A TIMELINE FOR THE PLANET
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The strange
Triassic animals
During the Triassic, dinosaurs and primitive mammals
were beginning to appear. Flying reptiles ruled the skies.
early mammals
The Triassic lasted from 245 to 200 million years
ago. It began with the ‘the Great
Dying’, the worst mass extinction since the Cambrian explosion (more).
And it ended with another lesser extinction. The great supercontinent of Pangaea was beginning to break up. And, whatever the space aficionados may say,
plate tectonic upheavals seem to have been the cause of both extinctions.
When conditions recovered, much of the planet was
empty and waiting for the few species that survived to expand into it. They did, and they developed in all sorts of
strange ways. It took them a while. All the creatures I’ve been able to find seem
to come from the late Triassic.
Pangaea extended from pole to pole. And whereas the climate over most of it was
hot and dry, the
Very few fossils have come down to us from the
Triassic Period. For a long time, the
only thing that palaeontologists had to go on was a few teeth and the
occasional identifiable bone. The teeth
in particular looked very much like dinosaur teeth. So in strict accordance with ‘Occam’s Razor’
(“always take the simplest explanation that fits the facts”), the creatures
were identified as primitive dinosaurs.
And the story was put about that the Triassic was the age of the early
dinosaurs.
Then complete skeletons started to emerge. And they weren’t dinosaurs at all. To be sure there were a few genuine early
dinosaurs among them. But this was the
age of a wide range of weird and wonderful animals, most of which died out in
the extinction that brought the Triassic to a close.
Wikipedia gives a comprehensive account, quoting all
sorts of strange names. We’ll confine
ourselves to a couple of main storylines.
The ‘crocodilians’ (crocodiles to you and me) were one
of the species that survived the second extinction. From what we’ve said about the climate, we
must imagine them mainly occupying the
Apparently so.
But palaeontologists had to study complete skeletons in great detail to
reveal their crocodilian nature. You or
I would never have guessed it in a million years. And as long as they had only a few teeth and
the odd bone to go on, neither could the palaeontologists!
Actually, if you look carefully at the skeleton, you
will see that the way its legs are attached is a bit weird. We discuss elsewhere
how amphibians had to stop ‘waddling’ before they could be regarded as true
land animals. The creature that provided
this skeleton may have been basically a crocodile. But it was clearly on its way towards being
able to walk properly.
And it all makes sense. These creatures were the forerunners of both
the dinosaurs and the mammals. The
aggressive-looking creature above (copyright Joe Tucciarone) may look like a
dinosaur. But in fact he’s Postosuchus
or ‘post crocodile’. He lived in the
late Triassic, some 220 million years ago, and weighed nearly a ton.
According to Wikipedia, these crocodilians were the
forerunners of the pterosaurs, or flying
reptiles, as well. The creature on the
right is an ornithoderan. These
apparently evolved into the pterosaurs “and a variety of dinosaurs”. Does this imply that other dinosaurs had
different roots? I can’t tell you.
But
all this was news to me. Other sources
have suggested that the flying reptiles appear in the fossil record quite
suddenly and already fully developed.
Hopefully the answer is that these other sources are out of date.
As we’ve mentioned, there were early dinosaurs around
too. This one (also copyright Joe
Tucciarone) is Chindesaurus. He’s a
primitive theropod, and also lived in the late Triassic. The theropods are widely acknowledged to have
been the ancestors of birds. And by adorning his specimen with bright
colours, Joe is suggesting (I think) that the theropods may have been sporting
feathers even as early as this.
Certainly signs of feathers have been found on theropod fossils from
long before flying was even on the horizon.
They may have been found on other dinosaurs too. I’m not too clear about this. Feathers are an excellent way of keeping cool
when it’s hot, and warm when it’s not.
And if you want to adorn yourself with bright colours, then feathers are
the way to go.
Early mammals
Primitive
mammals appeared at about the same time, though I’m not sure where they came
from.
But here’s an interesting thing. The dinosaurs and the birds kept the
reptiles’ not-very-good lungs. And at
some point they added to supercharger to it (more)
which is why modern birds have far and away the best breathing system on the
planet. We mammals evolved our own lung
system, which is much better than reptilian lungs. But it’s not a patch on those of birds.
The early mammals were about 10 cm long and ate
insects. They quickly evolved the
ability to provide milk for their young.
This enabled them to look after their babies much more effectively, and
enabled them to be born less developed.
The early mammals are also thought to have been mostly
nocturnal, which kept them out of the way of the reptiles and dinosaurs.
This is the only authoritative picture I’ve found so
far of a Triassic mammal. It’s a bronze
sculpture of Megazostrodon, from the 
According to Wikipedia, Megazostrodon is widely
accepted as being one of the first mammals, appearing in the fossil record
around 200 My. It had a few
non-mammalian characteristics, and is likely to represent the final stage of
the transition between ‘cynodont’ or mammal-like reptiles and true mammals.
Megazostrodon was a small furry shrew-like animal,
between 10 and 12 cm long, and it lived from the late Triassic to the early
Jurassic. It had a much larger brain than its cynodont relatives. And the enlarged areas were those that
process sounds and smells. This
reinforces the theory that it was nocturnal.
Wikipedia also offers us this picture of
Tricodonta. Note the ‘a’ on the end of
the name. Tricodonta is not a single
animal. It represents a group of early
mammals. Unlike Megazostrodon, the
Tricodonta had all the features of true mammals. Their line lasted from the late Triassic to
the late Cretaceous.
The name means ‘three conical teeth’, which is a
feature that they all shared. They
probably lived on small reptiles and insects.
However some of them appear to have been able to take on small
dinosaurs.
Triassic Plants
Several important plants survived both extinctions,
yielding descendents that are still around today. Wikipedia gives us the cycads, the ancestor
of the Ginkgo biloba and ‘the’ Spermatophytes or seed plants. In the northern hemisphere, conifers also
flourished, whereas the seed ferns preferred the south.
Triassic marine
life
Wikipedia implies that modern coral first appeared in
the Triassic, though that may not be what they actually mean.
Very few fish lines survived the Permian extinction,
so the fish fauna was very uniform and boring.
That’s not to say that they weren’t plenty of them 
though. And there were many types of marine reptiles
to feed on them.
Perhaps the most famous of the Triassic marine reptiles
are the ichthyosaurs. This picture, from
UCMP Berkeley, is of an early ichthyosaur, from the Triassic. Later they developed into superb swimming
machines, looking for all the world like dolphins. But dolphins are mammals, and the
ichthyosaurs were reptiles.
This similarity represents a superb example of
‘convergent evolution’. There’s possibly
only one way to design a really-good fast-swimming predatory sea creature. And the marine reptiles, and
later the marine mammals, gradually homed in on it.
© C B Pease, February 08