Cedarosaurus

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.

Gastroliths
In 2001 Frank Sanders, Kim Manley, and Kenneth Carpenter published a study on 115 gastroliths discovered in association with a Cedarosaurus specimen.[5] The stones 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] Nearly all of the Cedarosaurus gastroliths were found within a .06 m volume of space in the gut region of the skeleton.[6]

The total mass of the gastroliths themselves was 7 kilograms (15 lb).[7] Most were less than 10 millilitres (0.35 imp fl oz; 0.34 US fl oz) in volume.[8] The least massive clast was .1 grams (0.0035 oz) and the most was 715 grams (25.2 oz), with most of them being toward the smaller end of that range.[8] The clasts tended to be close to spherical in shape, although the largest specimens were also the most irregular.[8] The largest gastroliths contributed the most to the total surface area of the set.[9] Some gastroliths were so large and irregularly shaped that they may have been difficult to swallow.[9] The gastroliths were mostly composed of chert, with some sandstone, siltstone, and quartzite clasts also included.[10] Some of the chert clasts actually contained fossils.[10]

Since some of the most irregular gastroliths are also the largest, it is unlikely that they were ingested by accident.[9] Cedarosaurus may have found irregular clasts to be attractive potential gastroliths or was not selective about shape.[9] The clasts were generally of dull coloration, suggesting that color was not a major factor for the sauropod's decision making.[5] The high surface area to volume ratio of the largest clasts suggests that the gastroliths may have broken down ingested plant material by grinding or crushing it[11] The sandstone clasts tended to be fragile and some broke in the process of collection.[10] The sandstone gastroliths may have been rendered fragile after deposition by loss of cement caused by the external chemical environment.[12] If the clasts had been that fragile while the animal was alive, they probably rolled and tumbled in the digestive tract.[11] If they were more robust, they could have served as part of a ball-mill system.