Chapter 12 – Overview of Sauropodomorpha

Why Study Sauropodomorphs

Many BIG! sauropodomorphs, especially sauropods

Must have had big affect on vegetation

Sauropods were up to 40 meters in length & six meters at the shoulder; some weighed more than 50,000 kilograms

Had long necks and tails

System of girders and air pockets to maximize lightness and strength

At least 10 elongated cervical vertebrae; a total of 25 presacral (including cervical) vertebrae

Pillar-like legs made of denser bone than found in upper parts of skeleton

Short hindlimbs in comparison to torso length

Relatively small heads

Simple peg like or spatulate teeth, with bladed or serrated crowns

Nostrils tend to migrate toward the top of the head

Widespread trace and body fossil

Well-documented tracks

Nests, eggs, embryo and juvenile skeletons

Rare coprolites and gastroliths associated with skeletons

Definition and Unique Characteristics of Sauropodomorpha

Introduction

Sauropodomorpha = lizard-foot form

Sauropoda Created by O. C. Marsh in 1878

Characteristics

Major characteristics – SEE Figure 12.2

Hands

Large digit I

Stance

All sauropods and some prosauropods were obligate quadrupeds; many prosauropods were facultative bipeds

Teeth and Jaws

Relatively puny teeth and jaws adapted for raking and shearing foodstuff before swallowing

Skulls

Skulls lack evidence for attachments of large chewing muscles

Skulls were the smallest in comparison to body size of all dinosaurs

Sauropodomorphs had the lowest EQs of any dinosaurs

Skulls often missing from sauropodomorph skeletons; held in place by a small atlas

Vertebrae

Pleurocoels (cavities in the side of vertebrae) lightened vertebrae and may have been filled with air sacs

Abundant transverse processes, neural spines and chevrons for muscle attachment and preventing damage to nerves and blood vessels

Used to identify sauropod species

Includes how centra are expressed and articulated with one another

Opisthocoelus (ball forward), Procoelus (ball backward), Amphicoelus (no ball)

Trace fossils

Largest tracks ever left by any animal and major bioturbated zones where large numbers walked

Nests, eggs, embryo and juvenile skeletons are relatively abundant

Gastroliths rarely associated with skeletons, but concentrations of unusual rocks in some deposits have been interpreted as sauropodomorph gastroliths

Some sauropod coprolites have been identified tentatively

No toothmarks

Clades and Species of Sauropodomorpha

SEE Figure 12.1 and Tables 10.2, 12.1 and 12.2

Diversity

More than 65 genera (more than 100 species) of Sauropodomorphs

A little more than a quarter (at least 17) lived during the Late Jurassic

Clade Prosauropoda

Late Triassic to Early Jurassic herbivorous dinosaurs, with small but long, laterally-compressed heads, long necks & large bodies

Mostly facultative bipeds

Range from 2.5 to 11 meter in length

Simple serrated and leaf-like teeth

Enlarged, deviated claw on manus digit I

Probably not ancestral to sauropods

Vestigial pes digit V

See Figure 5.5 and 12.3 for the archetypical prosauropod Plateosaurus

Also Coloradisaurus/Mussaurus & Riojasaurus (Late Triassic as well) and Anchisaurus (Early Jurassic) plus at least 12 other genera with a WORLDWIDE distribution

Clade Sauropoda: Camarasaurids, Diplodocids, Titanosaurids, and Others

Some differences from Prosauropods

Cervicalization

Conversion of dorsal vertebrae to cervical vertebrae

Lots of caudal vertebrae

At least 45 to more than 80

Femur longer than humerus and radius combined

Except for brachiosaurids

Five digits on pes

Claws on digits I, II and III

Nares migrated to top of skull

Nostrils still near mouth though

Teeth not serrated

Four Major Clades: Diplodocids, Camarasaurids, Brachiosaurids, Titanosaurids, and the basal “Cetiosaurids”

Diplodocidae

Huge (maximum length of at least 27 meters, and maybe as much as 38 meters) Sauropods with long necks & tails and small heads, & built like suspension bridges

Mamenchisaurus (Middle Jurassic), Diplodocus, Apatosaurus, Seismosaurus, and Barosaurus (Late Jurassic), & Amargasaurus (Early Cretaceous) and many other genera

Mamenchisaurus has an incredibly long neck - more than half of its 22-meter body length

Barosaurus found at Tendaguru in Tanzania & in the Morrison Formation

Amargasaurus has incredibly long spines on its neck vertebrae

Brachiosauridae

Among the largest (weight, at least 50 tons, and height, at least 13 meters) sauropods, with elongate forelimbs and nostrils on top of the head, & in existence only during the Late Jurassic

Brachiosaurus, Ultrasauros & Supersaurus & a few other genera

Brachiosaurus found at Tendaguru in Tanzania & in the Morrison Formation

Camarasauridae

Sauropods with short, high and powerfully built heads and spatulate teeth

Camarasaurus (Late Jurassic) & many other genera

Titanosauridae

Among the poorest known sauropods, found mostly in Cretaceous (particularly Late Cretaceous) strata, mostly in parts of the former Gondwana (southern) continents, but also found in Europe and North America

Titanosaurus, Alamosaurus, Argentinosaurus, & Saltosaurus & a few other genera

Alamosaurus is perhaps the best-known Titanosaurid - a quarter of an articulated skeleton has been recovered

Alamosaurus migrated to North America from South America in the Late Cretaceous

Saltosaurus was covered with a pavement of nodular and button like osteoderms

Argentinosaurus cast mounted at Fernbank

Diplodocidae and Titanosauridae are sister clades, as are Brachiosauridae and Camarasauridae

More than two-thirds of sauropodomorph genera are sauropod genera

Paleobiogeography and Evolutionary History of Sauropodomorpha

Main Points

Sauropodomorphs, like theropods, are among the earliest dinosaurs

Body fossils appear in the earliest Late Triassic, ~230 my ago, and include fragmentary specimens of prosauropods from Africa and Brazils

Sauropodomorph body and trace fossils occur from the Late Triassic to the Late Cretaceous on all continents (except Antarctica for trace fossils) and in a wide variety of environments

*However, the fossil record of individual sauropodomorphs is quite poor

A few basal forms are known from complete skeletons

Most other Sauropodomorphs are known only from incompletely preserved material, often missing their heads, parts of their tails, and their feet

This probably results from the fact that Sauropodomorphs are so big that it is difficult to bury them and because skulls were held in place by a small cervical vertebra

Prosauropod body fossils are the only sauropodomorph body fossils from the Late Triassic

Prosauropods became extinct at the end of the Early Jurassic

Sauropods first appear in the Early Jurassic

Prosauropods and Sauropods appear to be sister clades

Prosauropods are probably not ancestral to sauropods because prosauropods have a vestigial pes digit V, while sauropods retain the ancestral large pes digit V

Exact relationships are unresolved because of the 20+ million year gap between the first appearance of Prosauropods and Sauropods

It’s not clear why sauropods became so big

Predator-prey interactions

Ecologic separation from other dinosaur herbivores

Accommodation of large alimentary canal to process food of low nutritional quality

Long necks and tails to vent heat

May have been a unique set of circumstances involving changing climate and continents

Sauropodomorphs as Living Animals

Reproduction

No traces of mating

Oldest nests and eggs are Prosauropod from the Late Triassic

Massospondylus nest with eggs and juvenile bones and nearby adult bones

Coloradosaurus probable parental species of Mussaurus, hatchlings in a nest with eggshell fragments

Sauropodomorph eggs, however, are rare in rocks older than the Cretaceous, although they are widely distributed geographically

Generally eggs are interpreted as sauropodomorph based on sheer size, because embyos or hatchlings are not usually associated with the eggs

Hypselosaurus (a titanosaurid) eggs associated with adult remains in France

Only sauropodomorph embryos known are from a recent discovery of spectatcular sauropod (again titanosaurid) nesting horizons in Late Cretaceous rocks of Argentina

Skin patterns preserved also

Site fidelity

Similar to other supposed sauropod eggs elsewhere

One egg-laying pattern from the Cretaceous of France suggests that 5 or 6 sauropod mothers walked along, squatted and laid eggs in semi-circles

Growth

Growth Sequences Available For Only a Few Species

Plateosaurus (Late Triassic) and Camarasaurus & Apatosaurus (Late Jurassic)

Bone Histology

Rapid growth early in life, then slowing

May have been inertial homeotherms

Long necks and tails to expel excess heat

Locomotion

Based on trackway and anatomical (hands, forelimb/hindlimb ratios, trochanter position on femur) data

Prosauropods facultatively bipedal, Sauropods quadrupedal

Sauropods didn’t live submerged in bodies of water to buoy up their huge bulk as suggested by their long necks and nostrils on top of their heads

Water pressure would have prevented breathing

The lungs of a sauropod under up to 6 meters of water would experience pressures up close to 2 atmospheres and the animal would not be able to breath

Trackways not in appropriate environments

*Sauropodomorphs are found, and presumably lived, in a myriad of sedimentary depositional environments

Lakes, rivers (floodplain & channel deposits contain remains) and even eolian environments

Well studied in Late Jurassic Morrison Formation of the western U.S.

Studies of the Morrison indicate that Sauropods here had to deal with seasonal dryness & may have had to migrate to more lush environments

Studies in Tendaguru, Texas & Maryland, however, indicate a shoreline setting and more humid year-round conditions

Feeding

Teeth

Prosauropod teeth are leaf-shaped and serrated – used to shear vegetation

Sauropod pencil-like teeth used to rake vegetation

Long necks

Thought for use in browsing high in trees, but probably for foraging on low growing vegetation with huge horizontal sweeps of their necks, except for Brachiosaurids

Blood pressure problems - Humans & most other large mammals have blood pressures of about 110 to 150 mm of mercury; giraffes have blood pressures of about 320 mm of mercury; blood pressure in Brachiosaurus would have been 629 mm of mercury

Low nutritional value for conifers and slow recovery rate

Computer modeling suggests necks couldn’t be elevated more than 10 to 20 degrees above the horizontal for most sauropods

Gastroliths

Teeth not adapted for chewing and limited to the front of the mouth usually

Basically, sauropodomorphs nipped or stripped off vegetation and delivered a bolus of foliage to the gullet without much modification in the mouth

At least some sauropodomorphs (Seismosaurus, Plateosaurus & Massospondylus) had gizzards filled with stones for mechanically breaking food down prior to movement further along the gastrointestinal tract

Sauropodomorphs had large guts that probably housed fermentation chambers

Sauropodomorphs were probably constant eaters

Coprolites

Not definitively associated with sauropod remains

Social Life

Many Sauropodomorphs probably lived in herds that migrated large distances

Trackways showing many individuals moving in the same direction

Late Jurassic of Colorado and Portugal (showing juvenile and adult tracks together)

Early Cretaceous of Texas

Cretaceous of South Korea

Nesting horizons

Monospecific bone beds with juveniles and adults

Health

Healthy animals in general

Prey animals

Apatosaurus bones with Allosaurus tooth marks

Extinction

Prosauropods extinct at the end of the Early Jurassic

Sauropods extinct at the end of the Late Cretaceous, but locally extinct in the Early Cretaceous

North America has a sauropod “gap” in the Late Cretaceous, Alamosaurus only at the end of the Late Cretaceous

Titanosaurids thriving at this time in South America, Africa and Asia