PROSAUROPODS

     A typical prosauropods is Plateosaurus of the Upper Triassic of western Europe.  Plateosaurus belongs to the family Anchisauridae.

Figure 1. Plateosaurus, based on Galton (1990). (From:  Lecture 12 - Triassic: Keuper, Fleming Fjord http://rainbow.ldeo.columbia.edu/courses/v1001/keuper11.html)

      Plateosaurus was 6 to 8 meters long and had many characteristics typical of prosauropods in general. Plateosaurus is the best known of the prosauropods.  About 35 well preserved skeletons were found together in Germany from deposits interpreted to be from an ancient mud slide.

• 1) Robust
• 2) Jaw joint below the level of the teeth, so when the jaws were closed the force of the bite was distributed evenly over all the teeth nearly simultaneously.
• 3) Numerous coasely serrated, leaf-shaped teeth (with serrations at about 45 degree angle to the tooth surface).
• 4) Small head.
• 5) Long neck.
• 6) Long back and tail.

     Prosauropods are often restored as bipedal dinosaurs, but footprints indicate that they usually walked on all fours.  So they were probably facultative bipeds (usually walked on all fours [quadrapeds], but could walk on two legs).  The fore limbs of most prosauropods are at least 2/3 the length of the hind limbs, as in the later diplodocid sauropods (which are considered to be obligatory quadrapeds).

     The first digit of the hand is much larger than the other digits and was held clear of the ground while walking.  They could most likely rear-up on their hind legs to eat vegetation from trees.

Evidence for Plant Eating of Prosauropods

• 1) Long necks - probably feed like giraffes from tall trees.
• 2) Cheeks present (like in ornithischians) - to retain food in the mouth as it was chewed.
• 3) Jaw hinge below the line of the upper tooth row (as in ornithischians).  This offset of the jaws allows tooth rows to be almost parallel, thus contact would have occurred almost simultaneously along the entire length of the tooth rows during chewing (as in herbivorous mammals).
• 4) Spatulate (leaf-shaped) teeth - about 20 coarse serrations per tooth at an anlge of about 45 degrees to the cutting edge.
• 5) Gastroliths have been found associated with at least one genus (Massospondylus of Africa).

     Prosauropods are among the first dinosaurs to appear in Late Triassic.  They had a world wide distribution and were one of the most successful plant eating vertebrates of Late Triassic and Early Jurassic.

     The prosauropods became extinct by the end of Early Jurassic time.  This was the first signicant extinction of a group of dinosaurs.  The extinction of the prosauropods coincides with the appearance of sauropod dinosaurs and they were replaced by these larger herbivores.
 
 

SAUROPODA

     About seventy five genera of sauropods are known from the fossil record.  The most well known to the general public are Apatosaurus (formly known as "Brontosaurus"), Diplodocus, and Brachiosaurus.  However, Camarasaurus is the most commonly found sauropod (see Figure 2).

     The oldest known sauropods are Early Jurassic in age and they ranged to Late Cretaceous.  They had a world wide distribution by Late Cretaceous time.  However, in terms of size and diversity, the sauropods reached their zenith of evolution during the Jurassic - Cretaceous transition (Late Jurassic - Early Cretaceous).

     Following are some of the characters which unit the sauropods into a monophyletic group:

• 1) Very large body size.
• 2) Very small skulls.
• 3) Long necks - increased number of cervical vertebrae and lengthened cervical vertebrae.
• 4) Long tails - increased number of caudal vertebrae and lengthened caudal vertebrae.
• 5) Dorsally placed nasal openings.
• 6) Limb bones robust and solid.
• 7) Five fingers on hand and foot with reduced phalanges.
• 8) Deep pleurocoels on presacral vertebrae (lightened the backbone).

      The most well known sauropod families are 1) Diplodocidae, 2) Camarasauridae, and 3) Brachiosauridae.
Sauropods are mainly distinguished by features of the skull, but other features are also distinctive (such as the shape and number of vertebrae).  There appear to be two main skull types in sauropods, the camarasaurid skull type and the diplodocid skull type.  However, there are variations within the two skull types.

Diplodocidae

     The diplodocidae have long and slender skulls with elongate muzzels (see Figure 3).  Slender, peg-like teeth are restricted to the front part of the mouth.  The nostrils are on top of the skull, anterior to and above the orbits.

     The two most well known genera of the diplodocidae are Diplodocus and Apatosaurus ("Brontosaurus").  Recently, two large diplodocid sauropods have been described from western North America (however, based on limited skeletal material); Supersaurus and Seismosaurus (TRY THIS LINK: Seismosaurus ) have been estimated to be close to 40 meters in length and perhaps weighed as much as 50 tons.

     According to Lucas, 1997, Supersaurus is known from a huge shoulder blade found in Upper Jurassic rocks of the Morrison Formation in Colorado.  This sauropod was originally thought to be a brachiosaur, but now thought to be more similar to Diplodocus.  If Supersaurus had Diplodocus-like proportions it would have weighed perhaps as much as 50 tons, with a length of 42 meters (139 feet).  Seismosaurus was an enormous diplodocid known from portions of the tail, back, pelvis, and hind limb from Upper Jurassic rocks of New Mexico (Lucas, 1997).  Seismosaurus was originally estimated to be 58 meters (190 feet) in length, but this appears to have been an erroneous estimate (Lucas, 1997).  It is now thought that Seismosaurus was about the same size as Supersaurus (or perhaps slightly smaller at about only 30 meters)(McIntosh, Brett-Surman, and Farlow, 1998; http://www.nmmnh-abq.mus.nm.us/nmmnh/seismosaurus.html).

General Characteristics of the Diplodocidae (primarily from Lucas, 1997):

• 1) Long slender skull with peg-like (or pencil-like) teeth confined to the front of the mouth.
• 2) The nostrils are on top of the skull above and in front of the orbits.
• 3) Very long neck, additional cervical vertebrae and elongated cervical vertebrae.
• 4) V-shaped neural spines on cervical vertebrae (for the placement of a ligament that helped hold the neck up).
• 5) Modified chevrons on caudal vertebrae - double tuning fork shape.
• 6) Whip-like tail - tail very long with the last 30 or 40 caudal vertebrae just short rods.
• 7) Humerus approximately 0.66 the length of the femur.

     Camarasaurus (see Figure 2) typifies members of the family Camarasauridae.  Camarasaurus is the best known sauropod, with the number of fossil bones found of this sauropod numbering in the thousands (DeCourten, 1998).

     Camarasaurus was a medium sized sauropod with a maximum known length of about 18 meters (59 feet) and an adult weight of 25 to 30 tons.  Camararsaurus stood about 3.7 meters (12 feet) high at the hips and had a relatively short and thick neck.  Very abundant fossil bones of Camarasaurus are found in the Jurassic Morrison Formation of the western U.S., particularly in Colorado, Utah, and Wyoming.

     The most obvious difference between camarasaurids and diplodocids can be seen in the skull (see Figure 3).  The skull of camarasaurids (as typified by Camarasaurus) was short and heavy with a blunt snout.  Relatively large, spatulate (spoon-shaped) teeth lined the entire length of the jaw.  The nostrils were large and located on the sides of the skull just anterior to the orbits.

     Camarasaurus had a relatively short (for a sauropod) body and neck, having only 12 cervical vertebrae (the primitive number for sauropods).  The humerus to femur ratio was 0.7, longer than for the diplodocids (which were about 0.66) (Lucas, 1997).

     The general characteristics for the Camarasauridae are the following:

• 1) Short and heavy skull with blunt snout.
• 2) Teeth large and spatulate-shaped, along the entire length of the jaw.
• 3) Large nostrils located on the sides of the skull in front of the orbits.
• 4) Relatively short by stout body and neck.
• 5) Only 12 cervical vertebrae, the primitive condition for sauropods.
• 6) U-shaped neural spines on first four dorsal vertebrae.
• 7) Neural spines on the sacrum are shorter and thicker than on diplodocids.
• 8) Pleurocoels extensively developed in cervical and dorsal vertebrae.
• 9) Simple, standard sauropod chevrons on caudal vertebrae.

     The brachiosaurids are typified by the heaviest land animal of all time, Brachiosaurus (about 55 tons).
The brachiosaurids closely resemble (and are thought to be closely related to) the camarasaurids.  However, the fore limb was relatively long with a humerus to femur ratio of greater than 1; thus, the brachiosaurids were higher at the shoulders than the hips (note: camarasaurids were slightly higher at the shoulders than the hips, but this was more pronounced in the brachiosaurids).

     The brachiosaurids had relatively long necks, but only 13 cervical vertebrate (but the cervical vertebrae were elongated).  They had a shortened tail with about 50 caudal vertebrae that were shortened.  There were 11-12 dorsal vertebrae (Lucas, 1997).

     Brachiosaurus was about 17 meters (56 feet) long, but could raise its head 12 meters (39 feet) off the ground.

     Brachiosaurus lived from Late Jurassic through Early Cretaceous (the Jurassic-Cretaceous transition), and is known from the Morrison Formation of western North America and also from Late Jurassic-Early Cretaceous deposits of Tanzania in Africa (Tendaguru Formation).

     The following is a summary of the characteristics of the brachiosaurids:

• 1) Skull similar to the camarasaurids, but with a longer rostrum (snout).
• 2) Fore limb longer that hind limb (humerus to femur ratio greater than 1).
• 3) Cervical vertebrae numbered 13 and were elongated.
• 4) Dorsal vertebrae numbered 11 to 12.
• 5) Neural spines of cervical and anterior dorsal vertebrae did not bifurcate (fork, as in diplodocids and camarasaurids).
• 6) Simple chevrons on caudal vertebrae.
• 7) Very large nostrils located high on the head, above and in front of the orbits.
• 8) Large chisel-shaped teeth (but more like camarasaurid teeth than diplodocid teeth) that lined the entire margin of the mouth.

Cetiosauridae

     The Cetiosauridae are a poorly defined sauropod group with relatively short necks and small bodies (Norman, 1985).  They are considered to be a polyphyletic grouping of sauropods (Fastovsky and Weishampel, 1996; Lucas, 1997).

     The cetiosaurids are primarily of Early to Medial Jurassic age, but ranged to Medial Cretaceous.  They are a well known group of small, primitive sauropods.  They had very few pleurocoels in vertebrae.  The genus Shunosaurus had a club at the end of the tail.

Titanosauridae

     The titanosaurids are primarily of Cretaceous age and the fossils of most have been found on the southern continents of India, South America, and Africa.  One titanosaurid, Saltasaurus (Cretaceous of Argentina) had body armor.  Others may have had body armor also, but complete skeletons of titanosaurids are relatively rare.

     One of the better known titanosaurids is Alamosaurus, from Cretaceous deposits in New Mexico, Texas, Utah, and Montana (Lucas, 1997).  Alamosaurus is known only form a few teeth (diplodocid type), a shoulder blade and fore limb, some pelvic bones, a femur, a few dorsal vertebrae, and a tail.  It is thought that Alamosaurus probably migrated to North America from South America near the end of the Cretaceous (note: Sauropods completely disappeared from North America after the Jurassic-Cretaceous transition, then returned to North Americal during Late Cretaceous; this is often referred to as the sauropod hiatus in North America).
 

SAUROPOD LIFESTYLES

     SAUROPODS DID NOT LIVE SUBMERGED IN WATER OF SWAMPS AND LAKES!!!

Diet

     Obviosly, all sauropods were herbivores.  However, they had no grinding or shearing teeth.  The peg-like teeth of diplodocids, the spatulate teeth of camarasaurids, and the chizel-like teeth of brachiosaurids were well suited to cropping vegetation, but not of chewing vegetation.  Sauropods most likely swallowed their food whole into a vat-like stomach, where chemicals and bacteria, aided by the grinding action of gastroliths, broke down the food.

     If sauropods had a reptilian metabolism, a 29 ton sauropod would require 50 kilograms (110 pounds) of vegetation each day (Lucas, 1997).  If they had a higher rate of metabolism (like mammals) they would have had to eat much more than if they were cold-blooded (ectothermic).

      There is no conclusive evidence that sauropods had a high rate of metabolism.  So, it appears reasonable to assume that they were ectothermic, but not like modern ectotherms.  Because of their huge mass, sauropods would have been homeotherms (once they got warmed up, because of their low ratio of volume to surface area, they would tend to keep a rather constant body temperature - this is also referred to as gigantothermy or inertial homeothermy).  Thus, they could have maintained a fairly constant body temperature because of their thermal inertia.

Reproduction

     Sauropods laid eggs, probably while walking.  There is evidence for this from a titanosaurid, Hypselosaurus, from France; the eggs of Hypselosaurus are 25 centimeters long and were found arranged in a line (as if laid while walking) (Lucas, 1997).

Social Behavior

     Sauropods may have lived in small herds.  Of course, many sauropods have been found together in mass death assemblages, but this is not necessarily indicative of gregarious behavior.  The carcasses may have accumulated on sand bars in rivers (much as the deposits which formed the bone bed at Dinosaur National Monument).

     Perhaps better evicence of group behavior is the information from dinosaur trackways.  Sauropod trackways have been found at several locations, most noteably along the Paluxy River near Glen Rose, Texas and along the Purgatory River in southeastern Colorado, that indicate a group of sauropods walking in the same direction.

     There is some evidence to support the idea that sauropods migrated in small herds to keep up with seasonal changes in their food supply.

Sauropod Evolution

     Most dinosaur paleontologists believe that sauropods evolved from a prosauropod-like ancestor about the end of Triassic time or the beginning of Jurassic.  The oldest known sauropods are of Early Jurassic age and are cetiosaurids, small, short necked forms with camarasaurid-like heads.  Sauropods probably evolved first in Gondwana, then spread to the rest of the northern continents.

     The zenith of size and diversity of the sauropods was attained in the Late Jurassic - Early Cretaceous, with forms like Diplodocus, Apatosaurus, Brachiosaurus, and Camarasaurus.

     Sauropods were the dominant herbivores of the Late Jurassic - Early Cretaceous.  Their diversiyt waned during the Cretaceous, with fewer and smaller sauropods.

     Perhaps the rise of ornithopods and flowering plants in Early to Medial Cretaceous time caused the decline of sauropods (most sauropod diversity in the Cretaceous was limited to southern continents, where ornithopods were not as successful).

     Of course, sauropods became extinct by the end of Cretaceous time, as did all dinosaurs.
 

REFERENCES (NOT IN ALPHABETICAL ORDER)

Gillette, David D.; 1994; Seismosaurus - The Earth Shaker; Columbia University Press; New York and Chichester, West Susssex; 205 p.

DeCourten, Frank; 1998; Dinosaurs of Utah; The University of Utah Pres; Salt Lake City; 300 p.

Fastovsky, David E. and David B. Weishampel; 1996; The Evolution and Extinction of Dinosaurs; Cambridge University Press; Cambridge (U.K.), New York, and Melbourne (Australia); 460 p.

Upchurch, Paul; 1999; The Phylogenetic Relationships of the Nemegtosauridae (Saurischia, Sauropoda); Journal of Vertebrate Paleontology, V. 19, No. 1, p.p. 106-125.

Norman, Dr. David M.; 1985; The Illustrated Encyclopedia of Dinosaurs; Crescent Books; New York; 208 p.

Lucas, Spencer G.; 1997; Dinosaurs - The Textbook (2nd ed.); Wm. C. Brown Publishers; Dubuque, Iowa; 292 p.

Lambert, David; 1993; The Ultimate Dinosaur Book; Dorling Kindersley; London, New York, Stuttgart; 192 p.

Galton, Peter M.; 1990; Basal Sauropodomorha - Prosauropoda; In: Weishampel, David B., Peter Dodson, and Halszka Osmolska (eds.); The Dinosauria; University of California Press; Berkeley, Los Angeles, London; p.p. 320-344.

McIntosh, J. S.; 1990; Sauropoda; In: Weishampel, David B., Peter Dodson, and Halszka Osmolska (eds.); The Dinosauria; University of California Press; Berkeley, Los Angeles, London; p.p. 345-401.

Dodson, Peter; 1990; Sauropod Paleoecology; In: Weishampel, David B., Peter Dodson, and Halszka Osmolska (eds.); The Dinosauria; University of California Press; Berkeley, Los Angeles, London; p.p. 402-407.