Ankylosaurians have generally been on
the back burner for vertebrate paleontologists and the public at large. Think of
it this way: how many of you prefer fierce predators armed with tooth and claw,
or mighty sauropods, or powerful horned dinosaurs, or bizarre stegosaurs?
Iguanodonts and hadrosaurs get a pass because they're so abundant, so
researchers can consider questions that aren't appropriate for groups with
smaller sample sizes, and many did intriguing things with their heads. Now, how
many of you want to work on armored dinosaurs, which (and I say this as someone
who is a fan) were kind of stubby, portly, and lumpy. For about half of them,
their primary "action feature" was "stand in one place and look
intimidating or inedible". Until about the 1990s, it seemed like all examples were either
based on scrappy fossils or were severely under-described. Furthermore, they do
not lend themselves to restoration, the major issue being the presence of all
those bits of bony armor not anchored to any other bones. Many artists before
the Dinosaur Renaissance basically faked it, creating these glowering
horned-toad-like creatures with a neat gridwork of large scutes, a fringe of conical
spikes along the sides of the body, and occasionally a flat blob at the end of
the tail meant to represent a club. They would then identify their creations as Palaeoscincus
and call it a day. If they were good, you could tell that the front half was Edmontonia,
which is known, coincidentally, from an articulated torso and skull. To be fair,
this specimen does include rows of large scutes and lateral spikes, but 1) there
are only three rows, 2) there are noticeable gaps between the rows, 3) they are
only present over the neck and shoulder, 4) there is plenty of the rest of the
torso to show the absence of additional neat rows of large scutes, and 5) the
lateral spikes also peter out after the shoulders. In other cases, you'd get
these "dachshund nodosaurs", with tubular bodies and Stegosaurus-like
heads, or toad-like ankylosaurs, but in those cases at least the heads would be
recognizable. These two incarnations also usually had neat grids of scutes.
From the initial discoveries of ankylosaurs until the late 1970s, ankylosaur classification was simply not done in polite society, so untested pet schemes ruled the day, and ankylosaurs were sort of a faceless crowd (no doubt composed of grumpy Palaeoscincus). Then Walter Coombs came along and found that they could be separated into ankylosaurids and nodosaurids, which could be distinguished by features such as the presence (ankylosaurids) or absence (nodosaurids) of tail clubs. In the 1990s, a third group, Polacanthidae, was distinguished by some authorities. Although an early misinterpretation put a tail club on them, they were eventually put forward by their advocates as featuring ankylosaurid-like skulls with nodosaurid-like bodies. Other authorities disagreed, as they are wont to do, with some considering the polacanthids a subgroup within Ankylosauridae or Nodosauridae, or not a group at all. Current research favors a group within Nodosauridae, near the base, but it would be nice to get more than a couple of opinions. I used to have a separate page for Polacanthidae, but in hindsight there wasn't much need to give a half-dozen entries their own page. They're living on Nodosauridae at the moment.
Ankylosauria consists of two main groups, Ankylosauridae and Nodosauridae. All ankylosaurians had armor over much of their bodies, mostly scutes and nodules, with large spines in some cases. The scutes, or plates, are rectangular to oval objects organized in transverse (side to side) rows, often with keels on the upper surface. Smaller nodules and plates filled in the open spaces between large plates. In all three groups the first two rows of plates tend to form a sort of half-ring around the neck; in nodosaurids, this comes from adjacent plates fusing with each other (and there is a third row as well), while ankylosaurids usually have the plates fused to the top of another band of bone. The skull has armor plastered on to it, including a distinctive piece on the outside-rear of the lower jaw. Feeding was generally accomplished similarly to how Scelidosaurus did it, with precise meeting of the teeth leading to a puncture-crush style like a mortar and pestle.
Besides body armor, which is also known lower in Thyreophora, all ankylosaurians (except Mymoorapelta) rewalled the acetabulum (the socket for the femur; it is open in most dinosaurs) for strength and flared the upper surface of the ilium outward. Ankylosaurians were very tubby beasts, suggesting that their somewhat feeble teeth were backed up by an impressive internal digestion system.
Ankylosaurians are a mostly K group from North America and Asia, although isolated finds put them in a number of odd places, including the Campanian (LK) of Antarctica, the late Maastrichtian (LK) and the Toarcian (EJ) of India, and the Campanian-Maastrichtian (LK) of Argentina. Interestingly, ankylosaurians as a group are also the second-most common dinosaurs, next to hadrosaurids, found in marine sediments; this likely is due to their solid construction and (inferred) spacious digestive tracts and other viscera, allowing whole bodies to float out to sea with surprising buoyancy despite the armor.
At this time, this page isn't much more than a holding ground for dubious or poorly known forms, and a convenient place for the preceding essay.
|Taxon or Taxa:||Time/Place:||Comments:|
|?"Acanthopholis" eucercus (N.D.) Seeley, 1879||late Albian (EK) of England||This animal is doubtfully ankylosaurian.|
|Aletopelta coombsi Ford and Kirkland, 2001||mid Campanian (LK) of "California" (paleo-Mexico)||California's first unique named dinosaur, Aletopelta is based on a partial skeleton, originally thought to belong to a nodosaurid. It was found on a tectonic block that appears to have been rafted north from Mexico, making Aletopelta (whose name means "wandering shield" referring to this change in location) a representative of a heretofore-unknown ankylosaurid radiation, according to the authors. Unlike most ankylosaurids, it had some respectable plates and spines, and the pelvis was covered with locking scutes. It may have been a "stegopeltine" or a traditional ankylosaurid, but nodosaurid is most likely.|
|Cryptosaurus eumerus (N.D.) Seeley, 1869||Oxfordian (LJ) of England||Based upon an unusual femur, this animal is better known in the literature as Cryptodraco (a replacement name that turned out to be unnecessary). Cryptosaurus is the true name.|
|Dracopelta zbyszewskii Galton, 1980||Kimmeridgian (LJ) of Portugal||Dracopelta is one of the better-known early ankylosaurians, based on material including part of a rib cage and some armor in situ.|
|"Hanwulosaurus" (N.N.) Anonymous, 2001||?LK of China||This unofficially-named animal is apparently a very large (~9 m long) ankylosaurian, known from many remains including a large flat skull, verts, ribs, scapula, ulna, femora, fibulae, and armor. It may belong to a new clade within Ankylosauria. Alternatively, it may well have been described by now, under a different name.|
|Hierosaurus sternbergi (N.D.) Wieland, 1909||late Coniacian (LK) of Kansas||Sometimes synonymized with Nodosaurus, this animal is rather late in the fossil record to be so. It is known from armor.|
|"Iguanodon" phillipsii (?N.D.) Seeley, 1869 (Priodontognathus)||Oxfordian (LJ) or EK of England||Better known as Priodontognathus Seeley, 1875, this is a poorly-known early ankylosaurian based on a partial upper jaw. It was once thought to be a stegosaurian. It may be valid, and is not to be confused with the putative stegosaur species "Omosaurus" phillipsii Seeley, 1893, although in this case Seeley went out of his way to make the situation confusing by giving the two the same species name out of the belief that they might turn out to be the same thing.|
|Onychosaurus hungaricus (N.D.) Nopcsa, 1902 (?Struthiosaurus)||Campanian (LK) of Romania||This is an indeterminate ankylosaurian based on verts and armor. It is sometimes described as a synonym of Rhabdodon, which suggests there is more than one animal represented in the material.|
|Rhodanosaurus ludgunensis (N.D.) Nopcsa, 1929 (?Struthiosaurus)||Maastrichtian (LK) of France||Based on armor plates, this animal is an obscure indeterminate ankylosaurian, possibly the same as Struthiosaurus.|
|Sarcolestes leedsi Lydekker, 1893||Callovian (MJ) of England||One of the earliest nodosaurids (?polacanthine; well, ankylosaurian at any rate), Sarcolestes is based on a jaw once thought to have belonged to a theropod.|
|Sauroplites scutiger (N.D.) Bohlin, 1953||Barremian-early Aptian (EK) of China||Sauroplites may be the same as the better-known Shamosaurus, or a polacanthine.|
|Stegosaurides excavatus (N.D.) Bohlin, 1953||LK of China||This is just an obscure, indeterminate ankylosaurian.|
|Tianchiasaurus nedegoatpeferima (?N.D.) Dong, 1993||Bathonian (MJ) of China||This is one of the most basal known ankylosaurians. Its odd species name comes from the cast of Jurassic Park (the name for a while was going to be Jurassosaurus nede...), wherein the first two letters of the last names of the actors were combined. Unfortunately, its remains are rather fragmentary.|
Nodosauridae and Ankylosauridae: Next come the good old nodosaurids and the (usually) tail-clubbed, squat-bodied ankylosaurids.
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