Ch 14-25 Flashcards
1
Q
What are the advantages to an Amniotic egg?
A
Protects developing embryo
– Development on land does not require it
– Requires internal fertilization and related reproductive structures
• sperm cannot pass through shell following egg deposition
• Includes three new extraembryonic
membranes: amnion, chorion, and allantois
2
Q
What are the Extraembyronic Membranes of the amniotic egg and what are they for?
A
-Amnion surrounds embryo, protects it from
mechanical shock
• Chorion facilitates gas exchange and protects other membranes
• Allantois stores nitrogenous wastes of embryo
3
Q
What does the shell do for the amniotic egg?
A
– Provides protection for embryo
– Serves as medium of gas exchange
– More or less rigid due to deposition of calcium
4
Q
Why did the amniotic egg develop?
A
• Resistance to desiccation
– Use of marginal environments unavailable for non-amniotes
• Improved respiratory capacity and increased
structural support
– Exchange gases more efficiently
– Better protected developing embryo
– Facilitated evolution of large body size…?
• Egg size and adult size correlated
5
Q
What are Synapsids and Sauropsids?
A
• Earliest amniotes had few derived terrestrial characters
• Each lineage evolved independent solutions to challenges of life on land
– Conflict of locomotion and respiration
– Thermal insulation and endothermy
6
Q
What were some problems that an early amniote had?
A
Rib Ventilation
• Costal muscles (derived hypaxial muscles) move ribs, expanding thoracic cavity
• Creates pressure differential strong enough to draw air in down the trachea
Locomotion and Respiration
• Problem: hypaxial muscles that help with breathing were also needed for locomotion (lateral undulation) in earliest amniotes
• Created physiological conflict: impossible to run and breathe at same time
7
Q
What happened when Primitive Amniotes ran?
A
- When running, axial muscles compress one lung as other expands
- Little expiration of old air and intake of new air
- Sprinting constrained to short distances
8
Q
How did Synapsids run?
A
• When running, bend vertebral column
- Compression of lungs generates positive pressure:
forces air out
- Straightening expands lungs generates negative
pressure: causes air to fall in
- Gait and breathing are synchronized
9
Q
What is bipedalism?
A
• More derived forms (birds) exhibit bipedalism
– Axial muscles do not contribute to locomotion
– Resolves conflict of locomotion and respiration
10
Q
What is Endothermy and why did it evolve?
A
• Maintenance of elevated body temps due to metabolic activity rather than external heat
• Requires high metabolic rate and insulation
– Lack of either prevents endothermy from evolving
• Thermogenic opportunity model
– Higher body temps permitted nocturnality
• Warmer-is-better model
– Physiological and biochemical processes run faster or more stronger at warmer internal temperatures
11
Q
How does Heat Retention in Synapsids work?
A
Mammals evolved hair
– Increases whole body insulation
– Originally primarily sensory structures (vibrissae)
12
Q
How does Heat Retention in Sauropsids work?
A
• Feathers initially served as display features
– Secondarily modified for insulation
13
Q
What is Temporal Fenestration?
A
• Amniotes categorized by # of skull fenestrae
– Each fenestra has bony arch (apse) beneath it
– Apse lost in derived groups
• Provide room for jaw muscles to bulge
14
Q
What are the characters of Temporal Fenestrae
in Anapsid?
A
: no fenestrae, thus no temporal arch
– Primitive condition for amniotes
– Also seen in modern turtles
• Probably derived from diapsid condition
15
Q
What are the characters of Temporal Fenestrae
in Synapsid?
A
one fenestra
– Modern mammals
– Extinct “mammal-like reptiles”
16
Q
What are the characteristics of Temporal Fenestrae
in Diapsid?
A
two fenestrae
– Lepidosaurs (lizards, snakes, tuatara)
– Archosaurs (crocodilians, birds, “dinosaurs”)
17
Q
What is the name of Turtles and how many species?
A
Testundines, • ~350 species
of turtle
18
Q
What are the Characters of Turtle shells?
A
• Shell gives
distinctive body architecture
• Dorsal carapace and ventral plastron
• Outer covering of epidermal scutes
19
Q
How are the Ribs of turtles different than other species?
A
• Bones of carapace underneath scutes – Ribs and vertebrae expand and fuse; – Only turtles have ribs external to girdles
20
Q
What are the benefits to turtles hiding their head? What are the disadvantages?
A
• Hinged plastron allows head, appendages to be withdrawn tightly into shell
– Benefit: effective armor from many predators
– Cost: weight and structure limit mobility and niche diversity
21
Q
What are the different type of hide-neck turtles?
A
• Cryptodires (hidden-neck turtles)
– Withdraw head into shell by bending neck into
vertical S-shape
– 75% of living species, and found on all
continents
• Pleurodires (side-neck turtles)
– Withdraw head into shell by bending neck
horizontally
– Now found only in Southern Hemisphere
22
Q
What is the reproductive biology of turtles?
A
• All turtles are oviparous
– Eggs deposited in nests, covered by sand or soil
– Small species lay 4-5 eggs; large marine turtles can lay 100+ in single event
• Many species exhibit temperature-dependent sex determination (TSD)
– Offspring sex a function of background temps experienced during embryonic development
– Change in offspring sex typically occurs across a narrow range (3-4°C)
23
Q
What are the different types of TSD?
A
- Type Ia: males at low temps, females high
- Type Ib: females at low temps, males high
- Type II: females at high and low temps males intermediate
- What is advantage to linking offspring sex to environmental temperature…?
- Females may be able to assess sex frequencies in population, then select nest site more likely to generate offspring of rarer sex
23
Q
Why is turtle conservation important?
A
• Delayed reproduction limits capacity of population to recover from decline quickly
• Largest turtles endemic to small islands
– Vulnerable to habitat disturbance and invasive species
• Harvesting of turtles for food and traditional medicines, especially in China and SE Asia
– Most species in region are highly threatened
• Illegal collection for pet trade
– Largest markets in N. America, Europe and Japan
– Rarest species command highest prices, putting further pressure on most endangered species
• Skew in offspring ratios due to effects of global warming on TSD
– May generate too few males or females to keep populations viable
24
What is the Diapsid skull in lepidosaurs?
• Two temporal fenestrae
• Seen in all lepidosaurs (lizards, snakes, tuatara) and most archosaurs
• Tuatara show the ancestral “classic” form
– Other groups show variations
25
What are Lepidosaurs?
• Largest group of non-avian reptiles (>10000 sp.)
– Lizards (6500)
– Snakes (3600)
– Tuatara (1)
• Important mid- and high-trophic level vertebrates wherever they occur
26
What is the General Biology of Lepidosaurs?
• Largely terrestrial but have exploited virtually all forms of habitat available
• Reduction or loss of limbs is common (>60 times!)
• Limblessness associated with life in fossorial and grassland habitats
- Decreases resistance to moving through soil
- Easier to maneuver around vegetation
• Skin covered with epidermal scales
– Prevents desiccation
– Shed periodically
27
What are Rhyncocephalia (Tuatara)?
• One living species endemic to New Zealand
• Superficially resemble lizards but morphologically primitive
• Restricted to islands off New Zealand coast
• Eliminated on mainland following human settlement
– High predation from introduced animals
• Low reproductive rate inhibits population recovery
28
What is the Reproductive Biology of Tuatara?
• Oviparous with internal fertilization
– No intromittent organ (unique for lepidosaurs)
– Male and female bring cloacae together (birds)
• Type Ib TSD
– Eggs incubated above 21ºC are mostly males; cooler temps produce females
29
What is Tuatara ecology?
• Unusual activity pattern for ectotherm
– Feed at night, when temperatures of (already moderate) temperate region even colder
– Body temps may be as low as 6ºC
– Warm up during day but not active then…why?
• Live in seabird burrows
– Primarily feed on seabirds, their eggs, and insects associated with seabird nest activities
– Hunting most effective at night, despite suboptimal thermal conditions
30
What is so interesting about lizard size?
* Dramatic size variation
* Dwarf chameleons (< 3 cm)
* Monitor lizards (~3 m)
31
What is Lizard Feeding Ecology?
• Small lizards mostly insectivores or carnivores
• Large lizards usually herbivores
– Plants have lower nutritive value
– Larger body needed to extract sufficient nutrients
32
How does lizard reproduction work?
• Sperm transfer by paired hemipenes
– Each connected to separate testis
– When mating multiply over short time periods, males will alternate inserted hemipene
– Helps prevent sperm depletion
• Oviparity is most common mode
– Females usually deposit soft, leathery eggs
– Not calcified like bird eggs
• Viviparity less common; limits reproductive output and constrains female locomotion
• More common in species at colder climates
– Females can better control embryonic temps by retaining eggs for longer period in cold habitats
33
What are Hunting Strategies in Lizards?
```
• Widely foraging
– Active
– Elongate body
– Not territorial
– Eat many sedentary,
small prey
• Sit-and-Wait
– Little movement
– Stocky body
– Territorial
– Eat few large
mobile prey
```
34
What are characteristics of Geckos?
• Widely distributed in tropics and subtropics
• Many specialized for arboreality
– Toe pads provide exceptional climbing ability
– Setae adhere by subatomic van der Waals forces
• Largely nocturnal
– Exceptional in use of vocalization (rare in lizards)
– Used in courtship and aggressive social contexts
• Some colorful species are secondarily diurnal
35
What is so cool about Whiptails?
```
• Some species exhibit
parthenogenesis
– usually formed by hybrid
crosses of two sexual species
– Offspring are female clones
– Arise from unfertilized ova
• Common in arid western U.S.
– Possibly adaptive when
environments are stable
– Limited genetic diversity
constrains adaptation to
climate change
```
36
What are characteristics of Monitors?
• Large, active predators of Old World tropics
– Includes largest living lizard (Komodo monitor)
– Capable of tracking relatively large vertebrate prey
• Closely related to snakes
• Deeply forked tongue permits acute olfactory capability
– Venom glands important in subduing prey
37
What are Serpentes (Snakes)?
```
• Morphologically,
ecologically
diverse clade of
limbless lizards
(3600 sp.)
```
38
What is snake feeding ecology?
• All snakes consume vertebrate or invertebrate
animal prey
– No snakes are herbivores
– Swallow prey whole
39
What are snake Feeding Specializations?
```
• Highly kinetic skulls that
can move in 3 dimensions
• 8 movable joints on each
side of the skull
Seize and Swallow
• Most common form of
prey capture
– Probably primitive for
snakes
• Limits types of prey
that can be safely
consumed
– Prey with claws and
teeth can inflict injury
Constriction
• Loops thrown around body of prey
• Tighten with each exhalation of prey
• Suffocate prey or induce cardiac arrest
Envenomation
• Delivery of salivary gland products
– kills prey and initiates digestion
• Prey often released, then recovered by following scent trail
– reduces chance of injury to snake
```
40
What are different Snake Dentition?
* Aglyphous: no fangs
* Ex: pythons, boas
* Ophistoglyphous: rear-fanged
* Ex: boomslang
* Proteroglyphous: fixed-fanged
* Ex: mamba, cobra
* Solenoglyphous: hinge-fanged
* Ex: vipers, rattlesnakes
41
What are Crocodilians?
* Important predators of tropical and subtropical aquatic habitats
* Only 27 described extant species
42
What are characteristics of Early Crocodilians?
• Evolved in Triassic
• Originally terrestrial predators
– long limbs, small body sizes
– Possibly bipedal
• Derived species (and living taxa) mostly aquatic
– small limbs, large body sizes
– Some extinct species exhibited gigantism
43
What are Crocidilian Foraging Strategies?
* Most frequently hunt in ambush in water
* Some catch prey on land by ambush or short bursts of running
* Aggregate to collect fish
* Use sticks as lures to capture wading birds
44
What are Characters of Crocodilians?
• Dorsal nostrils allow breathing by floating at surface of water
• Laterally-flattened tail helps propel
efficiently through water
- Legs held close to body to reduce drag
45
How is Parental Care in Crocodilians?
• Complex and probably universal
– Construct nest and attend to its care
• TSD, but large nests usually have wide range of temps
– Respond to calls of hatchlings
• Complex and probably universal
– Defend offspring in creches for 2-3 years
• Parental care probably synapomorphic for
archosaurs
– Probably in extinct pterosaurs and dinosaurs too
46
What are Lepidosauramorphs?
```
• Lineage including living lepidosaurs
• Also includes several extinct marine forms
– Placodonts
– Plesiosaurs
– Ichthyosaurs
– Mosasaurs
```
47
What are Placodonts?
• Least specialized lepidosauromorphs
– Probably near-shore herbivores similar to modern-day manatees
– Some had turtle-like carapace formed of dermal bones possibly to reduce buoyancy
48
What are Ichthyosaurs?
• Dolphin-like, with limbs modified into paddles
– Primitive species swam with full body lateral undulations (like lizards)
– Derived species used carangiform swimming with aid of caudal fin
• Paddle-like limbs
- Exhibited hyperdactyly and hyperphalangy, as well as extended soft tissues
• Included species with largest vertebrate eyes
– Fed in deep water with limited ambient light
• All species were viviparous
49
What are Plesiosauroids?
• Specialized for pelagic marine life
– Oar-shaped limbs formed via hyperphalangy
• Viviparous: gave birth to single large offspring
50
What are Mosasaurs?
• Marine radiation of monitor lizards (varanids)
– Initially swam with lateral undulations, then via
large caudal fin and paddle-like limbs
– Highly kinetic skulls facilitated wide prey base
– Viviparous, though all living varanids are oviparous
51
What are Archosauromorphs?
```
• Includes birds, crocodilians and several major
extinct groups
– Extinct dinosaurs
– Pterosaurs
• All species oviparous
```
52
What are Pterosaurs?
• First of two lineages of archosaurs to evolve flight
– Preceded birds by 80 my, and overlapped with them
for ~100 my
– Largest species >200 kg with wingspans of 30 ft
– Walked quadrupedally
• Long fourth finger supported skin membrane attached
to hind leg
• Hairlike pycnofibers on skin
– Probably provided insulation, and when colorful,
may have served in social communication
53
What are Dinosauria?
* Perhaps 2500+ species
| * Two major groups: ornithischians and saurischians
54
What are characteristics of Dinosaurs?
• Evolved from small terrestrial archosaurs
• Earliest species probably bipedal, which facilitated created new adaptive opportunities
– Seizing prey
– Support wings for flight
55
What are Social Behaviors of dinosaurs?
* Large numbers of fossils suggests some species may have herded
* Hadrosaurs had sexually dimorphic crests with nasal passages that amplified sound
* Colorful feathers and skin probably used to distinguish species, sex, and social status
* Many species built complex nests and show evidence of parental care
56
What are Ornithischians (dino)?
• All were herbivorous; most were secondarily quadrupedal
• Heavily armored with modified tails for weapons
- stegosaurs, ankylosaurs, ceratopsians
57
What are the characteristics of Sauropods?
* Long intestinal tracts to effectively extract nutrients from plant material
* Low metabolic rate, but maintained high body temperature by gigantothermy
* Limbs held underneath body (like elephants)
* Head small to make it easier to lift
* Neural arches supported ligament that helped raise neck and head
* Bones were pneumatized, and pleurocoels along cervical vertebrae contained air sacs
58
What are the characteristics of Saurischians: Therapods (dino)?
* Various small and large bipedal carnivores
| * Gave rise to living birds
59
What are the characteristcs of Tyrannosaurs?
• Distinctive body form: long hindlimbs, short
forelimbs, and large skull
• Killed prey by crushing or slashing with jaws
– Teeth up to 15 cm in length
60
What are the characteristics of Maniraptorans (dino)?
* Small speedy (cursorial) carnivores with feathers, but initially not capable of flight
* Enlarged claw on 2nd toe
61
Birds- What are the characteristics of Archaeopteryx?
* Earliest bird (~150 mya) or very close relative
| * Asymmetrical feathers permitted flapping flight
62
What are Feathers and Protofeathers?
* Multiple experiments in feather-like structures
* May have first been part of social displays
* Later served as insulation, then flight
63
What was the Origin of Flight: Top-Down?
• Proposes that bird ancestors lived in trees
• Glided to cross gaps in canopy and pursue prey
– Selection for distance and accuracy in travel
between trees selected for true flight
64
What was the Origin of Flight: Ground-Up I?
* Ancestral birds were speedy bipedal ground-dwellers
* Model 1: Initially used wings to swat or seize insect prey
* Wings later helped with jumps to catch larger prey
65
What was the Origin of Flight: Ground-Up II?
• Model 2: wing-assisted incline running (WAIR)
• Early birds may have walked or run on flat surfaces, but used wings to help climb vertical structures (trees)
– Similar behavior seen in some extant birds
66
What was the Origin of Flight: Balancing Raptor?
• Feathers helped provide stabilization after
impaling prey with enlarged second toe
• Flapping evolved in response to efforts to
retain balance
67
What were Early Cretaceous Birds?
• Exhibited many features characteristic of
| modern birds
68
What are Characteristics of Birds?
```
• Defined by ability to fly
– Access to habitats
unavailable to other
vertebrates
– Capacity to make long-distance migrations
```
69
What are Diurnal endotherms?
– Conspicuous during day
| – Successful in colonizing cold environments
70
Why is Acoustic communication fundamental?
```
– Species-specific birdsong performed by males
(and often females)
– Alarm calls to warn kin of predators
• Nonvocal sounds important in
many species
– Bill-clapping in storks
– Stridulation in manakins
• Wings vibrate to produce
sound
```
71
Why is color so important for birds?
• Color is another important signaling channel
– Excellent vision; can see colors hidden to humans
– Visual displays often reveal colorful patches
– Males often strongly sexually dimorphic
72
What is the Anatomy of Feathers?
• Calamus (quill) at base gives rise to rachis that
supports barbs (side branches)
– Adjacent barbs held together by hooks of barbules
• Vane: flat area of locked barbs that acts as airfoil
• Downy region: fluffy insulating portion at base
73
What are Contour Feathers?
• Stiff body feathers of flight and body plumage
• Asymmetrical and slotted
– Gaps between adjacent feathers reduce drag
74
What are Downy Feathers?
• Rachis short or absent
• Specialized for insulation
– Can be used to line nest
75
What are Bristle Feathers?
* Stiff rachis with few barbs
* Protect eyes and nostrils
* Act as tactile organs
76
How does Streamlining and Weight Reduction work?
```
• Drag plays major role in body plan
• Both skeletal modifications and changes to
internal organ anatomy help reduce mass
– lack a urinary bladder
• Reproductive organs are minimized
– usually only one ovary and no phallus
– gonads small until breeding season when they
hypertrophy
```
77
What are Pneumatic bones in birds?
– Reduce mass of skull and
wings
– Weight redistributed to
posterior of body
78
What is an Enlarged, keeled sternum in skeletal adaptations?
• Enlarged, keeled sternum
– Site of attachment for
strong flight muscles
79
What is a Fused clavicles (furcula) in bird skeletal adaptations?
• Fused clavicles (furcula)
– Acts like spring to reduce
energy during flapping
80
What are two skeletal adaptations in birds with the tail and legs?
```
• Shortened tail with
pygostyle
– Supports tail feathers
• Tarsometatarsus bone
– Fusion of most tarsals
with most metatarsals
– Supports body weight
– Allows toes to be flat on
ground
```
81
What are Avian Wings?
• Feathered wings serving as cambered airfoils
- Convex dorsally and concave ventrally
- Air pressure higher under wing then above it, giving lift (vertical upward force)
- Slightly increasing angle of attack can provide additional lift, but also increases drag; too steep an angle of attack can generate a stall
82
What is Formation Flight?
• Vertically spiraling vortices generated from
leading bird in V-formation induce drag
• These vortices arrive at trailing birds, which
space themselves out to hit upturn of vortex
(generating lift) of leading bird(s)
83
What are characteristics of Flightless Birds?
• Loss of flight has evolved multiple times
– Reduced wings and pectoral girdle
– Lack a keeled sternum
84
What are Ratites (flightless birds)?
– 10 spp. in S. America, Africa, Australia
– Others went extinct following human
settlement of Madagascar and New Zealand
– Ostriches, kiwi, cassowary
85
What are Penguins (flightless birds)?
– ~20 spp. from Antarctica to Galapagos Islands
– Wings adapted as flippers
– Streamlined shape allows efficient, fast swimming
86
What are Island endemics?
– Evolved repeatedly (>15 different families)
• Adaptation to lack of predators
• Reduced risk from trying to return to mainland
– Vulnerable to introduced predators
87
What are different types of Terrestrial Locomotion?
• Hopping (passerines)
– Sequence of small jumps; many perching birds
cannot walk at all
• Running (ostrich, roadrunner)
– Legs move alternately with an aerial phase
– Long thin legs with small feet
88
How does Fertilization in Birds work?
```
• Internal fertilization is universal
– Sperm transfer usually via “cloacal kiss”
• Females can store sperm from multiple males
– Multiple paternity common
– Fertilizations biased towards sperm from
preferred males (cryptic female choice)
• In ~3% of species, males have
a copulatory organ; what are
the possible benefits?
– ensures sperm transfer without
loss to background water
• Waterbirds (ducks, swans)
– easier for sperm to reach
female reproductive tract
• Large species (ostriches)
– helps remove existing sperm
• species where females mate
multiply (weaverbirds)
```
89
What are Reproductive Strategies in birds?
• Internal fertilization is universal, but all birds are
| oviparous
90
Why is there no viviparity in bird reproduction?
Theories:
1. • Flight constraint hypothesis
– Viviparity interferes with flight mechanics
– Adds weight and increases drag
• Important observations against:
– Bats are viviparous
– Flightless birds are oviparous
2.• Avian endothermy hypothesis
– Birds have internal temps around 40-42 C, but
egg temps during brooding are cooler (33-37 C)
– Oviparity may ensure eggs develop at optimal
temps
91
What were Pelycosaurs in group Synapsids?
• Least specialized synapsids; not endothermic
“Sailbacks” with dorsal crest derived from modified vertebrae
– Possible roles in communication or heat exchange
– Ex: Dimetrodon
92
What were Therapsids in group Synapsids?
• Derived synapsids that show evidence of increase
in metabolic rate
– Larger temporal fenestra to expand jaw muscles
– Teeth differentiated into incisors, canines, molars
– Ex: Gorgonopsids
93
What were Cynodonts in group Synapsids?
• Group of highly derived therapsids
– Exhibit reduction in body size across time
– Ex: Thrinaxodon
• Anatomy suggests close relationship to mammals
– Facial pits may have supported vibrissae
– Turbinates in nasal passages for humidifying and warming inspired air
94
How are the jawbones like in group Synapsids? And what is derived in what we have today?
• Lower jawbone (dentary) expands posteriorly
• Postdentary bones shrink, forming ossicles
– Malleus (derived from mandibular)
– Incus (derived from palatoquadrate)
– Stapes (derived from hyomandibula)
95
How does hearing work and how did it evolve? (synapsids)
• Hearing compromised when ossicles part of jaws
– Separating ossicles from jaws allow derived synapsids to chew without sound interference
– Shrinking allowed ossicles to vibrate more easily, transmitting sound (especially high-freq. sounds) more efficiently
96
What were Mesozoic Mammals?
• Earliest mammals: small nocturnal insectivores
– Appeared ~ 200 mya (Morganucodon)
• Diversified into larger forms (> 15 cm) after end
of Cretaceous (66 mya)
– Did dinosaurs inhibit mammals from radiating?
97
What are five characteristics of mammals? (synapsids)
• Hair: originally evolved as sensory structures
(vibrissae); secondarily adapted to serve for
insulation
• Endothermic: internal temps maintained by
capturing heat generated from metabolism
• Diphyodontous teeth
– Only two teeth of sets only
– Most other vertebrates are polyphyodonts
• Molars with precise occlusion: upper and lower
teeth interlock
– Allows for chewing (mastication), which efficiently
cuts food, increasing surface area for digestion
• Lactation: secretion of milk produced in
mammary glands from mother to offspring
– Provides source of nutrition to developing young
– Transfers antimicrobial proteins to offspring
• Lactation uncouples reproduction from seasonal
food supply
– Young nourished by energy reserves acquired by
mother during other times of year
98
What are Monotremata (Prototheria)?
• Monotremes: most archaic living mammals (5 sp.)
– Duck-billed platypus and echidnas
• Restricted to Australia and New Guinea
99
How does reproductive ecology work for Monotremes?
• Deposit offspring in eggs (oviparous)
– 1-3 soft-shelled eggs laid per clutch
– In echidnas, eggs are deposited into abdominal
pouch, hatching about 10 days later
• Lack nipples: milk released directly into hair
• Retain cloaca: single opening for materials from
reproductive and excretory systems
– Primitive condition for amniotes
100
How do monotremes have an electrosensory system?
```
• Electrosensory organs
in bill or beak
– Help in locating buried
or submerged prey
– Unique among
terrestrial tetrapods
• Much more abundant in
platypus…why?
• Early monotremes may
have been semiaquatic
```
101
What are Multituberculates?
```
• Extinct lineage of mostly small
terrestrial and semi-arboreal
rodent-like mammals
– Persisted about 100 my:
Mesozoic into early Cenozoic
– Anatomy suggests they did not
lay eggs
• Possibly driven extinct through
competition with eutherian rodents
(kinda look like squirrels with a monkey tail)
```
102
What are Marsupials (Metatheria)?
• 330 spp. mostly in Australia and New Guinea,
| with a few species in North and South America
103
How does reproductive ecology work for Marsupials?
• Viviparous with highly altricial young
– Placentation followed by live birth
– Gestation time much shorter than eutherians
• Newly-born offspring continue development in
marsupium (pouch)
– Crawl unassisted from vagina into pouch, which
usually encloses nipples, providing access to food
104
How are Marsupials distributed?
• Two major clades
– Ameridelphia: restricted to Americas
– Australidelphia: Australia and S. America
105
What are characteristics of the Ameridelphia marsupials?
• Includes Didelphimorpha (opposums)
– Largely arboreal or semi-arboreal omnivores
– Yapok is aquatic freshwater specialist
• Ex: Diprotodontia (kangaroos, koala, possums)
– Most speciose clade of marsupials (~140 spp.)
– Living species are herbivorous or omnivorous
106
What are characteristics of the Australidelphia marsupials?
• Ex: Microbiotheria: monito del monte
– Arboreal species of forests of southern Andes
– Relict of early lineage that gave rise to Australian
marsupials
107
How did the Evolution of Australian Marsupials happen?
• Australidelphians evolved in S. America, not
Australia
• Dispersed to Australia via land bridges through
Antarctica
- late Cretaceous or early Tertiary (65 mya)
108
What are the Placentals (Eutheria)?
• Most diverse clade of mammals (~5000 spp.)
| – Dominant mammals on most major landmasses
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What are reproductive Characters of Placentals?
• Viviparous with extended gestation relative to marsupials, but shorter lactation period
• Offspring development more variable than in marsupials
– Some species have altricial offspring, others precocial
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What are Afrotheria?
• Sister taxon to other placentals (~75 sp.)
– Evolved during Cretaceous when Africa isolated
• Morphologically and ecologically diverse group
– elephants, hyraxes, manatees
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What are Xenarthra?
• Evolved in S. America; dispersed into N. America
by land bridges (~30 sp.)
– Includes anteaters, armadillos, and sloths
• Low metabolic rates and body temperature
– Many specialized for consumption of insects
– Sloths consume plant material
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What are Boreoeutheria?
• All other placental mammals; evolved in the
Northern Hemisphere (~4900 sp.)
• Two major groups:
– Euarchontaglires: primates, rodents, rabbits
– Laurasiatheria: carnivorans, bats, ungulates
