The Size of Animals in the Fossil Record

One question better answered by creation by God than by other explanations is why animals were so big in the past and so small today. In Smithsonian Magazine for September/October 2026, Dr. Floyd Shockley, the collections manager of entomology at the National Museum of Natural History, gives the traditional explanation for the size of animals in the fossil record.

The data on this issue involves two things. One is the fact that the level of oxygen in Earth’s atmosphere was higher in the past than it is today (35% in the past as opposed to 21% today). The other is the fact that all major groups of animal life have become smaller today. We are all familiar with the fossil remains of huge dinosaurs. Less publicized is the fact that insects were also huge compared to their relatives today. Is an animal’s size related to how much oxygen it breathes? If so, animals living at higher elevations should be smaller than those at lower elevations. That is simply not the case.

Size is more directly related to diet than to a 14% difference in oxygen levels. The ecology of various environments is also a factor. Habitat design involves interactions between plant and animal life. Scientists have conducted interesting experiments in which they tried to design a closed habitat that would last for many years. Without external interference from the scientists, those habitats have collapsed.

The size of animals in the fossil record shows great intelligence in how animal and plant sizes interact. God was preparing the planet for humans and the resources we would need. No single factor accounts for how life was created, and no chance process can explain the facts we see. It reminds us of Romans 1:20, which tells us that “…since the creation of the world God’s invisible qualities – His eternal power and divine nature have been clearly seen, being understood from what has been made, so that men are without excuse.”

— John N. Clayton © 2026