Dinosaurs their
Story & Extinction

"K" is for
Chalk?

Why it is called K/T: "K" is for Kreide; German for chalk. Referring to formations such as the white cliffs of Dover (shown below) an important cretaceous formation. "C" as a possible abbreviation for the Cretaceous could be mixed up with "C" for Carboniferous. "T" is for Tertiary for the first period of the Cenozoic era. The K/T extinction is the most famous and popularly known because of the death of the dinosaurs.

  

Facts about the
K/T extinction

The K/T extinction affected both marine and terrestrial faunas and a wide variety of organisms. There is considerable stratigraphic evidence that marine and continental extinctions were simultaneous.

All dinosaurs living at the end of the Cretaceous were killed at the K/T boundary: titanosaurs (last surviving sauropods), abelisaurs (last surviving ceratosaurs), a few basal coelurosaurs (dryptosaurus in eastern North America, for instance), various clades of toothed birds (that is, all birds but Aves itself) nodosaurids, ankylosaurids, Hypsilophodontids, tyrannosaurids, ornithomimosaurs, oviraptors, therizinosauroids, troodontids, dromaeosaurids, alvarezsaurids, hadrosaurids, pachycephalosaurs, basal neoceratopsians and ceratopsids.

Marine invertebrates including coccolithophorids, ammonoids, inoceramids and rudists also died out. In North America freshwater mussels and snails suffered heavy losses and as many as 57% of the plants species may have become extinct as well. Marine vertebrates such as mosasaurs and plesiosaurs, as well as terrestrial vertebrates like pterosaurs and the Asiamerican marsupials also died out.

It was not a total loss; although on land, nothing bigger than 55lb (25 kg) survived. Survivors included insects - who showed no sign of change in diversity, unlike at Permian extinction. Amphibians, turtles, lepidosaurs (snakes and lizards), crocodilians, toothless birds (Aves) survived. Smaller mammals such as monotremes (egg-laying mammals), marsupials in Gondwana, multituberculates (although extinct today, survived and flourished in the early part of the Tertiary) and placentals outlasted the K/T Extinction.

Possible Causes of
the K/T extinction

There are a number of anthropomorphic ideas trying to explain dinosaur extinction: predation, epidemic disease, disappearance of available food or competition with other species. Although each of these might have been a contributing factor, they are scientifically less accepted as the main cause of the die-off. Other proposed causes are climatic change (especially cooling and drying), change in sea levels, chemical poisoning of ocean waters, changes in atmospheric chemistry, rocks falling out of the sky, cosmic radiation, and global volcanic activity. The three most accepted - and argued upon - causes of the extinction are listed below.

Maastrichtian Regression / Climate Change

Change in mid-ocean ridge activity means ocean levels drop and the shallow seaways of the Late Cretaceous drain, exposing extensive tracts of land. Climates worldwide become more continental (more extreme: hotter summers, colder winters). Change in climate produces change in ocean circulation (and the amount of nutrients) and in the growing seasons of plants. This gradually alters the environment and the food chain to such a degree that leads to extinction of certain groups of animals.

Increased Volcanism – Deccan Traps

Extinction due to flood basalt volcanism is hotly debated, but evidence has been found that some believe support this theory. In Western India, gigantic series of lava flows (Deccan Traps) were discovered. They are 2.4 km thick and are known to have all formed in 1 million years or less - centered on K-T boundary. It is the second largest volcanic event in last half-billion years; only Siberian Traps are bigger. Their formation was not a single continuous event. It occurred in stages with sediments and fossils between the lava layers.

Enormous basaltic volcanism, with its accompanying release of gases and dust into the atmosphere would have similar climatic effects to impact. The formation of the Deccan Traps itself was a major event, and might have contributed greatly to the extinction event. However, the third intertrappen sediments contain dinosaur remains and a layer of iridium rich clay was found above the dinosaur remains, leading experts to believe that the dinosaurs must have survived the first three basalt flows.

Extraterrestrial Impact

Around 1980, "Extraterrestrial Cause for the Cretaceous-Tertiary Extinction" claimed a group from Berkeley after studying the K/T boundary at Gubbio, Italy. The group found anomalous Iridium readings in a thin layer of clay interbedded in the Gubbio limestone. Similar anomalies were later found at other locations in Canada, Denmark, Spain, Tunisia, the United States. Since Iridium is an element common only in asteroids, the group hypothesized the origin of the anomaly must be an extraterrestrial body colliding with Earth.

Other proofs of impact include tsunami deposits, shocked quartz, tektites (glassy spherules – melt-products of terrestrial rocks formed by the impact), a soot layer around the Caribbean and in North America, and the Chicxulub crater itself buried underneath the Yucatán Peninsula in Mexico.

Effects of the impact included wildfires, evidence of which are found today as soot layers. Initial global cooling and darkness due to the amount of dust in the atmosphere. The release of gases later lead to global warming as the greenhouse effect became dominant. The average global temperature is thought to have increased by 10 degrees. Sulphuric acid and carbon dioxide in the atmosphere produced widespread acid rain destroying plant communities. The continents became virtually inhabitable as the environment and the food chain collapsed ending in a global chain reaction. These effects probably lasted for hundreds of thousands of years changing life on the Earth forever.

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