Transcript Tiktaalik slides

Discussion of
A Devonian tetrapod-like fish and the evolution of
the tetrapod body plan
by
Edward Daeschler – Academy of Natural Sciences, Philadelphia
Neil Shubin – University of Chicago and the Field Museum
Farish Jenkins – Harvard University and Museum of Comparative Zoology
Nature
440:757-763
BIO101, Oct. 26, 2011
Serious questions remain in the evolution of animals.
How did terrestrial animals with four-legs (tetrapods)
evolve from marine animals with fins?
Big evolutionary transition!
Major changes in morphology (legs vs. fins) and respiration
Many more smaller changes (ears, head shape, etc.)
Lobe-Limbed Fish
Sarcopterygians – Living members include coelacanths, lungfish and tetrapods!
Rod-shaped bones with muscles in the pectoral fins
not simple rays supporting a very thin fin
Big evolutionary transition!
?
Should be able to find transitional species
Transitional species should be
approximately 365-375 MYA
Middle to late Devonian age
tiktaalik.uchicago.edu
Where are mid-to-late Devonian
rocks exposed on the surface?
In addition:
sparsely populated
freshwater in Devonian
Three sites in North America,
only one was largely unexplored
Welcome to Northern Canada!
Welcome to Northern Canada!
Fossil Site
Part of the Fram Formation
Laid down in late Devonian
Alternating sandstone and
siltstone layers. Probably a
meandering stream.
Fossil Site
Fossil Site
Fossils
28 partial fossils of this species found.
Each gets a name NUFV 108 through NUFV 135 (Nunavut Fossil Vertebrate Collection)
Three were fairly complete, with skulls and pectoral girdles and articulated
NUFV 108 is the holotype
All specimens are currently in the Canadian Museum of Nature in Ontario
Tiktaalik as a Transitional Species – Ancestral Characteristics
Body was covered in scales
Dorsal view
Tiktaalik as a Transitional Species – Ancestral Characteristics
True fins
Tiktaalik as a Transitional Species – Ancestral Characteristics
Gills
Ceratobranchial Element
Tiktaalik as a Transitional Species – Ancestral Characteristics
Probably had lungs too (like coelacanths and lungfish)
Large Gular Plates
Tiktaalik as a Transitional Species – Derived Characteristics
Flat skull
Eyes are more on top of the head, not on the sides
Tiktaalik as a Transitional Species – Derived Characteristics
Flattened Ribs
Tiktaalik as a Transitional Species – Derived Characteristics
Functional, flexible neck.
Pectoral girdle (collar and
shoulder bones) are tetrapodlike.
Loss of opercular, subopercular
and extrascapular bones.
Tiktaalik as a Transitional Species – Derived Characteristics
Wrist bones
Tiktaalik as a Transitional Species – Derived Characteristics
Wrist bones
Tiktaalik as a Transitional Species – Derived Characteristics
Wrist bones
Tiktaalik Ecology
Life in shallow water has it’s advantages
Tiktaalik Phylogeny
Evaluated 114 morphological characteristics for Tiktaalik and others
Tiktaalik Phylogeny
Evaluated 114 morphological characteristics for Tiktaalik and others