#weeks formation

This month has been dedicated to the Cambrian Period. Something most people are not aware of is that Paleozoic and Mesozoic periods are broken down into epochs and stages...just like the Cenozoic.

Just for fun I wanted to use this column of the Cambrian Period to show where all the major deposits and animals we've talked about (and a few we haven't) occurred.

Like our favorite trilobites!

Trilobites appeared in the fossil record at about 521 Ma, right at the end of Stage 2 of the Terreneuvian Epoch. Not long after that, the Chengjiang and Sirius Passet lagerstatten were deposited. This was towards the end of Stage 3 of Series 2. This is when the animal Haikouella lived.

Next is Emu Bay Shale. We haven't talked about that one yet. As you can imagine, Emu Bay is in Australia on Kangaroo Island.

It is one of two sites containing Redlichiidan trilobites.

The Burgess Shale was deposited at the beginning of the Drumian Age during the Mialingian Epoch. This is when Hallucigenia and Marella lived.

This is followed by the Wheeler Shale, Marjum and Weeks Formation sequence in the Guzhangian Age.

The final lagerstatten is the Orsten Fauna of Sweden. The fossils are just a little bit younger than the Utah ones and much smaller. This site preserved larval stages and the first fossil tardigrades.

By the end of the Cambrian there was a major faunal turnover into the Ordovician Period. Many brachiopods and conodonts died but the group that was hit the hardest was the trilobites. Those that lived on the outer edges of the shelfs and slope environments were hardly affected but those that lived in the shallow seas on the shelf were wiped out.

The Cambrian Period was important and I hope you enjoyed learning about it this month. Next month we will switch from geochronology to paleontology with comparative anatomy! There will be a video on the basics posted to youtube on October 19th but if you want to see it sooner then join my new Patreon! The video will be posted two weeks earlier.

There will also be interviews with my fellow paleontologists as well as lesson videos and access to the Minerals Rocks and Fossil Talks discord server. Thanks for all the support and fossilize you later!

goldbugsofficial

Name: Cedaria minor 

Location: Utah, USA, Weeks Formation

Age: 444-461 million years ago, Cambrian Period

No one has ever seen a living Cedaria, or any other trilobite. Even though they were one of the most diverse groups of animals ever known, the last living trilobite died 250 million years before any human walked on Earth. 

Trilobites were ocean-dwelling animals with many legs and hard, outer plates. So far, researchers have recognized and named over 20,000 species of trilobite. That’s an amazing diversity. In comparison, all of the different kinds of birds alive today, from ostriches to sparrows to penguins, add up to only half as many species. There are more than three times as many species of trilobites as there are species of mammals. 

Trilobites had more than large numbers. They also came in a diversity of forms and sizes. 

Cedaria was small, and would fit on a dime. In contrast, some of the other trilobite species grew forty times larger, and reached 72 centimeters, about the size of a freight-truck tire. Others grew to be only a tenth of a centimeter, about the width of a grain of rice. 

The abundance and diversity of trilobites helped them make it through two mass extinctions, times when many other groups went extinct. 

However, by the time a third mass extinction hit 250 million years ago, trilobites had lost the diversity and abundance that had helped them thrive. At the end, only a handful of trilobite species were left to go extinct.

Specimen Number: NPL 15006

Sources:

Gon, Sam III. “A Guide to the Orders of Trilobites,” accessed 9 October 2012. http://www.trilobites.info. 

Hughes, Nigel C. “The evolution of trilobite body patterning.” Annual Review of Earth and Planetary Sciences 35(2007):401-434.

IUCN. “Summary of number of animal species in each Red List Category in each taxonomic class.” In: IUCN  Red List of Threatened Species. Version 2012.1. Accessed 9 October 2012. http://www.iucnredlist.org/documents/summarystatistics/2012_1_RL_Stats_Table_3a.pdf