Fish Out of Water Almost 20 Million Years Faster

Discovered in an abandoned mountain quarry, the tracks suggest that tetrapods were traipsing the planet 18 million years earlier than previously indicated by the fossil record.The tracks are also ten million years older than the oldest known fossils of lobe-finned fishes called elpistostegids, which are widely considered to be transitional forms between fish and tetrapods. (See a surviving lobe-finned fish, the coelacanth.)The age of the newfound tracks suggest that "these transitional fish continued to exist alongside the tetrapods for quite some period of time," said Per Ahlberg, a paleontologist at Uppsala University in Sweden, who led the new research.It's not so strange for one type of animal to live alongside its evolutionary successors, Ahlberg noted. Several feathered dinosaurs, for example, "continued to exist alongside the birds for millions of years." Marine EnvironmentThe finding also suggests the fins-to-limbs evolution occurred in an intertidal or lagoon environment rather than a seasonally flooded forest, as indicated by earlier finds.The tidal "scenario has considerable explanatory power," the researchers write in Nature.Due to the regular coming and going of the tides, marine ancestors of tetrapods, for example, would have had easy access twice a day to marine animals stranded at low tide.This reliable smorgasbord would have helped tetrapod ancestors find their legs, so to speak."If you're picking off dead and moribund animals in the strand landthose things left behind by the receding tidewell then you don't need to be terribly good at moving around," Ahlberg noted."You just need to be able to haul your way out, eat what you want to eat, and then haul your way back into the water again."

Rethinking the why and where is another aspect of this explosive discovery. The first tetrapods have been recognised as animals that lived in water. People have wondered whether fins evolved into legs as the animals negotiated plant material in shallow waters, perhaps brackish or even freshwater. These ideas may still be applicable to Acanthostega and Ichthyostega, but they are not realistic for the new tetrapod trackways - which are found in marine tidal flat sediments."Niedzwiedzki and colleagues' apparently anachronistic Eifelian 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."The ID interest in this story is for at least two reasons. First, the case documents an example of a failed evolutionary prediction - although, for a while, evolutionists have claimed it as a triumph (see the blog by Casey Luskin on this). Second, the evolution of tetrapods is an important test case for the relevance of design thinking - we ask the question whether tetrapods are here by Design or whether Law+Chance processes are sufficient explanation. Research is proceeding assuming the latter option, but the new discovery suggests that pursuing multiple working hypotheses (including design-based options) might be more prudent.

How can you illustrate something that is undetermined (and why does it look like tiktaalik?)