Oldest horse brains: more advanced than previously realized.

The research revolves around the examination of the oldest horse brains, suggesting that they were more advanced than previously thought. An incorrect identification of a fossil endocast had earlier skewed our understanding of these ancient brains, but newly prepared endocasts of Hyracotherium, the earliest horse species, show a larger and more complex brain structure than assumed.

Incorrectly Identified Fossil Endocast

• The study reevaluates the interpretation of horse brain evolution that was previously based on a misidentified fossil endocast. An endocast is a cast or impression of the internal structure of an organism, commonly formed from sediments that have filled the interior part of an animal’s skull.
• Previously, researchers attributed this endocast to an early horse, which led to somewhat inaccurate conclusions about the development of horse brains. In this research, it appears that the endocast was actually from an animal called a condylarth, a non-ungulate mammal that lived during the Paleocene and Eocene epochs.

The Brain of Hyracotherium

• The researchers prepared and studied endocast samples from Hyracotherium, one of the earliest horse species and an early perissodactyl, a group of mammals that includes present-day horses, rhinoceroses, and tapirs.
• The findings from these newly prepared endocasts revealed a significantly larger brain with a more developed neocortex in comparison to the condylarth ancestors of perissodactyls.

Structure of Ancient Horse Brains

• The study found that approximately 50 million years ago, the brain of horses already had well-formed suprasylvian, ectolateral, and lateral sulci. Sulci are the depressions or grooves found in the brain. These structures divide different regions of the brain and allow a large amount of brain tissue to be accommodated in a smaller skull, indicating advanced cognitive abilities.
• However, the research also noted that the frontal lobe in these ancient horse brains was still undeveloped.

Implications of the Research

• This study greatly impacts our understanding of brain evolution in horses and other perissodactyls, indicating that these animals developed advanced brain structures earlier than previously thought.
• The research not only corrects a previous error in fossil interpretation but also provides important insights into the neuroanatomical evolution of early horses, thus contributing to our knowledge of mammalian brain evolution as a whole.