Cardiodon

Cardiodon is a genus of herbivorous sauropod dinosaur from the Middle Jurassic period. Its existence is known primarily from a single tooth discovered in Wiltshire, England, which dates to the late Bathonian stage. The genus was named by Richard Owen, and its name, derived from Greek words for "heart" and "tooth," refers to the distinctive heart-shaped profile of its dental remains. Cardiodon holds the distinction of being the first sauropod genus to be formally named.

History and Taxonomy

Richard Owen initially named the genus in 1841 based on a tooth from Joseph Chaning Pearce's collection, found near Bradford-on-Avon. At the time of its naming, Owen was unaware of its sauropod nature. He later added the specific name rugulosus in 1844, meaning "wrinkled" in Latin, a reference to the texture of the enamel on the tooth. For many years, Cardiodon was often considered a synonym for Owen's more well-known sauropod, Cetiosaurus. This view was reinforced when Richard Lydekker assigned teeth from Oxfordshire, associated with a skeleton of Cetiosaurus oxoniensis, to the genus Cardiodon in 1890. However, more recent analyses have challenged this synonymy. In 2003, Paul Upchurch and John Martin reviewed Cetiosaurus and found insufficient evidence to link the C. oxoniensis teeth to its skeleton, noting that the teeth differed from those of Cardiodon. They supported retaining Cardiodon as a distinct genus. Further research by Upchurch et al. in 2004 classified its teeth as belonging to a eusauropod. More recently, in 2006, Royo-Torres et al. suggested that Cardiodon might be related to the giant sauropod Turiasaurus, placing it within the group Turiasauria.

Description and Paleobiology

As only a tooth is known, the description of Cardiodon is limited. Surviving illustrations of the original tooth reveal a unique combination of characteristics: it is spatulate, meaning it has a broad, flattened crown. The inner side of the tooth is convex, though only slightly, while the outer side is strongly convexly curved from front to rear. A shallow groove runs parallel to the rear edge on the outer side. The crown tapers to a point, and the edges are smooth, lacking denticles. The enamel exhibits the fine wrinkles that inspired the specific name rugulosus. As a sauropod, Cardiodon would have been a large, quadrupedal herbivore, but the scanty remains provide little further detail about its paleobiology.