Cedarosaurus

Cedarosaurus Temporal range: Early Cretaceous, 126Ma 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:	†Cedarosaurus Tidwell et al., 1999
Species:	† C. weiskopfae
Binomial name
Cedarosaurus weiskopfae Tidwell et al., 1999

Cedarosaurus (meaning "Cedar lizard" - named after the Cedar Mountain Formation, in which it was discovered) was a nasal-crested macronarian dinosaur genus from the Early Cretaceous Period (Barremian). It was a sauropod which lived in what is now Utah. It was first described by Tidwell, Carpenter and Brooks in 1999.^[1]

It shows similarities to the brachiosaurid Eucamerotus from the Wessex Formation of southern England, as well as to Brachiosaurus from the Morrison Formation.

Anatomy

Cedarosaurus had a more gracile ulna and radius than its relative Venenosaurus.^[2] The ratio of the radius' least circumference to its length is .31 in Cedarosaurus. Metatarsal II is more gracile in Cedarosaurus.^[2]

Its middle tail vertebrae's neural spines angled anteriorly when the vertebrae are aligned.^[3] These vertebrae resemble those of Gondwanatitan, Venenosaurus, and Aeolosaurus.^[3]

The related Venenosaurus had unusual lateral fossae, which looked like deep depressions in the outside walls of the vertebral centra.^[4] Some fossae are divided into two chambers by a ridge inside the depression.^[4] In most sauropods the fossae would form pneumatic openings leading to the interior of the centrum, rather than just being a depression.^[4] Less well-developed, but similar fossae are known from Cedarosaurus itself.^[4]

Gastroliths

In 2001 Frank Sanders, Kim Manley, and Kenneth Carpenter published a study on 115 clasts discovered in association with a Cedarosaurus specimen.^[5] These clasts were the first discovery of in situ gastroliths from the Cedar Mountain Formation.^[5] The clasts were "partially matrix supported" and there were many contacts between clasts and bones and between the clasts themselves.^[5] The clasts were identified as gastroliths on the basis of their tight spatial distribution, partial matrix support and an edge-on orientation indicative of their being deposited while the carcass still had soft tissue.^[5] Their high surface reflectance values are consistent with other known dinosaur gastroliths.^[5] The clasts were generally of dull coloration, suggesting that color was not a major factor for the sauropod's decision making.^[5] All but three of the Cedarosaurus gastroliths were found within a .06 m volume of space.^[6] This space was located within the gut area.^[6] No other clasts were found within the quarry, which at the time had a volume of about 11 m cubed.^[6] The set of gastroliths is believed complete due to their being discovered in a single pocket deep in the quarry.^[6] The skeletal position suggests that the skeleton came to rest on its belly.^[7]

The total mass of the gastroliths was 7 kilograms, total volume 2703 ccs and the total surface area 4410 cm2.^[8] A majority, 67 of the 115 gastroliths, were less than 10 cc in volume.^[9] Individual clasts ranges from .04 cc to 270 cc in volume.^[9] The least massive clast was .1 gram and the most was 715 grams.^[9] Most of the gastroliths tended to be small.^[9] The clasts tended to be close to spherical in shape, with the largest specimens being the most irregular.^[9] 43% were oblate spheroids, 34% spheroids, 16% prolate spheroids, and 7% ellipsoidal.^[10] The largest gastroliths contributed the most to the total surface area of the set.^[11] Since some of the most irregular gastroliths are also the largest, it is unlikely that they were ingested by accident.^[11] Cedarosaurus may have found irregular clasts to be attractive potential gastroliths or was not selective about shape.^[11] Some gastroliths were so large an irregularly shaped that they may have been difficult to swallow.^[11] The gastroliths includes chert, sandstone, siltstone, and quartzite clasts.^[12] Some of the chert clasts actually contained fossils.^[12] The sandstone clasts tended to be fragile and some broke in the process of collection.^[12] 62% were chert, 31 percent were sandstone and siltstone, 7% were quartzite.^[12]

None of the gastroliths had the "soapy" texture popularly used to distinguish gastroliths from other types of clast.^[12] The researchers dismissed using a soapy texture to identify gastroliths as "unreliable."^[12] Gastroliths tended to be universally dull, although the colors represented were varied including black, dark brown, purplish red and grey-blue.^[12] Reflectance values greater than 50% are very diagnostic for identifying gastroliths.^[12] Clasts from beaches and streams tended to have reflectance values of less than 35%.^[13] Less than ten percent of beach clasts have reflectance values lying between 50 and 80%.^[14] The most reflective gastroliths were composed of chert.^[14] Some of the gastroliths couldn't be tested for reflectance due to a confounding metallic coating, which may have been hematite.^[14] Expansion and contraction of the supporting mudstone around the inflexible clasts actually left series of parallel scratches in the coating.^[14] The metallic coating "probably originated from the iron rich mudstone" surround the fossils.^[14] The sandstone gastroliths may have been rendered fragile after deposition by loss of cement caused by the external chemical environment.^[15] If the clasts had been that fragile while the animal was alive, they probably rolled and tumbled in the digestive tract.^[14] If they were more robust, they could have served as part of a ball-mill system.^[14] The high surface area to volume ratio of the largest clasts "also supports a grinding or crushing model."^[14]

Footnotes

References

• Sanders, F.; Manley, K.; & Carpenter, K. 2001. Gastroliths from the Lower Cretaceous sauropod *Cedarosaurus weiskopfae*. pp. 166–180. In: Tanke, Darren; Carpenter, Ken (eds.) (2001). Mesozoic Vertebrate Life: New Research Inspired by the Paleontology of Philip J. Currie. Indiana University Press. ISBN 0-253-33907-3.  Cite uses deprecated parameters (help)
• Tidwell, V., Carpenter, K. and Brooks, W. (1999). "New sauropod from the Lower Cretaceous of Utah, USA". Oryctos 2: 21-37
• 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.

External links

• The Brachiosauridae
• Photograph of the Cedarosaurus skeleton and list of bones
• Cedarosaurus at The Paleobiology Database
• Cedarosaurus skeleton (see p. 9).