Posts Tagged ‘Million Years’

What are the Dinosaurs?

Saturday, December 12th, 2009

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The inturned head of the femur (the beginnings of the full right-angled femur head seen in dinosaurs and in a different from in mammals); the straight knee joint; the reduced hinge-like ankle joint (technically termed the advanced mesotarsal, or AM, ankle); the long toes and the digitigrade posture of the foot, in which only the toes touch the ground, not the sole of the foot as in earlier archosaurs – and in humans today.

Most of the dinosaur-like characters are also seen in the flying pterosaurs. Certain paleontologists argue that Lagosuchus, the pterosaurs, and the dinosaurs together form a major clade that arose in the Middle to Late Triassic, some 230 million years ago.

The dinosaur-like synapomorphies of this clade, and their further modification in the dinosaurs proper, are part of a major series of related anatomical changes that took place among the archosaurs during the Triassic, and which may have been the key to the origin of the dinosaurs.

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Dinosaur Family Tree

Saturday, December 5th, 2009

The evolutionary tree of dinosaurs contains a great deal of information. The horizontal axis represents time, and the vertical axis represents dinosaurian diversity. All the major families of dinosaurs are indicated with horizontal lines that record their known distribution in time, as based upon present fossil evidence. Future finds of dinosaur skeletons may extend the time ranges backwards or forwards in time.

There are two “fixed” time lines that do not seem to be breached, however. The dinosaurs arose from a single ancestor some 230 million years ago, in the Middle to Late Triassic, and it is unlikely that older dinosaur skeletons will be found. The second “fixed” time line corresponds to the extinction of the last dinosaurs 66 million years ago. Despite strenuous efforts to find post-Mesozoic dinosaur specimens, and many reports of supposed discoveries, no such remains have withstood close scrutiny. Most usually, post-mesozoic dinosaur bones have been reworked, that is, removed from the rock by natural erosion and redeposited in a younger sediment.

The most important aspect of this phylogenetic tree is the representation of the relationships between the different families. This is based on recent cladistic anlyses, carried out by a number of North American and European vertebrae paleontologists after 1985, and the pattern shown here is quite revolutionary in the sense that it is dramatically different from anything in popular books of this sort. It is also important because it shows a much higher degree of resolution than the earlier phylogenies; that is, the pattern of relationships is shown in a much more detailed way than was possible before.

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Origin of the Turtle’s Shell

Tuesday, October 13th, 2009

The origin of the turtle’s shell has not been convincingly explained to any length or depth.   A small reptile now named Eunotosaurus that lived approximately 250 million years ago in the “Permian” age has often been stated and referred to as  a probable turtle or turtle based ancestor.  It had ribs which were broadened in such a way that suggests it played the role of a rudimentary “shell”. But whatever  the beginnings of turtles may have been – then the shell itself is now the mark  of the turtle clan.

In spite of the millions of years of evolution that have seen turtles established nearly everywhere on the earth except for the air , with “flying turtles”.  the shell itself has been retained and is the most recognizable form and indeed trademark of this group and grouping of type of animals.

Oldest Turtle Found; May Crack Shell-Evolution Mystery – Care2 … – Fossils of the oldest known turtles, unearthed in southwestern China, may help answer an evolutionary enigma—how did the turtle get its shell?

How the Turtle got It’s Shell… « Nirvana Peace – Xiao-chun Wu, a palaeontologist at the Canadian Museum of Nature in Ottawa and a member of the research team, said: “Since the 1800s, there have been many hypotheses about the origin of the turtle shell. Now we have these fossils of the …

NeuroLogica Blog » Turtle on the Half-Shell – The turtle shell is a dramatic evolutionary adaption, and yet it appeared fully formed in the fossil record, so paleontologists could only speculate about its origins. A report is about to be published in the journal Nature by authors …

Evolution of Turtle Shell: The Mystery Gets Cracked Open by Scientists – Uncovered in south west China last year, Odontochelys semistestacea seems to be the oldest known turtle fossil – believed to date 220 million years back. More.

A Clue to the Evolutionary Riddle of How the Turtle Got Its Shell … – Says researcher Xiao-chun Wu: “Since the 1800s, there have been many hypotheses about the origin of the turtle shell. Now we have these fossils of the earliest known turtle. They support the theory that the shell would have formed from …

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