Mammals of Indiana: A Field Guide

How Mammals Are Identified

25 How Mammals Are Identified Each “kind” or species of mammal is different from every other. They differ from each other genetically in the DNA they carry and also in the characteristics expressed by the DNA. Individuals within a species differ from each other, thus police departments can use DNA evidence to solve crimes and we can use DNA evidence to separate individuals of bats within a species. The differences are much greater between species than between individuals, so we can use DNA analysis to determine species. DNA analysis can also be used to classify; that is, DNA relationships can be used to build groups of organisms into an evolutionary system including species and also higher groups. However, most of us do not have access to the high-priced equipment necessary to run DNA analysis on all those species we want to identify. Even if we did, we would not be able to use it to identify species in the field. Therefore, we use the characteristics of the animals to identify them, and we cluster the species into taxonomic keys using those characteristics. Here we will discuss some of the main characteristics used in identification of mammals. Usually we want to identify the whole animal, the stuffed skin, or the skull. WHOLE ANIMAL Standard measurements are normally taken in mm (1' = 25.4mm).Inthedescriptionslaterinthebook,unitsareunderstood to be mm or grams (for weight) unless otherwise noted. They consist of the following: Total Length: From tip of nose to tip of tail bone (not hairs). Tail Length: From base of tail (bent upward at right angle to body) to tip of tail bone. Hind Foot: From posterior of ankle to end of longest toenail. Ear: From notch to tip of ear (not all workers measure this). Mammals.indb 25 3/31/10 3:08 PM 26   Naming and Identifying Mammals Weight: Usually in grams (1 ounce = 28.6 grams). And in addition, the following measurements are included for bats: Forearm Length (FA): Total length of the long bone of the wing. Tragus (TR): Total length of ear lobe (vertical portion inside of the ear from notch to tip). Wingspan (optional): From wingtip to wingtip. Standard measurements are always written in order; for example: TL—181 T—76 HF—23 Ear—12 Wt.—21.0 Feet: Mammals may have hooves, but most have claws. The number of toes on front and hind feet can be counted; for example, 5-4 means that there are five toes on the front feet, fouronthehindfeet.Sometimesathumbmaybedifferentiated (opossum) or a toe may be represented by a nail only. Wings of a Bat: The wings of a bat are modified forelimbs. They are formed of skin over the finger bones. The thumb of a bat is the claw on the front of the wing at the end of the forearms; the other four finger bones are the bones that support the wing. Interfemoral Membrane of a Bat: This is the skin membrane that stretches between the hind legs, enveloping most of the tail, and it connects to the hind part of the wing membranes. Uropatagiumisanothernamefortheinterfemoralmembrane. Calcar of Bat: A small cartilage protruding from the ankle into and helping to support the interfemoral membrane. Patagium: The flattened skin between front and hind limbs of a flying squirrel. THE SKULL AND TEETH Teeth are much used in keys to various mammals. Mammalogists write a “tooth formula” to indicate the numbers of each kind of teeth as follows: Incisors: The front teeth, those in the premaxillary bones of the upper jaw and in the anterior end of the mandible. Canines:Thesingletooth,usuallyelongatedandoftenpointed , situated behind the incisors and in front of the molariform teeth; that is, the first tooth in the maxillary bone. Molariform Teeth (cheek teeth): The teeth behind the caMammals .indb 26 3/31/10 3:08 PM How Mammals Are Identified   27 nines. They consist of the premolars (anterior ones) and the molars. It is often best to count them just as molariform teeth because it is not possible to distinguish premolars from molars just by looking at them. Technically they differ in that the premolars are preceded by milk or “baby” teeth, whereas the molars are not. Dental Formula is written (for the dog) as I 3 C 1 P 4 M 2 = 42 3 1 4 3 although the letters I, C, P, and M for incisors, canines, premolars , and molars are often omitted. The tooth...