A multivariate study of the family molossidae (mammalia, chiroptera) : morphology, ecology, evolution

Abstract

Bats of the family Molossidae are as distinctive as they are elusive. Free-tailed bats are thought to be the swiftest of all bats and tend to fly well above the canopy and out of human reach. Because of such habits, specimens of some species of molossids are not abundant and taxonomic and ecologic knowledge of the family is not extensive. Molossids are distinctive not only because of their vespertilionoid shoulder, which is at its highest development, narrow wing, and tail, which extends well beyond the posterior border of the uropatagium; but also because of their unique faces, their short, velvety fur, and their tough, leathery skin Vaughan, 1972, pp. 111-113). The first molossid to receive a scientific name was Vespertilio Molossus Pallas, 1766, from the New World, and so named because of its resemblance to a black mastiff from the Greek province of Molossis. This dog-faced appearance is common to several genera within the family. Actually, Vespertilio Molossus included specimens that are now called Tadarida macrotis and Molossus molossus Husson, 1962). Many members of the family have deeply wrinkled lips and large ears that project anteriorly and laterally to look like a wide-brimmed hat; others have widely separated, smaller, and more pointed ears and no wrinkles on the lips. Most of the species have unusual spoon-shaped hairs on the muzzle and toes, as well as a gland on the chest which emits an odor unique to molossids. Molossids are insectivorous and live in tropical and temperate parts of the world. More than half the species are members of the genus Tadarida, which historically includes four subgenera: Chaerephon, Mops, Mormopterus, and Tadarida. The remaining species are spread among 11 other genera. Species of Tadarida sensu lato) are found in both hemispheres, but each region has its own endemic molossid genera: Molossus, Eumops, Promops, Cynomops, Molossops, and Neoplatymops in the New World; and Otomops, Myopterus, Platymops, Sauromys, and Cheiromeles in the Old World. The purpose of my study is to examine as many species of the family Molossidae as possible and to determine, with the aid of numerical methods, whatnatural groups exist within the family. Sneath & Sokal 1973) discuss the methods and reasons for this kind of analysis. Anatural group of organisms as here defined is one in which its members share a close phenetic relationship. Phenetic relationship is defined as "similarity resemblance) based on a set of phenotypic characteristics of the objects or organisms under study," Sneath & Sokal, 1973, p. 29), and is distinct in definition from phylogenetic relationship. However, I have used phenetic relationships to help estimate phylogenetic ones. I think that the estimation of the evolutionary relationships from phenetics is best observed when size of the organism is not a factor, and for this reason, I place much emphasis on the shape analyses in my study for a discussion, see Sneath & Sokal, 1973, pp. 168-178). analysis with size included can be very important in the estimation of ecological relationships. A natural group of bats in the family Molossidae includes individuals of a certain shape category and can be distinguished from individuals of a different shape category. I think each shape category or group indicates a certain way of life. Often, thesenatural shape groups correspond with classical genera or subgenera and are described in terms of those taxonomicnames. Here, I examine the family Molossidae phenetically, determine how manynatural shape groups have evolved within it, predict the resulting diverse ways of life, and estimate the evolutionary relationships among the species and groups. A few of the characters can be graded as to their primitive-derived nature and accompany the evolution discussion. The analyses used were designed not so much to distinguish one species from another, but to detect underlying morphological trends. No intensive world-wide study of molossids has been attempted. Miller 1907) reviewed the nominal genera known at the beginning of this century and provided morphological descriptions which are precise and meticulous. Early reviews of genera are by Miller 1913) of Molossus, by Shamel 1931) of New World Tadarida, and by Sanborn 1932) of Eumops. All three studies were done with far less material than is available today. Recently, Eger 1977) has examined more closely the genus Eumops and rigorously defined the species in that genus. Prominent taxonomic studies of molossids in the Old World are those by Hill 1961) of Indo-Australian Tadarida sensu lato) and by Hayman & Hill 1971). The latter authors offer keys and compilations of information on all African Chiroptera. Koopman 1975) has reviewed the bats of the Sudan and provided much data about Old World Molossids. Important systematic papers on individual species of molossids are by Peterson 1965, 1967, 1969, 1971a,b, 1972, 1974), who has not only examined many specimens in museums, but has also spent much time in the field collecting the bats and gathering data on their habits and habitat. Recently, Koopman 1978) has added significant zoogeographic and systematic notes on Peruvian molossids. Vaughan 1959, 1966) has studied the wing musculature and flight characteristics of some molossids, and Pye 1966) and Simmons et al. 1978) have done much to reveal the echolocating abilities in molossids. The following outline is the current status of species of Molossidae examined in this study for details see Appendix B).