LABS AMNIOTA: MAMMALIA MATERIALS 1. Preserved mammals, including the domestic rat. 2. Preserved brain of sheep. 3. Mounted (articulated) and disarticulated rat skeletons. 4. Whole skeletons and individual skulls of mammals of a variety of taxa. 5. Read Chapter 19 (pages 552-580) and Chapter 21 (pages 599-651) in Pough et ai., (1999). "The history ofsynapsid classification illustrates how using overall similarity to infer phylogenetic relationships, and the paraphyletic groups that method so often specifies, invariably impede attempts to reconstruct the historyijf life." - Jacques Gauthier et ai., 1989 SUMMARY CLASSIFICATION The following summary classification places emphasis upon the main groups of placental mammals. Refer to Fig. 8.1 for more complete resolution of relationships among the placental mammals. Mammalia - mammals Monotremata - duck-billed platypus and echidnas Theria - therians Marsupialia - includes opposums, kangaroos, and 223
Tasmanian devil Placentalia - placental mammals Edentata - anteaters, sloths, armadillos Insectivora - includes hedgehogs, moles, and shrews Carnivora - includes bears, dogs, cats, and seals Primates - includes lemurs, monkeys, and apes Chiroptera - bats Rodentia - includes rats, mice, squirrels, and capybara Lagomorpha - pikas, rabbits, hares Ungulata - ungulates Artiodactyla - includes pigs, goats, deer, and giraffe Cetacea - dolphins, porpoises, toothed and baleen whales Perissodactyla - includes horses, zebras, tapirs, and rhinoceroses Hyracoidea - hyraxes Sirenia - dugongs and manatees Proboscidea - elephants -oa:l (f) ~ 32 '" (5 E '& ct MAMMALIA THERIA PLACENTALIA JJ >. a:l a:l U~GULATA t5 Q> ~ C1l -c.- "'0.- co (,) o0q) (f) (f) ().- co C.0 CD ~ ~ 0 a.. I: en a: INTRODUCTION Mammalia is the CER to Reptilia and is comprised of Monotremata, Marsupialia, and Placentalia (Fig. 8.1). There are three species of monotremes (duck-billed platypus and two spieces of echidnas), about 280 species of marsupials, and over 4,200 species of placentals. Mammals vary enormously in size, from 50 millimeters (shrews) to 30 meters (blue whale). The majority of species are terrestrial, but chiropterans (bats) are capable of true flight, and cetaceans (whales) and sirenians (manatees and dugongs) are obligate to aquatic habitats, primarily marine. Mammals occupy all of the continents, oceans, and larger oceanic islands. Synapomorphies for Mammalia include a pair of single lower jaw bones called the dentaries, dentary-squamosal articulation, incus and malleus (modification of the articular and quadrate to become middle ear bones), heterodont dentition, hair, pinnae (external ears), mammary glands in females, a muscular diaphragm, four-chambered heart, enucleated erythrocytes, and endothermic metabolism (Fig. 8.1). Several synapomorphies are associated with modifications of the lower jaw region. The mammalian middle ear is generally enclosed in a bony bulla (= auditory bulla). The angular bone (a bone of the lower jaw in osteichthyans) is modified in mammals and is called the tympanic bone, which supports the tympanum and in many cases forms part or all of the bulla. Instead of possessing a single auditory bone, the stapes, as in other tetrapods, the middle ear contains an articulated chain of three bones (malleus, incus, and stapes) leading from the tympanum to the inner ear (Fig. 8.2). Studies in embryology, Figure 8.1. A phylogeny of the major clades of mammals Mad'f d f. ammotes, Reptilia is the CER of Mam l' S. I Ie rom Novacek (1992, 1993). Among extant muscular, thoracic diaphragm four_ch:~~~re~n~po~or.p~~sfor the various clades are numbered 1-15. 1 :0:: e t :ortic)arch only, endothermy, single bone in pinnae. 2 :::: teeth absent in ad~lts, ankles with ho: ' e ear. ones I swe~ gl.a~dsi ma~mary g~ands, hair, placentation, male gonads external (scrotllm) cl' Yb spurs.m males. 3 ~ vivipary with chono-vitelline h., oaca a sent mpples 4 rna. 5 c ~no-allantoic placentation, 6 ::::: carnassial teeth. 7 ::::: enlar y'db' - rsup.mill. ::::: corp~s callosum, lower jaw (dentary), heterdon;y incus and rnal1eu;(f.:~; pairs of upper incisors, one posterior to the other 10 _. g.e ody scales., 8 ::::: wmgs, echolocation. 9 ::::: two absent, reduction of pelvic girdle. 13::::: weight ern hasis~t~ciso~s e~erg~o~mg. 11 ~ hooves. 12 ::::: hindlimbs arranged in a row. 15 ::::: eyes positioned forward i6 _ I ~~g third, ~Igit. 14::::: WrIst bones compressed and. - e ongate proboscis, elongate canines (tusks)., 224 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 225
comparative anatomy, and paleontology have revealed the evolutionary history of these bones. Remember that the stapes is a unique character for tetrapods, and it represents a modified hyomandibular bone (Lab 6). The malleus and incus are homologous to the articular and quadrate bones, respectively, and in non-mammalian osteichthyans they form the jaw joint. Recall (Fig. 1.6) that Synapsida and Sauropsida are sister taxa within Amniota, and that each represents a stem clade such that Synapsida includes Mammalia and Sauropsida includes Reptilia. Early synapsids possessed (retained) the ancestral state of articular-quadrate jaw articulation, however all mammals possess the dentary-squarnosal jaw articulation (Fig. 8.2). A number of modifications of the skull, associated with feeding mechanics, occurred throughout synapsid evolution (Pough et ai., 1999), including the development of a large coronoid process on the dentary which provides a large area for muscle attachment. As muscle attachment changed from the area of the articular and quadrate to the dentary and squamosal, the articular and quadrate became available to function exclusively in sound transmission, and, as such, they migrated to the position of the middle ear and are now referred to as the malleus and incus, respectively. Fossil representatives of the synapsid Diarthrognathus, who possessed a double jaw joint in which both the ancestral articular-quadrate and the derived dentary-squamosal articulations were present, provide a classic example of an evolutionary intermediate. Through the series of changes, the dentary remains as the only bone of the lower jaw in mammals. Other synapomorphies of the hard anatomy are heterodont dentition. Synapsids prior to mammals evolved heterodont dentition, in which the teeth are of different sizes and shapes for distinctive functions. Incisors and canines evolved first in early synapsids, and distinctive molariform teeth (premolars and molars) evolved later (Pough et ai., 1999). Several non-skeletal synapomorphies also diagnose Mammalia. Hair is present on nearly all extant mammals (see Fig. 8.1 for examples of exceptions). It has a variety of functions, including camouflage (crypsis) and conspecific communication, but its basic function is insulation. Hair is composed of keratin, both soft (plesiomorphic in amniotes) and hard (derived in amniotes). Hair is epidermally derived and is not homologous to dermally derived bony scales; the two structures may have existed concurrently in some ancient synapsids. All mature female mammals possess mammary glands which produce and secrete a nourishing milk of casein, lactose, fats, and salts, for their young. Mammary glands are specialized derivatives of sweat glands. In monotremes, milk from the mammary glands is exuded onto surface hairs where, because there are no nipples, it is simply lapped by the young. All other mammals (Theria) possess nipples (of varying sizes) in which the young (Fig. 8.1) suckle the milk... '..).,:",:'.-;,:.;-:,~::."'" Dentary.' Squamosal Tympanic (auditory bulla) Middle Ear Osslcles Figure 8.2. Mammalia: Dentary-squamosal jaw articulation and middle ear bones of a generalized mammal (dog, Canis). The muscular diaphragm, which separates the abdominal and thoracic cavities of mammals, functions in the expansion and contraction of the lungs. Contraction of the diaphragm increases the volume of the thoracic cavity and lowers pressure in the lungs so that air flows inward (inspiration), and relaxation of the diaphragm decreases the volume of the thoracic cavity and raises pressure in the lungs so that air is forced out (expiration). The muscles of the diaphragm appear to be derivatives of the abdominal muscles. Convergent with archosaurs, mammals possess a distinctly separated four-chambered heart,with two atria and two ventricles (Fig. 8.3). The fourchambered heart allows complete separation of the pulmonary circuit (which carries oxygen-poor blood) and the systemic circuit (which carries oxygen-rich blood). Only the left aortic arch remains. Ancestrally in tetrapods, there are both right and left aortic arches, and in archosaurs, only the right aortic arch remains. Also associated with the circulatory system, the erythrocytes of mammals are enucleated (the mature red blood cell extrudes the nucleus). As a result, more space is available in the erythrocytes for the hemoglobin, a molecule that allows for increased oxygen transport. 226 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 227
Cranial vena cava ----f). (right) Aortic arch----f: Auricle (right) ---me- Ventricle (right) ----K~7~:; Brachiocephallc artery ---- Common carotid artery (left) <~" 'J!L: --- Subclavian artery (left) Cranial vena cava (left) Descending aorta Pulmonary trunk --'"ii,bf--- Auricle (left) Finally, mammals are endothermic, a condition which is convergent in birds. Endothermy is the condition where metabolic processes generate sufficient internal body heat rather than dependence on the environment (ectothermy). The only true endothermic vertebrates are mammals and birds, and all other taxa you have studied thus far are ectotherms. Endothermy permits individuals to regulate their high body temperatures by mechanisms that precisely balance metabolic heat production and heat loss to the environment. Activity of skeletal muscles can produce large amounts of heat, both through locomotion and shivering. In mammals, heat loss can be regulated behaviorly and by the insulatory properties of hair, and in birds by feathers (Pough et al., 1999). @ What is a possible relationship between enucleated red blood cells and endothermy? Coronary blood vessels ~--- Ventricle (left) A Cranial vena cava -------t (right) Atrium (right)---7: Interatrial septum---t Atrioventricular valve ----r (right) B Ventricle (right)---+- Interventricular septum ---':- Cranial vena cava (left) ~-- Entrance to pulmonary veins ""4~;i:ll\-+-- Atrium (left) ~----:I- Atrioventricular valve (left) ---f- Ventricle (left) Papillary muscle Figure 8.3. Mammalia: Heart of domestic rat. (A) Ventral view of external heart. (B) Ventral view of sagittal section. MAMMAL DIVERSITY The following taxa represent the three main clades of extant mammals; thus, the taxonomy is strictly crown-based (Fig.,S.l). MONOTREMATA The three extant species of monotremes are restricted to Australia and New Guinea, and include the monotypic duck-billed platypus (Ornithorhynchus anatinus) and two species of spiny echidna (Tachyglossus and Zaglossus). Monotremes are unique among mammals in their reproductive mode: they lay shelled eggs (oviparous). 8 Is oviparity a synapomorphy for monotremes? Why or why not? Bu. /J I esf {Hoi... (. np, ~ «1;011)" ~l.c.~?q. 1-"1 228 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 229
Female monotremes do produce milk from mammary glands. However, nipples are not present but the young do suckle or lap the milk from milksaturated hairs. A synapomorphy for monotremes is the loss of teeth in adults. An odd character (synapomorphy) is that all male monotremes possess horny spurs on their hindlimbs, and in the duck-billed platypus the spurs are grooved and conduct venom (Nowak, 1991). Platypuses represent the only mammals with a venom delivery system. ewhat other amniotes have independently evolved venom delivery systems? Echidnas and platypuses are quite distinct from one another. Echidnas have a body covering of fur intermixed with dorsal and lateral barbless spines. The limbs have broad, powerful feet modified for digging. The rostrum is long, tubular, and tapering and the mouth is small. Platypuses have streamlined and dorsoventrally compressed bodies. The limbs are short and stout, and the webbed feet are broad. The tail looks similar to a beaver's (Placentalia), and the snout, which looks like a duck's bill, is elongated and covered with moist, soft, naked skin. Platypuses forage for food in the water, and they are good divers. The bill is an electroreceptive and mechanoreceptive organ that allows detection of muscle activity in prey animals (e.g., aquatic insects, snails, small fish). the cloaca, for both reproductive and excretory materials. Monotremes retain the cloaca, but therian mammals have lost the cloaca and, instead, possess two excretory openings, including the anus for intestinal waste (feces), and the urethral opening for wastes derived from the kidneys (urea). In therians, mammary glands open to the skin surface through projecting nipples from which the young suck the milk. Mammary glands become fully developed when a female reaches sexual maturity, and they become functional at the time of parturition (birth of their young). The number of nipples is generally correlated with the number of young produced at birth. In marsupials, nipples are are enclosed in the abdominal pouch, and they are distributed along the abdomen in a U-shaped or circular orientation. In placentals, the nipples are arranged in two longitudinal rows along the abdomen. In all craniates except therian mammals, the gonads of adult males generally retain their ancestral position in the upper part of the coelomic cavity. In male therians, the position of the testes changes during embryonic development. Paired pouches form in the floor of the abdominal cavity and cause external swellings on the ventral surface of the body just anterior to the pelvis. These are the scrotal sacs, and each testis moves posteriorly and ventrally from its original position and descends into the scrotal sac. ~What were the possible selective pressures for the male gonads to migrate outside of the abdominal cavity? l",l<p...j.e"+- +'''''fera-j..rt. (..,..,-.-) THERIA Theria is the CER to Monotremata. Theria is composed of two major crown clades: Marsupialia and Placentalia. Several synapomorphies support the monophyly of Theria, including a viviparous mode of reproduction, the absence of the cloaca and the derivation of two separate excretory openings, the presence of nipples in females, and the presence of external male gonads in a scrotal sac. Vivipary evolved independently in several other vertebrate clades. In therians, some degree of placentation develops between the mother and the embryo. A placenta is formed from a union of maternal uterine tissues and fetal tissues, which are modifications of embryonic membranes found in other arnniotes. The exact tissues involved vary in the two major lineages of therian mammal (see below). Recall that virtually all other craniates possess a common collecting duct, MARSUPIALIA There are about 280 species of extant marsupials, which include the famous kangaroos, koalas, Tasmanian Devil, and wombats of Australia and New Guinea. Over 90 species of marsupials are found in the New World (North, Central, and South America), which includes the well-known opossums (didelphids). Although marsupials evolved in North America and were speciose, only one species of opossum naturally occurs in the United States. Although not as ecologically diverse as marsupials in Australia, the opossums of Central and South America, for example, occupy a diversity of habitats including grasslands, forests, and habitats near freshwater streams and lakes. Female marsupials have a ventral pouch or marsupium in which the offspring are carried and fed. A marsupial embryo has a short-lived placenta formed of the chorion and yolk sac, which is termed a yolk-sac placenta or 230 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 231
chorio-vitelline placenta, and the embryo during this time receives little nourishment from the mother. Because of this, gestation in marsupials is quite brief (e.g., several weeks) and, therefore, the majority of development occurs with the embryo strongly attached to its mother's nipple within the marsupmm. PLACENTALIA Placentalia is the crown name for - 4,200 species of extant mammals, including humans. Eutheria is the stem name that includes placental mammals and is the sister taxon to Metatheria, which includes the marsupials (see de Queiroz and Gauthier, 1992, for correct use of these terms). Eutheria and Placentalia are often incorrectly used as interchangable, synonymous names for the crown clade that includes all extant placental mammals. Placentalia is diagnosed by numerous synapomorphies, including the development of a chorio-allantoic placenta in females and the formation of the corpus callosum in the brain. The placenta, as noted above, is a therian structure through which the embryo receives food and oxygen from the mother and handles waste materials. The placenta is formed by a union of the embryonic membranes with the surrounding maternal uterine tissues. The chorion develops finger-like processes on its outer surface, which project into the maternal tissues. A thin membrane separates the embryo's bloodstream from the mother's so that only nutritive and waste materials pass between. The allantois is well developed below the chorion as an integral part of the placenta; its vessels are vital carriers of food materials as well as oxygen to the embryo, and carbon dioxide and wastes are carried back to the mother's bloodstream. With this type of welldeveloped placenta, placental females generally carry their young for much longer periods than do marsupials, and the young are much further developed. The neopallium, present in mammals and some reptilians, is an area of gray matter of the brain. The neopallium is an association center, that receives fibers that relay sensory stimuli from the brain stem and, in turn, send "commands" directly to the motor centers of the brain. In mammals, the cerebral hemispheres are extremely enlarged, particularly due to the great expansion of the neopallium, and they tend to cover and envelop the other brain structures. Because of the increased volume of gray matter fibers, folding of the surface often results. These folds are called gyri. In placentals, the neopallial structures are connected by a unique structure, the corpus callosum, which functions to allow both cerebral hemispheres to share memory and learning. Below are brief descriptions and characters of the main lineages of placental mammals (see overview by Nowak, 1991). Edentata There are 33 species of extant edentates which includes the sloths, anteaters, and armadillos. All species of edentates are restricted to the New World. One interesting synapomorphy is the presence of xenarthroles, which are additional articulations between the lumbar vertebrae. Despite the name of this lmeage, which implies lack of teeth, only the anteaters are entirely toothless. Armadillos possess a unique integument, which involves a flexible double-layered covering of horn (bands or plates) and bone over the majority of the body Pholidota There are 7 extant species called pangolins. These interesting creatures have enl~rged ~cales (Illodified hair) that cover their entire body and largely replace typical hmr. Phohdota IS the CER of Edentata (Fig. 8.1), and all species are distnbuted in Africa and Asia. Glires The members of this large clade are Macroscelidea (elephant shrews; 15 species), Rodentia (rodents; > 1810 species), and Lagomorpha (pikas, rabbits, and hares; - 70 species). Rodents are clearly the most speciose (and one of the most successful) groups of extant mammals, with chiropterans (> 986 species) and msectivores (> 390 species) following. A synapomorphy of Rodentia is ever-g~owingincisors. Lagomorphs possess two pairs of upper incisors, one postenor to the other (Fig. 8.1). What. is :he adaptive significance ofevergrowing incisors in rodents? ~ l",e1~ors ""I/. wor" cio... d. r;ai...""'" I e..j...;,,~ Q'lJ Ilv!",? (.J, It. e.tr,;wl~'../1.<, Me.. ~Ie -l".. I...'s ~.'-'e IOA1'!U'h.. Primates. There are - 235 extant species of mammals called primates. Humans (Homo sapiens) are members of this clade and are classified as primates, specifically the Pongidae (Great Apes ), and also includes the orangoutans, gorillas, and chimpanzees (Fig. 8.4) 232 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 233
GREAT APES PONGIDAE rq;\ Compare the skeletal anatomy ofthe pigeon (Lab 7) to the bat. How do they differ V zn their anatomy to accomplish true flight? How are they similar? Gibbons til.ill Chimpanzees Orangoutans Gorillas Humans and Bonobos 2 &.!l! 0.Q t:: ~ E t:: 0 t d: ~ ~ d': Insectivora This large clade of about 390 species includes the moles, shrews, and hedgehogs. Insectivores have a worldwide distribution. In hedgehogs, hairs have been modified into spines. ~ In what lineages have hair been modified into spines? What are the possible functions ofspines? Carnivora Figure 8.4. A phylogeny for the primate clade Pong~dae ~ase~ on behavioral, morphological, and molecular data sets. Gibbons are the CER to Pongidae. As depicted In this cladogram, humans share a m.o:e recent common ancestor with chimpanzees and bonobos than to either gorillas or orang-utans, ModIfIed from Uchida (1996). This clade has with 270 extant species including dogs, bears, cats, hyaenas, and weasels, and currently includes members of Pinnipedia (sea lions, seals, and walrusas). A synapomorphy for carnivores is the presence of carnasial teeth, an adaptation for capture and feeding on large prey (Pough et ai., 1999). In addition to walruses, what other lineage has highly elongated canines?, Ungulata Chiroptera The bats form a large clade with over 986 extant species. Chiropterans or bats are the only mammals that have wings and are capable of true flight. In addition to specializations for flight, they show great diversity in feeding specializations, such as the infamous sanguivory (blood-eating) of vampire bats. The members of this large and extremely diverse clade are Cetacea (whales and porpoises; 80 species), Artiodactyla (even-toed ungulates; swine, hippos, deer, giraffe, sheep, cattle; 213 species ), Perissodactyla (odd-toed ungulates; horses, tapirs, and rhinoceroses; 17 species), Hyracoidea (hyraxes; 7 species), Proboscidea (elephants; 2 species), and Sirenia (manatees and dugongs; 4 species). Many species of ungulates (e.g., artiodactyles and perisodactyles) possess hooves rather than claws. Cetaceans have modified forelimbs (and absence of hind limbs) to form fins for aquatic living. Both species of elephants have an elongated proboscis (nose) and modified canines (tusks). 234 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 235
ANATOMY OF THE RAT To better understand and interpret mammalian structure and function, you will examine and study a preserved domestic rat (male and female). ~ue to its small, but adequate, size, accessibility, and low cost, rats are good subjects for dissection; however, your instructor may choose to use the cat or another species. External Anatomy Examine the preserved rat that has been provided for you. Beginnin~at the region of the head, note the relatively large external ears (pmnae). Postenorly note the long,. hairless tail. Note that each of the feet has claws. In the male rat, observe the scrotum, which contains the externally placed gonads (testes). ~ For which taxon are claws a synapomorphy? Pinnae? Scrotum? ~ I I \, """,,,..,,,,,c.l;e:... #u"( '" Pancreas - ~ Cecum.,.,!. Small intestine """''7~;lU:r~ Mesentery proper ''!i<+'~,--- Lobe of liver (left) Stomach ~I;'-- Greater omentum _,10'" ~~~ ;';~f'-- Spleen ~.;,;;~-- Large intestine 'i#-~",,--- Ureter f*--=::>"'--- Uterus "----+-- Urinary bladder Internal Anatomy Carefully make a longitudinal incision from the region of the pubis to a point caudal to the sternum. Do not cut through the muscular diaphragm. Pry apart the thick skin to expose the viscera. Digestive System Be able to identify the following internal organs, and when asked, their functions (Fig 8.5):. The liver receives blood from the intestinal tract and processes nutnents and detoxifies various substances, as well as produces bile. The forepart of the stomach is the cardia, which receives the esophagus and serves as a holding chamber for food. The fundus is the central portion of stomach. Secretory cells release pepsin (a protein-digesting enzyme), hydroc~loricacid, and mucus. The pylorus is the caudal portion of stomach. The pylonc valve.regulates movement of food into the small intestine. The small mtestme chemically digests material and absorbs nutrients. The pancreas secretes a variety of digestive enzymes through pancreatic duct into the duodenum. The pancreas Figure 8.5. Mammalia: Internal anatomy of domestic rat (digestive system). also produces and secretes the hormones glucagon and insulin. The large intestine absorbs water and functions in the formation and elimination of solid waste called feces. > Urogenital System Examine the urogenital system (reproductive and excretory systems). Identify the kidneys and the ureters that connect to the urinary bladder. Male rats have an external scrotum, which contains the gonads (testes) (Fig. 8.6). The testes produce spermatozoa which exit through the penis. Cut one of the testes in half (sagittal section) and identify the coiled seminiferous tubules where spermatozoa are produced. If you have a female (or if you do not, be sure to observe one), identify the ovaries, which may be partially obscured by fat (Fig. 8.7). The fallopian tubes empty into the paired uteri (singular = uterus), and these structures converge to form the vagina. 236 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 237
Respiratory and Circulatory Systems Coagulating gland -----,L----lP,1!J-1::.1!S\\- ~,!.~-.1f~~~ Prostate gland... Scrotum -1-----1 Kidney (left) II----t-- Ureter tt/-"-"cr:",,",---f--- Vesicular gland -'<:- Urinary bladder o:s;;;,-----'t- Ductus deferens 'gj,;...,ifil------_j Urethra Epidldymus --\-----n)\ 1*-i~'tt---+-Penis Testis (right) -.J,,----f'1tJe Figure 8.6. Mammalia: Internal anatomy of domestic rat (male urogenital system). To examine the main respiratory and circulatory structures, make a longitudinal incision with strong scissors slightly to one side of the midventral line from the diaphragm to the throat region. Make lateral incisions to spread the thoracic walls outward, breaking the ribs. Identify the trachea, lungs, muscular diaphragm, and four-chambered heart. V How does the diaphragm function in breathing? jj co",+.r",ds ~ ~r<....".c /"'"1 r f. Identify, externally, the right and left atria, as well as the right and left ventricles (Fig. 8.3). To identify the chambers internally, section the heart completely across the frontal plane. Note the septa that separate the chambers from one another, and the valves that control blood flow from one chamber to the next. ~ For which other amniote taxon is the four-chambered heart a synapomorphy? Kidney (right) -1---1- Ovary ---f-+ Fallopian tube--+--it\ Uterine blood vessel -+----I\ +- Urethra External vaginal orifice _--\,.- Lt-----:-- Descending aorta fl---jft-t--- Ureter Iff-+-- Left horn of uterus ~"-;;r~~-"\- Cervix -IfI:1H----'~--I;-- Urinary bladder ~jif;f-----_')-vagina Clitoris --'".J.".-..-_-+ Anus Identify the spleen, which is part of the circulatory (lymphatic) system. This organ manufactures and stores red blood cells and white blood cells. Skeletal System Learn to identify the main skeletal components (head skeleton and postcranial components) labelled in the illustration of the rat (Fig. 8.8). Observe that the lower jaw is composed of a pair of single bones each called the dentary (mandible). An additonal exercise on skeletal diversity is provided below. @) The presence ofa single bone in the lower jaw is uniquely derived for mammals. What is the fate ofthe articular bone during development? What is the fate of the quadrate bone, a bone ofthe skull in other osteichthyans? Figure 8.7. Mammalia: Internal anatomy of domestic rat (female urogenital system), 238 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 239
Which auditory bones are located in the auditory bullae? Skull Atlas Scapula Lumbar vertebrae I The last exercise for the rat involves a puzzle of sorts. Obtain from your instructor a disarticulated (bones separated from each other) rat skeleton. Attempt to reconstruct the skeleton without using the mounted skeleton as a guide. After you have completed this task, compare your work to the wholemount and to Fig. 8.8. For a variety of disciplines, it is important to be able to identify isolated, individual bones. Tibio-fibula Sacral vertebrae I \...,-",'E"~-- Innominate (ilium, Ischium and pubis) ~ Why is it important in various unrelated disciplines to be able to identify isolated bones? -Carpals - Metacarpals ] Phalanges!i]; ~~~:::=Tarsals Metatarsals --... Phalanges.. Caudal vertebrae Mammalian Skeletal Diversity A Although it is usually difficult to study mammal diversity in the lab, largely due to the fact that so many species are quite large and/or difficult to obtain, it is still possible to study one aspect of diversity using skeletal systems, particulary skulls, from a variety of clades. The examples we list are usually available from biological supply companies (see Appendix I). The main bones of the skull to inspect in the rat and representatives of other taxa include the frontal, parietal, occipital, temporal, zygomatic, sphenoid, nasal, lacrimal, ethmoid,vomer, maxilla, and dentary (mandible). The variation in morphology of these skull bones is tremendous. There are four main tooth-types of the skull and mandible of mammals. These are the incisors, canines, premolars, and molars (Fig. 8.9) (DeBIase and Martin, 1981; Pough et ai., 1999). Incisors are rooted in the premaxillaries and lower jaws, and are generally chisel-shaped and function in nipping. Canines are unicuspid with a single root and are the most anterior teeth rooted in the maxillae and dentaries; they are usually long and conspicuous, varying widely among taxa (e.g., elephants, walrus). Premolars are located posteriorly to the canines and molars are located posterior to premolars. Premolars tend to be smaller than molars and possess fewer cusps. Often it is next to impossibe to differentiate between these tooth-types, and they are thus collectively identified as postcanines or molariforms. Upper incisor B Lacrimal Zygomatic arch Dentary Squamosal Parietal Figure 8.8. Mammalia: (A) Skeletal system of the rat. (B) Head skeleton of rat. Coronoid process Condyloid process ~-- Occipital AngUlar process External auditory meatus Mastoid process 240 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 241
Using the entire head skeleton, compare the skulls and various tooth-types (incisors, canines, premolars, and molars) of therian mammals from various lineages. The domestic dog (Canis) can be used as a general model or representative mammal for this exercise; refer to Fig. 8.9.). Compare size, shape, position, sexual dimorphism, present/absent, and so forth. Another aspect of this excerise involves determining dental formulae. This is a method that shows the numbers of each tooth-type of a particular species. For example, the dental formula (OF) for the upper jaw (values above the line) and the lower jaw (values below the line) of the domestic dog (Canis; Carnivora) is: OF =I 3-3/3-3 + C 1-1/1-1 + P 4-4/4-4 + M 2-2/3-3 =20/22 =42 total teeth, As you will see in the exercise that follows, some species of mammals lack certain tooth-types, such as premolars in rats (Rattus), and zeros are thus used for premolars in the OF. Further, as mentioned above, the distinction between pre-molars and molars is often very difficult and, therefore, they are often combined (P+M) in the OF. Using the head skeleton (skull and lower jaw) of a domestic dog (Canis) for comparison, inspect and compare all (or several) of the following taxa. Describe the differences and similarities. Be certain to determine dental formulae. (1) Coyote (Carnivora): where I = incisors, C = canines, P =premolars, and M =molars. (2) Domestic cat (Carnivora): Lacrimal Frontal Parietal Premaxilla (3) Armadillo (Edentata): Squamosal ::::~~~:... Occipital bone Zygomatic Arch (of squamosal) Occipital condyle ~ Hedgehog (Insectivora): Canine (1) Premolars (4) Pterygoid Tympanic (auditory bulla) Coronoid process Premolars (4) 7-- Mandibular condyle y4 New World Monkey (Primates): Incisors (3) - :,;."-~4.!".-..J.d,<Y'0ln"",,",,-~ Ramus region Dentary (mandible) Masseteric fossa Angular process (6) Bat (Chiroptera): Figure 8.9. Mammalia: Head skeleton of a dog (Canis), Lateral view of skull, with tooth-types labelled (values are numbers per quadrat). Lateral view of dentary (mandible), with tooth-types labelled (values are numbers per quadrat). 242 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 243
(7) Domestic rat (Rodentia): Frontal Coronal suture (8) Rabbit (Lagomorpha): "r--- Parietal ~Deer or pig (Artiodactyla): Sphenoid ----ili~..m inferior nasa concha ---~liffij+."i~ t~'i,41...- Temporai ft: a:~~fzt=lilacrimal Nasai.,-:-,~- Zygomatic ~~-cill~'h-- Vomer '"ii';h(--- Maxilla ~ Horse (Perissodactyla): A (10) Opossum (Marsupialia): Frontal Coronal suture Parietal Temporal Q16 How have the skulls and teeth been modified in various lineages? Describe how the size, shape, and presence or absence ofvarious teeth provide clues to their diet. What other factors might affect the evolution of particular skull and toothtypes? Ethmoid --~r- Lacrimal Lamboidal suture 7"'--- Occipital Next, compare the skulls and tooth-types (i.e., morphological variation and dental formulae) of the Great Apes (i.e., orang-utan, gorilla, human, chimpanzee, and bonobo). Refer to Figure 8.4, the cladogram of Pongidae which includes humans. Humans will be used as the representative pongid for comparison in this exercise (Fig. 8.10). El Maxilla External auditory meatus Dentary (mandible) Figure 8.10. Mammalia: Head skeleton of human (Homo) (A) Frontal view. (B) Lateral view. 244 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 245
Q17 Q18 What are the major differences of the head skeleton (skull and jaws) between humans and the (1) chimpanzee, (2) gorilla, and (3) orang-utan? What are the main similarities? Does the human head skeleton appear to be more similar to the chimpanzee head skeleton than to either the gorilla and urang-utan? Why? What specific skeletal characteristics suggest close affinities? neopallium, gyri, cerebral hemispheres (controls body movements, receives most brain inputs), cerebellar hemispheres (helps maintain body equilibrium, such as in motor activity), and the medulla oblongata (continuous with the nerve (= spinal) cord, maintains many of the body's visceral reflexes, such as respiration). In mammals, particularly, the cerebrum has become expanded so that dorsally it overlies other parts of the brain. Also identify the olfactory bulbs (olfactory nerves extend down into the nasal olfactory mucosa). ~ Compare the same regions of the brain of the sheep to that of the shark. Describe both the similarities and differences. MAMMALIAN BRAIN Obtain a sheep (Artiodactyla) brain from your instructor (Fig. 8.11). The sheep brain is often used because of its large size and availability. Identify the QUESTIONS FOR DISCUSSION othe distribution of marsupials is restricted compared to placental mammals. What are some hypotheses that can be tested to explain this pattern? @What are some possible selective agents for the evolution of variable toothtypes in mammals? Loss of body hair has occurred multiple times among placental mammals. What are some of the environmental conditions that might select for this state? ~r-- Cerebral hemisphere WEB SITES <http://www. aza. org>....~i1z):::::=- Median sulcus Gyri In addition to the Web sites, such as the Tree of Life and the Animal Diversity Web (ADW) to learn more about mammals, visit the home page and ther many links of the American Zoo and Aquarium Association (AZA). Do you want to see and know more about endangered mammals, such as tigers, rhinoceroses, and Indian elephants? This is the place to go! '---- Cerebellum REFERENCES ~'----Spinal cord Figure 8.11. Mammalia: Brain (dorsal view) of sheep (Artiodactylia). DeBIase, A.F., and R.E. Marlin. 1981. A Manual ofmammalogy. 2nd. edn. Wm. C. Brown Publishers, Dubuque, Iowa. de Queiroz, K., and J. Gauthier. 1992. Phylogenetic taxonomy. Annual Review of Ecology and Systematics 23: 449-480. 246 LABS FOR VERTEBRATE ZOOLOGY Lab 8: AMNIOTA: MAMMALIA 247
Gauthier, J., D. Cannatella, K. de Queiroz, A.G. Kluge, and T. Rowe. 1989. Tetrapod phylogeny. In The Hierarchy oflife (Ed. by B. Fernholm, K.Bremer, and H. Jornvall), Pl'. 337-353. Elsevier Science Publishers, New York, New York. Novacek, M.J. 1992. Mammalian phylogeny: shaking the tree. Nature 356: 121-125. Novacek, M.J. 1993. Reflections on higher mammalian phylogenetics. Journal of Mammalian Evolution 1: 3-30. Nowak, RM. 1991. Walker's Mammals ofthe World. 2 Vols. 5th edn. The Johns Hopkins University Press, Baltimore, Maryland. Pough, FH, e.m. Janis, and J.B. Heiser. 1999. Vertebrate Life. 5th edn. Prentice Hall, Upper Saddle River, New Jersey. Romer, A.S., and T.S. Parsons. 1986. The Vertebrate Body. 6th edn. Saunders College Publishing, New York, New York. Szalay, FS., M.J. Novacek, and M.e. Mckenna (Eds.). 1993. Mammalian Phylogeny. Vols. 1-2. Springer, New York, New York. Uchida, A. 1996. What we don't know about great ape variation. Trends in Ecology and Evolution 11: 163-168. APPENDIX I Perhaps the principal frustration in establishing a lab for vertebrate zoology is acquiring high-quality specimens. In addition to the vendors provided below, we highly recommend consulting zoos, public aquaria, petshops, private breeders, and other sources for specimens. Carolina Biological Supply Company 2700 York Road Burlington, NC 27215 (800) 364-5551 Web site: <http://www.carosci.com> Email: carolina@carolina.com Connecticut Valley Biological Supply Company, Inc. P.O. Box 326 South Hampton, MA 01073 (800) 628-7748 Edmund Scientific Company 101 East Gloucester Pike Barrington, NJ 08007 (609) 573-6270 Web site: <http://www.edsci.com> Fisher Scientific - EMD 4901 West LeMoyne Avenue Chicago, IL 60651 (800) 955-1177, Forestry Suppliers, Inc. P.O. Box 8397 Jackson, MS 39284 (800) 647-5368 Glades Herp, Inc. 5207 Palm Beach Blvd. Fort Myers, FL 33905 (941) 693-1077 Web site: <http://207.30.59.98/gherp> 248 LABS FOR VERTEBRATE ZOOLOGY I I, APPENDIX I 249