Cosmic Calendar: The first reptiles and the first trees

December 23rd on the Cosmic Calendar: The first reptiles and trees, sort of.

In researching the first trees of the carboniferious period, I discovered new information about trees that grew as early as the devonian period.  Which means ideally I’d have posted about the first trees 2 days ago, on December 21st.  Oh well.  Figuring out exactly when these firsts were is a moving target as new discoveries are continually made.

The currently earliest known trees were Wattieza in the middle devonian period — December 21st on the Cosmic Calendar.    They’re related to modern ferns and reproduced with spores instead of the yet-to-evolve seeds.



Ok, back to the carboniferous and the first reptiles!  The earliest known reptile is Hylonomus.  Hylonomus was an 8 inch (20 cm) long lizard with tiny teeth, the better to eat bugs with.  The main differences between reptiles and the amphibians they evolved from are scales and egg shells.  Generally speaking even today amphibians cannot stray too far from the water’s edge because their skin dries out so quickly.   The development of scales which keep moisture in solved this problem and let reptiles roam farther to hunt.  Likewise egg shells did the same for their eggs.  Amphibians need to lay their eggs in water.  Like fish eggs they do not have shells, and would dry out long before hatching if left on land.  Egg shells solved this problem, again by holding in moisture.  As reptiles vertebrates were finally freed to really conquer the land!



By the Permian period our ancestors like Hylonomus had evolved into the mammal-like reptiles, the Synapsids and Therapsids.

Dimetrodon, everyone’s favorite synapsid!

These are not dinosaurs.  Dinosaurs are yet to come from a separate line of reptiles.  These are our ancestors, dinosaurs are not.  Synapsids have jaws and teeth like mammals.  Canine teeth, molars, and incisors — just like us.  Synapsids dominated the Permian, enjoying their moment in the sun before being overshadowed by the dinosaurs.  By then synapsids will have evolved fur and shrank to the mouse-like mammals we usually think of hiding in the shadows from dinosaurs.  But Dimetrodon here was 5 to 10 feet (2-3 meters) long and is more like modern mammals than modern reptiles.  In the same sense that birds can be considered dinosaurs, mammals, including ourselves, can be considered synapsids.

Therapsids are another group of synapsids from later in the Permian.  Therapsids are even more like mammals:

Biarmosuchus, a Therapsid. Nice doggie!

Therapsid Inostrancevia in the middle, flanked for scale by a person and smilodon, the famed “saber-tooth tiger”

Oligokyphus, a therapsid cynodont

You may remember Cosmos, the 1980 PBS series by Carl Sagan. Maybe you also recall Sagan’s “Cosmic Calendar” from the series, where in order to put the immensely vast history of the universe into a comprehensible scale, he mapped it onto a calendar year. In other words, if the entire history of the universe were one year, with the big bang in the first second of midnight on January first, and the present day on the last second of December 31st, New Year’s Eve. A project of mine this year has been to note the major events in the Cosmic Calendar, on the real calendar, on this blog!


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