Too Many Herbivores!
One question I'm often asked is: why are there so many more plant-eating than meat-eating dinosaurs? After all, kids (especially boys) are more interested in carnivorous beasts like T. Rex or Velociraptor than gentle vegetarians like Iguanodon or Protoceratops. If you look at my (still incomplete) lists of herbivorous dinosaurs and carnivorous dinosaurs, you'll see that the herbivores outrank the carnivores by about two to one.
The quick explanation is that, in the Mesozoic Era when the dinosaurs lived, the earth's landmasses were covered with thick vegetation. This provided plenty of food to sustain large populations of herbivores; the herbivores, meanwhile, became the main food source of the carnivores that quickly appeared on the scene (to take advantage of this evolutionary niche). Because carnivores can't prey on herbivores with 100 percent efficiency (most plant-eaters run away and escape), there was simply less room for comparable numbers of predatory dinosaurs. The result: many more genuses (and a larger population) of herbivores than of carnivores.
Comments
There are always more herbivores than carnivores, as there are more plants than herbivores.
If a carnivore needs to eat one herbivore a day, that’s 365 a year.
The herbivores need at least a 365 to 1 proportion just to keep the carnivore from starving. Not to mention the herbivores need to maintain a sustainable number to allow for reproduction. So the ratio of herbivores to carnivores has to be in the neighborhood of 1000 to 1 for the herbivores and the carnivores to survive.
We must also remember that because there lived more herbivores than carnivores, the chances that a herbivore be fossilized was greater.
We therefore know more genuses of herbivores because we are able to observe more fossilized herbivores.
This distorts our view of the actual ratio of carnivore to herbivore genuses that once existed.