-like ankylosaurid.|
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