wow.
Originally, the tyranids and genestealers were two different races in
40k. the genesteales were based of of the "fluf" of the "Aliens" cannon, about absorbing the genetic material of a host organism to reproduce,hence hybrids. In the original artwork, there was no head, just a gaping maw with feeder tendrils. there was not much spimilarity with Gieger's phalic designs.
here is the first description of a tyranid:
"They have evolved over countless millennia within the hive fleets. They are centauroid in appearance, with six spindly limbs. The rear limbs have webbed appendages which serve as both hands and feet, helping to stabilize the creature in the lo-gravity of the hive fleet shifts. The frong limbs are manipulative, having double thumbs, while the middle limbs are hooved and from the primary locamotive limbs." The accompanying picture very closly resembled the current gaunt holding a flesh bore. The tryand range was then expanded with the tyranid warrior (as can be seen here
http://www.solegends.com/citcat9x3/c92399tyrwarriors-01.htm)model as well as the "screamer killer" carnifex. I prefer the second sculpting they made however;
http://www.nugax.com/WH40K/Warriors.html. It was around this time that
GW made Hive War for Epic, which most of the curent unit types of the tyranid race were introduced, esp monsterout creatures and bio-titians.
http://wh40k.lexicanum.com/wiki/Hive_War
I would have to venture that the tyranids are pretty much
GWs original concept/ IP, and it is more likely that starcraft stole the zerg from
GW.
If anyone has a copy of the 2nd edition tyranid codex, it would be extremly helpful to this discussion.