#index fossils

[mineralsrocksandfossiltalks]

Throwback Thursday: Charles Lapworth

This is Charles Lapworth, though perhaps we should call him professor or headmaster since he was both. He was incredibly important in geology for several reasons.

1.) Through mapping and use of index fossils, he showed that a sequence of Silurian rocks long thought to be a thick sequence, was actually much thinner, just folded and faulted to look thicker.

2.) He pioneered analysis of index fossils (mostly graptolites) to date Silurian rocks.

3.) Using those index fossils he determined that a new geologic period should be placed between the Cambrian and Silurian: the Ordovician.

4.) Proposed that older rocks were lying on top of younger rocks in Durness, Scotland (not a popular hypothesis) thanks to complex folding and faulting.

5.) He used Olenelloid trilobites to date Cambrian rocks previously thought to be Silurian in age because they sat below Carboniferous rocks.

Tune in tomorrow to learn about some important Ordovician fossils! Fossilize you later!

[actual-haise]

So you know how paleontologists use different species of ammonites/trilobites/etc as index fossils to pinpoint geological time periods? You can now do that with people by asking them about a blue cartoon dog

[cheetahtrout]

worked on index fossils today for a little project. Please ignore the era-names , since they are not all relevant to the fossils depicted on the same page.

[calmwaterdesigns]

Lurking on the ocean floor since the Devonian Age the ammonite bides its time until it can rise from the depths once more...

Ammonite Fossils carefully embedded in an Art Nouveau vase by Stephanie Young of Calm(but are they really?)water Designs

[mineralsrocksandfossiltalks]

Wordplay Wednesday: Index Fossil

Trilobites have come up a bunch this month and on Monday I mentioned they were used to date certain rocks. We call these kinds of fossils index fossils.

Now, not everything can be an index fossil. There are some very important qualities needed to be considered an index fossil.

1.) They must be distinctive and easily recognizable.

Look at how easy it is to identify different trilobites (and this is an incredibly small selection of the thousands of types out there).

However, if you were to look at hadrosaurinae, it is very difficult to tell Kritosaurus from Gryposaurus from Brachylophosaurus.

2.) They must be widespread. Trilobites can be found on every continent including Antarctica. In contrast, hadrosaurs have not been found in Africa or Australia so they are not very widespread.

3.) They must be abundant. There are over 22,000 kinds of trilobites while there are only about 60 kinds of hadrosaurs. Not even a competition there.

4.) They must live in a limited amount of geologic time. That means they can only be found in like one stage rather than an entire Era. Each of the 22,000 trilobites out there has their own distinct time they lived. For example, Elrathia lived from 513-499 Ma while Walliserops lived from 407-388 Ma.

Some may argue that hadrosaurs have a fighting chance here. Gryposaurus only lived from 80-75 Ma. That's a short time. We could use them to date rocks. But guess who else lived within that time frame?

Maiasaura.

Kritosaurus.

Hadrosaurus.

Brachylophosaurus.

Corythosaurus.

The list goes on. So, as you can see, dinosaurs do not make good index fossils but trilobites make great ones.

Fossilize you later!

[mineralsrocksandfossiltalks]

Fossil Friday! TRILOBITES

Trilobites are some of the most well-known invertebrates of the fossil record. They popped up during the Cambrian Explosion

and lasted all the way until The Great Dying of the Permian.

That's 469 million years!

Trilobites are a type of sea-faring arthropod. This phylum includes crustaceans, arachnids, millipedes and kin and insects. In other words, their bugs. Big, sea bugs.

The name trilobite means "three lobes" in reference to the vertical lobes their bodies are split into. They also happen to have three horizontal segments too.

The horizontal segments are split as follows: 1.) the cephalon (head), 2.) the thorax (abdomen) and 3.) the pygidium (butt). The vertical lobes are 4.) the right pleural lobe, 6.) the left pleural lobe and 5.) the central axial lobe.

Trilobites are found on all modern continents and occupied every paleo ocean. There are thousands of known species and because they appeared and disappeared quickly and left behind hundreds of molts they make excellent index fossils.

Representations of all the trilobite orders.

There are tons of immaculate specimens from various quarries around the world including the Cambrian-age Wheeler Shale of Utah where I got this specimen:

[mineralsrocksandfossiltalks]

THROWBACK THURSDAY: Carl Albert Oppel

Albert Oppel was a German paleontologist in the late 19th century.

Although he only lived until he was 34 due to a bout of typhoid fever, he made huge leaps and bounds for geology and paleontology. While studying part of the German Alps, he discovered that palaeontologic and lithologic zones need not be identical or even mutually dependent. He is considered the founder of zone stratigraphy and the use of INDEX FOSSILS.

He specifically used Jurassic-age ammonites to date the rocks they were found in and it was quickly adopted by other stratigraphers.

[mineralsrocksandfossiltalks]

WORDPLAY WEDNESDAY: STRATIGRAPHY

Stratigraphy is an important piece of vocabulary for paleontology. It is a branch of geology concerned with the relative position of strata (rock layers) and their relationship to the geologic time scale. It is primarily used for sedimentary and igneous rocks (metamorphic rocks don't tend to layer).

Nicolas Steno, a Catholic priest, established the basis for stratigraphy by introducing the Law of Superposition, the Principle of Original Horizontality, and the Principle of Lateral Continuity.

In other words, all rocks are deposited horizontally,

are laterally continuous,

and the oldest rocks are on the bottom.

There are three major branches of stratigraphy: lithostratigraphy, biostratigraphy, and chronostratigraphy.

Lithostratigraphy looks at the variations in lithology (physical characteristics of rocks) such as vertical and lateral bedding, and reflects changes in depositional environment (river, lake, desert).

Biostratigraphy correlates rock layers using fossils. This is based off of William Smith's Principle of Faunal Succession.

wherein fossils flora and fauna succeed each other in vertical layers and can be found over wide horizontal distances.

Lastly, there is chronostratigraphy which aims to put an absolute date (an actual number) rather than a relative date on rock strata. This means we can tell you where on the geologic time scale a formation belongs as shown below.

I personally love stratigraphy. It involves a lot of rigorous outdoor adventuring including hiking, mapping, drawing, picture-taking, and sample collection. In fact, I am currently working on a stratigraphic paper for our Evil Tree Bonebed. It's taken a few years but we should be done soon! I'll share when we are finally published!