Fossils-only tip-dating of deinonychosaurian

theropodsApril M. Wright

Nicholas J. MatzkeGraeme T. LloydDavid W. Bapst

www.slideshare.net/wrightaprilm/wright-svp2014

Can we use fossils-as-tips methods to co-estimate phylogeny and divergence dates in

the absence of molecular data?

Theropods as a test case for tip-dating● Controversial● Implications for the evolution of flight● Well-documented ages and relationships

among taxa in the tree

Placement of Archaeopteryx

Placement of Archaeopteryx

Placement of Archaeopteryx

A paleontological question

A paleontological question

A paleontological question

A paleontological question

Archaeopteryx as a calibration

node

Applying tip-dating methods

● Used Xu et al. matrix● 89 taxa, 389 morphological characters

○ Missing data ranges between ~5% and ~85% per taxon

○ 363 characters from Hu et al. 2009, 10 added by Xu et al.

○ Mix of cranial and post-cranial characters

Applying tip-dating methods

● Dates associated with every terminal in the matrix○ Both a minimum and a maximum age

Applying tip-dating methods

● Dates associated with every terminal in the matrix○ Both a minimum and a maximum age

● BEAST2 and MrBayes tip dating○ Both methods use the dates of the terminal taxa

instead of calibration points○ Both use Lewis’ 2001 Mk model

Applying tip-dating methods

● BEAST2○ Birth-death serial sampling prior: Allows for

speciation and extinction in tree for data sampled from multiple time-points

● MrBayes○ Uniform prior on clock trees○ Ingroup date calibration

Applying tip-dating methods

● BEAST2○ More explicit process-driven model

● MrBayes○ More vague with respect to biology and taphonomy

} Aves

} Deinonychosauria

175200 150 125 100 75 50 25

} Aves

} Deinonychosauria

175200 150 125 100 75 50 25

} Aves

} Deinonychosauria

175200 150 125 100 75 50 25

Placement of Archaeopteryx

MrBayes

● We were unable to obtain a topology with dates in which we had confidence○ Well-known clades being broken up○ Unrealistic dates that contradict the weight of

existing evidence

MrBayes

Xu et al. 2006

MrBayes

Conclusions

● Tip-dating is a viable method for estimating divergence dates○ Tip-dating can be performed with fossil-

only datasets● BEAST returns a topology and dates that

correspond well to known information about deinonychosaurian and avian relationships

Thanks!● Participants● Hillis Lab

Group● Nadia

Fröbisch, Jonathan Bloch, Anjali Goswami