First thing is first, who, or what was the first mammal? It may seem unbelievable but the common ancestor of all living mammals today looked like a rodent (image below). “The scientists then worked with an artist to illustrate this ancestor. In addition to a furry tail, the researchers suggest the four-legged creature likely ate insects, weighed from 6 grams (about the weight of some shrews) up to 245 grams — less than half a pound — and was more adapted for general scampering than built for more specialized forms of movement, such as swinging from trees.” This small mammalian ancestor appeared about 200,000 to 400,000 years after the extinction of the dinosaurs, which when compared to how long it took humans to evolve (5 to 8 million years), it was as if they were just waiting for the extreme threat to go away. But how did what makes a mammal a mammal come along?
The type of mammal that gives live birth (placental), is the type of mammal that is populating the Earth. We are currently in the “Age of Mammals,” which, as I stated earlier, started 200,000 to 400,000 (roughly 65 million years ago) after the “Age of Dinosaurs” came to an end. The synapsids were around millions of years before they evolved into mammals. “These reptiles arose during the Pennsylvanian Period (310 to 275 million years ago). A branch of the synapsids called the therapsids appeared by the middle of the Permian Period (275 to 225 million years ago).” In hindsight, evolving over a span of 100+ million years into a mammal, the evolution of humans is not so bad. That said, throughout these millions of years, the therapsids had to lose their scales thus growing hair (or fur), produce milk producing glands, and above all adapt to the changing times by having a uterus.
All that said, it really is not that hard to believe the mammalian ancestor was so small. If you were a new species, a completely new branch of animal, being small was the best to ensure your survival. Primates for example, our, chimpanzee's, gorilla's, lemur's, every primates out there, we are all closely related to tupaiids (tree shrews...image below). Even though our mammalian ancestor evolved from a reptile, modern mammals cannot in anyway be linked to reptiles, or to any other group. “Since it can be shown that each of the 32 orders of mammals are separate and distinct groups set apart from one another and from all other creatures by unbridged gaps, it seems evident that collectively as mammals they are set apart as well.”
Please feel free to comment on what you thought of the blog, or other physical anthropological subjects you would like me to cover.