Dinosaurs and Fossils: The Ultimate Guide!

Earth has been around for a while, actually a very long while. If you think your parents or grandparents are old, then consider this:

If your grandmother was eighty, then the earth would be 5,625,000 times older than your grandmother. Not bad, for a planet some 4.5 billion years old, the earth is doing pretty well! Scientists realize that 4.5 billion years is a little hard to grasp, so they divide it up, into the geologic time scale.

Anyways, at some point a very, very long time ago, life was showed up (for the sake of avoiding anger on both sides, we will leave out any discussion of how said life came to be). But anyways, life happend and began to expand and evolve.

Life started out as single celled organisms that did little other than eat and reproduce (some would say that not much has changed since then!).

This was during the precambrian era, which makes up 7/8 of the earth's history. We don't really know all that much about it though, because not much fossil evidence has survived that long, and single-celled organisms don't make great fossils in the first place. However, against all odds, scientists have discovered fossils of bacteria around 3.5 billion years old, so we can assume that the Precambrian era saw the origins of life on earth.

Towards the end of the Precambrian, the diversification of life really started to heat up. multi-celled, soft-bodied organisms started to appear around 600 million years ago.

For more information of this section, visit the
Wikipedia article

Around 530 million years ago, a period called the "Cambrian Explosion" began. This 70-80 million year period saw a massive increase in the diversity of life. The explosion of diversity was so abrupt that scientists have suggested that we lack a good deal of fossil evidence from the period leading up to the Cambrian Explosion.

We are actually very lucky that we have as much evidence of the Cambrian explosion as we do. The remarkable Burgess Shale formation in western Canada, likely formed by a massive underwater mudslide around 515 million years ago, preserved many specimens that normally would not have been fossilized.

Many of our favourite fossils appeared during the Cambrian, notably the Trilobite, Anomalocarid, Opabinia and many many other bizarre forms. Many of the creatures of the Cambrian Explosion were anthropods, and anscestors of the modern varieties. Chordates also made an appearance, providing some of the earliest known human anscestors! However, some creatures defy categorization, suggesting that their families did not survive to modernity.

The Cambrian explosion ended with the Cambrian extinction, the first major extinction event on record. This wiped out a good deal of diversity, and ushered in the Ordovician period.

For more details see Wikipedia:
Cambrian Explosion
Cambrian Period
Cambrian Extinction

And I also promised more information about Trilobites!

A Guide to the Orders of Trilobites

Dinosaurs tend to be the most noticed of all fossils, and sadly, in this case, size does matter. If fossils were musicians, dinosaurs would be rock stars!

Dinosaurs appeared on the scene around 230 million years ago, and over the next 160 million years, dominated life on land all over the planet. When they hear the word dinosaur, most people think of a few specific, famous types (Think Velociraptor, T-Rex and Brachiosaurus). However, in reality, the ancient landscape was chock-full of thousands of different species of dinosaurs, ranging from tiny (chicken sized!) to really, ridiculusly huge (Think imperial walker from Star Wars).

Dinosaurs are often put into two wide groups, Herbivores (vegetarions, real PETA-types!), and Carnivores. Numerically, there were far more herbivores than carnivores.

But now let's get to what I really want to talk about... birds! That's right! Modern birds are widely thought to be descended from the Theropod group of dinosaurs, a group that includes T-rex, and many smaller, meat eating dinosaurs.

The Dinosaur-bird theory got it's start a long time ago, but was generally rejected until fossils of theropods with feathers started popping up all over the place. Since these discoveries began, the evidence has become very strong for the theory, growing to include similar bone structures and the use of gizzard rocks for disgestion.

Pretty cool eh? It looks like we can add another item to things that taste "just like chicken..." Dinosaurs!

So anyways, Dinosaurs remained highly dominant life-forms until around 65 million years ago, when they died out suddenly, fo reasons that are still a little mysterious.

What we do know, is that there was a large asteroid impact near the gulf of Mexico. We know this because we've found the crater, and also because of the KT boundary. This is an iridium rich, thin layer of rock found worldwide, formed from the dust that settled after the asteroid impact (apparently the asteroid belt is rich in iridium). Interestingly, a dinosaur find has never been confirmed above the KT boundary, so we can assume that the asteroid impact caused the final extinction of the dinosaurs.

Be that as it may, we now know that the dinosaurs had been in decline for some time prior to the asteroid hit, and that it was likely only the final knock-out blow. To bad really, They were super-cool.

Wikipedia has the details:
Dinosaurs