Venenosaurus

Venenosaurus Temporal range: Early Cretaceous, 112Ma PreЄ Є O S D C P T J K Pg N ↓
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Suborder:	†Sauropodomorpha
Clade:	†Titanosauriformes
Family:	†Brachiosauridae
Genus:	†Venenosaurus Tidwell et al., 2001
Species:	† V. dicrocei
Binomial name
Venenosaurus dicrocei Tidwell et al., 2001

Venenosaurus (/vɛˌnɛnɵˈsɔrəs/ ve-NEN-o-SAWR-əs; Latin venenum meaning "poison" and Greek sauros meaning "lizard") was a sauropod dinosaur, named after the Poison Strip Member of the Cedar Mountain Formation in Utah, United States, where the fossils were discovered by a Denver Museum of Natural History volunteer Tony DiCroce in 1998. Venenosaurus dicrocei was first described as a new species in 2001 by Virginia Tidwell, Kenneth Carpenter, and Suzanne Meyer.^[1] Venenosaurus is a relatively small (probably around 10 m (33 ft) long) titanosauriform sauropod, known from an incomplete skeleton of an adult and a juvenile. The holotype is DMNH 40932 Denver Museum of Natural History. The specimen consisted of tail vertebrae, the left scapula, right radius, left ulna, metacarpals, forefoot phalanges, right pubis, left and right ischia, metatarsals, chevrons, and ribs.

Geological and environmental context

The Venenosaurus type specimen was found in the Early Cretaceous (Aptian-Albian) Poison Strip Member of the Cedar Mountain Formation in Grand County, Utah.^[2] The Denver Museum of Natural History opened a small Cedar Mountain Formation quarry in Eastern Utah.^[3] This quarry has produced diverse dinosaur fossils including sauropods, theropods, and ornithopods of varying states of growth.^[3] Of the sauropod remains from the quarry only one individual was fully grown.^[3] Carbonate growths appear on bones in the quarry from which Venenosaurus was extracted.^[2]

Anatomy

The scientists who first described V. dicrocei observed that the new species most closely resembles Cedarosaurus, while still being distinct.^[1]

Body

The describers of V. dicrocei's noted that many dorsal rib fragments belonging to the species had been discovered.^[4]

Limbs

The radius is deceptively slender despite appearing robust.^[5] The proximal end is only 22% of the width rendering it more slender than the radii of Alamosaurus, Chubutisaurus, Opisthocoelicaudia, and Saltasaurus.^[5] 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.^[5] The team finds that Brachiosaurus brancai's radius is the closest anatomical match to that of Venenosaurus.^[5] The metacarpals of Venenosaurus are long and slender.^[5] With the exception of the incomplete first metacarpal, all of the right metacarpals are known.^[5] Metatarsal I is the shortest and most robust of the three recovered metatarsals.^[6] Cedarosaurus had a more gracile ulna and radius than Venenosaurus.^[7] Metatarsal II is more gracile in Cedarosaurus.^[7]

Pelvis

Venenosaurus shows a mixture of titanosaur and non-titanosaur ischium-to-pubis proportions.^[8] Its hips most closely resemble those of Brachiosaurus.^[8]

Vertebrae

The researchers who named Venenosaurus observed that the growing known diversity "of sauropod caudal centrum articulations" challenges "traditional descriptive terminology" for such features.^[9] Tidwell et al. opined that "more precise identification of anterior and posterior articular face morphology" need to be devised.^[1] The researchers described a vertebra from near the base of the tail that was well preserved.^[10] Only its prezygapophyses were missing.^[10] Tidwell et al. claimed its physical characteristics were unique among sauropods.^[10]

The seven middle and distal tail vertebral centra were short, distinguishing it from titanosaurs like Andesaurus, Malawisaurus, Aeolosaurus, Alamosaurus, and Saltasaurus.^[11] Two of the recovered middle tail vertebrae preserve partial neural spines.^[12] These spines are angled anteriorly when the vertebrae are aligned.^[12] These vertebrae resemble those of Cedarosaurus, Aeolosaurus, and Gondwanatitan.^[12] The vertebrae are located at a transitional position from anterior to posterior caudal vertebrae.^[12] The authors estimated them to be the eleventh and twelfth vertebrae.^[12]

The authors documented a single posterior tail vertebra that was well preserved.^[13] Its neural spine was reduced in size and resembled a rod facing the rear of the animal that ended with the rear of the centrum.^[14] Venenosaurus had unusual lateral fossae, which looked like deep depressions in the outside walls of the vertebral centra.^[14] Some fossae are divided into two chambers by a ridge inside the depression.^[14] In most sauropods the fossae would form pneumatic openings leading to the interior of the centrum, rather than just being a depression.^[14] Less well-developed, but similar fossae are known from Cedarosaurus.^[14] Fossae that similarly resemble shallow depressions are known from Saltasaurus, Alamosaurus, Aeolosaurus, Gondwanatitan, and Malawisaurus.^[14] 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.^[14]

The proximal caudal vertebrae is extremely diagnostic for sauropods.^[7] Derived titanosaurs had biconvex vertebrae.^[7] The primitive condition is either amphiplaty or amphicoely.^[15] Venenosaurus may have had a condition intermediate between the two.^[15] The possession of amphiplatyan caudal centra with anteriorly facing neural spines is a unique identifier of this species.^[16] Sometimes the form of central articulations change within a single individual's vertebral column.^[17]

Footnotes

References

• Tidwell, V., Carpenter, K. & Meyer, S. 2001. New Titanosauriform (Sauropoda) from the Poison Strip Member of the Cedar Mountain Formation (Lower Cretaceous), Utah. In: Mesozoic Vertebrate Life. D. H. Tanke & K. Carpenter (eds.). Indiana University Press, Eds. D.H. Tanke & K. Carpenter. Indiana University Press. 139-165.