Tiktaalik Fills Another Gap

Searching for Transitionals

• Estuary or tidal flat• Warm, equatorial climate• Late Devonian era, around 370 million

years ago• Presently exposed for exploration• Incorporating knowledge from ecology,

geology, and paleogeography, a site was chosen

Transitional Characteristics

• Skull shape

• Mobile neck

• Functional wrists

• Fins with digit-like bones

• Muscled limbs and pectoral girdle

• Development of the ear

Skull Shape

Neck Mobility

• Devonian fish have bony gill covers that prevent extensive movement immediately behind the head.

• All tetrapods lack a bony gill cover. Amphibians have gills but no bony cover.

• Tiktaalik has gills but a reduced bony cover, which allows for movement of the neck.

Functional Wrists

Digit-like Bones

Muscled Limbs & Pectoral Girdle

• While Devonian fishes have relatively weak fins merely for swimming, Tiktaalik’s limbs were more muscled

• Tiktaalik also had a pectoral girdle that supported its forelimbs

• This means that Tiktaalik was capable of lifting its own weight out of the water to breathe air

Muscled Limbs & Pectoral Girdle

Development of the Ear

• Changes in the bony gill cover allow a gill slit called a spiracle to be further exapted into a component of the ear in later species.

• Though the exaptation of existing characteristics to form the ear is well known, especially in the amphibian-to-mammal transition, this is yet another example of evolution’s powerful creativity.

Richard Crowson--The Wichita Eagle

Intermediate Characteristics

Neil Shubin, research project leader and Nature article author, realizing that the multiple intermediate characteristics of Tiktaalik demonstrate the transition from fish to tetrapod (tetra- meaning “four,” pod meaning “foot”) , dubbed the species a

fishapod.

Intermediate Characteristics

• Fish– Gills

– Scales

• Fishapod– Half-fish, half-tetrapod limb bones and joints

– Half-fish, half-tetrapod ear region

• Tetrapod– Rib bones

– Mobile Neck

– Lungs

Creationist Responses

Ken Ham states in his blog:

“I only saw the article briefly tonight, and, of course, none of us have seen a detailed analysis of what has been found—so until we do that, we obviously can’t make any detailed comments on this particular find.”

http://blogs.answersingenesis.org/aroundtheworld/?p=696

Creationist Responses

• Why is Ham not aware that there were two Tiktaalik articles published?

• Why does Ham not have access to the information in Nature?

• Also, where does he think he’ll ever find a “creationist palaeontologist”?

Creationist ResponsesRobert Crowther of Discovery Institute’s evolutionnews.org writes:

“These fish are not neccesarily [sic] intermediates, explain Discovery Institute scientists I queried about the find. Tiktaalik roseae [sic] is one of a set of lobe-finned fishes that include very curious mosaics--these fishes have advanced fully formed characteristics of several different groups. They are not intermediates in the sense that have half-fish/half-tetrapod characteristics. Rather, they have a combination of tetrapod-like features and fish-like features. Paleontologists refer to such organisms as mosaics rather than intermediates.

[…]

What is clear is that forms like Tiktaalik [sic] are a melange [sic] of primitive and more developed features. It is not clear whether they are true transitional forms.”

http://www.evolutionnews.org/2006/04/latest_fossil_find_no_threat_t.html

Creationist Responses“alienward” on IIDB.org wrote in response:

“In One Look dictionary search the quick definition for mélange is “a motley assortment of things”. So, we’re finally starting to see ID proponents describe how the intelligent designers come up with new designs. Intelligent designers hack together motley assortments of primitive and more developed features. Ummm…”

“Super Squirrel” on IIDB.org paraphrased:“Discovery Institute: ‘They're not transitional forms! They are just organisms that share characteristics from organisms that came before and after them!’

Me: ‘... *Smacks forehead* How is that not transitional?’”