Ornithischia

   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 rotated 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 ceratopsians, 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-ŕ-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
      |   |--Echinodon
      |   |--Fruitadens
      |   |--Tianyulong
      |   `--Heterodontosaurinae
      |        |--Lycorhinus
      |        `--+--Abrictosaurus
      |             |--Heterodontosaurus
      |             `--+--Manidens
      |                  `--Pegomastax
      `--+--Eocursor
           `--Genasauria
                |--Thyreophora
                |    |--Scutellosaurus
                |    `--+--Emausaurus
                |         `--+--Scelidosaurus
                |              `--Eurypoda
                |                   |-->Ankylosauria
                |                   `-->Stegosauria
                `--Neornithischia          
                     |--Lesothosaurus
                     `--+--Stormbergia
                          `--+--Agilisaurus
                               `--+--Hexinlusaurus
                                    `--+--Kulindadromeus
                                         |--Othnielosaurus
                                         `--Cerapoda
                                              |-->Ornithopoda
                                              `--Marginocephalia
                                                   |-->Pachycephalosauria
                                                   `-->Ceratopsia  

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 Norian (LTr ) of Argentina This small animal is based on a partial skeleton, partial skull, and impressions of bones (not all of which are still extant) that show an ur-ornithischian. It has been allied to heterodontosaurids, "fabrosaurids," and hypsilophodonts over the years. The type material is both fragmentary and includes a few bones (forelimb and girdle elements) that may come from other animals.
Eocursor parvus Butler, Smith, 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 Lesothosaurus. Fabrosaurus in fact is the name usually used for restorations of what is actually Lesothosaurus in older dinosaur books.
Laquintasaura venezuelae Barrett, Butler, Mundil, Scheyer, Irmis, and Sánchez-Villagra, 2014 Hettangian (EJ) of Venezuela Laquintasaura is a basal ornithischian known from a bonebed that preserves representative elements of most of the skeleton, except the arms. It is the first dinosaur named from northern South America, and lived right after the end-Triassic extinction event and the massive volcanic outpouring of the Central Atlantic Magmatic Province. Anatomically, it's broadly your basic-issue basal ornithischian.
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. With the alvarezsaurids and compsognathids, they were among the smallest dinosaurs, with the largest known example estimated at a whopping 1.75 m (5 ft, 8 in) long, most of which would have been tail, and 10 kg (22 lb) in weight. They have been wild-cards, given the paucity of other early ornithischians to compare them to, and have also 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 of Ornithischia, which I'm using here. This is still a hot issue, or at least it would be if ornithischians were charismatic predators. Heterodontosaurids appear to have done well for themselves early on, with at least four taxa (named and unnamed) in their classic stomping grounds of EJ southern Africa (well, maybe a little small-bodied for "stomping" grounds. Cavorting grounds?). Heterodontosaurid material is also known from the Sinemurian-Pliensbachian (EJ) of the southwest U.S.

Taxon or Taxa: Time/Place: Comments:
Echinodon becklesii Owen, 1861 mid Berriasian (EK) of England Echinodon (sometimes seen as Saurechinodon in older references) has long been 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 appears to be a heterodontosaurid. It is based on jaw remains, with many other jaws and teeth referred. Unlike classic Heterodontosaurus, the caniform tooth on the upper jaw is behind the dentary fang, on the maxilla, and there was apparently some kind of small tooth in front of the dentary fang (a feature found in several other heterodontosaurids, including Fruitadens and Lycorhinus, but not the famous namesake), which just goes to show what heterodontosaurids get up to if you leave them alone long enough. Keeping with the dinky heterodontosaurid tradition, it was on the order of a half-meter long.
Fruitadens haagarorum Butler, Galton, Porro, Chiappe, Henderson, and Erickson, 2009 early Tithonian (LJ) of Colorado At long last, the "Fruita Echinodon" has been unveiled to the public. Those of you who have followed the popular and technical literature since the 1980s will be aware of numerous brief references to a "possible second species of Echinodon" from the Fruita area of Colorado. As advertised, it turns out to be a basal-ish heterodontosaurid. Unlike some other heterodontosaurids, it lacked upper "canines". It is particularly known for its diminutive size, measuring 65-75 cm long and less than a kilogram (1 to 2 lbs estimated) at about 5 years of age. Material known includes 
 jaw remains, a femur, a tibia, a fibula, and a partial humerus, from at least six individuals of varying stages of growth. It and fellow late heterodontosaurids Echinodon and Tianyulong seem to have hit upon the strategy of being generalists, and were less specialized in the skull than Heterodontosaurus. Fruitadens has even been proposed as an omnivore.
Tianyulong confuciusi X.-T. Zheng, H.-L. You, X. Xu, and Z.-M. Dong, 2009 Oxfordian (LJ) of China Tianyulong has attracted quite a bit of attention for its integumentary impressions, including short fuzzy stuff over the body and longer filaments on the tail. It's also noteworthy in being the first Asian heterodontosaurid that hasn't turned out to be a sphenosuchian croc. It is based on the partial skeleton of a subadult about 70 cm long, including a partial skull and jaws, some presacrals, a good-sized chunk of the tail, a scapula, the upper arms and an ulna, part of the hips, and much of the legs. The body proportions can be charitably described as "awkward", with a large skull and long legs paired with short arms, neck, and truck. The partial skull is like that of Heterodontosaurus in general profile, with no antorbital fenestra and a premaxilla fang followed by a larger dentary fang.

Heterodontosauridae i.s.:

Taxon or Taxa: Time/Place: Comments:
Geranosaurus atavus (N.D.?) Broom, 1911 Sinemurian (EJ) of South Africa Geranosaurus is an apparently indeterminate heterodontosaurid based on jaws.

Heterodontosaurinae:

Taxon or Taxa: Time/Place: Comments:
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. The obscure Lanasaurus is probably a synonym.
Abrictosaurus consors Hopson, 1975 (Thulborn, 1974 [originally Lycorhinus consors]) Hettangian (EJ) of Lesotho Abrictosaurus is known as the "tuskless" heterodontosaurid, although it gained that reputation through a mislabeled figure. Its type actually does have enlarged albeit comparatively modest pointy teeth; at least two were present in the premaxilla, although a prominent dentary tusk is indeed lacking.  
It has been suggested that it is actually a juvenile (although juvenile Heterodontosaurus had tusks), as suggested by its steeply-sloping face (another reconstruction artifact), or female of another taxon.
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. Juveniles also had tusks. The jugals were equipped with bosses, giving it modest cheek "horns", an innovation which would be periodically reinvented by various other ornithischians before the end of the Mesozoic (no doubt claiming each time either that it was unique, or an homage).
Manidens condorensis Pol, Rauhut, and Becerra, 2011 Aalenian-Bathonian (MJ) of Argentina Manidens, a relatively basal heterodontosaurid, is known from a partial skull and jaws, cervical and dorsal vertebrae, the left shoulder girdle, and a pelvis. Like heterodontosaurids in general, it was tiny as dinosaurs go, less than a meter in length.
Pegomastax africana Sereno, 2012 Hettangian-Sinemurian (EJ) of South Africa Like several other taxa, including this site's namesake, Pegomastax is based on a specimen found decades before its description. It is known from a few bones of the skull and jaws, showing it to have had a short beak on a robust mandible.

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.
Peishansaurus philemys (N.D.) Bohlin, 1953 ?early Campanian (?LK) of China It may be that this animal is a juvenile ankylosaurian, or a pachycephalosaurian, although once in the 1990s it was described without comment as a synonym of Psittacosaurus, possibly from the EK.
Serendipaceratops arthurcclarkei Rich and Vickers-Rich, 2003 EK of Australia This gives recognition to the informally discussed Australian "neoceratopsian" ulna. It was thought to have been similar to Leptoceratops (the gold standard for non-Protoceratops basal neoceratopsians), but realistically cannot be diagnosed beyond Genasauria.

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 was 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.
Emausaurus ernsti Haubold, 1991 early Toarcian (EJ) of Germany This recently-described animal is best known from a virtually complete skull that has some similarities to that of Huayangosaurus.
Scelidosaurus harrisonii Owen, 1860 Sinemurian-mid Pliensbachian (LJ) of England and ?Arizona Known from a couple of mostly complete skeletons, among other material, this animal superficially looked 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 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.

Thyreophora i.s.:

Taxon or Taxa: Time/Place: Comments:
Bienosaurus lufengensis Dong, 2001 Sinemurian (EJ) of China This animal is based on a partial skull (well, mostly the lower jaw) discovered in 1938. It may be related to Scelidosaurus.
Lusitanosaurus liasicus (N.D.) Lapparent and Zbyszewski, 1957 Sinemurian (EJ) of Portugal This dubious basal thyreophoran is known from a skull fragment that is similar to the corresponding elements of Scelidosaurus.
"Omosaurus" hastiger (N.D.) Owen, 1877 early Kimmeridgian (LJ) of England Based on two spikes thought to be from what we now know as a stegosaurid genus, this species does not appear to be stegosaurian.
Tatisaurus oehleri (N.D.) Simmons, 1965 Sinemurian (EJ) of China This poorly-known genasaurian is based mainly on a partial jaw. It is not the same as Scelidosaurus, as is sometimes claimed, and there is no evidence that it was a stegosaurian. It has also been regarded at times as a heterodontosaurid or ornithopod.

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.

Neornithischia: Here again we see a spray of "fabrosaurs," this time grading into hypsil-type animals. 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.
   "Othnieliidae" was never much more than a "vanity project" for Othnielia (now Othnielosaurus). There may be a new, undescribed Spanish "othnieliid".  

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. It may just represent adults of Lesothosaurus, though.
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. 
Kulindadromeus zabaikalicus Godefroit, Sinitsa, Dhouailly, Bolotsky, Sizov, McNamara, Benton, and Spagna, 2014 MJ-LJ of Siberian Russia Kulindadromeus is an excellent example of an othy-grade ornithopod imitator. It is known from numerous individuals discovered in two bonebeds. It is not unusually specialized anatomically, although the rods of the ischia and pubic bones point closer to 9 o'clock than to between 7 and 8.
Also, it is notable for its extensive integument impressions, showing both feathers and scales. In the feather department, most of the body featured monofilaments ranging from about 1-1.5 cm long on the head to up to 3 cm long on the body, like Sinosauropteryx. Larger compound structures of multiple filaments are found on the upper arm and thigh, and  compound structures of ribbon-like elements are present on the upper shins. In the scale department, there are the usual nonoverlapping structures and longitudinal rows of large scales partially ringing the tail. This discovery is notable for putting truly feather-like structures on ornithischians and potentially all dinosaurs.
Othnielosaurus consors Galton, 2006 (originally Laosaurus consors Marsh, 1894) Kimmeridgian (LJ) of Colorado, Utah, and Wyoming Othnielosaurus is what is usually represented in illustrations of Nanosaurus (and now Othnielia, to tell the truth). A common Morrison dinosaur, it is known from several specimens, including an articulated skeleton missing only the hands, skull, and part of the tail, other partial skeletons, and a possible juvenile individual. It was some sort of basal hypsil-type thing, although what sort remains obscure for the moment.
To make a long story short, Othnielia was named for Nanosaurus rex, which was just based on a femur that was not distinctive, whereas Laosaurus consors was based on a partial skeleton that was referred to Othnielia. Galton decided to go with the partial skeleton and not the femur. Otherwise, Othnielosaurus is the same thing you knew fondly as Othnielia. Since the Morrison is getting crowded with basal ornithopods (Drinker and Nanosaurus agilis) and ornithopod-like critters (the Fruita heterodontosaurid Fruitadens), it was a good idea to go with the most distinctive of the old remains.

Neornithischia i.s.: This grouping is mostly for taxa that appear to fit somewhere in the vicinity of Othnielosaurus, basal Cerapoda, and the hypsilophodonts.

Taxon or Taxa: Time/Place: Comments:
Drinker nisti Bakker, Galton, Siegwarth, and Filla, 1990 (?Othnielosaurus) Kimmeridgian (LJ) of Wyoming Closely resembling Othnielosaurus, Drinker is named after Edward Drinker Cope, contrasting Othnielosaurus, which is named after his arch-rival, Othniel Charles Marsh. It may end up as a species of Othnielosaurus. Drinker had unusual long spreading toes, suggesting it could negotiate swampy terrain well. Bob Bakker has reported finding the remains of over thirty individuals in what might have been a burrow.
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.
"Laosaurus" gracilis (N.D.) Marsh, 1878 Kimmeridgian (LJ) of Wyoming This is a hypsilophodont-grade dinosaur known from dorsal and caudal verts and hindlimb material.
?Nanosaurus agilis Marsh, 1877 Kimmeridgian (LJ) of Colorado and Utah At one time considered a "fabrosaur"-type ornithischian, Nanosaurus is most likely a basal ornithopod or in the cerapod-to-ornithopod limbo zone, although it could be related to Fruitadens. It is based on molds of its teeth, with other material, including an ilium, femora, tibiae, and a fibula, referred to it.
"Nanosaurus" rex (N.D.) Marsh, 1877 Kimmeridgian (LJ) of Colorado It was a nice run while it lasted. Marsh named this species for a femur, that Galton later deemed worthy of its own genus which, when combined with a couple of good partial skeletons, ruled the Morrison of our imaginations for nearly three decades as Othnielia (and you thought I was going to say Allosaurus). However, the femur wasn't that distinct, while the skeletons were, so a Lagosuchus\Marasuchus has been pulled, with the skeletons transferred to Othnielosaurus consors (from an obscure species of Laosaurus that had better remains for a type specimen), leaving Othnielia, and "Nanosaurus" rex, to the dustbin of history (which is too bad, because it was always funny to have an ornithopod with rex as its species name; it's like naming a tiny dog Rex).  
Phyllodon henkeli (?N.D.) Thulborn, 1973 early Kimmeridgian (LJ) of Portugal This is a tooth taxon of uncertain affiliation, from the cerapod-basal ornithopod nexus. It could be a valid genus akin to Drinker.
Siluosaurus zhangqiani Dong, 1997 Barremian-Albian (EK) of China Siluosaurus, based on two teeth, is possibly the smallest known ornithopod.

Cerapoda i.s.: Cerapoda comes from Ceratopsia+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. Technically, it was defined to be the same as Neornithischia, but we could use a name for the Ceratopsia+Ornithopoda node, and Cerapoda's just standing around doing nothing much...

Taxon or Taxa: Time/Place: Comments:
Albalophosaurus yamaguichiorum Ohashi and Barrett, 2009 Hauterivian-Valanginian (EK) of Japan Albalophosaurus is known from a partial skull. It may be a basal ceratopsian, but it is not dissimilar to ornithopods, either. Thus, it gets to sit here until it is better known.
Claorhynchus trihedrus (N.D.) Cope, 1892 ?late Maastrichtian (LK) of ?South Dakota Based on skull bones, this dubious and obscure taxon has unaccountably been a football, sometimes classified as a hadrosaurid (bones interpreted as premaxillae and a predentary), sometimes as a ceratopsid (bones interpreted as a partial frill of Triceratops) 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 neoceratopsian.
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 was ironically very small for a dinosaur. 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 ceratopsian. As no ceratopsian 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 Ceratopsia, 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 ceratopsians.

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 ceratopsian. Either way, it would be the oldest-known well-supported marginocephalian.
Stenopelix valdensis Meyer, 1857 Barremian (EK) of Germany This animal is apparently a marginocephalian. Every so often someone comes up with a new case as to why it's a pachycephalosaurian or ceratopsian, but without a head the partial skeleton has proven difficult to pin down.

 

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