Kenyanthropus

Credit: Mauricio Antón.

*Kenyanthropus* is an extinct genus of australopithecine hominid that lived in Kenya during the Middle Pliocene.

## History

Field technician Blasto Oyango discovered a partial left maxilla (KNM-WT 38350) at Lomekwi in August 1998, which was overseen by Meave and Louis Leakey. In August of the next year, research assistant Justus Erus discovered a very flat-face skull, KNM-WT 40000. During these two years, the expedition recovered 34 more cranial and dental hominin specimens, but they were unable to confirm if they belonged to the same taxon. They were found near the Nabetili tributary in the Nachukui Formation in a mudstone layer of the Lomekwi site. 40000 was recovered from the Kataboi Member, 8 meters below the 3.4 million-year-old Tulu Bor Tuff and 12 meters above the 3.57 million-year-old Lokochot Tuff; they found an estimate of 3.5 million years in the Middle Pliocene. Other specimens were found in this layer, the deepest being KNM-WT 38341, probably being ~3.3 million years old. KNM-WT 38350 was found at Lomekwi 17 meters above Tulu Bor and is also around the same age. Others are 16-24 meters over Tulu Bor, and are also about the same age. The highest specimens are -WT 38344, 38355 and 38356, at around 3.2 million years.

## Classification

Meave Leakey et al. (2001) assigned them to *Kenyanthropus* as a new genus, with 40000 as the holotype and 38350 as a paratype. The specific epithet is after the Greek platus and opsis: "flat face". At time of discovery, only *Praeanthropus afarensis* and *"A." afarensis* were believed to have lived 3-4 million years ago. They considered this genus evidence of greater diversity of Pliocene australopiths. This was proven true by the discovery of *A. deyiremeda*. Leakey et al. thought that namely the non-prognathous face and small cheek teeth could distinguish from *Ardipithecus*, *Australopithecus* and *Paranthropus*. They thought it could be subsumed into *Australopithecus* sensu lato, but that this would make it polyphyletic, which they decided against. They drew parallels with *Homo rudolfensis* -1470, finding differences between nasal and braincase morphology to be basal. They thus suggested the combination *"Kenyanthropus" rudolfensis*. White (2003) thought that the holotype was too distorted to draw traits, because it was split into over 1100 pieces before reassembly, with most under 1 centimeter in width. He argues that this is rare and cannot be reliably assembled. He thought it may prove to be a form of *Praeanthropus afarensis* because it was contemporaneous and apes are very variable in skull architecture. Spoor and the Leakey's (2010) produced a detailed topological digitized scan of the maxilla, creating accurate landmarks and comparing them to similar models of other apes (including gorillas, chimpanzees, all early hominins and humans). This new scan verifies distinctness. Camilo José Cela Conde and Francisco J. Ayala (2003) resurrected *Praeanthropus* to hold all non-*Ardipithecus*/*Paranthropus*/*A. africanus* taxa and sunk *Kenyanthropus* into *Homo* as *Homo platyops*, which is not accepted today.

## Description

The holotype was very distorted during fossilization, with the braincase forced down and back, the nasal region to the right and the maxillary region forward. It's sex is unknown. It has a relatively non-prognathous face, inclusign subnasal. The clivus inclines 45°, maxing subnasal prognathism relaxed and steeper than most australopithecines (on the upper variation range of *Paranthropus*), more comparable to *Homo rudolfensis* and *Homo habilis*. This is the first flat face in the hominin record. It lacks anterior pillars, unlike *Praeanthropus afarensis*. One of the longest clivi (32 millimeters, 1.3 inches) is seen in this specimen. The nasal aperture is narrower than other australopiths, the cheekbones are tall and steep and the anterior surface of such is above the premolars, most seen in *Paranthropus*. The zygomaticoalveolar crest is low and curved. The face resembles *Homo rudolfensis*, but has longer nasals, a narrower nasal aperture, shorter postcanines and less midfacial prognathism. *Kenyanthropus* lacks the bite force adaptations seen in later flat-faced *Paranthropus*. Only the upper M2 and left tooth sockets were well preserved enough to create measurements. This molar is 11.4 x 12.4 millimeters2 (0.0177 x 0.0192 inches2) in dimensions area and 141.4 millimeters (5.57 inches) in surface area, being one of the smallest early hominin teeth. The enamel is about as thick as *"A." anamensis* and *P. afarensis*. 40000 retains ancestral ape premolar root morphology (a lingual root and two buccal roots), although the upper P4 is 38350 may only have one buccal root. More derived species typically have single-rooted premolars. The canine jugum is not visible, which may suggest reduced canines. The upper I2 has a cross section that is ~90% of the upper I1, which is much more than the typical 50-70% of related apes. The incisor roots do not appear to be outward splaying, though there is no alveolar prognathism, which justifies this. The cranial volume cannot be calculated due to distortion, but it was probably similar to other australopiths. There is no frontal trigon like *Paranthropus* and there is no sulcus behind the brow, like *Homo rudolfensis* but unlike *Homo habilis*. The postorbital constriction isto a similar degree to *Australopithecus*, *Homo rudolfensis* and *Homo habilis* and less than *P. boisei*. The tympanic retains ancestral morphology like *Ardipithecus* and *"A." anamensis* (lacking petrous crest; narrow canal with small opening). The foramen magnum was probably oval shaped, unlike *P. boisei*.

## Paleobiology

### Technology

Harmand et al. (2015) identified the industry that this taxon used as Lomekwian, after Lomekwi. Spoor (2015), however, suggested that some indeterminate specimens may belong to *Australopithecus deyiremeda*, since they bear similar maxillary morphology and have a similar age. Today, Lomekwian is known as the oldest industry. The assemblage has 83 cores, 35 flakes, 7 (?)anvils, 7 (?)hammerstones, 5 pebbles (possibly used as hammers) and 12 in indeterminate (52 sourced from basalt, 51 from phonolite, 35 from trachyphonolite, 3 from vesicular basalt, 2 from trachyte and and 6 indeterminate). The cores average 167 x 147.8 x 108.8 millimeters (6.57 x 5.82 x 4.28 inches) and 3.1 kilograms (6.8 pounds), making them large and heavy. The flakes are 19-205 millimeters (0.75-8.07 inches) long, shorter than Oldowan. The anvils are havy, being up to 15 kilograms (33 pounds). The flakes are seemingly cleaved using primitive hammering and/or the bipolar method. They made unifaces and bifaces, though they may have shaped them beforehand to ease work. Knappers typically poorly executed this technique, fracturing and cracking fissues in several cores or using multiple blows to strike a piece from the core. Harmand et al. suggested that such primitiveness may place this as intermediate of a simple pounding industry likely used by earlier hominins and Oldowan, which used flaking. *kenyanthropus* made multiple flakes from one core and flipped them over to use the other side, which suggests intention. Domínguez-Rodrigo and Alcalá (2016) argues that Harmand et al. did not convincingly justify in situ discovery, finding that they may be younger tools worked into a younger layer. There is a 700 kya gap in the fossil record between Lomekwian and the oldest Oldowan (by *Homo* sp.), suggesting either loss and regaining of technology or preservation bias (destroyed or undiscovered material), the latter suggesting evolution into Oldowan. The technology at the site suggests that toolmaking required much anticipation, selection, understanding of properties, and complexity.

## Paleoecology

4.5-4 million years ago, Lake Turkana may have grown 28,000 kilometers2 (11,000 miles2), with Koobi Fora probably having depth of a minimum of 36 meters (118 feet). Volcanic hills by Lomekwi moved basalt into lake sediment, with the lake breaking up 3.6-3.2 million years ago, becoming a characteristic series of smaller lakes (each covering a maximum of (2500 kilometers2 (970 miles2)). Bovids at Lomekwi suggest a wet mosaic environment with grasslands and forests sat lakeside or in a floodplain. *Theropithecus brumpti* is the most common monkey here and in the remaining Turkana Basin, which lived in forested and closed environments and thus suggests something similar at Lomekwi. *Theropithecus darti* is another very common monkey, which preferred dryness and wood, similar to grasslands. Leakey et al. argued that this indicates *Kenyanthropus* dwelled in somewhat more forested habitats than *Praeanthropus afarensis*, which was more northern. During this time, the latter two and *Australopithecus deyiremeda* was contemporaneous in various environments. They likely niche partitioned drew to different tooth mechanics and diets.

## Synonyms

* *Homo platyops*
* *Australopithecus platyops*
* *Paranthropus platyops*
* *Homo habilis platyops*
* Turkwel hominid?

## References

1. ↑ 1.0 1.1 1.2 https://en.wikipedia.org/wiki/Kenyanthropus
2. ↑ https://paleoanthropology.org/ojs/index.php/paleo/article/view/1022/985
3. ↑ https://www.bradshawfoundation.com/origins/kenyanthropus\_platyops.php
4. ↑ https://commons.wikimedia.org/wiki/File:Em\_-\_Hominidae\_sp.\_-\_2.jpg
5. ↑ https://books.google.ca/books?id=440TmWXToLAC&dq=%22proanthropus%22&source=gbs\_navlinks\_s