In my previous topic , (a serious question) i admit that the example chosen wasnt adequate and convincing through the eyes of the evolutionist because he beliefs that the human eye-brow havent been placed there from nothing but that its is the result from natural selective effects on our previous "ancestors", thus the hair from the primate forehead have minimized into our modern eyebrows.
Please keep in mind that in the end of the previous topic , (if you could read between the lines) you would find that it was meant to be only a simple example , thus expressing something much more difficult to explain.
However ill get to the real issue now: Natural selection could have led to less hair through means of "evolution" because that the genetic sequence required to do it is there , that is to say that through sexual processes it is possible to loose hair.
Its just the same with the famous examples of the lighter moth population that became black because the lighter moths died when the effects of the industrial evolution had done their job keeping the trees black. HOWEVER before the industrial revolution there had always been black moths, the genetic requirements had always been there, it was only the relation between quantity that was different.
The same with the development of the human races, if a caucasian tribe decides to live in Africa for a very long time(lets say 25000)years the tribe would eventually be black, they would have the best weapons against the sun . So far the creationist absolutely agree with his companions, the evolutionist.
But please separate the above examples from lets say the "evolutionary process" required to transform a reptile into lets say a mammal. As mentioned before natural selection doesnt have a concioussness so the great differences couldnt have occured through a random selective process, the complex organs required to give birth to a living specie instead of laying an egg just isnt in the genetic information of the reptile. Everything had to be planned ahead through random mutations inorder for the birth process to work while having the same function required to lay an egg in the meanwhile until the final function of all those halfdone complex organs could actually work and replace the earlier way of giving birth.
Indeed such a creature doesnt exist and such a fossil remain has never been found(shouldnt there be millions and millions of them)
Hope youll be able to answer this honestly and please dont dissicate my post as before and give un awkyard answer.
Once again guys : ) Good luck!
Edit by Adminnemooseus: Added spaces between paragraphs, and tweeked other formatting a bit
[This message has been edited by minnemooseus, 09-25-2002]
I'll take up your challenge. The shift from reptilian oviparity (laying eggs) to mammalian viviparity (live birth) is not too great once you are able to appreciate that there are intermediates between the two extremes. Most reptiles lay eggs, but some retains it within their bodies (ovoviviparity); and there are some which have true viviparity, although not as elaborate as modern mammals. And the most primitive living mammals, the monotremes (platypus & echidna--both Australian natives). These living models are hints to the stages in the evolution of mammalian viviparity. Finally, mammalian embryos still develop an empty yolk sac, which is a vestigial organ inherited from their egg-laying ancestors
Andya gave an excellent synopsis. Just to provide a few more details:
A brief synopsis of the development of placental mammals from egg laying reptiles:
Theriodont (mammal-like reptiles; egg layers) -> pantothere (monotreme, or egg-laying mammals; c.f. echidna and platypus) -> metathere (marsupial, or pouched mammal; c.f. kangaroo, opossum) -> euthere (placental mammal; all others)
Going beyond this, we have to get pretty detailed on the differences between oviparity in reptiles/amphibians, oviparity in pantotheres where the egg (containing limited yolk) develops for a period within the uterus nourished by endometrial secretions, then the gradual development of choriovitelline placenta in the metatheres and finally true placentae in modern mammals. In addition, for it to make sense, you need to understand the trade-off in the “maternal dependent growth model” where duration and extent of intrauterine and post-natal care are variations that can be operated on by natural selection. Finally, you need to understand the role that may have been played by differential production of the hormone dehydroepiandrosterone in the gradual replacement of egg by placenta over the course of 175 million years, based on comparisons between modern monotremes, marsupials, and placental mammals.
Hi Andya and quetzal, thanks for responding so quickly
You are both using the term vestigial organs very frequently and Andya even mentions the yoc sac in the mammalian embryo to be an ancient leftover.
I have have to mention that sciencist document that they have been witnessing a constant reduction in what was previously called vestigial organs.
The yolk sac is one of the protective membranes surrounding the embryos of birds reptiles AND mammals. The embryo derives nourishment from the yolk sac via a system of blood vessels. In birds and reptiles the yolk sac encloses the yolk but in most mammals a fluid replaces the yolk.
So it isnt a vestigial organ.
And this isnt the only mistake that has been made. The constant reduction of vestigial organs since the latest fifty years have only one answer, knowledge replacing ignorance.
According to the theory of common ancestry between reptils and mammals, answer this question please: The differences between those two groups isnt only that one lies an egg and the other gives birth to living creatures although none of you succeded in answering that previously (without stating that species such as the therian reptiles where transitional forms, they had only ONE way of giving birth and no sign of an alternative way on its making).
There are also more differences: reptiles are cold blooded and mammals are warm blooded, reptiles have scales and mammals have hair(the previous example of the hair of the human eyebrow existing only through mutation is appliable here).
More examples is the jaw and the ear, all the mammallian ears consists of three bones and the reptilian of one, the jaw structure is also very different where on mammals all the teeths are located on a single mandibular bone but on reptiles there are three bones in each mandibular side.
Evolutionists claim however that the single reptilian earbone evolved into three, this theory has been disproved because no such fossils have been found(not even one that implies that that transitional bones are on theyre making), and the question of how the species would be able to hear or eat or (give birth mean while) is unanswered by evolutionists.
So if evolutionists claim some theories, why dont they back it up with proofs instead of speculations.
This is why the famous evolutionist paleontologist Roger Lewinis forced to state in an interview: "The transition to the first mammal wich happened in just one ore mostly to lineages, is still an enigma"
Edit by Adminnemooseus: Added spaces between paragraphs and tweeked other formatting a bit
[This message has been edited by minnemooseus, 09-25-2002]
Uhh, Delshad - what part of my post didn't you understand? I tried to keep it as simple as your apparent lack of knowledge required. If you really desire to know the answer to your question, the gist of the answer is in my post. If you have specific questions about any element in my response, please show you understand what was originally posted before asking for more - and more technical - details.
quote:Evolutionists claim however that the single reptilian earbone evolved into three, this theory has been disproved because no such fossils have been found(not even one that implies that that transitional bones are on theyre making),
This is a misrepresentation of what evolutionists claim as the origin of the three ear bones in mammals. Hopefully, the misrepresentation was not intentional.
Based upon a whole series of fossils as evidence, two of the bones in the mammalian ear are clearly modified reptilian jaw bones. Some of the fossils demonstrating the reptile to mammal transition show both reptilian jaw joint and mammalian jaw joint features simultaneously. Here is a summary of the evidence that addresses the origin of ear bones and many of the other features that distinguish mammals from reptiles:
Please Quetzal, dont misunderstand me, I understood very clearly what you were trying to express in your previous post and I`m sorry if you thought otherwise. Its just that, and I hope you agree with me here, NO scientific evidence really proofs your theory to be correct, and ill try to explain why: Lets say for an example that we are both proffesional archeologists and we both share the same view about evolution ,thus we place each of those fossils we would find into one of the two categories, mammals or reptiles. Then whenever we find a fossil that has its own quite distinct skeletal structure yet resembling one of the categories we have set up(even in a very little way), we hurry to place it under one of the fixed categories or at its peak we would say ,"well it maybe is an ancient subspecie evolving to this or that" and possiblitys that suggest anything else but the theory of evolution is completely out of the question. That way of thinking isnt so scientific at all because our conclusion will be influenced by the parameters we have set up.
And let me once again repeat that each fosil that has been found has all the the features required to live successfull. In other words none of the foosils shows that they were "transitional" forms caused by random mutation because NONE of them has the caracteristics indicating it(asymmetrical forms or useless ineffective halfdone organs). Evolution has no conscioussness and between the time a mutation has ocurred and the time needed to by means of natural selection establish a symmetrical form, there is plenty of time for generation after generation to have traits possessing these "abnormal" shapes. But none exists, I hope youll be able to open your eyes and see things from a different perspective, that is the scientific way of approaching the issue.
Please Quetzal, dont misunderstand me, I understood very clearly what you were trying to express in your previous post and I`m sorry if you thought otherwise. Its just that, and I hope you agree with me here, NO scientific evidence really proofs your theory to be correct, and ill try to explain why:
The same can be said of gravity as well.
Lets say for an example that we are both proffesional archeologists and we both share the same view about evolution ,thus we place each of those fossils we would find into one of the two categories, mammals or reptiles.
1. An anthropologist who studies prehistoric people and their culture
You mean a palaeontologist.
Then whenever we find a fossil that has its own quite distinct skeletal structure yet resembling one of the categories we have set up(even in a very little way), we hurry to place it under one of the fixed categories or at its peak we would say ,"well it maybe is an ancient subspecie evolving to this or that" and possiblitys that suggest anything else but the theory of evolution is completely out of the question. That way of thinking isnt so scientific at all because our conclusion will be influenced by the parameters we have set up.
That is why there a peer reviewed journals and the like so that a consensus can be reached.
Evolution has no conscioussness and between the time a mutation has ocurred and the time needed to by means of natural selection establish a symmetrical form, there is plenty of time for generation after generation to have traits possessing these "abnormal" shapes. But none exists, I hope youll be able to open your eyes and see things from a different perspective, that is the scientific way of approaching the issue.
What I see is that you visit the ICR site too much and they filled you full of their pesudo-science nonsense. You didn't even know the proper title of those who study fossils (In fact you couldn't even spell fossil).
[This message has been edited by nos482, 09-26-2002]
quote:Originally posted by Delshad: Please Quetzal, dont misunderstand me, I understood very clearly what you were trying to express in your previous post and I`m sorry if you thought otherwise.
Misunderstand you? I'm afraid I understand you all too well - except that I was willing to grant you the benefit of the doubt. However, I fear you will never understand any evidence presented in answer to your question.
quote:Its just that, and I hope you agree with me here, NO scientific evidence really proofs your theory to be correct, and ill try to explain why:
Of course I don't agree. In the first place, it's not my theory. It is the concensus result of a half dozen disciplines from paleontology to embryology and evolutionary developmental biology. In the second, there is quite sufficient evidence to lend high confidence to what I posted. Evidence, by the way, which has been thoroughly tested by multiple methods. Based on your erroneous statement concerning the development of the mammalian ear structures from reptilian jaw bones, I repeat it's unlikely you would be able to understand it.
However, I'll give you a second chance to prove me wrong: please explain the differences in reptilian oviparity and monotreme oviparity (probably the easiest bit of evidence) with relation to modern organisms (I figure examination of the fossil evidence is asking you too much). We can take that as a basis for discussion. Obviously, you can claim from there that the differences are based on biblical taxic discontinuity, whereas I will show that the differences are easily derived from natural selection. If you can at least show that much knowledge, I'll consider continuing this conversation.
quote:Lets say for an example that we are both proffesional archeologists and we both share the same view about evolution ,thus we place each of those fossils we would find into one of the two categories, mammals or reptiles. Then whenever we find a fossil that has its own quite distinct skeletal structure yet resembling one of the categories we have set up(even in a very little way), we hurry to place it under one of the fixed categories or at its peak we would say ,"well it maybe is an ancient subspecie evolving to this or that" and possiblitys that suggest anything else but the theory of evolution is completely out of the question.
Unless you're talking about the evolution of culture, I don't think archeologists are going to have much to say about evolution - especially the fossil record.
On the other hand, I agree with you about the somewhat arbitrary taxonomic designations that occasionally happen. It's quite obvious when you deal with the difference between reptile and mammal characteristics in the synapsids. Of course, that poses absolutely no problem for evolutionary theory - it's what we expect to see: a gradual "fading" in between taxa where the designation "mammal" from "reptile" is pretty arbitrary. Fortunately, molecular phylogentics (the basis of the science of cladistics) helps to confirm or disconfirm classifications based only on morphology - that's why it's so useful.
quote:That way of thinking isnt so scientific at all because our conclusion will be influenced by the parameters we have set up.
This makes absolutely no sense whatsoever. Care to explain what you're trying to say? Please keep it simple, you're dealing with an ignorant scientist type.
quote:And let me once again repeat that each fosil that has been found has all the the features required to live successfull.
An amazing statement of the obvious. What's your point?
quote:In other words none of the foosils shows that they were "transitional" forms caused by random mutation because NONE of them has the caracteristics indicating it(asymmetrical forms or useless ineffective halfdone organs).
I think you're seriously confused as to what constitutes a transitional form - there is no such thing as a "useless" or "half-done organ". Is this some kind of saltationist strawman "evolution" you're playing with? What we see is the gradual improvement, adaptation, or morphological change (could be elimination) of various structures.
quote:Evolution has no conscioussness and between the time a mutation has ocurred and the time needed to by means of natural selection establish a symmetrical form, there is plenty of time for generation after generation to have traits possessing these "abnormal" shapes.
Except any mutation that caused such an "abnormal" form (in the sense I think you are using it) would result in the death of the organism either before or immediately after birth. We don't see abnormality in the fossil record because the kind of gross abnormality/hopeful monster you propose wouldn't live. A mutation that effects the phenotype of an organism can only become fixed or dominant in a population IF it is capable of co-existing polymorphically for a period of time with the original allele. It will also only become dominant (generally) if it provides a net survival advantage to the organisms that have it. So your "transitional form = abnormal form" is a ludicrous strawman based on a massive misunderstanding of the science.
quote:But none exists, I hope youll be able to open your eyes and see things from a different perspective, that is the scientific way of approaching the issue.
ROTFLMAO. Ahh, me. Thanks for the lecture on scientific epistemology. Too bad it's probably highly unlikely you'll be able to apply the theory.
quote:In other words none of the foosils shows that they were "transitional" forms caused by random mutation because NONE of them has the caracteristics indicating it(asymmetrical forms or useless ineffective halfdone organs).
Your definition of a transitional form is unscientific. It is a straw man. There are in fact fossils that show features of both reptiles and mammals. Please read the FAQ from Talk.Origins to which I linked above. The fact that these organisms were "fully formed" and obviously fully functional (after all they survived to become fossils) does not mean they were not transitional. And despite your feeling that there should be millions of fossils that even you would recognize as transitional were evolution true, the simple fact that fossilization is something of a haphazard process guarantees there will be gaps, even if the process had been smooth (which it almost certainly was not when you consider the effects of mutations in genes controlling development).
Part of the problem is that you want to see a series of fossils that show the smooth, unbroken, ladder-like progression of generations in order to be convinced. This is not how evolution or fossilization works, even though that is how you think it should. So I guess your faith is safe.
But let's apply your logic to the opposite case so you can perhaps see what your argument is really like: Give me a list of all your ancestors back to Adam without any gaps. If you cannot give me that list, creationism must be false.
Naldacon, in theory, isnt it possible to find such a fossil?, if we keep looking, however you wrote that it is the same as you telling me to come up with a complete list of all my ancestors from Adam and Eve. First of all, Im not a christian, Im a muslim, so for instance there is nothing that implies it. In sura 2 ( it is decreed" We have made guardians ( or something similar in english) on the earth, thus the angels replied" what! have you made them guardians , those who destroy the earths customs, and shed blood" this makes it clear that there were people living on earth before, and if you ponder deep enough youll see that Adam and Eve are meant to be an allegory symbolizing mans common ancestry. You see, in the quran there isnt anything rejecting the scientical evidence at all, none, its only a guidance for man to behave and it also contains some miracles for us to appreciate it as a holy book, nothing else. In short , he created everything in its full form and natural selection is a way maintaining our distinct attributes for generations to come.
quote: Paleothyris (early Pennsylvanian) -- An early captorhinomorph reptile, with no temporal fenestrae at all.
Protoclepsydrops haplous (early Pennsylvanian) -- The earliest known synapsid reptile. Little temporal fenestra, with all surrounding bones intact. Fragmentary. Had amphibian-type vertebrae with tiny neural processes. (reptiles had only just separated from the amphibians)
Clepsydrops (early Pennsylvanian) -- The second earliest known synapsid. These early, very primitive synapsids are a primitive group of pelycosaurs collectively called "ophiacodonts".
Archaeothyris (early-mid Pennsylvanian) -- A slightly later ophiacodont. Small temporal fenestra, now with some reduced bones (supratemporal). Braincase still just loosely attached to skull. Slight hint of different tooth types. Still has some extremely primitive, amphibian/captorhinid features in the jaw, foot, and skull. Limbs, posture, etc. typically reptilian, though the ilium (major hip bone) was slightly enlarged.
Varanops (early Permian) -- Temporal fenestra further enlarged. Braincase floor shows first mammalian tendencies & first signs of stronger attachment to rest of skull (occiput more strongly attached). Lower jaw shows first changes in jaw musculature (slight coronoid eminence). Body narrower, deeper: vertebral column more strongly constructed. Ilium further enlarged, lower-limb musculature starts to change (prominent fourth trochanter on femur). This animal was more mobile and active. Too late to be a true ancestor, and must be a "cousin".
Haptodus (late Pennsylvanian) -- One of the first known sphenacodonts, showing the initiation of sphenacodont features while retaining many primitive features of the ophiacodonts. Occiput still more strongly attached to the braincase. Teeth become size-differentiated, with biggest teeth in canine region and fewer teeth overall. Stronger jaw muscles. Vertebrae parts & joints more mammalian. Neural spines on vertebrae longer. Hip strengthened by fusing to three sacral vertebrae instead of just two. Limbs very well developed.
Dimetrodon, Sphenacodon or a similar sphenacodont (late Pennsylvanian to early Permian, 270 Ma) -- More advanced pelycosaurs, clearly closely related to the first therapsids (next). Dimetrodon is almost definitely a "cousin" and not a direct ancestor, but as it is known from very complete fossils, it's a good model for sphenacodont anatomy. Medium-sized fenestra. 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, but there was no eardrum yet, so these reptiles could only hear ground-borne vibrations (they did have a reptilian middle ear). Vertebrae had still longer neural spines (spectacularly so in Dimetrodon, which had a sail), and longer transverse spines for stronger locomotion muscles.
Biarmosuchia (late Permian) -- A therocephalian -- one of the earliest, most primitive therapsids. Several primitive, sphenacodontid features retained: jaw muscles inside the skull, platelike occiput, palatal teeth. New features: Temporal fenestra further enlarged, occupying virtually all of the cheek, with the supratemporal bone completely gone. Occipital plate slanted slightly backwards rather than forwards as in pelycosaurs, and attached still more strongly to the braincase. Upper jaw bone (maxillary) expanded to separate lacrymal from nasal bones, intermediate between early reptiles and later mammals. Still no secondary palate, but the vomer bones of the palate developed a backward extension below the palatine bones. This is the first step toward a secondary palate, and with exactly the same pattern seen in cynodonts. 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). The amphibian-like hinged upper jaw finally became immovable. Vertebrae still sphenacodontid-like. Radical alteration in the method of locomotion, with a much more mobile forelimb, more upright hindlimb, & more mammalian femur & pelvis. Primitive sphenacodontid humerus. The toes were approaching equal length, as in mammals, with #toe bones varying from reptilian to mammalian. The neck & tail vertebrae became distinctly different from trunk vertebrae. Probably had an eardrum in the lower jaw, by the jaw hinge.
Procynosuchus (latest Permian) -- The first known cynodont -- a famous group of very mammal-like therapsid reptiles, sometimes considered to be the first mammals. Probably arose from the therocephalians, judging from the distinctive secondary palate and numerous other skull characters. Enormous temporal fossae for very strong jaw muscles, formed by just one of the reptilian jaw muscles, which has now become the mammalian masseter. The large fossae is now bounded only by the thin zygomatic arch (cheekbone to you & me). Secondary palate now composed mainly of palatine bones (mammalian), rather than vomers and maxilla as in older forms; it's still only a partial bony palate (completed in life with soft tissue). Lower incisor teeth was reduced to four (per side), instead of the previous six (early mammals had three). Dentary now is 3/4 of lower jaw; the other bones are now a small complex near the jaw hinge. Jaw hinge still reptilian. Vertebral column starts to look mammalian: first two vertebrae modified for head movements, and lumbar vertebrae start to lose ribs, the first sign of functional division into thoracic and lumbar regions. Scapula beginning to change shape. Further enlargement of the ilium and reduction of the pubis in the hip. A diaphragm may have been present.
Dvinia [also "Permocynodon"] (latest Permian) -- Another early cynodont. First signs of teeth that are more than simple stabbing points -- cheek teeth develop a tiny cusp. The temporal fenestra increased still further. Various changes in the floor of the braincase; enlarged brain. 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. Single occipital condyle splitting into two surfaces. The postcranial skeleton of Dvinia is virtually unknown and it is not therefore certain whether the typical features found at the next level had already evolved by this one. Metabolic rate was probably increased, at least approaching homeothermy.
Thrinaxodon (early Triassic) -- A more advanced "galesaurid" cynodont. Further development of several of the cynodont features seen already. Temporal fenestra still larger, larger jaw muscle attachments. Bony secondary palate almost complete. 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. Dentary still larger, with the little quadrate and articular bones were loosely attached. The stapes now touched the inner side of the quadrate. First sign of the mammalian jaw hinge, a ligamentous connection between the lower jaw and the squamosal bone of the skull. The occipital condyle is now two slightly separated surfaces, though not separated as far as the mammalian double condyles. Vertebral connections more mammalian, and lumbar ribs reduced. Scapula shows development of a new mammalian shoulder muscle. Ilium increased again, and all four legs fully upright, not sprawling. Tail short, as is necessary for agile quadrupedal locomotion. The whole locomotion was more agile. Number of toe bones is 126.96.36.199.3, intermediate between reptile number (188.8.131.52.4) and mammalian (184.108.40.206.3), and the "extra" toe bones were tiny. Nearly complete skeletons of these animals have been found curled up - a possible reaction to conserve heat, indicating possible endothermy? Adults and juveniles have been found together, possibly a sign of parental care. 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. NOTE on hearing: 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. These animals could now hear airborne sound, transmitted through the eardrum to two small lower jaw bones, the articular and the quadrate, which contacted the stapes in the skull, which contacted the cochlea. Rather a roundabout system and sensitive to low-frequency sound only, but better than no eardrum at all! 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. All early mammals from the Lower Jurassic have this low-frequency ear and a double jaw joint. By the middle Jurassic, mammals lost the reptilian joint (though it still occurs briefly in embryos) and the two bones moved into the nearby middle ear, became smaller, and became much more sensitive to high-frequency sounds.
Cynognathus (early Triassic, 240 Ma; suspected to have existed even earlier) -- We're now at advanced cynodont level. Temporal fenestra larger. Teeth differentiating further; cheek teeth with cusps met in true occlusion for slicing up food, rate of replacement reduced, with mammalian-style tooth roots (though single roots). Dentary still larger, forming 90% of the muscle-bearing part of the lower jaw. TWO JAW JOINTS in place, mammalian and reptilian: A new bony jaw joint existed between the squamosal (skull) and the surangular bone (lower jaw), while the other jaw joint bones were reduced to a compound rod lying in a trough in the dentary, close to the middle ear. Ribs more mammalian. Scapula halfway to the mammalian condition. Limbs were held under body. There is possible evidence for fur in fossil pawprints.
Diademodon (early Triassic, 240 Ma; same strata as Cynognathus) -- Temporal fenestra larger still, for still stronger jaw muscles. True bony secondary palate formed exactly as in mammals, but didn't extend quite as far back. Turbinate bones possibly present in the nose (warm-blooded?). Dental changes continue: rate of tooth replacement had decreased, cheek teeth have better cusps & consistent wear facets (better occlusion). Lower jaw almost entirely dentary, with tiny articular at the hinge. Still a double jaw joint. Ribs shorten suddenly in lumbar region, probably improving diaphragm function & locomotion. Mammalian toe bones (220.127.116.11.3), with closely related species still showing variable numbers.
Probelesodon (mid-Triassic; South America) -- Fenestra very large, still separate from eyesocket (with postorbital bar). Secondary palate longer, but still not complete. Teeth double-rooted, as in mammals. Nares separated. Second jaw joint stronger. Lumbar ribs totally lost; thoracic ribs more mammalian, vertebral connections very mammalian. Hip & femur more mammalian.
Probainognathus (mid-Triassic, 239-235 Ma, Argentina) -- Larger brain with various skull changes: pineal foramen ("third eye") closes, fusion of some skull plates. Cheekbone slender, low down on the side of the eye socket. Postorbital bar still there. Additional cusps on cheek teeth. Still two jaw joints. Still had cervical ribs & lumbar ribs, but they were very short. Reptilian "costal plates" on thoracic ribs mostly lost. Mammalian #toe bones.
Exaeretodon (mid-late Triassic, 239Ma, South America) -- (Formerly lumped with the herbivorous gomphodont cynodonts.) Mammalian jaw prong forms, related to eardrum support. Three incisors only (mammalian). Costal plates completely lost. More mammalian hip related to having limbs under the body. Possibly the first steps toward coupling of locomotion & breathing. This is probably a "cousin" fossil not directly ancestral, as it has several new but non-mammalian teeth traits.
GAP of about 30 my in the late Triassic, from about 239-208 Ma. Only one early mammal fossil is known from this time. The next time fossils are found in any abundance, tritylodontids and trithelodontids had already appeared, leading to some very heated controversy about their relative placement in the chain to mammals. Recent discoveries seem to show trithelodontids to be more mammal- like, with tritylodontids possibly being an offshoot group (see Hopson 1991, Rowe 1988, Wible 1991, and Shubin et al. 1991). Bear in mind that both these groups were almost fully mammalian in every feature, lacking only the final changes in the jaw joint and middle ear.
Oligokyphus, Kayentatherium (early Jurassic, 208 Ma) -- These are tritylodontids, an advanced cynodont group. Face more mammalian, with changes around eyesocket and cheekbone. Full bony secondary palate. Alternate tooth replacement with double-rooted cheek teeth, but without mammalian-style tooth occlusion (which some earlier cynodonts already had). Skeleton strikingly like egg- laying mammals (monotremes). Double jaw joint. More flexible neck, with mammalian atlas & axis and double occipital condyle. Tail vertebrae simpler, like mammals. Scapula is now substantially mammalian, and the forelimb is carried directly under the body. Various changes in the pelvis bones and hind limb muscles; this animal's limb musculature and locomotion were virtually fully mammalian. Probably cousin fossils (?), with Oligokyphus being more primitive than Kayentatherium. Thought to have diverged from the trithelodontids during that gap in the late Triassic. There is disagreement about whether the tritylodontids were ancestral to mammals (presumably during the late Triassic gap) or whether they are a specialized offshoot group not directly ancestral to mammals.
Pachygenelus, Diarthrognathus (earliest Jurassic, 209 Ma) -- These are trithelodontids, a slightly different advanced cynodont group. New discoveries (Shubin et al., 1991) show that these animals are very close to the ancestry of mammals. Inflation of nasal cavity, establishment of Eustachian tubes between ear and pharynx, loss of postorbital bar. 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, and mammalian tooth occlusion. Double jaw joint, with the second joint now a dentary-squamosal (instead of surangular), fully mammalian. Incipient dentary condyle. Reptilian jaw joint still present but functioning almost entirely in hearing; postdentary bones further reduced to tiny rod of bones in jaw near middle ear; probably could hear high frequencies now. More mammalian neck vertebrae for a flexible neck. Hip more mammalian, with a very mammalian iliac blade & femur. Highly mobile, mammalian-style shoulder. Probably had coupled locomotion & breathing. These are probably "cousin" fossils, not directly ancestral (the true ancestor is thought to have occurred during that late Triassic gap). Pachygenelus is pretty close, though.
Adelobasileus cromptoni (late Triassic; 225 Ma, west Texas) -- A recently discovered fossil proto-mammal from right in the middle of that late Triassic gap! Currently the oldest known "mammal." Only the skull was found. "Some cranial features of Adelobasileus, such as the incipient promontorium housing the cochlea, represent an intermediate stage of the character transformation from non-mammalian cynodonts to Liassic mammals" (Lucas & Luo, 1993). This fossil was found from a band of strata in the western U.S. that had not previously been studied for early mammals. Also note that this fossil dates from slightly before the known tritylodonts and trithelodonts, though it has long been suspected that tritilodonts and trithelodonts were already around by then. Adelobasileus is thought to have split off from either a trityl. or a trithel., and is either identical to or closely related to the common ancestor of all mammals.
Sinoconodon (early Jurassic, 208 Ma) -- The next known very ancient proto-mammal. Eyesocket fully mammalian now (closed medial wall). Hindbrain expanded. Permanent cheekteeth, like mammals, but the other teeth were still replaced several times. Mammalian jaw joint stronger, with large dentary condyle fitting into a distinct fossa on the squamosal. This final refinement of the joint automatically makes this animal a true "mammal". Reptilian jaw joint still present, though tiny.
Kuehneotherium (early Jurassic, about 205 Ma) -- 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 (early Jurassic, ~205 Ma) -- A group of early proto-mammals called "morganucodonts". The restructuring of the secondary palate and the floor of the braincase had continued, and was now very mammalian. Truly mammalian teeth: the cheek teeth were finally differentiated into simple premolars and more complex molars, and teeth were replaced only once. Triangular- cusped molars. Reversal of the previous trend toward reduced incisors, with lower incisors increasing to four. Tiny remnant of the reptilian jaw joint. Once thought to be ancestral to monotremes only, but now thought to be ancestral to all three groups of modern mammals -- monotremes, marsupials, and placentals.
Peramus (late Jurassic, about 155 Ma) -- A "eupantothere" (more advanced placental-type mammal). The closest known relative of the placentals & marsupials. Triconodont molar has with more defined cusps. This fossil is known only from teeth, but judging from closely related eupantotheres (e.g. Amphitherium) it had finally lost the reptilian jaw joint, attaing a fully mammalian three-boned middle ear with excellent high-frequency hearing. Has only 8 cheek teeth, less than other eupantotheres and close to the 7 of the first placental mammals. Also has a large talonid on its "tribosphenic" molars, almost as large as that of the first placentals -- the first development of grinding capability.
Endotherium (very latest Jurassic, 147 Ma) -- An advanced eupantothere. Fully tribosphenic molars with a well- developed talonid. Known only from one specimen. From Asia; recent fossil finds in Asia suggest that the tribosphenic molar evolved there.
Kielantherium and Aegialodon (early Cretaceous) -- More advanced eupantotheres known only from teeth. Kielantherium is from Asia and is known from slightly older strata than the European Aegialodon. Both have the talonid on the lower molars. The wear on it indicates that a major new cusp, the protocone, had evolved on the upper molars. By the Middle Cretaceous, animals with the new tribosphenic molar had spread into North America too (North America was still connected to Europe.)
Steropodon galmani (early Cretaceous) -- The first known definite monotreme, discovered in 1985.
Vincelestes neuquenianus (early Cretaceous, 135 Ma) -- A probably-placental mammal with some marsupial traits, known from some nice skulls. Placental-type braincase and coiled cochlea. Its intracranial arteries & veins ran in a composite monotreme/placental pattern derived from homologous extracranial vessels in the cynodonts. (Rougier et al., 1992)
Pariadens kirklandi (late Cretaceous, about 95 Ma) -- The first definite marsupial. Known only from teeth.
Kennalestes and Asioryctes (late Cretaceous, Mongolia) -- Small, slender animals; eyesocket open behind; simple ring to support eardrum; primitive placental-type brain with large olfactory bulbs; basic primitive tribosphenic tooth pattern. Canine now double rooted. Still just a trace of a non-dentary bone, the coronoid, on the otherwise all-dentary jaw. "Could have given rise to nearly all subsequent placentals." says Carroll (1988).
Cimolestes, Procerberus, Gypsonictops (very late Cretaceous) -- Primitive North American placentals with same basic tooth pattern.
------------------ Occam's razor is not for shaving with.
Okay, Delshad, so we agree on some terms. I am a Muslim too and I understand that Allah planted signs for the faithful to see and contemplate. Now look back to the reptile-mammal sequence and this time, look at the ages of the fossils. See a pattern there? The morphological change fits perfectly with the temporal sequence. Now think. Would Allah create them separately in such a manner, that He created in such a sequence that strongly hints a change? The signs, the ayats in nature, screams for an explanation! There is change and continuity between them. I believe that Allah is not a deceiver, and He tries to sent a scientific message to us.
[btw i have suspected that you're a Muslim. Your arguments sound familiar...]
quote:Originally posted by Andya Primanda: Okay, Delshad, so we agree on some terms. I am a Muslim too and I understand that Allah planted signs for the faithful to see and contemplate. Now look back to the reptile-mammal sequence and this time, look at the ages of the fossils. See a pattern there? The morphological change fits perfectly with the temporal sequence. Now think. Would Allah create them separately in such a manner, that He created in such a sequence that strongly hints a change? The signs, the ayats in nature, screams for an explanation! There is change and continuity between them. I believe that Allah is not a deceiver, and He tries to sent a scientific message to us.
[btw i have suspected that you're a Muslim. Your arguments sound familiar...]
Why would you god do this? To test your "faith"? Doesn't he/she/it already know if your faithful or not?
I may have misunderstood, but I thought someone once told me that there are 99 beautiful names for God in the Koran. It is my understanding that one of those names was "The Evolver." I always thought that was interesting. Something to think about anyway.