An Unusual Spinosaurid Tooth Morphotype from the Early Cretaceous of Eastern Thailand

At the Lower Cretaceous Phra Prong locality in eastern Thailand, isolated spinosaurid teeth show two distinct morphotypes: one with well-marked apicobasal enamel ribs and one without ribs, with the enamel showing only a subtle wrinkling. The latter morphotype is unusual, since most spinosaurid teeth from Asia show a well-marked ribbing. The occurrence of two tooth morphotypes at Phra Prong is interpreted as corresponding to the presence of two distinct spinosaurid taxa. These two morphotypes probably indicate different feeding habits and niche partitioning. However, the functional significance of enamel ribbing (or its absence) remains poorly understood.