Behold, I teach you the tetrapod; he is this uber, he is this fishy!
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 Environment
The 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 land—those things left behind by the receding tide—well 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."
Admittedly, the NG is a tabloid; but it sounds like something like a hellbender or giant newt was working the shoreline a few geological moments earlier than we had suspected. These guys sound more significant than mere lungfish or walking cat, ie more ancestral and less fraternal.
Read, call attention to any interesting points, enjoy.
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.
I was thinking about this when I first read the story. It reminds me of all the times we have discovered man overlapping people like neanderthal we had thought were ancestral. I don't take it too seriously, coelecanths and newts are still alive now.
There is also the issue of whether the evolution to tetrapod from fish occurred once or several times. Seeing as we see existing organisms with mobile ability in tidal mud flats it is not unreasonable that such adaptation to a new opportunity occurred several times.
The tracks left by organisms are among the most difficult of fossils to interpret. But just such evidence puts debate about the origins of four-limbed vertebrates (which include ourselves) on a changed footing.
Philippe Janvier & Gaël Clément
Abstract
The tracks left by organisms are among the most difficult of fossils to interpret. But just such evidence puts debate about the origins of four-limbed vertebrates (which include ourselves) on a changed footing.
The term 'tetrapodomorph fishes' scarcely rolls off the tongue, but these are fossil animals that have a special place in the evolutionary history of vertebrates. It was through the stepwise transformation of paired fins in this lineage of lobe-finned fishes that paired limbs with digits arose, marking the advent of the four-limbed vertebrates, or tetrapods.
1. Philippe Janvier and Gaël Clément are at the Muséum National d'Histoire Naturelle (CNRS UMR7207), 8 rue Buffon, 75231 Paris Cedex 05, France.
Nature 463, 40-41 (7 January 2010) | doi:10.1038/463040a; Published online 6 January 2010
Tetrapod trackways from the early Middle Devonian period of Poland p43
The earliest body fossils of tetrapods (vertebrates with limbs rather than paired fins) date to the Late Devonian period. There have been claims of tetrapod trackways predating these body fossils but the age and identity of the track makers have remained controversial. The discovery of well-preserved and securely dated tetrapod tracks from Polish marine tidal flat sediments of early Middle Devonian age, around 18 million years older than the earliest tetrapod body fossils, is now presented.
Grzegorz Niedźwiedzki, Piotr Szrek, Katarzyna Narkiewicz, Marek Narkiewicz & Per E. Ahlberg
Tetrapod trackways from the early Middle Devonian period of Poland
Grzegorz Niedźwiedzki1, Piotr Szrek2,3, Katarzyna Narkiewicz3, Marek Narkiewicz3 & Per E. Ahlberg4
1. Department of Paleobiology and Evolution, Faculty of Biology, Warsaw University, 2S. Banacha Street, 02-097 Warsaw, Poland 2. Department of Paleontology, Faculty of Geology, Warsaw University, 93 Żwirki i Wigury Street, 02-089 Warsaw, Poland 3. Polish Geological Institute, 4 Rakowiecka Street, 00-975 Warsaw, Poland 4. Subdepartment of Evolutionary Organismal Biology, Department of Physiology and Developmental Biology, Uppsala University, Norbyvägen 18A, 752 36 Uppsala, Sweden
Abstract
The fossil record of the earliest tetrapods (vertebrates with limbs rather than paired fins) consists of body fossils and trackways. The earliest body fossils of tetrapods date to the Late Devonian period (late Frasnian stage) and are preceded by transitional elpistostegids such as Panderichthys and Tiktaalik that still have paired fins. Claims of tetrapod trackways predating these body fossils have remained controversial with regard to both age and the identity of the track makers. Here we present well-preserved and securely dated tetrapod tracks from Polish marine tidal flat sediments of early Middle Devonian (Eifelian stage) age that are approximately 18 million years older than the earliest tetrapod body fossils and 10 million years earlier than the oldest elpistostegids. 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.
Nature 463, 43-48 (7 January 2010) | doi:10.1038/nature08623; Received 21 July 2009; Accepted 29 October 2009
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