Transition from primitive bony fish to amphibians (Talk.Origins)
CreationWiki response: (Talk.Origins quotes in blue)
- Paleoniscoids again (e.g. Cheirolepis) -- These ancient bony fish probably gave rise both to modern ray-finned fish (mentioned above), and also to the lobe-finned fish.
This is a broad category that includes some previously mentioned types.
- Osteolepis (mid-Devonian) -- One of the earliest crossopterygian lobe-finned fishes, still sharing some characters with the lungfish (the other lobe-finned fishes). Had paired fins with a leg-like arrangement of major limb bones, capable of flexing at the "elbow", and had an early-amphibian-like skull and teeth.
This is another broad type that includes the coelacanth which still exists today, but it is somewhat different from its fossil counterparts.
The fact that an animal like the coelacanth can be alive but be absent from the fossil record for what is alleged to be 65 million, shows that fossilization is determined by some factor other than whether or not an animal was living when the rocks they are in were formed.
We have here a common evolutionary trick. They call a set of bones by the same name and that is supposed to prove evolution. Here they have only a very superficial resemblance to each other. The shape and position are dissimilar.
- Reference: Axelrod Institute of Ichthyology at the University of Guelph Homepage
- Reference: Evolution vom Fisch zum Amphibium
- Reference: Osteolepis sp.
- Reference: Forey, P.L. 1998. History of the Coelacanth Fishes. Springer Verlag.
- Eusthenopteron, Sterropterygion (mid-late Devonian) -- Early rhipidistian lobe-finned fish roughly intermediate between early crossopterygian fish and the earliest amphibians. Eusthenopteron is best known, from an unusually complete fossil first found in 1881. Skull very amphibian-like. Strong amphibian-like backbone. Fins very like early amphibian feet in the overall layout of the major bones, muscle attachments, and bone processes, with tetrapod-like tetrahedral humerus, and tetrapod-like elbow and knee joints. But there are no perceptible "toes", just a set of identical fin rays. Body & skull proportions rather fishlike.
- Eusthenopteron fins actually seem less foot-like than those of Osteolepis, see above.
- The pectoral fin skeletons of all osteolepiform fish (including Osteolepis and Eusthenopteron) are nearly identical and follow general patterning that is more like tetrapods than like any ray-finned fish (Andrews and Westoll, 1970a,b) but such similarities are not by themselves sufficient to prove ancestry without substantial intermediate forms. It simply shows that some traits were once spread between classes of animals that are narrower today because of extinction.
- Reference: Eusthenopteron sp
- Reference: Eusthenopteron foordi
- Reference: Andrews, S.M, and Westoll, T.S. 1970a. The postcranial skeleton of Eusthenopteron foori Whiteaves. Transactions of the Royal Society of Edinburgh: Earth Sciences 68, 207−329.
- Reference: Andrews, S.M, and Westoll, T.S. 1970b. The postcranial skeleton of rhipidistian fish excluding Eusthenopteron. Transactions of the Royal Society of Edinburgh: Earth Sciences 68, 391−489.
- No information available on this type.
- Panderichthys, Elpistostege (mid-late Devonian, about 370 Ma) -- These "panderichthyids" are very tetrapod-like lobe-finned fish. Unlike Eusthenopteron, these fish actually look like tetrapods in overall proportions (flattened bodies, dorsally placed orbits, frontal bones! in the skull, straight tails, etc.) and have remarkably foot-like fins.
- Panderichthys is based on several complete and partial skeletons described by Vorobyeva (see Vorobyeva and Schultze, 1991; Ahlberg et al. 1996, Brazeau and Ahlberg, in press).
- Reference: Reference: Vorobyeva, E.I. and Schultze, H.-P. 1991. Description of panderichthyid fishes with comments on their relationship to tetrapods. In: Schultze, H.-P. and Trueb, L. (eds.) Origins of the Higher Groups of Tetrapods: Controversy and Consensus, Cornell University Press (Canstock), Ithica, NY.
- Reference: Ahlberg, P.E., Clack, J.A., Luksevics, E. 1996. Rapid braincase evolution between Panderichthys and the earliest tetrapods. Nature 381, 61-64.
- Reference: Brazeau, M.D. and Ahlberg, P.E. In press. Tetrapod-like middle ear architecture in a Devonian fish. Nature.
- Elpistostege seems to be based on less complete fossil evidence than Panderichthys. There are two partial skulls; the rest of the available skeleton is an incomplete spine that does not extend to the tail (Schultze and Arsenault, 1985).
- Reference: Elpistostege watsoni
- Reference: Schultze, H.-P. and Arsenault, M. 1985. The panderichthyid fish Elpistostege: a close relative of tetrapods? Palaeontology 28, 293-309.
These fragmented limbs and teeth are considered to be slightly younger than Panderichthys, Elpistostege, Eusthenopteron and Sterropterygion. Furthermore, all that has been found of Obruchevichthys is part of its jaw, so there is no real basis for connecting them to Obruchevichthys other than extensive character congruence with tetrapods (Ahlberg and Clack, 1998). It is even possible that these fragmented limbs and teeth are from different animals. More information would be preferable.
- Reference: Obruchevichthys gracilis
- Reference: Ahlberg, P.E., and Clack, J.A. 1998. Lower jaws, lower tetrapods — a review based on the Devonian genus Acanthostega. Transactions of the Royal Society of Edinburgh: Earth Sciences. 89, 11-46.
GAP: Ideally, of course, we want an entire skeleton from the middle Late Devonian, not just limb fragments. Nobody's found one yet.
Fragmented limbs and teeth, a typical case of a lack of evidence at a crucial point in the sequence. That is the transition between fins and legs.
Now this gap as well as Panderichthys, Elpistostege, Eusthenopteron and Sterropterygion are all classified as Mid-Late Devonian, raising some questions about the objectiveness of the order — but there is no way to tell this based on available information. For example, unless they are found in different strata in the same area, the order could be based mostly on the presumption of evolution than objective facts. More information on where the fossils were found, and how they were dated, is needed to check the legitimacy of the order given in this list.
The fact that these forms only occur in the Mid-Late Devonian at first glance seems to defy a creationist interpretation. But this not the case. One clue is that those we have information on (Panderichthys, Elpistostege, Eusthenopteron) all seem to be freshwater fish. If they lived in relatively shallow water, they would have been buried in strata over deep ones and under land animals. All factors that could have led to the Mid-Late Devonian classification. More information on where they were found, and in relation to what fossils, is needed for a full explanation — but this seems a good possibility based on the available information.
- The remains of Hynerpeton are fragmented. They include the left shoulder bones, a lower jaw, small skull fragments and belly scutes. This means there is insufficient evidence to make a real case for a transition because plenty of parts cannot be compared.
- Reference: Hynerpeton bassetti
- Acanthostega is at least based on a complete skeleton and clearly a distinct kind from others in the list. It seems to have been a totally aquatic amphibian. Both reptiles and mammals have totally aquatic kinds, so it is no surprise to find totally aquatic amphibians as well.
- Acanthostega did have some fish-like traits in the form of a fish-like vertebral skeleton, fin rays surrounding the tail fin, lack of a neck joint, grooved gill bars, simple joints between limb elements, and a large bony cleithrum. However, as both are aquatic some similarities are to be expected and do not necessarily show a relationship. Given the incompleteness of fossil remains of some of the previous types, there is no direct link to fish. Without this connection it would seem that they are a distinct kind from others in the list.
The material belonging to Acanthostega gunnari is largely complete
- Reference: Acanthostega gunneri
- Clack, J.A. Acanthostega gunnari. Tree of Life
- Coates, M.I. 1996. The Devonian tetrapod Acanthostega gunnari Jarvik: postcranial anatomy, basal tetrapod interrelationships and patterns of skeletal evolution. Transactions of the Royal Society of Edinburgh; Earth Sciences, 87, 363-421.
- Ichthyostega was a largely aquatic amphibian capable of walking on land. This is known to occur in mammals such as seals. Furthermore, there are too many differences from Acanthostega to support evolution, in the absence of any intermediate forms. The similarities and differences between these taxa are discussed in detail by Clack (2002).
- Reference: Ichthyostega stensioei
- Reference: Ichthyostega: fossils
- Reference: Clack, J.A. 2002. Gaining Ground: The Origin and Evolution of Tetrapods Indiana University Press, Bloomington.
- Reference: Clack, J.A. Icthyostega Tree of Life
What we have here is a sudden appearance of legs. No indisputable transitional fossils between fins and legs — just a gap where the transition should be. Of course, this statement would be overturned by the discovery of fossils that do in fact show intermediates between fin radials and digits.
There are too many differences between Pholidogaster, Pteroplax, Ichthyostega and Acanthostega to show any connection. These differences included posture and other aspects of body structure. While differences between these forms is to be expected since evolution predicts that forms change, the differences are too great to make a case for a relationship without intermediate forms.
- Reference: Pteroplax sp
Many of the fossils on this list are too fragmented to make an objective case for a transition. While this is one of the better cases made by Evolutionists, there is no solid evidence of a transition here, several of the links are fragmented and as is often the case they are located at a critical point.
The fact that none of these forms can be shown to be ancestors is evident from the fact that for well over half a century the ideas about orthogenesis (i.e. straight-line evolution) have been discounted (even by evolutionary biologist). There is not even a tacit implication that these animals represent ancestors. Instead, they are alleged to represent the growth of a bush with a tendency towards a more terrestrial way of life.