Overview of Sauropod Phylogeny and Evolution

This year marks the one hundred sixty-fourth anniversary of Richard Owen’s (1841) description of the first sauropod—Cetiosaurus, the “whale lizard”—on the basis of vertebrae and limb elements from localities across England. Although these remains “had been examined by Cuvier and pronounced to be cetaceous” (Buckland 1841:96), Owen (1841:458–459) demonstrated the saurian affinities of Cetiosaurus on the basis of several features, including the absence of epiphyses (growth plates) on caudal vertebrae (fig. 1.1). He differentiated Cetiosaurus from other extinct saurians on the basis of its large size and characteristics of its vertebrae (see Upchurch and Martin 2003:215). Owen (1841:462) concluded his initial description with this assessment: “The vertebræ, as well as the bones of the extremities, prove its marine habits . . . the surpassing bulk and strength of the Cetiosaurus were probably assigned to it with carnivorous habits, that it might keep in check the Crocodilians and Plesiosauri.” He regarded Cetiosaurus as a crocodilian by the “form of the long bones” and “the toes being terminated by strong claws” (Owen 1842:102), but this assessment was based on limited anatomical evidence (Owen 1875:27). Key data emerged with the discovery of abundant Cetiosaurus bones in Oxfordshire by John Phillips. Thomas Huxley examined this “splendid series of remains” before the publication of Phillips’ (1871) monograph and was the first to place Cetiosaurus within Dinosauria (Iguanodontidae [Huxley, 1869:35]). Phillips (1871) interpreted Cetiosaurus as a planteating dinosaur and hypothesized that its limb bones were “suited for walking.” He could not rule out the possibility that it was amphibious, however, concluding that it was a “marsh-loving or riverside animal.” Owen (1875:27) later acquiesced, referring Cetiosaurus to the Dinosauria because of its four sacral vertebrae. He admitted that it may have had some terrestrial capabilities but concluded that Cetiosaurus was an estuarine or marine animal based on its “organ of swimming,” the tail (Owen 1875:41). These early interpretations, based on somewhat limited samples, were followed by the discovery of abundant sauropod skeletons in western North America and eastern Africa during