Cathetosaurus lewisi

Cathetosaurus lewisi  (Lewis is Arnie Lewis, his friend who got him finally into paleontology at Harvard.)

Taxon: Sauropoda
Name means: ‘upright lizard’ (pronounced: kuh-THEE-tuh-SAW-rus)
size: Large
Time: Late Jurassic
Place: Colorado
Citation:A fourth new sauropod dinosaur from the Upper Jurassic of the Colorado Plateau and sauropod bipedalism. Jensen, J. GREAT BASIN NATURALIST 48(2) ; 121-145 (1988).

“According to “Dinosaur Jim” Jensen, who named Cathetosaurus,  the unique pelvis of this sauropod made it possible for it to rear up on its hind feet to reach for plants or to defend its young. The large, four-legged plant eater’s pelvis was inclined like those of bipedal  or two-legged dinosaurs. Scientists who disagree with Jenson say the  teeth and tooth marks show a number of scavengers of every size fed  on the lifeless body of this Cathetosaurus specimen before it was fossilized.”


Jurassic Late, Kimmeridgian Tithonian

Saurischia Sauropodomorpha Sauropoda Camarasauridae Camarasaurinae


Morrison Formation, Colorado, US



Camarasaurus = Caulodon (diversidens / leptoganus) (Cope,1877) Morosaurus (Marsh,1878) Uintasaurus (Holland,1919) Camarasaurus > Camarasaurus supremus (Cope,1877) >> C.leptodirus (Cope,1879) Amphicoelias latus (Cope,1877) Caulodon diversidens (Cope,1877) Caulodon leptoganus (Cope,1878) Camarasaurus > C. grandis (Marsh,1877) = Apatosaurus grandis (Marsh,1877) >> Morosaurus impar (Marsh,1878) Morosaurus robustus (Marsh,1878) Pleurocoelus montanus (Marsh,1896) Camarasaurus > C.lentus (Marsh,1889) = Morosaurus lentus (Marsh,1889) >> Camarsaurus annae (Ellinger,1950) Uintasaurus douglassi (Holland,1919) Camarasaurus > C. alenquerensis (Lapparent & Zbyszewski,1957) = Apatosaurus alenquerensis (Lapparent & Zbyszewski,1957) Camarasaurus lewisi (Jensen,1988) = Cathetosaurus lewisi (Jensen,1988)

Nearly complete postcranial skeleton.


             The above paragraph was taken from another source and I do not think that the writer got it right. It was not the “unique pelvis” alone that enabled the sauropod to rear up on its hind legs. It was the combination of the pelvis, and perhaps more importantly, the structure of the neural arch that showed that the creature stood up.
           The neural arch was remarkable for several reasons. First, the neural arch was unusuall robust for a sauropod, which normally didn’t exert great force on these structures. They sort of held the engine room in place and together. And second, the transverse process were canted upward at a fairly steep angle for a sauropod.
           Now what would be the reason for having robust transverse processes running from the pelvis to the shoulder? The space between each process and the spine was large meaning that it was normally filled. With what was it filled?  With Muscles, big heavy muscles. And what happened when big heavy muscies that stretched from stem to stern are actuated? They contract, thank you, and when they contract, they shorten. What happens to the front end of the animal when these huge muscle cables contracted?  The front end actually raised UP off from the ground. A sauropod that could stand on its hind legs.
           I saw the vertegrae and they are impressive and there is no other explanation for those structures than to life the fore limbs off the ground. Unfortunately, I have no photos of the vertebrae but I can show a model that dad created: Without seeing the vertebrae it is ludicrous to believe that a sauropod could rear up this way but after seeing them, it is self-evident.
           Now one asks why would a sauropod develop this way?  One answer would be that the upright posture gave it greater range for feeding.  Another answer it that it allowed the creature to defend itself.


Above is one more of dad’s images of dad and a double model he built using the same Cathetosaurus model and a large theropod like  T. Rex. The skull is too small so perhaps is is something between T Rex and Antrodemus.