The hadrosaurids come in two basic
varieties; hollow-crested and non-hollow-crested. At each of these levels, there are
several groups, but this page will not cover them, because there is quite a bit of
housekeeping to do before we get there, namely, slogging through the indeterminate
members (interestingly, once a piece of petrified wood was described as being
hadrosaurid remains [Aachenosaurus]). If you want to skip this page, I don't blame
you (although I have a soft spot for Claosaurus; it was one of the first
obscure dinosaurs I learned about, back around the late 1980s-early 1990s, from
an article in a kid's magazine about dinosaurs).
Additional basal hadrosaurid material is known from the late Santonian (LK) of Italy, the mid Turonian (LK) of Alaska, late Maastrichtian (LK) of Spain and possibly Antarctica. In addition, a hadrosaurid femur discovered in New Mexico may be evidence that some dinosaurs were able to make it into the earliest part of the Paleocene, just beyond the K-T boundary, although most authorities consider it to have been reworked from older sediments.
From the early 1980s into the first decade of the 21st century, the standard model for ornithopod chewing involved a system of skull bones with flexible joints, the upshot being that the maxillae pivoted inward during chewing to grind things. More advanced computer modeling now allows this to be tested in finer detail, and it appears that, instead, the lower jaws were moving to permit grinding, with a combination of fore and aft motion and rotation of the two halves of the lower jaw (joined loosely at the front by the predentary) along their long axes.
In addition to mobile jaw bones, hadrosaurids were amply equipped with teeth. The old kids' books say 2,000, but this is an overestimate; about 1,600 is the most that has been reliably estimated, and lambeosaurines had fewer than half of that total, perhaps 700 at most. Still, this is significantly more than you or I could be reasonably expected to exhibit. Because these teeth were distributed in columns of three to six teeth, most of them were not in use, and would only come into play when the tooth above had been shed; the animals had more or less a conveyor belt of teeth. Furthermore, the teeth were composed of six different tissues (mammals have four), with varying hardnesses, and as teeth wore down, different tissues became more or less prominent. This is an excellent way to promote specialization and differentiation of species, and early results indicate that different groups of hadrosaurids used their elaborate dentitions differently, with at least some lambeosaurines emphasizing grinding, and saurolophinids emphasizing slicing.
Hadrosauridae: Hadrosaurids were long thought to have lived in
water, another set of victims of the mindset that condemned sauropods as well to the watery
regions. In the case of hadrosaurids, they were they because they were supposedly
swimmers, as shown by their tall tails and "webbed" hands found on
"mummies," and because their teeth seemed weak However, it turned out the
tail was very inflexible due to bony tendons, and the webs of the hands were shown to be
dried-out cushions for the hands. As for the teeth, that is a patent lie. Hadrosaurids were very well adapted to feed at low levels on land, much like
bison. Their backs
even show a striking resemblance to the way bison spines are curved. The best
analogue for a hadrosaurid would have to include this low-browsing ability with a hint of
the bewildering variety of display devices hadrosaurids were equipped with. Many
hadrosaurids are known to have lived in groups, possibly not true herds, but groups
nonetheless. In fact, it has been suggested that one mass "grave" of Maiasaura
contains the remains of a gathering 10,000 individuals strong.
Hadrosaurids show some sort of unusual midline spinal phenomenon. Some appear to have dragon-like rectangular nonbony segments running down the midline of the back, while others suggest a deep, horse-like muscular neck. Hadrosaurids appear to have had rather thin, leathery skin, with large polygonal or oval tubercles surrounded by many smaller ones. The scale patterns may have some diagnostic value.
It is an unfortunate fact that without a decent skull, it is difficult to differentiate most hadrosaurids, due in part to the basic overall similarity of the skeletal plan, and in part to the relative lack of attention given to hadrosaurid postcrania. Lambeosaurines can be told from saurolophines in some elements, such as the hip bones and height of the neural spines (many lambeosaurines have slight "sails" down the back), but that is about as far as one can go with separating hadrosaurids from postcranial material at this point; people are looking for differentiating characters, though. Ceratopsids have a similar problem, but probably worse, as the frill is necessary as everything else is pretty much the same across taxa, and the frill didn't come in until the animal was nearly an adult.
|Taxon or Taxa:||Time/Place:||Comments:|
|Telmatosaurus transsylvanicus Nopcsa, 1903 (originally Limnosaurus transsylvanicus Nopcsa, 1900)||early-mid Maastrichtian (LK) of Romania, France, and Spain||This possible basal hadrosaurid (position currently uncertain) is very similar to Iguanodon and its ilk. It is known from 5 to 10 fragmentary skulls, plus some postcranial material.|
|Claosaurus agilis Marsh, 1890 (originally Hadrosaurus agilis, Marsh, 1872)||mid Santonian-early Campanian (LK) of Kansas||Based on a mostly complete postcranium, Claosaurus is one of the most primitive hadrosaurids. However, this is a good place to explode the myth of it retaining the first metatarsal, which all other hadrosaurids for which the foot is known have lost. There was no MT I!|
|Hadrosaurus foulkii Leidy, 1858||early-middle Campanian (LK) of New Jersey||Sadly, this historically important genus is based on remains that do not include a good skull. It is known mostly from a partial postcranium (more would have been known if people had known about dinosaurs in the 1830s and had kept the bones together, but that's life), and traditionally it has been thought of as like Gryposaurus or Kritosaurus, although this cannot be established. This was the first classic dinosaur to be known from a decent postcranium, and through the limb proportions showed early researchers that some dinosaurs were bipedal.|
|Lophorhothon atopus Langston, 1960||Campanian (LK) of Alabama and North Carolina||A rare Southeastern iguanodontian (heck, rare Southeastern dinosaur!), Lophorhothon is based on a partial skull and skeleton from a juvenile animal. The skull has a small pyramidal crest between the eyes. In the past, this animal was interpreted as a basal "saurolophinid", but new research has suggested both that it actually may be closer to Tenontosaurus, or that it is a basal saurolophine.|
|Plesiohadros djadokhtaensis Tsogtbaatar, Weishampel, Evans, and Watabe, 2014||late Campanian (LK) of Mongolia||Plesiohadros is known from skull and postcranial remains, representing a basal hadrosauroid/hadrosaurid-type animal (although note that it is apparently bad paleontological karma to give a genus a name suggesting it is near the base of the hadrosaurid radiation; see Eolambia and Protohadros). It is of note for being one of the few ornithopods known from the Djadokhta Formation, better known for almost everything but ornithopods.|
|Shuangmiaosaurus gilmorei You, Ji, Li J., and Li Y., 2003||Cenomanian-Turonian (LK) of China||Described as the sister taxon to Hadrosauridae, Shuangmiaosaurus is based on partial remains of the upper and lower jaws.|
|Tethyshadros insularis Dalla Vecchia, 2009||late Campanian-early Maastrichtian (LK) of Italy||At last, the hadrosaurid formerly known as
"Antonio" is described (hadrosauroid if Hadrosauridae is
restricted to Lambeosaurinae and Saurolophinae, Hadrosauridae using the
definition that includes Telmatosaurus). I was pleased to
learn that several other individuals are known as well, from the same
sedimentary lens. It becomes the second classic dinosaur to be named
from Italy, after Scipionyx.
Reconstructions are of course not as good as seeing the real thing, but on the other hand if you've seen enough reconstructions, you begin to get a feel for proportions and such (or perhaps that's just me). One of my pastimes as a kid back in the 1980s was tracing the skeletons from The Illustrated Encyclopedia of Dinosaurs, and so I've long liked going to the big picture. In this case, turning to the reconstruction of the lovely articulated and nearly complete type (the layout as found vaguely echoes a Bernissart Iguanodon), I am struck by several things. Starting up front, the skull is quite large, with impressively large infratemporal fenestrae, and similar in build to the gracile iguanodont Mantellisaurus. There is no gryposaur-like nasal arch, unlike some early reports (probably a bone was jogged out of place). Going farther back, the tibiae are very long compared to the thighs, and the ischia extend back into yesterday. There is also something interesting with the hand. It takes a few moments, but then it becomes clear: there is no little finger. Unlike other hadrosaurids which had digit V hanging out beyond the II-III-IV column, Tethyshadros made do without that extra manipulator. Checking the diagnosis, I'm doing quite well, as all of these are deemed autapomorphic. Of course, in this case the dinosaur made it easy; I doubt I'd do so well with a troodontid, for example.
|Zhanghenglong yangchengensis Xing H., Wang D., Han F., Sullivan, Ma Q., He Y., Hone, Yan R., Du F., and Xu X., 2014||middle Santonian (LK) of China||Zhanghenglong is a transitional iguanodont-hadrosaurid based on a partial skull. Material including part of the anterior torso of a smaller individual is also known. The jugals are deep, giving it fairly droopy "cheeks", and the neural spines are on the long side. The forearms are proportionally long and slender.|
|Taxon or Taxa:||Time/Place:||Comments:|
|Cionodon arctatus (N.D.) Cope, 1874 (?Thespesius)||late Maastrichtian (LK) of Colorado||This indeterminate hadrosaurid is based on a maxilla, two dorsals, partial third metatarsal, and the ends of an ulna.|
|"Cionodon" stenopsis (N.D.) Cope, 1875||late middle-early late Campanian (LK) of Alberta||This is an anonymous indeterminate hadrosaurid from the early days of North American dinosaur research, based on part of a maxilla.|
|"Claosaurus affinis" (N.N.) Wieland, 1903||early Campanian (LK) of South Dakota||This animal is based on toe bones, which became mixed-up with a toe bone from C. agilis. They are mostly of interest for documenting the presence of hadrosaurs living at this time in the vicinity of the Western Interior Seaway.|
|Diclonius: (N.D.) Cope, 1876||D. pentagonus (N.D.) (type) Cope, 1876||middle-late Campanian (LK) of Montana||Because the teeth (and one partial lower jaw, from D. pentagonus) these various species are based on all came from the same area, they are retained in Diclonius. They may very well all belong to the same animal, or from a collection of Judith River hadrosaurids.|
|D. calamarius (N.D.) Cope, 1876|
|D. perangulatus (N.D.) Cope, 1876|
|Glishades ericksoni (N.D.) Prieto-Márquez, 2010||Campanian (LK) of Montana||Glishades is based on two partial premaxillae from the Two Medicine Formation. It was described as a derived hadrosauroid, but not a true hadrosaurid, possibly related to Bactrosaurus. More recent research indicates that it is a juvenile hadrosaurid, possibly a saurolophine.|
|"Hadrosaurus":||"H." breviceps (N.D.) Marsh, 1889||middle-late Campanian (LK) of Montana||This is just another indeterminate hadrosaurid, possibly the same as Prosaurolophus, although it has been referred to Kritosaurus (in the guise of Gryposaurus) in the past. It is based on part of a dentary.|
|"H." cavatus (N.D.) Cope, 1871||late Campanian-early Maastrichtian (LK) of New Jersey||These two species may well be the same thing. "H." cavatus is based on caudal vertebrae, "H." minor on dorsals, with referred material comprised of a partial hindlimb, verts, ribs, and hips. The [currently missing] ischia are described as unexpanded, possibly indicating a saurolophine.|
|"H." minor (N.D.) Marsh, 1870||late Campanian-early Maastrichtian (LK) of New Jersey|
|Hypsibema crassicauda (N.D.) Cope, 1869||Campanian (LK) of North Carolina||Hypsibema is a gigantic hadrosaurid based on caudals, a partial humerus, a partial tibia, and a partial metatarsal. The species "Neosaurus" missouriensis, another giant hadrosaurid from the eastern part of the United States, is sometimes assigned to Hypsibema, but given the limited remains, I don't find that justified. The original material also mixed in a theropod femur for good measure.|
|"Jaxartosaurus" fuyunensis (N.D.) Wu, 1984||LK of China||This indeterminate (or possibly not even described) hadrosaurid could be a lambeosaurine.|
|Lapampasaurus cholinoi Coria, González-Riga, and Casadio, 2013||late Campanian-early Maastrichtian (LK) of Argentina||Lapampasaurus appears to be known from material including at least cervicals, shoulder girdle bones, and toe bones.|
|Microhadrosaurus nanshuingensis (N.D.) Dong, 1979||early Maastrichtian (LK) of China||Based on a small dentary, this is most probably a juvenile hadrosaurid.|
|"Neosaurus" missouriensis (N.D.) Gilmore and Stewart, 1945 (Parrosaurus)||?early Maastrichtian (LK) of Missouri||This dubious giant hadrosaurid may masquerade as either Parrosaurus (because Neosaurus was preoccupied) or as Hypsibema missouriensis (or even H. crassicauda, as I used to have it); as the latter, it is most commonly seen, and has become the official state dinosaur of Missouri. "Neosaurus" is based on caudals, at first thought to belong to a camarasaurid-like sauropod because of their large size. A few other fossils have since been uncovered, including jaw material.|
|Ornithotarsus immanis (N.D.) Cope, 1869 (?Hadrosaurus)||Campanian (LK) of New Jersey||Sometimes synonymized with Hadrosaurus, this animal is based on a partial hindlimb of a very large individual.|
|?Orthomerus dolloi (N.D.) Seeley, 1883||Maastrichtian (LK) of the Netherlands||Often considered the same as Telmatosaurus in older works, this animal may not even be a hadrosaurid.|
|"Orthomerus" weberi (N.D.) Riabinin, 1945||Maastrichtian (LK) of Ukraine||"O." weberi is based on hindlimb bits.|
|Pteropelyx grallipes (N.D.) Cope, 1889 (?Corythosaurus)||middle-late Campanian (LK) of Montana||Pteropelyx is usually thrown out as a synonym of Corythosaurus, and then ignored because the type has no skull and it would have priority over Corythosaurus of several decades. It is known from a collection of postcranial remains. Almost no one has talked about Pteropelyx since Lull and Wright in 1942, or has taken it seriously as a useful name since Lambe in 1902 (who thought it to be a subgenus of Trachodon). Interestingly, for a supposed synonym of a lambeosaurine, it is described as having slender ischia, which is more of saurolophine thing.|
|"Saurolophus" kryschtofovici (N.D.) Riabinin, 1930||early Maastrichtian (LK) of China||This species, usually synonymized with Saurolophus angustirostris, is based on a fragmentary partial ischium.|
|Thespesius occidentalis (N.D.) Leidy, 1856||late Maastrichtian (LK) of South Dakota||This indeterminate hadrosaurid used to get a lot more play (if you go back in the literature, a bunch of species now referred to Edmontosaurus were put here). It is based on caudals and a pedal phalanx.|
|Trachodon mirabilis (N.D.) Leidy, 1856||middle-late Campanian (LK) of Montana and Alberta||Made famous in countless cheesy children's toys, Trachodon is actually a fraud, a dubious tooth taxon. In fact, of the type teeth, some belong to a ceratopsid, and others to a hadrosaurid. The name today is usually restricted to the hadrosaurid teeth, which may have come from an animal like Corythosaurus.|
|"Trachodon":||"T." altidens (N.D.) Lambe, 1902||middle-late Campanian (LK) of Alberta||Based on a partial maxilla, this specimen has been mooted as a "procheneosaur", which for our purposes means a juvenile lambeosaurine, which it may well be.|
|"T." marginatus (N.D.) Lambe, 1902||middle-late Campanian (LK) of Alberta||This collection of postcranial remains and teeth has sometimes been referred to Kritosaurus (as Gryposaurus), although a chunk of it has ended up in Lambeosaurus. It probably represents Gryposaurus.|
|"T." selwyni (N.D.)
|This species is based on a lower jaw with teeth, the latter most like those from "Hadrosaurus" breviceps. It seems to be most like Gryposaurus and Lambeosaurus.|
|"Troodon" isfarensis (N.D.) Nesov, 1995||early Santonian (LK) of Tajikistan||This was described as a troodontid based on a frontal (currently missing), but more recent study using the description and photograph of the bone shows that it was really a hadrosaurid, based on a prefrontal.|
Saurolophinae and Lambeosaurinae: These two groups are the derived hadrosaurids. They have some of the best fossil records of any dinosaurs, with skulls and skeletons known for most taxa.
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