Kenyanthropus is a 3.5 to 3.2-million-year-old hominin fossil discovered in Lake Turkana, Kenya in 1999 by Justus Erus, who was part of Meave Leakey's team. Archaeological discoveries in Lomekwi 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 "to appear, to look", referring to the appearance of 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.
Excavation sites
In 1999, Meave Leakey led an expedition in Kenya to search 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. 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. 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.
Taxonomy
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 middlePliocene, and that non-forward-projecting jaws evolved earlier that previously thought. Its facial structure and derived features of were very different from those of Paranthropus, including almost every cranial feature. As such there was no reason to assign the new skull to the genus Paranthropus, unless it could somehow be linked to be an earlier Paranthropus species. It is still thought that the differences in cranial structure are too different for even that to be a possibility. It also shows many differences to Homo and Ardipithecus, and, while its cranial structure bears a few similarities to those of Australopithecus – such as brain size, parts of the nasal, the suborbital and the temporal regions – the differences far outweigh the similarities leading to it being placed in its new genus. White considered the Kenyanthropus platyops holotype a distorted specimen of Australopithecus afarensis, viewing features cited as diagnostic for Kenyanthropus as caused by taphonomic distortion. Cela-Conde and Ayala, for their part, proposed that Kenyanthropus should be consider a synonym of Homo, with K. platyops being a primitive Homo species. Spoor et al. provided additional morphological evidence to rebuke White's conclusions by noting that the maxilla of KMN-WT-40000 is distinct from that of all australopithecines, and a 2016 study reinforced the conclusions of Spoor et al. by highlighting differences between the maxilla of Kenyanthropus and that of A. afarensis and A. deyiremeda. Having smaller molars at the date they existed, it is possible that the previous sister taxon of all modern hominins, Praeanthropus afarensis, should be replaced by Kenyanthropus. Fragmentary specimens which have proven difficult to classify are now being reassessed to see if they fit with Kenyanthropus.
Morphology
The Kenyanthropus platyops was examined by Collard and Wood 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.
Evolutionary path
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 , the Australopithecus group were known to be one of the older hominins before the finding of the Kenyanthropus platyops fossils in 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.
