ORNITHISCHIA
- Dinosauria
- Herrerasauridae
- Saurischia
- ORNITHISHCHIA
-
Fabrosauridae [Lesothosaurus]
-
Genasauria
-
Thyreophora
-
Ankylosauria
-
Stegosauria
-
Cerapoda
-
Marginocephalia
-
Pachycephalosauria
-
Ceratopsia
-
Ornithopoda
Characters
- herbivorous, with blunt or leaf-shaped teeth
- predentary bone in lower jaw [D&R p. 173]
- rostral tip of premaxilla toothless, forming a beak.
- ossified tendons along at least part of spinal column
- reduced antorbital fenestra
- buccal emargination of the jaws
- at least 5 sacral vertebrae
- antorbital fenestra reduced or absent
- premaxillae expanded, form part of nares
- ornithischian (tetraradiate) pelvis with a prepubic process, process of pelvis
points backward [D&R p. 172] to make room for the long digestive tract
The Ornithischian pelvis. Note the open acetabulum,
the anterior (to the left) extension of the ilium, and the backward (to the right)
extension of the pubis below and adjacent to the ischium. Illustration from O. C.
Marsh. 1896. The dinosaurs of North America. 16th Annual Report, U.S.
Geological Survey, pp. 133-244, 84 plates.
Included taxa
- Pisanosaurus, Fabrosauridae [Lesothosaurus] and Genasauria
- see Jack Horner's Ornithischia
page for a cladogram and characteristics
Comment
- The earliest well-known ornithischian. Carnian (late Triassic) of Argentina[B7.9a]
- small (7-10 kg; 1 m long), bipedal.
Fabrosauridae
Distribution
Characters
- these primitive ornithischians are small (1-2 m.) and facultively bipedal
- lack the derived, inset tooth-rows of the genosaurs
Example
- Lesothosaurus (=Fabrosaurus)
[D&R p. 173]
- the primitive ornithischians Technosaurus and Tecovasaurus from the
upper Triassic of west Texas may belong to this group.
- drawing from Jack
Conrad
Genasauria [D&R p. 174]
Characters
Included Taxa
- Thryeophora [ankylosaurs and stegosaurs]
- Cerapoda [Pachycephalosaurs and Ceratopsians and Ornthopods]
Characters
- armored, predominantly quadrupedal, primitive ornithischians
- bony scutes cover back and/or flank
- tibia shorter than femur (convergent with sauropodomorphs)
- see Jack Horner's Thyreophora
page for a cladogram and characteristics
Included taxa
- Scutellosaurus
(illustration by Shiraishi
Mineo) primitive, small (1.2 m) semi-bipedal thyreophore from the lower Jurassic
- Sclelidosaurus
(illustration by Shiraishi
Mineo): larger (3-4 m), quadrupedal, primitive thyreophore from the lower Jurassic
- plus Eurypoda (Ankylosauria and Stegosauria)
- synapomorphy: anterior portion of illium longer than posterior
Ankylosauria (?m.-u. Jurassic; Cretaceous)
Characters
- the most extensively armored dinosaurs - armor of small, interlocking plates (demal
scutes in the skin) over much of body
- Brendan Smith: Photograph of the heavy armor of
the nodosaurid Sauropelta edwardsorum
- skull broad and dorso-ventrally flattened
Included taxa
- Ankylosauridae
- Nodosauridae
Ankylosauridae
Characters
Examples
- Ankylosaurus,
(10-11 m, 4 tonnes) Late
Cretaceous, Judith River beds, Alberta, Canada (image from James
Miller)
- Euoplocephalus, Late
Cretaceous, Judith River beds, Alberta, Canada
Nodosauridae
Characters
- large armor plate on top of center of skull
Examples
- Nodosaurus, Early Cretaceous, Cloverly Formation, Montana
- Edmontonia, (6-7 m) Late Cretaceous, Judith River beds, Alberta, Canada
(Peter Buchholtz image of two
Edmontonia seen from above.
- Polacanthus
- Pawpawsaurus, Cretaceous, Texas
Stegosauria (middle Jurassic-late Cretaceous)
Characters
- mostly Jurassic
- scutes enlarged to form a double row of plates or spines along the back. It has
been suggested that these plates functioned in thermoregulation.
Kentrosauridae
Characters
- armor starting as plates, but continuing as spines on most of back
Example
- Kentrosaurus, (2.5-5 m) (illustration by Shiraishi
Mineo) Late Jurassic, Tendaguru Formation, Tanzania
Stegosauridae
Characters
Examples
- Stegosaurus, Late Jurassic, Morrison Formation, western USA.
The largest stegosaur.
- It had an extremely small head for its size and
an extremely small brain. It had a ganglion larger than the brain
itself in the hip region to control the movement of the hindquarters.
Read more about encephalization
quotients in stegosaurs and other dinosaurs from ZoomDinosaur. The area
for the spinal ganglion is a storage site for glycogen in birds, and may
have been the same in stegosaurs.
- thermoregulatory role of plates
- Stegosaurus,
from the Dinosauricon
- Kelly E. Taylor: Painting
-- Stegosaurus ungulatus and Ceratosaurus nasicornis do battle.
Illustration from O. C. Marsh.
1896. The dinosaurs of North America. 16th Annual Report, U.S. Geological
Survey, pp. 133-244, 84 plates.
Cerapoda
Characters
- uneven distribution of enamel on teeth (more enamel on outside versus inside of uppers
and on inside versus outside of lowers).
- see Jack Horner's Cerapoda
page for a cladogram and characteristics
- Ornithischia
- Fabrosauridae
- Genasauria
- Thyreophora (Ankylosaurs and
Stegosaurs)
-
CERAPODA
-
Marginocephalia (Pachycephalosaurs and ceratopsians)
-
Ornithopoda
Characters
- expanded shelf on back of skull.
- this group is distinguished by modifications of the skull; the monophyletic status of
this group is subject to debate
Included taxa
- Pachycephalosauria
- Ceratopsia
Pachycephalosauria (early-late Cretaceous)
(web page by Nick Snells).
Characters
- dome-headed dinosaurs, with thickened bones of skull roof, often ornamented with knobs
and bumps (Rowe CD: possible function in species recognition or sexual
display)
- what a bonehead
- Brendan Smith: Photograph of the skull
of Pachycephalosaurus wyomingensis
- occipital plate rotated ventrally beneath skull
- simple dentition with leaf-like teeth
- broad pelvis
- bipedal
- The thickened skull roof (as well as the rotated occipital plate) has been interpreted
as being used in head butting behavior as in big horn
sheep. However, there is no
histological evidence of the bone being damaged by trauma (Goodwin, M., E. Buchholtz, and
R. Johnson, 1998, JVP 18(2):363-375; Horner, J. and M, Goodwin, 1998, JVP 18(3):52A).
Flank butting behavior has also been proposed. UC news release about Mark
Goodwin's research.
Examples
- Stegoceras:
more information from the Royal
Tyrrell Museum
- Stygimoloch, late Cretaceous, Hell Creek Formation, North Dakota
- Pachycephalosaurus, (illustration by Shiraishi
Mineo) Late Cretaceous, Judith River beds, Alberta, Canada. The largest
pachycephalosaur (8 m)
- Homalocephale
CERATOPSIA
(early-late Cretaceous) [D&R p.176]
Characters
- skull with a narrow, sharp beak formed by a terminal rostral bone; flaring jugals; etc.
- see Jack Horner's Ceratopsia
page
Included taxa
- Psitticacosauridae and Neoceratopsia
PSITTACOSAURIDAE
Psitticasaurus Early Cretaceous, Mongolia (illustration by
Shiraishi
Mineo)
Characters
- parrot-beaked dinosaur from the lower Cretaceous of Asia
- the most primitive ceratopsian
- small size (< 2m)
- reduced manus
- faculatively bipedal
- may provide a link with basal ornithischians
Neoceratopsia (Cretaceous)
Characters
- stocky, quadrupedal herbivores; relatively large skulls with a posterior frill
Included taxa
- Protoceratopsidae and Ceratopsida
Protoceratopsidae
Characters
- small size
- incipient nasal horn
Example
Ceratopsidae
Characters
- medium to large size; complex dental batteries; variably developed nasal and orbital
horns; elongate neck frill (parietal and squamosal bones); largest skulls of any
terrestrial vertebrate (Torosaurus 2.6m); long limbs & digitigrade (for
galloping)
Examples
Illustration from O. C. Marsh.
1896. The dinosaurs of North America. 16th Annual Report, U.S. Geological
Survey, pp. 133-244, 84 plates.
- Ornithischia
- Fabrosauridae
- Genasauria
- Thyreophora (Ankylosaurs and
Stegosaurs)
- Cerapoda
-
Marginocephalia (Pachycephalosaurs and ceratopsians)
-
Ornithopoda
ORNITHOPODA
(earliest Jurassic-latest Cretaceous)
Characters
- strong depression of the mandibular condyle beneath the level of maxillary and dentary
tooth rows
- Ventral offset of the premaxilla from the maxilla
- Crescentic paraoccipital processes
- see Jack Horner's Ornithopod
page for a cladogram and characteristics
Included Taxa
- Heterodontosauridae and Euornithopoda [Hypsilophodontidae plus Iguanodontidae plus Hadrosauridae]
HETERODONTOSAURIDAE
(early Jurassic)
Characters
- primitive sister group of other ornithopods
- small forms (1 m)
- bipedal
- chisel-like cheek teeth
- "canine-like" teeth form tusks in some taxa (possible sexual dimorphism)
- teeth on premaxilla (primitive);
Example
EUORNITHOPODA (Hypsilophodontidae plus Iguanodontidae plus Hadrosauridae)
Characters
- more advanced ornithopods have a pleurokinetic hinge which
allowed the maxilla to rotate to create shearing
- High angle between prepubic process and the body of pubis
HYPSILOPHIDONTIDAE (mid Jurassic-late Cretaceous)
Characters
- small to medium size (3-5 m)
- bipedal, cursorial
- Rod-shaped prepubic process
- Loss of ridges on crowns of cheek teeth
Example
IGUANODONTIA
- Tenontosaurus plus Dryosauridae, Iguanodontidae and Hadrosauridae
Characters
- Enlargement of the external nares
- Loss of premaxillary teeth
Iguanodontidae (middle
Jurassic-late Cretaceous)
Iguanodon bernissartensis from the Cretaceous of
Belgium. Illustration from O. C. Marsh.
1896. The dinosaurs of North America. 16th Annual Report, U.S. Geological
Survey, pp. 133-244, 84 plates.
Characters
- large body size; graviportal posture
- digit 1 of hand reduced to a thumb spike (Why?)
- possibly a paraphyletic group ancestral to the hadrosaurs
Example
HADROSAURIDAE
(upper Cretaceous)
Characters
- "duck-billed" dinosaurs
- premaxillae and maxillae flattened
- Webbed feet
- stiff tails, supported by ossified tendons
- dentitions organized into dental batteries of closely packed tooth families, three to
five replacement teeth per tooth position
- "dinosaur mummies": skin impressions. Learn more from the AMNH
- more on hadrosaurs from the Royal
Tyrell Museum
Classification
Hadrosaurinae
- Character
- lack a crest on the skull
Examples
Lambeosaurinae
Character
- have a crest on the skull which contains the nasal passages.
- Why the crest? see the UCMP
web page
Examples
Return to:
