Homo rudolfensis

Background of discovery

Age

2.4 to 1.8 million years

Important fossil discoveries

The key specimen of this species is skull KNM-ER 1470. When it was discovered by Richard Leakey’s team in 1972, it was not attributed to a species, only a member of the genus Homo. In 1986, a Russian anthropologist gave the skull the species name Pithecanthropus rudolfensis. The genus name of Pithecanthropus was later dropped and replaced with Homo.

Other cranial remains attributed to this species include the KNM-ER 1802, 1590, 1801 and 3732. Possible limb remains may include KNM-ER 1472 and 1481, but these were not found with skulls so attribution is questionable.

What the name means

Homo is a Latin word meaning ‘human’ or ‘man’. It is the same genus or group name as the one given to modern humans, which indicates the close relationship between this species and our own. The species name rudolfensis comes from the location where the type specimen KNM-ER 1470 was found – Lake Turkana, East Rudolph, Kenya.

Distribution

Fossil have been found in Urhara, Malawi, and Lake Turkana in Kenya.

Relationships with other species

The scientific name Homo rudolfensis was originally proposed for the specimen skull KNM-ER 1470, discovered in 1972. It was once thought by many to be a member of the species Homo habilis but the differences compared to other Homo habilis skulls were considered too great.

As in the case of H. habilis, there is large amount of controversy about the classification of H. rudolfensis. Debate continues as to whether these fossils should be named Homo rudolfensis, Kenyanthropus rudolfensis or Australopithecus rudolfensis, or returned to Homo habilis.

Analysis shows this species shows more affinities to australopithecines than to Homo. So it is not certain if H.rudolfensis was ancestral to the later species in Homo, or if H.habilis was, or if some undiscovered species was.

In 2007, a team led by Timothy Bromage, an anthropologist at New York University, reconstructed the skull of KNM-ER 1470. The new construction had a more ape-like projecting jaw and a smaller brain size. They claim this new reconstruction makes it more like other Homo habilis specimens.

The Homo habilis and Homo rudolfensis debate

Scientists often disagree about naming fossil specimens. Scientific names may be changed following new discoveries, different interpretations or new lines of investigation. Homo habilis is a well-known but poorly defined species and scientific opinions about the attributed specimens vary widely. Two specimens at the centre of the debate are KNM-ER 1470 and KNM-ER 1813.

KNM-ER 1470 (discovered 1972)

• about 1.7 million years old
• large brain, about 750-800ml
• teeth not preserved; roots and sockets suggest they were large, as in Australopithecus, with larger molars than other Homo habilis specimens
• square upper jaw
• slightly developed brow ridge
• face large and flat and longer than KNM-ER 1813 (although this is now questioned)

KNM-ER 1813 (discovered 1973)

• about 1.7 million years old
• small brain, about 500ml
• small upper jaw with human-like teeth
• rounded upper jaw
• strongly developed brow ridge
• face small and not very flat

The differences between KNM-ER 1470 and KNM-ER 1813 can be interpreted in various ways.

• They are different sexes: other things being equal, large bodied individuals have a bigger head and brain than small individuals. KNM-ER 1813 may be a female and KNM-ER 1470 may be a male of Homo habilis. However, they do not differ from each other in the sort of ways that males and females of modern apes (including humans) differ from one another.
• They are different species: many scientists claim that 1813 and 1470 represent two species, or even two genera. Suggestions include Australopithecus africanus, Homo habilis and Homo rudolfensis. The discovery of a skull of Kenyanthropus platyops in 1999, and its similarity to KNM-ER 1470, has led some to consider reclassifying KNM-ER 1470 into the Kenyanthropus genus.

Key physical features

Brain

• average size of about 750cc (larger than Homo habilis specimens)

Body size and shape

• general lack of postcranial remains makes size assessment difficult. The larger teeth and skulls compared to Homo habilis suggest it may be larger than this species.

Jaws and teeth

• large molars and broader lower molars than Homo habilis
• complex crowns and roots

Skull

• relatively flat and long face (although more recent reconstructions debate this and suggest the face was more protruding))
• small brow ridge
• lack of crests and heavy muscle markings that are found in australopithecine skulls

Limbs

• limb proportions unknown because of lack of skeletal material
• assumed to be bipedal but without the ability to move in a fully human locomotion

Lifestyle

Environment and diet

The area was predominantly a grassland environment. The climate was becoming cooler and drier at this time.

Limited studies have been done on the diet of this species, but the tooth shape and comparisons to other species suggests plant material and probably meat were eaten.

Culture

Although no associated archaeological evidence was found with any Homo rudolfensis remains, they were living at a time when it is known that human ancestors were making tools.

The first crude stone tools consisting of simple choppers, core tools and scrapers were made as early as 2.6 million years ago and are classified as Mode 1 technology or Oldowan. It is uncertain who the makers of these earliest stone tools were. The tool makers may have been early populations of Homo habilis or they may have been made by another species. One such candidate is represented by the fossil AL 666-1, which has been provisionally named Homo sp. (meaning a human whose species is currently unknown).