III: Mesozoic Mammals

Inner-ear structure in Morganucodon, an early Jurassic mammal

“…Birds and reptiles have relatively shorter membranes which do not fit the plotted mammalian relationship. Morganucodon, with an estimated body weight of 20 g (Crompton &Jenkins, 1978) and a maximum basilar membrane length, from our material, of 3.1 mm, falls well below the 95% confidence limits of the mammalian regression line. Based on these data, the basilar membrane length of Morganucodon resembles that of extant reptiles more closely than that of mammals, suggesting a resemblance to its reptilian ancestors.…”

“…Previous studies of early mammalian petrosals have been limited to descriptions of the external surface (Simpson, 1928;Kermack, 1963Kermack, , 1967Crompton & Jenkins, 1978, 1979Kermack, Mussett & Rigney, 1981;Crompton & Sun, 1985). The external surface of the petrosal of Morganucodon was described by Kermack et al ( 198 1).…”

Are geckos olfactory specialists?

“…Using arguments parallel to those above, Marcellini (1 977) suggested that nocturnality was responsible for the evolution of acoustic behaviour in gekkonids. Nocturnality has also been invoked as the selective regime promoting the evolution of increased olfactory and auditory senses in early mammals relative to their therapsid ancestors (Jerison, 1973;Crompton &Jenkins, 1978. These ideas could be tested in squamates, to some extent, by comparative studies of chemosensory development in other nocturnal or fossorial lineages.…”

The origin and evolution of mammals

“…Most are still represented only by isolated teeth from various localities in Europe (Clemens 1986;Kielan-Jaworowska et al 2004), but two virtually complete skeletons have been found in the Red Beds of the Stormberg Series of South Africa (Crompton 1974;Crompton and Jenkins 1978), which are dated as Late Triassic, possibly Norian but otherwise Rhaetian. In Megazostrodon (Fig.…”

“…On the one hand were the therian mammals, which include the modern marsupials and placentals along with their more primitive Mesozoic relatives; on the other hand were the nontherian mammals, which included the living monotremes amongst many fossil groups (e.g. Hopson and Crompton 1969;Crompton and Jenkins 1978). Kemp (1983Kemp ( , 1988a first questioned this simple phylogenetic division at the base of mammal evolution on the grounds of the inadequacy of the characters used to support it, and before long it had been largely abandoned.…”