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WASHINGTON (Reuters) Oct 15, 2008:
An extraordinary fish that existed 375 million years ago had unique features in its head that helped pave the way for vertebrate animals to live on land, scientists said on Wednesday.
Scientists for the first time described features in the underside of the skull of Tiktaalik roseae, the so-called "walking fish". It is considered an important transitional animal in the evolution of fish into amphibians, the first land-dwelling vertebrates.
The findings showed that the migration from water to land was more complicated than merely having a fish's fins transform into legs, the scientists wrote in the journal Nature. Source
The head showed changes from more primitive fish that helped adapt to the new feeding and breathing conditions presented by a terrestrial environment. Like some other fish of its time, it had gills and lungs.
The scientists described key features in its head and braincase and the decline in size of a bone called the hyomandibula. In fish, this bone links the braincase, roof of the mouth and gill structures and coordinates their motions during underwater feeding and respiration.
As land animals evolved, the hyomandibula eventually became the stapes, one of the tiny bones in the middle ear.
Tiktaalik has features of some of the more primitive fish it lived with as well as features of the first four-legged amphibians that lived on land. Its fins had discernible wrists and elbows in an evolutionary step toward legs that could be used to walk around on dry land.
Panderichthys is yet another fossil Crossopterygian fish that has been declared to be an ancestor of tetrapods. Panderichthys lacks dorsal and ventral fins and has a relatively small tail fin (thus looking less obviously fish-like than Eusthenopteron).
Like the other Crossopterygian fish, Panderichthys has thick bony pectoral fins. Evolutionists argue that the shape of these fins and their pectoral girdle look more like that of tetrapods than Eusthenopteron. But Daeschler, Shubin, and Jenkins—the discoverers of Tiktaalik—claim that “Panderichthys possesses relatively few tetrapod synapomorphies, and provides only partial insight into the origin of major features of the skull, limbs and axial skeleton of early tetrapods.” As a result, they insist that “our understanding of major transformations at the fish-tetrapod transition has remained limited.”4
Tiktaalik to the rescue?
In the April 2006, issue of Nature, Daeschler, et al. reported the discovery of several fossilized specimens of a Crossopterygian fish named Tiktaalik roseae. These well preserved specimens were found in sedimentary layers of siltstone—cross-bedded with sandstones—in Arctic Canada.4
Like the other lobe-fin fish, Tiktaalik was declared to be late Devonian (between 385-359 million years old) by means of a “dating” method known as palynomorph biostratigraphy. This method presumes to date sedimentary rock layers on the basis of the assumed evolutionary age of pollen and spores contained in the rock. Most importantly, the discoverers of Tiktaalik claim that it “represents an intermediate between fish with fins and tetrapods with limbs.”
Tiktaalik is a fish
Whatever else we might say about Tiktaalik, it is a fish. In a review article on Tiktaalik (appearing in the same issue of the scientific journal Nature that reported the discovery of Tiktaalik), fish evolution experts, Ahlberg and Clack concede that “in some respects Tiktaalik and Panderichthys are straightforward fishes: they have small pelvic fins, retain fin rays in their paired appendages and have well-developed gill arches, suggesting that both animals remained mostly aquatic.”
In fact, when more characteristics than just one are analysed, homoplasies become even more necessary to explain away anomalies, as will be explained in the section Mosaic rather than transitional.
Another major problem is that evolutionists appeal to the common pentadactyl 5-digit pattern as evidence for their common ancestry from a 5-digited creature. Yet the nearest creatures they have to a common ancestor did not have five digits! Acanthostega had eight, while Ichthyostega had seven.
by means of a “dating” method known as palynomorph biostratigraphy. This method presumes to date sedimentary rock layers
But on closer examination, scientists found telling anatomical traits of a transitional creature, a fish that is still a fish but exhibiting changes that anticipate the emergence of land animals — a predecessor thus of amphibians, reptiles and dinosaurs, mammals and eventually humans.
This is truth but it's not the whole truth.
Fossils are used to determine the order and dates of the strata in which they are found. But the fossil order itself is based on the order of strata and the assumption of evolution. Therefore, using fossil progression as evidence for evolution is circular reasoning.
Many strata are not dated from fossils. Relative dates of strata (whether layers are older or younger than others) are determined mainly by which strata are above others. Some strata are dated absolutely via radiometric dating. These methods are sufficient to determine a great deal of stratigraphy.
1. Many strata are not dated from fossils. Relative dates of strata (whether layers are older or younger than others) are determined mainly by which strata are above others. Some strata are dated absolutely via radiometric dating. These methods are sufficient to determine a great deal of stratigraphy.
What Talk.Origins neglects to say is that all of these dating methods are subordinate to dating by fossils. That is, whenever stratigraphic superposition, radiometric dating or any other dating method disagrees with the fossils, the date based on fossils always wins.
If stratigraphic superposition says a T-rex fossil is older than a trilobite fossil it is called an overthrust.
If radiometric dating places a fossil as too young or too old the radiometric date is dismissed as resulting from contamination.
Reference: New Age Data of Buried Peat Deposits From the Site "Fili Park".
This is by no means an isolated event. It happens all the time in geochronology.
“ Biologic evolutionary history, especially for Phanerozoic time, has given us not only the principal means of time-correlation but the basis of the unique progressive traditional stratigraphic scale. ”
Harland, W.B.; R.L. Armstrong; A.V. Cox; L.E. Craig; A.G. Smith; and D.G. Smith, 1990, "A Geologic Time Scale 1989," Cambridge University Press, Cambridge
"Strata layers are dated by fossils and fossils are dated by strata layers and is therefore circular reasoning" is misleading as it leaved out salient facts that make it not circular reasoning
Scientists can use different chemicals for absolute dating:
* The best-known absolute dating technique is carbon-14 dating, which archaeologists prefer to use. However, the half-life of carbon-14 is only 5730 years, so the method cannot be used for materials older than about 70,000 years.
* Radiometric dating involves the use of isotope series, such as rubidium/strontium, thorium/lead, potassium/argon, argon/argon, or uranium/lead, all of which have very long half-lives, ranging from 0.7 to 48.6 billion years. Subtle differences in the relative proportions of the two isotopes can give good dates for rocks of any age.
The first radiometric dates, generated about 1920, showed that the Earth was hundreds of millions, or billions, of years old. Since then, geologists have made many tens of thousands of radiometric age determinations, and they have refined the earlier estimates. A key point is that it is no longer necessary simply to accept one chemical determination of a rock’s age. Age estimates can be cross-tested by using different isotope pairs. Results from different techniques, often measured in rival labs, continually confirm each other.
Every few years, new geologic time scales are published, providing the latest dates for major time lines. Older dates may change by a few million years up and down, but younger dates are stable. For example, it has been known since the 1960s that the famous Cretaceous-Tertiary boundary, the line marking the end of the dinosaurs, was 65 million years old. Repeated recalibrations and retests, using ever more sophisticated techniques and equipment, cannot shift that date. It is accurate to within a few thousand years. With modern, extremely precise, methods, error bars are often only 1% or so.Source
The argon-argon dating method has been widely used to determine the age of rocks...now have lowered this uncertainty to 0.25 percent and brought it into agreement with other isotopic methods of dating rocks. As a result, argon-argon dating today can provide more precise absolute dates for many geologic events...Cretaceous period and the beginning of the Tertiary period. That boundary had previously been dated at 65.5 million years ago, give or take 300,000 years. According to a paper, the best date for the Cretaceous-Tertiary, or K/T, boundary is now 65.95 million years, give or take 40,000 years...
Argon-argon dating, developed at UC Berkeley in the 1960s, is based on the fact that the naturally-occurring isotope potassium-40 decays to argon-40 with a 1.25-billion-year half-life. Single-grain rock samples are irradiated with neutrons to convert potassium-40 to argon-39, which is normally not present in nature. The ratio of argon-39 to argon-39 then provides a measurement of the age of the sample.
"This should be the last big revision of argon-argon dating," Renne said. "We've finally narrowed it down to where we are talking about fractions-of-a-percent revisions in the future, at most." Source