New Insight Into Horse Evolution

Genetic evidence is shedding new light on the origins of horses in the New World, during a particularly hazy period in their evolution.

As the Great Ice Age came to an end, some 11,000 years ago, North America was thought to be home to as many as 50 species and subspecies of horse.

But studies of ancient DNA tell a rather different story, suggesting the horses belonged to just two species.

"It looks like, as far as we can tell from the DNA, there is only evidence of two species in North America," Dr Alan Cooper from the University of Adelaide, Australia, told the BBC News website.

"We think that, in fact, people have been looking at these fossils and over-interpreting signs of changes in shape and size," he added.

"Probably these animals are adapting to local environments and perhaps they are [anatomically] more [changeable] than the palaeontologists had perhaps thought."

The work has implications for understanding other animals because horses are a textbook example of using fossil evidence to explain evolution.

Although the horse fossil record is very rich, our picture of when and where different species arose is clouded.

Analysis of mitochondrial DNA from fossilised bones, only possible in recent years, gives scientists a new tool to study evolution.

In research published in the open access journal Plos Biology, Dr Cooper and colleagues at Oxford University, UK, analysed mitochondrial DNA from fossilised horse bones.

Mitochondria, the powerpacks of the cell, have their own DNA and are inherited along the maternal line. Their DNA mutates at a stable rate, allowing researchers to look back in time at when different species diverged.

The Oxford research suggests that the stilt-legged horse, which was thought to have migrated into North America from Asia, at a time when the continents were linked by a land bridge, appears, in fact, to be native to North America.

And the Patagonian Hippidion horse found in South America appears to be much younger than previously thought.

It probably moved into South America about 3 million years ago, when the gap between North and South America closed up.

This was a seminal period of evolution, when animals from the two continents were able to mix after a long period of isolation.

"OK, what gives here? How is it that fossilized bones can contain any DNA. Isn't everything replaced during the fossilization process. I've really got to get out from under this rock more."

There are a number of ways for organic material to fossilize, the most common is by replacement and that is the one everyone is aware of. However, under certain conditions, a type of fossilization called permineralization can occur where the pores and voids are mineralized but some material remains bone. In most cases of this, depending on length of time the fossil is unexposed, even the remaining bone is eventually replaced. With something as recent as North American Equids and Equines many fossils are simply permineralized.

If you are interested, Google on 'Taphonomy'.

If you are interested, Google on 'Taphonomy'.

Did some looking around and didn't find anything all that convincing(to this layman). Fact is, I didn't find an article in my brief search that attributed any DNA from "permineralized" fossils. From this(one of the less academized) article they seem to imply that amber and similar substances which hermetically seal the future fossil(shades of Jurassic Park), is about the only way to retain any DNA over long periods of time.

Amber and Copal:
In amber and copal specimens, an organism becomes entrapped over a relatively short period of time in the various plant resins [exuded from trees such as Agathis, Araucaria (Araucariaceae), Bursera, Protium (Burseraceae), Hymenaea (Fabaceae), Liquidambar (Hamamelidaceae), Pinus (Pinaceae), Shorea (Dipterocarpaceae), and various Taxodiaceae-see Langenheim (1969) for a detailed breakdown of plant sources] that form copal and amber [Schlüter (1990) and Henwood (1992a) give detailed accounts of the imbedding process for specimens in amber and Pike (1993) and Henwood (1993) discuss taphonomy and collecting bias]. Though what is found in these amber and copal media is the actual specimen that died from thousands to millions of years ago, in many specimens, some amount bacterial action may have taken place over time and membranous material supporting the exoskeletal sclerites is often missing. Thus, when one attempts to recover the entrapped specimen by dissolving the amber or copal in a solvent, the result is often a disappointing slurry of floating chitinous plates. However, in some specimens preserved in this fashion, little or no decay has taken place and some muscle tissue complete with mitochondria survives and DNA can still be recovered (Henwood, 1992b). This had led to the exciting field of paleomolecular entomology in which the DNA of fossil organisms over 100 million years old can be studied and comparisons made with putative extant relatives.

Also, at the end of this same article, this item(specifically referring to insects???):

Other Forms of Preservation or Recovery:
Some forms of preservation of fossil insects do not encounter deterioration or mineral substitution of any kind. Those listed in this catalogue include subfossil and tar pit or brea recovery. The ages of these types of fossils listed in this catalogue are relatively young (most from the Pleistocene or Pliocene). In these fossils, all or parts of the insect specimen are visible in three dimensions much the same as those imbedded in amber or copal. Subfossil recoveries of Diptera have been made in peat bogs, caves, and ancient middens of small mammals.

Now if that says what I think it says, THESE specimens should have every cell intact. Which would lead one to believe the DNA would also be intact??? Color me confused.

FGS

DNA could be intact, but there's still the problem of cosmic ray bombardment.

GEEZ! Always something. Did some snooping around to learn a little about cosmic rays; found this interesting piece from HERE:

What happens when they hit earth?

The combined energy of all the cosmic rays approaching Earth is massive. Fortunately the atmosphere and magnetosphere [§] protect us from them as effectively as a slab of concrete four metres thick. Even so, when cosmic rays collide with atoms in the upper atmosphere, they release showers of gamma rays, X-rays and subatomic particles. Most of these secondary particles will make it to the Earth’s surface. And the most energetic fragments, although rare, are capable of penetrating miles underground. [9]
Atomic structures mainly consist of space - space between the nucleus and electrons, space between the individual atoms. Because of this, sub-atomic particles can travel a great distance before they collide with anything. Consequently most cosmic rays and secondary particles pass right through houses, trees, rocks, birds and humans. But a few will occasionally crash into atoms within these structures and beings. Don’t be too alarmed; this cosmic radiation is minor compared to the Earth’s natural background radiation, which in total hardly affects any of us at all anyway.
Thousands of rays and fragments pass through our bodies every minute. [10] Outside of the Earth’s atmosphere, where some satellites and astronauts roam, cosmic rays are very dangerous indeed - their sheer frequency means they can ionise electronic circuitry and mutate the genes of astronauts.

Now, what I found interesting is the author, at least in this snippet, said the actual cosmic rays never make it through our atmosphere(only acting as a super collider it seems), but then goes on to consistantly discuss them as if they do make it this far. Color me more confused!

In any case, my point was that it would seem that DNA is being extracted from something other than these extremely rare hermetically sealed fossils. That is, they are able to extract DNA from what is essentially........rock?

So did I miss something?

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