Chapter 13 – Overview of the Clade Ornithopoda

Why Study Ornithopods

One of the most diverse and GEOGRAPHICALLY WIDESPREAD dinosaur clades

Successful from the Early Jurassic through the end of the Cretaceous

Wide range of sizes from 1 meter up to 15 meters (and up to 3000 kilograms)

“Cows” of the Mesozoic

Great chewers

Behaviorally more like birds though

Best fossil record after theropods – found on all continents and at high paleolatitudes from the Arctic to the Antarctic

Complete skeletons from embryos & juveniles to adults in some species

Many eggs and nests

Skin impressions, stomach contents and internal organ preservation

Numerous trackways

Numerous coprolites

Fossil record provides the most complete and compelling evidence about the social lives of dinosaurs

Communal nesting grounds, where juveniles restricted to nests while parents took care of them

Elaborate head structures probably used for communication

Migratory herds

Definition and Unique Characteristics of Ornithopoda

Introduction

Ornithopoda = beast foot

Created by O. C. Marsh in 1881

Should be Theropoda (beast foot) - Ornithopod feet (particularly those of later large ornithopods) resemble mammal feet more than Theropod feet do

Characteristics - Wide Range of Characteristics Among Different Groups

Major characteristics – SEE Figure 13.1

Relationships with other ornithischian dinosaurs (and each other) - SEE Figure 13.2

Basal Fabrosauridae, including Lesothosaurus

Genasauria (Cheek lizard) – Thyreophora (shield bearer, Chapter 14) plus Cerapoda (horn foot)

Cerapoda – Ornithopoda plus Marginocephalia (margin head, Chapter 15)

Ornithopoda – Heterodontosauridae plus Euornithopoda

Euornithopoda – Hypsilophodontidae plus Iguanodontia

*Beaks for cropping vegetation common to all

*Impressive teeth (from chisels to dental batteries) and moveable skull parts for chewing plant material

Quadrupedal (facultative) limb posture among later, larger Ornithopods

Bipedal stance for earlier, smaller Ornithopods

*Forelimbs shorter than hindlimbs

Toes & some fingers ended in hooves in later, larger Ornithopods

Toes & fingers clawed in earlier, smaller Ornithopods

Basal Iguanodontians had spikes for thumbs!

Enlarged nares and flattened, elongated snout for later, larger Ornithopods

Clades and Species of Ornithopoda

SEE Figure 13.2 and Table 13.1

Diversity

At least 55 genera (more than 80 species) of Ornithopods

At least 60% (at least 33) lived during the Late Cretaceous

Clade Heterodontosauridae

Early Jurassic bipedal dinosaurs, about 1-2 m long

Heterodontosaurus (See Figure 13.3) & 3 other genera (2 based on sparse skeletal material) from South Africa

Name comes from canine-like teeth at front of mouth

May have something to do with intraspecific display and combat for social ranking and courtship

Canine-like teeth are apparently present only in mature “males”

Otherwise teeth are high-crowned & chisel-shaped (unique among dinosaurs)

Heterodontosaurids may have used powerful forelimbs and clawed hands to grab at vegetation or dig up roots and tubers

Heterodontosaurus has a long tail and modified hindlimbs interpreted to indicate that this dinosaur was a fast runner

Heterodontosaurids are found in semi-arid paleoenvironments

*Heterodontosaurids chewed by combining vertical lower jaw movement with a slight rotation of the mandibles about their long axes

Clade Hypsilophodontidae

Small to medium bipedal dinosaurs, about 1.5-4 m long, in existence from the middle Jurassic to the late Cretaceous

Hypsilophodon (Early Cretaceous), Orodromeus & Thescelosaurus (Late Cretaceous), and Othniela & Drinker (Late Jurassic) and five other genera found in North America, Europe, China, Australia & Antarctica

Tail vertebrae stiffened by ossified tendons

Didn’t live in trees

Hypsilophodontids (and all other Euornithopodans) had mobility of their upper jaws (pleurokenesis), particularly the maxillary, as well as the lower jaw - When the upper and lower teeth were brought into contact on both sides, the upper jaws rotated outward, the lower jaws moved inward, and the opposing surfaces of the teeth sheared past one another

Specimen of Thescelosaurus has evidence that it had a 4-chambered heart with a single aorta

Othniela & Drinker named after Marsh and Cope!

Clade Iguanodontia

Large facultative quadrupedal dinosaurs, 4-15 m long, in existence from the late Jurassic to the late Cretaceous

Consists of basal forms like Dryosaurus & Camptosaurus (Late Jurassic) and Iguanodon, Tenontosaurus, Muttaburrasaurus & Ouranosaurus (Early Cretaceous), plus the very diverse Hadrosauridae

Iguanodon was one of the first dinosaurs named

30+ beautifully preserved specimens of Iguanodon bernissartensis from the Early Cretaceous of Bernissart, Belgium desribed by Louise Dollo, who demonstrated these were bipedal dinosaurs

Tenontosaurus is the most primitive Iguanodontian, and is very similar to Hypsilophodontids

Dryosaurus, Camptosaurus and Muttaburrasaurus are more advanced than Tenontosaurus, but more primitive than Iguanodon

Ouranosaurus, from Niger and closely related to Iguanodon, had elongate processes on its dorsal vertebrae, thought to support a sailback or a hump

Iguanodontians were socially complex and important components of Late Jurassic through Late Cretaceous terrestrial ecosystems, partially or completely replacing sauropods as the largest herbivores

Hadrosauridae

“Duck-billed” dinosaurs, in existence from the early Cretaceous to the late Cretaceous (all but one genus (Eolambia) occur in the late Cretaceous), & comprising one-half of ornithopod genera (at least 28)

One of the best-studied clades

Hadrosaurus foulkii was the first discovery of a nearly complete skeleton from New Jersey! in 1857 and soon after described by Joseph Leidy, who reconstructed it as a bipedal dinosaur

Well-developed dental batteries

Lost antorbital fenestrae and manus digit I

Development of hooves on pes

Possible tracks in Early Cretaceous strata near Denver

Divided into Hadrosaurinae & Lambeosaurinae

Hadrosaurinae

Flat-headed hadrosaurs & those with solid bone crests, including Maiasaura, Edmontosaurus, Gryposaurus, Anatotitan, Saurolophus, Prosaurolophus & Hadrosaurus

Lambeosaurinae

Hollow-crested Hadrosaurids, including Lambeosaurus, Corythosaurus, Parasaurolophus & Hypacrosaurus, as well as Tsintaosaurus

Paleobiogeography and Evolutionary History of Ornithopoda

Main Points

Ornithopods first appear in the Early Jurassic, later than Theropods and Sauropodomorphs, and continue to the end of the Cretaceous

Fabrosaurids are early ornithischians with some ornithopod features and are Late Triassic through Late Jurassic dinosaurs that may be ornithopod ancestors

Ornithopods occur on all continents and in a wide variety of environments

Heterodontosaurids limited to South Africa in the Early Jurassic

Hypsilophodontids and Iguanodontians widespread after the Middle Jurassic

Hypsilophodontids were more important during the Late Jurassic; Iguanodontians during the Cretaceous

Fluvial, Lacustrine, Swamp, Deltaic and Coastal Marine

Diversity driven by splitting of the continents and large-scale changes in vegetation

Appear to have displaced sauropods during the Cretaceous

Ornithopods as Living Animals

Reproduction

Introduction

At least some Ornithopod species stayed by their nests and brought food to hatchlings for an extended period of time, and so are not like modern sea turtles, which lay eggs in nests and then leave, or crocodilians, which may remain by the nest and help dig out the hatchlings, but do not sit on the nest or take care of the hatchlings after they have hatced out

Attracting mates

Lambeosaurines like Parasaurolophus & Tsintaosaurus had elaborate head ornamentation

There may have been sexual dimorphism with regard to head ornamentation

Originally thought to relate to aquatic habits or olfactory functions

Now thought to be resonating chambers used for communicating aurally (as well as visually if brightly colored)

Hadrosaurines had large nasal cavities that may have been covered with inflatable skin flaps that may have extended up onto the solid crests of species with such features

Maiasaura may have had dewlaps

Ouranosaurus, like Spinosaurus, had extremely high spines on their vetebrae, forming a sail-like ridge down their backs, or a bison- or camel-like hump

Heterodontosaurid tusks?

Building nests and laying eggs

Well-documented nests with eggs in large nesting colonies for Maiasaura pebblesorum and Hypacrosaurus

Maiasaura & Hypacrosaurus nests are spaced a mother’s body size apart, suggesting that they were regularly attended by parents

Hatchlings were altricial (delaying maturation) and stayed in the nest under parental care for many months, based on poorly ossified limb joints of smaller juveniles, broken eggshells and skeletons of juveniles up to 3 m long in nests

No conclusive evidence of brooding

Hypacrosaurus egg horizon can be traced for 3 km

*Probably all hadrosaurid hatchlings were altricial

*Precociality probably was ancestral for Euornithopoda, while altriciality evolved sometime prior to the origin of Hadrosauridae

*R-strategy vs. K-strategy

R-strategy = lots of offspring, no or little parental care, majority of offspring don’t survive

K-strategy = few offspring, much parental care, majority of offspring survive

Dryosaurus and Camptosaurus embryos are known from the Late Jurassic

Heterodontosaurid and Hypsilophodontid embryos, eggs and nests are unknown

Troodon eggs originally assigned to Orodromeus

Growth

Growth Sequences Available For Only a Few Species

Maiasaura, Hypacrosaurus, Dryosaurus and Orodromeus

Small skulls with large orbits are “cute”

Bone Histology

Maiasaura shows thick deposits of fibrolamellar bone between LAGs, indicating fast juvenile growth

Reached 3-meter length within 1 year

Orodromeus shows intermediate growth rates

Trackways with juvenile and adult prints can give an independent source of estimates of growth

Locomotion

Bipedalism vs Quadrupedalism

Ornithopods were variously obligate bipeds, facultative bipeds or quadrupeds

Based on skeletal and abundant trackway data

Heterodontosaurid and Hypsilophodontid tracks are not well documented

May be due to similarity of pes of these small ornithopods to those of theropods

Smaller Ornithopods were faster than larger Ornithopods, probably reaching maximum speeds of about 20 kph (12.5 mph)

Ornithopod hindlimbs are longer than forelimbs and probably preclude quadrupedal running, even in larger Ornithopods

Heterodontosaurids, hypsilophodontids and some iguanodontians must have been primarily bipedal, although they also may have adopted a quadrupedal stance when foraging or standing still

Some of the larger ornithopods may have engaged in extensive quadrupedal locomotion - they had solidly built hands and trackways indicate a quadrupedal stance while moving slowly (~ 7 kph [4 mph])

Juveniles may have been more bipedal than adults because limb elements change proportion with age

Ornithopods were not aquatic

Ornithopod tails were long, muscular, strengthened by ossified tendons and held at or near horizontal, making an excellent counterbalance for the front of the animal were primarily terrestrial animals

“Webbing” in mummies is the result of dessication of foot pad muscalature and flattening of the skin between the toes

Lambeosaurine hollow crests were not snorkels

Hadrosaurid “duck“-bills covered dental batteries superb for tough not soft vegetation

Feeding

Ornithopods had great mouths for eating vegetation

A beak for cropping vegetation

A well-developed dental battery for grinding coarse plant material

Teeth replaced every 200 days or so

A large, robust coronoid process for serious masticatory muscles

Fleshy cheeks

Heterodontosaurids and Hypsilophodontids had teeth under their sharp beaks & probably had selective cropping ability

Iguanodontians had no front teeth, a broad snout & a stronly serrate margin to their beaks, indicating that they were not selective feeders, but instead, just cropped whatever they could get at

Ornithopod (Edmontosaurus) Mummies

Stomach contents (twigs, berries and needles from conifers), in addition to skin and dried, stretched tendons & muscles, have been preserved

Coprolites of Maiasaura contain groundup conifer tissue

Dung beetle traces

No Definitive Gastroliths for Ornithopods

Ornithopods apparently employed fementation in their internal digestive tract, based on the large volume of the gut, as well as milling with their teeth

Social Life

Many Ornithopods probably lived in herds

Maiasaura and Hypacrosaurus nesting grouds and Hypacrosaurus mass burial site

Skeletal material from more than one individual in the same deposit in a small area

Trackways

Hadrosaurid headgear indicates sophisticated social behavior using aural communication

Herding helped protect against predators

Sheer numbers

Communication

Health

Mostly healthy

Some tail and hip injuries

Evidence of predation

Four-Chambered heart for Thescelosaurus

Extinction

Heterodontosaurids extinct at the end of the Early Jurassic

All other Ornithopod clades extinct at the K-T boundary