Dinosaurs

Best Links

bp_blog — Tue, 16 Sep 2008 13:15:52 +0000

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Impact event

bp_blog — Fri, 12 Sep 2008 22:29:39 +0000

The Chicxulub Crater at the tip of the Yucatán Peninsula; the impactor that formed this crater may have caused the dinosaur extinction.
The asteroid collision theory, which was brought to wide attention in 1980 by Walter Alvarez and colleagues, links the extinction event at the end of the Cretaceous period to a bolide impact approximately 65.5 million years ago. Alvarez et al. proposed that a sudden increase in iridium levels, recorded around the world in the period’s rock stratum, was direct evidence of the impact. The bulk of the evidence now suggests that a 5 to 15 kilometer (3 to 9 mi) wide bolide hit in the vicinity of the Yucatán Peninsula, creating the 170 kilometers (110 mi) wide Chicxulub Crater and triggering the mass extinction. Scientists are not certain whether dinosaurs were thriving or declining before the impact event. Some scientists propose that the meteorite caused a long and unnatural drop in Earth’s atmospheric temperature, while others claim that it would have instead created an unusual heat wave.
Although the speed of extinction cannot be deduced from the fossil record alone, various models suggest that the extinction was extremely rapid. The consensus among scientists who support this theory is that the impact caused extinctions both directly (by heat from the meteorite impact) and also indirectly (via a worldwide cooling brought about when matter ejected from the impact crater reflected thermal radiation from the sun).
In September of 2007, U.S. researchers led by William Bottke of the Southwest Research Institute in Boulder, Colorado, and Czech scientists used computer simulations to identify the probable source of the Chicxulub impact. They calculated a 90% probability that a giant asteroid named Baptistina, approximately 160 kilometers (100 mi) in diameter, orbiting in the asteroid belt which lies between Mars and Jupiter, was struck by a smaller unnamed asteroid about 55 kilometers (35 mi) in diameter about 160 million years ago. The impact shattered Baptistina, creating a cluster which still exists today as the Baptistina family. Calculations indicate that some of the fragments were sent hurtling into earth-crossing orbits, one of which was the 10 kilometers (6 mi) wide meteorite which struck Mexico’s Yucatan peninsula 65 million years ago, creating the Chicxulub crater (175 kilometers (110 mi)).
While similar to Alvarez’s impact theory (which involved a single asteroid or comet), this theory proposes that “passages of the solar companion star Nemesis through the Oort comet cloud would trigger comet showers.” One or more of these objects then collided with the Earth at approximately the same time, causing the worldwide extinction. As with the impact of a single asteroid, the end result of this comet bombardment would have been a sudden drop in global temperatures, followed by a protracted cool period.

Etymology

bp_blog — Fri, 12 Sep 2008 22:25:27 +0000

The taxon Dinosauria was formally named in 1842 by English palaeontologist Richard Owen, who used it to refer to the “distinct tribe or sub-order of Saurian Reptiles” that were then being recognized in England and around the world. The term is derived from the Greek words δεινός (deinos meaning “terrible”, “powerful”, or “wondrous”) and σαύρα (saura meaning “lizard” or “reptile”). Though the taxonomic name has often been interpreted as a reference to dinosaurs’ teeth, claws, and other fearsome characteristics, Owen intended it merely to evoke their size and majesty.
In colloquial English “dinosaur” is sometimes used to describe an obsolete or unsuccessful thing or person, despite the dinosaurs’ 160 million year reign and the global abundance and diversity of their descendants, the birds. This usage became common while dinosaurs were regarded as cold-blooded and sluggish.

Dinosaurs

bp_blog — Fri, 12 Sep 2008 22:22:58 +0000

Dinosaurs were the dominant vertebrate animals of terrestrial ecosystems for over 160 million years, from the late Triassic period (about 230 million years ago) to the end of the Cretaceous period (65 million years ago), when most of them became extinct in the Cretaceous–Tertiary extinction event. The 10,000 living species of birds have been classified as dinosaurs.

The discovery in 1861 of Archaeopteryx first suggested a close relationship between dinosaurs and birds; aside from the presence of fossilized feather impressions, Archaeopteryx was very similar to the contemporary small predatory dinosaur Compsognathus. Research since the 1970s indicates that theropod dinosaurs are most likely the ancestors of birds; in fact, most paleontologists regard birds as the only surviving dinosaurs and some believe dinosaurs and birds should be put together under one biological class.

Crocodilians are the other surviving close relatives of dinosaurs, and both groups are members of the Archosauria, a group of reptiles that first appeared in the very late Permian and became dominant in the mid-Triassic.

For about the first half of the 20th century, both scientists and the general public regarded dinosaurs as slow, unintelligent cold-blooded animals. However, the bulk of research since the 1970s has supported the view that they were active animals with elevated metabolisms, and often with adaptations for social interactions. This change of view was strongly influenced by evidence of the descent of birds from theropod dinosaurs.
Since the first dinosaur fossils were recognized in the early nineteenth century, mounted dinosaur skeletons have become major attractions at museums around the world. Dinosaurs have become a part of world culture and remain consistently popular among children and adults. They have been featured in best-selling books and films (notably Jurassic Park), and new discoveries are regularly covered by the media.
The term “dinosaur” was first coined in 1842 by Sir Richard Owen and derives from Greek δεινός (deinos) “terrible, powerful, wondrous” + σαῦρος (sauros) “lizard”. It is sometimes used informally to describe other prehistoric reptiles, such as the pelycosaur Dimetrodon, the winged pterosaurs, and the aquatic ichthyosaurs, plesiosaurs and mosasaurs, although none of these were dinosaurs.