Ornithischia (Predentata)

   The ornithischians are an amazingly diverse group of dinosaurs linked by their possession of, among other things: at least five sacrals (uncertain in most basal forms); pubis shifted backwards, with a prepubic process of varying development pointing forward; no gastralia; a palpebral bone in the orbit (prong of bone cutting across outside of eye socket to varying degrees); ossified tendons at least above the sacral region (lost for tail mobility in stegosaurians); no phalanges on digit V of the foot; a recession in the jaw margins for "cheeks;" and finally, and to my mind most importantly, possession of an extra bone at the beak-end of the lower jaw, called a predentary, which is where the name Predentata, sometimes used for this group, comes from.  Ornithischians were basally small, bipedal ?herbivores (it is suggested that some ornithischians, particularly those with heterodonty [differing teeth], and the basalmost forms, were omnivorous, including heterodontosaurids with their fangs and some marginocephalians; some of the basal ornithischians, including an unnamed tooth form, may have been carnivorous), who by the MJ had produced an astonishing variety of body plans, including the spiky quadrupedal stegosaurians, the heavy-set armored ankylosaurians, and the small, fast basal ornithopods known informally as hypsilophodonts.  By the end of the Cretaceous, more had arrived, like the bulky iguanodonts and their descendants, the hadrosaurids, the horned ceratopians, and the bone-headed pachycephalosaurians.
    Although ornithischians derive from bipedal ancestors, almost all of them show at least some ability to walk on all fours.  Ornithischians were primarily low browsers.  Unlike the other main group of classic dinosaurian herbivores, the sauropodomorphs, ornithischians display a wide variety of bodily features that appear to have been used for display and recognition, like the vertebral fins and headgear of hadrosaurids and some iguanodonts. 
    Large-scale ornithischian relationships have been stable and mostly unquestioned for the last 20 or so years, except for minor quibbles about where heterodontosaurids go, the position of Scelidosaurus vis--vis the ankylosaurians and stegosaurians, and if hypsilophodontids form a natural group.  There are some changes coming up, though, led by Richard Butler's work on basal ornithischians and new considerations on all of those tooth taxa from North America.  The main changes will affect the basal taxa and the hypsils.  This below is a version of the most current incarnation, which isn't too dissimilar to what came before except for Lesothosaurus and the heterodontosaurids.  Using Cerapoda and Ornithopoda may get harder, though.

<--Ornithischia
      |--Pisanosaurus       
      |--?Heterodontosauridae
      |      |--Abrictosaurus
      |      `--Heterodontosaurinae
      |           |--Heterodontosaurus
      |           `--Lycorhinus 
      `--+--Eocursor
           `--Genasauria
                |--Thyreophora
                |    |--Scutellosaurus
                |    `--Eurypoda
                |         |--Ankylosauromorpha
                |         |    |--Scelidosaurus
                |         |    `-->Ankylosauria
                |         `-->Stegosauria
                `--Neornithischia          
                     |--Lesothosaurus
                     `--+--Stormbergia
                          `--+--Agilisaurus
                               `--+--Hexinlusaurus         
                                    `--Cerapoda
                                         |-->Ornithopoda
                                         `--Marginocephalia
                                              |-->Pachycephalosauria
                                              `-->Ceratopia  

Ornithischia to Genasauria:  Unlike theropods and sauropodomorphs, there is little good material for basal ornithischians.  Most of what was thought to be known for them were distinctive teeth, but after the Revueltosaurus affair these may not even be dinosaurian (check here to find if your favorite tooth taxon has been banished).

Taxon or Taxa: Time\Place: Comments:
Pisanosaurus mertii Casamiquela, 1967 early Carnian (LTr ) of Argentina This small animal is based on a partial skeleton and skull that show an ur-ornithischian.  It has been allied to heterodontosaurids, "fabrosaurids," and hypsilophodonts, but is much too primitive; the condition of the sacrum and direction of the pubis are not certain (but it seems to be propubic, like classic saurischians).
Eocursor parvus Butler, Smith, R.M.H., and Norman, 2007 Norian (LTr) of South Africa Based on a partial skeleton including most of the lower jaw, portions of vertebrae, and much of the girdles and limbs minus the forearm and some of the hands, feet, and coracoid, Eocursor is the best-represent early ornithischian.  It clearly is opisthopubic, but unfortunately the tip of the lower jaw is poorly preserved, so the presence or absence of a predentary is unknown.  The animal was about 1 meter long, but given the preservation of the verts, I'd guess it wasn't fully grown.  It looks a lot like a Lesothosaurus with big heterodontosaurid hands.

Ornithischia to Genasauria i.s.: Years ago, when all ornithischians were thought to have sprung from some sort of ornithopod or another, most of these animals would have been known as the most basal ornithopods, the "fabrosaurids."  Something like these animals is known from the Late Triassic Lower Elliot Formation of South Africa.  

Taxon or Taxa: Time\Place: Comments:
Alocodon kuehnei (N.D.) Thulborn, 1973 late Callovian (MJ) of Portugal This animal is based on teeth which show some resemblance to "othnieliid" teeth, so it may belong in that "family".  Alternatively, it could be a thyreophoran.
Fabrosaurus australis (N.D.) Ginsburg, 1964 (?Lesothosaurus) Hettangian (EJ) of Lesotho Based on a partial dentary, this animal may well be the same as LesothosaurusFabrosaurus in fact is the name usually used for restorations of what is actually Lesothosaurus in older dinosaur books.
Gongbusaurus shiyii (N.D.) Dong, Zhou, and Zhang, 1983 Oxfordian (LJ) of China This is an indeterminate tooth taxon, somewhere close to Genasauria.
"Gongbusaurus" wucaiwanensis Dong, 1989 Oxfordian (LJ) of China This animal is known from a partial skeleton that may or may not belong in the same genus as the tooth-taxon Gongbusaurus.  It appears to be another  "fabrosaurid"-type ornithischian, but is in need of restudy.
Taveirosaurus costai (N.D.) Antunes and Sigogneau-Russell, 1991 late Campanian-early Maastrichtian (LK) of Portugal Based on teeth, this may be a small, late, basal European pachycephalosaurian, or a juvenile nodosaurid.
Trimucrodon cuneatus (N.D.) Thulborn, 1973 Kimmeridgian (LJ) of Portugal This is an indeterminate basal ornithischian based on teeth.  It could be a heterodontosaurid, and may be close to Echinodon.
Xiaosaurus dashanpensis Dong and Tang, 1983 Bathonian-Callovian (MJ) of China Possibly a basal ornithopod (although some have suggested that it could be a very basal marginocephalian, which wouldn't be all that different from a very basal ornithopod), this animal's remains are scrappy (the type is a partial maxilla, two cervicals, four caudals, and a hindlimb; a referred specimen is two teeth, a dorsal, two sacrals, a rib, a femur, and a phalanx; neither specimen can be found at this time) and just distinctive enough to stave off the dreaded nomen dubium.  In the past, it has been mostly thought of as a "fabrosaurid."  At this point, it's safest to consider it among the uncertain basal ornithischians, probably sorting out somewhere around Agilisaurus and Hexinlusaurus.  More material is needed.

Heterodontosauridae:  Heterodontosaurids are known mostly from skull material, with distinctive tusks found in most individuals.  They have been wild-cards, given the paucity of other early ornithischians to compare them to, and have been put with the ornithopods, or closer to the marginocephalians due to their jugal (cheek-area) bosses and tusks, the latter of which are also known in pachycephalosaurians, and some pelvic and hand details.  The most recent hypothesis is that they are a very basal offshoot, which I'm using here.  This is still a hot issue, or at least it would be if ornithischians were charismatic predators.  Heterodontosaurid material may also be known from the Sinemurian-Pliensbachian (EJ) of the southwest U.S., the Norian (LTr) of Argentina, and the LTr of Europe.

Taxon or Taxa: Time\Place: Comments:
Abrictosaurus consors Hopson, 1975 (Thulborn, 1974 [originally Lycorhinus consors]) Hettangian (EJ) of Lesotho and South Africa Abrictosaurus is known as the "tuskless" heterodontosaurid, although it gained that reputation through a mislabeled figure.  Its type actually does have tusks; two in the premaxilla are known, although the prominent dentary tusk is indeed lacking.  
It may be that it is actually a juvenile, as suggested by its steeply-sloping face, or female of another taxon.  However, it also may have unusually small hands.

Heterodontosauridae i.s.:

Taxon or Taxa: Time\Place: Comments:
?Echinodon becklesii Owen, 1861 early Berriasian (EK) of England Echinodon (sometimes seen as Saurechinodon in older references) is an enigmatic ornithischian.  At various times, it has been considered a "fabrosaurid," basal ornithischian, and basal thyreophoran (based on possible armor, which appears to belong to a turtle's limbs).  It instead may be a heterodontosaurid.  It is based on jaw remains, with many other jaws and teeth referred.  One or two maxillary teeth may be caniform.
Material from the Morrison Formation of Colorado may belong to another species or a closely-related genus; partial remains from several individuals are known, including jaw remains, a femur, a tibia, a fibula, and a partial humerus.  As an ornithischian fan and a Morrison Formation fan, I am very interested in what eventually comes out of this.  Hopefully, something comes out in the near future; it was mentioned as early as Glut's The New Dinosaur Dictionary, back in the early '80s!  
Geranosaurus atavus (N.D.) Broom, 1911 Sinemurian (EJ) of South Africa Geranosaurus is an indeterminate heterodontosaurid based on jaws.

Heterodontosaurinae:

Taxon or Taxa: Time\Place: Comments:
Heterodontosaurus tucki Crompton and Charig, 1962 Hettangian-Sinemurian (EJ) of South Africa Heterodontosaurus is the best-known heterodontosaurid.  A mostly complete skeleton is known for it, and shows it had relatively large, powerful hands and arms, including a strong thumb claw.
Lycorhinus angustidens Haughton, 1924 (including Lanasaurus scalpridens Gow, 1975) Hettangian (EJ) of South Africa This heterodontosaurine, based on a dentary fragment, was first considered to be a primitive relative of modern mammals.  Even with the referral of Lanasaurus, it is not particularly well-known, with only jaw material behind it.

Genasauria i.s.:

Taxon or Taxa: Time\Place: Comments:
"Acanthopholis": "A." macrocercus (N.D.) Seeley, 1869 late Albian (EK) of England Both of these animals are chimerical: "A." macrocercus is based on ankylosaur scutes and ornithopod vertebrae.  "A." stereocercus is based on ornithopod dorsal vertebrae and ankylosaurian tail vertebrae and armor.
"A." stereocercus (N.D.) Seeley, 1869
"Anoplosaurus" major (N.D.) Seeley, 1878 late Albian (EK) of England "A." major is based on an ankylosaurian neck vert and three ornithopod tail verts.
"Dysganus" peiganus (N.D.) Cope, 1876 late middle Campanian (LK) of Montana The type tooth of this obscure species has been considered as a hadrosaurid or ceratopid, but is more likely an ankylosaurian (or, less likely, a hypsilophodont).
Heishansaurus pachycephalus (N.D.) Bohlin, 1953 ?early Campanian (LK) of China This animal is a hard-headed ornithischian of some kind, either an ankylosaurian (seems more likely at this point) or a pachycephalosaurian.
Peishansaurus philemys (N.D.) Bohlin, 1953 early Campanian (LK) of China It may be that this animal is a juvenile ankylosaurian, or a pachycephalosaurian.
"Tianchungosaurus" (N.N.) Zhao, 1983 ?J of China This could be an early basal pachycephalosaurian, or possibly a misspelling of Dianchungosaurus, which was thought to be a heterodontosaurid but is really a crocodilian.

Thyreophora: Thyreophora was revived in the 1980s to contain the armored dinosaurs, which by the early 1990s consisted of the ankylosaurians and stegosaurians.  There are few characters which support this clade, but one, the possession of keeled, dorsal, parasagittal armor, running head to tail, is pretty strong.  However, some researchers believe that the stegosaurians may not belong, which would leave the ankylosaurians alone here with some basal taxa.  More basal thyreophoran material may be known from the EJ of China.

Taxon or Taxa: Time\Place: Comments:
Scutellosaurus lawleri Colbert, 1981 Sinemurian-mid Pliensbachian (EJ) of Arizona This animal was at first thought to be an armored "fabrosaurid," but as that group was disbanded, Scutellosaurus was reclassified as a basal thyreophoran, providing possibly the best example of what an ankylosaurian precursor would look like.  It is small, with a very long tail, limb proportions not too dissimilar from Lesothosaurus, and many small armor studs, nodules, and plates.  Remains from several individuals are known.

Eurypoda i.s.:

Taxon or Taxa: Time\Place: Comments:
Brachypodosaurus gravis (N.D.) Chakravarti, 1934 Maastrichtian (LK) of India Based on a heavily-built ?humerus, this animal is usually tossed off as a dubious ankylosaurian, but may be a stegosaurian.
Lusitanosaurus liasicus (N.D.) Lapparent and Zybszewski, 1957 Sinemurian (EJ) of Portugal This dubious basal eurypod is known from a skull fragment that is similar to the corresponding elements of Scelidosaurus.

Ankylosauromorpha:

Taxon or Taxa: Time\Place: Comments:
Scelidosaurus harrisonii Owen, 1860 Sinemurian-mid Pliensbachian (LJ) of England and Arizona Known from a couple of mostly complete skeletons, this animal superficially looks very much like a smallish nodosaurid.  It has unusual "tricorn" armor nodules directly behind the skull.  Interestingly, mixed in with what is now the type material were hindlimb elements from a "megalosaur"-type theropod.  This theropod material was unwittingly designated as the type at one point.  Fortunately, the type was officially redefined and no longer includes this extraneous material, now informally named "Merosaurus".  Before the type was removed from its matrix, Scelidosaurus was suggested to be anything from an ankylosaurian to a stegosaurian to, most unusually, a fleet bipedal early ornithopod.  Possible Scelidosaurus remains suggest that its armor was covered by a keratinous layer, a la turtles' shells.

Neornithischia: Here again we see a spray of "fabrosaurs," this time grading into hypsil-type animals.  Heterodontosaurus, Agilisaurus, and Hexinlusaurus appear to have lacked ossified tendons on the tail, an absence which would have made their tails much more flexible than most other ornithischians.

Taxon or Taxa: Time\Place: Comments:
Lesothosaurus diagnosticus Galton, 1978 Hettangian (EJ) of Lesotho and South Africa Lesothosaurus is the best-known basal ornithischian, with several skulls and most of a skeleton known.  It is a "step up" from Pisanosaurus, and may be the same as the dubious Fabrosaurus.  The arms appear to be rather short, with small hands.
Stormbergia dangershoeki Butler, 2005 Hettangian (EJ) of South Africa and Lesotho Stormbergia is the "large lesothosaur" of long-standing rumor.  Three individuals, including one juvenile, are known from partial postcranial remains.  Befitting its status in rumor, it was indeed a very large basal ornithischian, getting up to around 2 meters long, not unlike a scaled-up Lesothosaurus but with less of the proportions of a runner.
Agilisaurus louderbacki Peng, 1990 Bathonian-Callovian (MJ) of China This small ornithischian may be a very basal ornithopod.  Its body plan was suited for agility, as the generic name suggests (although maybe not as much as contemporaneous Hexinlusaurus, which had a longer tibia relative to its femur).  It is known from a complete articulated skeleton and skull, which is very tall (I've got to think that there's probably some funky crushing there) with a long rod over the eyes.
Hexinlusaurus multidens Barrett, Butler, and Knoll, 2005 (He and Cai, 1983 [originally Yandusaurus]) Bathonian-Callovian (MJ) of China Hexinlusaurus has been through quite a few names before it found where it fit.  It started as a species of Yandusaurus, which was more of a hypsil-type animal.  It then moved on to Agilisaurus, which still wasn't quite right but at least was closer and from the same formation.  Gregory Paul considered it a possible species of Othnielosaurus, which again was not quite right.  It is known from a nearly complete skeleton with skull, probably not fully grown, and another skeleton and skull have been referred to it; apparently 8 other individuals were referred here, but cannot be located.  It is one of those things that was somewhere between a "fabrosaurid" and a hypsil, a small, bipedal, running animal that probably was mainly an herbivore. 

Cerapoda i.s.:  Cerapoda comes from Ceratopia+Ornithopoda, and, as the name suggests, contains both, plus the pachycephalosaurians.  The name is rather unfortunate, in that mispronunciation can cause confusion with Sauropoda, which is composed of quite different dinosaurs. 

Taxon or Taxa: Time\Place: Comments:
Claorhynchus trihedrus (N.D.) Cope, 1892 late middle Campanian (LK) of Montana Based on partial premaxillae and a predentary, this dubious species has unaccountably been a football, sometimes classified as a hadrosaurid, sometimes as a ceratopid as originally described.
"Magulodon muirkirkensis" (N.N.) Kranz, 1996 late Aptian-early Albian (EK) of Maryland This animal is based on teeth which may have belonged to either a "dryosaur" or basal neoceratopian.
Micropachycephalosaurus hongtuyanensis (N.D.) Dong, 1978 early-mid Maastrichtian (LK) of China Famous for having the longest generic name of any classic dinosaur, this animal is ironically very small.  As its name suggests, it was originally described as a pachycephalosaurian, but its remains are too poor to refer it to that group.
Notoceratops bonarelli (N.D.) Tapia, 1918 early Maastrichtian (LK) of Argentina This animal is based on a now-missing dentary, originally considered that of a ceratopian.  As no ceratopian remains have ever been discovered in South America, it has been suggested that the bone actually belongs to a hadrosaurid, as hadrosaurids are known from the area.

Marginocephalia i.s.: The marginocephalian families, Pachycephalosauria and Ceratopia, are linked by several characters, including the bony shelf found at the back of the skull, which gives this group its name and forms a distinctive frill in ceratopians.

Taxon or Taxa: Time\Place: Comments:
Ferganocephale adenticulatum Averianov, Martin, and Bakirov, 2005 Callovian (MJ) of Kyrgyzstan Ferganocephale is a tooth taxon that was interpreted as a pachycephalosaurian, extending the pachy record back into the middle Jurassic.  The teeth are unusual for not having marginal denticles (little pointy bits on the edges, if you like).  Although the authors admit that there could be some damage if the teeth were swallowed and partially digested, they note a lack of enamel removal.  These teeth, one of which was originally tentatively considered stegosaurian, have a good solid unspecialized ornithischian look to them, with a leaf-like shape, except they don't have denticles, which makes them look a bit odd.  They share with pachies weak to nonexistent ridges and denticles, along with a few other characteristics, although the teeth could also belong to a basal ceratopian.  Either way, it would be the oldest-known well-supported marginocephalian.

 

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