Mammalogy Exam 1 Study Notes

Systematics and Evolutionary Terminology

• Taxonomy: Describing, naming, and classifying organisms.

• Phylogenetics: Investigates organismal relationships and their underlying evolutionary causes.

• Monophyly: A group containing one common ancestor and all of its descendants.

• Paraphyly: A group containing one common ancestor and some, but not all, of its descendants.

• Polyphyly: A group formed by organisms from different ancestral lineages where their most recent common ancestor is excluded.

• In-group: The primary group of organisms whose evolutionary relationships are being analyzed.

• Out-group: A closely related taxon outside the group under study used for comparison.

• Homology: Structurally similar character states inherited from a shared common ancestor.

• Convergence: Independent evolution of anatomical or functional similarity in distantly related lineages.

• Apomorphy: A derived trait or character state.

• Synapomorphy: A shared derived character state among multiple taxa reflecting common ancestry.

• Plesiomorphy: An ancestral or primitive character state.

• Symplesiomorphy: A shared ancestral character state present in two or more taxa.

• Parsimony: The principle choosing the simplest evolutionary explanation that requires the fewest character state transitions.

Key Mammalian Characteristics

• Endothermy & Homeothermy: Generation of internal body heat to maintain a relatively constant body temperature.

• Sensory Specializations: Highly developed senses, including $3$ middle ear ossicles (malleus, incus, stapes).

• Circulatory & Respiratory Systems: Complete separation of oxygenated and deoxygenated blood in a $4$-chambered heart; muscular diaphragm separating thoracic and abdominal cavities.

• Dentition: Heterodont dentition (incisors, canines, premolars, molars) and diphyodonty (two successive sets of teeth: deciduous and permanent).

• Integument & Skeleton: Body covered in hair made of keratin; skeletal simplification with a dentary-squamosal jaw articulation.

• Reproductive & Neural Traits: Lactation via mammary glands and increased parental care; enlarged brain relative to body size with a complex neocortex; double occipital condyles controlling head movement; secondary palate separating oral and nasal cavities; determinate growth.

Hair Functions and Skin Glands

• Hair Functions:

  • Insulation: Traps heat to maintain body temperature.

  • Tactile Perception: Specialized sensory hairs (vibrissae) containing mechanoreceptors.

  • Locomotion: Specialized hair configurations providing traction.

  • Defense: Modified sharp quills (e.g., porcupine, hedgehog).

  • Communication: Visual or tactile signals for warnings or threat displays.

• Skin Glands:

  • Sebaceous Glands: Produce lipids to lubricate hair and skin.

  • Sweat Glands: Facilitate evaporative cooling.

  • Mammary Glands: Produce milk for offspring via nipples or teats.

Dental Anatomy and Dental Formulas

• Tooth Layers:

  • Enamel: Extremely hard outer layer covering the crown.

  • Dentine: Comprises $30\%$ organic material, forming the main body and support of the tooth.

  • Pulp Cavity: Central chamber containing blood vessels and nerves.

  • Cementum: Bone-like substance securing the root in the socket.

• Jaw Bones:

  • Premaxillary: Anterior upper jaw bone holding incisors.

  • Maxillary: Main upper jaw bone holding canines, premolars, and molars.

  • Dentary: Lower jaw bone holding all lower teeth.

• Tooth Types:

  • Incisors: Front teeth specialized for cutting or snipping.

  • Canines: Pointed teeth adapted for holding, piercing, or tearing.

  • Premolars: Lateral teeth used for crushing and grinding.

  • Molars: Posterior teeth used primarily for grinding and crushing.

• General Dental Formula:   $\text{Upper}/\text{Lower}: I\frac{x}{x} C\frac{x}{x} P\frac{x}{x} M\frac{x}{x}$

• Ancestral Dental Formulas:

  • Placental Mammals: $I\frac{3}{3} C\frac{1}{1} P\frac{4}{4} M\frac{3}{3} = 44$

  • Marsupials: $I\frac{5}{4} C\frac{1}{1} P\frac{3}{3} M\frac{4}{4} = 50$

Mammalian Lineage and Evolutionary Origins

• Subclass Prototheria (Order Monotremata):

  • Combine mammalian features (hair, lactation) with oviparous (egg-laying) reproduction.

  • Possess electro- and mechanoreceptors on the bill/rostrum to detect electrical fields and prey movement.

  • Fossil record dates back to $110\,\text{mya}$ in Australia and $63\,\text{mya}$ in South America.

  • Taxa:

  • Family Tachyglossidae: $4$ species of echidnas.

  • Family Ornithorhynchidae: $1$ species (duck-billed platypus); semi-aquatic with webbed feet, dense pelage, venomous ankle spurs in males, and horny plates replacing adult teeth.

  • Retained Ancestral Traits: Sclerotic cartilage in eyes, absence of auditory bulla, presence of a cloaca, internal abdominal testes (testiconda), and lack of nipples (milk secreted onto skin/hair).

• Evolutionary Timeline & Synapsida:

  • Paleozoic Era: Origin of mammalian precursors including Synapsids, Therapsids, and Cynodonts.

  • Mesozoic Era: Appearance of first true mammalian fossils.

  • Synapsids: Characterized by a single temporal fenestra behind the orbit providing muscle attachment surfaces. Early synapsids include Pelycosaurs with caniniform dentition.

  • Therapsids: Possessed reduced temporal shelf, expanded dentary, reduced lumbar ribs, sagittal crest, and turbinal bones.

  • Cynodonts: Clade showing double occipital condyles, flaring zygomatic arches, secondary palate, and loss of lumbar ribs.

Permian-Triassic Extinction Event

• Timing & Impact: Occurred $252\,\text{mya}$, resulting in the extinction of approximately $70\%$ of terrestrial vertebrate species.

• Environmental Factors: Severe global heat and low atmospheric oxygen levels.

• Surviving Lineages: Small therapsids and cynodonts survived, while archosaurs and dinosaurs became dominant terrestrial vertebrates during the Mesozoic.

Infraclass Eutheria and Afrotheria

• Infraclass Eutheria:

  • Represent over $90\%$ of modern mammals throughout the Cenozoic Era.

  • Earliest fossil is Juramaia ($160\,\text{mya}$), a small shrew-like arboreal mammal.

  • Ancestral dental formula consists of $44$ teeth ($I\frac{3}{3} C\frac{1}{1} P\frac{4}{4} M\frac{3}{3}$).

  • Main clades: Afrotheria, Xenarthra, and Boreoeutheria.

• Order Afrosoricida:

  • Family Tenrecidae: $10$ genera, $31$ species in Madagascar and Africa; heterothermic, stiff vibrissae, some echolocate.

  • Family Chrysochloridae: $9$ genera, $21$ species of golden moles; fossorial, vestigial eyes, zalambdodont molars, enlarged malleus.

• Order Macroscelidea:

  • Family Macroscelididae: $5$ genera, $20$ species of elephant shrews; long mobile rostrum, large eyes, complete auditory bulla.

• Order Tubulidentata:

  • Family Orycteropodidae: $1$ species (Orycteropus afer, aardvark); fossorial termite/ant eater with tubulidentate enamel-less teeth and long sticky tongue.

• Order Hyracoidea:

  • Family Procaviidae: $4$ species of hyraxes; rabbit-sized herbivores with deep mandibles, ever-growing upper incisors, diastema, specialized traction foot pads, poor thermoregulation.

• Order Proboscidea:

  • Family Elephantidae: Columnar limbs, heavy skeleton, trunk (proboscis), incisors modified into tusks, horizontal tooth replacement, infrasound communication, male musth.

• Order Sirenia:

  • Families Dugongidae & Trichechidae: Fully aquatic herbivores ($>150\,\text{kg}$) with thick hairless skin, low metabolic rate, and horizontal tooth replacement.

Infraclass Metatheria (Marsupials)

• Morphological Traits:

  • Palatal vacuities, inflected angular process on mandible, epipubic bones, non-fused pelvic bones.

  • Dental replacement restricted exclusively to the $3\text{rd}$ premolar.

  • Ancestral dental formula consists of $50$ teeth ($I\frac{5}{4} C\frac{1}{1} P\frac{3}{3} M\frac{4}{4}$).

  • Testes positioned anterior to the penis; marsupium present in roughly half of species.

• Major Orders & Families:

  • Order Didelphimorphia: Family Didelphidae ($17$ genera, $87$ species); opossums, polyprotodont, prehensile tail, opposable hallux.

  • Order Paucituberculata: Family Caenolestidae; shrew opossums, diprotodont, no marsupium.

  • Order Microbiotheria: $1$ species (Dromiciops gliroides).

  • Order Dasyuromorphia: Carnivorous marsupials including Dasyuridae (quolls, dunnarts), Myrmecobiidae (numbat), and Thylacinidae (Tasmanian tiger, extinct in $1936$).

  • Order Notoryctemorphia: Family Notoryctidae; marsupial moles with spade-like digging claws and vestigial eyes.

  • Order Peramelemorphia: Families Peramelidae (bandicoots) and Chaeropodidae (pig-footed bandicoot, extinct); polyprotodont and syndactylous.

  • Order Diprotodontia: Characterized by diprotodont dentition and syndactyly (fused digits $2$ and $3$). Includes Vombatidae (wombats), Phascolarctidae (koalas), Burramyidae (pygmy possums), Phalangeridae (possums/cuscusses), Tarsipedidae (honey possum), Acrobatidae (feather-tailed gliders), Petauridae (wrist-winged gliders), Pseudocheiridae (ringtail possums), Hypsiprymnodontidae (musky rat-kangaroo), Potoroidae (potoroos/bettongs), and Macropodidae (kangaroos/wallabies with saltatorial locomotion and chambered stomach fermentation).