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Death to the Dinosaurs
May 03, 2009

This is a piece I wrote for my site in the palaeontology section. I'm copying it over to here because it's good and fits with dinosaur / extinction interests. If you enjoy the article, please visit World Ancestry.


The dinosaurs roamed the planet's surface and seas for more than 160 million years. We vision them as great reptilian giants that ruled the planet up until roughly 65 million years ago—and we believe they vanished in an single traumatic instance never to be seen again until their bones were unearthed in abundance during the late 19th century. What caused the disappearance of the Earth's largest animals? Were they obliterated by an asteroid impact? Did they actually even disappear?

In order to begin comprehending the extinction at the end of the Cretaceous period, some 65 million years past, we must have an idea of the environment they lived in and the nature of their biology. Since their discovery, dinosaur physiology and anatomy theories have changed drastically. Advances in technology in the fields of geology, palaeontology, and biology help us perceive these massive animals to a degree unprecedented.

Time

Without a perspective of time nothing makes sense. Though the dinosaurs populated the Earth for over 160 million years, they were only the big kids on the block for a fraction of their existence. The first dinosaurs—not like we picture today, but the first of their kind—did not appear until the middle of the Triassic period (roughly 230 million years ago). Not only that, the dinosaurs we picture today (Tyrannosaurus rex, Triceratops, Stegosaurus, Brontosaurus) were only around during the Cretaceous for no more than 50 million years. Yes, I state that as if it were a blink in time, but considering the world is 4.6 billion years old, it is just a blink. However, 160 million years is no joke: Homo sapiens have only been around for 200,000 years, less than a quarter million years!

Environment

The environment the dinosaurs lived in changed many times over tens of millions of years. Pangaea separated into the individual continents we see today throughout the Mesozoic (Triassic to Cretaceous periods). This allowed for cases of extreme flooding, volcanic activity, earthquakes, shifting in available plant life, etc. The North American continent was split, especially during the Cretaceous, by an epeiric sea—a warm, shallow inland sea.

Based on the plant fossils we've recovered the environment was relatively lush and temperate in climate, probably closer to tropical depending on the region. The largest desert in Earth history resided on the northwest part of North America (one that would mimic if not dwarf the Sahara), so there were regions rich in vegetation and also arid zones. Swamps and bogs existed, but they were by no means abundant. Most of North and South America was heavily vegetative. Aside from the vast desert to the west and the sea that separated North America, it is likely most of the continent was green. High amounts of carbon dioxide lingered in the atmosphere keeping the planet extremely warm—the temperature peaks in the hottest tropics today are considered cold when compared to the latter part of the Mesozoic.

The Dinosaurs - Some Assembly Required
For more than half a century we thought the dinosaurs to be large, sluggish reptiles dragging themselves in and out of swamps and bogs. Nothing could be further from the truth. In fact, even some of the largest of the dinosaurs were fast-roaming animals. Spending time in the African savannas, an academic could piece together behavior and locomotion in mammals that could easily reflect that of the ancient "lizards". The dinosaurs were much more diverse and complex than we originally thought—just as there is diversity in modern mammals.

There are two major groups of dinosaurs that emerged during the Mesozoic: Saurischians ("lizard-hipped") and Ornithischians ("bird-hipped"). I won't get into the details of each type but I will give you an idea.

Saurischians

 

  • Sauropods - herbivorous quadrupedal dinosaurs such as the Brontosaurus and Brachiosaurus.

  • Theropods - carnivorous bipedal dinosaurs such as the Tyrannosaurus and Deinonychus.



Ornithischains
  • Thyreophorans – armored dinosaurs such as Ankylosaurus and Stegosaurus.

  • Cerapods – beaked dinosaurs and others classified by their thick-layered enamel in their lower teeth. Cerapod examples include Pachycephalosaurus and Triceratops.

Many features of later species of dinosaurs mimic those of certain modern animals, particularly birds. Now, dinosaurs did not evolve into birds as a whole, however there is plenty of data that to support certain species did. Considering the proliferation of dinosaur species during the Mesozoic, it's not crazy to follow the logic that some eventually ended up as modern avians.

Extinction




There are two major conflicting theories that seal the fate of the dinosaurs: asteroid impact and volcanism. The impact theory is clearly the most popular and widely accepted. Evidence for both exists, but we really don't know for sure which is correct; it is likely the both are correct.

Impact Theory




Above all, the impact theory remains the most widely accepted theory causing the disappearance of the dinosaurs. The theory states that an asteroid six miles wide impacted the Earth in the Yucatan causing a debris cloud large enough to smother the planet. The result of this debris cloud is nuclear winter—what dinosaurs did not perish immediately from the impact froze and starved. The impact theory rests on circumstantial evidence at best. The foundation of impact theory is the amount of iridium found globally in rock strata dating to the end of the Cretaceous At the K/T boundary (Cretaceous/Tertiary). Iridium is a chemical element of the platinum family, a transitional metal. The significance of the global distribution of iridium at the K/T boundary is that iridium does not form in abundance in the Earth’s crust—so says the proponents of the impact theory. Iridium is more commonly found in celestial objects such as meteorites and asteroids. Therefore, this layer of iridium deposion in sedimentary rocks at the K/T boundary sends up a flag saying a foreign object impacted with Earth, kicking up debris filled with the element.

One other scientific piece of evidence to support an impact theory is what is called shock metamorphism. Shock metamorphism is when a rock or mineral is transformed from its original (and regular) state into a new one via a quick shock of heat/pressure. The dominating mineral in sandstone is quartz. When shock metamorphism occurs, the quartz is altered in a fashion that is quite unique called spherules—they become these nearly perfectly rounded, smooth spheres. The geometry of the quartz alters in such a way only found at sites where shock metamorphism occurred. An impact with Earth by a sizable celestial object would definitely cause shock metamorphism.

Volcanism Theory




Although not as popular, the volcanism theory holds more scientific water and the theory doesn’t rest on circumstantial evidence—there is a wealth of scientific evidence to support this theory. Iridium may not form abundantly in the Earth’s crust but it can form through volcanism. Extreme volcanism can gush elements from the mantle (and create elements during transmission) and form iridium. The argument by volcanism proponents against impact theory is that the iridium deposition spans too much time for it to be a result of a quick impact. Moreover, the most massive volcanic event during the Phanerozoic (the eon covering 570 million years of Earth’s history, from the Cambrian to today) occurred right around the K/T boundary. This event was the eruption fueled by the Réunion hotspot known now as the Decca Traps. The eruptions coming from Decca were like frequent bombing raids. A single eruption alone would have crippled the ecosystems of the planet, but they could recover. If the eruptions came frequent enough, the ecosystems would have not had time to fully recover, thus destroying them. Eruptions around the Réunion hotspot may have not been all massive, yet some were enough to produce iridium via shock metamorphism. Even if the eruptions were not massive, enough heat and pressure before an eruption can create shock metamorphism and produce iridium!

Furthermore, shock metamorphism is found the world over today as a result of volcanism. Basalt and quartz spherules once believed to be only found at impact sites have been discovered near volcanically active sites. If that was not enough, layers of sediment dated at the K/T boundary are primarily made up of volcanic clays. Mudslides from volcanic eruptions (like the one after Mt. St. Helens erupted in 1980) would eventually settle and form volcanic clay. Does this mean the volcanism theory prevails? Can proponents of this theory say, “In your face, impact theorists?” Of course not. The reality is much more complex, yet simple in its own right.

[Probable] Reality of the K/T Boundary

The extinction level event that destroyed the dinosaurs was not an event; it was a chain reaction that took millions of years. The fossil records show that many of the species were already on the decline long before the K/T boundary—long before any asteroid impacted the planet or single volcano eruption at Réunion. The dinosaurs, among other species of flora and faunal, were on the decline long before the boundary. By the late Cretaceous there were only as little as 10 species of dinosaurs still roaming the Earth; most had already become extinct. To put that into perspective, there are 700 recorded species of dinosaurs and estimates suggest there are still at least 700-900 more that remain to be discovered! There is no question the dinosaurs were already buried to the hip in their grave, proverbially speaking, by the time an asteroid impacted or a volcanic event occurred. In fact, most animals died out with the exception of a few. Mammals seemed unaffected by the extinction event, as did turtles, crocodiles, frogs, and other amphibians. In addition, oxygen and carbon isotopes show that the oceans were cooling nearly a quarter of a million years before the K/T boundary.

Many plants, such as angiosperms, were declining long before the “event”, along with various other species such as ammonoids—ancestors of the modern pearly nautilus. By the time of the K/T boundary many of the Earth’s species were already stressed. This is a trend we see long before the K/T boundary in extinctions at the end of the Permian 250 million years before the end of the Cretaceous, and the end of the Ordovician some few hundred million years even before the Permian extinction. When a species is stressed the smallest change in its ecology can lead to extinction. Today's polar bears are a perfect example. The terrestrial record in the 250 million years before the K/T boundary is relatively clean, meaning no major catastrophic events occurred such as glaciations or volcanism. This is natural selection hard at work, and whatever happened at the boundary was the straw that broke the camel’s back. If many of the species were stressed, a single large impact or volcanic eruption could easily finalize the extinction. In fact, some theories that oppose impact theory as the deathknell suggest dinosaur species were becoming stressed due to a combination of disease and frequent eruptions around Decca. When the asteroid impacted the Yucatan 65 million years ago, it was the final nail in the coffin. Also, the extinction wasn’t overnight, like suggested by impact proponents, but took up to a million years to work. Thus, neither theories mentioned are likely to be direct catalysts leading to the extinction of the dinosaurs. The reality of the situation may never be uncovered, however it was more than likely a combination of events.
__________________
Reverend J. Vance Tyree
Founder & Curator
 
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