Meeting Abstract
P1.213 Saturday, Jan. 4 15:30 Hide and seek patterning: using X-ray microcomputed tomography to explore the developmental basis, homology, and apparent re-emergence of primitive dental traits in macropodoids COUZENS, A.M.C*; SKINNER, M.M; EVANS, A.R; PRIDEAUX, G.J; Flinders University; University College London; Monash University; Flinders University aidan.couzens@flinders.edu.au
The re-emergence of primitive traits in derived taxa can offer insights into the developmental and evolutionary properties of phenotypes. In mammals the outer enamel surface (OES) provides information about taxonomy but the developmental basis of the OES is generally poorly understood. In mature teeth, the enamel–dentine junction (EDJ) delineates the position of the basement membrane, where species-specific cusp patterns emerge early in tooth morphogenesis. Analysing the relationship between EDJ and OES shape can thus provide insights into the development and homology of tooth structures. In macropodoid (kangaroo) molars, two transverse shearing blades (lophs) are often associated with longitudinal crests. An example is the posthypocristid, which is directed posterolingually from the hypoconid, marking the buccal end of the posterior lophid. This crest is present in macropodids and balbarids up to the middle Miocene, but is lost for at least 10 myr before apparently re-emerging in derived macropodids. We used X-ray microcomputed tomography to extract OES and EDJ surfaces from fossil and modern teeth. Posthypocristid expression in derived and primitive kangaroos seems to be underlain by an EDJ prominence suggesting posthypocristid establishment early in development and the re-emergence of an ancestral patterning pathway in derived taxa. Aberrant terminal molars in the extinct Pliocene kangaroo Prionotemnus and extant Red Kangaroo (Macropus rufus) seem to capture an extreme variant of posthypocristid patterning. The striking re-emergence of the posthypocristid in these teeth, and more subtle expression at species-level, may have been facilitated by interplay between enamel thickness and taller teeth.
