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Re: parthenogenetically derived reptile offspring
It may also have been an inherited characteristic from the beginning
of the origin of life. The missing link here (excuse the pun) is
recognizing that many, many primitive (poor term) organisms exhibit
parthogenesis. If parthenogensis is an independently created (on the
tree) characteristic that was/is replicated numerous times across
(parallel evolution) widely diverse and unrelated species, the
discussion may be weighted heavily in favor of it being a very early
ability indeed. This does seems to be a trait which is shared by
many "simple" organisms (excuse the term please) AND is even
exhibited in more further derived (more distantly related??) forms.
This is highly suggestive of an origin (in the code) much earlier in
life's lineage. This may simply show the selective pressure that
recreates the genetic expression of the ability at "will". Knowing
the tree's branching exact point may not be the issue because it may
be a trunk thing. Recognizing that many many simple forms exhibit
this trait is highly suggestive how far back it originated in the
tree life. This is useful by creating the inference that once it is
in the code, it can be expressed at the first need given the right
circumstances. Many very simple forms use this kind of reproduction
and obviously several highly derived forms are capable of expressing
the old genes. My overly belated point is, once a trait is in the
common shared genetic code, the ability exists in all species from
the original lineage whether it is ever expressed or not.
(self censored discussion of human parthogenesis 2000 years ago)
There is every reason to suspect that some dinos had the ability
though it will be pretty hard to prove since as any kind of shotgun
gene sequencing (do a google on that term!) isn't going to happen on
material that old. The statistical probability of successful virgin
egg drop in dinos over the millions (and millions) of generations of
thousands (and thousands) of different forms is huge. Taking into
account the sheer diversity in the lineage, the absolutely huge
number of individuals/forms involved and the propensity of somewhat
related species having the characteristic also has some bearing on
the discussion. The amount of time involved during the reign of the
dinosaurs alone is staggering. Talk about opportunity for evolution
to experiment. (and it did!)
Vertebrates certainly show a wide variety of abilities for sex-
determination mechanisms. In crocs, temperature is the determining
factor, some fish can morph mid-stream (no pun there!) from female to
male or vice-versa. The fact that many forms have "done it" via
parthogenesis is highly suggestive that other related forms have or
have had the ability. One certainly should not dismiss the
possibility. Absence of evidence is not evidence of absence
especially in a world where two headed fossils are just being found.
Uniformitarianism is alive and well.
It all may boil down to that Christmas turkey (no wait, ..... turkeys
have been parthogenetic too). Modern avian theropods...... Goes to
show that turkeys are so ugly that the only way some of them can
reproduce..... Too much caffeine!
Happy Holidays all on the DML...
Frank (Rooster) Bliss
On Dec 23, 2006, at 6:01 AM, David Marjanovic wrote:
Concerning parthogenesis and dinosaurs, the case of the turkey
would be more relevant. There is a domestic breed of turkey ( I
could look up the name somewhere but I'm too lazy to do it right
now) for which parthogenesis is a very normal or even the default
way of conception.
Really? I've heard of a case, but (as in the Komodo monitor) all
offspring of parthenogenesis in birds are automatically male and
can't repeat the trick.
I don't know how this has come to be; but nevertheless, it shows
the capacity for parthogenesis exists in the dinosaurian line.
We don't know where in that branch of the tree it evolved...