Phyllodon is
based on MGSP G5, a partial
lower jaw tooth recovered from a
lignite marl in a mine near the city of
Leiria. Richard Thulborn, who described the genus, added an
upper beak tooth (MGSP G2). He regarded the new genus as a
hypsilophodontid, and presented a conjectural restoration of the tooth arrangement.
Peter Galton, reviewing Late Jurassic North American hypsilophodontids a few years later, found that the
Phyllodon teeth best matched those of
Nanosaurus, and agreed with a hypsilophodontid identity because the lower jaw tooth is asymmetric in front and back views. Sometime before 2004, possible
Phyllodon remains were recovered from the
Chipping Norton Limestone of
England. Because of the sparse material,
Phyllodon has often been tossed off as a
dubious basal ornithopod of uncertain affinities. However, more material that might belong to this genus has been recovered from the original locality and described. Included in this material are over 120 more teeth from all parts of the jaw and four partial lower jaws with the teeth lost. Oliver Rauhut, who described the new material, tentatively identified the lower jaws as
Phyllodon due to there being no other similar dinosaurs found at the locality. The teeth were very small (up to 3 millimeters across, or 0.1 inches) and possibly
juvenile. He also found additional
diagnostic characteristics for
Phyllodon in the new material, including very tall
upper jaw teeth, indicating that it could be a valid genus after all. After comparing it to other hypsilophodonts, he found that it best matched the roughly contemporaneous
Drinker of the North American
Morrison Formation, with various details suggesting that they were closely related. Similarly, Galton found its teeth to be similar to those of
Drinker and
Nanosaurus in his 2006 review. ==Paleobiology==