Tiktaalik Demoted to a Has-Been

The highly-publicized tetrapod missing link or “fish-a-pod” that
made headlines in 2006 has been dethroned by new findings in Poland.
Trackways said to be 18 million years older than Tiktaalik, showing digits and alternating steps, were announced today in Nature.1 The authors said, “They force a
radical reassessment of the timing, ecology and environmental
setting of the fish-tetrapod transition, as well as the completeness
of the body fossil record.”

Here is a sample of the revolutionary talk being reported:
· “These results force us to reconsider our whole picture
of the transition from fish to land animals” said co-discoverer
Per Ahlberg in ScienceDaily.2
· The finding “could lead to significant shifts in our
knowledge of the timing and ecological setting of early
tetrapod evolution.” — Ted Daeschler in National Geographic
News.3
· “The team says the find means that land vertebrates
appeared millions of years earlier than previously supposed....
the Zachelmie Quarry tetrapods break the neat and simple timeline.” (BBC News4).
· “The fish-tetrapod transition was thus seemingly quite
well documented.... Now, however, Niedzwiedzki et al lob
a grenade into that picture.” — Janvier and Clement,
commenting on the find in Nature.5
· “It blows the whole story out of the water, so to speak.”
— Jenny Clack (Harvard), in PhysOrg.6
· “We didn’t know they existed at this point, and we
would not have expected to have found them in this environment.”
— Per Ahlberg, co-discoverer, in Live Science.7
No body fossils were found. This means that inferences about
the trackmakers will be limited. Readers should therefore take
caution at the artist reconstructions in some articles, such as
National Geographic, that try to give the animals a fish-like
appearance. PhysOrg noted, “Although she acknowledged their
importance, Clack warned against drawing conclusions exclusively
on small marks left by animals on the bottom of a muddy surface
hundreds of millions of years ago [mya].” The tracks are dated
397 mya, whereas Tiktaalik was dated around 380 mya. The
scientists inferred that the trackmakers were sizeable — about 2
meters long. Since no tail drag prints are seen, the animals must
have had limbs strong enough to hold their bodies above ground
(see illustrations in the BBC News).
Another bombshell is that this may not be the only grenade
to be lobbed into the picture. The discoverers noted with interest
that trackways from Glenisla dated late Silurian (418–422 mya),
thought to be those of arthropods, may actually be vertebrate
tetrapod tracks as well.8 And the new Polish trackways open the
door to more finds like it. “Obviously the hunt is on,” Ahlberg
said, for more trackways and body fossils from that period and the
locale’s presumed intertidal environment. Janvier and Clement
said,
Niedzwiedzki and colleagues’ apparently anachronistic Eifelian
[397–391 mya] tetrapod trackways will thus shake
up thinking about tetrapod origins. They show that the
first tetrapods thrived in the sea, trampling the mud of
coral-reef lagoons; this is at odds with the long-held view
that river deltas and lakes were the necessary environments
for the transition from water to land during vertebrate
evolution. And in guiding the search for a gradual timing
of the fin-limb transition during the Middle Devonian, they
are likely to trigger a burst of field investigations into
potential tetrapodomorph fish sites of Emsian [497–397 mya]
or earlier age.
1. Niedzwiedzki, G., P. Szrek, K. Narkiewicz, M. Narkiewicz, and P.E. Ahlberg.
2010. Tetrapod trackways from the early Middle Devonian period of Poland.
Nature 463:43–48.
2. Uppsala University (2010, January 8). Fossil footprints give land vertebrates
a much longer history. ScienceDaily. Retrieved January 22, 2010, from
www.sciencedaily.com/releases/2010/01/100107114420.htm
3. Roach, J. (2010, January 6). Oldest land-walker tracks found — pushes back
evolution. National Geographic Daily News. Retrieved January 22, 2010,
from http://news.nationalgeographic.com/news/2010/01/100106-tetrapodtracks-
oldest-footprints-nature-evolution-walking-land.html
4. Amos, J. (2010, January 6). Fossil tracks record ‘oldest land-walkers.’ BBC
News. Retrieved January 22, 2010, from
http://news.bbc.co.uk/2/hi/science/nature/8443879.stm
5. Janvier, P. and G. Clement. 2010. Palaeontology: Muddy tetrapod origins. Nature
463:40–41.
6. Uppsala University (2010, January 6). Fossil footprints give land vertebrates
a much longer history. PhysOrg. Retrieved January 22, 2010, from
www.physorg.com/news182005810.html