Mammalogy Exam 1

Monotremata

• monotremes

• egg laying mammals

• characteristics

  • cloaca

  • no auditory bulla

  • cervical ribs and fused pectoral girdle

• examples: echidna, platypus

Metatheria

• Marsupials

• live birth

• Order Didelphimorphia (opposums) and Diprotodontia (koala, sugar glider, kangaroo)

Eutherian Superorders

• Laurasiatheria - from North America

• Euarchontoglires - from North America

• Xenarthra - from South America

• Afrotheria - from Africa

Eleven Soft Anatomy Characteristics

1. Lactation

2. Vivipary

3. Hair

4. Sweat/Sebaceous Glands

5. Endothermy

6. 4-Chambered Heart

7. Annuculate RBCs

8. Renal artery

9. Muscular Diaphragm

10. Facial muscles

11. Dorsal Pallium expands cerebrum

8 Cranial Chracteristics

1. Double occipital condyle

2. Atkas/Axis complex

3. Tympanic bone

4. Three ear ossicles

5. Dentary is only bone in the mandiblr

6. Single external naris

7. Secondary palate

8. Respiratory turbinates

5 Dental Characteristics

1. Lack palatal teeth

2. Diphyodont - two sets of teeth in a lifetime

3. Thecodont - teeth embedded in deep sockets of jaw bone

4. Heterodont - teeth vary in structure

5. Multicuspate

2 Axial Skeleton Characters

1. Extreme regionalization

2. Ribs only on thoracic vertebrae

4 Appendicular Skeleton Characters

1. Limb bones have epiphyses - point where bones connect to joints

2. Calcaneus - heel bone

3. Reduction of elements in limb girdles

4. Parasagittal limb posture - upright (not sprawling)

Why do mammals have relatively low abundance, but high species richness?

Shortened definition of a mammal

A hairy, milk producing, endotherm, that usually gives birth to live young

• this is inadequate because there have been extinct non-mammals found that exhibit some of these traits

• they used to define mammals based of of their jaw bones, but they found a skull with all four of the jaw bones

3 extant mammal groups

1. monotremes - egg laying mammals

2. metatherians - marsupials

3. eutherians - the rest of mammals

Synapsids

• the group that gave rise to mammals

• characterized by two temporal fenestra

  • makes the skull lighter

  • more jaw power

  • saves energy

• 3 groups - Pelycosaurs, Early Therapsids, Cynodonts

Pelycosaurs

• early synapsids - existed through Carboniferous (320 mya) and persisted through Permian

• most important group - Demitrodon - large sail on back for regulation or sexual selection

• characteristics

  • weakly heterodont

  • small temporal fenestra

  • no secondary palate

Early Therapsids

• existed in middle Permian (265 mya) but most went extinct during the permo-triassic extinction event

• characteristics

  • they were dominant

  • enlarged temporal fenestra

  • gradually evolving secondary palate

  • complete cheek teeth

Cynodonts

• advanced therapsids - lived in the very late permian period and survived the P-T extinction

• characteristics

  • complete secondary palate

  • large temporal fenestra

  • strongly heterodont

  • small and likely went underground to protect themselves from dinosaurs

• Extinction of the dinos (end of Cretaceous led to adaptive radiation)

Anapsid (stem amniote) characeristic

• only one temporal fenestra

• ex: turtles

Describe the synapsid phylogeny and what happened during the P-T extinction event

• pelycosaurs were the early synapsids in the late Carboniferous/ early Permian and they did not exhibit mammalian traits (weakly heterodont, no secondary palate, small temporal fenestra)

• they split of into the early therapsids who were dominant in the late Permian - they were trasitioning to have more of these mammalian traits

• the P-T extinction wiped out these two groups and left the cynodont (late therapsids) - they had heterodont dentition, a large temporal fenestra, and a secondary palate

  • they were small and likely went underground to protect from dinos - after dinos went extinct, mammals radiated

Early lineages of mammals on geologic time scale

• pelycosaurs - Late Carboniferous/ Early Permian

• early therapsids - Middle Permian

• cynodonts - Late Permian

• first placental mammals - Jurassic

• radiation of mammals - end of Cretaceous

Describe the two approaches to classifying mammals

Why does the size refugium hypothesis provide a more robust approach to classifying mammals?

Explain the size refugium hypothesis

• when an animal is large they have a lower surface to volume ratio than a small animal

• lower surface to volume ratio means higher thermal inertia (larger animals can retain their heat for longer)

• the hypothesis shows that gigantotherms evolved in the early Permian and selection favored larger body size during the Permian

• when dinosaurs were dominant, cynodonts were forced to be smaller and to go underground - high thermal inertia lost

  • favored animals that could produce their own heat (endothermy)

Energy requirements and behavioral implications of endothermy

Energy

• endothermy requires lots of energy

• selection favored:

  • specialized dentition

  • secondary palate

  • cardipulmonary efficiency

Behavior

• endotherms can be active at cold temps because they produce their own heat

• selection favored:

  • hair

  • good smell and hearing for night time

adaptive radiation

• When there is a large group that goes extinct, there is a large opening for new niches to be filled by other groups

• allowed for diversification at the end of the Cretaceous period because of the dino extinction

crown mammals vs mammals

Crown mammals - all of the extant mammal groups that we know today (monotremes, marsupials, eutherians)

Mammals- all extant and extinct mammal ancestors (mammaliformes, stem mammals, morganucodontids)

What traits allowed mammals to survive and the synapsids to go extinct?

• specialized jaw (one dentary bone)

• better hearing created by the ossicles

• heterodont dentition

• early mammals remained small and adaptable whereas larger pelycosaurs were large and vulnerable

Primitive and derived characteristics of monotremes

2 families - Tachyglossidae (Echidnas) and Ornithorhynhus (platypus)

Primitive

• cloaca

• no auditory bulla

• fused pectoral girdle

• cervical ribs

• egg laying

Derived

• leathery bill

• venom

• raspy pads instead of teeth

• echidnas - have spines

• platypuses - electroreceptors in bill

6 characteristics of echidnas

• large spines

• external ears

• powerful limbs for digging

• lay one egg and incubate in their pouch

• hibernate

• males have non venomous spurs

7 characteristics of the platypus

• aquatic - webbed feet

• feed on crustaceans

• dense fur

• males have venomous spurs

• adults dont have teeth - young have teeth that dont pop out

• make dens in stream banks

• lays 2 eggs and incubates them

Where were the first metatherian fossils discovered

North America and China

Single dispersal hypothesis

• mammaliformes originate in Laurasia and some move to modern day Africa - Africa splits from land mass and Afrotheria is able to diversify

• Then some move to South America, where Xenartha diversifies

• some moved through Antarctica and to Australia from a land bridge where marsupials diversified

Marsupial Orders

South American orders

• Didelphimorphia - opposums

• Pauctiberculata - shrew opposums

• Microbiotheria - Monito del monte

Australian orders

• Diprotodontia - possum, sugar glider,koala, kangaroo, wallaby, wombat

• Notoryctes - marsupial mole

• Dasyuromorphia - Tasmanian devil, Tasmanian wolf, and numbat

• Peramelemorphia - bandicoot

2 characteristics of Diprotodontia

• most have only two lower incisors

• they have syndactylous feet (digits 2 and 3 are combined)

arboreal foliavore

• only eat leaves

• first example of this is a koala

• characteristics

  • eat constantly

  • sleep to digest

  • low metabolism

  • dense fur

5 Eutherian mammal groups

Laurasiatheria

• Cetartiodactyla, Perissodactyla, Pholidota, Carnivora, Chiroptera, Insectivora

Euarchontoglires

• Rodentia, Lagomorpha, Primates, Dermoptera, Scandentia

Xenarthra

• Pilosa, Cingulata

Afrotheria

• Afrosoricida, Macroscelidea, Tubulindantata, Proboscidea, Sirenia, Hyracoidea

Marsupialia

• Didelphimorphia, Diprotodonta

Afrotherian orders

• Proboscidea - Elephantidae

• Sirenia - manatee

• Hyracoidea - hyrax (more closely related to elephants than rodents)

• Macroscelidea - shrews

• Tubilindentata - aardvark

• Afrosoricida - tenrec

2 Xenarthra groups

• they have extra articulation between vertebrae

• Pilosa - Myrmecophaga (anteaters) and Bradypus (sloth)

• Cingulata - Dasypodidae

myrmecophagous species and examples

• long snout

• long tongue

• thin dentary bone

• sticky saliva

• forelimbs for digging

• examples

  • Australia - echidna

  • South America - anteater

  • Africa - aardvark

5 Euarchontoglires orders

• Rodentia

• Lagomorpha

• Primates

• Dermoptera

• Scandentia

characteristics of rodentia

• grinding cheek teeth and ever growing incisors

• suborders are ditinguished with their jaw and zygomasseteric condition

6 Laurasiatheria orders

• Insectivora

• Chiroptera - bats

• Carnivora

• Pholidota - pangolins

• Cetartiodactyla - even toed ungulates and marine mammals (giraffes, whales, dolphins)

• Perissodactyla - odd toed ungulates (rhinos, zebras, horses)

2 Chiroptera suborders

Yinpterochiroptera

• mega and microbats

• primarily frugivorous

• rely on vision

Yangochiroptera

• echolocating bats

• different feeding forms

2 forms of Cetartiodactyla

• aquatic - whales, dolphins

• terrestrial - giraffes, deer, cows, hippos, pigs

Describe the two general patterns seen in species distribution across the world

• there is a latitudinal gradient based on where you are in regards to the equator and the poles

• There is also biogeographic provincialism where regions of the world have similar species

Describe the abiotic processes that impact distribution

• continental drift

• climate change

• refugia during the ice age provided habitat

Define the biotic process of dispersal

• individuals or whole species will leave

• why?

  • avoid inbreeding

  • avoid competition for breeding and resources

What factors will influence the biotic process of faunal interchange

• climate change

• continental drift

• new land

Describe the three active dispersal pathways

• corridor route - minimal resistance to the passage of animals

• filter route - only certain animals can pass through (animals adapted to cold climates only or a mountain range to cross)

• sweepstakes route - unusual occurrence carries animals to new area

4 reason for why we see similar species on separate land masses

• faunal interchange - movement of mammals between land masses

• vicariance - separation due to geographic isolation (allopatric speciation)

• convergent evolution - similar traits evolved separately

• adaptive radiation - variance between species (example is Darwin’s finches)