What was lost tens of millions of years ago is now found.

A fossil animal locked in Lebanese limestone has been shown to be an extremely precious discovery - a snake with two legs.

Scientists have only a handful of specimens that illustrate the evolutionary narrative that goes from ancient lizard to limbless modern serpent.

Researchers at the European Light Source (ESRF) in Grenoble, France, used intense X-rays to confirm that a creature imprinted on a rock, and with one visible leg, had another appendage buried just under the surface of the slab.

"We were sure he had two legs but it was great to see it, and we hope to find other characteristics that we couldn't see on the other limb," said Alexandra Houssaye from the National Museum of Natural History, Paris.

True structural convergence: structures that have undergone convergent evolution can artificially result in incorrect tree topologies. Including more characters in the analysis also aids in overcoming convergent effects.

Character reversals: characters that revert to an ancestral state pose a challenge similar to convergence. Because DNA and RNA only have four different character states, they are especially prone to reversals during evolution.

Lost characters: lineages that have lost characters (such as whales and their hindlimbs) can also pose cladistic problems. Often, if a cladistic analysis indicates strongly that a certain character has been lost during evolution, it is best to omit this character in higher resolution analyses of that lineage.

Originally posted by madnessinmysoul
reply to post by Heronumber0

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...not in this thread. this thread is my retreat from oversciencing things. it's where i can just lay back, relax, and talk about a really cool fossil.

if you want me to lay down some heavy science, go to a different thread.

Here, one could see the fossil species "Eohippus" transformed into an almost totally different-looking (and very familiar) descendent, Equus, through a series of clear intermediates. Biologists and interested laypeople were justifiably excited. Some years later, the American Museum of Natural History assembled a famous exhibit of these fossil horses, designed to show gradual evolution from "Eohippus" (now called Hyracotherium) to modern Equus. Such exhibits focussed attention on the horse family not only as evidence for evolution per se, but also specifically as a model of gradual, straight-line evolution, with Equus being the "goal" of equine evolution. This story of the horse family was soon included in all biology textbooks.

There are no truly consistent "trends".
Tracing a line of descent from Hyracotherium to Equus reveals several apparant trends: reduction of toe number, increase in size of cheek teeth, lengthening of the face, increase in body size. But these trends are not seen in all of the horse lines. On the whole, horses got larger, but some horses (Archeohippus, Calippus) then got smaller again. Many recent horses evolved complex facial pits, and then some of their descendants lost them again. Most of the recent (5-10 My) horses were three-toed, not one-toed, and we see a "trend" to one toe only because all the three-toed lines have recently become extinct.

Additionally, these traits do not necessarily evolve together, or at a steady rate. The various morphological characters each evolved in fits and starts, and did not evolve as a suite of characters. For example, throughout the Eocene, the feet changed little, and only the teeth evolved. Throughout the Miocene, both feet and teeth evolved rapidly. Rates of evolution depend on the ecological pressures facing the species.

The "direction" of evolution depends on the ecological challenges facing the individuals of a species and on the variation in that species, not on an inherent "evolutionary trend

Originally posted by madnessinmysoul
reply to post by Heronumber0

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...not in this thread. this thread is my retreat from oversciencing things. it's where i can just lay back, relax, and talk about a really cool fossil.

if you want me to lay down some heavy science, go to a different thread.

We usually call that a lizard. Mystery solved.

Originally posted by Astyanax
reply to post by Heronumber0

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Hey there, Hero.

Your objections have to do with taxonomy and cladistics rather than evolution itself. What it amounts to is a statement -- accepted by all respectable biologists -- that evolution is not teleological; forms are not evolving towards some ideal of perfection.

Anyway, the taxonomic evidence linking Pakicetus with modern whales merely confirms what we already know from molecular evidence: that whales and modern hippopotami had a common ancestor antecedent to both forms. See (for instance) Dawkins, The Ancestor's Tale, 'Laurasiatheres' for more information.

It has been established for at least half a century that whales are the descendants of land-dwelling animals that returned to the sea. This is old, well-established knowledge you're attempting to contest here.