Temporal range: Pliocene
|Genus:||(?) Australopithecus or Kenyanthropus|
|Species:||A. platyops or K. platyops|
|†Australopithecus platyops or Kenyanthropus platyops
Leakey et al., 2001
Leakey (2001) proposes that the fossil represents an entirely new hominin species and genus, while others classify it as a separate species of Australopithecus, Australopithecus platyops, and yet others interpret it as an individual of Australopithecus afarensis.
Archaeological discoveries in Kenya in 2015, identifying possibly the oldest known evidence of hominin use of tools to date, have indicated that Kenyanthropus platyops may have been the earliest tool-users known.
Etymology and description
The name Kenyanthropus platyops was assigned to this unique species for several reasons: the genus name “Kenyanthropus” was proposed to recognize Kenya since so many different hominins have been discovered there, and those findings have played a significant role in understanding human evolution. The species name “platyops” is derived from two Greek words: platus, which means "flat", and opsis, which means "face", referring to the very flat face of the fossil cranium.
The discovery of these fossils led to the prediction of an early diet-driven adaptive radiation, which is when species diversify to fulfill new ecological niches; this would be attributed to the fact that many new species of Australopithecus and other hominins were being discovered that pre-dated or lived around the same time as Australopithecus afarensis. This indicated that species were much more diverse in the distant past than previously thought. Even with the findings of a skull, their diet is still relatively unknown at this time. Also, no evidence of material culture or anything that would lead to its behavioral adaptations or lifestyle has been discovered at this time.
Several aspects of the environment in which it may have lived have been proposed, basing on faunal comparison tests with other animals that lived during their time. It is believed that they lived in a “mosaic” environment, which had both grassland and some forested areas. This is quite different from their close relative, A. afarensis, which was found in sites such as Laetoli, Tanzania, and Hadar, Ethiopia, where they are believed to have spent a lot of time among trees.  
In 1999, Meave Leakey led an expedition in Kenya to dig for fossils, the second such expedition in the area. The first expedition was in 1998 in which the paratype, KNM-WT 38350 was discovered. They began to dig at a site that had yielded many other prominent hominin fossil specimens, Lake Turkana, which is located in the Kenyan Rift Valley and partially extends into southern Ethiopia. A member of the team, Justus Erus, discovered a skull in the Nachukui Formation at Lomekwi, an area of specific geology right next to the lake. The total number of fossils recovered from both expeditions at the dig sites included a temporal bone, three partial mandibles, two partial maxillae, and forty four teeth, but it was the skull dubbed KNM-WT 40000 that sparked the most scientific interest because of its relative completeness (Leakey 2001). This skull had many characteristics that had been seen before in other specimens, however the combination of features had never been seen before; this led scientists to realize that this was indeed a separate and unique species.
KNM-WT 40000 and the other bones were collected from a dark mudstone, which contained volcanic pebbles and solidified CaCO3. The mudstone was located in between the Lokochot Tuff and the Tulu Bor Tuff in the Kataboi Member. Beneath the Lokochot Tuff were the Moiti Tuff and the Topernawi Tuff. The KNM-WT 40000 specimen was dated at 3.5 million years, with the bed dated at 3.53 million years. Directly beneath the bed was the KNM-WT 38341 specimen, which was dated at 3.53 million years. Other specimens from various localities that were found above the b-Tulu Bor Tuff were dated at around 3.3 million years. The location of the mudstone was near a shallow lake, suggesting that the hominins lived near rivers or lakes.
KNM-WT 40000 is the holotype, the specimen of which the description and name of the species is based.
The fossils of Kenyanthropus platyops indicate that hominins were more taxonomically diverse during the middle Pliocene. The discovery of this fossil also dated non forward-projecting jaws further back than previous discoveries. The facial structure of the Kenyanthropus and its derived features were very different of that of the Paranthropus, including almost every cranial feature. This gave no reason to assign the new skull in the genus Paranthropus, unless it could somehow be linked to be a previous version of the Paranthropus. It is still thought that the differences in cranial structure are too different for even that to be a possibility. The Kenyanthropus also shows many differences to Homo, as well as Ardipithecus, which leaves only the Australopithecus. The cranial structure of the Kenyanthropus has a few similarities to the Australopithecus, such as brain size, parts of the nasal, the suborbital and the temporal regions, but the differences far outweigh the similarities leading to its new genus.
Having smaller molars at the date they existed, it is possible that the previous sister taxon of all modern hominins, Preanthropus afarensis, should be replaced by Kenyanthropus. Fragmentary specimens which were having trouble being classified are now being assessed to see if they fit with the Kenyanthropus.
The Kenyanthropus platyops was examined by Collard and Wood (2001) to have two types of characteristics categorized as craniometric and traditional. Craniometric characters represent size-adjusted linear measurements between standard cranial landmarks. Traditional characters represent those most commonly used in systematic studies of apes and early hominids. These characters can be quantitative and qualitative. Kenyanthropus platyops was singled out by the morphology of the maxilla, characterized by a flat and relatively orthognathic subnasal region, an anteriorly placed zygomatic process and small molars. In other words, the Kenyanthropus had small molars and a flat face which resembled anatomically modern humans. Other features of the Kenyanthropus are thick enamel, steep nasal cavity entrance and moderate mandibular depth.
Although it is an extremely difficult task to figure out the evolution of the hominins, knowledge of these hominins has been growing. As indicated in the image of the family tree of the evolution of hominins, Kenyanthropus platyops were previously known to be one of the older hominins until the finding of the fossils in Kenya in the year 1999. Kenyanthropus platyops actually made the evolutionary path of the hominins more confusing, because of the fact that the specific species represented a new type of species and genus. However, after the discovery of the fossil in Kenya, it came to the notion that the K. platyops were one of the earlier species, living in the same time of the Australopithecus afarensis. After the finding of the K. platyops skull, the common ancestor has shifted to the K. platyops from the A. afarensis.
- Kenyanthropus platyops
- BBC News, 21/05/2015: Oldest stone tools pre-date earliest humans
- Leakey, M. G., et al (2001). New hominin genus from eastern Africa shows diverse middle Pliocene lineages, Nature, Volume 410, pgs. 433-440
- Lieberman, D. E. (2001). Another face in our family tree, Nature, Volume 410, pgs. 419-420
- Cela-Conde, C. J. and Altaba, C. R. (2002). Multiplying genera vs. moving species: a new proposal for the family Hominidae, South African Journal of Science, Volume 98, pgs. 229-232
- Leakey, Meave G.; et al. (2001). "New hominin genus from eastern Africa shows diverse middle Pliocene lineages". Nature. 410 (6827): 433–440. PMID 11260704. doi:10.1038/35068500.
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