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From: Tracy Monaghan <firstname.lastname@example.org>
> I'm always getting my Triassic mixed up with my Cretaceous, and don't
> have a clue when Carboniferous fits in (if it does).
The Mesozoic Era, which is what is relevant to dinosaurs,
consists of the Triassic, Jurassic, and Cretaceous Periods,
in that order.
I am a little fuzzy on the dates, but I believe the Triassic
starts at about 240 million years ago, the Jurassic at about
195 million years ago. and the Cretaceous at about 115 million
years ago. (My exact references are at home).
The Cretaceous, and thus the Mesozoic, ends at 64 to 65 million
> This may be more of a lurker question, but a (brief) geologic time table
> would help me.
Ordovician (see below)
Silurian (or these two are switched - gack)
Holocene (= Recent)
> A summary of (major) extinction periods would be nice.
The biggies are: end Devonian, Permo-Triassic, Cretaceous-Tertiary,
and two more that I always get mixed up on.
> What does the K-T in K-T boundary mean?
Kretaceous-Tertiary, that is it is an abbreviation of the
statement that the extenction marks the boundary between the
Cretaceous and Tertiary periods.
> Were there other creatures besides dinosaur running about during the "Age
> of Dinosaurs"?
Lots. Dinosaurs had a "lock" on most of the large land animal niches,
but other niches were filled by other things.
Mammals were quite prominant in small animal niches, especially
in the Cretaceous. There were insectivores, granivores, foliovores,
and even small carnivores amoung the Cretaceous mammals.
Also common in the Late Triassic, Jurassic and Early Cretaceous
were "flying reptiles", or pterosaurs, which are not actually
dinosaurs, even though closely related to them. The known forms
of pterosaurs are mostly lake-side and beach specialists, but this
is probably due to bias in the fossil record. They probably covered
much of the range of modern birds in ecology. There were certainly
pterosaur "flamingos" and "pelicans" and "condors".
Crocodiles have been around as long or longer than dinosaurs,
and the largest animal at the very end of the Cretaceous was
probably a crocodile, not a dinosaur. I am talking about
Deinosuchus, the 50 ft crocodile of the Lance and Hell Creek
Formations in the USA. The only Maastrichtian dinosaur that was
larger than this was the last sauropod, Alamosaurus, which may
have died out well before the end of the Cretaceous.
[Maastrichtian is the name of the last short piece of the
Cretaceous - the last half of the Maastrichtian is also
sometimes called the Lancian].
By the Late Cretaceous, birds were starting to get diverse,
though the details are fuzzy because the fossil record of
birds is abysmal (probably even worse than the fossil record
In the seas there were plesiosaurs (long necked sea beasts),
ichthyosaurs (the reptilian equivalent of dolphins), mosasaurs
(giant marine lizards), shelled ammonites (relatives of the
living chambered nautilus) and oodles of fish, and much more.
> What came before dinos, et. al.?
Many things. The immediate ancestors of the dinosaurs are often
called "thecodonts", and were a moderately diverse group of
strange beasts. They were mostly carnivores, but a few were
herbivores. Some of them were four-legged armored animals,
like heavy crocodiles. Some were large, fast carnivores, many
were small bipedal, or nearly bipedal carnivores. Also
derived from this group were the early terrestrial crocodiles,
and the pterosaurs.
This is only a sketch, the full diversity of any time after
the Carboniferous is quite high, and cannot be easily summarized
in just a few pages.
The peace of God be with you.