Lehra Bogino, Justin Drake, Kellie Snooks

Adaptive radiation is the evolution of an animal or plant group into a wide variety of types adapted to specialized modes of life.

Mammals are defined as any member of the class of warm-blooded vertebrates having four limbs, feminine milk-secreting glands, and the presence of hair at some stage of development.

Permian Period (approximately 270 mya) True mammals were not

yet in existence, but their predecessors Synapsids were.

Synapsids, more specifically the order Therapsida, which included mammal like reptiles that walked on four legs, diversified and spread during this period giving rise to the first true mammals.

Diversification of the Therapsids began to occur at the second half of the Triassic to the early part of the Jurassic periods.

Small mammals (described as shrew like) thrived while dinosaurs still lived during the Jurassic Period.

During the mid-Jurassic period Therapsids had evolved many mammalian traits that further evolved with their descendants.

Hadrocodium- had a large brain and advanced ear structure but still remained small in size.

Being warm blooded allowed mammals to hunt at night, avoiding being eaten by their cold blooded predators. During this time 10

mammalian lineages evolved and diversified.

This included Multituberculates and the predecessors to Marsupials, Monotremes, and Placental Mammals.

The Hadrocoduim: It’s sensitive mammalian hearing allowed mammals to thrive to this day.

Approximately 65 mya During this period

dinosaurs still dominated, while small mammals continued to diversify.

When the asteroid struck (K/T Extinction Event) dinosaurs soon after became extinct, therefore mammals with characteristic adaptability had an entire world to fill.

Climate Changes Homeothermic

Small Size Oxygen

Climate Cooling Climatic and physical

changes were happening BEFORE KT extinction long sequence of events Angiosperms

Climatic trend + accentuation of seasons = BAD for dinosaurs Physiologically

could not handle cooling of environment

Mammals: have hair/fur could hunt at night

Possible Theory: Dinosaurs were a mix between endotherms

and ectotherms, but more closely related to endotherms Larger size, more costly metabolism, more

food needed Food chain disruption

Small rat to domestic cat size

Able to feed on organisms that could protect themselves from KT extinction

Lower demands for food

Able to burrow

Bininda-Emonds and Cardillo Super tree Divergence Rates

K/T Extinction Event

K/T Extinction Event

Orange: MarsupialsBlack: MonotremeAll Others: Placental

Log scale of lineages with extant descendents

Speciation and extinction events equal

All Mammals Placental

Mammals Marsupials

K/T Extinction Event

Bininda-Emonds, Olaf R. P., et al. The delayed rise of present-day mammals, Nature, 29 March 2007, Vol. 446. No. 7135. P. 507-512.

Luo, Zhe-Xi. Transformation and diversification in early mammal evolution, Nature, 13 Dec. 2007, Vol. 450. No. 7172. P. 1011-1019.

Russell, Loris S. Body Temperature of Dinosaurs and Its Relationships to Their Extinction, Journal of Paleontology, Vol. 39, No. 3 (May, 1965), pp. 497-501.

Strauss, Bob. “The First Mammals – Mammals of the Triassic, Jurassic and Cretaceous Periods.” About.com. 14 April 2010. <http://dinosaurs.about.com/od/otherprehistoriclife/a/earlymammals.htm>

Sudhir Kumar & S. Blair Hedges. A molecular timescale for vertebrate evolution, Nature, 30 April 1998, Vol. 392. P.917-920.