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SAUROPODS

MOST PRIMITIVE SAUROPODS  

    The earliest sauropod fossils are known from the Late Triassic.  

Analysis of bone tissue from sauropods indicates that they underwent extremely rapid growth rates early in life, comparable to those of large, modern mammals.  Given the pneumatization of their vertebrae, it is possible if some of the adaptations observed in avian lungs allowed them to grow so quickly (Sander, 2004).

     Sauropods possessed thick limbs that were held nearly vertical.  Like an elephant, the knee and elbow didn’t bend much and the stride was short.  They possessed 5 short fingers.  Apparently there was a great deal of cartilage in the hand and foot to distribute weight, since the bony elements were reduced or absent.  Diplodocus had only 2 carpal  (wrist) bones and Apatosaurus had only one, transferring the body’s weight directly to metacarpals.  Sauropods had 12-19 cervical (neck) vertebrae and these vertebrae were supported by cervical ribs.

     Although Vulcanodon was originally considered a prosauropod, it is now considered to be the most primitive sauropod with a number of primitive characteristics retained from prosauropod ancestors.  It is assigned to the family Vulcanodontidae with the primitive sauropod Barapasaurus. The expanded pubes of Vulcanodon are almost identical to those of prosauropods.  The vertebrae lack pleurocoels and the cervical vertebrae are shorter than those of all other sauropods.  The forearm is similar to both that of the prosauruopod Plateosaurus and Brachiosaurus.  The axial skeleton is intermediate between sauropods and prosauropods (Cooper, 1984; Lambert, 1990, Fastovsky, 1996).

In sauropod classification, Vulcanodon is considered the most basal species with Kotosaurus, Shunosaurus, Jobaria, and Altasaurus respectively forming the next branches in the clade (Royo-Torres, 2006).

     Isanosaurus is the earliest known sauropod, dating from the Late Triassic of Thailand.  While it has many primitive characteristics  compared to other sauropods (such as its vertebrae and femur), it also shows a number of differences from prosauropods, indicating that the separation between prosauropods and sauropods occurred even earlier.  The one specimen is estimated to have reached 16.5 meters, but may not have been full grown (Buffetaut, 2000).

Cetiosaurus
skulls

CETIOSAURS 

    The primitive cetiosaurs include Cetiosaurus, Tatagosaurus, Barapasaurus, Omeisasaurus, Euhelops, and Mamenchisaurus (Royo-Torres, 2006). Euhelopodidae or “good marsh feet”, is known from China and include Mamenchisaurus which possessed a neck which was almost half its 22 meter body length.

Mamenchisaurus

The family Cetiosauridae, “whale lizards”, are not a true clade but rather primitive sauropods which were ancestral to later groups.  Some have a primitive skull and lack the lesser trochanter on the femur that exists in later sauropods.  Their nostrils were located on the tip of their skulls and their vertebrae lack depressions or cleft spines to make them lighter.  Barapasaurus had depressions in vertebrae that can not yet be considered pleurocoels (Monbaron, 1999). The most primitive cetiosaurs, Lapparentosaurus and Volkherimeria, are known from two fossil sites on southern continents which were in close proximity on the supercontinent Pangaea. They are more primitive than all other sauropods in the unmodified structure of their vertebrae (such as its short vertebrae with flattened neural spines and the lack of features which strengthened the vertebrae). More advanced cetiosaurs, such as Amygdalodon, Patagosaurus, Rhoetosaurus, Haplocanthosaurus, Cetiosaurus, Baraposaurus, and Shunosaurus, are known from every continent except Africa and Antartica. Cetiosaurus could reach a length of 16 meters. In general, cetiosaurs had shorter necks than later sauropods. Shunosaurus possessed a fused mass of bone at the tip of its tail which could be swung like a club. A mass grave caused by a flash flood at a Chinese fossil site includes at least ten Shunosaurus individuals, suggesting that they traveled in groups (Czerkas, 1990).

A bit more advanced than cetiosaurs were the turiasaurs which include Turiasaurus, Losillasaurus, and Galveosaurus. Turiasaurus measured 30 meters and weighed 40-48 tons, the largest sauropod among the basal group (Royo-Torres, 2006).

DIPLODOCIDS

Diplodocus

     The members of the family Diplodocidae ranged in length from 16-27 meters and were very light–10 tons as opposed to the smaller Brachiosaurus which weighed 55 tons.  In Diplodocus, “double beam”, the neck vertebrae were 2 ½ times the length of the trunk vertebrae.  The tail at least 70 and perhaps 80 vertebrae.  Although tail would have made a horrific whip capable of quick speed and loud cracks, its frequent use as a weapon probably would have caused damage.  The base of the tail of specimens does seem to have received stress of frequent movement.  Trackways show that the tail didn’t drag on the ground.  Many rows of teeth existed to replace the ones which broke.  The astragalus was only ankle bone (Fastovsky, 1996).

Size increased in the Diplodocus clade which included Diplodocus, Amargasaurus, Apatosaurus, Barosaurus, Limaysaurus, and Dicreaeosaurus (Royo-Torres, 2006).

apatosaurus

Many children are disappointed to learn that “Brontosaurus” is not really the name of a dinosaur and the name Apatosaurus should be used instead.  In 1883 Marsh wanted a skull to put on his “Brontosaurus” skeleton which had been found without a head and he used a skull from a Camarasaurus found nearby the site where the Brontosaurus was excavated.  The first 2 Apatosaurus skeletons found were headless and thus all drawings depicted a Camarasaurus skull.  In 1916, Holland wanted to put the correct skull on his Apatosaurus specimen, but because it was Diplodocus-like rather than Camarasaurus-like (the incorrect skull), he was persuaded not to and this was not corrected until the 1970s. Why use the name Apatosaurus rather than Brontosaurus?  Marsh had named Apatosaurus in 1877 and Brontosaurus in 1879.  By international agreement, any earlier name takes precedence over later ones.  Apatosaurus had 82 tail vertebrae.

Apatosaurus

brachytrachelopan

One group of sauropods, the dicraeosaurs, possessed shortened necks. The Late Jurassic South American species Brachytrachelopan had a neck 40% shorter than those of other dicraeosaurs. Unlike most sauropods, the height of the neck vertebrae exceeded the length (Rauhut, 2005).

CAMARASAURS

  Between the diplodocus clade and the titanosaurs, a number of lineages branched including Camarasaurus, Bellusaurus, Lourinhasaurus, Haplocanthasaurus, and Brachiosaurus, the latter being the sister branch of the titanosaurs (Royo-Torres, 2006).
Camarasaurus
     Camarasaurs possessed 12 cervical vertebrae which is the primitive number. In the family Camarasauridae, the forelimbs are 2/3-4/5 length of hindlimbs.  Camarasaurus “chambered lizard” (named for the hollow chambers in its vertebrae) was the most abundant North American sauropod.  The neck vertebrae had a cleft in their neural spines (Lambert, 1990, Fastovsky, 1996).
     The family Brachiosauridae were large camarasaurs.  Brachiosaurus had elongated forelimbs that were as long or longer than hind legs.  The nasal bones and nostrils were elevated.  For several decades this was the largest known dinosaur (and the largest known terrestrial animal) at 22.5 meters tall and 50-60 tons.  Its head was held 40 feet above the ground. Its tail is relatively short for sauropods. The neck vertebrae were 3x the length of trunk vertebrae.  If Brachiosaurus was warm blooded, it would have required 200 kg (about 450 pounds) food/day and at least 10 years to reach adult size.  If it was cold blooded, it would have required much less food/day but would have needed 100 years to reach adult size (Lambert, 1990, Fastovsky, 1996). Brachiosaurus has been found in both Africa and North America (although it was apparently rare in North America), giving it one of the geographic greatest ranges among sauropods (Gillette, 1994).
Brachiosaurus Brachiosaurus
  Atlasaurus is more similar to Brachiosaurus than is any other sauropod but was also similar to Camarasaurus (Monbaron, 1999).   
 
   

  

  

TITANOSAURS

 Titanosaurs were much more lightly built than camarasaurs because of vertebral pleurocoels.  They had longer necks because vertebrae formerly part of trunk incorporated into neck.  Their tails were more free to move side to side.

Titanosaurs are known from every continent except Antarctica and lived from the Late Jurassic to the Late Cretaceous. They displayed a diversity of anatomical features, such as vertebral variations (Gonzalez Riga, 2009). The titanosaurs, the crown group of sauropods, included Austroasaurus, Maiawisaurus, Isisaurus, Alamosaurus, and Saltasaurus (Royo-Torres, 2006).

   Some had bony plates (perhaps with horns on top of them) and small bony lumps on their backs.  Saltasaurus had 2 kinds armor: dermal plates of 10-12 cm in diameter and bony ossicles 6-7 mm wide.  It is possible that all titanosaurs had armor (Weishampel). They ranged in size from 9-21 meters long.  Saltasaurus was a smaller sauropod, measuring 12 meters and possessed bony plates.  One skin impression shows thousands of bony knobs in the skin.  Paralititan had a humerus which measured 5 feet and is estimated to have reached 90 to 100 feet in length and 150-160,000 pounds.  Only Argentinosaurus was longer and even that species may not have been heavier (Begley, 2001; Lambert, 1990, Fastovsky, 1996).

Saltasaurus
     Laplatasaurus also had armor.  Ultrasaurus, Supersaurus, ad Dystylosaurus were giant sauropods which are unfortunately known from only a few bones. Seismosaurus was similar to Diplodocus in its form but comparable bones were 20% larger, giving length estimates ranging from 110 to 170 feet (Gillette, 1994). Ultrasaurus, despite original claims, was probably just smaller than Brachiosaurus.  Supersaurus was probably similar to Diplodocus in shape and measured 42 meters, weighing 50 tons.  Seismosaurus is a large sauropod that is still being excavated.  Argentinosaurus might have weighed 100 tons (Abrams, 1996). Enormous sauropods evolved separately on different continents: Sauroposeidon and Seismosaurus in North America, Puertosaurus and Argentinosaurus in South America, Paralititan and Brachiosaurus in Africa, and Turiasaurus in Europe (Royo-Torres, 2006). Titanosaur nests suggested that they laid a large quantity of eggs at once in a rimmed nest (Grellet-Tinner, 2006).