Vertebrate Zoology Final

Adaptive Changes in Primitive Birds

• Fusion of pelvis, sacrum

  • Helps absorb shock when landing

• Shortened tail (pygostyle)

• Opposable hind toe (perching)

• Flexible wrist (could fold wing against body)

• Shortened thorax

• Keeled sternum (larger flight muscles)

• Alula (= small cluster of feathers at wrist that aid in maneuverability)

• Teeth replaced with horny beak - occurred several times independently

• Some secondarily evolved flightlessness

Birds in the late Cretaceous

• Birds fared poorly during the K-T Extinction, with most groups going extinct

  • The few survivors diversified into all modern groups

  • Modern birds (Neornithes) probably appeared in the late Cretaceous

Feathers and their origin

• The single unique feature that distinguishes birds from all other living vertebrates

  • Origin of Feathers

    • Original function probably insulation, later modified for display, then for flight

    • Derived from scales - early development of reptile scale & bird feather identical

    • Made primarily of beta keratin, as is reptile scale and mammalian hair

Two primary functions of feathers

• Insulation - traps air space

  • Birds are endotherms

    • Maintenance of a high body temperature

    • Advantages: increased power and endurance

• Light-weight air foils for flight

Secondary functions of feathers

• Coloration

  • Social communication

  • Concealment from predators

  • Radiate heat

  • Pigments and structural colors

• Water repellency

  • Preening (spreading oil on feathers to maintain water repellency)

  • Tightly packed barbs

  • Powder down

• Display

• Sound Production or Muffling

Types of feathers

Contour feathers (calamus (quill), rachis (shaft), and vane consisting of barbs, both proximal and distal barbules (with hooklets))

• The calamus is a hollow structure with a superior and an inferior umbilicus embedded in a cutaneous follicle. The inferior umbilicus is continuous with the growing tissue of the dermal papilla.

• During growth the calamus is filled with mass of spongy tissue that dies away as the feather matures to leave a hollow structure. The dermal papilla remains as a bud of living tissue that will replace the feather after it is shed at moulting.

Flight feathers - large feathers of the wing and tail. Flight feathers of the wing are collectively known as the remiges, and are separated into three groups

• The primaries attach to the metacarpal (wrist) and phalangeal (finger) bones at the far end of the wing and are responsible for forward thrust. There are usually 10 primaries and they are numbered from the inside out.

• The secondaries attach to the ulna, a bone in the middle of the wing, and are necessary to supply "lift." They are also used in courtship displays. There are usually 10-14 secondaries and they are numbered from the outside in.

• The flight feathers closest to the body are sometimes called tertiaries

• The tail feathers, called retrices, act as brakes and a rudder, controlling the orientation of the flight. Most birds have 12 tail feathers.

• The bases of the flight feathers are covered with smaller contour feathers called coverts. There are several layers of coverts on the wing. Coverts also cover the ear.

Airfoils

Streamlined in cross section, with a slightly concave (cambered) lower surface

Air moving over the top of the wing travels faster than the air beneath the wing, causing lower pressure on the upper side, thus providing lift

Bernouli’s effect

• In calm air, the molecules are moving randomly in all directions. However, when air begins to move, most (but not all) molecules are moving in the same direction. The faster the air moves, the greater the number of air molecules moving in the same direction.

• So, air moving a bit slower will have more molecules moving in other directions. In the case of a wing, because air under the wing is moving a bit slower than air over the wing, more air molecules will be striking the bottom of the wing than will be striking the top of the wing.

• Creates lift

Newton’s Third Law and Wings

• As the wing moves through the air, the lower surface of the wing deflects some of the air downward

• As Newton's Third Law of Motion explains, an additional force is generated.

  • The deflected airflow underneath the wing is the action

  • The reaction is that the wing moves in the opposite direction (in this case, upwards)

  • This means that the development of low pressure above the wing (Bernoulli's Effect) and the wing's reaction to the deflected air underneath it (Newton's third Law) both contribute to the total lift force generated.

Stalling

• When the curvature over the top becomes greater by increasing the angle of attack, the air moves even faster over the top of the wing and more lift is generated.

  • Eventually, however, if the angle of attack becomes too great, the flow separates off the wing and less lift is generated. The result is stalling.

    • If the angle of attack is too great, air flow over the top of the wing may become more turbulent & the result is less lift.

• Birds also tend to stall at low speeds because slower moving air may not move smoothly over the wing

  • At low speeds (such as during take-off and landing), birds can maintain smooth air flow over the wing (and, therefore, maintain lift) by elevating the alula

    • The alula is formed by feathers (usually 3 or 4) attached to the first digit

Flight muscles

• Pectoralis major for the downstroke

  • Makes up 10-20% of bird’s body weight

• Supracoracoideus (with tendon) for the upstroke (wraps around coracoid and scapula)

Types of Bird Wings

Elliptical

• Short, broad elliptical wings with large wing slots at tips and distinct alula at midwing

• Low aspect ratio (ratio of length to width), high camber; birds that must maneuver in forested habitats, such as flycatchers, sparrows, warblers, doves, woodpeckers, and magpies

High aspect ratio

• Long, slender wings with no wing slots and pointed tips

• High-speed

• No alula

• Outer half sweeps back relatively sharply

• Birds that feed in flight, such as swallows and hummingbirds, or that make long migrations, such as sandpipers and gulls

Dynamic Soaring

• Long, narrow wings with no wing slots; only slightly sweeping back near outer third of the wing

• High-aspect ratio

• Oceanic soaring birds birds that include albatrosses and frigate birds

• Suited for high speed, high lift, and dynamic soaring.

• Possible only when there is a pronounced vertical wind gradient; friction with ocean slows the lower 15 m, constant high winds in the roaring 40's

  • Where most albatrosses and petrels are found

High-lift

• Static soaring - glide in air masses that are rising faster than they are sinking

• Relatively long, broad wings with large wing slots at tips and distinct alula at midwing, and pronounced camber, all of which provide high lift at low speed

• Many of these birds (vultures, hawks, eagles, and owls) are land-soarers that require

  • The ability to carry heavy loads (e.g. prey) provided by high-lift aspect

  • Maneuverability over terrestrial habitats (also provided by the broad, slotted wings)

• Also found in storks, pelicans

Skeletal modifications for flight

• Pneumatic bones - thin, hollow bones (filled with air)

  • Feathers may weigh more than skeleton

• Loss of teeth and heavy jaws; replaced by horny beak, which is lighter 

• Specialization of forearm bones to support flight feathers

• Loss of tail - pygostyle (fused 5 remaining caudal vertebrae; platform for tail feathers)

• Furcula - fused clavicles, only in birds and theropods; "wishbone” provides extra bracing for shoulder girdle

• Synsacrum - fused pelvis and 23+ vertebrae

  • Pelvic bones are fused with 23+ lumbar and sacral vertebrae. Composed of the last thoracic vertebra, the lumbars, sacrals, and anterior caudals 

  • This is an adaptation for protecting the vertebral column and pelvic girdle from the impact of landing.

• Bipedal (walking, hopping, perching)

Vocalization in birds

Syrinx - the vocal organ of a bird, consisting of thin vibrating muscles at or close to the division of the trachea into the bronchi. According to one model of syrinx function, sound is generated when:

• Contraction of muscles (thoracic & abdominal) force air from air sacs through the bronchi and syrinx

• The air molecules vibrate as they pass through the narrow passageways between the external labia and the internal tympaniform membranes

Synapomorphies of Aves

• Flight feathers

• Furcula (fused clavicles) present, as in modern birds

• Expanded sternum absent

• Thecodont teeth (during development; absent as adults)

• Pygostyle

• “Hand” reduced to 3 digits

• Capable of gliding or powered flight as evidenced from the structure of the feathers and the forearm

Paleognathae

These species have small wings, sternum without a keel (e.g., flightless), and free caudal vertebrae (although very short). Some examples include:

• Order Struthioniformes: Ostriches

• Order Rheiformes: Rheas

• Order Dinornithiformes: Moas; largest bird known. Found only in New Zealand. Reached up to 3 m and 450 kg. This group went extinct about 300 years ago.

Galloanserae

Order Anseriformes – ducks, geese, relatives

• Semiaquatic lifestyle. Beak broadened with many tactile nerve endings for tasting food. Some species with many filter ridges or “teeth” along margins of bill to filter food particles.

• Short legs and webbed feet. Many of these species are migratory.

• Body is well supplied with down feathers and oily feathers; well developed preen gland. These birds have nidifugous young (leave the nest a short time after hatching).

Order Galliformes – fowl, quail, etc.

• All are hen-like birds with short and rounded beaks; all are vegetarians; strong feet used for scratching and digging and running

• Gregarious species that often have distinct sexual dimorphism; most nest on the ground and often have complex reproductive behaviors.

• These birds do not fly that much (but can); they spend most of their time running and walking.

Apodiformes

Order Apodiformes

• Hummingbirds and swifts.

• Usually small birds with short legs and wings; weakly developed bill; hummingbirds with long tubular bill with a brushy tongue to assist in extracting nectar; metabolic rate exceedingly high; many of these small birds have to aestivate between feedings in cooler weather and at night.

Columbiformes

• Pigeons and doves.

• Generally short and slender birds; vegetarians; short neck and legs; excellent flyers and often used for homing.

• In these species the “crop” or “gizzard” produces a milky substance to feed their young.

  • Crop is characteristic of all birds; it is an expansion and heavily muscularized section of the esophagus used for the storage of food and assists in the mechanical breakdown of food.

  • Birds often eat gravel that is stored in the crop to assist in this mechanical breakdown. In dinosaurs these were referred to as gastroliths.

Charadriformes

• Gulls, turns, auks, sandpipers, snipes, woodcocks, killdeer, and many others.

• Called shorebirds, for the most part, these species are adapted to a semiaquatic lifestyle.

• These species are colonial, strong flyers, and many are migratory. They live along ocean or freshwater shores. Nest on the ground in very simple nests

Psittaciformes

• Parrots

• Zygodactyl feet (two toes pointed forward and two pointed backwards).

Falconiformes

• Hawks, eagles, falcons, kites, caracara, New World vultures.

• All are birds of prey - carnivores and carrion eaters.

  • Strong bill that is often hooked and with sharp edges.

  • Feet with sharp and curved talons.

  • These species have an opposable hind toe for grasping.

  • These birds have nidicolous young (remain in the nest after hatching until grown or nearly grown).

Strigiformes

• Owls

• Nocturnal predators

• Large rounded heads with large eyes seated in a feathered disk

• Large external ear openings with feathery flaps to assist in directing sound into their ears; right and left ear openings differ in size and shape; this characteristic, in addition to the sound funneling effect of the facial disk, enhances hearing efficiency 

• Soft fluffy plumage that is modified for silent flight 

• No crop - undigested prey regurgitated as pellets.

Piciformes

• Woodpeckers, toucans, New World Barbets

• Long and modified bills; long tongues used for feeding in small cavities cleared out with the bill 

• Cranium is heavily ossified where the bill attaches to protect the brain from the pounding activities

Passeriformes

• Usually referred to as “perching birds”; ca. 5,300 species (out of ca. 10,000 extant birds).

  • Feet are adapted for perching, no webbing; anisodactyl feet (three toes directed anteriorly and one posteriorly with all four toes on the same plane)

  • All produce complex songs and possess a highly developed syrinx where the songs are produced

• Suboscines: largely tropical group of about 1,000 species that reaches its greatest diversity in South America; most suboscines are thought to sing “innate” songs

  • Woodcreepers, antbirds, tyrant flycatchers, bowerbirds, and manakins

• Oscines (Passeri) - includes about 4,000 species and are what many laypersons refer to as “songbirds”; they are worldwide in distribution and are distinguished from suboscines by a complex voice box (syrinx) and song learning capacity.

Gaviiformes

• Loons

• Large, compact aquatic birds that are highly modified for foot-propelled diving. They are characterized by long, sleek bodies, long necks, sharply pointed bills, and palmately webbed toes.

Procellariiformes

• Tube-noses: Albatrosses, shearwaters and petrels.

• The order forms a large group of highly pelagic birds found primarily in the Southern Hemisphere.

• Large wingspan (3.5 m), long narrow wings

• Long, tubular nostrils - nostrils extend onto the bill in short tubes

• Have well-developed salt glands that aid in water balance (they can drink salt water)

• Individuals of most species have vast feeding ranges.

• All lay a single white egg, and all but the albatrosses nest in underground burrows. Incubation and fledging periods are long. The adults feed their nestlings a clear yellow stomach oil, which may be vomited up when disturbed.

Pelecaniformes

• Pelicans, gannets, boobies, cormorants, anhingas 

• Pelecaniformes are the only birds with totipalmately webbed feet (all four toes webbed) 

• Generally large birds with long wings, short legs, and bare gular pouches (highly modified in pelicans)

• Nidicolous (remaining in the nest after hatching until grown or nearly grown), altricial (helpless, naked, and blind when hatched) young are fed by regurgitation by both sexes

Ciconiiformes

• Herons, flamingos, storks, egrets, New World vultures and condors.

• Generally large aquatic birds with broad, rounded wings and (except for the New World Vultures) long legs

• Legs with counter current exchange (rete mirabile) system to concentrate body heat in upper legs and body

• All are carnivorous and/or scavengers

Avian Monogamy

• Pair bond with a single member of opposite sex; pair bonds may last for a single breeding attempt, a breeding season, or many breeding seasons

• Approx. 92% of all bird species

• Occurs when:

  • Male participation is essential for successfully raising young

  • Males cannot monopolize resources necessary for supporting extra mates

Polygyny

• Male mates with several females (but each female mates with only one male)

• Parental care usually by female

• Only 2% of all birds

• Why should a female pair with an already mated male while there are still unmated males available? This question is addressed by the Polygyny Threshold Model

  • Predictions of the PTM

    • A male's territory quality will be correlated with his mating success

    • Polygyny should be more common in patchy environments (where there is more variation in territory quality)

Polyandry

• Female associates with several males

• Typically involves sex-role reversal (females larger & more brightly colored); parental care typically by males (males incubate eggs & care for young)

• Fewer than 1% of all birds; evolved primarily in two orders of birds - Gruiformes (rails and cranes) and Charadriiformes (shorebirds and gulls)

• Key factor in evolution of polyandry may be the fixed, fouregg clutch of shorebirds

  • With a fixed clutch, the only way females can increase their reproductive success (assuming favorable conditions) is to lay more clutches

Promiscuity

• Indiscriminate sexual relationships, usually of brief duration

• The male's investment in offspring is limited to sperm, and the female raises the young alone.

  • Male hummingbirds, for instance, court females for a short time, mate, and then resume their quest for other females.

  • Males of many grouse species and some shorebirds display on leks (mating grounds used each year) to attract females that depart immediately after mating. The males may subsequently mate with additional females.

• Presumably promiscuous mating systems can evolve only where the advantage of the male remaining with the female to help in raising the young is negligible.

• About 6% of all birds

Brood parasitism

Intraspecific brood parasitism

• Most prevalent among waterfowl but also reported in grebes, gulls, pigeons & doves, & songbirds (e.g., Cliff Swallows, House Sparrows, & European Starlings) 

• Increases when there is a shortage of nest sites & when population density is high

• May reduce host fitness (if host responds by laying fewer eggs) 

• May be first step in evolution of obligatory brood parasitism [with occasional (or facultative) inter-specific brood parasitism the next step]

Obligate brood parasites

• always lay their eggs in nests of other birds

• behavior has evolved independently at least 7 times

• cowbirds (such as the Brown-headed Cowbird) & old world cuckoos are best known

Adaptations of brood parasites

• egg mimicry

• hard shelled eggs & destruction/removal of host eggs

• relatively small eggs

• baby brood parasites may dispose of competitors

Effects of brood parasites on their hosts

• may greatly reduce reproductive success, particularly for relatively small hosts

• large hosts (e.g., Northern Cardinals) suffer some reduction in reproductive success (because female cowbirds may remove eggs) but are usually able to raise their remaining young to nest leaving

Host responses to brood parasites

• Majority of cowbird hosts accept parasitic egg with no defensive response

• Some potential hosts actively defend nests against cowbirds, desert parasitized nests, bury cowbird eggs under a new nest floor, or eject cowbird eggs from parasitized nests

• Much attention has recently focused on the effects of cowbird parasitism on neotropical migrants

Legumes

New food source that helped mammals grow in size

Early Synapsid Locomotion

• Early synapsids had a sprawling posture and a small brain, like most early tetrapods 

  • The parasagittal gait characteristic of most mammals appeared gradually because some therapsids were apparently capable of sprawling and parasagittal gait, and this character may have appeared in the hind limb before the fore limb 

    • The limbs move parallel to the vertebral column, and are held relatively vertically

Synapsid characters

• Opening (temporal fenestra) on either side of the skull, located below the postorbital/squamosal suture

• Some features of synapsids represent the primitive condition in comparison to other amniotes

  • Glandular skin without the type of hard beta keratin typical of “reptiles” 

  • Inability to excrete uric acid

  • Absence of good color vision

Pelycosaurs

Sailback and non-sailback forms from the late Paleozoic

Paraphyletic group

The pelycosaurs exhibit the first substantial progress of crawling to running

• Required modification of the metabolism in the muscular system to provide the energy required for more strenuous activity

• The resulting change in the axial system brought about endothermy 

• Supporting this idea is the fact that as later pelycosaurs and later synapsids evolved, the surface area of sail to body mass ratio decreased. 

  • This shows the trend of reduced need for outside thermoregulation, which would require an increased use of endothermy, an important characteristic today separating the reptiles and mammals

Therapsida characteristics

Marginal dentition: a single canine, very much larger than any other tooth. The post-canine teeth are smaller, uniform, and not markedly recurved. There are no pre-canines on the maxilla

• In Haptodus, the premaxillary teeth are unspecialized and form a graded series in size, increasing anteriorly.

• Tetraceratops has one large pair of premaxillary teeth, but the remainder are small and relatively uniform.

• Biarmosuchus has the mammal -like condition with small, uniform incisor - like teeth

Lower jaw 

• Haptodus - dentary is already a very large - perhaps the largest - element in the lower jaw.

• Although the dentary does become progressively larger over the course of the Mesozoic, the Permian evolution of the therapsid condition does not seem to involve growth of the dentary so much as a progressive restriction of the angular to the posterior portion of the jaw

Postcranial skeleton

• Pectoral and Pelvic girdles were less massive (since no longer using sprawling posture)

• Limbs more slender and carried under the body

• Feet become shorter but retain five digits

• Shoulder joint appears to have allowed more freedom of movement of the forelimb

Temporal fenestra set into a depression called the temporal fossa - results in larger volume of jaw musculature

Non-mammalian therapsids

• Various evolutionary lineages, including both carnivores and herbivores 

• Most were large animals; dominated the Permian land fauna

• Most diversity was in late Permian (260-245 mya) but some lineages survived to the end of the Triassic (ca. 208 mya)

• Cynodont Therapsids:

  • Means “dog-tooth”

  • Group of therapsids that is closest to mammals (sister lineage)

  • Shared characters with mammals

    • Loss of lumbar ribs; possibly had a diaphragm

    • Reduction or loss of all lower jaw bones but one (dentary) 

    • Zygomatic arch (cheekbone) bowed outwards

    • Fully developed secondary palate (allows breathing while eating/drinking)

      • Also warms and humidifies air that enters

    • Calcaneal heel (basically the type of heel you have, in which the calcaneus (heelbone) extends backwards to form a level arm for the calf muscle)

  • Collectively, these characters lead to increased efficiency of feeding and energy intake; associated with the development of endothermy.

  • Progressive reduction in body size

Origin of the mammalian inner ear bones

• In early synapsids, the lower jaw includes the toothbearing dentary in addition to several postdentary bones.

• In mammals, this set of postdentary bones has been entirely lost from the lower jaw, and the dentary has enlarged to assume to the exclusive role of lower jaw function

• In early synapsids, the articular (future malleus) resides at the back of the mandible and establishes lower jaw articulation with the quadrate (future incus). In early to later therapsids, these two bones become reduced, along with the postdentary bones, eventually moving out of the lower jaw and taking up a position in the middle ear (functional result = better hearing)

Mammal characters

• Hair and mammary glands - but some therapsids may have had these features as well; can’t tell from fossils

• Most mammals bear live young

  • But, there are still a few egg-laying mammals (platypus, echidna)

• Precise tooth occlusion with molars that fit together precisely

• Heterodont dentition (canines, molars, incisors), are socketted (thecodont dentition) and usually replaced once (diphyodont dentition)

• Single lower jawbone (dentary)

• Three middle ear bones; there is typically an external ear (pinna)

• No cervical ribs (neck ribs); head is on a flexible neck with typically seven cervical vertebrae

• The buccal cavity is enclosed laterally by cheeks and roofed by a false (secondary) palate that separates it from the nasal cavity (see slide 16)

• Limbs tend to vertical orientation

• Most long bones and vertebrae have epiphyses, bony caps separated from the main bone during growth by cartilage

• Four-chambered heart, giving rise to distinct systemic and pulmonary circulations 

• Thorax and abdomen are separated by a diaphragm

• Endothermy

• The egg is minute and develops in the uterus (except in monotremes). The young remain with the female and are fed with milk from mammary glands

Prototheria

The only prototheria to survive until now are the Monotremes – the duckbill platypus and two species of spiny anteaters (echidnas)

Monotremes probably split from the lineage leading to other mammals sometime in the Mesozoic

They retain many characters of their therapsid ancestors

• A complex pectoral girdle

• Laying of eggs rather than bearing live young limbs

• Oriented with humerus and femur held lateral to body

• Cloaca

• Modern monotremes lack teeth as adults; skull sutures are hard to see; the rostrum is elongate, beak-like, and covered by a leathery sheath; and lacrimal bones are absent

• Monotremes have several important mammalian characters

  • Fur, a four chambered heart, a single dentary bone, three middle ear bones, and the ability to lactate.

All male monotremes have spurs on their ankles. Poisonous in platypi

Prototheria Reproduction

• The eggs laid by monotremes are small and covered by a leathery shell

• The number of eggs laid is usually 1-3 and they are placed in the mother’s pouch

  • Large yolk, which is concentrated at one end of the egg

• Young hatch quickly and are very small

  • Have a milk tooth to break out of the egg

• Mammary glands are longitudinal depressions

Metatherian Characteristics

• In females, the reproductive tracts of marsupials are fully doubled

  • The right and left vaginae do not fuse to form a single body, as they do in all placentals, and birth takes place through a new median canal, the pseudovaginal canal

  • Right and left uteri also are unfused (varying degrees of fusion are found in placentals).

• In males, the penis, like the female vagina, is bifid or doubled. The scrotum lies in front of the penis instead of posterior to it.

• The egg is yolky and covered with albumen and a membrane, but has no shell. It is retained within the uterus of the female.

• The young are born at an early stage of development and, in most species, transfer to a marsupium enclosing distinct mammary teats.

• The heart, kidneys, and lungs are all barely functional; even the brain is at a very early ontogenetic stage. Most development takes place in the pouch.

• Lactation period is prolonged

Invasion by placentals is correlated with a decline in number and diversity of marsupials

Great American Faunal Interchange

• An example of the interplay between continental drift and dispersal: Biotic interchange occurs when two previously separate faunas come into contact, often resulting in enormous changes in biodiversity.

• 3 MYA when the isthmus of Panama arose, connecting N. & S. America

• Over the previous 50 Myr, many modern orders of mammals originated in N. America, Africa and Europe, but S. America did not have these forms, and evolved its own distinctive fauna (e.g., forms of marsupials, armadillos, sloths, anteaters, ungulates).

• This interchange resulted in a fairly large extinction of S. American forms, but very few N. American forms

  • There were more species from the North, and they apparently speciated more rapidly when they came south than the S. American spp. did in the north

  • N. American species may have lived a more "competitive" life in a larger continent with more species; the "arms race" may have progressed further in the North (?)

  • Environmental factors were also changing (drying) the landscape as the Andes were pushing up-maybe this helped open habitats for the N. American species (?)

Ameridelphia

Didelphimorphia

• Opossums

• Prehensile tail, hallux

Paucituberculata

• Rat opossums

• Female lacks a pouch

• Paired sperm in males

Australidelphia

Microbiotheria

• “Monito del monte”

• Prehensile tail

Dasyuromorphia

• Includes the now extinct Tasmanian Wolf

Notoryctemorphia

• Marsupial moles

• Astonishingly like Eutherian Goldenmoles

• Blind, no external ears, insectivores, spade-like claws

Peramelemorpha

• Bandicoots and bilbys

Diprotodontia

• Largest order of marsupials

• Syndactylous

• Diprotodont

• Wombat, koala, kangaroo, etc.

Eutheria characteristics

• Egg shell membrane lost

• Intrauterine gestation prolonged with suppression of estrous cycle

• Corpus callosum connects cerebral hemispheres

• Fusion of Mullerian ducts into a median vagina

• Penis simple (not bifid at tip)

Eutheria reproductive characteristics

• Matrotrophic viviparity

  • Mother provides all the nutrition to the young

• A highly differentiated trophoblast derived from extraembryonal ectoderm.

  • Trophoblast = the outermost layer of cells of the blastocyst that attaches the fertilized ovum to the uterine wall and serves as a nutritive pathway for the embryo. Also called trophoderm.

  • The trophoblast together with the inner mesodermal layer is called the Chorion.

• Chorion and Allantois form the complex chorioallantoic placenta of Eutherians

Functions of the trophoblast in Eutheria

• Immunobiological separation of mother and fetus

  • Prevents molecular rejection of embryo by maternal tissue 

  • Allows for a long gestation

• Attachment of the embryo

• Active and passive transport (gas exchange, nutritional, and excretory function)

Types of Eutherian Placentas

• Diffuse placentae

  • Horses, pigs, camels, lemurs, opossums, kangaroos, and whales

  • The chorionic sac meets the uterine endometrium over its entire surface

  • The villi of the chorion are distributed evenly throughout the surface of the chorion, and they extend into processes in the uterine endometrium

• Cotyledenary placentae

  • Ungulates such as cows, deer, goat, and giraffe

  • The villi clumped together into circular patches called cotyledons

  • The fetal cotyledon meets with maternal regions called caruncles to form the placentome where maternal-fetal exchanges take place

• Zonary placenta

  • Carnivora

  • Chorionic villi have aggregated to form a broad band that circles about the center of the chorion. Such zones may be complete circles (such as those in dogs and cats) or incomplete (such as those in bears and seals).

  • It is thought that zonary placentae form from diffuse placentae in which the villi at the ends regress, leaving only those in the center to function

  • At the edges of the zonary placenta is the hemophagous organ which is green. The color is due to the degradation of hemoglobin into bilirubin. This provides iron for the developing fetus

• Discoid placenta

  • Humans, mice, insectivores, rabbits, rats, and monkeys

  • Part of the chorion remains smooth, while the other part interacts with the endometrium to form the placenta

Eutherian reproduction stages

• Gestation – 20 days (some rodents) to 18-24 months (elephants)

• Parturition (birth)

  • Relaxin produced by uterus, placenta or ovaries -> causes reabsorption of ligaments of pubic symphysis in prep. for birth 

  • Oxytocin produced by pituitary-> contraction

  • Birth – fetal part of placenta is expelled as "afterbirth"

    • The afterbirth is consumed by most mammals, except whales (Cetacea)

• Development of young

  • Altricial young (most eutherians)

    • Young helpless and poorly developed at birth 

    • Remain in nest for considerable time (almost equal to gestation period)

  • Precocial young (some rodents, rabbits, artiodactyls, perissodactyls)

    • Well developed, eyes open, able to move about shortly after birth

    • Can soon follow mother

Afrotheria

• Macroscelidea

  • Elephant shrews

• Tubulidentata

  • Aardvarks

• Hyracoidea

  • Hyraxes

• Sirenia

  • Manatees and Dugongs

• Proboscidea

  • Elephants, mastodons, mammoths

Xenartha

• Cingulara

  • Armadillos

• Pilosa

  • Sloths and anteaters

Glires

• Lagomorpha

  • Hares, rabbits, pikas

  • Lagomorphs (rabbits) differ from rodents in having two sets of incisors per jaw, as well as having unique skull and tooth morphology.

  • Coprophagy

    • Most fecal matter is eaten and digested again

      • Allows more nutrients to be absorbed from food

• Rodentia

  • Rats, mice, squirrels, guinea pigs, capybara

  • Rodents are unique from all other mammals in having one set of ever growing incisors, and having no canines.

  • Largest order of mammals

Euarchonta

• Scandentia

  • Tree shrews

• Dermoptera

  • Colugos or flying lemurs

• Primates

  • Lemurs, monkeys, apes, and humans

Primates

• Lemurs, monkeys, apes, and humans

• Opposable hallux (big toe) and pollex (thumb)

• Living primates are divided into two groups

  • Strepsirhini

    • Lemurs and tarsiers

    • Long rostrum

    • No plate separating orbits from temporal fossa

    • Naked noses (no fur)

    • Lower incisors form a toothcomb

    • Second digit on the hind foot of many strepsirhines is modified to form a “toilet claw” used in grooming

  • Haplorhini

    • All other primates

    • Short rostrum

    • Plate separate orbits from temporal fossa

    • Platyrrhini

      • Flat noses, outwardly-directed nasal openings

    • Catarrhini

      • Paired, downwardly-directed nasal openings

      • Hominidae

Laurasiatheria

• Eulipotyphla

  • Hedgehogs, moles, and shrews

• Chiroptera

  • Bats (900 extant species)

  • Modified forelimb with wing membrane (patagium)

  • Megachiroptera

    • Old world fruit bats

  • Microchiroptera

    • Echolocating bats

Artiodactyla

• Even-toed ungulates

• Paraxonic (plane of symmetry of each foot passes between the third and fourth digits)

• Horns and antlers often present

• Suiformes

  • Pigs, peccaries, hippopotamuses

• Tylopoda

  • Camels (dromedaries → one hump and bactrians → two humps), llamas

• Ruminantia

  • Deer, cattle, goats, sheep, antelopes, giraffe, etc.

Horns vs. Antlers

• Horns are permanent (not shed) and have a bony core and keratin sheath and are not forked. Both sexes have horns. North American species with horns include sheep, mountain goats, muskoxen, and bison.

• Antlers are shed annually and are composed totally of bone and are forked. Only males have antlers (except in caribou). North American species with antlers include members of the deer family (deer, moose, elk, caribou)

Cetacea

• Whales, dolphins, porpoises

• Mysticeti

  • Baleen whales

  • Balaenidae

    • Right and bowhead whales

  • Neobalaenidae

    • Pygmy right whale

  • Balaenopteridae

    • Rorquals

  • Eschrichtiidae

    • Gray whale

• Odontoceti

  • Toothed whales

  • Physeteridae - sperm whale

  • Monodontidae - narwhal and white whale

  • Ziphiidae - beaked whales

  • Delphinidae - ocean dolphins

  • Phocoenidae - porpoises

  • Platanistidae - river dolphins

• Archaeocety

  • Ancient extinct whales

  • Heterodont teeth (different from modern whales)

Characters that reduce drag in whales

• Streamlined body shape

• Paddle-shaped front limbs

• Vestigial hind limbs (within body wall)

• No external digits

• Tail flattened laterally and bearing horizontal flukes at the tip

• Vestigial ear pinnae

• Basically hairless body (some young have hair on their snouts)

• Thick subcutaneous blubber layer filled with fat and oil

• Telescoped skull bones

• External nares (blowhole) on the top of the head

• Addition of compressed vertebrae

• Shortening of the neck

• Lack of sweat glands

• Internal reproductive organs

• Airway reinforced with cartilage down to the alveoli

Perissodactyla

• Odd-toed ungulates

• Horses, tapirs, rhinos

• Mesaxonic: plane of symmetry passes through middle toe

• Enlarged middle toe

• Equidae

• Tapiridae

• Rhinocerotidae

Carnivora

• Carnassial teeth used for slicing and chopping

  • Secondarily modified in bears, raccoons, and seals

• Pinnipeds

  • Marine carnivores

• Fissipeds

  • Terrestrial carnivores

• Superfamily Canoidae (includes canines)

• Superfamily Feloidae (includes felines)

Pholidota

• Pangolin

• Scales made from agglutinated hairs

• Feed on ants