Asked in Zoology or Animal BiologyAnimal LifeMice and RatsProtozoa
Why are animals smaller today than they were in the distant past?
November 23, 2009 11:48PM
Actually, the modern Blue Whale is still the largest animal that
has ever lived, so your question should be "Are animals today
smaller than they were in the distant past?" and the answer is "not
really." That being said, during the age of mammals, certain
representatives were larger than current representatives, such as
the mammoths and mastodons for the elephants. However, one must
keep in mind that there were many species in the elephant family,
and many of them were smaller than today's elephants.
The discussions below seem highly speculative, but may be useful as hypotheses.
i can't give you a straight answer because there can be several things responsible. one is that there's less oxygen in the atmosphere now than in the past-about 1/2 as much. in the past animals could take in more oxygen and thus grow larger, basically. another answer comes from one of several evolution theories. over time, larger and smaller animals faded because larger ones were bigger targets (and of course not many carnivores were subject to this but when their food source dies off-large herbivores, so do they) and smaller ones were not adept at getting food easily. so you have a median-today's average size animals.
There were also horrible recordings of size. Inaccurate measurements had a lot to do with this. The mammoth was not really a "mammoth" but just a bit larger than modern day African elephants. An ecosystem may also not be able to support extremely large herbivores, like certain dinosaurs, and that causes a ripple effect through the entire food chain.
blue whale is not that large compared to the sauropod dinosaurs