Special guest presentation 20.9.2016

Hi All,

next week we will have a visitor from University of Cambridge; Rachel O´Meara will give us a talk titled “Understanding enamel formation and growth in non-mammalian cynodonts”. I hope I can see many of you in this interesting club meeting!


Abstract: “The evolution of mammals from non-mammals is associated with the linked evolutionary origin of several important characters, including diphyodont tooth replacement, mammal-like rapid juvenile growth and determinate adult growth. These characters likely evolved in the extinct cynodont and basal mammaliamorph lineages of the Triassic and early Jurassic, with Morganucodon the most basal known mammaliamorph to have had both mammal-like growth and diphyodonty. Histological techniques to assess periodic enamel increments have not previously been applied to non-mammalian cynodonts and mammaliamorphs, and are likely to improve understanding of their dental replacement and growth patterns. We prepared histological thin sections of postcanines of eight species of non-mammalian cynodont, and teeth from crown mammals and diapsids. Polarised light microscopy revealed two orders of incremental lines, resembling the daily laminations and longer period striae of Retzius of crown mammalian enamel, in all non-mammalian cynodont specimens. We used MANOVA to compare two measures of enamel growth, daily secretion rate (DSR) and crown extension rate (CER), in extant groups and in two non-mammalian cynodont groups, non-probainognathians and mammaliamorphs. DSR in all cynodont species was similar to that of non-hypsodont mammals. However, CER was extremely high in non-probainognathians, with enamel extending rapidly in sheath-like layers, in comparison with the gradual accretion of enamel in the more crownward mammaliamorphs. This is consistent with the reduction in rates of dental replacement in mammaliamorphs, which would permit slower crown extension, while greater rates of replacement in more basal non-probainognathians may have required more rapid rates of formation. In addition, it is possible that the low rate of ameloblast differentiation, which causes low CER in mammaliamorphs, may be coupled with reduced function of osteoblasts. This would suggest reduced rates of bone growth during late molar formation in these animals, which would be consistent with a more mammal-like, abrupt termination of growth in mammaliamorphs in comparison with more basal cynodonts, which likely had a more extended period of adult growth.”


See you on Tuesday 20.9.2016 at 16.00 in C108, Physicum!