How many billions of barrels have been harvested over the last hundred years. It is silly to think it is decayed dinosaurs.
The old elementary school science was that coal came from plants, oil from animals.
There is a lot of biomass that has been seen over the age of the earth. A lot of coal and oil is found in conjunction with it, this is one of the historical ways that coal and oil finds have been located. Not just dinosaurs but everything from insects to hippopotami.
Not dinosaurs. Vast mats of phytoplankton deposited in shallow marine, anaerobic environments. And it’s quite obvious that there were phytoplankton in such quantities...because we find their fossilized remains in the formations where oil is encountered. Hence the moniker “fossil fuels.”