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Re: Time Line



From: Scott <HORTON@bcrssu.agr.ca>
 > 
 > Can someone define some of the terms posted in the last Time Line?
 > 
 > > Last of the Pteridosperms

Pteridosperms = "seed ferns", the earliest group of seed plants.
This is a paraphyletic group since angiosperms and all extant
groups of gymnosperms are evolved from this group.

In general they looked like ferns but had true seeds instead of
spores like true ferns.

 > > First appearance of angiosperms
 >   (flowering plants?)

Yes, angiosperms are flowering plants.

Gymnosperms are non-flowering *seed* bearing plants, including
conifers (pines and relatives), cycads, and a few other obscure
groups.

 > > First placental animals
 >   (a specific subset of mammals?)

Yep, those mammals that, like us, give birth to live young at
a relatively advanced stage of development.  This is possible because
of a special tissue attaching the embryo to the uterus allowing
food and oxygen to be exchanged.  This tissue is called a placenta,
whence "placental".

The other living mammals are marsupials, which give birth to live
young at a very early phase of development and finish rearing them
in a pouch, and monotremes, which lay eggs.

 > > First Teleosts

Bony fish - pretty much all familiar fish except sharks and rays.

 > > First rudists

An early group of corals, rather different than the living hexacorals.

 > > First globigerinas

A group of giant shelled amoebas - a subgroup of the foraminifers.

 > > First grazing echinoids

Echinoids are starfish, sea-lilies, sea-cucumbers, sea-urchins
and so on.  The earliest ones were rather like sea-lilies, and
probably were what is known as filter feeders (a "passive" sort
of feeding).  Later forms, including most living forms, use a
more active form of feeding, involving searching for food - that
is the "grazing" forms and the even more derived carnivorous
forms, such as starfish.

[Ack, or are echinoids a *sub*group of the echinoiderms??].

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.