[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
--- Aegyptiacus@aol.com wrote:
> Dear listmembers
> I've seen in a cladogram that amniotes where at the base of sauropsids and
> synapsids. What evidence is there that it (the amniotic egg) didn't appear
> before within the reptilomorph lineage (eg seymouriamorphs or anthracosaurs
> or embolomeri)?
Sauropsids and synapsids *are* amniotes.
Clade _Amniota_ is not defined by the presence of the amniotic egg, which would
be near-impossible to determine in certain forms. Instead, it's defined as a
crown clade (a node-based clade anchored on extant specifiers). You could
define it thusly: "The last common ancestor of _Homo sapiens_ and _Lacerta
agilis_, plus all descendants." (Or select other specifiers.)
Doubtless the first amniotic egg did appear sometime before the first amniote
=====> T. Michael Keesey <email@example.com>
=====> The Dinosauricon <http://dinosauricon.com>
=====> BloodySteak <http://bloodysteak.com>
=====> Instant Messenger <Ric Blayze>
Do you Yahoo!?
U2 on LAUNCH - Exclusive greatest hits videos