No Transitionals?

Discussion in 'Creation vs. Evolution' started by UTEOTW, Jul 1, 2003.

  1. UTEOTW

    UTEOTW
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    The differences between mammals and reptiles are considerable. A chief difference is that reptiles have at least four jaw bones and one middle ear bone while mammals have one jaw bone and three middle ear bones. To make matters worse, two bones in the fetal reptile that turn into jaw bones turn into ear bones in developing mammals. Other key differences. Reptile have undifferentiated teeth while mammals have incisors, canines, premolars, and molars. Reptile teeth are continuously replaced, mammals teeth are replaced at most once. Reptile teeth only have a single root while mammal molars have two roots. Reptiles lack a diaphragm. Reptiles have their legs sprawled out to the sides while mammals have their legs underneath. The pelvis of a mammal is fused. They have different numbers of bones in their toes. Reptiles are cold blooded while mammals are warm blooded.

    A list of transitional animals with limited comments (still long and still a cut and hatchet job but editted to reduce length):

    Paleothyris - A reptile
    Protoclepsydrops haplous
    Clepsydrops
    Archaeothyris - Showed a slight change in teeth
    Varanops - Lower jaw shows first changes in jaw musculature...lower-limb musculature starts to change Too late to be a true ancestor, and must be a "cousin".
    Haptodus - Teeth become size-differentiated, with biggest teeth in canine region and fewer teeth overall...Vertebrae parts & joints more mammalian.
    Dimetrodon, Sphenacodon or a similar sphenacodont - More advanced pelycosaurs, clearly closely related to the first therapsids (next). Dimetrodon is almost definitely a "cousin" and not a direct ancestor... Teeth further differentiated, with small incisors, two huge deep- rooted upper canines on each side, followed by smaller cheek teeth, all replaced continuously. Fully reptilian jaw hinge. Lower jaw bone made of multiple bones & with first signs of a bony prong later involved in the eardrum..
    Biarmosuchia - Upper jaw bone (maxillary) expanded to separate lacrymal from nasal bones, intermediate between early reptiles and later mammals. Canine teeth larger, dominating the dentition. Variable tooth replacement: some therocephalians (e.g Scylacosaurus) had just one canine, like mammals, and stopped replacing the canine after reaching adult size. Jaw hinge more mammalian in position and shape, jaw musculature stronger (especially the mammalian jaw muscle)...more mammalian femur & pelvis. The toes were approaching equal length, as in mammals, with #toe bones varying from reptilian to mammalian.
    Procynosuchus - The first known cynodont -- a famous group of very mammal-like therapsid reptiles, sometimes considered to be the first mammals. Lower incisor teeth was reduced to four (per side), instead of the previous six (early mammals had three). Jaw hinge still reptilian. Scapula beginning to change shape. A diaphragm may have been present.
    Dvinia - First signs of teeth that are more than simple stabbing points -- cheek teeth develop a tiny cusp. The dentary bone was now the major bone of the lower jaw. The other jaw bones that had been present in early reptiles were reduced to a complex of smaller bones near the jaw hinge.
    Thrinaxodon - Functional division of teeth: incisors (four uppers and three lowers), canines, and then 7-9 cheek teeth with cusps for chewing. The cheek teeth were all alike, though (no premolars & molars), did not occlude together, were all single- rooted, and were replaced throughout life in alternate waves. First sign of the mammalian jaw hinge. Scapula shows development of a new mammalian shoulder muscle. All four legs fully upright, not sprawling. Number of toe bones is intermediate between reptile number and mammalian . The specialization of the lumbar area (e.g. reduction of ribs) is indicative of the presence of a diaphragm, needed for higher O2 intake and homeothermy. The eardrum had developed in the only place available for it -- the lower jaw, right near the jaw hinge, supported by a wide prong (reflected lamina) of the angular bone. Cynodonts developed quite loose quadrates and articulars that could vibrate freely for sound transmittal while still functioning as a jaw joint, strengthened by the mammalian jaw joint right next to it.
    Cynognathus - Teeth differentiating further; rate of replacement reduced, with mammalian-style tooth roots (though single roots). TWO JAW JOINTS in place, mammalian and reptilian. Limbs were held under body. There is possible evidence for fur in fossil pawprints.
    Diademodon - Mammalian toe bone numbers, with closely related species still showing variable numbers.
    Probelesodon - Teeth double-rooted, as in mammals. Second jaw joint stronger. Hip & femur more mammalian.
    Probainognathus - Additional cusps on cheek teeth. Still two jaw joints. Mammalian number of toe bones.
    Exaeretodon - Mammalian jaw prong forms, related to eardrum support. Three incisors only (mammalian). More mammalian hip related to having limbs under the body. This is probably a "cousin" fossil not directly ancestral, as it has several new but non-mammalian teeth traits.
    Oligokyphus, Kayentatherium - Alternate tooth replacement with double-rooted cheek teeth, but without mammalian-style tooth occlusion. Skeleton strikingly like egg- laying mammals (monotremes). Double jaw joint. Scapula is now substantially mammalian, and the forelimb is carried directly under the body. Various changes in the pelvis bones...this animal's limb musculature and locomotion were virtually fully mammalian. There is disagreement about whether the tritylodontids were ancestral to mammals or whether they are a specialized offshoot group not directly ancestral to mammals.
    Pachygenelus, Diarthrognathus - Alternate replacement of mostly single- rooted teeth. This group also began to develop double tooth roots -- in Pachygenelus the single root of the cheek teeth begins to split in two at the base. Pachygenelus also has mammalian tooth enamel. Double jaw joint, with the second joint ...fully mammalian. Reptilian jaw joint still present but functioning almost entirely in hearing. Highly mobile, mammalian-style shoulder. These are probably "cousin" fossils, not directly ancestral.
    Adelobasileus cromptoni - Currently the oldest known "mammal."
    Sinoconodon - The next known very ancient proto-mammal. Mammalian jaw joint stronger. This final refinement of the joint automatically makes this animal a true "mammal". Reptilian jaw joint still present, though tiny.
    Kuehneotherium - A slightly later proto-mammal, sometimes considered the first known pantothere (primitive placental-type mammal). Teeth and skull like a placental mammal. The three major cusps on the upper & lower molars were rotated to form interlocking shearing triangles as in the more advanced placental mammals & marsupials. Still has a double jaw joint, though.
    Eozostrodon, Morganucodon, Haldanodon - Truly mammalian teeth: the cheek teeth were finally differentiated into simple premolars and more complex molars, and teeth were replaced only once. Tiny remnant of the reptilian jaw joint. Thought to be ancestral to all three groups of modern mammals -- monotremes, marsupials, and placentals.
    Peramus - A "eupantothere" (more advanced placental-type mammal). The closest known relative of the placentals & marsupials.
    Endotherium
    Kielantherium and Aegialodon
    Steropodon galmani - The first known definite monotreme.
    Vincelestes neuquenianus - A probably-placental mammal with some marsupial traits.
    Pariadens kirklandi - The first definite marsupial.
    Kennalestes and Asioryctes - Canine now double rooted.
    Cimolestes, Procerberus, Gypsonictops - Primitive North American placentals with same basic tooth pattern.

    So we have a finely divided set of fossils going from purely reptile to purely mammal with intermediate features seen gradually changing throughout the sequence.

    To read more see http://www.talkorigins.org/faqs/faq-transitional/part1b.html

    and http://www.talkorigins.org/faqs/comdesc/section1.html#morphological_intermediates_ex2

    The latter has drawings of the jaw in transistion to see what it looked like. The former has the full text of most of what I posted above.

    Still think there are no transistionals?
     
  2. Johnv

    Johnv
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    UTEOTW , since you're discussing evidence, I doubt you'll get many YEC's posting here, other than an occaisional blanket statement.
     
  3. Helen

    Helen
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    I looked at it. I haven't followed it through yet for lack of time, but I would have the following questions first off:

    1. Were these specimen in appropriate stratas for the claimed evolutionary sequence?

    2. Was each in some approximation geographically to the area of the one 'before' and 'after' it?

    3. Who put together this sequence?

    4. Is this a sequence which is generally accepted in paleontology? (For instance, I know the horse sequence put up on Talk Origins is so full of holes you could use it to strain food!)

    5. Given the sequence proposed for a change in tooth and jaw structure, do these animals show concordant changes in other areas which would bring them from reptile to mammal?

    6. Since tooth eruption is NOT determined genetically (not when it starts, but how far the tooth erupts and why it stops when it does is not connected to any known genetics), how is it proposed that each of these organisms managed to have a change in tooth structure/jaw structure and still had the teeth behave properly for that organism?

    Just a few questions off the top of my head.

    You see, anyone can take ONE set of criteria and 'show' a progression. However it's a whole lot more difficult to show that this might have really happened given all of the other things involved.

    I could take dogs starting with a miniature poodle and going up to a great Dane and show how one had to be descended from another as an increase in size and characteristics -- but we know that didn't happen.

    Lists like the one in the lead post here are actually fairly easy to come by, or even to make up if one 'needs' to. That is not the point at all, though. The point is to show that this actually did happen in terms of one sort of things gradually changing into another sort. Lists are not really evidence, I'm afraid.

    What sort of mutations are being proposed here? Where in the genome did they take place to produce the 'changes' listed, or implied above? There are so many unanswered questions that the list is simply a list and really does not mean anything evolutionarily.
     
  4. The Galatian

    The Galatian
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    Let's deal with the technical ones, first:

    Absolutely. An entire suite of characters evolved together, (co-evolution is a frequent theme in evolution at the class level)

    The simplification of the lower jaw made a more powerful bite and prolonged chewing possible. At about the same time, we see an enlargement of the opening in the skull that gives synapids their name. The relatively weak reptillian jaw adductor was reconfigured in that enlarged space to form the mammalian massater. The remains of the lower part of that opening became the zygomatic arch, through which the muscle attached to the dentary.

    At roughly the same time, teeth began to differentiate. The major change were elaborations to the cheek teeth to make them more efficient at tearing/grinding food to make it smaller, which meant it was more digestable, making the animal more efficient at utilizing available resources.

    At roughly the same time, we see a progressive growth of the bony shelf in the mouth of some primitive therapsids, to form a secondary palate.
    No longer do such animals have to quickly gulp down food; they can chew and breath at the same time.

    At the same time, the single occipital condyle at the base of the skull first widens, and then splits into two parts, allowing a stronger joint, and more power for tearing meat or pulling vegetation.

    At the same time, the thoracic muscles enlarge and extend to form a sheet of tissue that becomes the diaphragm. (we know this one, because this is accompanied by a reduction in abdominal ribs in animals having a diaphraphm; the ribs are no longer needed to attach "bellows") which means that the animal can walk and breathe at the same time. It can be more quick and agile, because it can now have a higher metabolism, due to more efficient feeding.

    And all these occured more or less in concert. Some more rapidly in some forms than others, but each one made the advancement of the other possible.

    Good question. Like all the other features, it went slowly. Take a look here:

    http://tolweb.org/tree/eukaryotes/animals/chordata/synapsid_lichen/synapsida_synapomorphies.html

    The early reptillian teeth were merely for holding prey long enough to kill/swallow. Carnassals can still hold, even if their primary function is to slice. Notice, though, that the first "mammalian" teeth were doglike canines, with the molars developing later, after more secure "holding" teeth evolved.

    The evolution of mammalian teeth is complex and well-documented, (often the teeth are the only things that survive, especially in small mammals) if you want to get more detail.
     
  5. The Galatian

    The Galatian
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    Ah, the Gish "multiplying gaps" theory. The more transitionals we find, the more gaps between them.

    Most of the time, the evolution of horses is so finely detailed that we can see changes within genera. Even Gould was compelled to admit that the fossil evidence shows that horse evolution was gradual.
     
  6. UTEOTW

    UTEOTW
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    First, I cut off a bunch of data to shorten things up. Mainly, I tried to simplify the changes to a few specific areas instead of all the changes, just to keep it on a simpler level and to keep it short enough to maybe be read.

    Here is an more detailed read, if you wish. Everything summarized in a nice, easy to follow chart and drawings showing the step by step teeth changes.

    http://www.gcssepm.org/special/cuffey_05.htm

    Yes. I cut off the dates to keep things shorter. Besides, the dates were for the most part given like "latest Permian" or "early Triassic" and would have required most people to have to look that up. Again, I was trying to keep it short and simple. But the order was good. The animals that are a slightly out of order are noted as "cousins" when needed and I did not cut that information in the interest of full disclosure.

    Most do not have geographic data with them and I do not really feel like looking up that many animals. The ones for which locations were given were all in N. or S. America AFAIK. But this was a long process, about 140 million years. For much of that time the land was joined together as Pangaea and the animals would have been relatively free to move about, especially on geological time scales. About the time Pangaea started to break up, in the Jurassic, the list starts specifying where most of the fossils were found and that was in the Americas.

    Don't know.

    AFAIK, but I'm not a paleontologist. If it is not, I would love to see the correct list from some paleontology textbook, journal, etc.


    Yes. Again, I left out a lot of material to shorten and simplify. You are free to go read the full list. But most animals listed had multiple changes from one to the next. It was not just a tooth here and a bone there. For instance, here is the entire entry for one animal.

    What does cause this and why is it a problem? There was a very fine observed change from the reptilian teeth in which the teeth size differentiated, then started changing shape into more useful and more mammalian form, proceeding through a time when different teeth were replaced at different rates, and so on until you get a mammal.


    What has this strawman got to do with the discussion? Creationists like to say there are no transitionals and here is progressive transition that is well documented. Your dogs would all be found in the same geologic strata, not in order through over 100 million years.

    Is no evidence good enough? A set of transitional fossils between two very different types of animals is fairly convincing evidence. Hand waving around the sides does not make the fossils go away. Mammals and reptiles are very different and in all the key differences we have a set of fossils that shows continuous change with multiple changes happening in each fossil.

    The evidence is meaningful. The list is just bytes in cyberspace, but the fossils are real. So we produce the transitionals and now you want the genetic evidence from 300 million year old fossils? The goal posts keep moving. To be a little more direct would require getting into studies about the genetic diffrences between modern species and I think that is a topic for another thread.
     
  7. UTEOTW

    UTEOTW
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    Sorry...The 140 miilion years above should have been 240 million years. Apparently I have forgotten how to do simple math. [​IMG]
     

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