Extinction -Explanation

Thursday, February 18, 2010

Paleontologists generally divide extinctions into two categories. The first are the so-called background extinctions, isolated extinctions of species that occur in an ongoing fashion. The second type are called mass extinctions. The latter certainly have caught media and the public’s attention, and they appear to be something qualitatively as well as quantitatively different than background extinctions.

Background extinctions
Although background extinctions are less glamorous than mass extinctions, they are essential to biotic turnover: University of Tennessee paleobiologist M. L. McKinney has estimated that as much as 95% of all extinctions can be accounted for by background extinctions. Isolated species disappear from a variety of causes, including out-competition (the edge), depletion of resources in a habitat, changes in climate, the growth or weathering of a mountain range, river channel migration, the eruption of a volcano, the drying of a lake, the spraying of a pesticide, or the destruction of a forest, grassland, or wetland habitat. Dinosaur populations had a species’ turnover rate of around 2 million years per species. This means that each species lasted about 2 million years, before a new one appeared and the old one disappeared. 1 Although some dinosaur extinctions coincided with earlier mass extinction events (such as those at the Triassic–Jurassic and Cretaceous–Tertiary boundaries), most dinosaurs fell prey to background extinctions. By far the majority of favorite and famous dinosaurs – Maiasaura, Dilophosaurus, Protoceratops, Deinocheirus, Styracosaurus, Velociraptor, Iguanodon, Ouranosaurus, Allosaurus (to name a tiny fraction) – were the victims of background extinctions. The ultimate dinosaur extinction didn’t wipe out the total number of species accumulated over 160 million years, it killed only the latest-evolved representatives of the group (see Figure 13.1).

Mass extinctions
Mass extinctions involve large numbers of species and many types of species undergoing global extinction in a geologically short period of time. None of these has a truly precise definition, because there are no fixed rules for mass extinctions. Indeed, how do we know that there even were mass extinction “events” and how can we recognize them? A compilation of invertebrate extinctions through time (Figure B15.1.1) shows that, although extinctions characterize all periods (it is these that are termed background extinctions), there are intervals of time in which extinction levels are significantly elevated above background levels. Such intervals are said to contain the mass extinctions. Fifteen such intervals are recognized, of which five clearly towered above the others (Figure B15.1.1). The 15 mass extinctions are classified into “minor,” “intermediate,” and “major” mass extinctions, on the basis of the amount of extinction that took place above background. In the entire history of life, only one extinction qualifies as “major”; that is, the Permian–Triassic (commonly called Permo- Triassic) extinction. The remaining four of the Big Five – including dinosaur extinction – are considered to have been “intermediate.” The rest are considered “minor,” although undoubtedly not to the organisms that succumbed during them.

Dragon Roots

Tuesday, February 2, 2010

Researchers have long noticed the universality of dragon lore, and many have tried to explain why this monster is so common in world mythology. Both a Munich geology professor and American astronomer Carl Sagan have suggested that an ancient memory—carried in genes inherited from our mammalian ancestors—is responsible for an inborn fear of large reptiles. Prehistoric memories of dinosaurs seep from our subconscious into our impressions of the world, according to this theory, and turn old nightmares into legend.

These fears may have been confirmed in people’s minds whenever they accidentally uncovered fossilized dinosaur skeletons, seemingly real proof that such creatures existed. Some ancient saurians still live, however. The Komodo dragon, a lizard named after the Indonesian island where Westerners first learned of it in 1912, is the living creature that most closely resembles a traditional dragon. These carnivorous monsters may grow to more than 12 feet in length, and can eat large mammals such as goats. They are related to a fairly recently extinct Australian monitor lizard that could reach three times that length. Although they don’t breathe fire or fly, Komodo dragons still present a very formidable appearance and might easily provoke terror-stricken witness reports of dragons if encountered unexpectedly.

Author Peter Costello believes that human craft may have played a role equal to that of nature in reinforcing the idea of dragons. From the early to late Middle Ages, he says in The Magic Zoo, the custom of using giant, fluttering windsock dragons as battlefield banners spread from Asia to Europe. Each banner held a flaming torch to present the daunting illusion of a flying, fire-breathing dragon, and may have helped turn the tide of many medieval battles. At night, in the heat of battle, the billowing figures may have appeared real, and those who lived to tell the tale probably swore they battled dragons.

Tolkien’s dragons

Smaug by Angus McBride
By John D. Rateliff

There he lay, a vast red-golden dragon, fast asleep; a thrumming came from his jaws and nostrils, and wisps of smoke, but his fires were low in slumber. Beneath him, under all his limbs and his huge coiled tail, and about him on all sides stretching away across the unseen floors, lay countless piles of precious things, gold wrought and unwrought, gems and jewels, and silver red-stained in the ruddy light. —J.R.R. Tolkien The Hobbit

J.R.R. Tolkien’s contributions to fantasy in general and dragon-lore in particular are so great as to place him in a league of his own. The whole concept of the PC party (specialists of different backgrounds working together toward a common goal) derives from Tolkien’s “Fellowship of the Rings,” while his own particular “take” on all the major fantasy races — elves, dwarves, goblins, etc. — have become the common currency for a whole generation of successors. He is the most imitated fantasist of all time, and his masterly portrayal of Smaug, “the chiefest and greatest of all calamities,” is the standard by which all other fantasy dragons should be judged.

Whereas after Grahame the tendency had been to treat dragons as witty and cute, Tolkien restored the sense of them as deadly predators. All of Tolkien’s dragons — Smaug from The Hobbit, Glorund from The Silmarillion, the wily but not over-bold Chrystophlax Dives from Farmer Giles of Ham — are clever, unscrupulous, greedy, and exceedingly dangerous. They can be bargained with, but each is capable of wiping out a small army or good-sized town all by himself. Anyone who dares to talk with one of Tolkien’s dragons had better have an escape route planned if he does not want to become the creature’s next meal.

Furthermore, Tolkien’s dragons delight in mischief: rather than kill Turin, a brave but rash and not overly clever hero, Glorund convinces him to abandon the people who rely upon him and sends him on a fool’s errand, while Smaug sows the seeds of doubt in Bilbo’s mind that shortly afterward help wreck his friendship with the dwarves. People who listen to dragons are apt to fall under their enchantment (“Smaug had rather an overwhelming personality”), and any spark of greed inside them usually fares into full life. Sometimes this dragongreed is even contagious, transmitted by contact with treasure “over whom a dragon has long brooded” — as shown in the fate of Thorin Oakenshield and to a lesser extent that of Bilbo himself (whose secret theft of the Arkenstone was a thoroughly uncharacteristic act). Similarly, Fafnir’s treasure, the hoard of the Niebelungs, seems to bring disaster to all who possess or even lay claim to it, while Beowulf’s grieving countrymen wisely decline to take any of the dragon’s hoard after his death, instead placing it all on his pyre and burying what remains in his barrow.

Finally, Tolkien’s dragons are hard to kill. Smaug destroys Dale and the Kingdom Under the Mountain, sweeping aside all resistance, and that was when he was, in his own words, “young and tender.” Later in the book we’re given a vivid description of his attack on the mountainside and burning of Lake-Town. Had he not been slain by Bard’s expert shot with a special arrow to his one secret vulnerable spot, Tolkien speculated that Sauron might have later manipulated him into destroying Rivendell. [1] Likewise, Glorund destroys the elven city of Nargothrond, effortlessly scattering and destroying its battle-tried elven warriors, while other dragons help plunder the great hidden city of Gondolin. For his part, Chrystophlax shows great reluctance to melee with anyone armed with a sword of dragon-slaying like Giles’ Claudimorax (and no wonder), but when faced with the possibility of losing his whole hoard handily massacres the Little Kingdom’s assembled knighthood, then later effortlessly puts a second army to flight. It’s possible to slay one of the Great Worms, but only by careful planning and good luck.

[1] Unfinished Tales (1980), “The Quest of Gandalf’s point of view, telling us how the contrast to Bilbo’s narrative, this bit of “alter- Erebor,” contains a behind-the-scenes look at events appeared to the wizard and the alternate Hobbit” lets us learn more about the opening chapter of The Hobbit from dwarves. In addition to offering an amusing Gandalf’s motives and plans.


Meaning: Wing tail
Time: Early Cretaceous
Size: 2 ft. 3 in.
Diet: Insects
Information: One of the small theropods that show distinctive bird features. It was very lightly built and had feathers on the wings and the tail. However, the wings were too small to allow it to fly. Here it is shown in the bottom, right of the picture.

The discovery of Caudipteryx led to many intensive studies on and debate over the relationship of birds and dinosaurs. The possible positions in the debate can be summarized as follows: Caudipteryx  is either a member of the Oviraptorosauria, or a bird, or both, and birds are either dinosaurs or they are not.

Because Caudipteryx has clear and unambiguously pennaceous feathers, like modern birds, and because several cladistic analyses have consistently recovered it as a nonavian, oviraptorid, dinosaur, it provided, at the time of its description, the clearest and most succinct evidence that birds evolved from dinosaurs. Lawrence Witmer stated: “The presence of unambiguous feathers in an unambiguously nonavian theropod has the rhetorical impact of an atomic bomb, rendering any doubt about the theropod relationships of birds ludicrous.”

However, not all scientists agreed that Caudipteryx was unambiguously non-avian, and some of them continued to doubt that general consensus. Paleornithologist Alan Feduccia sees Caudipteryx as a flightless bird evolving from earlier archosaurian dinosaurs rather than from late theropods. Jones et al. (2000) found that Caudipteryx was a bird based on a mathematical comparison of the body proportions of flightless birds and non-avian theropods. Dyke and Norell (2005) criticized this result for flaws in their mathematical methods, and produced results of their own which supported the opposite conclusion.

Other researchers not normally involved in the debate over bird origins, such as Zhou, acknowledged that the true affinities of Caudipteryx were debatable.




Meaning: Named after Camille Arambourg, who first described it in the 1950s
Time: Late Cretaceous
Size: 39 ft. 4 in. (13m)wingspan
Diet: Probably fish
Information: Scientists continue finding bigger and bigger pterosaur bones and announcing that this must have been the biggest animal that could possibly fly. The current record holder is Arambourgiania.
The biggest pterosaurs are not known from complete specimens, so all the figures you see on this subject are only estimates based on extrapolation from smaller, more complete finds. Currently, the record holders amongst pterosaurs (and, indeed, all volant animals) are the giant azhdarchids, enormous pterosaurs that existed across the world in the Cretaceous. The best known of these is Quetzalcoatlus nothropi from the Javelina Formation of Texas. Known from a stupendously big humerus and other fragmentary elements, the wingspan of this animal is estimated at 10 - 11 m with a shoulder height of 2.5 m when it stood on the ground.

However, other azhdarchids known from even scantier material hint at bigger animals. Arambourgiania philidelphae, a pterosaur known from a solitary neck vertebrae and scrappy wing elements from Jordan, may have achieved a wingspan of 11 - 13 m. However, Hatzagopteryx thambema is the current record holder for the largest pterosaur known: with only a few pieces of skull and a couple of scrappy limb elements, estimates for this critter put it between 12 - 14 m across the wings.