The topics is snakes.
What is the earliest known snake fossil? How old is it? What do we know of it?
What is the earliest known snake fossil believed to be poisonous?
What is the largest known fossil snake? Does it exceed the Anaconda in size?
Finally, is there any fossil record of a herbivorous or ominivorous snake? I know that all modern snakes eat meat or insects.
Here
Astro’s link seems to run together a whole conglomeration of information about snakes and their ancestors.
Michael J. Benton’s Vertebrate Paleontology, 2nd edition (1997), indicates that snakes are known from the Early Cretaceous onwards, and are believed to have been derived from a lizard line, but with no clear evidence of that ancestry. The early forms appear to have been boids (boas and pythons) which killed by constriction, causing death by asphyxiation. Interestingly the evolution of the snakes parallels that of the mammals, which appear to have been their main prey throughout their evolution.
The forms injecting poison by fangs seem to have originated in the Late Eocene.
The largest modern pythons and anacondas are up to seven meters in length. (Measuring dead snakes is problematical owing to the elasticity of skin and skeleton: stretching them to “full length” gives them a length in death that they never possessed in life.) The size of a vertebra obtained from the Paleocene of North Africa suggests its bearer was nine meters long in life.
Snakes are highly specialized for killing prey of half to two-thirds their own size and swallowing the corpse whole. I found no evidence of any significant divergence from this specialization. A few small families have specialized for the eating of fish, snails, or eggs respectively, though.
Snakes are Suborder Serpentes (or Ophidia) of Order Squamata (also including the lizards) in Superorder Lepidosauria (which adds in the tuatara and its extinct relative and the extinct pleurosaurs). This in turn is in Subclass Diapsida, which includes most reptiles, excluding the turtles and a few extinct relatives and also the mammal-like reptiles of the Permian and Triassic.
There are 11 families of snakes in 3 superfamilies:
Superfamily Typhlopoidea
– Family Typhlopidae (the primitive blind snakes or worm snakes)
– Family Leptotyphlopidae (the slender blind snakes)
Superfamily Booidea
– Family Aniliiadae (one South American genus)
– Family Xenopeltidae (the sunbeam snakes of India)
– Family Uropeltidae (shieldtail snakes of South Asia)
– Family Boidae (boas and pythons)
– Family Acrochordidae (the wart snakes of Australia and Indonesia)
Superfamily Colubroidea
– Family Colubridae (the common non-poisonous snakes of Europe and North America, among others)
– Family Viperidae (vipers, rattlesnakes, moccasins, etc.)
– Family Elapidae (cobras, mambas, the coral snake, and numerous poisonous Australian forms)
– Family Hydrophiidae (sea snakes, tropical and subtropical Pacific and Indian Oceans)