they weren't lizards. they were megafauna, large birds and various kinds of large leaf and grass eaters. and they were buried under the tsunami floods of the global geomagnetic pole shift disaster 12000 years ago. the great canyon? yeah, that was formed during that flood too.
it's an important distinction that is not so well understood, the difference between igneous and sedimentary rocks. the first is rock, hard aluminosilicates with various other minerals, like iron, magnesium, chromium, vanadium, etc, and then when those break down into soil, what happens is when there is a massive amount of water washing away the dirt, it falls into the low lying parts of the landscape and packs down, the weight so enormous that all of the water is driven out, and stuff like calcium glues the dirt together.
all of the dinosaurs were found in sedimentary rock in low lying areas, and they were drowned and covered in megatons of this mud and this is how any part of them survived. most of the soft tissue oxidised and the CO2 leeched upwards but the bones especially remained.
thus, most of the "dinosaurs" all they are working on is bone structures, sometimes horn (keratin). very little skin or internal organs was found in anything, but more recently some examples have been found of fragments of feathers and hide and fur.
and no, it wasn't goddamn comets or asteroids, though those tended to follow up the geomagnetic disaster due to the amount of material thrown out in the micronovas and superflares of these disasters, later. like 10,000 years ago, there was a mini ice age, and the impactors actually ended this with a massive addition of heat from the kinetic energy of low angle impacts that soared across the sky like fire dragons, instantly carbonising everything underneath.
the volcanic and seismic and cloud formation activity dramatically increases during a magnetic field flip and these tend to trigger glaciation periods. this is also why there was a cold period around 6000 years ago, most likely in that case the disaster was a lot milder.
there is cave paintings in bulgaria, in the Magura caves, that i strongly suspect are depictions of the epic, country-spanning massive electric discharges that are called "cosmic thunderbolts". similar symbolic depictions of these have been found all across the world dating to that same 12-10,000 years ago period. those are the most frightening thing, really, in all of it. once the earth's new magnetic alignments settle down, they stop, but we are likely to see these start to rise. there was a record breaking lightning strike recently that had a duration of over 9 seconds. can you imagine, 9 seconds the sky is arcing to the ground... imagine how much electricity that is. then multiply that by a million to understand what a cosmic thunderbolt is.
