Cardiodon

Cardiodon (meaning "heart tooth", in reference to the shape) was a herbivorous genus of sauropod dinosaur, based on a tooth from the late Bathonian-age Middle Jurassic Forest Marble Formation of Wiltshire, England. Historically, it is very obscure and usually referred to "Cetiosaurus", but recent analyses suggest that it is a distinct genus, and possibly related to "Turiasaurus". "Cardiodon" was the first sauropod genus named.
History and taxonomy.
Richard Owen named the genus for a now-lost tooth, part of the collection of naturalist Joseph Chaning Pearce, found near Bradford-on-Avon, but did not assign it a specific name at the time. The generic name is derived from Greek καρδία, "kardia", "heart", and ὀδών, "odon", "tooth", in reference to its heart-shaped profile. A few years later, in 1844, he added the specific name "rugulosus", meaning "wrinkled" in Latin. "Cardiodon" was the first sauropod given a formal name to, though Owen was at the time completely unaware of the sauropod nature of the find.
Within a few decades, he and others were viewing "Cardiodon" as a possible synonym of his most well-known sauropod genus, "Cetiosaurus". Richard Lydekker formalized this view in a roundabout way in 1890, by assigning "Cetiosaurus oxoniensis" to "Cardiodon" on the basis of teeth from Oxfordshire associated with a skeleton of "C. oxoniensis". He also added a second tooth (BMNH R1527) from the Great Oolite near Cirencester, Gloucestershire. More typically, "Cardiodon" has been assigned to "Cetiosaurus", sometimes as a separate species "Cetiosaurus rugulosus", in spite of its priority.
In 2003, Paul Upchurch and John Martin, reviewing "Cetiosaurus", found that there is little evidence to assign the "C. oxoniensis" teeth to the skeleton, and the "C. oxoniensis" teeth differ from the "Cardiodon" teeth ("Cardiodon" teeth are convex facing the tongue); therefore, they supported "Cardiodon" being retained as its own genus. Upchurch "et al." (2004) repeated this assessment, and found that though the teeth have no known autapomorphies, they are those of a eusauropod. More recently, Royo-Torres "et al." (2006), in their description of "Turiasaurus", pointed out "Cardiodon" as a possible relative to their new, giant sauropod, placing it in the Turiasauria. Earlier, "Cardiodon" had been usually assigned to the Cetiosauridae or a Cardiodontidae of its own.
Description.
The original tooth shows, as far as can be deduced from the surviving illustrations, the rare combination of being spatulate and having a convex inner side, though the convexity is slight. Its crown is short and wide, slightly curving to the inside. The outer side is strongly convexly curved from the front to the rear. On this side a shallow groove is present, running parallel to the rear edge. The crown tapers towards its tip. The edges have no denticles. The enamel shows the little wrinkles to which the specific name refers.
Paleobiology.
As a sauropod, "Cardiodon" would have been a large, quadrupedal herbivore, but because of the scanty remains, much more cannot be said.