A. sediba is a splendid transitional fossil

A man holding a small, semi-human fossil skull

Lee Berger with A. sediba

Look at the quiet, yet awed, delight on this palaeontologist’s face. That is the reward of science. He has been analyzing two almost complete skeletons of Australopithecus sediba found together in South Africa.

Another gap in human evolution has been decisively filled. Australopithecus africanus, discovered by Raymond Dart in the 1930s, was a climbing, ape-like hominid. Homo habilis and Homo erectus were human-like and apparently tool–using. A. sediba seems to be right between them. It has longer legs than A. africanus and walks bipedally. It has features found in both A. africanus and H. habilis. Its hand is more like our own than is that of H. habilis. Carl Zimmer explains: The verge of human. Between this fossil and Ardipithecus ramidus, we seem to be getting a grasp on ape evolution.

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Transitional fossils: halfway flat fish

National Geographic’s 2009 roundup of transitional fossils included a fish that is evolving to lie concealed on the ocean floor. Modern flatfish are born symmetrical, with eyes an other side of their head, but as they age one eye moves around to the other side so that the fish can watch for danger with both eyes while lying flat on the sea floor.  The lack of “halfway” forms has been used to argue against evolution. Now, one has been found. This one appears to have one eye just over the midline. I wait for anti-evolutionists to acknowledge that the theory of evolution has been confirmed once again: Amphistium, transitional fossil, a half-way flat fish.

fossil fish

Amphistium, a transitional fossil in flatfish evolution

Transitions

Cranial capacity:

 

“Atlas of Creation” FAIL

Where’s FAILblog when we need it?  This self-parody is from that science-fantasy classic, the Atlas of Creation:

A 150-million-year-old salamander fossil showing frog-like skeletal elements

The Big Book o’ Creationist Nonsense claims that the fossil on the left is a frog from 280 million years ago that is identical to a modern frog. Unfortunately for that claim, the fossil’s tail and short legs are clearly visible.

Karasaurus

It looks as if Karaurus comes from here. In fact, it is A 150-million-year-old salamander fossil showing frog-like skeletal elements, such as a broad, enlarged head. It has been identified as Karaurus, which is from the Kimmeridgian in the Late Jurassic, between 150 and 155 megayears old.

As you can see, they’ve lightened up the image quite a bit and for some reason reversed left for right. I suppose that’s artistic licence, not quite as ridiculous as when the publishers included a picture of an artificial lure instead of an actual insect to illustrate a point of biology.

If it were a Permian fossil, it would have looked much more like the one described here, Gerobatrachus hottoni: Frog-salamander split found.

An Early Permian landscape, with Gerobatrachus hottoni lunging at the mayfly Protoreisma

The examination and detailed description of the fossil (Hotton’s elder frog) settles the dispute whether frogs and salamanders evolved from an ancient amphibian group called temnospondyls.

According to a press release garbled at eurekalert,

The dispute arose because of a lack of transitional forms. This fossil fills the gap, according to Jason Anderson, assistant professor, University of Calgary Faculty of Veterinary Medicine, and lead scientist in the study.

The Gerobatrachus fossil provides a much fuller understanding of the origin and evolution of modern amphibians. The skull, backbone and teeth of Gerobatrachus have a mixture of frog and salamander features: the fossil has two fused bones in the ankle, which is normally seen only in salamanders, and a very large tympanic ear (eardrum). It also has a lightly built and wide skull like that of a frog.

Its backbone is exactly intermediate in number [of vertebrae] between [choose one, article is unclear]:

  • EITHER the modern frogs & salamanders vs. the more primitive amphibians
  • OR the modern frogs vs. the salamanders & more primitive amphibians.

The new fossil also addresses a controversy over molecular clock estimates, or the general time salamanders and frogs evolved into two distinct groups.

“With this new data our best estimate indicates that frogs and salamanders separated from each other sometime between 240 and 275 million years ago, much more recently than previous molecular data had suggested,” says Robert Reisz, professor, University of Toronto Mississauga and second author on the paper.

Gerobatrachus was originally discovered in Texas in 1995 by a field party from the Smithsonian Institution that included the late Nicholas Hotton, for whom the fossil is named. It remained unstudied until it was “rediscovered” by Anderson’s team. [Hotton never got around to studying it before he died and it was his to do.]  It took countless hours of work on the small, extremely delicate fossil to remove the overlying layers of rock and uncover the bones to reveal the anatomy of the spectacular looking skeleton.

Caption: An Early Permian landscape, with Gerobatrachus hottoni lunging at the mayfly Protoreisma between stands of Calamites and under a fallen Walchia conifer.

Image credit: Michael Skrepnick

Seven major “missing links” since Darwin

Ambulocetus, a pre-whale, discovered in 1992; image by Shawn Gould

Ambulocetus, a pre-whale, discovered in 1992; image by Shawn Gould

National Geographic Magazine has published images and brief descriptions of seven transitional fossils discovered since Charles Darwin published his theory of evolution. Each of them is another  big piece of evidence confirming the explanation of how life’s diversity came developed.

Transitional forms: Tiktaalik and others

Here’s a brief review of several lovely transitional fossils in the tetrapod line, which tie together lobe-finned fishes with early land amphibians. The latest discovery is, from 300 million years ago, Tiktaalik roseae:Hello, Beautiful.”

a famous series of transitional fossils in the tetrapod lineage

Tiktaalik is an example of the predictive power of evolutionary theory. The discoverers noted the kind of fossil that they were missing, its expected environment, and the approximate age that it should be, then looked in rocks of the right age and geological origin in northern Canada. And voila! There was their fossil.

Liaoning fossils

Sinosauropteryx, fossil with protofeathersI still don’t have access to my pictures of the fossils from China exhibit in Miami, but some of these look very familiar: “Dragons of Liaoning” on Discover (UPDATED) is about early fossil birds and shows the transition from protofeathers to feathers with shafts to flight feathers.

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