IVth International Conference on Dormice (Rodentia, Gliridae)13 - 16 September 1999 EDİRNE - TURKEY |
THE USE OF GEOMETRIC MORPHOMETRIC APPROACH TO THE ANALYSIS OF DENTAL VARIATION IN GLIRIDAE
Pavlinov, I.Ja.
Zoological Museum, Moscow M.V.Lomonosov State University, ul. Bolshaya Nikitskaya 6, 103009 Moscow, Russia, e-mail: pvl@2.zoomus.bio.msu.zu
Dental crown pattern is of ultimate importance in phylogeny and stratigraphy of Gliridae. It consists of transverse ridges which undergo the following transformations: they tend to become shorter/longer, to fuse/split at their ends, and to appear/disappear. These variations are usually represented by sets of discrete morphotypes, and the taxa are compared by morphotype frequencies.
Geometric morphometrics is a new numerical technique that enables to describe and to analyze similarities among morphological shapes by means of the so called "shape variables". It is most appropriately applied to 2-dimensional flat objects with continuous transformations. This presentation is the first attempt to show the possible uses of geometric morphometrics in the case of glirid dentition under an assumption that the differences among glirid crown patterns can be considered as shape transformations.
The study case is a sample of M2 crowns of seven glirid genera, both recent and fossil. Crown pattern was described by 29 landmarks placed at the ends and middle regions of the ridges. The landmark coordinates were taken using the program TPSdig. Consensus configurations for respective taxa were calculated using the program TPSsplin. Afterward, pairwise Procrustes distances were calculated between those configurations using the latter program. Cluster analysis and multidimensional scaling were used for graphic representation of the similarity relations among dentitions.
The results obtained indicate the following. By morphology of M2 crown, the genus Myomimus is most similar to Peridyromys; the genus Dryomys is similar to Microdyromys and, to a somewhat less extent, to Glirudinus. The genera Muscardinus and Glis are most dissimilar both from each other and from the remainder of the glirids studied. The pair Myomimus–Peridyromys is specific basically by the configuration of the anterior centroloph, while the pair Dryomys–Microdyromys differs from the other taxa mainly by the proportions of the posterolingual part of the tooth.
These results, though preliminary, are quite promising. First of all, they indicate that similarities among glirid dentitions can be evaluated numerically and directly without prior extraction of "pseudo-discrete" morphotypes. The geometric morphometrics seems to be most useful in comparing close species or populations of the same species, in comparing variation of different teeth in the same and/or different toothrows – in particular, in analysis of fluctuating asymmetry of crown pattern, etc. Thus, this approach to analysis of variation of glirid dentition deserves close attention.
On the other hand, there are several yet unresolved points, both formal and non-formal, that impose certain restraints on using geometric morphometrics in this particular case. So, further developments of the geometric morphometrics toward possibility of more adequate description of discrete transformations displayed by dental crown in Gliridae are needed.