mammalian characteristics:

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Mammalian characteristics:. Cranial (skull) features. Lizards & snakes Crocodiles Dinosaurs & birds. Mammals & reptile-like mammals. Turtles. Anapsida. Diapsida. Amphibians. Saurapsida. Synapsida. -ca. 320 mya. Amniota. -evolution of cleidoic (shelled) egg; - PowerPoint PPT Presentation


  • Mammalian characteristics: Cranial (skull) features

  • AnapsidaDiapsidaSynapsidaSaurapsidaTurtlesLizards & snakesCrocodilesDinosaurs & birdsMammals &reptile-like mammalsAmniota-evolution of cleidoic (shelled) egg; ca. 350 mya (late Paleozoic)Amphibians-ca. 320 mya

  • -apsid conditionsAnapsidSynapsidDiapsidPelycosaurModern mammal

  • Double occipitalcondyle:

    greater range of motion

  • PelycosaurTherapsidsSingle bone in mandible: dentary

  • post-dentary bonesDentary-squamosal articulation

  • Reptile:Mammal:stapesstapesstapes(incus)incusmalleus(malleus)(stapes)(incus)(malleus)3 inner ear ossicles

  • Tympanic bone (="annulus" or "tympanic ring")tenrec skull; no auditory bulla

  • Mammalian characteristics:Dental features

  • Heterodont dentition

  • Diphyodonty (vs. polyphyodonty)

  • Matched shear surface on upper & lower teeth

  • Complex occlusal surface on cheeckteeth

  • Secondary palate

  • Mammalian characteristics:Postcranial (skeletal) features

  • Modified limbs and pelvic girdleReptile-likeMammal-likeSprawling postureUpright postureLateral gaitFore-aft gaitPoorly developed calcaneusWell-developed calcaneuscalcaneusfibulafemurtibiapelvicgirdlecalcaneusfibulatibiafemurastragalusastragalus

  • Indeterminite growth vs. Determinite growth Long-bone epiphyses

  • Stabilized and regionally specialized vertebral column

  • AtlasAtlasAxisDorsal-ventralflexionRotation

  • Simplified skeleton

  • Mammalian characteristics:Soft anatomy, sensory,and physiological features

  • Hair (=fur or pelage)

  • Mammal hair:invaginationBird feather: evagination

  • cuticlecortex: pigmentmedulla: dead cells containing air; variably present.Hair structure

  • New PNAS article on originof hair: PNAS November 25, 2008 vol. 105 no. 47 18419-18423

  • Hair function: tactile perception (vibrissae)

  • Hair function: locomotory specializations

  • Hair function: defense

  • Hair function: aggression and display

  • Hair function: communication

  • Mammary glands (=mammae), structural variationMonotremeNipples(most mammals)Teat(e.g., cows)Skin glands

  • 4-chambered heartMammal Crocodyle

  • Enucleated blood cellsMuscular diaphragm

  • Improved olfaction

  • Endothermy---Body temperature regulated internally.

    Homeothermy---Body temperature maintained within a narrow range.

  • An integrated package?Natural selection favored increasingly efficient use of energy

    Endothermy facilitated nocturnal activity

    Endothermy is especially difficult for young

    Diphyodonty, lactation, social behavior

  • Did these all appear simultaneously????

    How do we know???

  • Occipital condylesDentary, ear ossiclesDentitionUpright postureDeterminite growth/ephiphysesSimplification of skeletonVertebral columnMammary glands4-chambered heartEnucleated red blood cellsDiaphragmEndothermy/homeothermyOlfactionHairFossil evidence?

  • Occipital condylesDentary, ear ossiclesDentitionUpright postureDeterminite growth/ephiphysesSimplification of skeletonVertebral columnMammary glands4-chambered heartEnucleated red blood cellsDiaphragmEndothermy/homeothermy(??)Olfaction (??)HairFossil evidence?

    *Three major amniote lineages recognized based on the number of holes in the temporal region of the skull.*Why form holes? Debated, and no consensus, but some hypotheses. 1) reduces the amount of bone, skull is lighter. 2) By allowing muscle attachment higher up on the skull, longer muscles and wider GAPE. 3) Muscles bulge when contracted, so holes necessary to allow contraction.

    temporal fenestra has been drastically modified in mammals by ventral processes of the frontal and the parietal that occlude the temporal fenestra. The location of the old fenestra is still visible between the zygomatic arch, the orbit, and the dorsal part of the skull, but it is no longer a hole in the skull(from*Reduces tention on the spinal cord when head is moved up and down, allows finer control of headmovements. BUT, at the cost of side-to-side (lateral) movement.*single dentary bone:Gradual increase in relative size over time. "Dentary" is now the only bone in the mandible of living mammals. All other amniotes have >1 bone towards back of jaw. *a DEFINING characteristic of mammals.

    Primitively, b/w quadrate & articular.

    In reptiles and mammal-like synapsids, Quadrate-Articular joint served dual purpose: jaw articulation and sound transmission (to tympanic membrans)*Derived from postdentary bones.

    *Also called "annulus," "Tympanic ring," Supports tympanic membrane.

    Originated from the reflected lamina of angular bone.

    Development of a bony covering (auditory bulla) is variably present in mammals and can be composed of several different bones in different combinations.*complex dentition---

    Heterodonty (differentiated teeth, form reflects diff. function, vs. peg-like "homodonty", *Diphyodont (only 2 sets of teeth in lifetime, vs. many).


    Some species (e.g., toothed whales) are MONOphyodont, only 1 set of teeth.Others replace their deciduous dentition before they're even born (e.g., shrews).Marsupials only replace 1 tooth.*This is one reason NOT to continually replace teeth---you lose the precision of the occlusion. Trade-off: permanent teeth, if knocked out, won't be replaced.*composed of maxillary and palatine bones (crocs, some other tetrapods have, but different bones).

    allows for more efficient airflow and simultaneous breathing and chewing.

    May also facilitate suckling.*modified limbs and pelvic girdle (less splayed, more energetically efficient).

    Refer back to HEARING---head no longer on ground*limited growth (=determinate growth), vs. indeterminate growth NOT IN TEXTBOOK.

    long bone epiphysesNeed stronger limb bones; epiphyses *Atlas & axis---improved head mobility*At the same time, much of the skull and postcranial skeleton in mammals has become more SIMPLIFIED. One myth about evolution is that theres progress, and some people define progress incorrectly as more complex. NOT THE CASE FOR MAMMALS.*HAIR is one of the few characteristics unequivocally unique and universal in mammals.*ca. 85% of E in food goes towards body T regulation; don't want to waste!*NOT homologous. Feathers are homologous to reptile scales.

    Development---fundamentally diff. from scales & feathers (Invag. vs. evag).

    Feathers develope from both the dermis and epidermis; hair follicles of mammals develop from within the epidermis.*Why did hair evolve? Most believe for insulation and thermoregulation. ca. 85% of E in food goes towards body T regulation; don't want to waste! But hair serves several other functions in modern mammals...**male emperor tamarinNot just visual, but audio communication.**Probably evolved from sweat glands.Not sure when they evolved, but probably related to milk teeth.

    Nipples: numerous small glandular ducts exit from the tip of a small, fleshy projection (nipple).

    Teats: numerous ductes drain into common reservoir or cistern that opens via a single duct.

    Milk, teats (vary from 2 prs to 20 in some marusps (in pouch) to 28 or more in tenrecs). Location varies, too; Manatees have axillary (near armpit); humans are pectoral; zebras & horses, abdominal.

    Both sexes have, but don't develop in males beyond puberty.*Some don't consider what monotremes have to be truly modified mammary glands, but rather slightly modified sweat glands.No teats in monotremes; secreted into depressions, licked off fur by young.

    WHALES actually forcefully extrude into calf's mouth since no lips!*Acts as DOUBLE-PUMP: right side receives venous blood from body, pumps to lungs. Left side receives oxygenated blood from lungs and pumps to body.

    Oxygenated and NONoxygenated blood kept separate.

    Reptiles have 3 chambered: ventricles only partially divided ('cept crocs)*w/funtional left aortic arch (vs. birds, w/4-chambered heart: RIGHT aortic arch is functional; reptiles have 3-chambered.)*(enhances oxygen-carrying capacity of cells).Nuclei are extruded from cells when they mature.

    separating thoracic and abdominal cavities.Some other verts have membrane-like septum, but only mammals have MUSCULAR diaphram*Including enlarged olfactory bulbs, extensive and complex mucous membranes for chemoreception, and other associated features.*ENDO VS. HOMEO (FORMER NOT NECESSARY FOR LATTER...

    THERMAL INERTIA...As LENGTH increases, AREA increases as length SQUARED

    Mammals need ca. 10 times amount of food and oxygen that reptiles of similar size need just to maintain body temperature.

    (more in later chapter/lecture)*