Graboid - Origins

Origins

• The graboid's evolutionary origins are intentionally kept very vague; the creators of the film were unconcerned with this detail, offering no explanation as to where the graboids came from in the original film, (wanting to avoid the typical clichés of the monster movie genre.) The main characters even satirize this convention by attempting to guess where they came from- outer space, nuclear mutations, genetic engineering and prehistory are all offered up as possible explanations.

• The answer was revealed in Tremors 2, when a fossil graboid spike was discovered and dated back to the Precambrian, making it at least 600 million years old- the graboids are apparently from earth, or have at least existed on earth for a very long time. Strangely, no prey large enough for graboids to eat had evolved yet at the time; in fact there was no life on the land at all, and most of the land was composed of bare rocks. A write-up written by the SciFi channel for Tremors: The Series retconned this by saying the fossil was incorrectly dated and actually from the Devonian period. By that time, prey big enough for graboids to eat had evolved (amphibians), though they don't rule out a possible extraterrestrial origin.
• Whether the subimago Shrieker and imago Ass-blaster always hunted using infrared or whether this is a more recent adaptation is unknown, although in either the Precambrian or Devonian periods there would've been a complete lack of warm-blooded prey.
• It is unknown if the imago and subimago forms were always part of the graboid life-cycle or if they are the result of becoming reproductively bound with another species, but the distinctly vertebrate-like appearance of the subimago and imago stages and apparently invertebrate nature of the larval stages would seem rather difficult to explain otherwise, save perhaps as being basal pre-vertebrate chordates whose metamorphosis loosely resembles their evolutionary history, much like the larval stages of amphibians resemble fish.