Sahelanthropus tchadensis

Looking at the human family tree can be a bit too confusing, as we can’t really make out that much from fossils. For example, from fossils, we may never know if an animal liked one kind of fruit better than another or if two human species got on better than other human species. However, it depends. With humans and early hominids (which are just human ancestors that came after the split with chimps and their family tree), we can actually deduce a lot of behaviour by looking at ourselves and our closest relatives, chimpanzees and bonobos.

One of the hardest things to determine from a fossil is where exactly a specimen is located in its family tree. Since DNA is very rare in fossils and only survives for about 10,000 years, we don’t know exactly when the split between humans and chimpanzees occurred, but it was probably around 6-7 million years ago, or m.y.a. for short. The hominin that existed around this time was Sahelanthropus tchadensis, or the Sahel Man of Chad. The Sahel is a strip of Central Africa that makes up the transition from the Sahara Desert to the tropical grasslands below. Today, the Sahel is arid, dry, and not a very hospitable place altogether. However, 7 m.y.a., the Sahel was one of the lushest, greenest places in Africa. Sahelanthropus existed in this habitat and looked very much like a chimpanzee.

Sahelanthropus was probably able to walk on two legs, as evidenced by its braincase, which shows signs of being supported by an upright body. Its brain was actually smaller than that of a chimpanzee, which shows that brain enlargement was at work simultaneously in both branches of the ape family tree. One of these signs is the fact that the spinal cord opening is under the skull and not behind it, which is a thing seen only in bipeds. Sahelanthropus is considered to be the first hominin after the human-chimpanzee split, but there are contenders who believe that Sahelanthropus is the last common ancestor of us and chimps. As of now, Sahelanthropus’s position is not determined yet.

Sahelanthropus, and many apes after it, were mainly herbivorous, eating tough plants. Therefore, they had wide faces for their huge jaw muscles to anchor on and large molars. These facial characteristics would become a marked difference between apes and humans, since humans were omnivorous with a liking for soft meat and had small molars and narrow faces. Sahelanthropus had small canines, which point to a more humanlike affinity, since chimpanzees have huge canines and humans have small ones. One thing to note here is that while the last common ancestor was herbivorous, both humans and chimpanzees evolved omnivority and a liking for meat. This was probably because of changing environmental conditions where plants became fewer and harder to digest, which will be very important in the next few articles.