I state points in prehistoric times for a good reason.  There is a myth of a vague “primeval time” when everything one knows about lived at the same time.  Then I mean different animals, larger than current ones and more or less strange.  Moreover, cavemen are supposed to have lived at the same time as them.  Common ideas of cavemen are themselves outdated.  For example, it was never that common for people to live in caves.

The truth is the Earth’s history stretches over thousands of millions of years.  Just the time with visible life covers hundreds of millions of years.  People have hard to imagine there being such a long time-span.  However, we can at least keep track of which orders of magnitude it is about.  We can also make an effort to keep track of in what order things have happened.  Oftentimes an event presupposes another event to have already taken place.  Then we can in a way get a grasp on geologic time.

The last 635 million years is divided in 12 periods.  Each one of them lasted for tens of millions of years.  The exception is the last period which has been measured to 2.58 million years.  The human genus is just a little older than that.  Then I am talking about Homo habilis, which it can be discussed if they should be considered people.  In contrast I see Homo erectus as this.  All species descended from this one can be considered this too.

There is very much which can happen over hundreds of millions of years.  The result is that well-known animals did not all live at the same time.  In many cases it was not possible for them to do that.  Large dinosaurs filled the same niches as large prehistoric mammals.  They could very well have done so in the same part of the world.  I don’t think ecology allow such animals to coexist during any longer time.  Neither is the result of evolution static.  Some animals may change anatomically relatively little over millions of years.  But these are not the same species as existed millions of years ago.

All dinosaurs did not live at the same time.  Dinosaurs divided from crocodiles 249 million years ago.  This gives 183 million years before the mammals could take over.  No more or less warm-blooded genera exist for anywhere near that long.  Consequentially, there were many groups of different types of dinosaurs succeeding each other.  Some survived longer in another part of the world.  However, these were as mentioned not the same species.

A few other examples of famous prehistoric animals:

• Trilobites were a type of arthropod vaguely resembling woodlice.  Their name comes from their upsides being divided in three along the length.  They existed in different varieties all the way from the Cambrian to the Permian.  This means the group existed for 269 million years.  During hundreds of millions of years many different subgroups must have appeared and disappeared.

• Griffenflies seems to have been the only insects reaching giant size.  They existed in the late Carboniferous and during the entire of the Permian.  Like present-day dragonflies they likely ate smaller animals.  The largest known species had a wingspan of 71 centimetres (28 inches).  Due to decreased fraction of oxygen they would not have been able to breath in today’s atmosphere.

• Sail-backs actually consisted of two groups.  The genera Edaphosaurus and Dimetrodon both evolved spine sails independently of each other.  I think it was for attracting mates.  The difference was in their diet.  Edaphosaurus was herbivore while Dimetrodon was carnivore.  Both lived partially at the same time during the first half of the Permian.  They were outcompeted by proto-mammals which had evolved higher metabolism.

• Ichthyosaurs were the Mesozoic equivalent of toothed whales.  They were contemporary with the dinosaurs although they died out before them.  Their origin is unclear but it is still clear they descended from quadrupeds.  Several evidence indicate they were warm-blooded.  The earliest forms of ichthyosaurs already had higher metabolism.  Their adaption to water was so high they must have arisen in the late Permian.

• Plesiosaurs were completely aquatic predators.  They and similar short-necked animals were contemporary with the dinosaurs.  Towards the end of the age of dinosaurs these replaced the ichthyosaurs.  Like for the ichthyosaurs their origin is uncertain.  Were they most closely related to turtles or to lizards and snakes?  The indicators of their metabolism are moreover ambiguous.

• Glyptodonts were gigantic armadillos which were herbivorous or omnivorous.  They somewhat resembled ankylosaurs which may have made some to mix them up.  This is like mistaking Triceratops for a present-day rhino.  Glyptodonts lived after the dinosaurs in the age of mammals.  The last glyptodonts were partially contemporary with humanity.  To me it appears sensible humanity wiped them out.

Neither is the vegetation something which always existed.  Vegetation on land first arose in the middle of the Ordovician.  Then it was a matter of mosses and lichen.  Lycopods and later ferns arose during the Devonian.  Through their well-developed roots vegetation could spread more.  At the transition Devonian ‒ Carboniferous wind pollinated plants with seeds arose.  This applies to both herbs, shrubs and trees although the herbs are now extinct.  They have been outcompeted by flowers which arose in the early Cretaceous.  Grasses existed from the middle of this period.  However, they did not become particularly common until after the mammals took over.

Finally, I want to point out that all can’t be found everywhere.  Different life-forms are adapted to different environmental conditions.  Everywhere this applies to temperature and the degree of seasonal difference.  In water light levels, pressure and salinity matter.  For stationary life-forms on land the soil’s characteristics matter.  All life on land is affected by the access to water.  Such factors set limits to how far life-forms can spread.  The opportunity to spread to a certain specific area can’t be taken for granted.  Does it not exist the life-form will not be indigenous there.  For example, deer are not indigenous to Sub-Saharan Africa.  There several groups of bovids has occupied their niche.  The same kind of limits has applied in prehistoric times too.

 

Uploaded on the 13th of June 2024.