Transitional Fossils Show Evolution in Process

We often see complaints or comments about the absence of fossil evidence for transitions in evolution. This usually comes in two parts:(1) There are no transitional fossils PRATT CC200

quote:

---

There are no transitional fossils. Evolution predicts a continuum between each fossil organism and its ancestors. ...

---

Often this is due to a misunderstanding of what "transitional" means in evolutionary biology:Transitional fossil - Wikipedia

quote:

---

Transitional fossils (popularly termed missing links) are the fossilized remains of intermediary forms of life that illustrate an evolutionary transition. They can be identified by their retention of certain primitive (plesiomorphic) traits in comparison with their more derived relatives, as they are defined in the study of cladistics. Numerous examples exist, including those of primates and early humans.

​

According to modern evolutionary theory, all populations of organisms are in transition. Therefore, a "transitional form" is a human construct of a selected form that vividly represents a particular evolutionary stage, as recognized in hindsight. Contemporary "transitional" forms may be called "living fossils", but on a cladogram representing the historical divergences of life-forms, a "transitional fossil" will represent an organism near the point where individual lineages (clades) diverge.

---

Thus all fossils that show intermediate characteristics between ancestral forms and descendant forms are by definition transitional. Thus whenever we see a clear lineage of fossils from an ancestral form (plesiomorphic) to derived descendant form (apomorphic), and thus they are transitional fossils.Transitional fossils will be intermediate in form between ancestral forms and descendant forms, and they will share some, but not all, traits with both ancestors and descendants, and some traits shared by ancestors, the transitional fossil and descendants may themselves be shown in intermediate stages of development, between the ancestral and descendant forms of the traits.(2) There should be billions of transitional fossils PRATT CC200.1

quote:

---

Given all the species that exist and have existed, there should be billions of transitional fossils in the fossil record; we should have found tens of thousands at least.

---

A recent example of this misunderstanding was presented by Kaichos Man on An ongoing report on S366:Evolution Message 19: This thread is intended to discuss and answer this issue.Enjoy.ps - I will also add 3 responses as subthreads, which will cover my initial response at Message 20, so please let me complete those before promotion.Edited by Admin, : Fix rendering.

---

In the post that inspired this thread Kaichos Man claimed (Message 19): This, of course is the hoary old "absence of evidence is evidence of absence" logical fallacy.The complete absence of fossil evidence for the Coelacanth between the end of the Cretaceous period and modern day clearly proves that these fish did not exist between then and now ....Clearly this statement is false when the Coelacanths are living organisms in the modern world.Other logical fallacies are the argument from ignorance (there are no transitional fossils) and the argument from incredulity (we should be up to our necks in transitional fossils).Logical fallacies are invalid arguments.Enjoy.

---

In the post that inspired this thread Kaichos Man claimed (Message 19): There are many examples of transitional fossils, and I will discuss two of these as they apply at the species level and they show precisely the "tiny dawinian step" involved in the process of speciation.(1) Foramiinifera: Evolution at Sea
Complete Fossil Record from the Ocean Upholds Darwins Gradualism

quote:

---

Tony Arnold and Bill Parker compiled what may be the largest, most complete set of data on the evolutionary history of any group of organisms, marine or otherwise. The two scientists amassed something that their land-based colleagues only dreamed about: An intact fossil record with no missing links.

​

"It's all here--a virtually complete evolutionary record," says Arnold. "There are other good examples, but this is by far the best. We're seeing the whole picture of how this group of organisms has changed throughout most of its existence on Earth."

​

The organism that Arnold and Parker study is a single-celled, microscopic animal belonging to the Foraminiferida, an order of hard-shelled, planktonic marine protozoans. Often shortened to "forams," the name comes from the Latin word foramen, or "opening." The organisms can be likened to amoebas wearing shells, with perforations through which their protoplasm extends. The foram shell shapes range from plain to bizarre.
...
"There's a nifty passage in Darwin," says Arnold, "in which he descirbes the fossil record as a library with only a few books, and each book has only a few chapters. The chapters have only a few words, and the words are missing letters."

​

"Well, in this case, we've got a relatively complete library," says Arnold. "The 'books' are in excellent shape. You can see every page, every word."

​

As he speaks, Arnold shows a series of microphotographs, depicting the evolutionary change wrought on a single foram species. "This is the same organism, as it existed through 500,000 years," he says. "We've got hundreds of examples like this, complete life and evolutionary histories for dozens of species."

​

About 330 species of living and extinct planktonic forams have been classified so far. After thorough examinations of marine sediments collected from around the world, micropaleontologists now suspect these are just about all the free-floating forams that ever existed.

​

The species collection also is exceptionally well-preserved, which accounts largely for the excitement shared by Parker and Arnold. "Most fossils, particularly those of the vertebrates, are fragmented--just odds and ends," says Parker. "But these fossils are almost perfectly preserved, despite being millions of years old."
...
Darwin termed the process gradualism, a theory that invokes the slow accumulation of small evolutionary changes over a large period of time, as a result of the pressures of natural selection. What Arnold and Parker found is almost a textbook example of gradualism at work.

​

​

We've literally seen hundreds of speciation events," syas Arnold. "This allows us to check for patterns, to determine what exactly is going on. We can quickly tell whether something is a recurring phenomenon--a pattern--or whether it's just an anomally. This way, we cannot only look for the same things that have been observed in living organisms, but we can see just how often these things really happen in the environment over an enormous period of time.

---

Not just transitional fossils between one species to the next, but the whole pattern of this foraminifera phylum laid out in detail.(2) Pelycodus: A Smooth Fossil Transition: Pelycodus, a primate

quote:

---

​

Pelycodus was a tree-dwelling primate that looked much like a modern lemur. The skull shown is probably 7.5 centimeters long.

​

The numbers down the left hand side indicate the depth (in feet) at which each group of fossils was found. As is usual in geology, the diagram gives the data for the deepest (oldest) fossils at the bottom, and the upper (youngest) fossils at the top. The diagram covers about five million years.

​

The numbers across the bottom are a measure of body size. Each horizontal line shows the range of sizes that were found at that depth. The dark part of each line shows the average value, and the standard deviation around the average.

​

The dashed lines show the overall trend. The species at the bottom is Pelycodus ralstoni, but at the top we find two species, Notharctus nunienus and Notharctus venticolus. The two species later became even more distinct, and the descendants of nunienus are now labeled as genus Smilodectes instead of genus Notharctus.

​

As you look from bottom to top, you will see that each group has some overlap with what came before. There are no major breaks or sudden jumps. And the form of the creatures was changing steadily.

---

This fossil record clearly shows the "tiny dawinian steps" from generation to generation. Note that the "gaps" in time for the fossils are more than covered by the overlap in the variation within each level, each level has organisms similar to the ancestral population below it and to the descendant population above it.ConclusionClearly transitional fossils exist at the species level, fossils that clearly show the "tiny dawinian steps" from generation to generation.Enjoy.Edited by RAZD, : spling

---

In the post that began this thread Kaichos Man claimed (Message 19): We can ascertain the veracity of this arguement from incredulity by comparing the fossil record for the Foraminifera, Pelycodus and the Coelacanth.As we see in the case of Foraminifera, transitional fossils between species (and higher) exist in abundance at all levels, and in this one case they cover millions of years in a continuous record. This is because the accumulation of these fossils in this location is not reliant on haphazard fossilization, random environmental factors or other things affecting the fossilization of individual organisms.Thus we see, that when there are no causes preventing the reservation of fossils, or for disrupting fossils after deposition, that there is indeed the well preserved record of evolving life year after year, generation after generation, species after species, etc etc, for millions of years.Next we look at Pelycodus and we do see gaps between the fossil layers. There are several reasons such gaps can exist:

• the organisms can migrate between areas and thus are only fossilized in one area when they die in that area,
• natural disasters that kill and cover organisms to begin the fossilization process may be relatively rare in the ecology, and
• the ecology may alternate between wet and dry, with fossils only being preserved during dry periods,
• etc.

Finally, we look at the Coelacanth. The last fossil evidence for Coelacanths is over 65 million years old:Coelacanth - Wikipedia

quote:

---

Although now represented by only two known living species, as a group the coelacanths were once very successful with many genera and species that left an abundant fossil record from the Devonian to the end of the Cretaceous period, at which point they apparently suffered a nearly complete extinction. Before the living specimens were discovered, it was believed by some that the coelacanth was a "missing link" between the fish and the tetrapods. It is often claimed that the coelacanth has remained unchanged for millions of years, but, in fact, the living species and even genus are unknown from the fossil record. The most likely reason for the gap is the taxon having become extinct in shallow waters. Deep-water fossils are only rarely lifted to levels where paleontologists can recover them, making most deep-water taxa disappear from the fossil record.

---

Here we have a gap in the fossil record of ~65 million years, and yet we have living Coelacanths that clearly show that the absence of fossil evidence is not evidence of absence of Coelacanths. This also shows that fossils do not have to be preserved for intermediate forms.ConclusionsWhat is clear, from comparing these three cases, is:

1. there is a significant difference in the degree of preservation of fossils between Foraminifera, Pelycodus and Coelacanths,
2. when there are no reasons for fossils not to be preserved (Foraminifera), that there are extensive fossil transitional records,
3. when there are reasons that fossils may not be preserved (Pelycodus), that there are gaps in the fossil record due to missing fossils, and
4. even when there are massive gaps in the fossil record (Coelacanths), that this does not mean that the intermediate organisms were missing, just that they did not fossilize where fossils have been discovered

Simply put, fossils do not need to exist to fill in gaps in the fossil record for intermediate forms to have existed.Enjoy.

---

Thread copied to the Transitional Fossils Show Evolution in Process thread in the Biological Evolution forum, this copy of the thread has been closed.