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

Orange: Marsupials Black: Monotreme All 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 No P  Luo, Zhe-Xi. Transformation and diversification in early mammal evolution, Nature, 13 Dec. 2007, Vol No P  Russell, Loris S. Body Temperature of Dinosaurs and Its Relationships to Their Extinction, Journal of Paleontology, Vol. 39, No. 3 (May, 1965), pp  Strauss, Bob. “The First Mammals – Mammals of the Triassic, Jurassic and Cretaceous Periods.” About.com. 14 April  Sudhir Kumar & S. Blair Hedges. A molecular timescale for vertebrate evolution, Nature, 30 April 1998, Vol P