ORNITHOPODA

     The Onithopoda (Bird + Foot) are bipedal, ornithischian dinosaurs lacking body armor.  Ornithopods consist of the clade of all the descendents of the common ancestor of the Heterodontisauridae and Euornithopoda (Fastovsky and Weishampel, 1996, Figure 10.10, p. 202).  The ornithopods first appeared in Early Jurassic (perhaps Late Triassic ?) and became extinct by the end of Cretaceous time.  They were a very diverse group and among the last dinosaurs to become extinct.  (TRY THIS WEB SITE:  Introduction to the Ornithopoda http://www.ucmp.berkeley.edu/diapsids/ornithischia/ornithopoda.html)

     Four main families of ornithopods have been recognized, and they contain the well known and popular duck-billed dinosaurs (see cladogram below from: Lecture 18 - Late Jurassic: Morisson, Tendaguru http://rainbow.ldeo.columbia.edu/courses/v1001/morisson14.html).

Figure 1.

1. uneven enamel on teeth
2. jaw joint below level of tooth rows
3. bony shelf on back of head
4. prepubic process well developed
5. reduction in digits I and V on hand (and large nares)
6. elongate hand
7. strong ridge on side of teeth
8. spike-like digit I on hand (and very large nares)
9. duckbill like snout
10. rostral bone on snout
11. dome-like thickening on skull
12. reduction in manus
13. long frill
 

     Many features of the skull were derived characters, including two very diagnostic derived characters: 1) a ventrally offset premaxillary bone and 2) the lower jaw joint located well below the level of the maxillary and lower tooth rows (i.e., mandibular condyle depressed below level of upper and lower tooth rows) (see Figure 2).

 
HETERODONTOSAURIDAE

     Heterodontosaurids are known only from Lower Jurassic rocks of southern Africa.  They were small dinosaurs with a length of 1 to 1.5 meters that had uniquely shaped cheek teeth, chisel-shaped with tiny cusps restricted to the apex of the crown (unique to all dinosaurs).  They also had canine-like teeth  in the front part of the mouth that had a different shape than the chisel teeth.

(LOOK HERE:  Heterodontosaurus http://www.ucmp.berkeley.edu/diapsids/ornithischia/heterodontosaurus.html)

     Heterodontosaurus(means different toothed reptile) is a typical and characteristic heterodontosaurid with the following characteristics:

• http://www.cmm1.com/thumbs/6/4/4/644000/t644000.html
• 1) Heterodontosaurus was 1.2 meters long, with short forelimbs and long hind limbs (considered to be bipedal).
• 2)  Dental battery set in massive lower jaws and the teeth are usually heavily worn (thus a plant eater).
• 3) Long tail and short neck (typical of primitive ornithischian).
• 4) Ossified tendons in the back region (along the vertebrae).
• 5) Fusion of the fibula and tibia and their fusion to the tarsals, this stabilized the lower leg and ankle for fast running (bird-like feature - example of convergent evolution).
• 6) Hands stout and flexible (perhaps to grasp vegetation).
• 7) Large canines (tusk like)- may have been used for defense and display (this may be a sexual dimorphic feature, some heterodontosaurid skulls lack canines).  The canines may also have helped to stabe and tear vegetation.
• 8) Bones found in arid paleoenvironments (deserts and arid alluvial fans).

The Heterodontosaurus was a bipedal/quadrupedal dinosaur. Its diet was low-growing plants. It had three kinds of
teeth while most dinosaurs only have one type. The names of the three types are sharp upper front teeth, long canine
tusks and high-crowned cheek teeth. It had three toes that faced forward on each foot. They had muscular arms and
each hand had three large clawed fingers and two small fingers.

The Heterodontosaurus was 4 feet (1.2m) long and weighed 5.5 pounds (2.5kg). It lived in South Africa Cape, Province
and Lesotho Quthing during the late Triassic and early Jurassic Periods

Adult male Heterodontosaurus have sharp canine like teeth that they most likely used to threaten and/or bite other
competing males. Females and young males probably did not have those teeth. Their predators included theropods and
crocodilians. While running it was probably on two legs and its tail wagged back and forth furiously unlike later
ornithopods whose tail would straight. "
(From: http://www.sta.cathedral.org/lowerschool/chronicle/Issue03/Prehistory/Heterodontosaurus.htm)

     Thus in summary, heterodontosaurids were primitive ornithischians that lived in sparsely vegetated arid regions, as agile bipeds (but could be quadrapedal diggers), browsing on plants close to the ground.
 

HYPSILOPHODONTIDAE

     The hypsilophodontidae were small (2 to 4 meters), bipedal ornithischians that are known from Middle Jurassic to Upper Jurassic rocks of North America, Europe, Asia, and Australia (SEE THIS LINK RELATIVE TO AUSTRALIAN HYPSILOPHODONTIDS: Dann's Dinosaur Info: HYPSILOPHODONTIDS http://www.alphalink.com.au/~dannj/hypsilof.htm).  The best known genus is Hypsilophodon.
http://www.cmm1.com/thumbs/6/4/4/644000/t644000.html

Figure 2. Hypsilophodon foxii, redrawn from Galton (1974) (From: http://rainbow.ldeo.columbia.edu/courses/v1001/morisson14.html)

     The hysilophodontidae are the most primitive members of Euornithopoda (see cladogram page on page 202 in Fastovsky and Weishampel, 1996) and are a sister group within this clade to Iguandontia (which encompasses all more derivied euornithopods, including the Iguanodontidae and the Hadrosauridae [duck bills]).

     The following characters for Hysilophodon are general characters of the hysilophontidae:

• 1) Bipedal runner, hind limbs much longer than forelimbs.
• 2) Ankle elongate.
• 3) Long tail - stiffened by ossified tendons.
• 4) Skull resembles that of Heterodontasaurus, but does not have the large canine teeth.
• 5) Large eyes.
• 6) Massive jaws, dental battery of interlocking cheek teeth that wore-down to produce a continuous, inclined cutting edge.
• 7) A joint in the skull allowed the upper jaw to move outward over the lower jaw when chewing (a dynamic skull feature).

     Two euornithopods that are very similar to the hypsilophodontids, and that may be very close to the evolutionary ancestral stock that links the hypsilophodontids to the iguanodontids, are Tenontosaurus (Lower Cretaceous of North America) and Dryosaurus (Upper Jurassic of North America and Africa).

Figure 3. Dryosaurus altus from the Tendaguru Formation (redrawn from Sues and Norman, 1990) (From: http://rainbow.ldeo.columbia.edu/courses/v1001/morisson14.html)

Both lack premaxillary teeth (see Figure 5) and had other characters midway between the two groups (Lucas, 1997).  However, some prefer to place these two dinosaurs as primitive members of Iguanodontia (which includes all more derived euornithopods above the hpsilophodontidae) (see cladogram on page 204 in Fastovsky and Weishampel, 1996).

 
IGUANODONTIDAE

     The Iguanodontidae may not be a monophyletic group.  Fastovsky and Weishampel (1996) do not include this grouping as a valid family of the Euornithopoda (see cladogram page 204).  They place the traditional members of Iguanodontidae (Camptosaurus, Iguanodon, and close relatives) and the more primitive Tenontosaurus and Dryosaurus (and close relatives) as successively more derived forms (again, see cladogram page 204).  However, for the sake of simplicity, we will consider the dinosaurs Camptosaurus, Iguanodon, Ouranosaurus, and close relatives as belonging to the family Iguanodontidae.  We will further consider Iguanodontidae to be a sister clade to the monophyletic Hadrosauridae (the most derived members of the Ornithopoda).

     The iguanodontids were bipedal herbivores that lived during Late Jurassic to Late Cretaceous time.  Of course, the genus Iguanodon has a special place in the history of dinosaurs, as it was the second dinosaur to be described in the literature by Gideon Mantel, 1825 (LOOK AT THIS:  A history of dinosaur hunting and reconstruction ) (the first dinosaur that was described in publication was Megalosaurus by William Buckland in 1824).

     The iguanodontids were most all relatively large, heavily built ornithopods with heavy shoulders and forelimbs.  The hind limbs were massive, with broad feet that had hoof-like tips on their toes.  They had a spike-like thumb.  The head was large with a horse-like snout that ended in a broad, toothless beak.  As in the transitional genera (between Hypsilophodontidae and Iguanodontidae) Tenontosaurus and Dryosaurus, there were no teeth on the premaxillary.

"Tenontosaurus dossi and hypsilophodonts"
© Copyright by Karen Carr
Figure 4. (From:  Karen Carr, Natural History and Wildlife Artist http://www.karencarr.com/Image_Index.htm)
 

The Genus Camptosaurus

Figure 5. Camptosaurus dispar from the Morrison Formation (redrawn from Norman and Weishampel, 1990) (From: http://rainbow.ldeo.columbia.edu/courses/v1001/morisson14.html)

     Camptosaurus is the oldest iguanodontid known from a complete skeleton.  It was relatively small (as compared to other iguanodontids) at 5 to 7 meters and did not have a fully developed thumb spike.  There were four digits on the hind foot and Camptosaurus had massive hind limbs and relatively long forelimbs.  It was primarily bipedal, but probably spent quite a bit of time on all fours while feeding.  The hand had fused wrist bones for stable hand walking.
 

The Genus Iguanodon

Figure 6.  Iguanodon adult and juvenille (From: A history of dinosaur hunting and reconstruction at  http://www.dinohunters.demon.co.uk/)

      Iguanodon is best known from Lower Cretaceous rocks of Bernissart, Belgium (where 31 adult skeletons were found in a coal mine at a depth of 321 meters) (SEE THIS WEB SITE:  A history of dinosaur hunting and reconstruction http://www.dinohunters.demon.co.uk/.  It is much larger and more specialized than Camptosaurus.

     Iguanodon had the following characteristics:

•  Had very long forelimbs (70 to 80% as long as hind limbs).
• The wrist bones were fused (for stable hand walking).
• Central 3 digits of the hand ended in hooves.
• Large conical thumb spike (perhaps a defensive weapon).
• Extensive boxwork of ossified tendons extending along the back vertebrae from the shoulder region to the middle of the tail.

Summary of Iguanodontids

• 1) Iguanodontid snouts were long with many more teeth than in heterodontosaurids or hypsilophodontids.
• 2) The beaks were used to crop vegetation.
• 3) Teeth leaf-shaped with long ridges on their sides and small cusps on the cutting edges (resembling teeth of the living iguanas - thus the name for the family).
• 4) Camptosaurus is the oldest iguanodontid and is best known from Upper Jurassic rocks of North America and Europe.
• 5) The zenith of iguanodontid diversity occurred in Early to Medial Cretaceous time in Europe, North America, Africa, Asia, and Australia.
• 6) Iguanodon, Lower Cretaceous of Europe, is the most typical representative of the Iguanodontidae and is the best known genus (with several complete skeletons known).
• 7) A particularly unusual Lower Cretaceous iguanodontid is Ouranosaurus from Niger, Africa, which had a very distinctive head and long neural spines along the back (see page 212 in Fastovsky and Weishampel, 1996).
• 8) There was a marked decline of iguanodontids in Late Cretaceous due (probably) to the appearance of the hadrosaurids (duck-bills).

     The Hadrosauridae (ANOTHER GOOD WEB SITE:  Hadrosaurian Dinosaurs http://www.ucmp.berkeley.edu/diapsids/ornithischia/hadrosauria.html) are commonly known as the duck-billed dinosaurs.  They first appeared in Medial Cretaceous time and were the last group of ornithopods to evolve.  There is more known about this family than any other group of dinosaurs.  Their fossil record includes many complete skeletons, eggs and nests, footprints, and two mummified individuals with skin intact (there are also other fossilized skin impressions of these dinosaurs).

     The hadrosaruids were large ornithopods, with lengths of 7 to 10 meters.  They had broad, toothless beaks and intricate dental batteries.  The dental batteries consisted of hundreds of teeth with a washboard-like grinding surface and three replacement teeth in each tooth position.  As in the hyspsilophodontids, they had kinetic jaws such that the upper jaw moved outward and the lower jaw moved inward during chewing.  They could process fibrous vegetation, even twigs.

     There was a loss of the first digit (thumb) on the hands.

     They had up to 8 to 10 sacral vertebrae.

     Two mummified hadrosaurids from Canada have stomachs full of conifer needles and twigs, seeds, and other tough plant material.

     There is very little variation among hadrosaurid skeletons, so identification is based on skull structure.  There are two major subfamilies based on skull type, the Hadrosaurinae and the Lambeosaruinae.

Hadrosaurinae

     The hadrosaurines were the more primitive subfamily with rather flat skull roofs or solid crests on the skull.  They were large "Roman-nosed" hadrosaurids with long nasals, which often peaked near the posterior end of the nostrils.  Examples are Edmontosaurus and Maisauria.
 

Lambeosaurinae

     These were the "crested" duck-bills.  They are distinguished by convoluted tubes and crests on the tops of their skulls.  The crests contained modified nasal passages and a nasal cavity that was relocated to a position above the orbits.  The crests and tubes changed during the growth of individuals, suggesting that sexual dimorphism may have been present.  The Upper Cretaceous genera Parasaurolophus and Corythosaurus are representative examples of lambeosaurines.

Figure 7.  Parasaurolophus, the "trombone duckbill" is a rare lambeosaurine hadrosaur known from the Late Cretaceous of
the San Juan Basin, New Mexico. This is a drawing by Robert Bakker from his book The Dinosaur Heresies (From:  Parasaurolophus, A Strange Duckbill Dinosaur From New Mexico http://www.nmmnh-abq.mus.nm.us/nmmnh/parasaur.html).

     They also had elongated neural spines on the vertebrae and very robust limbs.

Figure 8. Corythosaurus skeleton at The Carnegie Museum of Natural History.  Notice the helmeted crest and the tall, deep paddle-like tail  (photo by E. L. Crisp, 1999).
 

Summary of Hadrosauridae

• 1) Like iguanodontids, hadrosaurids were large, strong, quadrapedal walkers, but also could walk on two legs.
• 2) Mummies from Alberta have flaps of skin between fingers, has been suggested that they may have had webbed hands; however, the shrunk and stretched skin from mummification may only make it appear that way.
• 3) They had a tall, paddle-like tail, perhaps for propelling in water.
• 4) Their skeletons are found in river, lake, swamp, deltaic, and sea depositis.  Perhaps they were aquatic dinosaurs.  But hadrosaurids were also well suited to living on dry land and thus may have entered the water only for feeding or for defensive purposes.
• 5) Had a very wide geographic distribution, known from North America, Asia, Europe,  and South America.  But they were most abundant and diverse in Asia and North America.
• 6) The hadrosaurids were the dominant plant eating dinosaurs of the Late Cretaceous and they were among the last dinosaurs to become extinct.