Mammalian characteristics and specializations

Chapter 20 and 21

Features shared by all mammalsFeatures shared by all mammals

• LactationLactation– Mammary glands are absent in male

marsupialsmarsupials– Present and potentially functional in

monotremes and placentals (human males inmonotremes and placentals (human males in some circumstances, a type of fruit bat)

– Only therians have nipplesy pp

Features shared by all mammalsFeatures shared by all mammals

• Skeletomuscular systemSkeletomuscular system– Epiphyses on the long bones (determinate

growth)growth)• Cranial features

Completely enclosed brain case zygomatic– Completely enclosed brain case, zygomatic arch, heterodont dentition, diphyodonty (two sets of dentitionsets of dentition

Features shared by all mammalsFeatures shared by all mammals

• Postcranial features– Upright posture with limbs under the body– Crurotarsal joint (between the Tibia and astragalus), with a heal

projection (Calcaneum) for muscle attachmentp j ( )– Ilium is rod shaped and directed forward, pubis and ischium are

short– 7 cervical vertebrae with atlas and axis are first two (additional7 cervical vertebrae with atlas and axis are first two (additional

rotation points)

Features shared by all mammalsFeatures shared by all mammals

• IntegumentIntegument– Hair – three main functions: insulation,

camouflage communication sensationcamouflage, communication, sensation• Vibrissae (whiskers) for sensation

– Insulation is a function of the density of hairInsulation is a function of the density of hair and its length

• Length can be adjusted with the erector pili muscle which pulls the hairs erect and shows noticeable bumps (goose pimples) on humans

Integument i dcontinued

• Glandular structures– Eccrine, sebaceous, apocrine glands

• Sebaceous and apocrine are associated with hair follicles– Eccrine usually restricted to soles of feet or other surfaces that make

contact but are all over the body in humans– Sebaceous glands produce oily secretions (lubricates and waterproofs)

Apocrine glands have restricted distributions and mainly used for– Apocrine glands have restricted distributions and mainly used for chemical communication but for evaporative cooling in ungulates, also produce ear wax

– Skunks have modified apocrine glands, cats have apocrine glands on f h difi d b l d t k bj tface, some have modified sebaceous glands to mark objects

Integument continuedIntegument continued

• Claws nails hooves hornsClaws, nails, hooves, horns– Accumulations of keratin that

protect the terminal phalanxprotect the terminal phalanx– Ungulate horns have bone

covered by keratinized sheathcovered by keratinized sheath– Rhinocerous horn is

completely made of keratin p yfibers

Internal AnatomyInternal Anatomy

• Adipose tissue – energy store insulationAdipose tissue energy store, insulation (marine mammals)

Brown fat generates heat and can break– Brown fat – generates heat and can break down lipids and glucose, present in newborn mammals and adults that hibernate

• Cardiovascular system – erythrocytes (RBCs) lack nuclei(RBCs) lack nuclei– Complete ventricular septum and single

systemic archsystemic arch

Internal anatomyInternal anatomy

• Respiratory system – lobed lungs theRespiratory system lobed lungs, the sites of gas exchange are aveoli (tiny thin walled chamberswalled chambers– Diaphragm – divides the pleuroperitoneal

cavity into a peritoneal cavity (surrounds thecavity into a peritoneal cavity (surrounds the viscera) and paired pleural cavities (surround the lungs)

• Urogenital system– Separate openings for the urogenital andSeparate openings for the urogenital and

alimentary systems

Sensory systemsSensory systems

• Olfaction – olfactory receptors located on theOlfaction olfactory receptors located on the nasoturbinal and ethmoturbinal bones, the olfactory bulb is prominent in most mammals (not primates or whales)

• Vision – most mammals evolved as nocturnal animals, therefore sensitivity to light was most important. Retinas are composed mostly of rodcells acute vision possible in the fovea which iscells, acute vision possible in the fovea which is made up of cones, primates are unique in having good color visionhaving good color vision.

Sensory systemsSensory systems• Hearing – complex middle ear with

three bony ossicles (stapes, malleus, incus)– Stapes – derived from the old

hyomandibular – Malleus – derived from the articular– Incus – derived from the quadrate

• These small bones were first found to be derived from the ancestral jaw bones through embryological d l t d l t t d i thdevelopment and later traced in the fossil record

• The ancestral jaw joint is retained in th ti l ti b t th M ll

A) Cynodont B) DidelphisC) Embryonic mammal

the articulation between the Malleus and Incus

Hearing continuedHearing continued

• Other features that increase auditoryOther features that increase auditory acuity

Long cochlea (so long that it must be coiled)– Long cochlea (so long that it must be coiled)– Pinna (external ear) (cetaceans use the lower

jaw to channel sounds to the inner ear butjaw to channel sounds to the inner ear, but that is through a different medium)

Mammal groupsMammal groups

• MonotremesMonotremes

MonotremesMonotremes

• FeaturesFeatures– Lay eggs

No nipples have mammary hairs– No nipples, have mammary hairs– Shorter cochlea (<2.5 coils)

No pinna– No pinna– Cloaca

L k t th– Lack teeth– Male platypus have a spur on the hind leg that

i tt h d t l dis attached to a venom gland

Metatherians(Marsupials)

Marsupial featuresMarsupial features

• Have initial choriovitelline placenta haveHave initial choriovitelline placenta, have short gestation and the baby is born at an undeveloped stateundeveloped state.– They continue development in the pouch

Different tooth formula– Different tooth formula – Usually lack auditory bulla

Epipubic bones– Epipubic bones

Cranial differencesCranial differences

Eutherians (Placentals)Eutherians (Placentals)

• Have both choriovitelline andHave both choriovitelline and chorioallantoic placenta

• Auditory bulla• Auditory bulla• Most placentals replace all teeth except

l i l l l th l tmolars marsupials only replace the last premolar

• Some placentals have a postorbital bar

ReproductionReproduction

• Embryonic diapause – theEmbryonic diapause the ability to maintain an embryo in suspended animation priorin suspended animation prior to implantation. Allows females to space litters outfemales to space litters out and give birth at optimal times of year Well developed inof year. Well developed in Kangaroos but seen in other mammals including placentalsmammals including placentals

Reproductive specializationsReproductive specializations

• Mole RatsMole Rats– Eusocial – like ants and bees

Have one reproductive female in a colony of– Have one reproductive female in a colony of up to 40

– Castes – small frequent workers– Castes – small frequent workers• Small infrequent workers• Larger nonworkers that care for youngLarger nonworkers that care for young• Males and females equally rep.• Only large males breed queen

• Spotted hyenas –masculinized p ygenitalia– Elongated clitoris– Labia fused and look similar

to a scrotum• Have high levels of male• Have high levels of male

hormones• Use genetalia for behavioral

displays

DentitionDentition• Bunodont – rounded cusps,

omnivores (a)• Lophodont – lophs with

enamel ridges and exposed dentine (g)

• Hypsodont – high crowned, division between crown and root not as in –

• Brachydont – low crowned• Selenodont – crescent lobes

(f)• Hypselodont – ever growing • Carnassial pair – P4 on topCarnassial pair P4 on top

M1 on bottom

Special tooth adaptationsSpecial tooth adaptations

• Myrmecophagy – ant and termite eatingMyrmecophagy ant and termite eating– Elongated snoutn no or reduced teeth

Toothed aquatic mammals• Toothed aquatic mammals– Homodont dentition many pointy teeth

• Baleen whales – have baleen instead of teeth to strain food

Digestion for herbivoresg• Plant material is difficult to digest. Two main digestive

tract types for this process, both use symbiotic microoganisms to produce cellulase enzymesmicrooganisms to produce cellulase enzymes

• Hindgut and Foregut fermentation

Hindgut fermentersHindgut fermenters

• Need to chew thoroughly and haveNeed to chew thoroughly and have enlarged large intestine and cecum

• Some small rodents and rabbits ferment the food largely in the cecum and rely on coprophagy

Foregut fermentersForegut fermenters• 4 chambered stomach

– Rumen, Reticulum, Omasum, Abomasum

– Digestion occurs in the gAbomasum

– Microorganisms break down cellulose in the Rumen and Reticulum and the material is returned back to the mouth as a bolus to be rechewed (chewing the cud), only minute particles will pass through the opening to the omasum.

LocomotionLocomotion• Cursorial – running

– Limbs are elongated forLimbs are elongated for longer strides

• Fossorial – burrowing– Limbs are short for more

power

Adaptations to life in waterAdaptations to life in water