Everyone has either owned or been around dogs in their lifetime. We keep them as constant companions and in turn they reward us with years of affection. But how did our canine friends evolve in the first place? And what caused them to do so? In a recent study, released August 18th in Nature, it seems that climate change was the culprit. The vastly changing world had a massive effect on the flora and fauna on our planet, especially canines.
Modern wolves and dogs began to evolve approximately 40 Myr ago from small, weasel- or mongoose-like creatures called miacids. These small furry animals were also the ancestors to the carnivorous mammals we see today such as cats, canines, bears and more. In fact, these strange creatures are responsible for the evolution of the entire Carnivora order! These miacids existed when dinosaurs still roamed the Earth, but they were small, mouse-sized creatures resembling modern day rodents. Their prominence didn’t come into play until after the dinosaurs died out and they could fill the ecological niche (or role) that the dinosaurs used to occupy.
At the same time that canine evolution was going on, another huge process began to change our world. The climate, and even the geography, of the land began to alter. At the beginning of the Eocene Epoch about 58 Myr ago the climate began to rapidly warm; this caused tremendous changes in greenhouse gases. Scientists even estimate that CO2 was higher here than ever before or after, until modern times. Tropical landscapes stretched over much of the Earth, even as far as the Canadian-US border. When the Eocene began to come to a close and move into the Oligocene there was a massive rapid cooling of the globe, which transformed tropical regions in the North into grasslands, where wolf ancestors were then living.
A research team including B Figuerido of Spain and an American Museum of Natural History scientist named Jack Tseng worked with Brown University to investigate the mystery of why canines evolved. They studied the anatomical shapes of the AMNH’s fossil dog collection as well as several skeletal specimens of both modern felines and canines. The team was especially interested in the elbow joints of the animals. As it turns out, cats and dogs have very specific differences in elbow structure when it comes to environmental adaptations. The team discovered that over the Eocene, as the geography changed from tropical forests to open grasslands, the miacids not only began to split into their eventual forms but that their skeletal features adapted to the environment as well.
When first looking at the fauna of the Paleogene (the Eocene and the Oligocene are part of this Period) it was thought that the predators evolved as the prey evolved in a so-called “arms race”. The idea behind this was that the prey evolved to escape predators more efficiently. Prey animals would do this by evolving better speed, agility, or defensive anatomical features (like horns and sharp hooves), and predators in turn would evolve better offensive weapons (teeth, claws, brains, etc.) with which to catch them. The research that the AMNH and the Spanish team did in the elbows proved that this was incorrect. Not only did the prey evolve to better suit the landscape changes, but so did the predators. It is unusual to see predatory animals clearly evolving in response to the terrain rather than prey, and this study helped to uncover that.
It just so happens that while cats evolved their own branch away from the miacids and kept many of the same hunting features, canines evolved separately. Canines evolved limbs that are much less flexible and much more accustomed to long term use. What this means is that they adapted wrists and elbows that only went up and down, and not side to side. If you’ve ever seen a cat climb or jump you know they can be quite flexible, especially in their wrist movements. Canines on the other hand are not. This more rigid bone structure is mean for long distance running that would be advantageous on the plains and grasslands that developed in North America at the end of the Paleogene.
It’s amazing to think that taking something as small as the measurement of elbow joints in a dog bone can lead to figuring out how an animal evolved into what it is today. The dogs and cats we see today were once one and the same millions of years ago, but have changed vastly since that time. As far as the canines are concerned, this cause was most likely due to the rapid climate change that engulfed their environment at the end of the Paleogene. This drove their flexible limbs that were once adapted to climbing and pouncing into rigid, sturdy grassland running machines. The climate change and greenhouse gas emissions during the Eocene are paralleled to our own today. It will be interesting to see if animals today can adapt and evolve as quickly to the changing climate as the North American canines did 60 Myr ago.