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Re: the start
> ... Was there a bunch of
> little lizards of various types that just got so competitive that
> only the bigger and bigger and bigger survived? Were these little
> lizards (if there were any) some kind of fish turned land animal?
> Or did the dinosaurs develop first in the water and arrive on land
> big already?
This is a more complex question than it might seem at first.
(At least the whole question).
For one thing, dinosaurs were not universally large. They
covered the whole range of sizes. The large one probably evolved
that size for much the same reason as large mammals evolved,
escape from predation and/or access to new food resources
(including the ability of carnivorous forms to eat the large
The lineage containing dinosaurs split off from that leading to
lizards and snakes a good long time before the dinosaurs evolved.
This lineage, called the archosaurs (or, by some, the archosauro-
morphs), also includes rhynchosaurs, thecodonts, crocodiles and
alligators, and pterosaurs.
The more or less direct ancestors of most of these groups fall
within the group called the thecodonts. The earliest thecodonts
are called proterosuchians, meaning "first crocodiles". They
were apparently semi-aquatic carnivores, similar in life-style
to the living crocs, but differing in appearance.
Some of the descendents of these forms switched to acting
as terrestrial carnivores, and adapted (gradually) an improved
leg joint arrangement that allowed a sustained erect posture,
and thus more efficient land locomotion. At some (aribtrary)
point one of these improved terrestrial lineages reached a
point that we call them dinosaurs. Closely related to the
dinosaurs were the flying reptiles, or pterosaurs.
Also descended from the proterosuchians are the phytosaurs,
and several other thecodont groups (such as the pseudosuchians,
or "false crocodiles"). From this group evolved the true
The peace of God be with you.