SKULLS OF CHIROPTERA AND ANALYSIS OF PREY IN CARNIVORE SCATS AND OWL PELLETS: IDENTIFICATION OF MAMMALS FROM TEETH
Today's lab has two main components, the identification of bats to the genus level using skull and dental characteristics, and the identification of mammalian prey in carnivore scats and owl pellets. You are responsible for the identification of all of the genera of rodents and insectivores from last week's lab and the following genera of bats on today's quiz and the final lab practical.
Identifying the skulls of bats of Texas:
Use the characteristics of the skulls of the bats of Texas and the simple key to the bats of Texas (located at the end of this lab) for help identifying the bat skulls.
Biologists often are interested in learning about the dietary habits of certain animal species. For example, predatory mammals and birds are of special interest due to their potential impact on both game and non-game prey species. Therefore, analysis of carnivore feces (scat) and regurgitated owl pellets serves to provide insight into prey use, as well as give information as to relative abundance and distribution of prey.
Carnivore scats may be collected from roads or trails in areas where predators are known to frequent. Information that is sometimes gathered includes animal identification and presence, location of centers of activity, dietary habits, seasonal changes in dietary composition, and presence of particular prey species. Owl pellets are obtained from beneath trees used by roosting owls. Pellets are formed in the owl's gizzard, which serves as a trap to prevent sharp bones and other indigestible material from proceeding down the alimentary canal. These pellets, containing teeth, feathers, hair, cellulose, or chitin, are then regurgitated by mouth.
In this lab, we will be identifying mammalian prey species from teeth found in cast owl pellets and/or carnivore scats, as well as from the study skulls provided in previous labs. To simplify the identification of prey species, owl pellets and/or scats are soaked in sodium hydroxide (NaOH) solution, which serves to dissolve the matrix of congealed fur, feathers and/or other materials. Small prey are often swallowed whole by both mammalian and avian carnivores, whereas larger prey must first be torn into smaller pieces. Thus, feeding on large prey may result in less consumption of bones and teeth, which are useful in identifying prey. Therefore, samples of hair are removed from the pellets and/or scat before they are digested in the NaOH solution and too are used in prey identification.
A characteristic unique to mammals is the presence of hair. Hairs are outgrowths of dead epidermal cells, which develop from living cells within a hair follicle, and are strengthened with a hard, proteinaceous tissue called keratin. Associated with hair and hair follicles are specialized sebaceous glands that lubricate the dead cells of the hair to prevent cracking and brittleness. Together, the coat of hair (pelage), hair follicles, and related glands provide (1) protection, (2) insulation, and/or (3) serve as sensory structures. Additional functions of the pelage may include adaptive coloration, transfer of messages during behavioral interactions, and aid with buoyancy in aquatic mammals.
Structural components of a hair include the cuticle, cortex, medulla, pigment granules, and air cells. The cuticle is the outermost layer of cells and is organized in a scale-like pattern. The arrangement of cuticular scales is an important characteristic in hair identification. The cortex is found between the cuticle and the medulla, and is usually transparent but may have pigment granules. The innermost region of a hair is the medulla. It too may contain various pigments. Air cells may also be present in the medulla and add insulation qualities to the hair. Medullae are grouped into different types such as continuous, discontinuous, fragmental, intermediate, or absent. These and other medullary configurations also are helpful in identifying hairs.
Types of hairs
Mammals possess different types of hair on their bodies some of which insulate and help retain body heat, while others have erectile tissues and are primarily sensory in function. Because sensory hairs are structurally the same in all species, they are not useful in hair identification.
Protective and insulation hairs are divided into two types: guard hairs and underhairs (underfur). Guard hairs may be stiffened throughout their length (e.g. porcupine quills) or have only a firm tip with a softer, weaker base. These hairs usually have a medulla, with bat hair being an exception. Guard hairs are generally protective, but provide some insulation, and give mammals their characteristic appearance. Underhairs are much smaller than guard hairs and are uniformly soft and pliable. This type of hair usually contains no medulla. The underhairs also insulation and aid in heat retention. Dorsal guard hairs are preferred for hair identification purposes because they provide the most between species variation yet preserve within species likeness.
Knowledge of the age structure of a population of mammals is very important in the management of a species and in understanding life history strategies of mammals. Because of this, considerable effort has been used to develop techniques to age mammals. Techniques for aging can be grouped into two classes, relative age and absolute age. Techniques used for relative aging of mammals assign ages to individuals by comparing each individual to other individuals in the population. In contrast, techniques used for absolute aging of mammals determine ages by counting incremental growth lines in various structures of the body.
Relative ages which are assigned to mammals are adult, subadult, juvenile, and nestling. Adults are the largest individuals in the sample and are presumed to belong to the breeding population. Subadults are smaller than adults and may or may not be a part of the breeding population. Juveniles are smaller than subadults and often but not always have a pelage which is distinct from subadults and adults. Nestlings are recently born and confined to the nest. This stage may be absent in some mammals which have precocial young (e.g., hares, artiodactyls). In Peromyscus leucopus, note the changes in pelage coloration between juvenile, subadults, and adult. The progression of the molt in subadults can be observed by examining the series of subadults available in lab. The black areas on the underside of the skin denote areas of maximum pigmentation (note how these areas correspond to the areas of activity on the upperside of the skin). Note the lack of a distinct pelage change from young to adults in Mus musculus.
Other commonly used structures in mammals to assess or assign relative age include (1) linear dimension and weight of the body, (2) degree of fusion of epiphyseal cartilage in the radius and humerus, (3) teeth (tooth wear and tooth eruption), and (4) weight and protein content of eye lenses. The crystalline eye lens grows throughout the life of a mammal and it is the only organ that does not shed cells. Thus the weight of a lens can be an index to aging. However, a more accurate index involves determining the amount of tyrosine, an insoluble protein, present in the lenses.
Growth of teeth and bones are not uniform throughout the year thus they
can be used to place long
lived mammals in year classes. Growth lines or ridges can be observed in the cementum of teeth, horns, and bones of mammals as well as baleen and epithelial ear plugs of mysticete whales. The basic pattern seen is a wider or lighter colored band laid down in the summer (favorable season) and a narrower or darker band in the winter (unfavorable season). In the baleen plates, new material is added at the base of the keratinized structure each year. The ear plug of the whale can be used to age this mammal because the auditory meatus is closed by a layer of blubber. When the epithelial lining is sloughed, it can not escape and hence forms a layered ear plug. Alternating light (higher fat content) and dark bands found apparently represent different seasonal feeding patterns. The most commonly used absolute aging technique is the analysis of cementum in wildlife species due to the ease of obtaining a tooth and the accurate age it provides.
Characteristics of the skulls of bats:
ORDER CHIROPTERA-small size with maximum length < 30 mm, jaw teeth with high-pointed cusps that unit to form a W-shape (called dilambdodont), never more than 2 incisors above, number of teeth variable
Click here for a simple key to the skulls of Texas bats
Vespertilionidae: palate terminating well behind last upper molars
1. 38 teeth (DF = 2/3, 1/1, 3/3, 3/3)
2. occasionally P3 may be crowded out of line or missing
3. space betweem upper incisors
4. lacks postorbital processes
1. 36 teeth (DF= 2/3, 1/1, 2/3, 3/3)
2. auditory bullae not noticeably inflated, about same size as foramen magnum
3. rostrum broadened and inflated, upper surface with distinct paired concavities between lacrimal and nares
4. forehead nearly flat
1. 34 teeth (DF = 2/3, 1/1, 2/2, 3/3)
2. auditory bullae not enlarged but elongate
3. zygomata of uniform height throughout
4. rounded profile
1. 32 teeth (DF = 2/3, 1/1, 1/2, 3/3)
2. dorsal profile straight and sloping upward from nares to occipital crest
3. upper canine partially split
1. 32 teeth (DF = 1/3, 1/1, 2/2, 3/3)
2. skull high and short, greatest height equal to half total length
3. greatest width of rostrum equal greatest width of braincase
1. 30 teeth (DF = 1/3, 1/1, 1/2, 3/3)
2. rostrum about same length as braincase, not inflated anteriorly pterygoids parallel
3. upper incisor not in contact with canine
1. 36 teeth (DF = 2/3, 1/1, 2/3, 3/3)
2. forehead conspicuously elevated
3. auditory bullae much enlarged
1. 28 teeth (DF=1/2, 1/1, 1/2, 3/3)
2. relatively large skull
Molossidae (free-tailed bats) - Palate terminating only slightly behind last upper molars
1. 32 teeth (DF= 1/3, 1/1, 2/2, 3/3)
2. rostrum relatively broad and compact