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Author Topic:   Plausible Evolutionary Chains for Educational Use
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 16 of 25 (378145)
01-19-2007 6:25 PM
Reply to: Message 14 by arachnophilia
01-18-2007 1:31 PM


Trilobites to Spiders
trilobitomorpha and chelicerata (spiders and horseshoe crabs) are separate subphyla of arthropoda.
Trilobites to spiders would be even better, as this would be another transition from aquatic to terrestrial.

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This message is a reply to:
 Message 14 by arachnophilia, posted 01-18-2007 1:31 PM arachnophilia has replied

Replies to this message:
 Message 17 by arachnophilia, posted 01-19-2007 6:37 PM RAZD has replied
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arachnophilia
Member (Idle past 1344 days)
Posts: 9069
From: god's waiting room
Joined: 05-21-2004


Message 17 of 25 (378150)
01-19-2007 6:37 PM
Reply to: Message 16 by RAZD
01-19-2007 6:25 PM


Re: Trilobites to Spiders
spiders and trilobites share a common ancestor -- something like a neotonous trilobite. looks like the larval form. you won't see a transition from trilobites to spiders and more than you will see one from dogs to cats.
i'm not actually very clear on arthropod evolution. i can point lith in this way, he'll explain to you why the initial request is silly.


This message is a reply to:
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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 18 of 25 (378199)
01-19-2007 8:31 PM
Reply to: Message 17 by arachnophilia
01-19-2007 6:37 PM


Re: Trilobites to Spiders
i can point lith in this way
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).

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Lithodid-Man
Member (Idle past 2931 days)
Posts: 504
From: Juneau, Alaska, USA
Joined: 03-22-2004


Message 19 of 25 (378291)
01-20-2007 3:22 AM
Reply to: Message 16 by RAZD
01-19-2007 6:25 PM


Re: Trilobites to Spiders
Like arach mentioned, trilobites and chelicerates (horse shoe crabs, spiders, etc) are very distantly related.
Traditionally four subphyla of arthropods, Crustacea, Chelicerata, Trillobitomorpha, and Unirama (although the latter is almost certainly polyphylectic) were recognized. The relationship between the four is unknown, and it is possible that at least one of those represents an independantly derived arthropod bauplan.
Where the trilobites differ in a signicant manner from chelicerates is in the presence of antennae in front of the mouth. Chelicerates lack preoral appendages. This may not seem like a big difference, but is really significant.
More recent analyses are strongly suggesting that the 'uniramians' (insects, millipedes, centipedes) are close to the crustaceans (united as the Mandibulata) and are a sister taxon to the Trilobitomorpha - Chelicerata clade (called the Arachnomorpha).
A good summary of this and other suggested phylogenies can be found at: Palaeos: Page not found
About the evolution of terrestrial arthropods... Well not much is known. In all liklihood the arachnids (spiders and their kin) derived from forms similar to the extinct sea scorpions, the Euryptida. Modern scorpions are the least derived of the arachnids (mites and ticks, the Acarii, being the most derived).
There is a possible centipede-like marine arthropod from the Cambrian, and clear terrestrial primitive myriopods from the Silurian. My invert zoo papers are at school in my office. Somewhere here at home in all of my reprints I have an excellent article by Ed Bousfield on arthropod mouthpart morphology that I think has subsequently (more or less) been in agreement with more recent genetic work and cladistic analyses.

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Equinox
Member (Idle past 5142 days)
Posts: 329
From: Michigan
Joined: 08-18-2006


Message 20 of 25 (379528)
01-24-2007 2:46 PM
Reply to: Message 19 by Lithodid-Man
01-20-2007 3:22 AM


Re: Trilobites to Spiders
RAZD wrote:
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.
It certainly is a tall order if each step is to be supported by a complete fossil (or even an incomplete one). However fossil proof is not needed for a plausible chain. Since I’m only talking about plausible chains, they are NOT a tall order. It’s just a matter of an artist taking a few minutes to do it in consultation with an appropriately specialized biologist (like many people here - maybe lithoid man for the spider chain?). In fact, just this morning I watched, on the Cosmos series (Carl Sagan), the following plausible chains, with literally hundreds of steps in each one:
Molecules to camels
Molecules to turtles
Molecules to sponges
Molecules to monkeys
Molecules to dinosaurs
Molecules to birds
Molecules to starfish
Molecules to humans
They are on episode #2 (“one voice in the cosmic fugue”), and start around 25 minutes in. I’m looking for things like that which are more accessible to everyone, like say on a webpage or in a JPEG format, or such. Plus, more detail beyond the line drawings in Cosmos would be nice too. (If anyone doesn’t have the cosmos series, I highly recommend it - it single-handedly inspired thousands of people to enter the sciences). It’s at: Cosmos: Carl Sagan (1980) (just read the reviews if you are unsure - my 5 year old loves it already, it’s our special daddy-son “movie”).
I hope I’m being clear that these are plausible (as in “not contradicted by the fossil record, nor by other evidence, such as genetic evidence”), chains. I’m not asking for cases where we have every leg bone of every creature at every step (or even a fossil of every step), or any such level of proof.
Edited by AdminPD, : Fixed Link

-Equinox
_ _ _ ___ _ _ _
You know, it's probably already answered at An Index to Creationist Claims...
(Equinox is a Naturalistic Pagan -  Naturalistic Paganism Home)

This message is a reply to:
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Replies to this message:
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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 21 of 25 (385815)
02-17-2007 10:10 AM
Reply to: Message 20 by Equinox
01-24-2007 2:46 PM


url fix?
Could you (or an admin) shorten your url to:
Cosmos: Carl Sagan (1980)
using [url=(your url)]Cosmos: Carl Sagan (1980)[/url]
It's so long it forces the page width too wide.
Thanks.

This message is a reply to:
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Equinox
Member (Idle past 5142 days)
Posts: 329
From: Michigan
Joined: 08-18-2006


Message 22 of 25 (386274)
02-20-2007 5:08 PM
Reply to: Message 21 by RAZD
02-17-2007 10:10 AM


Re: url fix?
Thanks for telling me how to do it. Now I know.

This message is a reply to:
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Equinox
Member (Idle past 5142 days)
Posts: 329
From: Michigan
Joined: 08-18-2006


Message 23 of 25 (386276)
02-20-2007 5:11 PM
Reply to: Message 19 by Lithodid-Man
01-20-2007 3:22 AM


Re: Trilobites to Spiders
you know, I could even imagine a very plausible chain going back from a spider to the common ancestor, and then forward to the trilobite. As long as the common ancestor were noted, then this would work too.
I wonder if Lith knows of drawing or such of those transitions - not actual fossils, but plausible, scientifically consistent estimates?
Thanks-

-Equinox
_ _ _ ___ _ _ _
You know, it's probably already answered at An Index to Creationist Claims...
(Equinox is a Naturalistic Pagan -  Naturalistic Paganism Home)

This message is a reply to:
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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 24 of 25 (404861)
06-10-2007 9:04 AM


bump for new people
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.
Enjoy.

  
RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 25 of 25 (410335)
07-14-2007 12:11 PM


Another Fossil Chain?
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.
Names in the article:
Therapsid (or Therapsida)
tritylodont
cynodonts
Probainognathus (genus under cynodont)
ictidosaurians
Diarthrognathus
Morganucodonts
On tritylodont it quotes
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.
Resources I have found include
(1) http://www.geocities.com/...naveral/Hangar/2437/therapsd.htm
(2) Palaeos: Page not found
Enjoy.

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RebelAAmericanOZen[Deist
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