After learning about the more recent Daeodon of the Eocene period, I am going to take you way back to the other side of history to talk about an animal called Inostrancevia, an animal that predated the oldest dinosaurs and represented a transitional state in evolution between reptiles and mammals.
Inostrancevia lived in the middle to late permian period, between 265 and 252 years ago, in what is now Western Russia. It grew to a length of roughly 11 feet long and a weight of around 1,000 pounds, which is about the same size as a grizzly bear. Its general body shape was also somewhat similar to bears, though it had a longer tail, lower hips, and canine teeth that grew to be nearly 6 inches long.
These are a pretty confusing species as far as classification. Given how old they are and their general appearance, they are often assumed to be dinosaurs (Diapsids), but they are actually Synapsids, a group which includes both mammals as well as reptiles that very closely resemble mammals. It is difficult to place them exclusively in either the mammal or reptile category simply because Inostrancevia has so much in common with both.
For instance, Inostrancevia had relatively short legs that were splayed out to the sides of its body, which is a characteristic trait of reptiles. You can see this with turtles, crocodiles, and lizards in the way they lay flat on their stomachs. Mammals tend to have longer legs that support the animal from directly below, which they have fold under them to sit. Inostrancevia also appears to have laid eggs. However, the arrangement of its teeth, nasal cavities, and overall head shape are very mammalian traits, and it is debated whether or not Inostrancevia had hair.
Way back in the Permian period, the region of Europe in which this animal lived had a much drier climate, like a cold desert, so the environment likely functioned like a colder version of Africa’s grasslands. Inostrancevia was almost certainly the apex predator of its environment, and filled the same ecological niche as big cats do today. It is believed that they were ambush hunters, but analysis of their bone structure suggests that they were extremely coordinated and fast runners. Their massive canines also suggest that they hunted like Jaguars or tigers, lunging onto prey and using their teeth to latch on and take the animal down. This is further supported by how far back these canines were seated, so that they could still use them to kill, but they were out of the way of the shorter front teeth which could then be used to rip at meat more precisely when eating.
Though this was an extremely well-adapted and successful species, Inostrancevia could not survive what became known as “The Great Dying,” a series of volcanic eruptions that led to ocean acidification, a dramatic greenhouse gas effect, and other catastrophic environmental changes. This would go on to wipe out 95% of both land and ocean species, and forms the boundary between the Permian and Triassic periods, allowing dinosaurs to rise as the dominant form of life on earth.
Sources:
http://www.prehistoric-wildlife.com/species/i/inostrancevia.html
https://www.britannica.com/animal/Synapsida
This was super interesting! The classification of the Inostrancevia not fitting in the mammal or reptile category is interesting, since they shared many similar traits to both. I also wonder if in the future we could find out if the Inostrancevia had hair, since its so unclear with most of the animals from that time. That would change a lot of our understanding of these animals and how we teach others about them. It’s interesting how they are compared to big cats and were the apex predators of their time, and that definitely shows the mammal traits of them.
This post was really intriguing! I really liked reading about the inostrancevia, and how you described it as an, “animal that predated the oldest dinosaurs and represented a transitional state in evolution between reptiles and mammals.” The images really helped understand the topic better as well. Great post, Matt!