Overview:

There is only one really good fossil of this Homo rudolfensis: KNM-ER 1470, from Koobi Fora in the Lake Turkana basin, Kenya. It has one really critical feature: a braincase size of 775 cubic centimeters, which is considerably above the upper end of H. habilis braincase size. At least one other braincase from the same region also shows such a large cranial capacity. 

Originally considered to be H. habilis, the ways in which H. rudolfensis differs is in its larger braincase, longer face, and larger molar and premolar teeth. Due to the last two features, though, some scientists still wonder whether this species might better be considered an Australopithecus, although one with a large brain!

History of Discovery:

Russian scientist V.P. Alexeev named the species in 1986 after Richard Leakey’s team uncovered Homo rudolfensis fossils near the shores of Lake Rudolf (now known as Lake Turkana) in 1972. Alexeev originally named the species Pithecanthropus rudolfensis, but the genus name Pithecanthropus was later replaced by Homo.

How They Survived:

Homo rudolfensis had large and wider molars compared to Homo habilis. While their teeth were only slightly smaller than those seen in robust australopithecines, H. rudolfensis didn’t have the heavily-built jaw and strong jaw muscle attachments seen in robust early humans. These anatomical differences likely indicate different diets between H. rudolfensis and earlier australopith species capable of more powerful chewing.

Like other early Homo species, Homo rudolfensis may have used stone tools process their food. However, because more than one species of early human lived at the time tool manufacture and use originated, it’s hard for scientists to be certain which species is responsible for the making and using the first stone tools. There are currently no stone tools found in the same layers as the H. rudolfensis fossils, but there are stone tools existing in the same time period that H. rudolfensis lived. 

Evolutionary Tree Information:

KNM-ER 1470, the type specimen for Homo rudolfensis was originally thought to belong to Homo habilis, along with KNM-ER 1813. While both skulls are about 1.9 million years old, KNM-ER 1470 had a large face and brain size around 700 cc, while KNM-ER 1813 had a smaller face and brain around 500 cc. The explanation was that KNM-ER 1470 was a male, and the smaller KNM-ER 1813 was a female in a strongly sexually dimorphic species; however, the anatomy of the two skulls differ considerably.

KNM-1470’s tooth roots and sockets imply the individual’s teeth were large with broad molars, while KNM-1813 had a small upper jaw with smaller, more modern-like teeth. KNM-1470 had a square upper jaw, while KNM-1813’s was rounded. KNM-1470’s browridge was slight, while KNM-1813’s was strongly developed and pronounced. These anatomical differences between KMN-ER 1470 and KNM-ER 1813 have caused many scientists question whether the two individuals were just different sexes of the same species. However, the hypothesis that two species of Homo lived at the same time went against the traditional view that humans evolved one after another in a single lineage.

Today, most scientists recognize four species that lived in the Turkana Basin, northern Kenya, sometime between 2.0 and 1.5 million years ago: Homo rudolfensis, Homo habilis, Homo erectus, and Paranthropus boisei.

Questions:

We don’t know everything about our early ancestors—but we keep learning more! Paleoanthropologists are constantly in the field, excavating new areas, using groundbreaking technology, and continually filling in some of the gaps about our understanding of human evolution.

Below are some of the still unanswered questions about H. rudolfensis that may be answered with future discoveries:

1. Was Homo rudolfensis on the evolutionary lineage that evolved into later species of Homo and even perhaps our species, Homo sapiens?
2. Are Homo rudolfensis and Homo habilis indeed different species, or are they part of a single, variable species? Or was one the ancestor of the other?
3. Are Homo rudolfensis fossils more like australopithecines than other Homo fossils, as some scientists have suggested?
4. How big was Homo rudolfensis? Was this species sexually dimorphic?

References:

First Paper:

Alexeev, V.P., 1986. The Origin of the Human Race. Moscow, Progress Publishers.            

Other recommended reading:

Wood, B., Collard, M., 1999. The changing face of genus Homo. Evolutionary Anthropology 8, 195-207.