Why Head Gear? Defense: Combat: Mate Recognition: Ornamentation: EXTREME!!!
Natural Selection Differential survival and reproduction
Sexual Selection Certain evolutionary traits are the result of intraspecific competition Intrasexual Competition: Generally Male- Male competition, female mates with the “winner” Intersexual Competition: Female Choice EXTREME!!!
Types of Head Gear? Ossicones: Horns: Antlers: Pronghorns: EXTREME!!!
Head Gear: Horns Fossils: Brontotheriidae EXTREME!!!
Mylagaulid rodents Why do they have those crazy horns? 30-5 Ma North America EXTREME!!!
Mylagaulid Ecology Herbivorous Body size: ~ 0.5-5 kg. Fossorial (burrowing), but how? One of the only fossorial animals with horns Millions of years ago EXTREME!!!
Fossorial adaptation in rodents Figure from Stein 2000 Scratch digging Chisel tooth digging Head lift digging EXTREME!!!
Head digging in mylagaulids Features consistent with head- digging: Thickened, projecting nasal bones Tall, forward-tilted occipital plate Shortened skull Powerful forelimbs EXTREME!!! Likely evolved from head-lift diggers
Why horns? Possible uses of horns: Species recognition Digging Sexual display/combat Defense EXTREME!!!
Horns : digging implement In favor: Higher occipital plate with taller horns Against: Position, orientation of horns Change in horns through time Increases force needed to dig CONCLUSION: unlikely EXTREME!!!
Horns : sexual display/combat Not sexually dimorphic Lack of visual ability Display useless underground Orientation of horns CONCLUSION: unlikely EXTREME!!!
Horns : defense Passive or active defense Predator diversity: mustelids (weasels and stoats), snakes? CONCLUSION: Likely, consistent with available evidence. EXTREME!!!
Horns…or Not Horns Coelodonta Late Pleistocene (~20,000 years ago) Europe EXTREME!!!
NOT “true” horns Coelodonta Late Pleistocene (~20,000 years ago) Europe EXTREME!!!
Homotherium Smilodon Is the evolution of the sabertooth convergent evolution or parallel evolution?
Convergent Evolution vs. Parallel Evolution? Convergent Evolution: describes the acquisition of the same biological trait in unrelated lineages. Parallel Evolution: the development of a similar trait in different not closely related species (that is in species of a different clade), but descending from the same ancestor.
Question: How do we distinguish how closely an organism is related? How to Solve this? Hall (2003) Biological Reviews
Question: How do we distinguish how closely an organism is related? How to Solve this? Convergence: Similarity arising through independent evolution having different developmental pathways Parallelism: A feature present in closely related organisms but not present continuously in all members of the lineage, and uses similar developmental pathways. Hall (2003) Biological Reviews
Evolution of saberteeth How do they develop? Thylacosmilus Machaerodus EXTREME!!!
Who’s the Baddest?: Polar Bear Wins!! EXTREME!!!
Who’s the Baddest?: 2. Andrewsarchus mongoliensis3. Daeodon hollandi Height: up to 8 ft at shoulder Length: 11 feet long Weight: up to 2200 lbs. Age: 40 Ma Height: up to 7 ft at shoulder Length: 12 feet long Weight: up to 2200 lbs. Age: 25 Ma V. EXTREME!!!
Who’s the Baddest?: EXTREME!!! Andrewsarchus mongoliensisDaeodon hollandi
Who’s the Baddest?: Andrewsarchus Wins!! EXTREME!!!
Who’s the Baddest?: V. 6 ft. tall at shoulder Weighs up to 2000 lbs Can stand up to 11 feet tall 1. Ursus maritimus tyrannus 2. Andrewsarchus mongoliensis Height: up to 8 ft at shoulder Length: 11 feet long Weight: up to 2200 lbs. EXTREME!!!