Dr. Light Mammology review

What is the adaptive significance of enucleated red blood cells in mammals?

More space for hemoglobin → increased oxygen-carrying capacity → supports high metabolic rate and endothermy. More efficient and carries o2 more efficiently

Why is the mammalian shoulder girdle reduced to two bones (scapula and clavicle)?

Increases limb mobility and flexibility; more efficient.

How does surface area-to-volume ratio affect heat regulation in animals?

Smaller animals lose heat faster (higher SA:V); larger animals retain heat longer

What is an "endothermic homeotherm"?

Organism that generates internal heat and maintains a constant body temperature—like mammals

Define monophyly.

A group containing a common ancestor and all its descendants (a clade).

Define paraphyly

A group with a common ancestor and some but not all descendants.

Define polyphyly.

A group lacking the most recent common ancestor—traits due to convergence.

What is a major downfall of using traits from convergent or parallel evolution in phylogenetic trees?

They can mislead evolutionary relationships by suggesting similarity due to shared traits rather than ancestry, potentially resulting in polyphyletic groupings.

What is continental drift and what mechanism causes it?

Continental drift is the slow movement of Earth's continents; caused by plate tectonics.

Who first proposed the idea of continental drift

Alfred Wegener.

) During the Permian Period, all landmasses formed one continent called __________.

Pangaea

What major event occurred at the end of the Mesozoic Era?

The Cretaceous-Paleogene (K-Pg) extinction, likely due to an asteroid impact, wiped out non-avian dinosaurs and many marine species

What are the three things animals can do in response to geological and climate changes?

Move, adapt, or go extinct.

What is the Gondwana effect?

Shared evolutionary and biogeographic patterns among southern continents due to their origin in Gondwana.

Why study early tetrapods, amniotes, and synapsids in mammal evolution?

Mammals evolved from synapsid amniotes, which came from tetrapods—this helps trace mammalian traits.

Give two facts about Pelycosaurs.

Early synapsids from the Paleozoic Era.

Included both herbivores and carnivores like Dimetrodon.

Mammalian roots within Synapsida appear in the cynodont family ____________, during the __________ period of the __________ era.

Cynodontia

Triassic

Mesozoic

When and during what period did the first true mammals appear?

End of the Triassic Period, around 225 million years ago.

What caused the extinction of Multituberculata, and when?

Competition with placental mammals (e.g., rodents); Eocene, ~35-40 million years ago.

What is an "endothermic homeotherm"?

An animal that regulates its internal temperature and maintains it constantly—like mammals and birds.

How does surface area to volume ratio affect heat loss?

Small animals (high ratio): lose heat fast, need high metabolism.

Large animals (low ratio): retain heat longer.

Name the two traditional subclasses of Class Mammalia

Prototheria (monotremes)

Theria (marsupials and placentals)

Which hypothesis—monophyly or polyphyly—is better supported by fossil evidence for mammals?

Monophyly—all living mammals share a common ancestor.

List four reasons marsupials may not compete well with placentals.

Less efficient placenta.

Longer pouch development limits reproduction.

Less adaptable to niches.

Outcompeted in shared habitats.

Give one unique biological feature of monotremes.

They lay eggs but produce milk and have fur; milk is secreted from skin (no nipples).

Why is the extinct order Condylarthra important?

They are ancestral to modern ungulates and key to understanding placental herbivore evolution.

Describe the evolutionary history of Cetacea.

Evolved from terrestrial artiodactyls.

Major extinct groups: Pakicetidae, Ambulocetidae, Basilosauridae.

Modern groups: Mysticeti (baleen), Odontoceti (toothed).

Closest relatives: hippos; together they form Cetartiodactyla.