Sarah Dion

Cast # KNM-ER 1813

Specimen # KNM-ER 1813

Element: Cranium

Taxon: Homo habilis

Introduction and Discovery

Homo habilis KNM-ER 1813 is an extremely important fossil in current debate on human evolution and is at the center of the controversy regarding taxon classification of Homo habilis. This fossil may represent a remarkably sexually dimorphic female of H. habilis compared with larger presumed male fossils typified by KNM-ER 1407, or a separate species altogether. This paper seeks to address this debate through a comparison of KNM-ER 1813, KNM-ER 1470, and KNM-ER 1805, another Homo habilis from Koobi Fora.

With the discovery of Homo habilis at Olduvai Gorge in the early 1960’s came the earliest evidence of many changes in human evolution. A leap in encephalization, facial development, and tool use marked advances seen in the new Genus Homo (Lieberman et al, 1996). Intermediate between earlier and less evolved Australopithecines and Homo erectus, it exemplifies a non-robust and fully bipedal hominid. Still primitive to H. erectus in brain and tooth size, members of the genus Homo had culture beyond Australopithecines and are associated with the Olduwan tool tradition (Wood, 1992).

The Homo habilis cranium identified as KNM-ER 1813 was discovered as part of the Koobi Fora Remains, which were formerly known as the East Rudolf Hominids. The Koobi Fora Remains were discovered during the East Rudolf (Koobi Fora) Research Project directed by R. Leakey and G. Isaac (Day, 1986). All of the fossil remains found in this site are classified in the family Hominidae. K. Kimeu found KNM-ER 1813 in 1973 as an almost complete cranium in Area 123 of the Koobi Fora Formation (Ferguson, 1987). Koobi Fora is located in present-day Kenya at East Turkana. It is approximately

15 km from the Eastern shore of Lake Turkana (Day, 1986). Koobi Fora has made the largest contribution to fossils belonging to Homo habilis at this time (Wood, 1993). Although Olduvai Gorge produced the first Homo habilis, KNM-ER 1813 and KNM-ER 1470, two of the most complete habilis crania, both came from Koobi Fora. KNM-ER 1813 is considered contemporary with the H. erectus fossil KNM-ER 3733 and OH 13, another H. habilis (Ferguson, 1987).

Geologic Context

KNM-ER 1813 was uncovered from the site of Koobi Fora near the shores of Lake Turkana (Lake Rudolf) in the East Turkana (Rudolf) Basin. This region of present-day Kenya is within the Rift Valley and due to the enormous volcanic and tectonic activity many fossils have been exposed at the surface well-preserved volcanic tuffs, provide relative dates. The Plio-Pleistocene, as represented at Koobi Fora, spans 325 meters of sediments (Vondra and Bowen, 1976). These sedimentary strata are interspersed with volcanic tuffs, aiding in dating of the fossils recovered from the site. The Plio-Pleistocene sediments at Koobi Fora are broken into three formations: the Guomde Formation disconformity, the Koobi Fora Formation, and the Kubi Algi Formation. The Koobi Fora Formation, which housed the KNM-ER 1813 fossil, is divided into the Upper Member and Lower Member. These sedimentary formations are separated by the KBS volcanic tuff. The Koobi Fora Formation is 565 meters thick and contains many hominid fossils. Most that have been uncovered were found within the Okote, KBS and Burgi members of the formation. These strata are composed of siltstones, claystones, sandstones, and limestones (Vondra and Bowen, 1976). The Upper Member of the formation, where the KNM-ER 1813 fossil was deposited, was created by successive deposition of floodplain silts and sands (Johnson and Raynolds, 1976).

The paleoenvironment of Koobi Fora included intermittent volcanism, lake sedimentation, earthquakes related to volcanism and fault movement and climate change (Fitch and Vondra, 1976). Lake Turkana was a larger lake in Plio-Pleistocene times, as seen in lake sediments within the Koobi Fora Formation. The Turkana Basin, during Plio-Pleistocene times, was a grassy savannah teeming with big game, all sizes of mammals, and more than one species of Hominid. Camel, elephant, hippopotamus, birds, rhinoceros, horses and crocodiles were just some of the fauna present (Coppens and Howell, 1976). Varied ecological niches including forest, rivers, savannah and steppe filled the landscape of the African Rift Valley near Lake Turkana almost 2 million years ago. Hominid sites such as Koobi Fora and the Omo region were wooded savannah interspersed with riverine woodlands and montane forest in higher elevations (Bonnefille, 1976).

“Quite apart from being attractive habitats, lake basins provided extraordinarily favorable conditions for the preservation of animals who died there over the last three to four million years. Their bones were fossilized because of rapid burial after death by sediments brought by rivers draining into the lakes and by rises and falls in the lake levels. More recent movements of the earth’s crust have uplifted ancient land surfaces and, as a result of the natural forces of erosion, fossils and habitation sites have been exposed, providing a wealth of information for the reconstruction of the earliest stages of human existence.” (Harris, 1981)

Dating of KNM-ER1813 was accomplished by a combination of many dating techniques. Biostratigraphy utilizing elephant, pig, and hippopotamus remains found in each level was used. Biostratigraphy functions on the idea that animals found associated with a stratigraphic layer can offer knowledge of when that layer was deposited. Species, with a well-known chronology of habitation in a region can be used to estimate rough dates for a fossil. Stratigraphic, paleomagnetic and radiometric dating have also yielded dates for the H. habilis fossil KNM-ER 1813. Steno’s Law, the assumption that lower undisturbed strata will be older than higher strata, is used in the relative dating method of stratigraphy. Paleomagnetism dates strata using the tiny magnetic particles found inside and their orientation to the magnetic pole. The magnetic pole shifts periodically and the orientation of the particles can indicate which pole was magnetic at the time. Radiometric dating techniques, such as Potassium Argon and C14 dating, offer absolute dates. The volcanic tuffs that overlay the sedimentary members of the formation have been reliably correlated with other volcanic deposits in the region, similar to how dates are correlated in overlapping dendrochronographic samples. Analysis of the sediments, calibrated with the world’s geomagnetic pole reversal time scale (Day, 1986), along with Potassium-Argon dates put the fossil at about 1.8 mya. In addition, the upper limit of the Koobi Fora Formation itself has been dated by associated fauna and K/Ar to 1.3 mya, backing up the 1.8 mya date for KNM-ER 1813. While a more precise chronology for the Formation strata, along with dates for fossils, has not been established, it is agreed that KNM-ER 1813 came from sediments of the lower portion of the Upper Member or upper portion of the Lower Member (Dean and Wood, 1982).

The paleoenvironment in which H. habilis lived and died, producing the KNM-ER 1813 fossil, was typical of the Plio-Pleistocene epochs. The continents had come to rest in roughly their present positions. The earlier Tethys Sea had been closed off as Eurasia and Africa collided. A cooler climate from past epochs ensued including glaciers in the northern hemisphere. The transfer of flora and fauna from Africa and Eurasia, a cooler climate and a radiation of primates characterize the Late Pliocene and Early Pleistocene. In the Koobi Fora region specifically, a permanent lake of fluctuating size distinguished the area (Wood, 1991).

Fossil Description

KNM-ER 1813 is one of the most complete H. habilis fossils recovered. It represents an almost complete cranium with out the mandible. Although it was not found intact, the availability of almost all fragments assured that the reconstruction is accurate. Most of the missing fragments are from the basal section and temporal regions on both sides. The right portion of the foramen magnum is missing. Also on the right side, the lower portion of the zygomatic arch and some of the temporal bone is missing. The left zygomatic arch is also almost completely absent. Besides a few other small cranial vault fragments, that is all that was not recovered. There is also slight deformation of the right eye orbit and right posterior mastoid region.

Overall, KNM-ER 1813 is a gracile specimen. It has a cranial capacity of ~510 cc, exhibits a slight prognathism and occipital torus. Moderate brow ridges and postorbital constriction also characterize KNM-ER 1813. Post-cranially, H. habilis heights varied from 109 cm to 152 cm (Bunney, 1988).

The basicranium is elongated in the anterior portion and may reflect the reduction in tooth size. Cheek teeth exhibit buccolingual narrowing in the lower premolars and lower molars (Rightmire, 1993). In other Homo fossils teeth are described as megadont, while KNM-ER 1813’s teeth are describes as mesodont, smaller in size (Ferguson, 1987). H. habilis teeth generally range from Australopithecus size and H. erectus size. In addition to teeth, the habilis crania differ in other ways.

The face of KNM-ER 1813 is short and more prognathic than some other H. habilis fossils, although still less than australopithecines. Facial characteristics include the brow ridges, which are arched and thick. The nuchal region of the occipital bone is advanced, resembling H. erectus (Rightmire, 1993). A slight torus also fits this suite of advanced characteristics. In his essay, Wood (1993) conveys that while Homo habilis may represent advances in the cranial features, it retained primitive australopithecine characteristics in the post crania.

Nasal aperture is a trait that varies by fossil among Homo habilis. Previous australopithecines had unprojecting noses. This feature may have been evident in KNM-ER 1805 (Franciscus and Trinkaus, 1988). KNM-ER 1813 and KNM-ER 1470 most likely exhibited a projecting, more advanced nose found in modern humans.

In addition to a mosaic of features found in both more primitive hominids and more modern hominids, 1813 offers a controversy on the sex of the fossil. Most anthropologists agree it represents a female, however there is dissent. Ferguson (1987) posits that KNM-ER 1813 is a male, representing a separate species. While I will discuss this later in the paper, it is important to mention it here.

A comparison of KNM-ER 1813 and KNM-ER 1470 offers one a chance to observe the extent of the variation currently occurring in the taxon Homo habilis. KNM-ER 1470 has a cranial capacity of ~750 cc, compared with 1813’s ~510cc. In 1470, the supraorbital torus is almost nonexistent. It is moderate in KNM-ER 1813. They both exhibit oblique angles in the occipital and nuchal squama. The KNM-ER 1470 cranium has a large temporal fossa, while 1813 is still larger. Face length is long in KNM-ER 1470, and short in KNM-ER 1813. Nasal opening size is small in both. KNM-ER 1470 has a thin-walled cranium. It is long-faced, and wide across the orbits. The face itself is lower on the skull than KNM-ER 1813. Postorbital constriction is slightly more pronounced in 1470 and it has more area for muscle attachment along the mastoid processes than 1813. In KNM-ER 1813, the eye orbits are concave on the face, while 1470 exhibits no concavity.

KNM-ER 1470 and KNM-ER 1813 each represent a “morph” of the H. habilis species. Characteristics that differentiate between these two morphs include facial shape, sphenoid expansion, mandible size, robusticity and dentition (Wood, 1993). Overall size is another important differentiating factor.

KNM-ER 1805 is another unique fossil crania from Koobi Fora. Unlike other H. habilis fossils, it has cranial cresting and robust mastoid processes. In most ways, it is similar to KNM-ER1813 and is grouped in the 1813 morph.

Discussion and Theme

Homo habilis KNM-ER 1813, along with the remaining Koobi Fora habiline fossils, offer anthropologists an opportunity to evaluate taxonomic classifications refining classifications. The multiple species versus sexual dimorphism debate regarding Homo habilis is one of these opportunities. Wood (in Lieberman et al, 1988) states that in higher primates sexual dimorphism accounts for the greatest degree of difference between members of a species.

The issue of sexual dimorphism versus multiple species in Homo habilis has been thoroughly examined by many. Still, there is no consensus. Studies by Tobias (In Wood, 1993) have asserted Homo habilis as one species. He cited the total morphological pattern didn’t justify any divisions of the fossils currently in the genus. With the one species conclusion as the null hypothesis, he is correct in his stance that most studies with contrary findings are tenuous. A 95% level is often not reached, or just barely reached.

Two years ago, Miller (2000) reviewed many past studies on this matter and challenged all rejections of the null hypothesis citing too small samples and problems with measurement differing from study to study, or from casts. Endocranial volume variation, probability estimates of sexual dimorphism, cranial angle variation, and multivariate analysis of the facial region were just a few of the methods reviewed and rejected.

On the other hand, most primary literature regarding this debate proposes the opposite. In a study focusing on cranial features, Ferguson (1987) challenges the commonly held assumption that KNM-ER 1813 is a female. Through new analysis of the sexing traits, most of which are present on 1813, he concludes it is actually a male cranium. With this new conclusion, he compares KNM-ER 1470 and KNM-ER 1813 as males. Differences in features included supraorbital ridges, occipital protrusions, facial measurements, alveolar prognathism, dental characteristics, and parietal thickness and shape. Because of his conclusion of a male sex for the KNM-ER 1813 fossil, some features of the cranium are of particular interest in his argument for two species. He measured auricular heights and found that it was greater in KNM-ER 1813. Since auricular height should be greater in males, this lends credence to his claim. Another male characteristics exhibited by the 1813 fossil are supraorbital ridges. Ferguson cites primitive features present in KNM-ER 1813 as evidence of its place in a more primitive taxon, Homo antiquus. These traits included cranial capacity, the ratio of tooth mass to brain size, and prognathism.

One year later, Lieberman and colleagues (1988) also proposed a multiple species hypothesis based on facial height and width. The KNM-ER 1470 was classified as having an australopithecine face, while KNM-ER 1813 was associated with modern traits. Their results stated that KNM-ER 1470 and KNM-ER 1813 exhibited more sexual dimorphism relative to Gorilla variation. In addition, they also stated that if the Homo habilis fossils did represent one species, it had another pattern of sexually dimorphic traits not seen in any other high primate.

Wood (1992) conducted a study utilizing measurements of brain size and also found that more variation existed in H. habilis than in male and female gorilla crania. He called for a better definition of the genus Homo. In 1993, Wood added that habilis should be defined either temporally or geographically to avoid confusions. Since the cranial capacity in early Homo was more different than expected in a single hominid species, he raised the KNM-ER 1470 crania as the type fossil for a new taxon, Homo rudolfensis.

Another craniofacial analysis of Homo habilis crania in relation to both chimpanzee and human variation found extreme difference. The degree of sexual dimorphism found was comparable to that in Orangutans (Kramer, 1995). Rightmire (1993) and McHenry (1991) both suggest that extreme sexual dimorphism may actually be evidence of multiple species.

Phylogenic assessment of KNM-ER 1813 has been complicated. When KNM-ER 1813 was discovered, along with KNM-ER 1470 at Koobi Fora, it was recognized that they did not fit into an existing genus. They were neither A. africanus or H. erectus. Brain size and cranial morphology precluded them from erectus classification. These same characteristics also precluded it from africanus classification. Leakey called KNM-ER 1813 something besides H. habilis, but recognized that it was a gracile Homo fossil (Lieberman et al, 1988). In the period 1.6 mya to 2.4 mya there were already several hominid species in both Homo and Australopithecus. Where did they belong?

In phylogenies, “splitting” is preferable to “lumping” in the creation of sister taxa. One can always recombine as more evidence presents itself. Lieberman (1996) claims the most parsimonious cladogram groups KNM-ER 1813 with H. erectus as sister taxa. Africanus is also grouped with them. Then, KNM-ER 1470 is equally related to those three. Wood (1992) draws a cladogram grouping H. erectus, H. ergaster, and H. sapiens together with H. habilis and H. rudolfensis equally ancestral. Africanus is placed as ancestral to all.

Whether these phylogenies are accurate has yet to be seen. With time and more fossils, our picture of human evolution will become more and more clear. For now, Homo habilis is an anomaly to be studied and used to improve techniques of cladistics, biometrics, and physical anthropology as a whole.

Conclusion and Summary

The Homo habilis fossil KNM-ER 1813 remains a controversy. While most involved agree it belongs in Homo habilis where does that leave other H. habilis fossils such as KNM-ER 1470? The degree of variation expressed in these fossils may be too great to be one species. A lack of definitive sexing of KNM-ER 1813 also complicated its classification among the genus. While the null hypothesis has not been satisfactorily disproved, more evidence must be found and studied. Sexual dimorphism is not an adequate answer to this debate. Until we uncover enough fossils to increase the sample, this controversy will persist. And it should. Science is a self-correcting process. Peer evaluation and open discourse of ideas is crucial to the advancement of our understanding

The Homo habilis cranium identified as KNM-ER 1813 was discovered as part of the Koobi Fora Remains, which were formerly known as the East Rudolf Hominids. The Koobi Fora Remains were discovered during the East Rudolf (Koobi Fora) Research Project directed by R. Leakey and G. Isaac. All of the fossil remains found in this site are classified in the family Hominidae. KNM-ER 1813, itself, was found in 1973 as an almost complete cranium by K. Kimeu. The Koobi Fora site is located in present-day Kenya at East Turkana, formerly known as East Rudolf. It is approximately 15 km from the Eastern shore of Lake Turkana.

KNM-ER 1813 was uncovered from the Koobi Fora Formation, one of Late Pliocene to Early Pleistocene sediment beds dating roughly to 1.8 mya. These sedimentary strata are interspersed with volcanic tuffs, aiding in dating of the fossils recovered from the site. The Plio-Pleistocene sediments at Koobi Fora are broken into three formations: the Guomde Formation disconformity, the Koobi Fora Formation, and the Kubi Algi Formation. The Koobi Fora Formation, which housed the KNM-ER 1813 fossil, is divided into the Upper Member and Lower Member. These sedimentary formations are separated by the KBS volcanic tuff. The Koobi Fora Formation is 565 meters thick and contained many hominid fossils. Most were found within the Okote, KBS and Burgi members of the formation.

Dating of this fossil was accomplished by a combination of many dating techniques. Biostratigraphy utilizing elephant, pig, and hippopotamus remains found in each level was used. Stratigraphic, paleomagnetic and radiometric dating have also yielded dates for the H. habilis fossil KNM-ER 1813. The volcanic tuffs that overlay the sedimentary members of the formation have been reliably correlated with other volcanic deposits in the region, similar to how dates are correlated in overlapping dendrochronographic samples. Analysis of the sediments, calibrated with the world’s geomagnetic pole reversal time scale (Day, 1986), along with Potassium-Argon dates put the fossil at about 1.8 mya. In addition, the upper limit of the Koobi Fora Formation itself has been dated by associated fauna and K/Ar to 1.3 mya, backing up the 1.8 mya date for KNM-ER 1813.

The paleoenvironment in which H. habilis lived and died, producing the KNM-ER 1813 fossil, was typical of the Plio-Pleistocene epochs. The continents had come to rest in roughly their present positions. The earlier Tethys Sea had been closed off as Eurasia and Africa collided. A cooler climate from past epochs ensued including glaciers in the northern hemisphere. The transfer of flora and fauna from Africa and Eurasia, a cooler climate and a radiation of primates characterize the Late Pliocene and Early Pleistocene. In the Koobi Fora region specifically, a permanent lake of fluctuating size distinguished the area (Wood, 1991). Volcanic and tectonic events also characterized the Koobi Fora region of Kenya.

KNM-ER 1813 is a moderately well preserved fossil of H. habilis. The successive volcanic layers have sealed in each sedimentary layer, causing preservation of the fossils within. KNM-ER 1813 was subjected to only minor tectonic disruptions while it was in situ. The fossil is almost complete. Both eye orbits are incomplete. The left zygomatic arch is missing. A portion of the foramen magnum is missing, as well.

KNM-ER 1813, a Homo habilis fossil is extremely relevant to human evolution. Current phylogenic classifications place H. habilis as an ancestor of H. erectus, which eventually led to H. sapiens. In other words, without Homo habilis, we might not be here today as modern Homo sapiens. In addition to this paramount relevance as a primitive human ancestor, H. habilis is an interesting species for other reasons. First, morphologically it has traits of both A. africanus and H. erectus. H. habilis is a small, gracile specimen with a light build, a globular cranium shape, and only moderate post-orbital constriction. It has no cranial cresting, and a small degree of nasal prominence. It exhibits facial characteristics similar to that of the Homo genus. KNM-ER 1813 is unique within its species classification, in that it has cranial capacity of only 510 ml. That is well within the A. africanus range. Other H. habilis have over 600 cc usually. H. habilis has a large brain for its body size and is associated with the Olduvai tool tradition. KNM-ER 1813 is similar to Olduvai Hominids habilis fossils in its dental features. Some scientists posit that KNM-ER 1813 represents a small female, while other fossils represent larger males.

In summary, KNM-ER 1813 represents a unique H. habilis specimen. It was found in the Koobi Fora Formation in East Turkana, Kenya. Little depositional damage was done to this fossil, as it lay protected under volcanic tephra for approximately 1.8 million years. It represents a transitional stage of human evolution more advanced than previous Australopithecines such as A. africanus, but less derived than other Homo species such as H. erectus or ergaster. This is important, as it may be an evolutionary link between Australopithecines and later Homo species leading to modern H. sapiens.

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Tobias, PV (1991) Olduvai Gorge Vol. IV: The Skulls, Endocasts and Teeth of Homo

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Wood, BA. (1991) Koobi Fora Research Project Vol. 4. Hominid Cranial Remains.

Clarendon Press, Oxford.