Limb Development and Our “Inner Fish”

Science Daily has a story on research delineating the relationship between us and fish.  The work, which examined some cartilaginous fish, as well as the three surviving lungfish species, was led by Peter Currie of the Australian Regenerative Medicine Institute at Monash University. The story notes:

"We examined the way the different fish species generated the muscles of their pelvic fins, which are the evolutionary forerunners of the hind limbs," said Professor Currie, a developmental biologist. Currie and his team genetically engineered the fish to trace the migration of precursor muscle cells in early developmental stages as the animal's body took shape. These cells in the engineered fish were made to emit a red or green light, allowing the team to track the development of specific muscle groups. They found that the bony fish had a different mechanism of pelvic fin muscle formation from that of the cartilaginous fish, a mechanism that was a stepping stone to the evolution of tetrapod physiology. "Humans are just modified fish," said Professor Currie. "The genome of fish is not vastly different from our own. We have shown that the mechanism of pelvic muscle formation in bony fish is transitional between that in sharks and in our tetrapod ancestors."

The paper is in the online journal PLoS and can be found here.  Another piece of the puzzle.  So...is it worse that we share common ancestry with chimpanzees or with fish?

More Information about the Origin of Tetrapods

Tom Spears of the Ottawa Citizen has a story on research being done to determine the genetic link between current animals and the earliest tetrapods. He writes:

A tetrapod is something with four legs and a spine. A frog, a dinosaur, a giraffe in the high veldt. There has been life on Earth for nearly four billion years, but tetrapods for only one-tenth of that.

Before tetrapods, however, there were lots of fish. So, what's the connection?

In the zebrafish, Akimenko found a new family of genes that seemed important to how fins develop in the embryo. These genes appear in different fish species, but have disappeared from animals with legs. The genes allow fish to produce a fibrous material in fins called actinotrichia. Here's where her detective work starts.

She suggests that two mutations were necessary for the suppression of that gene which led to the earliest tetrapods. Another piece of the puzzle.

----------------
Now playing: Peter Gabriel - Kiss of Life
via FoxyTunes

Australia's Fossil Graveyard

The Brisbane Times is reporting on the Billabong graveyard in western Australia that is teaming with fish. Deborah Smith writes:

DEATH came on a grand scale 360 million years ago in the state's central west.

When severe drought caused a large billabong to dry up, the fish in it expired en masse, forming a uniquely rich fossil site near Canowindra.

''There are literally thousands of fishes, crowded together like sardines in a gigantic tin,'' said Per Ahlberg, a palaeontologist at Uppsala University in Sweden.

The extraordinarily well-preserved fish fossils, excavated 17 years ago, have helped make Canowindra a popular tourist destination.

But the money is running out and there is much more to be found. Dr. Ahlberg believes that among the fish could be early tetrapod remains, which would make this area one of the earliest tetrapod locations.

Oldest Tetrapod Footprint Discovered in Poland

NewScientist has an article on the oldest tetrapod footprint yet discovered. Shanta Barley writes:

Tetrapod footprints dating back 397 million years have been discovered in the Świętokrzyskie mountains in southern Poland in what was, at the time they were made, a seashore. All previous fossil evidence for these earliest known four-limbed vertebrates has been found in river deltas and lakes.

"Our discovery suggests that the current scientific consensus is mistaken not only about when the first tetrapods evolved, but also about where they evolved," says Grzegorz Niedźwiedzki of the Department of Palaeobiology and Evolution at the University of Warsaw in Poland, who discovered the footprints in 2002 in an old quarry near the town of Kielce.

A bit later:

"It was assumed that tetrapods evolved in river deltas and lakes, partly because all previous fossil evidence has been found in these environments," says Jenny Clack, curator of vertebrate palaeontology at the University Museum of Zoology in Cambridge, UK. "This research suggests that the first tetrapods that crawled onto land were, in fact, living in shallow seas."

The link to the Nature article appears to be free (for the moment). The article authors write:

Until now, the replacement of elpistostegids [animals like Tiktaalik and Panderichthys] by tetrapods in the body-fossil record during the mid–late Frasnian has appeared to reflect an evolutionary event, with the elpistostegids as a short-lived ‘transitional grade’ between fish and tetrapod morphotypes (Fig. 5a). In fact, tetrapods and elpistostegids coexisted for at least 10 million years (Fig. 5b). This implies that the elpistostegid morphology was not a brief transitional stage, but a stable adaptive position in its own right. It is reminiscent of the lengthy coexistence of non-volant but feathered and ‘winged’ theropod dinosaurs with volant stem-group birds during the Mesozoic.

One of the most exciting areas in palaeontology right now is the origin of the tetrapods. As with most scientific discoveries, this will answer a bunch of questions and pose even more.

----------------
Now playing: Todd Rundgren - Chain Letter
via FoxyTunes

Phylogenetics: A Horse of a Different Color

New research on horse DNA suggests that the number of horse species in the fossil record has been overestimated. The report, in Science Daily has this to say:

Lead author of the paper, Dr Ludovic Orlando from the University of Lyon, says the group discovered a new species of the distinct, small hippidion horse in South America.

"Previous fossil records suggested this group was part of an ancient lineage from North America but the DNA showed these unusual forms were part of the modern radiation of equid species," Dr Orlando says.

A new species of ass was also detected on the Russian Plains and appears to be related to European fossils dating back more than 1.5 million years. Carbon dates on the bones reveal that this species was alive as recently as 50,000 years ago.

"Overall, the new genetic results suggest that we have under-estimated how much a single species can vary over time and space, and mistakenly assumed more diversity among extinct species of megafauna," Professor Cooper says.

"This has important implications for our understanding of human evolution, where a large number of species are currently recognised from a relatively fragmentary fossil record.

The thorns in the side of phylogenetic analysis have always been intraspecies variation and the overall incompleteness of the fossil record. How do you know that the fossil sample that you have of any given species is representative of the entire range of variation for that species?

This does not have implications for evolutionary trajectories as much as it does for evolutionary taxonomy. Maybe Tiktaalik roseae had considerably more variation in traits than we know based on the sample that we have. But we do know that some of the individuals of the species had traits that link them to later tetrapods as well as some traits that link them to late fish.

----------------
Now playing: Earth, Wind & Fire - Love's Holiday + Brazilian Rhyme (Interlude)
via FoxyTunes

New Issue of Evolution Education Outreach on Transitional Forms

The new issue of Evolution Education Outreach, which is free to the public is devoted to transitional fossils. There is a very good article on the recent "fishapod" transition by Jennifer Clack, which tackles all of the transitional forms that we have and makes coherent sense of them. The conclusion hits the nail on the head:

In summary, we now have a much richer fossil record that has improved our understanding of the timing, sequence of events, and conditions in which the origin of tetrapods took place. The boundary between “fish” and “tetrapods” is becoming progressively more difficult to draw, and a more complex story is emerging in which, for example, the origin of limbs with digits, the origin of walking and terrestriality, and the origin of tetrapods in a strict sense, may be three different things.

A great article. Read the whole thing, and the other articles, as well. With more articles like this coming out, the creationist/ID lie that there are no transitional fossils is becoming hollower and hollower.