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Re: Sex

  Here's a couple more options. In general, dinosaurs would be internal
fertilizers that face the bulky-tail-in-the-way problem, complicated
further in some species by the spiny-back problem. These problems are not
unique to dinos. Extant animals with these problems solve them in a
variety of ways:
  (a) male stands bipedally or even bent over backwards a bit. Female
crouches way down in front, elevates her butt, arches her tail as much as
she can - usually at least getting the tail vertical. The male
does not drape himself over the female in classic horse-style, but stands
well back, balanced on hind legs, sometimes using front legs lightly on
the female's sides for balance.  Porcupines for example.  (Another animal
that does this is the spotted hyena - a tricky proposition because the
vaginal entrance is in a pseudo-penis between the female's legs, requiring
some acrobatics on the part of the male.)
  (b) male and female stand at angles, even right angles sometimes. Male's
tail is under female. Male may lie down. Male curls around female in a
doughnut-shape, often biting her neck (for balance?), lifting one hind leg
and twisting his pelvis. The bases of both tails come close together. Male
bridges the short remaining gap with whichever or his two hemipenes/
claspers is closest to the female.  (Lizards & sharks, for example)
  (c) male walks ahead of female, drops sperm packet on ground. Female
comes along behind, sniffing the ground. When she finds the sperm packet
(spermatophore) she lowers her vent and picks it up. (Salamanders.
A very clever solution - internal fertilization without copulation!)

  And of course, external fertilization is highly unlikely for dinos
because in amniotes, the sperm must reach the egg cell (the yolk) *before*
the egg white, membranes, and shell are laid down.  (The white, membranes
& shell are key for the egg's survival in a terrestrial environment).
Since the white, membranes and shell must be laid over the egg cell in
the female's oviduct, the sperm must reach the egg when it is higher up in
the oviduct. Hence internal fertilization.

Just some thoughts from the extant world,
Kathleen Hunt
U. Washington