Introduction

In 1907, at the Mauer sand pits in Germany, a nearly complete mandible was discovered by a quarry worker. This mandible (Mauer 1) validated Otto Schoetensack's conviction that there would be Pleistocene human remains found in the quarry amid the more common rhino, bear, elephant, bison, deer, and horse remains. Schoetensack published an extensive monograph on the mandible a year later in which he designated it to a new species of hominid, Homo heidelbergensis. Schoetensack named a new species without justifying it by describing the unique anatomical features of the species. Along with this lack of morphological comparisons and differentiation from other known species, the lack of older specimens (and just about any specimen at all for a long period of time) kept heidelbergensis from becoming accepted among paleoanthropologists.

However, though Schoetensack did not justify his species designation, there are features that set Mauer 1 apart from Neanderthals and H. sapiens. The age of the specimen also creates a distinction, as it dates to appromiately 500 kyr. With a wealth of newer discoveries in the last 30 years, the species designation of heidelbergensis has been revived. The validity of heidlebergensis seems to be current among many researchers at this time, but it is by no means universally accepted. Many researchers argue that heidelbergensis is invalid, and is simply a chronospecies (though, that is exactly what some proponents argue for, among those who see anagenesis as a valid speciation event).

Diagnostic Features

Due to the fact that there have been so many different specimens attributed to the erectus offshoots, it is difficult to create a list of features that differentiate heidelbergensis from erectus or H. neanderthalensis. In general, heidelbergensis specimens show a continuation of evolutionary trends that occurred in the Lower Pleistocene into the Middle Pleistocene. Along with changes in robustcity of cranial and dental features, there is a marked increase in brain size from erectus to heidelbergensis. Some of the features of Middle Pleistocene Homo that shows these trends include:

• An increase in brain size (early Homo approximately 900 cc, heidelbergensis specimens approximately 1200cc).
• A shift from the widest part of the brain case from the cranial base to the parietal regions.
• The rear of the cranial vault becomes more vertical.
• A gradual reduction in cranial robusticity.
• A decline in postcranial robusticity also.
• A tendency for a shift from shorter more robust stature to taller more leaner bodies.
  

The increase in brain size may have also come with an increase in brain complexity, although this is difficult to determine from endocasts, and may have to remain supposition only. However, the increase in absolute size, and the change to larger frontal and parietal lobes indicate that there may have been a reorganization of the functional anatomy of the hominid brain. The increase in size itself indicates changes in behavior that lead to the ability to more easily acquire nutritional resources. This is due to the high nutrition requirements of brain tissue, especially during development. There is increasingly more convincing evidence in the use and control of fire, and in the hunting of animals for food. This time period is important for many reasons, and may be the time period when more modern behavior began to develop.

The type specimen of heidelbergensis is Mauer 1. This specimen shows a host of both primitive and derived features that, in general, have been accepted as proof of ancestry to the Neanderthal line. The specimen was discovered in 1907 in the Mauer sand pits near Heidelberg, Germany. The exact age of the specimen is uncertain, but it dates at least as old as 400 kyr, and possibly as old as 700 kyr. However, a date of 500 kyr is generally accepted as most likely. Some of the traits that distinguish this specimen include:

• A sloping symphysis that contains two mandibular tori on its inner side (primitive).
• An especially broad ramus (primitive).
• An M2 that is larger than the M1 (primitive).
• A very robust mandible (primitive).
• Taurodont molars (derived).
• A reduced M3 (derived).
• Dramatic buccal cusp dominance in the P3 (derived).
  

Another Middle Pleistocene hominid that may or may nor be attributed to heidelbergensis is the Bodo cranium. Bodo was discovered in 1976 at Bodo d'Ar, Ethiopia, in the Middle Awash Valley. The specimen is important because of its age (600 kyr), and its suit of features. The cranium is extremely robust and sports the biggest face known among hominid specimens. Acheulean tools were found near the site with the remains of hippos, baboons, and antelopes, indicating that Bodo may have been butchering animals for meat, and may have even hunted them. However, Bodo himself was also the victim of butchery, as seen by the distinctive cutmarks on several parts of the cranium. Bodo has also been at the center of controversy among scientists and, as such, has had relatively few publications describing it. Some of the features that distiguish Bodo include:

• Approximately 1100cc brain.
• A broad massive face.
• An extremely broad nose (the largest of any Pleistocene hominid).
• The lower nasal margin is guttered.
• Robust zygomatics that angle backwards from the nasal margins.
• An expanded maxilla, and an associated lack of a canine fossa (though there is a very shallow fossa lateral to the nose).
• A long sloping frontal bone.
• A thick browridge with a fery deep temporal fossa.
• A remarkably flexed cranial base.
• A flat sloping anterior face on the mandibular fossa, that is the result of emphasis on anterior tooth loading.
  

The cave site of Arago, at Tautavel, France, in the eastern Pyrenees mountains has yielded the remains of many hominids, with the cranium Arago XXI the most complete. Due to its size and robust facial features, Arago XXI is generally considered a young male, though some consider it female. The dating of the material is problematic, with a wide range of dates being claimed. Henry de Lumley considers the material to be approximately 400 kyr, though it is much more likely that the material dates 200 kyr to 300 kyr. Arago 21 is fairly complete, lacking only the temporal and occipital bones. Some of its distinguishing features include:

• An approximately 1166cc brain.
• Broca's cap and other speech areas are well-developed.
• Evidence of an extensive right parietal association area.
• Evidence of right-handedness from an asymmetric endocast.
• Lacks a frontal boss.
• Presence of marked parietal boss.
• Presence of an angular torus.
• A low broad sagittal keel.
• A deep supraorbital sulcus.
• A short and prognathic face, with an expanded maxilla.
  

The material from Petralona is very similar morphologically to the Arago material. The Petralona 1 cranium was discovered in 1960, hanging suspended from a stalagmite in a cave of Katsika Hill, in Petralona, Greece. The specimen has a very ambiguous morphology, which led to several different species attributions. It was originally attributed to neanderthalensis, and was later classified as erectus, but it falls much closer to the morphology of the various heidelbergensis specimens, especially Arago XXI. The specimen was originally thought to be approximately 70 kyr, as young as many Neanderthal specimens, and later estimates put that number at closer 700 kyr. However, ESR dating has given a date of between 247 kyr and 127 kyr, though some researchers estimate its likely date to be around 300-400 kyr due to its morphology. Some of its features include:

• A large brow ridge - a double-arched supraorbital torus.
• Lacks a canine fossa.
• An open occipital angle.
• A 1220 cc brain estimate.
• A massive face, though it is non-projecting.
• A prominent transverse torus.

There are many other specimens that can be (and have been) attributed to heidelbergensis, and they generally have all the same common traits that have been mentioned for the specific specimens discussed above. Material from Apidima, Kabwe, Steinheim, Atapuerca, etc. can be and have been designated as heidelbergensis, or erectus. In general, there is a decrease in robusticity, an increase in brain size, and a tendency towards more derived features of neanderthalensis or sapiens.

Conclusions

The validity of heidelbergensis as a chronospecies depends on whether one accepts anagenesis as a valid method of speciation. H. heidelbergensis specimens are generally Middle Pleistocene hominids in Europe or Africa (though some specimens from Asia such as Dali have been designated to heidelbergensis by a few individuals), with the major difference from erectus being spatial.

Bibliography

Adam, K.D. 1985. "The chronological and systematic position of the Steinheim skull." In Ancestors: The Hard Evidence, ed. by E. Delson, pp. 272-276. New York: Alan R. Liss.

Arsuaga, J.L., J.M. Carretero, A. Gracia, and I. Martínez. 1990. "Taphonomical analysis of the human sample from the Sima de los Huesos Middle Pleistocene site (atapuerca/Ibeas, Spain)." In Human Evolution, vo. 5, no. 6, pp. 505-513.

Arsuaga, J.L., I. Martínez, A. Gracia, J.M. Carretero, and E. Carbonell. 1993. "Three new human skulls from the Sima de los Huesos Middle Paleolithic site in Sierra de Atapuerca, Spain." In Nature, vol. 362, pp. 534-537.

Clark, J.D., J. de Heinzelin, K.D. Schick, W.K. Hart, T.D. White, G. Woldegabriel, R.C. Walter, G. Suwa, B. Asfaw, E. Vrba, and Y.H. Selassie. 1994. "African Homo erectus: Old radiometric ages and young Olduwan assemblages in the Middle Awash Valley, Ethiopia" In Science, vol. 264, pp. 1907-1909.

Conroy, G.C., C.J. Jolly, D. Cramer, and J.E. Kalb. 1978. "Newly discovered fossil hominid skull from the Afar depression, Ethiopia." In Nature, vo. 276, pp. 67-70.

Cook, J., C.B. Stringer, A.P. Currant, H.P. Schwarcz, and A.G. Wintle. 1982. "A review of the chronology of the European Middle Pleistocene hominid record." In Yearbook of Physical Anthropology, vol. 25, pp. 19-65.

de Lumley, H., and M.A. de Lumley. 1971. "Découverte de restes humains anténéandertaliens datés du début de Riss á la Caune de l'Arago (Tautavel, Pyénées-Orientales)." In Comptes Rendues des seances de l'Acacdemie de Sciences de Paris, vol. 272, pp. 1729-1742.

de Lumley, H., and M.A. de Lumley. 1974. "Pre-Neanderthal human remains from Arago cave in southwestern France." In Yearbook of Physical Anthropology, vol. 17, pp. 162-168.

Holloway, R.L. 1982. "Homo erectus brain endocasts: Volumetric and morphological observations with some comments on cerebral asymmetries." In L'Homo erectus et la Place de l'Homme de Tautavel parmi les Hominidés Fosiles., ed. by H. de Lumley, pp. 355-369. 1er Congrès International de Paléontologie Humaine, Nice, Prètirage. Vol. 1. Nice: Louis-Jean.

Johanson, D., and B. Edgar. 1996. From Lucy to Language. New York: Simon and Schuster Editions.

Jones, S., R. Martin, and D. Pilbeam, eds. 1992. The Cambridge Encyclopedia of Human Evolution. Cambridge: Cambridge University Press.

Keith, A. 1926. The Antiquity of Man. London: Williams and Norgate.

Klein, R.G. 1973. "Geological antiquity of Rhodesian Man." In Nature, vol. 244, pp. 311-312.

Kokkoros, P., and A. Kanellis. 1960. "Découverte d'un crane d'homme paléolithique dans la peninsula Chalcidique." In Anthropologie, vol. 64, pp. 132-147.

Lovejoy, C.O. 1982. "Diaphyseal biomechanics of the locomotor skeleton of Tautavel man with comments on the evolution of skeletal changes in Late Pleistocene man. In L'Homo erectus et la Place de l'Homme de Tautavel parmi les Hominidés Fosiles., ed. by H. de Lumley, pp. 447-470. 1er Congrès International de Paléontologie Humaine, Nice, Prètirage. Vol. 1. Nice: Louis-Jean.

Poulianos, A.N. 1973. "Petralona: A Middle Pleistocene cave in Greece." In Archaeology, vol. 24, pp. 6-11.

Schoetensack, O. 1908. Der Unterkiefer des Homo heidelbergensis aus den Sanden von Mauer bei Heidelberg. Leipzig: Wilhelm Engelmann.

Stringer, C.B. 1974. "A multivariate study of the Petralona skull." In Journal of Human Evolution, vol. 3, pp. 397-404.

Stringer, C.B. 1993. "Secrets of the Pit of Bones." In Nature, vol. 362, pp. 501-502.

White, T.D. 1986. "Cut marks on the Bodo cranium: A case of prehistoric defleshing." In American Journal of Physical Anthropology, vol. 69, pp. 503-509.

Wolpoff, M. 1999. Paleoanthropology. second edition. Boston: McGraw-Hill.

Woodward, A.S. 1921. "A new cave man from Rhodesia, South Africa." In Nature, vol. 108, pp. 371-372.