Image from Wikimedia Commons
In this past unit, we have studied evolutionary history in animals to see how we have gotten to the level of diversity we have today. We saw how animals slowly moved from life in the ocean to life on land. Animals with amniotic eggs were crucial to allowing for terrestrial life. Scientists have been reconstructing the evolutionary history of animals since the idea was first presented. Recently, scientists discovered and analyzed a set of fossil remains in Kansas that explain some of the first herbivores. Dr. Larry Martin from the Dyke Museum of Natural History at the University of Kansas collected a partial skull, vertebral column, pelvis, and a hind limb. They determined the species to be from Eocasea martini.
Eocasea were chordates that lived about 300 million years ago. Adults are thought to have eaten insects and other small animals while the young were herbivorous. Over time, however, Eocasea became increasingly dependent on plants. Their ability to consume plants opened up animals to a vast new source of food and energy. Eocasea began the system of having predators receive their energy from consuming lower level plant eaters. Over time, many more species evolved and became dependent on plants for survival, some directly and others indirectly.
The discovery of herbivorous traits in Eocasea was rather curious. Eocasea developed teeth and a digestive system that were specialized for breaking down the cellulose from plants. Scientists have found multiple other instances where a mammal or reptile has developed similar qualities that allowed them to survive off plants. These started showing up after the first Eocasea began consuming plants. Paleontologist Robert Reisz describes it as, “it seems as though a threshold was passed.” The cause of these relatively sudden evolutions is unsure. However, something must have happened that pushed species to grow, adapt, and evolve.
Observations of Eocasea make very apparent the benefits of consuming plants. The groups of animals that adapted to being herbivores showed extreme growth in size. The group of caseids showed the largest range. Some of the first caseids were very small at about 2 kg as adults. By the time they were dying out, they could easily exceed 500 kg. The ability to use plants as a source of food is beneficial for both the species itself as well as the other animals in their environment. Predators of Eocasea were able to acquire nutrients and energy from the plants indirectly by consuming the Eocasea.
The discovery of Eocasea reveals more about the evolutionary history of animals. It explains more about from where herbivores originated. It adds another piece to the puzzle of reconstructing the history of life on earth. It also, however, brings up questions about the past. Something must have occurred to trigger such a change, especially since it was seen in multiple unrelated species. Perhaps Eocasea faced a shortage of food from other animals and needed a different energy source to survive. There are likely multiple other factors that pushed for this adaptation since other animals had not evolved like this in the past. Everything just aligned in a way to allow for Eocasea to become herbivores. This was an extremely important point in evolutionary history since it forever changed animals and the entire ecosystem.