2 results
Multivariate stasis in the dental morphology of the Paleocene-Eocene condylarth Ectocion
- Aaron R. Wood, Miriam L. Zelditch, Adam N. Rountrey, Thomas P. Eiting, H. David Sheets, Philip D. Gingerich
-
- Journal:
- Paleobiology / Volume 33 / Issue 2 / Spring 2007
- Published online by Cambridge University Press:
- 14 July 2015, pp. 248-260
-
- Article
- Export citation
-
Evolutionary stasis has often been explained by stabilizing selection, intrinsic constraints, or, more recently, by spatially patterned population dynamics. To distinguish which of these mechanisms explains a given case of stasis in the fossil record, stasis must first be rigorously documented in a high-resolution stratigraphic time series of fossil specimens. Furthermore, past studies of evolutionary mode in fossil mammalian lineages have often been limited to univariate traits (e.g., molar crown area). It is reasonable to assume that tooth shape, a multivariate trait, reflects important additional aspects of tooth form and function. Here we present the results of a geometric morphometric analysis of the lower dentition of the Paleocene-Eocene condylarth species Ectocion osbornianus collected from the Bighorn and Clarks Fork Basins of northwestern Wyoming. Tooth margin shape, cusp configuration, and shearing crest shape were digitized for the last lower premolar, p4, and for two lower molars, m1 and m3. Multivariate statistical tests of evolutionary mode were used to analyze the change in shape variance over time in addition to the magnitude and direction of shape change. Test results characterize the shape time series as consisting of counteracting changes with less change than expected under a random walk (i.e., stasis). The temporal structure of shape variance implies that the sampled E. osbornianus most likely represent a single population, which is not concordant with the population dynamic mechanism of stasis. Stabilizing selection and/or intrinsic constraints remain as the mechanisms that could explain stasis in the lower dental shape of E. osbornianus despite the variable environmental conditions of the Paleocene–Eocene.
7 - African Vespertilionoidea (Chiroptera) and the antiquity of Myotinae
- Edited by Gregg F. Gunnell, Duke University, North Carolina, Nancy B. Simmons, American Museum of Natural History, New York
-
- Book:
- Evolutionary History of Bats
- Published online:
- 05 June 2012
- Print publication:
- 29 March 2012, pp 252-266
-
- Chapter
- Export citation
-
Summary
Introduction
Vesper and evening bats (Family Verspertilionidae) are a diverse group (about 350 living species) that has a nearly global distribution (being absent only in polar regions, on some oceanic islands and in harsher desert climates). Vespertilionids often have been included with molossids, mystacinids, myzopodids, thyropterids, furipterids and natalids in the superfamily Vespertilionoidea (Koopman, 1994), but many other variations of the superfamily exist (e.g., Simmons, 1998; Jones et al., 2002; Hoofer and Van Den Bussche, 2003; Hoofer et al., 2003; Horáček et al., 2006; Miller-Butterworth et al., 2007). Our prime focus in this chapter is on two subfamilies of the Vespertilionidae, Vespertilioninae and Myotinae, as defined by Simmons (2005).
Osteologically, the basic dichotomy between myotines and vespertilionines can be typified by differing patterns of dental morphology. All myotines share myotodont lower molar morphology, in which the postcristid extends to the entoconid and isolates the hypoconulid (as opposed to nyctalodonty where the postcristid extends to the hypoconulid and does not reach the entoconid). Myotines also share the presence of three premolars, with the middle premolar being reduced. Some vespertilionines have myotodont lower molars, but only a few exhibit both myotodonty and the retention of three premolars (e.g., Plecotus and Idionycteris). No vespertilionines have the middle premolar reduced. Recent phylogenetic analyses suggest that all vespertilionines are far removed from myotines (e.g., Hoofer and Van Den Bussche, 2003), implying that any shared morphological similarities are likely to be convergences.