Graham SlaterDepartment of Paleobiology, National Museum of

Natural History

Tempo or Mode in Evolution? The Case of Mammalian Body

Size Evolution

www.fourdimensionalbiology.com

- Gene Hunt- Pete Wagner- Jon Marcot- Dave Bapst- Tom Ezard- Gavin Thomas- Andy Purvis

- Peter Smits- Greg Wilson

authors

- Luke Harmon*- Rob Freckleton- Sam Ponton

- Arne Mooers- Dave Polly- Folmer Bokma- Graeme Lloyd

organization reviews

data

“Unifying Fossils and Phylogenies for Comparative Analyses of Diversification

and Trait Evolution”

How fast do animals evolve? That is one of

the fundamental questions regarding evolution.

Photo: Florida Museum of Natural History

Simpson (1944, 1953)

is our emphasis on rates appropriate?

Illustration by Mark Hallet

Eoce

ne

Olig

oce

ne

Mio

cene

Alroy (1999) Systematic Biology

fossil data show a rapid increase in body size disparity after the K-Pg

Sd

(m

ass

)

Venditti et al. (2011) Nature

K Pg NgJ

relative rate

phylogenetic data suggest increased rates with the origin of modern

orders

Do we really think the Tempo of mammalian

body size evolution increased after the K-

PG extinction?

the mammalian body size zone

the mammalian body size zone

the mammalian body size zone

variation in tempo

evolution slow

evolution fast

variation in mode

evolution constrained

evolution unconstrained

3 paleo-motivated models for mammalian body size evolution

BM rate 1 BM rate 2

Mesozoic CenozoicK-Pg rate shift

Ornstein-Uhlenbeck BM

Mesozoic Cenozoicecological release

Mesozoic Cenozoicrelease and radiate

BM*Ornstein-Uhlenbeck

time calibrated phylogeny of living and fossil mammals

Estimating body masses for Mesozoic mammals

standard models paleo-inspired models

Brownian motion

directional

evolution

Ornstein-Uhlenbeck

Accelerating /

Decelerating

white noise

K-Pg Shift

ecological

release

release & radiate

extant taxa only

extant + fossils

release & radiate fits best for extant taxa...

standard models paleo-inspired models

Brownian motion

directional

evolution

Ornstein-Uhlenbeck

Accelerating /

Decelerating

white noise

K-Pg Shift

ecological

release

release & radiate

extant taxa only

extant + fossils

...and more so for the fossil dataset

standard models paleo-inspired models

Brownian motion

directional

evolution

Ornstein-Uhlenbeck

Accelerating /

Decelerating

white noise

K-Pg Shift

ecological

release

release & radiate

extant taxa only

extant + fossils

Parameter Mesozoic Cenozoic

rate (σ2) 0.97 0.1

faster rates of body size evolution in the Cenozoic?

Brownian motion is a diversifying process

time

ph

en

oty

pe

rate σ2

starting state starting state

σ2 * time

time

ph

en

oty

pe

σ2 / 2α

rubber band parameter α

OU is an equilibrium process

rate σ2

starting state starting state

time

ph

en

oty

pe

Brownian motionOrnstein-Uhlenbeck

BM and OU simulated at the same rate give very different disparities

the OU process has an equilibrium disparity

ln(b

ody m

ass

) dis

pari

ty

Mesozoic CenozoicT J PgK Ng

α= 0.01σ2 = 0.97

Mesozoic CenozoicT J PgK Ng

a low BM rate increases disparityln

(body m

ass

) dis

pari

ty

σ2 = 0.1α= 0.01σ2 = 0.97

Do we really think the Tempo of mammalian

body size evolution increased after the K-

PG extinction?

Variation in the Mode of evolution is a more intuitive and

more likely explanation that

variation in Tempo

Do we really think the Tempo of mammalian

body size evolution increased after the K-

PG extinction?

How fast do animals evolve? That is one of

the fundamental questions regarding evolution.

Photo: Florida Museum of Natural History

Simpson (1944, 1953)

From Simpson (1953)

Simpson’s adaptive zones