Fish Moved Onto Land 395 Million Years Ago...

[Big Orange]

According to this article, backboned animals adapting to the land had possibly occurred eighteen million years earlier than originally assumed:

Oldest Land-Walker Tracks Found--Pushes Back Evolution

The first vertebrates to walk the Earth emerged from the sea almost 20 million years earlier than previously thought, say scientists who have discovered footprints from an 8-foot-long (2.4-meter-long) prehistoric creature.

Dozens of the 395-million-year-old fossil footprints were recently discovered on a former marine tidal flat or lagoon in southeastern Poland (prehistoric time line).

The prints were made by tetrapods—animals with backbones and four limbs—and could rewrite the history of when, where, and why fish evolved limbs and first walked onto land, the study says.

Because they are thought to have evolved from such creatures, reptiles, birds, and mammals—including humans—are today classified as tetrapods.

(Related: "Before tetrapods: Fishy Ancestors of Humans Surprisingly Diverse.")

"These are the oldest tetrapod tracks and also the oldest evidence of true tetrapods," study co-author Grzegorz Niedƃwiedzki, a paleontologist at Warsaw University, commented via e-mail.

The tracks were made by several individuals of a four-limbed species that had digits, or toes, on each foot, according to the research.

"We are dealing with creatures that were walking," said Marek Narkiewicz, a geologist at the Polish Geological Institut and co-author of the study, to be published tomorrow in the journal Nature.

The footprints vary in size, some as wide as 10 inches (26 centimeters). The track sizes and shapes indicate flat-bodied, lizard-like creatures up to 8.2 feet (2.5 meters) long with stout legs, the researchers said.

Oldest Tetrapod Tracks

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."

More Tetrapod Footprints Fossils Needed

The new tetrapod finding "could lead to significant shifts in our knowledge of the timing and ecological setting of early tetrapod evolution," said paleontologist Ted Daeschler via email. Daeschler studies fish-to-tetrapod evolution at the Academy of Natural Sciences in Philadelphia, Pennsylvania, but was not involved in the Nature study.

Daeschler notes, however, that tracks and trackways are notoriously difficult to interpret "with full confidence," and he's awaiting more evidence before abandoning existing explanations for the transition.

"No doubt that I will keep an open mind and keen eye on future developments," he said.

National Geographic

[Covenant]

I figured they'd discover something like this. The flimsy explanations as to why this one fish critter had so many valuable traits were obviously insufficient, and an explanation that some fish--like fish today--hop up on land to chase bugs, fruit, or just to scour the shallows for carrion... that makes a ton of sense. If you're in competition for limited resources, like fish that spit down bugs and stuff to catch them, it makes total sense that you'd evolve a method of extending your snuffling snout a little further up the shoreline. And for this transition to be soooo muuuuch slooower and a smoother learning curve than what some people had said before.

The more and more people discover tends to support very slow, very gradual, extremely basic forms of advanced forms being present long, long before we had seen their eventual use. And that these same pressures exert themselves on more than one creature. It seems like even scientists need to remember, time to time, that evolution is not predestination. There's not a One True Progenitor. ;D Would it be so hard to imagine several tetrapods of varying make and model all scrabbling for the same resources, at different evolutionary periods, and even continuing those lines on to today?

People don't seem to have an issue with those concepts when it comes to fish, sharps and whales--whose evolutionary logic trees are a bit confounded. Talk about mammals though, and everyone wants us to be special. ;D

[Alyrium Denryle]

Not surprised, not shocked, totally expected. Unfortunately I have to deal with the creationists, so here are the cliffs notes.

When we find fossils (And when I say we, I mean various individuals involved in the study of evolution. I study the evolution of predator prey interactions and do not myself find fossils to be useful in my research except for calibrating phylogenetic trees) we are not able to directly trace evolution down to the common ancestor. We find snapshots of life in a given area that form under very particular conditions. When we get those, we can use the morphology of the organisms to reconstruct a phylogeny but we cannot reconstruct everything. We get representatives of clades that are extant at the time of death in an area. However that does not mean that one clade is the linear ancestor of another.

I will use snakes as an example.

We have a pretty good phylogeny for snakes. We know they evolved from Anguimorph lizards and we have a pretty good idea of what snake groups are ancestral in the lineage. These are all extant snakes and lizards. Each clade has continued to exist side by side with the others long after the initial divergence. Species do not evolve Pokemon style into a more advanced form. Populations diverge and radiate from their parent populations in what can only be described as a fractal pattern. One population branched off and some of its eventual progeny would become snakes, however the lizards kept chugging along.

All this means is that the ancestral clade remained long after the divergence of its more derived relatives and we just have not found earlier fossils because of the freakish difficulty of fossilization and the fact that many of the ancient fossil beds we would need to look for are inaccessible or destroyed by subduction.