The onondaga contains an abundance of coral fossils, along with crinoids, brachiopods, and trilobites. Why are fossils of ferns, rushes, and primitive conifers unlikely to be found in these rocks

Due to presence of water in these rocks.

Explanation:

The fossils of ferns, rushes, and primitive conifers can not be found in these rocks because these rocks are present under the sea millions of year ago. In this onondaga contains an abundant amount of coral fossils, crinoids, brachiopods, and trilobites due to their aquatic habitat. These organisms are present millions of years ago when this area comes under the sea so that's why the fossils of these organisms are present in these rocks.

there's no big difference.

explanation:

the only little different between a rabbit and bunny is just that bunnies are much smaller than rabbits. bunnies are basically baby rabbits.

the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.