Geology in the News

A 330 million year old shark head fossil has been found in Mammoth Cave, Kentucky. Mammoth is a Limestone cave. The limestone was deposited at a time that both Kentucky and Arizona were at the bottom of an ocean.

Rocks of this age in Pinal County have almost all been erroded, but a few outcrops can be found. You can stop by the museum, for instance, and see the Pinal Limestone (pictured at right, with fossil corals) that was deposited about the same time the shark died in Kentucky. That shark also probably swam in the waters above Arizona.

Fossils of sharks other than their teeth are rare. Most of a shark's body is cartilidge (like the center of your nose, or in the outside parts of your ears). Cartilidge does not fossilize well. Shark teeth, though, are among the most common fossils. They are made of bone, and very hard, and a typical shark may grow and shed teeth in the thousands during their lifetime.

Link to article on CNN:

You can see a number of fossil shark teeth at the Museum, including Megalodon teeth, from the extinct animal that was the largest known shark at over 50 feet. Kids can also find and take home fossil shark teeth from our fossil dig.

24 January 2020

Scientists recently announced confirmation of the world's oldest impact site, found east of Perth in western Australia. It's 2.2 billion years old. It's not really a crater after so long, It was found because of geophysical anomalies in the area.

Interestingly, it's thought the Earth was undergoing a "Snowball Earth" phase at the time, with pole-to-pole glaciation. They theorize that the impact of this meteorite could have triggered greenhouse gasses to start warming the planet and melting the ice.

Arizona's oldest rocks are schists that date to 1.6 billion years. One of them is the Pinal Schist named for a location in our county. The other Arizona schist of that age is at the very bottom of the Grand Canyon.

When this meteorite landed, Arizona was under the ocean, and located at approximately the South Pole.

You can find the BBC article on the impact site at:

24 January 2020

Allosaurus jimmandsi is a new dinosaur named from the Morrison Formation at Dinosaur National Monument in Utah.

The name has been around for quite awhile, so you may have heard of it before, but ithis is the formal naming and description.

Though found in Utah, other species found in the same area have been found in Arizona, so it's quite possible this could be added to the dinosaurs of Pinal County. It lived about 5 million years before the more common Allosaurus fragilis.

A new dinosaur species is named and described about every 7 weeks. There are only about 750 species known, which is just a small fraction of the dinosaurs that probably existed.

Image from the article.

Read the article at:


Article citation: Chure DJ, Loewen MA. 2020Cranial anatomy of Allosaurus jimmadseni, a new species from the lower part of the Morrison Formation (Upper Jurassic) of Western North AmericaPeerJ 8:e7803