#paleogene

If you have no opinion on this/don't like ancient history prehistoric periods/etc, choose Quaternary.

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"See? Snake!" Palaeophis/Presbyornis/Striatolamia/Myliobatis/Pseudamia/Eutrichiurides Paleogene, 49 million years ago, Margaret Formation This was posted last week on my Patreon, available to $10 supporters!

For millions of years, the Earth has existed in a hothouse age.

Water evaporates and rains down, increasing the amount of freshwater flowing through Earth's rivers. As they drain into the enclosed Arctic Ocean, a non-salty layer of water emerges at the top.

Right now, the arctic is warm. It's practically entirely free of ice, even during the long polar darkness. Alligators lurk in the lakes under the midnight sun. And today, in the ocean, so does an enormous, almost-twenty-foot snake, coming up for air and startling a gaggle of Presbyornis in the process. Large even for her kind, she made her way through the ancient North Sea to bask in the polar summer. Warm-blooded, she is more resistant to changing temperatures than your average snake, and the bounty of food has encouraged her to remain here for the time being. With the ability to drink from freshwater on the ocean's surface, this Palaeophis toliapicus thrives in an environment where this is the norm. As the sun sets over the next few weeks, she will swim back the way she came, and repeat the journey every year.

Bizarrely, the Eocene arctic possesses relatively low diversity in marine life. It appears to be dominated by scores and scores of shed teeth belonging to relatives of sand tiger sharks and eagle rays. Aside from that, we see hairtail, smelts, and potentially bowfin. With the mingling of fresh and salt water, this ocean can potentially accomodate species from both environments.

Also notable is the presence of a dense plant carpeting the sea surface: Azolla. They capture carbon dioxide from the air, and as they die, sink to the seafloor, locking it away from the atmosphere. It is these plants that will send the planet spiralling into a cooling climate, culminating in the famous ice ages. Lush forests will slowly but surely be replaced by hardier fare, and then by sprawling glaciers. The arctic will freeze over, and the area will be rendered unrecognizable until a strange species of hairless apes dig up a plethora of shark's teeth in the Margaret Formation millions of years later.

But today, there's no need to worry about that. Today, a visitor arrives, takes a breath of that fresh, fresh air, and submerges herself in the water again, swimming off into the blue, as she has done for much of her life.

Palaeophis is a "sea snake" (actually related to the adorable elephant trunk snake) the size of a python. The toliapicus species is part of a clade of more flattened species with distinct oceangoing adaptations. I like to think that maybe they drank rainwater from the ocean's surface much like modern sea snakes, but that's speculation. It's possible the tropical climate of the time was what allowed them to grow to such massive sizes, and we have another species, colossaeus, from Mali that grew longer than an anaconda. We have no evidence of them ever going this far north, but I think it's possible. Presbyornis is a bird that looked as if one stretched a duck into the proportions of a flamingo, that was common during the Eocene. Its lineage has a long and storied history dating back to the latest Cretaceous, though none of its kind exists today.

Deep time is not an easy thing to try and comprehend and it certainly doesn’t help when there’s all these crazy names being thrown at you. Let’s take a moment to break it down and really understand what we are seeing. The largest unit of geochronologic time is an eon. There are four formally defined eons: the Hadean, the Archean, the Proterozoic, and the Phanerozoic. The Hadean Eon is the oldest eon going from 4.6-4 Ga years ago. Its name is derived from the Greek god, Hades in reference to the still molten surface of the newly formed planet.

Following the Hadean Eon is the Archean Eon. This eon went from 4-2.5 Ga years ago. As mentioned in my Barberton Greenstone Belt video two weeks ago, this eon saw the creation of oceans and mountains as well as the appearance of the first living organisms known as stromatolites which would put oxygen into the atmosphere. Archean means “beginning or origin” which is fitting.

Next came the Proterozoic Eon. Lasted from 2.5 Ga-545 Ma. During this eon, the atmosphere became oxygenated, there were several glaciations, and the first eukaryotes evolved represented by the Ediacaran Biota. The name Proterozoic means “before life” because initially, fossils hadn’t been found until the Cambrian Period.

The last eon which we are currently in is the Phanerozoic Eon. It means “visible life” which makes sense as most living organisms have existed within this eon.

Okay, eons make sense? Excellent. Eons are broken down into eras. Now the Hadean is not broken into eras simply because the only evidence of this eon are detrital zircons in Australia.

The Phanerozoic Eon is the current eon and most of you are probably familiar with its eras: The Paleozoic Era, the Mesozoic Era, and the Cenozoic Era. These names mean “old life”, “middle life”, and “new life” respectively.

Eras are then split into periods. Like the Hadean before it, there isn’t enough evidence to split the Archean eras into periods. Again, we will use the Phanerozoic eras to show the break down starting with the Paleozoic.

The Paleozoic Era is split into six periods: the Cambrian Period,

the Ordovician Period,

the Silurian Period,

the Devonian Period,

the Carboniferous Period

and the Permian Period.

These will be discussed in more detail later on down the road. I have already made posts on the Cambrian and the Ordovician Periods and this month is all about the Silurian Period.

The Mesozoic Era is split into three periods of which most people know the names: The Triassic,

the Jurassic,

and the Cretaceous Periods.

Each of these will be discussed in detail further down the road as well.

The Cenozoic Era is also split into three periods: The Paleogene Period,

the Neogene Period,

and the Quaternary Period.

These will also be discussed in detail later.

Periods are further broken down into epochs. There are no formal epochs outside of the Phanerozoic Eon. Some early Paleozoic periods also do no have formal epochs. Many such as the Triassic and Jurassic Period are split into Early, Middle and Late. Strangely, the Cretaceous is only split into Early and Late though I think an argument could me made to create a middle.

The most well-known epochs are those of the Cenozoic Era. The Paleogene Period is split into three epochs: the Paleocene Epoch meaning “old dawn”,

the Eocene Epoch meaning “dawn”,

and the Oligocene Epoch meaning “few new”.

The Neogene Period is split into two epochs: the Miocene Epoch meaning “less new”

and the Pliocene Epoch meaning “more new/recent”.

The Quaternary Period is split into two epochs as well: the Pleistocene Epoch meaning “most new/recent”

and the Holocene Epoch meaning “whole new” and is the epoch we are currently in.

Epochs can then be broken down into still smaller categories called ages. For example, the Late Jurassic Epoch is broken up into three ages: Oxfordian Age, Kimmeridgian Age and Tithonian Age.

Now let’s put all these, eons, eras, periods, epochs, and ages into perspective. Let’s pretend Earth’s current lifespan is a clock. At 12:00, the Earth’s crust forms (Hadean Eon). At 2:10, the oldest rocks are preserved (Archean Eon). At 3:17, the first bacteria appear (Proterozoic Eon). At 11:52, the Cambrian Explosion occurs. At 11:53, first plants and fish. 11:54, first insects. 11:55, first reptiles and amphibians. 11:56, Mesozoic Era begins. 11:57, first dinosaurs, mammals, and birds. 11:59 Cenozoic Era.

Need a different visual? Try a calendar. The Hadean starts in January and ends halfway through February where the Archean picks up. The Archean lasts until halfway through June. From there, the Proterozoic starts and doesn’t end until about Thanksgiving. The Paleozoic Era then goes until about a week before Christmas. The Mesozoic covers Christmas to the December 30. New Year’s Eve represents the Cenozoic Era.

Thanks for coming to this lesson and make sure to tune in tomorrow for some fun trivia! Fossilize you later!

Here the result of tonight's formation stream! Corral Bluffs is a locality of the Denver formation that has become more and more important in recent years as it has yielded a huge number of important fossils that were deposited not even a million years after the K-Pg extinction.

Especially the mammals, some of them larger than expected, are preserved from complete skulls and show a surprising diversity. Central to the composition here is Taeniolabis, the largest known multituberculate. I chose to show the scene here by night for several reasons.

First of I think that only because the non-avian dinosaurs were gone, animals didn't start to be more active during the day right away, some of these forms were still quite similar to their Cretaceous ancestors. Secondly, we have no birds from here (so far), the branches and the sky would be empty

(art by Patrick Lynch of Yale University, taken from here)

TIL that this little guy, Purgatorius, who lived in North America (specifically, Montana and Western Canada, along the foothills of the recently-formed Rocky Mountains) from just over 100 thousand years after the non-avian dinosaurs died out until about 3 million years later, is generally considered to be the oldest known primate