Fossil reveals transition from fins to feet

The presence of the pelvic girdle suggests the evolution of four-legged movement began with fishes long before it was seen in land animals.
By Ananth Baliga  |  Jan. 14, 2014 at 9:22 AM
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Analysis of the hind quarters of a 375-million-year-old Tiktaalik fossil has given researchers insight into the transition of animals from the water to land.

Researchers until now were only able to study the front of the creature, which was first reported in 2006, but newly unearthed fossils have revealed details of the rear side of the creature, which features of both fish and animals that walk on land, or tetrapods.

Researchers have discovered the presence of a thick and powerful rear fin and a pelvic girdle to support it.

The study, published in the journal PNAS, attempted to answer how the Tiktaalik propelled itself through shallow waters. The 2.5-meter-long creature had scales and webbed fins, but also a flat head, shoulders, forearms and wrists, making the genus a precursor to four-limbed land animals.

"The pelvis is as large as the shoulder girdle, and that's not what we would have expected in this finned stage in the fin-to-limb transition. We would have expected the pelvic fins to be smaller," said Dr. Ted Daeschler, of Drexel University in Philadelphia.

The team also said that this provides evidence that the evolution of locomotion based on a four-appendage system started long before it was seen in land animals.

[BBC] [University of Chicago] [PNAS]

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