Here is a pretty good article I found online at http://scienceblogs.com/pharyngula/2006/04/tiktaalik_makes_another_gap.php
Tiktaalik makes another gap
Category: Evolution • Fossils • Organisms • Science
Posted on: April 5, 2006 1:28 PM, by PZ Myers
Paleontologists have uncovered yet another specimen in the lineage leading to modern tetrapods, creating more gaps that will need to be filled. It's a Sisyphean job, working as an evolutionist.
This creature is called Tiktaalik roseae, and it was discovered in a project that was specifically launched to find a predicted intermediate form between a distinctly fish-like organism, Panderichthys, and the distinctly tetrapod-like organisms, Acanthostega and Ichthyostega. From the review article by Ahlberg and Clack, we get this summary of Tiktaalik's importance:
First, it demonstrates the predictive capacity of palaeontology. The Nunavut field project had the express aim of finding an intermediate between Panderichthys and tetrapods, by searching in sediments from the most probable environment (rivers) and time (early Late Devonian). Second, Tiktaalik adds enormously to our understanding of the fish-tetrapod transition because of its position on the tree and the combination of characters it displays.
Here's the beautiful beastie as preserved:
a, Left lateral view; b, dorsal view with enlargement of scales; and c, ventral view with enlargement of anterior ribs. See Fig. 3 for labelled drawing of skull in dorsal view. Abbreviations: an, anocleithrum; bb, basibranchial; co, coracoid; clav, clavicle; clth, cleithrum; cbr, ceratobranchial; ent, entopterygoid; hu, humerus; lep, lepidotrichia; mand, mandible; nar, naris; or, orbit; psp, parasphenoid; ra, radius; suc, supracleithrum; ul, ulna; uln, ulnare. Scale bar equals 5 cm.The analysis of the fossil clearly positions it as an intermediate: it has a more mobile skull/neck than a fish, and although its limbs are clearly fin-like, they also have features that presage the digits of tetrapods.
The lineage leading to modern tetrapods includes several fossil animals that form a morphological bridge between fishes and tetrapods. Five of the most completely known are the osteolepiform Eusthenopteron; the transitional forms Panderichthys and Tiktaalik; and the primitive tetrapods Acanthostega and Ichthyostega. The vertebral column of Panderichthys is poorly known and not shown. The skull roofs (left) show the loss of the gill cover (blue), reduction in size of the postparietal bones (green) and gradual reshaping of the skull. The transitional zone (red) bounded by Panderichthys and Tiktaalik can now be characterized in detail. These drawings are not to scale, but all animals are between 75 cm and 1.5 m in length. They are all Middle–Late Devonian in age, ranging from 385 million years (Panderichthys) to 365 million years (Acanthostega, Ichthyostega). The Devonian–Carboniferous boundary is dated to 359 million years ago.
The limbs alone have a whole paper dedicated to them. Tiktaalik's limb is third from the right in the diagram below, and you can see how it still has the fin rays of its predecessor, Panderichthys, but also has a robust bony axis with smaller bones branching off of it—it's not quite the clear digits of Acanthostega, but it's a step in that direction.
Unlike other tetrapodomorph fishes (1), Tiktaalik has reduced the unjointed lepidotrichia, expanded the radials to a proximal, intermediate and distal series, and established multiple transverse joints in the distal fin. The fin also retains a mosaic of features seen in basal taxa. The central axis of enlarged endochondral bones is a pattern found in basal sarcopterygians and accords with hypotheses that a primitive fin axis is homologous to autopodial bones of the tetrapod limb. In some features, Tiktaalik is similar to rhizodontids such as Sauripterus. These similarities, which are probably homoplastic, include the shape and number of radial articulations on the ulnare, the presence of extensive and branched endochondral radials, and the retention of unjointed lepidotrichia. Figures redrawn and modified from Glyptolepis, Eusthenopteron, Panderichthys, Acanthostega and Tulerpeton.
Those limbs tell us something about the evolution of limbs. Tiktaalik was definitely not a terrestrial animal, but had developed muscular, bony limbs and a strong pectoral girdle that had helped it prop itself up on the substrate, perhaps even holding itself partly out of the water. Those jointed digits were capable of extension and flexion, splaying out when they were pressed against the ground. That simple function, of spreading out to increase the surface area of limb contact, could be the precursor to the flexibility we now have in our hands.
a, b, Anterolateral view. c, d, Ventral view. a, c, Resting posture with the fin partially flexed at the antebrachium. In this position the radius is slightly more flexed than the ulna. b, d, Resistant contact with a firm substrate entails flexion at proximal joints and extension at distal ones. The shoulder joint is flexed by ventral muscles, including the trans-coracoid muscle. The elbow is flexed (d, arrow 1), with slight pronation of the radius (d, arrow 2) and rotation of the ulna (d, arrow 3). The transverse joints distal to the ulnare and intermedium are extended (d, arrows 4).
Same Ol' Same Ol' Most evolutionists look to crossopterygian fish for the ancestors of tetrapods—even though unlike many living fish, none of these fish are known to be capable of either walking or breathing out of water.
ReplyDeleteThese fish have fleshy pectoral fins containing bony elements (considered similar to tetrapod legs). These similarities have prompted evolutionists to confidently declare that crossopterygians evolved into tetrapods.
According to evolutionists, the crossopterygians flourished about 380 million years ago and all were once believed to have become extinct about 80 million years ago. However, in 1938 a fishing trawler netted a fish in the Indian Ocean off the coast of Madagascar that was identified as a crossopterygian fish, previously known only from the fossil record as the coelacanth. Since then, dozens of living coelacanths have been discovered.
This came as a huge shock to evolutionists who assumed that the reason the coelacanth disappeared from the fossil record was because they evolved into land-dwelling tetrapods; yet, here they were very much alive—and swimming!
At the very least, evolutionists expected to observe some hint of walking behavior in the coelacanth, but nothing of the kind has ever been observed. Coelacanths have been observed swimming backward, upside–down, and even standing on their head but they have never been observed to walk on land or in the sea.
Read more actual Science Journal Articles not Internet news articles from the kooks.
Same ol' same ol', more creationist lies and propaganda, just to make them feel better about their silly beliefs.
ReplyDeleteThis lie is exposed at talkorigins.org.
Index to Creationist Claims, Claim # CB930.1:
1. The modern coelacanth is Latimeria chalumnae, in the family Latimeriidae. Fossil coelacanths are in other families, mostly Coelacanthidae, and are significantly different in that they are smaller and lack certain internal structures. Latimeria has no fossil record, so it cannot be a "living fossil."
2. Even if the modern coelacanth and fossil coelacanths were the same, it would not be a serious problem for evolution. The theory of evolution does not say that all organisms must evolve. In an unchanging environment, natural selection would tend to keep things largely unchanged morphologically.
3. Coelacanths have primitive features relative to most other fish, so at one time they were one of the closest known specimens to the fish-tetrapod transition. We now know several other fossils that show the fish-tetrapod transition quite well.
Perhaps you need to read actual scientific journals and not creationists' distortion of facts. Also, if you read actual scientific journals, you would see the mixture of fish and tetrapod traits which Tiktaalik has, such as fins, gills, lungs, eyes on the top of the head and a flat body and head like a crocodile, etc (Source: http://tiktaalik.uchicago.edu/meetTik.html).