Placodonts were durophagous reptiles of the Triassic seas with robust skulls, jaws,
and enlarged, flat, pebble-like teeth. During their evolution, they underwent gradual
craniodental changes from the Early Anisian to the Rhaetian, such as a reduction in
the number of teeth, an increase in the size of the posterior palatal teeth, an elongation
of the premaxilla/rostrum, and a widening of the temporal region. These changes are
presumably related to changes in dietary habits, which, we hypothesise, are due to
changes in the type and quality of food they consumed. In the present study, the dental
wear pattern of a total of nine European Middle to Late Triassic placodont species
were investigated using 2D and 3D microwear analyses to demonstrate whether there
could have been a dietary shift or grouping among the different species and, whether
the possible changes could be correlated with environmental changes affecting their
habitats. The 3D analysis shows overlap between species with high variance between
values and there is no distinct separation. The 2D analysis has distinguished two
main groups. The first is characterised by low number of wear features and high percentage
of large pits. The other group have a high feature number, but low percentage of small
pits. The 2D analysis showed a correlation between the wear data and the size of the
enlarged posterior crushing teeth. Teeth with larger sizes showed less wear feature
(with higher pit ratio) but larger individual features. In contrast, the dental wear
facet of smaller crushing teeth shows more but smaller wear features (with higher
scratch number). This observation may be related to the size of the food consumed,
i.e., the wider the crown, the larger food it could crush, producing larger features.
Comparison with marine mammals suggests that the dietary preference of Placochelys
, Psephoderma and Paraplacodus was not exclusively hard, thick-shelled food. They
may have had a more mixed diet, similar to that of modern sea otters. The diet of
Henodus may have included plant food, similar to the modern herbivore marine mammals
and lizards.
