THE YOLK-SAC OF THE MOLE TALPA EUROPAEA

Evolution of the placenta and associated reproductive characters in bats

Recent advances in molecular phylogenetics indicate that the order Chiroptera is monophyletic and that one of four lineages of microbats (Rhinolophoidea) shares a common origin with megabats. Against this background we undertook a comprehensive analysis of placental evolution in bats. We defined a range of characters and character states associated with female reproduction, early development, placentation and the neonate. These were then mapped on a pre-existing hypothesis of bat relationships that represents the current view from molecular studies. Our purpose was threefold. First, on the assumption of bat monophyly, we wished to establish the stem species pattern of extant chiropterans. Secondly, we asked whether there are derived character conditions in support of a common origin for Rhinolophoidea and the megabats. Thirdly, we looked for evolutionary character transformations that characterize higher-level clades within Chiroptera, i.e. the megabats and the four lineages of microbats. The character condition occurring in the last common ancestor of Chiroptera was unequivocal for 21 of the 25 characters included in the analysis. The data did not offer support for a megabat-rhinolophoid clade or the implication that microbats are paraphyletic. However, analysis of early development, placentation and other reproductive parameters resulted in derived character conditions for the megabats as well as for each of the four major lineages of microbats.

Evolutionary transformations of fetal membrane characters in Eutheria with special reference to Afrotheria

Analysis of molecular data sets has provided new insights into higher-level relationships of living Eutheria, including the recognition of Afrotheria as a novel taxon. This offers an opportunity to take a fresh look at the evolution of organ systems, including some that are little used in traditional systematics. In the present study, we attempted a reconstruction of the evolution of characters associated with placentation, the fetal membranes and the female reproductive tract. The evolutionary history of 21 characters has been traced, based on a current hypothesis of eutherian relationships, by applying the computer program MacClade. Accordingly, the analysis provides a first comprehensive interpretation of the stem species pattern of Eutheria. Of particular note, this pattern includes an endotheliochorial chorioallantoic placenta. The reconstructed pattern of Eutheria does not change in the basal nodes of the group. Thus, no character transformations occur on the stem lineages of Laurasiatheria or Euarchontoglires, and even Afrotheria has mostly plesiomorphic character conditions. However, two character transformations occur on the common stem lineage of Afrotheria and its sister taxon Xenarthra, i.e., amniogenesis by cavitation instead of folding and the precocial state of the newborn. In addition, we recognized one character transformation on the stem lineage of Afrotheria, i.e., the occurrence of a four-lobed allantoic sac. Thus, contrary to previous assertions, it is possible to identify morphological characters that could be synapomorphic for this novel taxon.