Sunday, 2 August 2015

Fossil evidence

In a previous post, I wrote about what evidence we should expect to find and whether gaps in the evidence were deal-breakers.  in brief, I tried to show there are places where we shouldn’t expect a lot of evidence (Smaller plants and animals are generally less likely to fossilize, as are soft bodied plants and animals.  Soft body parts, such as organs are less likely to fossilize.  Chemical traces are similarly fragile and their lack does not mean they never existed).  This isn’t to mean that there is no evidence for evolution or that we should accept evolution, or any scientific theory, on bad evidence.  Only that pointing out a lack of evidence in one area does not mean other similar areas are also lacking.

Here’s an example.  I personally don’t know what transitional fossils there are between dinosaurs and mammals.  Similarly, I don’t know what early carnivore might have transitioned into canines, felines and mustelids (the group containing weasels, otters, wolverines and more).  Partly, this may be due to my own ignorance as I have not dug into evidence or fossils in these areas.  On the other hand, there is excellent, finely graduated evidence for transitions between fish and amphibians. There are good transitionals between an ancient land mammal and whales.  There are so many fossils showing a transition from dinosaurs to birds that I personally don’t know which ones best show bird ancestors.

I blamed my own ignorance above but I also see ignorant people on Twitter claim there is no evidence for fish to amphibians.  I wish they would investigate where they lack knowledge before proclaiming it wildly to make a claim.  I have admitted my own ignorance above but not as a claim or to promote a conclusion.

Alright, to the evidence!

1: Fossils

First, it should be noted that fossils are found in assemblages that support an ancient Earth and evolution over a long period.  There are (very few) fossils of soft bodied organisms that pre-date the Cambrian Explosion.  In 2014, in the Cambrian fossil beds, a vertebrate fish was found, the Metaspriggina. This early fish was jawless.  Another, similar fish existed: Haikouichthys. The Pikaia, a chordate, also lived during the Cambrian.

I have heard and read the claim that all phyla were present during the Cambrian so they must have been created.  Again, there are fossils older than the Cambrian era and a phylum is a big group.  I have given examples of a chordate and two vertebrate fish but there are no jawed fishes, no amphibians, no reptiles, no birds, dinosaurs, mammals, crocodiles, or turtles.  Sharks don’t have bones the way other vertebrates do so I am uncertain on this point, but I believe there are no examples of them, either.

So, we have a period of sealife only, a period where, among vertebrates, only amphibians existed.  A period of dinosaurs, a period of giant mammals, then a period, continuing now, with humans.  There are animal groups that bridge some of these eras - sharks, turtles and crocodiles existed with and even before dinosaurs- but the groups I first named are discrete.  In one group of fossils, there are no land vertebrates.  In another group, there are dinosaurs but no large mammals or people.
We don’t need to stick to vertebrates.  Another famous group of animals that existed at one point and not with animals of other periods are the Ammonoidea.

The evidence I have given is, I would say, weakly supportive of evolution.  This is a broad strokes, a long distance look, at the evidence and at this scale we can only say that a primitive group of fish existed, then more advanced fish, then amphibians, then other terrestrial vertebrates.

While it offers only weak support to evolution, it seems, ah, the first nail in the creationist coffin.  Comparing the broad strokes of the fossil record to the creationist claim that all creatures were created in one week and that specimens of all such species died in a single year during the flood shows great conflict.

I’m describing it thus to emphasize the difference between support for one explanation with conflict for another.  If a piece of evidence appeared that conflicted with evolutionary accounts, that would not mean that creationism must then be correct.  On this blog I primarily deal with Biblical Young Earth Creationists, but Hindus have their own creation beliefs as do other religions and there are probably other propositions as well.

Transitional Fossils

What is a transitional fossil?
It is:
  • A snapshot of the existence of a single individual of a population
  • It has features of two distinct groups
  • Almost entirely lacking in organic molecules.
  • Without DNA, it is impossible to say if it is the direct ancestor or not (a grandfather or a great-uncle)
  • What they show is that a transition from group to group is possible .

In finding one, or a few, specimens, much can be determined of how the creature ate and lived, but not the range of its species’ survival.  Statistically, a fossil is likely to be made when the species is at peak population and geographic spread.  But when did the first individual of this group appear?  When did the last go extinct?  We can’t know.  This means that the fossil Archaeopteryxs, which are found later in the geological records than true birds appear, might still be the ancestor to true birds.  To my knowledge, scientists do not think so but the placement of the fossils is not definitive.   Archaeo has feathers but also a long bony tail and teeth.  there are other features which belong to one group or the other but are a little technical for me. Since Archaeo, many dinosaurs have been found with feathers.  Yet another new feathered dinosaur was recently found.

Some fossils do contain some organic molecules but these have so far been too degraded to run any tests suitable for identification or DNA comparison.

To be completely fair, transitional fossils do not mean that creatures must have transitioned from one species to another, but only that it is possible. Many creationists plaintively ask, "What good are feathers on an animal that can't fly?" From Creationtoday:
Reptiles have four legs, while birds have two legs and two wings. If the front legs turned into wings, the evolutionist has to believe that somewhere in the evolutionary spectrum they had to be half-leg, half-wing. This means, during that time, the creature couldn’t run or fly, and had a serious survival problem.
In this post, I am discussing evidence here, not arguing against specific claims, but briefly: Dinosaurs are not reptiles, many dinosaurs move on two legs.  One of the most famous dinosaurs has tiny, nearly uselessly small arms (T rex) which might be good evidence for evolution on its own.  There are lots of birds that have wings and run well but cannot fly.

Dr Kevin Padian, at the famed Dover Intelligent Design Trial, displayed some remarkable presentation slides on bird evolution that even show how the feathers evolved. His other slides are at the same site and show more transitions. The Fish to Amphibian transitional series is wonderful at least partially due to a creationist joke.
Creationist: There is a huge gap between A and Z.Evolutionist:  We found fossilized M.Creationist: There are now two big gaps.Evolutionist: We found fossilized F.Creationist: There are now three big gaps.
Padian’s slides show a full five or more transitional fossils between fish and amphibians.  Around the time of the trial, a new fossil was found, Tiktaalik, which filled in even more of the space between fish and amphibians.

Just last year, researchers raised a group of Senegal fish, bichirs, out of the water to see how they would adapt.  They already possessed gills and lungs and learned better how to walk and wriggle around out of water.

I should have a post on DNA evidence for evolution soon.

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