Spinosaurus Tooth

Here is a fossil tooth I recently acquired, from a Spinosaurus, which is likely the largest carnivorous dinosaur, if not the largest land predator, that ever lived. It's somewhat difficult to say for certain as a complete skeleton has never been found (only scanty partial specimens). They have prominent dorsal neural spines for which various theories have been proposed. Some people think they were used for thermal regulation, others for sexual display, others to show aggression and dominance. It could also have been a hump. Regardless, this is one of the larger fossil teeth I own and one of my favorite specimens.

http://www.thefossilforum.com/index.php?/gallery/image/29231-spinosaurus-tooth/

Spinosaurus Tooth

Kem Kem Beds, Morocco

Upper Cretaceous

70 million years old

Pyritized Ammonite

Here is a beautiful Jurassic ammonite preserved in iron pyrite, commonly known as fool's gold. Almost hard to believe that this came from a squid-like animal with a shell (instead of a snail -- though I have plenty of those fossil shells as well). Ammonite fossils make great index specimens for dating rock formations, and have been found in every continent of the world. Sadly, they went extinct in the late Cretaceous, after what was likely a catastrophic bolide impact, alongside the dinosaurs.

http://www.thefossilforum.com/index.php?/gallery/image/28933-pyritized-ammonite/

The Trilobite

No fossil collection would be complete without the trilobite. The trilobite is the most-studied fossil arthropod, and was likely the dominant life form during the Cambrian age (though they lasted well into the Late Permian). They were probably the first animal to have compound eyes. Their form is easy to recognize and enigmatically beautiful, like a strange visitor from an alien world. The trilobite is a boon to fossil collectors. Many species are quite common and readily available, though there is plenty of diversity around to satisfy the most exotic of tastes. This little guy holds a special place in my heart as one of my first fossils. 

http://www.thefossilforum.com/index.php?/gallery/image/28462-flexicalymene-trilobite/

Like a Dirty Snowball from the far-flung reaches of our Solar System

Some scientists believe certain meteorites to originate from comets, which have colloquially been termed "dirty snowballs" -- a mixture of frozen water and accreted stony material. Carbonaceous chondrites such as the CI chondrites have never been heated above 50°C during their formation and subsequent history. Otherwise, the water would have rapidly evaporated and the hydrous phyllosilicates would have been metamorphosed into other minerals due to the loss of water.

CI chondrites and the closely related CM chondrites are particularly rich in volatile substances, including water. It is possible that the CI meteorites could have originally formed in the outer solar system, at a distance greater than 4 AU (1 AU is the distance between our Earth and the sun). They were formed beyond our solar system's "snow line", a division representing a temperature of 160° K. At this temperature, any water present in the cometary/asteroidal body would have condensed to ice and been preserved. This is supported by the similarity of CI chondrites with the icy moons of the outer solar system, such as Europa and Triton. Based on mineralogical and chemical evidence, including the high deuterium/hydrogen ratio of CI meteorites, it is possible that the CI meteorites could be fragments of comets or extinct cometary nuclei. These are the extinct bodies of comets that have exhausted their volatiles, losing their tails, and subsequently being captured by the inner asteroid belt between the gravities of Mars and Jupiter.

Here is an article discussing the outer asteroid belt origins of the Tagish Lake meteorite:

"Tagish Lake -- A Meteorite from the Far Reaches of the Asteroid Belt"

"Peter Brown and friends noted that the orbit of Tagish Lake extended to that part of the asteroid belt where asteroids classified by astronomers as C, P and D types predominate. These asteroids are know to have hydrated silicates (water-bearing minerals) on their surfaces, and because of their dark color, are suspected to be rich in carbon compounds. These are also characteristics of the most primitive meteorite types known -- the carbonaceous chondrites, especially the types classified as CI and CM. This was the first clue that Tagish Lake might be a primitive type of chondrite." 

Thought to contain the most primitive matter in our solar system, could Tagish Lake have also been a comet in it's long and mysterious past? D-type asteroids are thought to have originated in the Kuiper Belt, a region of the solar system beyond the orbit of Neptune. Tagish Lake's characteristics strongly suggest that it is a primitive body coming from the far reaches of our solar system. 

We too are stardust

Here is an interesting Scientific American article on the Murchison meteorite, and why I have unofficially dubbed it "The Biologist's Meteorite." Murchison was found to contain more than 70 amino acids, as well as other organics (purine and pyrimidine precursors) that may have provided the raw materials for life.

http://www.scientificamerican.com/article.cfm?id=murchison-meteorite

They say that you can actually smell the carbonaceous compounds in freshly-cut specimens. Well, I recently won an auction for one and will soon see for myself! Waiting for it to come in the mail is killing me!

Additionally, powdered samples of the Murchison meteorite, when heated up to 900°C, show strong similarities in their reflectance spectra to C- and G-type asteroids. G asteroids exhibit strong UV absorption, a good example being the large asteroid / dwarf planet 1 Ceres. C asteroids, additionally, are thought to be the parent bodies of the carbonaceous chondrites.

Here is another (BBC Science) article discussing organics found in the Tagish Lake and Murchison meteorites:

"Space Rock Yields Carbon Bounty"

Murchison

Allende

The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The bolide was witnessed on February 8, 1969; falling over the state of Chihuahua, Mexico. The Allende meteorite is notable for possessing many, large calcium-aluminium rich inclusions (CAIs), which are among the oldest objects formed in our solar system.

Some portion of the carbonaceous chondrites are thought to originate from 1 Ceres. While no meteorites have conclusively come from Ceres, it is possible that the reflectance spectrum of the surface of Ceres is not indicative of its crustal rocks.

The present models assume instantaneous cold accretion of Ceres from approximately 1-km-sized objects. These may have accreted earlier from solar nebula during a duration period of about 2.4 million years from nebula cooling and formation of CAIs. This means that Ceres may have evolved further from the simple aqueous thermal evolution found in CC meteorites.

Allende