| Cedarosaurus Temporal range: Early Cretaceous, 126 Ma |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | Dinosauria |
| Order: | Saurischia |
| Suborder: | †Sauropodomorpha |
| Infraorder: | †Sauropoda |
| Branch: | †Laurasiformes |
| Genus: | †Cedarosaurus Tidwell et al., 1999 |
| Species: | †C. weiskopfae |
| Binomial name | |
| Cedarosaurus weiskopfae Tidwell et al., 1999 |
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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.
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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 Cedarosaurus relativeVenenosaurus 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]
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]