Mammalogy -- Quiz Two

Inner ear ossicles cont.

Jaw reduced to dentary bone; three previously jaw bones became inner ear bones

Becoming nocturnal cont.

Must develop endothermy (the sun can’t warm you up at night); what supports endothermy?

• Eating more

  • Specialized dentition to improve food handling and processing

  • Secondary palate strengthens skull and separates nasal and oral cavities (allows breathing while eating)

  • Large temporal fenestra allows for increased volume of musculature; greater amounts of food eaten per day

• Breathing more

  • Secondary palate

  • Nasal turbinals reduce water loss

  • Thoracic diaphragm pumps air more efficiently

  • Biconcave red blood cells

• Conserving heat

  • Pelage for insulation

What about milk?

Mammary glands = modified sweat glands; early Mesozoic mammals likely had them (Microdocodon); bones for powerful suckling; don’t know when milk evolved → little fossil evidence (timing remains unclear)

Why milk?

• Synapsids never evolved calcified eggshell → sweat to keep eggs moist; to prevent desiccation, could lay eggs in wet environments or keep eggs moist using bodily secretions (ding, ding!)

• Early milk evolved first to keep eggs moist; became source of nutrition across the eggshell

Mammalian niches in Mesozoic

Most insectivores and herbivores → many arboreal; many terrestrial, some carnivorous, some semi-aquatic piscivores; some even fed on dinosaurs

Mesozoic taxa

Large, varied, and diverse groups; mammals, by our current definition; included placentals, marsupials, and monotremes

K-Pg

Asteroid impact → global cooling → ocean acidification → ecological collapse; nothing bigger than 50 pounds survives; extinction of non-avian dinos and many mammals

Cenozoic — 66 mya to today

Age of the Mammals; Pangaea fully breaks apart; 3 main groups of mammals persisted (Prototherians, Metatherians, and Eutherians [placentals, marsupials, and monotremes]); mutlituberculates survive for a few million years before going extinct (probably outcompeted by rodents); surviving groups = Crown Mammals

190 mya - MRCA of monotremes and placentals and marsupials (monotremes split off)

160 mya - MRCA of marsupials and placentals

Are mammals the only group with a secondary palate?

No → crocodilians; turtles (almost)

Birds do not have a secondary palate → instead, they nearly fused their upper jaw bones

Why didn’t other groups abandon egg-laying?

Birds → they need to fly (weight)

Fish → are ectothermic; rely on numbers (eggs are easier)

Reptiles → are ectothermic; use warm climates to incubate eggs

Monotrema

Ornithorhynchidae - platypuses

Tachyglossidae - echidnas

Restricted to Australia and New Guinea; low diversity (5 species); historically very successful (originated in Australia; once likely a dominant group across the polar south [Antarctica and South America]); name refers to cloaca

Monotrema - eggs

All monotremes are oviparous → no placenta; eggshell is parchment-like; nutrients are transferred across it before it is laid; young have an eggtooth for breaking through the shell; highly altricial at hatching (development completed through nursing)

Monotrema - milk patches

True mammary glands, BUT, no nips or teats; hairs collect milk; milk is secreted from skin onto specialized stiff tufts of fur (young suckle from patches); highly nutritious and full of antibacterial proteins

Baby monotremes = puggles!!!

Echidnas - reproductive

Typically lay 1 egg; temporary pseudo-pouch; egg incubates in pouch (abt. 10 days); puggle lives and feeds in pouch (abt. 2 months)

Platypuses - reproductive

Typically lay 2-3 eggs; no pouch (aquatic lifestyle [babies would drown ☹ ]); mother incubates eggs in burrow (abt. 10 days); puggles live in burrow (3-4 months)

Monotrema - specialized and primitive traits

First platypus specimen brought to London was believed to be a fake

• Endothermic, but have lower metabolism and body temp; reptile-like pectoral and pelvic girdles (sprawling stance);

• Males’ repro traits (abdominal [internal] testes; no scrotum; penises have 2 [plat.] or 4 [echid.] heads [females have a pair of uteri]; thread-like [filiform] sperm; platypuses have 2 ovaries, but only one is functional [birds]);

• Adults are edentate (young plats. lose their teeth in favor of keratonized pads);

• Heel spurs (specialized; only in male plats.; venomous during breeding season [80 toxins similarly found in lizards, snakes, starfish, and sea anenomes])

• Highly innervated bill (over 40,000 electro and 60,000 mechanoreceptors [plats.]; can sense electrical pulses from prey movement and muscle contractions; echids. have weaker [400 electroreceptors])

Early Metatherians

Arose during Cretaceous; oldest fossil is from North America (prev. thought Asia); diversified quickly at first (small insectivores, many mid-sized carnivores and omnivores); species distributed on all major continents during Cretaceous (most diversity = N. America); most early taxa (all N.A. clades) extinct at the K-Pg → some survived into the Cenozoic and diversified to fill empty niches in S. America, and then went extinct (e.g., saber-toothed metatherian)

Only marsupials survived until today

S. American Metatherians

Thylacosmilus (conv. evo. with placental saber-toothed cat)

Convergent Evolution

When unrelated species independently evolve similar physical traits to adapt to similar ecological niches to environmental pressures

Same test, same solution: that’s convergent evolution

Early Marsupials

First true marsupials arose in S. America; migrated to Australia through Antarctica post K-Pg; only marsupials in S. A. and Australia survived and diversified long-term

Seven orders of modern marsupials

Abt. 335 species

3 med-high-diversity orders:

• Didelphimorphia (S.A.)

• Dasyuromorphia (A.)

• Diprotodontia (A.)

4 low-diversity orders:

• Paucituberculata (S.A.)

• Microbiotheria (S.A.)

• Norotycetemorphia (A.)

• Peramelemorphia (A.)

Didelphimorphia

New World opossums

Mostly in S.A.; high diversity (abt. 100 species); small- to medium-sized omnivores and generalists; re-invaded Central and N.A. during Great American Biotic Interchange (3-5 mya; why Virginia oppossum is in N.A.)

Paucituberculata

Rat or shrew opossums

S.A.; low diversity (7 species); nocturnal insectivores or omnivores; small, shrew-like with elongated snout

Microbiotheria

Monito del monte

S.A. (in high elevations); just one species; small, nocturnal, mouselike frugivores and insectivores; arboreal (prehensile tail)

Peramelemorphia

Bandicoots and bilbies

Australasia; med. diversity (21 species); small-medium omnivores, carnivores, and insectivores; more complex placenta than the other marsupials

Why are there no marsupials in Asia?

Wallace’s Line (deep trench between Australia and Asia); Australia and Asia were never connected

Marsupials - reproductive

Bifurcated (two-headed penis [in most]); branched vagina; sperm travels up lateral vagina; young are born through median vagina; simple and short-lived placenta (most)

Four embryonic membranes

Amnion - surrounds embryo (all amniotes)

Yolk sac - nutrient storage (all vertebrates)

Chorion - gas exchange (acc. eggshell in oviparous)

Allantois - waste collection

Monotremes - membranes

Amnion → same function in all mammals

Yolk sac, chorion, allantois → same function as in birds and reptiles

Marsupials - membranes

Amnion → same function as in all mammals

Yolk sac → simple placenta (most)

Chorion and allantois → complex placenta (some)

Placentals - membranes

Amnion → same function as in all mammals

Yolk sac → part of umbilical cord

Chorion and allantois → complex placenta

Long gestation; maternal and embryonic tissues in prolonged and intimate contact; diverse

Marsupium

Young marsupials are born highly altricial; crawl into marsupium; latch onto nips inside or externally to finish development

Annabella’s guest lecture - Background

Managing human-wildlife conflict → needs of humans and wildlife overlap and lead to negative outcomes; becoming more frequent, serious, and widespread (pops. increasing → need more ag. and space) → agricultural expansion (req. more meat) sprawling into wildlife habitat (or clearcutting it); climate change forces animals to forage in areas of more food opportunities (i.e., near us)

• Can occur in any space

  • Roadway (collisions)

  • Ag. pests (Asiatic elephants)

  • Depredation

Anabella’s G.L. - Manifestation

Black bear conflict → drought forced them to come near people and forage in dumpsters

Crop damage → locusts, Asiatic elephants, monkeys, deer

• Asiatic elephants → crop rotation might be a good mitigation, or fencing → incredibly smart and good at exploiting humans’ attempted solutions

Livestock depredation → Constant threat in unfenced areas; Acaçia bomas can lead to panic and spree kills

• Lions → smart; threat to cattle

• Hyenas

• Leopards

• Bears in Norway → #2 cause of livestock injury/death

Human injuries/fatalities

• Tourons → not respecting wildlife or being cognisant of their behavior

• Animals might also seek out humans → tigers

• In US, 47,000 people sought med. attention for animal bites (8 died)

• Wildlife-vehicle collision → 59,000 injuries; 440 deaths

Property damage

• Squirrels and raccoons nesting in houses

• Black bears opening cars (and getting stuck)

• Wildlife-vehicle

• Elephants → globally, the worst → destroying homes, cars, telephone poles

Anabella’s G.L. - Mitigation

Preventative Measures

• Education and awareness campaigns → #1

• Habitat conservation and restoration

• Land use planning (putting livestock in the center of villages, etc.)

• Reducing attractants

• Human behavior modification

• Ag. practices

• Avoiding conflict-prone areas

Deterrence Methods

• Predator-proof boma (reduced lion depredation by 90%)

• Livestock guardian dogs

• Scarecrows (or adjacent)

• Flashing lights

Compensation and insurance schemes → preventing retaliatory killing attempts (which never go well)

Anabella’s G.L. - BioBoundaries

What if there was a way to “speak” their language? → Spotted hyenas and leopards are the most common killers → exploiting their olfactory communication behavior

• Identified compound in leopard and hyena scent marks that says “KEEP OUT” → attached to nearby entrance point; wind carries it like a chemical fence

• Decreased the probability of threshold crossing from 64% - 48%

• Approach-retreat is still common in BioBoundaries, but the research is still in the works