Human evolution during the Plio-Pleistocene of eastern Africa
Ongoing fieldwork in Kenya's Turkana Basin by the Koobi Fora Research Project, directed by Meave Leakey and Louise Leakey, has recovered important fossil remains of human ancestors and their relatives ('hominins'). An important part of my research focuses on the description and analysis of the skull remains among these fossils. This has resulted in the description of a new Pliocene hominin genus, Kenyanthropus platyops, based on the cranium KNM-WT 40000 from 3.5 million year old layers at Lomekwi on the west side of Lake Turkana (Leakey et al., 2001 and Spoor et al., 2010).
- Left to right: Kenyanthropus platyops cranium KNM-WT 40000 from Lomekwi (Kenya), 3.5 Myr old;
Juvenile Australopithecus afarensis skeleton DIK-1-1 from Dikika (Ethiopia), 3.3 Myr old;
Homo erectus crania KNM-ER 42700 (small) and OH 9 (large), 1.4-1.6 Myr old.
More recent fieldwork at Koobi Fora and Ileret (east of Lake Turkana, Kenya) has provided important new evidence documenting the radiation of early Homo in the period between 1.4 and 2.1 million years ago. Fossils discovered at Koobi Fora between 2007 and 2009, confirm that in addition to Homo erectus two further species of early Homo occurred (Leakey et al., 2012). These are most commonly known as Homo habilis and Homo rudolfensis. Most prominent among the new finds are a remarkably complete lower jaw (KNM-ER 60000) and a face (KNM-ER 62000). Based on affinities with the well-known cranium KNM-ER 1470 these are attributed to Homo rudolfensis.
Earlier we had found fossil evidence that Homo habilis survived in eastern Africa until at least 1.4 million years ago (Spoor et al., 2007). Hence, this species and Homo erectus did not form a single evolutionary lineage, but lived side by side in eastern Africa for nearly half a million years. Moreover, the discovery of a particularly small calvaria of H. erectus (KNM-ER 42700) indicates that this taxon overlapped in size with H. habilis, and may have shown marked sexual dimorphism (Spoor et al., 2007).
- CT-based reconstructions of KNM-ER 62000 (left) and KNM-ER 60000 (right), and the 2009 discovery site of the latter on the east side of Lake Turkana, Kenya (middle).
Additional projects concern a detailed assessment of the Pliocene juvenile Australopithecus afarensis skeleton DIK-1-1 from Dikika, Ethiopia, in collaboration with Zeresenay Alemseged (California Academy of Sciences; Dikika Research Project), and the Pleistocene partial Homo cranium KNM-OG 45500 from Olorgesailie, Kenya, in collaboration with Rick Potts (Smithsonian National Museum of Natural History).
Leakey MG, Spoor F, Dean MC, Feibel CS, Antón SC, Kiarie C, & Leakey LN (2012) New fossils from Koobi Fora, northern Kenya, confirm taxonomic diversity in early Homo. Nature 488, 201-204.
Spoor F, Leakey MG, Leakey LN. (2010) Hominin diversity in the middle Pliocene of eastern Africa: the maxilla of KNM-WT 40000. Phil. Trans. Roy. Soc. B 365, 3377-3388.
Spoor F, Leakey MG, Gathogo PN, Brown FH, Antón SC, McDougall I, Kiarie C, Manthi FK & Leakey LN (2007) Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya. Nature 448, 688-691.
Alemseged Z, Spoor F, Kimbel WH, Bobe R, Geraads D, Reed D & Wynn JG. (2006). A juvenile early hominin skeleton from Dikika, Ethiopia. Nature 443, 296-301.
Leakey MG, Spoor F, Brown FH, Gathogo PN, Kiarie C, Leakey LN & McDougall I (2001) New hominin genus from eastern Africa shows diverse middle Pliocene lineages. Nature 410, 433-440.
Spoor, F (1997) Basicranial architecture and relative brain size of Sts 5 (Australopithecus africanus) and other Plio-Pleistocene hominids. South Afr. J. Science 93: 182-187. [PDF]
NB: If you own, or are considering to buy a BoneClones "cast" of the Kenyanthropus cranium KNM-WT 40000, please read this: Spoor F, Leakey LN & Leakey MG (2002) Bone Clones "re-creation" of Kenyanthropus. Physical Anthropology 3: 2. [PDF]
My views on two important discoveries of human fossils can be found here:
- Spoor F (2013) Small brained and big mouthed. Nature 502, 452-453. (Homo erectus at Dmanisi) [PDF]
- Spoor F (2011) Malapa and the genus Homo. Nature 478, 44-45. (Australopithecus sediba) [PDF]
The bony labyrinth and inner ear: comparative and functional morphology
The bony labyrinth inside the petrous temporal bone houses the organ of hearing in the cochlea and the organs perceiving movement and spatial orientation in the vestibule and semicircular canals (structures jointly known as the inner ear). The size and shape of the bony labyrinth often differs between species and even subspecies (Spoor and Zonneveld, 1998; Gunz et al., 2012), and can thus aid taxonomic identification of fossils. A good example is the possibility to distinguish between modern humans and Neanderthals, just on their bony labyrinths alone (Hublin et al., 1996; Spoor et al., 2003).
- Side view of the right bony labyrinth of a modern human (left) and
a Neanderthal (right). Scale bar is ~5 mm.
Species differences shown by the bony labyrinth are related to a number of factors. These include, among others, functional requirements of the sense organs of balance and hearing, and the spatial integration with the surrounding cranial base and brain. Because of its link with both brain morphology and body coordination (i.e. 'keeping balance') the bony labyrinth is of particular interest when studying human evolution; it provides information about the emergence of bipedal locomotion and about the process of brain expansion. Examining hominin fossils does indeed show that the bony labyrinth changes substantially in the course of human evolution, but the timing of the changes is not always as expected. For example, the semicircular canals, which sense head rotations, do not appear to change much when bipedal locomotion first emerged at least 4 million years ago. Instead, the main change is seen from about 2 million years ago, when our ancestors acquired a body plan and the types of gait broadly similar to modern humans (Spoor et al., 1994; Spoor, 2003).
Originally the bony labyrinth was studied using medical computed tomography (CT), which strongly restricted both the morphological details that could be observed and the accuracy of measurements that could be taken. Now high-resolution CT images are increasingly available and the bony labyrinth is studied in much more detail and with greatly improved methods in a joint effort with my colleagues Romain David, Philipp Gunz and Alex Stoessel. Among the new approaches are the use of 3D landmarks and geometric morphometrics to analyse size and shape differences (Gunz et al., 2012), and the application of sophisticated models of the semicircular canal system to assess how morphological differences relate to modified sensory function (see here).
Braga J, Thackeray JF, Dumoncel J, Descouens D, Bruxelles L, Loubes J-M, Kahn J-L, Stampanoni M, de Beer F, Spoor F. (2013) A new partial temporal bone of a juvenile hominin from the site of Kromdraai B (South Africa). J. Hum. Evol. 65, 447-456.
Gunz P, Ramsier M, Kuhrig M, Hublin JJ & Spoor F (2012) The mammalian bony labyrinth reconsidered, introducing a comprehensive geometric morphometric approach. J. Anatomy 220, 529-543.
Spoor F, Hublin JJ, Braun M & Zonneveld F (2003) The bony labyrinth of Neanderthals. J. Hum Evol. 44, 141-165.
Spoor F (2003) The semicircular canal system and locomotor behaviour, with special reference to hominin evolution. Cour. Forsch. Senckenberg. 243: 93-104 [PDF]
Spoor F & Zonneveld F (1998) Comparative review of the human bony labyrinth. Yrbk Phys. Anthrop. 41, 211-251.
Hublin J-J, Spoor F, Braun M, Zonneveld F & Condemi S. (1996) A late Neanderthal from Arcy-sur-Cure associated with Upper Palaeolithic artefacts. Nature 381, 224-226.
Spoor F, Wood B & Zonneveld F (1994) Implications of early hominid labyrinthine morphology for the evolution of human bipedal locomotion. Nature 369, 645-648.
Mammalian morphology & evolution
Past research systematically explored the relationship between the arc size of the semicircular canals and locomotor behaviour among primates and other groups of mammals. Empirically it was found that the semicircular canals are significantly larger in species that are agile and acrobatic than in those that are more cautious in their locomotion. A plausible factor underpinning this relationship appears to be that arc size is among the factors that affect the functional response characteristics of the canal system. This functional relationship was used to assess the locomotor behaviour of a wide range of fossil and subfossil primate taxa.
- Lateral view of the left bony labyrinth of a galago (left) and a
loris (right). Scale bar is 1 mm. The semicircular canals of the
leaping galago are substantially larger than those of the slow,
quadrupedal climbing loris (both have similar body size).
Ryan TM, Silcox MT, Walker A, Mao X, Begun DR, Benefit BR, Gingerich PD, Köhler M, Kordos L, McCrossin ML, Moyà-Solà S, Sanders WJ, Seiffert ER, Simons E, Zalmout IS, Spoor F. (2012) Evolution of locomotion in Anthropoidea: the semicircular canal evidence. Proc. Roy. Soc. B. 279, 3467-3475
Silcox MT, Bloch JI, Boyer DM, Godinot M, Ryan TM, Spoor F & Walker A (2009). The semicircular canal system in early primates. J. Hum. Evol.56, 315-327.
Walker A, Ryan TM, Silcox MT, Simons E & Spoor F (2008) The semicircular canal system and locomotion: the case of extinct lemuroids and lorisoids. Evol. Anthrop. 17, 135-145.
Spoor, F., Garland, Th., Krovitz, G., Ryan, T.M., Silcox, M.T. and Walker, A. (2007) The Primate Semicircular Canal System and Locomotion. Proc. Nat. Acad. Sci. 104, 10808-10812.
Additional work with Nathan Jeffery (University of Liverpool) studied the fetal development of the primate inner ear, as well as the structural relationship between the subarcuate fossa and the semicircular canals. The latter to assess if spatial constrains of the fossa and its brain contents (the petrosal lobule of the paraflocculus) are a factor influencing the arc size of the surrounding semicircular canals.
Jeffery N, Ryan TM & Spoor F. (2008) The primate subarcuate fossa and its relationship to the semicircular canals part II: adult interspecific variation. J. Hum. Evol. 55, 326-339.
Jeffery N, Spoor F. (2006) The primate subarcuate fossa and its relationship to the semicircular canals part I: prenatal growth. J. Hum. Evol. 51, 537-549.
Jeffery N, Spoor F. (2004) Prenatal growth and development of the modern human labyrinth. J. Anatomy. 204, 71-92.
Cetaceans (whales and dolphins) are the order showing the most derived inner ear and bony labyrinth among mammals. Most strikingly, they have remarkably small semicircular canals, a phenomenon which appears related to the transition from a terrestrial to a marine environment. In collaboration with Hans Thewissen (North Eastern Ohio College of Medicine, USA) the evolutionary history of this dramatic change is investigated by examining Eocene archaeocete fossils.
Spoor F and Thewissen JGM (2008) Balance: Comparative and functional Anatomy in Aquatic Mammals. In: Sensory Evolution on the Threshold, Adaptations in Secondarily Aquatic Vertebrates (Thewissen JGM and Nummela S, eds), Chapter 16. University of California Press, Berkeley, 257-284.
Spoor F, Bajpai S, Hussain ST, Kumar K., Thewissen JGM (2002) Vestibular evidence for the evolution of aquatic behaviour in early cetaceans. Nature 417, 163-166.
Computed tomography & palaeontology
Ever since the discovery of x-rays, palaeontology has greatly benefited from radiography and computed tomography (CT) to visualize both internal and external aspects of fossils. Some research and reviews of the practical aspects of using CT to study fossils can be found here:
Spoor F, Jeffery N & Zonneveld F. (2000a) Using diagnostic radiology in human evolutionary studies. J. Anatomy 197, 61-76.
Spoor F, Jeffery N & Zonneveld F. (2000b) Imaging skeletal growth and evolution. In: Development, Growth and Evolution: implications for the study of the hominid skeleton. (O'Higgins P and Cohn M eds.). Academic Press, London, pp.123-161. [PDF]
Spoor CF, Zonneveld FW & Macho GA (1993) Linear Measurements of Cortical Bone and Dental Enamel by Computed Tomography: Applications and Problems. Am. J. Phys. Anthrop. 91, 469-484. [PDF]
- Imaging the Homo erectus cranium KNM-WT 15000: lateral radiograph (left), parasagittal CT scan at the level
of the right dental row and inner ear (middle), and 3D surface visualization extracted from a stack of CT scans
(right). Unlike radiographs, CT scans
have the ability to distinguish between fossil bone and the sedimentary
matrix in the maxillary sinus (asterisk), and to resolve
details such as the root canals of the molars(arrowhead), and structures
of the bony labyrinth (arrow).
Selected blasts from the past
Corbeddu Cave (Sardinia)
Between 1982 and 1990 I participated in the palaeontological excavations at Corbeddu Cave, Sardinia, under the direction of the late Paul Sondaar (Institute of Earth Sciences, Utrecht University). Prior to my PhD, and as a first venture into hominin palaeontology I described the human maxilla and temporal bone we had found in pre-Neolithic layers (~9000 yBP). These specimens, and other evidence, suggest that humans co-existed for substantial time with the endemic island fauna of Pleistocene Sardinia. Such co-existence, as opposed to near-instant eradication of endemic island species, is now a phenomenon of particular interest, following the discovery of hominin ("hobbit") remains as part of the Pleistocene fauna of the island Flores (Indonesia).
- Left: the 1983 Utrecht University team at Corbeddu Cave. Right: occlusal view of the left
maxilla CB85.3013 from Corbeddu Cave, combined with a mirror-imaged cast of the specimen
and an extant human molar that fits the wide M1 alveolus.
Spoor F (1999) The human fossils from Corbeddu Cave, Sardinia: a reappraisal. Deinsea 7, 297-302. [PDF]
Spoor CF and Sondaar PY (1986). Human fossils from the endemic island fauna of Sardinia. J. Human Evol. 15, 399-408.
Hyena locomotion and morphology
For part of my MSc Biology in the Netherlands I did some work on hyenas: skeletal proportions, gait analysis and muscle dissection of Hyaena hyaena and Crocuta crocuta. Following occasional requests for reprints the resulting articles are listed below, with links to PDFs.
Spoor CF and Badoux DM (1989). Descriptive and functional morphology of the locomotory apparatus of the spotted hyena (Crocuta crocuta Erxleben, 1777). Anat. Anz. 168, 261-266. [PDF]
Spoor CF and Badoux DM (1988). Descriptive and functional myology of the back and hindlimb of the striped hyena (Hyaena hyaena L. 1758). Anat. Anz. 167, 313-321. [PDF]
Spoor CF and Badoux DM (1986). Descriptive and functional myology of the neck and forelimb of the striped hyena. Anat. Anz. 161: 375-387. [PDF]
Spoor CF and Belterman Th (1986). Locomotion in Hyaenidae. Contrib. to Zool. 56, 24-28. [PDF]
Spoor CF (1985): Body proportions in Hyaenidae. Anat. Anz. 160, 215-220. [PDF]
The other half of my MSc Biology concerned Myotragus balearicus, an endemic island bovid from the Pleistocene of the island of Mallorca. I analysed its body proportions and the functional morphology of its limb bones.
Spoor CF (1988) The limb bones of Myotragus balearicus Bate 1909. Proc. Kon. Ned. Ak. Wetensch. B91:295-309. [PDF]
Spoor CF (1988) The body proportions in Myotragus balearicus Bate 1909. Proc. Kon. Ned. Ak. Wetensch. B91:285-293. [PDF]