It is a classic tale of evolutionary biology that tall or high-crowned molars (hypsodonty) in mammals only evolved when grasslands evolved.1
This supposedly took place during the Cenozoic2 when the cooling climate caused forests to change into extensive grasslands. It was thought the high-crowned molars developed as a result of wear from eating grass containing phytoliths (silica-rich granules).
Worn-out teeth supposedly caused the mammals to develop taller, longer-lasting teeth (figure 1). New evolutionary research calls into question this classic tale.
Researchers using Cenozoic dating methods for various groups of ungulates (hoofed animals), as well as rodents and rabbits, discovered that the origin of hypsodonty was out of phase with the supposed spread of grasslands in the United States’ Midwest. Some animals developed high crowns before and some after the supposed ‘evolution’ of the grassland. Moreover, many mammal families did not evolve tall teeth at all. Therefore, the researchers have mostly abandoned the classic tale but have adopted a new hypothesis. They now claim high-crowned teeth were not due to the evolution of grasslands but from the effects of grit and soil:
This hypothesis seems even less plausible because previously the abrasive agent was in the food, while in the new idea the abrasive agent is the soil, which would rarely be consumed.
The first lesson learned from this story is to be aware of the speculation advanced for the purpose of maintaining the evolutionary status quo. The hypothesis of evolution often requires ‘just so stories’ to explain difficulties when interpreting fossils, radiometric dating, or paleoenvironments. In the biological sciences in particular, recourse is often had to the assumption that non-existent genetic information will somehow be created in response to a perceived environmental need.
Secondly, we must always be alert to the fact that circular reasoning is common within evolutionary biology and paleontology.3,4,5,6 Just as with uniformitarian paleoenvironmental interpretations,7 we must be aware of circular reasoning and the reinforcement syndrome, the tendency to keep evolutionary concepts going with ‘further research’. Circular reasoning is shown in the issue of hypsodonty in that evolutionists have used it as diagnostic of a grassland, when there is no paleobotanic evidence.1 They have also used hypsodonty as a measure of aridity:
It would not be surprising if the ‘degree of hypsodonty’ has been used to ‘date’ a particular mammal group during the Cenozoic, but the main article gave no indication of this. The assumed paleotemperature, based on the particular fossil assemblage, has been used as input to place the fossils within the Cenozoic era, which presumably was generally cooling throughout.7,8