Wednesday, December 16, 2009

Transitional Forms - Undeniable Evidence For Evolution

Transcription by me (if you find errors, correct me please. I'm not a native English speaker):

The following video demonstrates that the theory of evolution is useful for making sense out of biological observations. In my last video I addressed the prevalent misconceptions regarding evolution and fossil record namely they claimed that they are no intermediate fossil forms. By critically examining this claim I show that those who make it are usually harboring fundamental misconceptions about how evolution works. The purpose of this video is to explore several examples of fossil intermediate forms that were predicted using evolutionary theory prior to their eventual discovery.

This will illustrate the predictive power of evolutionary theory and once again show that evolution is real science. Before we look at some examples of actual intermediate forms, it is important to clear up one other misconception. It is sometimes argued that fossil specimen cannot be considered an intermediate form unless it has been showing to be direct ancestor of existent species or group of species. This argument sets up an impossible task because in words of paleontologist Colin Patterson "Fossil may tell us many things, but one thing they can never disclose is whether they were ancestors of anything else."

Those who make this argument often do so precisely because they know that is not possible to definitively determine ancestry based solely on fossil evidence. Any purpose transitional fossils could therefore be disputed on these grounds. The reply to this flawed argument is to point out that evolution pursuits a branching pattern of descent and not a long linear line from one species to the next. Therefore at any giving point in time, there will likely many possible lineages that exhibit intermediate characteristics even though only one of this lineages represents direct ancestor of existing group even though we cannot predict the exact combination of characteristics that should be found in ancestral species we can specify which sets of features must have changed and make predictions about what such a changes look like if evolution by common descent has occurred, then we look for fossils with those characteristics to test our predictions.

Evolution is REAL science because it has been used for numerable such predictions about which intermediate form should be found and when they should occur. These predictions are repeatedly confirmed by incredible new fossil discoveries. For the remainder of this video we will explore some examples of fossil intermediate forms there are predicted to exist before they were actually discovered.

The first example involves the evolution of frogs and salamanders from ancient amphibians. Modern molecular studies have suggested to that among the three groups of amphibians frogs and salamanders are more closely related to each other than to worm like caecilians. Based on this evidence paleontologists used evolutionary theory to predict the existence of a creature with a combination of frog like and salamander like features. That should have existed prior to the earliest known frog and salamanders in the fossil record. This prediction was confirmed by the discovery in Texas of fossil remains of Gerobatrachus a primitive amphibian that existed appr. 290 million years ago well before the earliest fossil evidence recognisable frogs and salamanders. Gerobatrachus isn't intermediate form that fits needly into the gap between frogs and salamanders.This intermediate form exhibits an unique mosaic of features and its teeth, ears, limbs and backbone that all suggested a close to modern frogs and salamanders.

The second example involves the evolution of turtles. Turtles are unique among the existing reptile groups and they have a beak instead of teeth and their bodies are protected by a bony shell. In modern day turtle embryos the lower shell forms first and then their ribs and backbone expand and wided to form into upper shell. Based on this evidence, some herpetologists have hypothesized that the lower shell probably formed first in turtle evolution, followed by an outgrowth and broadening of the ribs and the backbone to form the upper shell. Paleontologists predicted that the oldest turtles should show evidence of these changes. This prediction was confirmed by the discovery of fossil remains of the oldest known turtle, and deposits of China. Three specimens of the species named Odontochelys were fossilised and rocked stating back to 220 million years ago. Just as predicted this intermediate form had a false teeth and no beak, also as predicted it had a complete an upper shell and an incomplete upper shell made from broad and ribs and back bone. This evidence confirms the hypothesis that the lower shell evolved first, followed later by upper shell.

Our third example involves the evolution of snakes. Evidence from the morphology and development of the existing snakes suggested that they evolved from limbed ancestors. Molecular evidence also supports this hypothesis showing that among living animal groups snakes are most closely related to lizards in fact the most primitive existing snakes Pythons and boa constrictors have tiny knob like legs beneath their skin and minuscule half inched claws that protruded around the bodies. Based on this evidence paleontologists used evolutionary theory to predict the existence of primitive snake fossils with evidence of limbs. This prediction was confirmed by the discovery of fossil remains the oldest known snakes dating back around the 90 million years ago. Each of which shows the evidence of hind limbs. Among these fossils is the most primitive known snake Najash found in 90 million year rocks from Argentina. This specimen not only shows evidence of robust functional hind limbs but also pelvic supported by sacrum. All of these features were predicted to be found in the limbed ancestors of snakes.

The next example involves the evolution of bats. Bats are unique among mammals because their ability to fly and ability to echolocate. For quite sometime the oldest known bast in the fossil record showed evidence of both this abilities. Using evolutionary theory paleontologists predicted that they should find primitive bats with one of these abilities but not the other. This prediction was confirmed by the discovery of Onychonycteris, the most primitive known species of bat discovered in Wyoming and bat ? in rocks that are around 50 million years old. Onychonycteris had underdeveloped inner ear that suggests unable to echolocate and also it has short, broad wings with claws and all five fingers longer hind legs and broader tail than modern bats. This evidence indicates that flying evolved first, and echolocation evolved later.

The fifth example involves the evolution of flatfish, the group of fish that includes flounder, place and halibut. All adult flatfishes have asymmetrical skulls with both eyes located on one side of the head. This unique arrangement arises early in the life of every flatfish. When asymmetrical larva under goes into a metamorphosis to produce asymmetrical juvenile flatfish. During this process one eye actually migrates up and over the top of the head before coming to rest adult position on the opposite side. Development of this unique arrangement is a such a significant transformation that paleontologists predicted evidence of this transition should be found in the fossils of primitive flatfish. This prediction was confirmed by the identification of fossils there are the most primitive known flatfishes, these specimen known as amphistium and heteronectes were found in European limestone deposits dating back 50 million years. They showed evidence slightly asymmetrical skulls with eyes still on opposite sides of the head. Each of these specimens represent an intermediate form between the peculiar eye arrangement in living flatfishes and arrangement found around other fishes.

Our final example involves the evolution of Sirenians, group of mammals that includes manatees and dugongs. Sirenians are fully aquatic mammals with flippers and no hind limbs. Morphological and molecular evidence indicates that among existing species the sirenians are most closely related with elephants. Based on this evidence paleontologists predicted the existence of primitive sirenians with hind limbs. This prediction was confirmed by unearthing Pezosiren the oldest and the most primitive sirenian in the fossil record which was found in 50 million year old deposits from Jamaica. Pezosiren was fully capable of walking on land with four well developed legs and long tail. However the details of its nasal opening and its stick ribs suggested that pezosiren also spent much of its time in water. This evidence makes pezosiren a clear intermediate form between land and animals and fully aquatic animal sirenians. So there you have it. Fossil discoveries combined with evidence of morphological and genetic and embryological studies of existing organisms led us to powerful explanation our biological observations. These six examples only scratch the surface.

Other transitional fossil series include fossils documenting the evolution of amphibians from lobe-finned fish, evolution of mammals from reptiles, evolution of birds from theropod dinosaurs, evolution of whales from hoofed animals, evolution of horses from five-toed ancestors, and of course evolution of humans from bipedal apes. The list of transitional fossil series truly goes on and on. These observations only make sense using the real science of evolution.

Watch the first part: Does The Fossil Record Support Evolution?

1 comment:

Gamze Gwen said...


Thank you for that useful informations about Evolution. I really found it simply perfect presentation for an unbending realty.

But I am not a native English speaker, either just like you:)

If you have a text for that video above, I will be so glad.

Thank you.


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