Geological and environmental contextEdit
The Venenosaurus type specimen was found in the Early Cretaceous (Aptian-Albian) Poison Strip Member of the Cedar Mountain Formation in Grand County, Utah. The Denver Museum of Natural History opened a small Cedar Mountain Formation quarry in Eastern Utah. This quarry has produced diverse dinosaur fossils including sauropods, theropods, and ornithopods of varying states of growth. Of the sauropod remains from the quarry only one individual was fully grown. Carbonate growths appear on bones in the quarry from which Venenosaurus was extracted.
The scientists who first described V. dicrocei observed that the new species most closely resembles Cedarosaurus, while still being distinct.
The radius of Venenosaurus is more slender than the radii of Alamosaurus, Chubutisaurus, Opisthocoelicaudia, and Saltasaurus. The ratio of the radius' least circumference to length produces a ratio of .33, more gracile than the radius of Camarasaurus lewisi and C. grandis. Cedarosaurus, however, has a slightly more gracile ration of .31. The team finds that Brachiosaurus brancai's radius is the closest anatomical match to that of Venenosaurus. The metacarpals of Venenosaurus are long and slender. With the exception of the incomplete first metacarpal, all of the right metacarpals are known. Metatarsal I is the shortest and most robust of the three recovered metatarsals. Cedarosaurus had a more gracile ulna and radius than Venenosaurus.
Venenosaurus shows a mixture of titanosaur and non-titanosaur ischium-to-pubis proportions. Its hips most closely resemble those of Brachiosaurus.
The vertebrae in the middle and toward the end of the tail were short, distinguishing it from titanosaurs like Andesaurus, Malawisaurus, Aeolosaurus, Alamosaurus, and Saltasaurus. The neural spines in the middle tail vertebrae are angled toward the front of the animal. These vertebrae resemble those of Cedarosaurus, Aeolosaurus, and Gondwanatitan. The vertebrae are located at a transitional position from anterior to posterior caudal vertebrae.
Venenosaurus had unusual lateral fossae, which looked like deep depressions in the outside walls of the vertebral centra. Some fossae are divided into two chambers by a ridge inside the depression. In most sauropods the fossae would form pneumatic openings leading to the interior of the centrum, rather than just being a depression. Less well-developed, but similar fossae are known from Cedarosaurus. Fossae that similarly resemble shallow depressions are known from Saltasaurus, Alamosaurus, Aeolosaurus, Gondwanatitan, and Malawisaurus. These taxa differ, however, in that their fossae are even shallower, lack the division into chambers, and do not extend as far into the vertebral columns as those of Venenosaurus.
The vertebrae near the base of the tail are extremely useful for classifying sauropods. Derived titanosaurs had vertebrae that were convex on the front and back. Primitive sauropods had vertebrae that were either flat on both ends (amphiplaty) or concave on both (amphicoely). Venenosaurus may have had a condition intermediate between the two. The possession of amphiplatyan caudal centra with anteriorly facing neural spines is a unique identifier of this species. Sometimes the form of central articulations change within a single individual's vertebral column.