Good start. I can think of a couple of other examples, but tonight is too late to pull them up here (maybe tommorrow).
It may also be difficult to keep this from being bombarded by discussion of the different chains (and the "gaps" in our knowledge) rather than the issue of providing them.
I think the place to start this is with the foraminifera information from Arnold and Parker. This is important for several reasons: it demonstrates speciation - "micro"evolution - over an extended period of time - not just natural selection (peppered moths and galapogos finches) - nor is it "macro"evolution (with the development of significant new features, and the issue of what is "significant" left undefined), and it also shows that the change over time is continuous (albeit at changeable rates) and there is no "stasis" observed in any species.
It will also bring out two main problems that creationists generally have: the age of the earth and the world wide flood mixing of sediments. These are issues that creationists need to address in order to deal with the issue of evolution on a rational level: if they cannot develop some practical physically possible scenario that makes this evidence compatible with either of these concepts then they need to consider that the concepts are wrong.
quote:The Foraminifera, or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net. They typically produce a shell, or test, which can have either one or multiple chambers, some becoming quite elaborate in structure. ... They are usually less than 1 mm in size, but some are much larger, and the largest recorded specimen reached 19 cm.
The form and composition of the test is the primary means by which forams are identified and classified. Most have calcareous tests, composed of calcium carbonate. In other forams the test may be composed of organic material, made from small pieces of sediment cemented together (agglutinated), and in one genus of silica. Openings in the test, including those that allow cytoplasm to flow between chambers, are called apertures.
Tests are known as fossils as far back as the Cambrian period, and many marine sediments are composed primarily of them. For instance, the limestone that makes up the pyramids of Egypt is composed almost entirely of nummulitic benthic foraminifera. Forams may also make a significant contribution to the overall deposition of calcium carbonate in coral reefs.
(Phase-contrast photomicrograph by Scott Fay, UC Berkeley, 2005. Image copied from wikipedia to save bandwidth. This image is licensed under the Creative Commons Attribution ShareAlike License v. 2.5: )
The image above shows the protoplasm covered test (shell) and several pseudopods of a living species of foraminifera. Fossil species would be similar, with different shape shells and different numbers of pseudopods (limited by the number of holes in the shells).
Forams are an 'order' in the macro-taxonomic classifications system, with 'suborders', 'superfamilies' and 'families' before we get down to the species level discussed below (we need not be concerned with the levels of taxonomy at this point in the debate, this is just for information).
quote:In recent years, however, scientists began revisiting the oceans, ... Some intriguing results turned up recently in the laboratories of two Florida State University (FSU) marine paleontologists.
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."
But it's the planktonic variety that chiefly interests Parker and Arnold. Unlike their oversized cousins, free-swimming forams are found almost everywhere in the oceans. Their fossilized skeletons, in fact, were among some of the first biological material recovered from deep ocean bottoms by scientists in the 1850s. For nearly a century, geologists have used the tiny fossils to help establish the age of sediments and to gain insight into prehistoric climates.
Only since the 1960s, though, have scientists begun to fully appreciate fossil forams' potential as a tool for use in evolutionary studies and a host of Earth sciences as well. Advanced deep-sea drilling techniques, combined with computer-assisted analytical tools, have ushered in a whole new vista of foram research. Arnold and Parker are among the first scientists to harness sophisticated technology to a foram project for the express purpose of studying evolution.
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."
(Image copied from ref (2) to save bandwidth. This same image also appears on ref (4).)
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."
By being so small, the fossil shells escaped nature's grinding and crushing forces, which over the eons have in fact destroyed most evidence of life on Earth. The extraordinary condition of the shells permits the paleontologists to study in detail not only how a whole species develops, but how individual animals develop from birth to adulthood.
What we have essentially is a jig-saw puzzle with all but maybe 2 or 3 pieces, the whole picture is evident, and where there are a few gaps, these are surrounded by other data that help complete the picture.
This picture shows a continual process of change in species over time, fully realized and documented microevolution, with no reappearance of archaic types in modern species, no "backing and filling" as we see with Peppered Moths and Galapagos Finches, because speciation has occurred, and change moves on to new mutations and new selections of those mutations.
We see significant change in the shape of the shell of one species as it evolves over a period of 6.5 million years.
Conclusions
Several conclusions are readily apparent from this information that apply directly to the issue of microevolution:
Microevolution has occurred.
Microevolution has been documented over several successive generations of species, and not for just one speciation event.
Microevolution is therefore a fact in this fossil record.
Because further speciation occurs, microevolution does not limit subsequent changes once speciation has occurred (beyond what can occur through mutation and natural selection of the then existing species - more microevolution).
But that's not all we can glean from this example of microevolution.
quote:Because of their diversity, abundance, and complex morphology, fossil foraminiferal assemblages are useful for biostratigraphy, and can accurately give relative dates to rocks. The oil industry relies heavily on microfossils such as forams to find potential oil deposits.
The foraminiferan life-cycle involves an alternation between haploid and diploid generations, although they are mostly similar in form. The haploid or gamont initially has a single nucleus, and divides to produce numerous gametes, which typically have two flagella. The diploid or schizont is multinucleate, and after meiosis fragments to produce new gamonts. Multiple rounds of asexual reproduction between sexual generations is not uncommon in benthic forms.
Forams are used to relatively date marine sedimentary layers due to the distinct morphological differences of the different species.
Also see Ref (5) for more information on relative dating with forams.
Forams reproduce by both sexual and asexual means.
quote:Through dating analysis, he and his colleague showed that the forams could produce a whole new species in as little as 200,000 years--speedy by Darwinian standards. "But as fast as this is, it's still far too slow to be classed as punctuational," says Arnold.
It may be in what the foram record suggests about how life copes with mass annihilation that eventually draws the most attention to the FSU paleontologists' work. The geologic record has been prominently scarred by a series of global cataclysims of unknown, yet hotly debated, origin. Each event, whether rapid or slow, wreaked wholesale carnage on Earth's ecology, wiping out countless species that had taken millions of years to produce. Biologists have always wondered how life bounces back after such sweeping devastation.
One of the last great extinctions occurred roughly 66 million years ago and, according to one popular theory, it resulted from Earth's receiving a direct hit from a large asteroid. Whatever the cause, the event proved to be the dinosaurs' coup de grace, and so wiped out a good portion of the marine life--including almost all species of planktonic forams.
The ancient record of foram evolution reveals that the story of recovery after extinction is indeed busy and colorful. "What we've found suggests that the rate of speciation increases dramatically in a biological vacuum," says Parker. "After the Cretaceous extinction, the few surviving foram species rapidly evolved into new species, and for the first time we're able to see just how this happens, and how fast."
As the available niches fill up with these new creatures, the speciation rates slow down, and the pressure from competition between species appears to bear down in earnest. The extinction rate then rises accordingly. This scenario, says Arnold, suggests that the speciation process is sensitive to how fully packed the biosphere is with other species, not the number of individuals.
The shortest observed time interval for speciation was 200,000 years.
The rate of speciation was observed to increase after a major extinction event as there was less natural selection pressure from competition between species on new mutations in their ability to fill available ecological niches.
quote:One of the findings already is being described -- perhaps too hastily -- as disproving Cope's Rule, so named for it's synthesis by the American paleontologist Edward Drinker Cope (1840-97). The time-honored evolutionary principle basically holds that all animal groups tend to start out small and increase in size over time.
"We've found out that apparently, lineages don't exactly work that way," Arnold said. "Many of the forams start out small, and essentially stay that way until extinction. Others do manage to wander into dramatically larger sizes, but they're the rare ones."
But the find doesn't necessarily contradict what Cope said, only what many scientists think he said, says Parker. "Cope's observation was simply that there are a few extremely large examples (of individuals) in any given lineage, and these examples always occur at the later stages of the organism's development. And that's apparently true.
"But our findings show that the vast majority of forams start small and end small, even though the mean size increases somewhat due to a few very large specimens. As you get more and more species evolving, some of them eventually manage to get moderately to very large, but most of them don't increase in size at all."
Of late, much ado has been made of the theory of punctuated equilibrium, formulated in the early 1970s by two paleontologists, Niles Eldredge and Stephen Jay Gould. New species may arise fairly quickly (over thousands instead of millions of years) from small animal populations that somehow become isolated, the theory postulates. Intermediate stages are thus too fleeting to become fixed in the fossil record.
Adherents of Darwin's theory of gradualism, in which new species slowly branch off from original stock, should be delighted by what the FSU researchers have found. The foram record clearly reveals a robust, highly branched evolutionary tree, complete with Darwin's predicted "dead ends" -- varieties that lead nowhere -- and a profusion of variability in sizes and body shapes. Moreover, transitional forms between species are readily apparent, making it relatively easy to track ancestor species to their descendants.
In short, the finding upholds Darwin's lifelong conviction that "nature does not proceed in leaps," but rather is a system perpetually growing in extreme slow-motion. This means that, in foram evolution at least, the highly touted Eldredge-Gould theory of punctuated equilibrium apparently doesn't work.
In divulging this revelation, Arnold could be forgiven for taking a modicum of perverse glee, the kind a highschool smart-aleck displays when he catches the teacher in a mistake. Gould, now among the most famous scientists in the world, directed Arnold's Harvard dissertation. But there's no room for that here, he says. Arnold maintains a warm professional relationship with his former mentor, who paid his lab a visit when FSU's Distinguished Lecture Series brought him to campus last year. Gould concedes that the forams don't fit his model of punctuated equilibrium, Arnold said.
"He was characteristically pleased to be contradicted with this information. His immediate response was that the forams are probably a special case."
The issue of punctuated equilibrium ("PunkEek") is a side issue in the evolution versus creation debate, but one that seems to reflect kinds to creationists and evolution to evolutionists. It is my opinion that this does not come into play until there is active sexual selection in a species that can select for an averaged individual type - stasis - and that until that stage is reached there should be no evidence of punkeek. That would match the evidence we see here - an organism that engages in random sexual reproduction and random asexual reproduction would not have this stasis selecting mechanism. Thus we will have to deal with this issue later if we come to evidence for punkeek.
Further Conclusions
Conclusions that bear on the debate here and further discussion of microevolution (MiE) in the next examples (yet to come):
The different age fossils form discrete layers in marine sediment that are identifiable around the world. These fossils all have essentially the same density, size and structure, and are generally less dense than surrounding marine sediment. These different age layers, now that Palmer and Arnold have classified the evolution of the different species of forams, are sorted by age AND evolution within the marine sediment, a fact that cannot be accomplished by any mixed water world wide flood scenario. (A WW Flood concept cannot explain this evidence.)
With several generations of speciation observed and the shortest observed time interval for speciation of 200,000 years, the layers of marine sediment together with the evolutionary structure of the foram fossils embedded within it, AND the evidence of the KT extinction event within the data, document an old age of the earth, much older than any YEC model can manage to accommodate. (A Young Earth concept cannot explain this evidence.)
Cope's "rule" was observed in some species and not in others, so it is not a universal "rule" or "law" (no real surprise there).
PunkEek was not observed in any of the speciation events in this fossil record, even though there was evidence of more and less rapid rates of evolution, particularly in response to the ecological vacuum created by the KT mass extinction event (at the end of the age of dinosaurs).
These organisms reproduce by random sexual and asexual means, and do not have an active sexual selection mechanism that could lead to stasis (and thus to the possibility of punkeek).
There could be other causes for PunkEek as well, that would not affect foraminifera.
People new to evolution often talk question the development of "distinctive" features, although it is sometimes difficult to pin them down on what they mean by a distinctive feature or how much change is enough.
We can talk about horses and the distinctive development of the modern horse and single-toe hoof from the splayed toed dog sized "eohippus":
quote:Look at how the bones in horse feet have changed over time. They became longer and more streamlined, enabling horses to run faster to avoid predators.
Check the above link to see images of the legs of four different horse ancestors. You can see a splayed toe stance for Hyracotherium and Miohippus but a single toe stance in Merychippus and Equus.
quote:Eohippus was a descendent of the Condylarth, a dog-sized, five-toed creature that lived about 75 million years ago. It lived during the early Eocene period, which took place 50 to 60 million years ago. Eohippus, which means "dawn horse," stood about twelve to fourteen inches at the shoulder and weighed about twelve pounds. It looked nothing like a horse. It had an arched back, short neck, short snout, short legs, and a long tail. Its color probably most resembled that of a deer, a darker background with lighter spots. The legs of Eohippus were flexible and rotating with all major bones present and unfused. It had a choppy, up-down gait and was not very fast. There were four toes on each front foot and three toes on the hind. The vestigial toes - two on the front feet and one on the hind - were still present.
It had a small brain and low-crowned teeth with three incisors, one canine, four distinct premolars, and three "grinding" molars in each side of each jaw. Browsing on fruit and fairly soft foliage, Eohippus probably lived in an environment with soft soil, the kind found on jungle floors and around the edges of pools. Since Eohippus walked on the pads of its feet, it was able to cross wet, marshy ground without much difficulty.
The coloration is pure speculation, of course, but the size and stance are based on the physiology of the skeleton. Now lets also look at the Condylarth:
quote:Back in the northern hemisphere, another family of condylarths, the Phenacodontidae, may include the ancestors of a more familiar ungulate order: The odd-toed ungulates or Perissodactyla, represented by horses, rhinos and tapirs in the recent fauna. Historically, phenacodontids form the core of the Condylarthra. Well-preserved skeletons are known for the type genus Phenacodus, which is a good model of an ancestral ungulate with beginning adaptations for running. Unlike arctocyonids, periptychids or mioclaenids, the phenacodontids are not part of the first wave of condylarths that populated North America. They first appear with the fox-sized Tetraclaenodon in the middle Paleocene of that continent. The appearance of the more advanced phenacodontids Phenacodus and Ectocion marks the beginning of late Paleocene time in North America. The type genus Phenacodus covers the large size range of phenacodontids and includes roughly sheep-sized animals. Members of the genus Ectocion were usually smaller, with a body mass of only 3 kg in the smallest species, but there is some overlap in size between the two genera. Phenacodontids were the dominant mammals in the latest Paleocene of North America and account for up to 50% of all mammal specimens in faunas of that age.
Figure 5: Reconstruction of the late Paleocene to middle Eocene Phenacodus, a sheep-sized herbivore with improved capabilities for running. From Savage & Long (1986).
This is the most "horse-like" image from this site, and it looks much more like a dog than a horse eh? Of course the coloration and fur are speculation, but the size and stance are again based on the physiology of the skeleton.
To see what the skeletons looked like for the four species used for the leg examples at the start we go to:
(NOTE: LINKS INTENTIONALLY BROKEN - this image is copied from the original to save bandwidth, go to the original Stratmap for the links to work).
(Hyracotherium)- This small dog-sized animal represents the oldest known horse. It had a primitive short face, with eye sockets in the middle and a short diastema (the space between the front teeth and the cheek teeth).
Although it has low-crowned teeth, we see the beginnings of the characteristic horse-like ridges on the molars.
Hyracotherium is better known as "eohippus" - which means "the dawn horse." The name also refers to the fact that it lived during the Eocene.
(Miohippus) - Species of Miohippus gave rise to the first burst of diversity in the horse family. Until Miohippus, there were few side branches, but the descendants of Miohippus were numerous and distinct. During the Miocene, over a dozen genera existed.
Fossils of Miohippus are found at many Oligocene localities in the Great Plains, the western US and a few places in Florida. Species in this genus lived from about 32-25 million years ago.
(Merychippus) - Merychippus represents a milestone in the evolution of horses. Though it retained the primitive character of 3 toes, it looked like a modern horse. Merychippus had a long face. Its long legs allowed it to escape from predators and migrate long distances to feed. It had high-crowned cheek teeth, making it the first known grazing horse and the ancestor of all later horse lineages.
Fossils of Merychippus are found at many late Miocene localities throughout the United States. Species in this genus lived from 17 - 11 million years ago
(Equus) - Equus is the only surviving genus in the once diverse family of horses. Domesticated about 3,000 years ago, the horse had a profound impact on human history in areas such as migration, farming, warfare, sport, communication and travel.
Species of Equus lived from 5 million years ago until the present. Living species include horses, asses, and zebras. Fossils of Equus are found on every continent except Australia and Antarctica.
I selected the same species as were listed for the legs above for convenience here - on the original link you select by clicking on the skulls.
So we have a sequence of species that starts with one standing on the fleshy pads of several splayed toes to the modern species that stands not just on one toe but on the toe-nail of that single toe. But that is not all:
quote:A horse's hoof is composed of the wall, sole and frog. The wall is simply that part of the hoof that is visible when the horse is standing. It covers the front and sides of the third phalanx, or coffin bone. The wall is made up of the toe (front), quarters (sides) and heel.
The wall of the hoof is composed of a horny material that is produced continuously and must be worn off or trimmed off. The hoof wall does not contain blood vessels or nerves. In the front feet, the wall is thickest at the toe; in the hind feet the hoof wall is of a more uniform thickness. The wall, bars and frog are the weight-bearing structures of the foot. Normally the sole does not contact the ground.
As weight is placed on the hoof, pressure is transmitted through the phalanges to the wall and onto the digital cushion and frog. The frog, a highly elastic wedge-shaped mass, normally makes contact with the ground first. The frog presses up on the digital cushion, which flattens and is forced outward against the lateral cartilages. The frog also is flattened and tends to push the bars of the wall apart (Figure 3). When the foot is lifted, the frog and other flexible structures of the foot return to their original position.
When the foot is placed on the ground, blood is forced from the foot to the leg by the increase in pressure and by the change in shape of the digital cushion and the frog. The pressure and the change in shape compress the veins in the foot. When the foot is lifted, the compression is relieved and blood flows into the veins again. In this way, the movement of these structures in the hoof acts as a pump.
This is much more difference in a feature than "just an increase in length" (as in an elephants trunk), it is a totally different structure to stand on (eohippus stood on his toes pads, equus stands on a hoof which not only is not a toe pad, but a feature that wasn't present in the eohippus) and it incorporates a new {added\changed} structure to increase blood flow by acting as a secondary pump.
Not only that the effect of changing the foot structure from a flat footed splayed toed eohippus to the single toed equus also involves standing the foot up on the tip of the toe and using each of the bones between the tip and the heel to effectively make the leg longer for faster running while also making it more flexible than just adding length to the bones of the leg. Probably useful for getting through tight spots and to keep from tripping ... it certainly helps horses jumping in shows from hitting that top bar.
Totally different foot structure, coupled with totally different leg structure (with some ex toe bones now effectively used as leg bones).
The question again is how much change is enough? Try walking around the house on the tip of one toe, then compare your foot to that of eohippus.
Enjoy.
References:
Anonymous, "Evolution of the Horse: Eohippus" Sarah's Horse Farm, Updated 10 Aug 2000, Accessed 12 Jan, 2007
Anonymous, "Fossil Horse Cybermuseum" The Florida Museum of Natural History, Updated 8 Jan 2007, Accessed 12 Jan, 2007
Jehle, Martin, "Condylarths: Archaic hoofed mammals" Paleocene mammals of the world, Updated ?, Accessed 12 Jan, 2007
McClure, Robert C. et al "Functional Anatomy of the Horse Foot" Department of Veterinary Anatomy, College of Veterinary Medicine, Updated 10 May 2006, Accessed 12 Jan, 2007
Edited by RAZD, : color change for note bedded within quote
Ideally, we are looking for hypothetical drawings over huge ranges, like from invertebrates all the way to rabbits.
This is a pretty tall order if sufficient detail is included for each step along the way. While this may be the ultimate goal, it would be better broken down into discussable sub-sets.
A good resource for one of these is "Use and Abuse of the Fossil Record: The Case of the ”Fish-ibian’" By Penny Higgins at Page not found | Skeptical Inquirer
I note that there doesn't seem to be any issue with the transitions of plants, bacteria, bugs, worms and the like from water to land. The reason, I suspect, is that there is not much morphological (to a creationist) difference between land versions and aquatic versions - a worm is a worm.
Once again it comes down to the degree of change involved in the process. Time and again a creationist will say that change {X} is "micro"evolution and that "micro"evolution does not equal "macro"evolution nor is there proof of "macro"evolution. The question they have is when does the big change that is "macro"evolution occur - generally because they don't understand what "macro"evolution is (mostly it is just a human observation that (X) is more different from (Y) than it is from (Z) - an artifact of human observation).
Thus the question becomes at what point do they think that "macro"evolution has occurred in a sequence like the horses above or in the fishibians in the linked article.
I was thinking of calling him in to discuss other transitions from water to land, the evolution of bugs with legs, etc. Probably have some difficulty finding fossil evidence (we are talking pretty small stuff).
Anyone that knows of a chain of evolution from (X) to (Y) feel free to post it here. This thread is for accumulating various evidence(s) of long term evolution (macroevolution) for use in the debates.
Synapsida to Therapsida to Cynodontia to Mammaliforms to Morganucodontidae to ...
From reference (1) below
quote:The fossil transition from reptile to mammal is one of the most extensive and well-studied of all the transitions, and detailed series of fossils demonstrate how this transition was accomplished.
...mammals can also be distinguished by a number of skeletal characteristics (particularly in the skull and teeth). In particular, mammals are distinguished from reptiles by a number of skeletal traits. Reptiles have a much larger number of individual bones in their skulls than do mammals. In reptiles, the teeth are all of the same shape, and although they vary slightly in size, they all have the same simple cone-shaped form. Mammals, however, possess a number of different types of teeth in their jaws, from the flat, multi-cusped molar teeth to the sharp cone-shaped canines. In reptiles, the lower jaw is made up of a number of different bones, and the jaw joint is formed between the quadrate bone in the skull and the angular bone in the jaw. In mammals, by contrast, the lower jaw is made up of a single bone, the dentary, which articulates with the squamosal bone in the skull to form the jaw joint. Reptiles also have a single bone in the middle ear, the stapes. In mammals, there are three bones in the middle ear, the malleus, incus and stapes (also known as the hammer, anvil and stirrup). At the top of the skull, reptiles have a small hole through which the pineal body, or "third eye", extends--this is absent in mammals. Finally, the reptilian skull is attached to the spine by a single point of contact, the occipital condyle. In mammals, the occipital condyle is double-faced.
The article then goes on to list a number of examples and their features, however it concentrates on the later fossils and the ones that are in transition (two jaw joints), and doesn't provide much information on the ones preceding them..
I would like to flesh this out with a list of the fossils involved from the first reptilian example to the final mammalian example, however my access to resources is limited at the moment, so help would be apprecieated.
quote:"In many respect, the tritylodont skull was very mammalian in its features. Certainly, because of the advanced nature of the zygomatic arches, the secondary palate and the specialized teeth, these animals had feeding habits that were close to those of some mammals . . . . Yet, in spite of these advances, the tritylodonts still retained the reptilian joint between the quadrate bone of the skull and the articular bone of the lower jaw. It is true that these bones were very much reduced, so that the squamosal bone of the skull and the dentary bone of the lower jaw (the two bones involved in the mammalian jaw articulation) were on the point of touching each other." (Colbert and Morales, 1991, p. 127)
On Probainognathus it quotes
quote:"Probainognathus, a small cynodont reptile from the Triassic sediments of Argentina, shows characters in the skull and jaws far advanced toward the mammalian condition. Thus it had teeth differentiated into incisors, a canine and postcanines, a double occipital condyle and a well-developed secondary palate, all features typical of the mammals, but most significantly the articulation between the skull and the lower jaw was on the very threshhold between the reptilian and mammalian condition. The two bones forming the articulation between skull and mandible in the reptiles, the quadrate and articular respectively, were still present but were very small, and loosely joined to the bones that constituted the mammalian joint . . . Therefore in Probainognathus there was a double articulation between skull and jaw, and of particular interest, the quadrate bone, so small and so loosely joined to the squamosal, was intimately articulated with the stapes bone of the middle ear. It quite obviously was well on its way towards being the incus bone of the three-bone complex that characterizes the mammalian middle ear." (Colbert and Morales, 1991, pp. 228-229)
On Diarthrognathus it says
quote:In describing a member of this group known as Diarthrognathus, paleontologists Colbert and Morales point out: "The most interesting and fascinating point in the morphology of the ictidosaurians (at least, as seen in Diarthrognathus) was the double jaw articulation. In this animal, not only was the ancient reptilian joint between a reduced quadrate and articular still present, but also the new mammalian joint between the squamosal and dentary bones had come into functional being. Thus, Diarthrognathus was truly at the dividing line between reptile and mammal in so far as this important diagnostic feature is concerned." (Colbert and Morales, 1991, p. 128)
On Morganucodonts it quotes
quote:"The axes of the two jaw hinges, dentary-squamosal and articular-quadrate, coincide along a lateral-medial line, and therefore the double jaw articulation of the most advanced cynodonts is still present . . . The secondary dentary-squamosal jaw hinge had enlarged (in the Morganucodonts) and took a greater proportion if not all of the stresses at the jaw articulation. The articular-quadrate hinge was free to function solely in sound conduction." (Strahler, 1987, p. 419)
and then it says
quote:Thus, the fossil record demonstrates, during the transition from therapsid reptile to mammal, various bones in the skull slowly migrated together to form a second functional jaw joint, and the now-superfluous original jaw bones were reduced in size until they formed the three bones in the mammalian middle ear. The reptilian quadrate bone became the mammalian incus, while the articular bone became the malleus. The entire process had taken nearly the whole length of the Triassic period to complete, a time span of approximately 40 million years. Since the determining characteristic of a mammal in the fossil record is the structure of the jaw bone and joint, all of the therapsids up to the Morganucodonts are classified as reptiles, and all those after that are considered to be mammals. As Romer puts it, "We arbitrarily group the therapsids as reptiles (we have to draw a line somewhere) but were they alive, a typical therapsid probably would seem to us an odd cross between a lizard and a dog, a transitional type between the two great groups of backboned animals." (Romer, 1967, p. 227)
and it also talks about modern snakes having double jaw joints
quote: ... every one of the 2,000 species of snakes living today does quite well with a double jaw joint, using an elongated quadrate bone with a joint at each end. (This enables the snakes to swallow large prey animals whole.)
Other facts on the transition given are
quote:
"In advanced forms, the skull was intermediate in type between that of a primitive reptile and a mammal; many of the bones absent in mammals were on their way toward reduction or were already lost. A small third eye was still generally present in the top of the skull, but its opening was a tiny one." (Romer, 1967, p. 226) "The differentiation of the teeth progressed in the therapsids to high levels of development, with the advanced genera showing sharply contrasted incisors, canines, and cheek teeth, which in some of these reptiles were of complex form, often with accessory cusps or broad crowns. In many therapsids, the occipital condyle became double, as in the mammals." (Colbert and Morales, 1991, p. 118)
...Cross sections of therapsid bones reveal a series of small holes called Haversian canals, which are typical of fast-growing, warm-blooded animals (and which are absent in cold-blooded reptiles), indicating that the therapsids developed a progressively more mammalian warm-blooded metabolism as time went on. And as the skull and jaws were becoming progressively more and more mammalian, the rest of the body structure was following suit:
"As for the post-cranial skeleton, other cynodonts closely related to Probainognathus show various features prophetic of the mammalian skeleton. In the genera Thrinaxodon and Cynognathus, for example, the vertebral column was distinctly differentiated into cervical, thoracic and lumbar vertebrae, thus delineating the three regions of the backbone in front of the pelvis so characteristic of the mammals. Although the cervical ribs were still defined in such cynodonts, they were very short and might well have been antecedant to the mammalian condition, in which the cervical ribs have become fused to become integral parts of the vertebrae. The lumbar ribs, too, were very short; indeed in Thrinaxodon they were in the form of small flat plates, instead of being elongated ribs. Such a distinct lumbar region in these mammal-like reptiles suggests that there was a diaphragm, a diagnostic mammalian feature that would seem possibly to have become established before the mammalian condition was reached." (Colbert and Morales, 1991, p. 229)
... In nearly every feature, then, the therapsids demonstrated a reptile-like condition at the beginning of the Triassic, grow progressively more and more mammal-like, and finally ended up as primitive mammals in the late Triassic.
From reference (2) below:
quote:The Therapsida, the basal members of which were traditionally called "mammal-like reptiles" are the advanced synapsids, and include the mammals. The traditional Linnaean classification groups the therapsids into several suborders - usually Phthinosuchia/Biarmosuchia, Dinocephalia, Anomodontia, and Theriodontia, this last often subdivided. See the unit Cladogram.
Overall, the story is as follows. Evolving from mid-Permian ancestors similar to Tetraceratops (a small synapsid completely unrelated to the well-known dinosaur Triceratops), these creatures evolved progressively more mammalian features, first in the disorderly branching of poorly known basal forms like the Biarmosuchia, Phthinosuchia, and Eotitanosuchia. From this basal group the tree developed a threefold branching. The earliest to develop were the somewhat more derived ungainly carnivores, omnivores and herbivores of the Dinocephalian lineages. Following them came two very distinct lines of adaptive evolution, the diverse and successful dicynodonts (Anomodontia), and the very mammal-like theriodonts. Mammals evolved from the later group through the various intermediate stages covered here and in the next two units.
There is a wealth of information on that and following (linked) pages.
It seems to me that this can be organized by fossil with a description of the initial reptilian example followed by the changes with each subsequent fossil, demonstrating the small level of change at each stage.
The intent would be to show that at the start there was a reptile head, jaw, teeth and ear structure and that at the end there was a mammal head, jaw, teeth and ear structure, thus the creationist "cannot change one kind into another" would be refuted -- unless "kind" included all reptiles and all mammals (including humans) in one "kind" -- through "microevolution" steps and stages.
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