STH 2083 Vertebrate BiologyFaisal Ali Anwarali Khan, PhD

Department of ZoologyFaculty of Resource Science and Technology

Universiti Malaysia Sarawak

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Vertebrate BiologySTH2083

Mammalogy

By

Faisal Ali Anwarali Khan, PhD

Introduction to Mammals

Mammalian diversity

General feature of mammals

Major mammalian skull and skeleton

Mammalian classifications

Brief introduction to mammalian order

Mammals are diverse?

• 29 Extant Orders• 153 Families• 1230+ Genera• 5,500+ Species

Wilson and Reeder 2006. Mammalian Species of the World. Johns Hopkins University Press.

How about other vertebrates?• Amphibians• Reptiles• Birds• Fish

7,000 species8,950 species10,000 species25,000 species

• >350,000 described plants• >1,000,000 described insects

However…… Geographically: Mammals are the most

widespread

Morphologically diverse group of vertebrates

Largest range of body sizes Smallest: Etruscan shrew or bumblebee bat, 2 g Largest terrestrial: African elephant, 6 metric

tonnes = 6 million g Largest vertebrate: Blue whale, 103-150 tonnes

= 150,000,000 g (75 million shrews!)

Typical Terrestrial

Truly volant – True flight

Truly subterranean-Underground

Semi-aquatic

Mostly aquatic

Truly aquatic

Who came first? Mammals or Dinosaurs

Oldest dinosaur fossil

(240 MYA):

Nyasasaurus

Oldest mammals

(form) fossil (225 MYA)

Both Late Triassic

Actually, aboutthe same time....

160 million-year-old fossil—the earliest known complete skeleton of a multituberculate—named Rugosodoneurasiaticus, a fast-running, agile omnivore similar to a modern-day African dormouse. -

Relationships: Mammals and other Vertebrate

1. Mississippian, (>320 MYA) : Reptiles diverged from amphibians - development of amniotic egg

2. Early Permian, (300 MYA) : Appearance of dominantterrestrial predators, pelycosaurs

Mid Permian (270 MYA): Radiation of mammal-like reptiles lineage, Therapsids

3. Mid Permian: Reptilian lineages (crocodiles, turtles, lizards, snakes, dinosaurs) and birds 1

23

4

5

6

1

23

4

5

6

4. End of Permian : Mostly extinct except Cynodonts that give rise to earliest true mammals.

Cenozoic: “The Age of Mammals”

Mesozoic (251 MYA): Dominated by dinosaurs, modern mammals (Therians) is only one of severallines of mammaliaformes

5. Cretaceuos (125 MYA): Therians diverge intoEutherians (placentals) and Metatherians (marsupials)

6. End of Cretaceous-Tertiary boundary (66 MYA): Extinction of dinosaurs, and radiation of mammals

Permian–Triassic extinction event90% species extinct

Ordovician–Silurian extinction eventsSecond largest /Marine life lostMovement of Gondwana

Cretaceous–Paleogene (K–Pg) extinction event3/4 plant and animal extinct

Triassic-Jurassic extinction eventLand and ocean / Asteroid

Late Devonian extinction eventMarine life lost / Sea level

Mammalian Characteristics Endothermic homeothermy: produces heat

metabolically instead of absorbing it fromenvironment, regulates body temp at astable level*

Lactogenic: produces milk to feed young Viviparous: live birth* Hirsute: epidermis has hair* Three Ear bone (Incus, Malleus, Stapes)

Other too....

Selected skeletal features -cranial

What are the major changes in the skull?

How about hearing?

What are the improvement

Selected skeletal features -cranial

• Stronger jaw structure(single bony element in lower jaw = dentary; stronger, simpler jaw articulation between dentary andsquamosal bones)

• Improved hearing(3 ear ossicles = malleus, incus,stapes; tympanic bone supportstympanic membrane)

The homologous bones in mammalsReptile Mammal

Middle ear Stapes StapesQuadrate Incus

Lower jaw Articular MalleusAngular Ectotympanic

Secondary hard palate(more efficient air flow,allows breathing whileeating, suckling)

Skeletal - cranial

Specialized teeth (restricted tomargin of jaw, diphyodont,thecodont, generally heterodontand multicuspidate; process foodbetter = improved mastication)

1. Diphyodont: 2 generations (not always true!) 1 set of Deciduous and 1 set of permanent teeth

2. Heterodont: division of labour, specialized morphologies (not always true!)

3. Thecodont: sunk in sockets

Skeletal - cranial

Mammalian teeth:

Loxodonta(African elephant)

Tusks: incisors or canines?

Odobenus (walrus)

Babyrousa (babirusa)Moschus (musk deer)

• 5 zones of vertebralcolumn (cervical, thoracic, lumbar, sacral, caudal)

• Double occipitalcondyles plus atlas/axis complex (reduces stresson spinal column whilepermitting flexion and extension [atlas] androtation [axis], finer control of headmovements)

Selected skeletal features - axial

Axial skeleton• Thoracic ribs only

(no cervical orlumbar ribs; lighter skeleton, moreflexible movement ofspine)

• Zygapophyses onvertebrae (strengthensvertebral columnwhile permittingflexion/extensionand torque)

Selected skeletal features -appendicular

• Epiphyses on long bones(allows development of well-formed joints)

• General trend to decreasecomplexity and number ofbones in various functional units of skeleton (Esp. pectoral girdleand pelvis; less energy requiredfor development and maintenance of skeleton, lighterframe for quicker movement)

• 4-chambered heart (improved circulation, betteroxygen delivery)

• Enucleated red blood cells (carry moreoxygen)

• Highest concentration of mitochondria(supports higher metabolic rate)

• Large complex lungs, muscular diaphragm (enhanced breathing, gas exchange rate)

Selected non-skeletalcharacteristics

Selected non-skeletalcharacteristics• Masseter muscles associated

with jaw (new set of muscles inmammals for greater control ofjaw movements)

• Enlarged neopallium(cerebral hemispheres ofbrain, greater coordinationand learning ability = larger, more complexbrain)

Sustained energy production...all of these features did not evolve independently!

More or less related to a general trend for a greater capacity for sustained energy production (including acquisition and processing), which is essential for endothermic homeothermy at high body temperatures, and high levels of activity.

Mammals need about 10X more energy (food andoxygen) than a reptile of the same mass.