23 Identification and Description of Fossil casts

Dr. Vijeta Dr. Vijeta

Contents:

• Introduction
• Cast of fossils
• Identification and Description of Fossil casts (Kenyapithecus, Dryopithecus, Sivapithecus, Ramapithecus, Australopithecines)
• History and context of the fossil discoveries
• Early Humans (homo habilis, Homo erectus, Homo neanderthalensis)
• Modern Humans (Cro-Magnon, Grimaldi and chancelade)
• Summary

Learning Objectives:

1.  To know about the cast of fossils.

2.  To explain the identification and description of fossil casts.

Introduction

Evolution is confined almost entirely to the Miocene epoch, from 23 to 5 million years ago, which probably covers most of the earlier history of the group. The first evidence for a diversification of the apes is in the early Miocene, and an origin of the group in the latest Oligocene or earliest Miocene seems likely. During the middle and late Miocene, apes underwent an extensive phyletic and geographic radiation, expending their range throughout the equatorial and subequatorial regions of the Old World. Before the end of the Miocene, apes had become extinct over much of the area that they had once occupied. Ape lineages did persist into the Plio-Pleistocene, although some subsequently became extinct. All these surviving lineages were probably more widespread than they are today. However, their record after about 8 million; years ago includes only scanty remains of Pleistocene gibbons and orangutans, dental remains of a recently extinct Pleistocene giant ape (Gigantopithecus) and Pliocene fossils of uncertain affinity, all from southeastern Asia (Hills, 1992). The discovery of human remains more than 10000 years old is always a cause for scientific celebration. Such finds are rare and valuable, as each new sample or technique may reveal threads of evidence in our understanding of human evolution. Consequently, there is a persistent requirement to measure, cast and sample from existing and newly discovered human bones (Cook & Ward, 2008).

Fig-1: Fossil Records of Human Evolution

(Source Link: www.googleimage.com)

Cast of fossils: Cast, the positive replica (plaster, plastic, bronze etc.) made from the mold and mold is the material (usually a type of rubber) that is brushed or poured over the original to make the negative. The cast may be made from the bone or soft tissues. The important points about the original are:

• What is the material and condition of your original? (Note: porous materials may be darkened by the molding process).

The easiest material to use is plaster, which comes in any varieties. Some casting in material include the following-

• Common Plaster of Paris is soft & easily scratched.
• High strength gypsum cements & dental plasters are harder, especially when mixed with hardener instead of water. Details on casts in these materials can be excellent & shrinkage is minimal.
• Many plastics & epoxys are also available but shrinkage of these materials combined with their tendency to shorten mold lives.

There are various techniques for colouring casts of all materials to bring out details. All involve a vehicle such as alcohol for dissolving and spreading artist’s pigments. Artist’s fixatives and spray lacquer add a long-lasting appealing & protective finish to the final protect (White at al., 2011).

Identification & Description of Fossil casts: The fossil record shows a sequence from simple bacteria to more complicated organisms through time and provides the most compelling evidence for evolution. There are fossil casts from African, Asian, and European hominids to study the process of evolution.

Kenyapithecus: In Africa, Kenyapithecus is found at sites that span most of the middle Miocene, such as Maboko, Fort Ternan and Nachola in northern Kenya. Kenyapithecus has derived facial and dental features that differ from those of the early Miocene genera and are more like those of modern apes. The identifying features are:

• It has thick layer of enamel on its molar teeth.
• Very robust jaws (which indicate a shift in food preferences and habitat).
• Its teeth and jaws certainly suggest powerful biting and prolonged chewing, perhaps on very hard and tough foods a diet unlike that of any living primate.
• There was substantial sexual dimorphism in the danines and probably in body size.
• The recently discovered Otavipithecus from the late middle Miocene of Namibia represents the first record of Miocene apes from southern Africa. It is so far known from one specimen, a lower jaw that, unlike Kenyapithecus, appears to have restively thin-enamelled teeth. Dryopithecus: Somewhat later than the earliest Eurasian representatives of apes with thick-enamelled teeth is Dryopithecus, sporadically known from western and central Europe. The distinctive features are: Dryopithecus has thin-enamelled teeth and probably had a diet different from that of the apes with thick enamel. The genus ‘Ramapithecus’ (which is historically important in the study of human evolution) was once thought to be present at some of these sites as well as at the middle Miocene sites of Fort Teman, Maboko and Pasalar, but it is now clear that the only distinguishing feature of specimens attributed to this genus was their small size. These are probably females or small species of the genera at these various sites (Hills, 1992).

Sivapithecus: The Siwalik record of Sivapithecus favors the more recent of each range and none of these dates conflicts with the fossil evidence. Sivapithecus shares with the orangutan several features of the skull and face that are almost certainly derived within the Hominoidea, and some of which are uniquely shared to the exclusion of all other simian primates. These include:-

• The absence of a bony sinus in the brow area of the skull.
• A very narrow bony partition between the eyes
• Vertically elongated orbits and,
• A set of features in the sub-nasal area that relates to the way the hard palate joins the pre-maxillary bone at the base of the nose where the incisors are embedded, (the naso-alveolarclivus). Forelimbs of Sivapithecus are monkey-like, implying quadrupedal walking and climbing.

Oreopithecus: A virtually complete skeleton of Oreopithecus has been unearthed. This is similar to modern apes in many features of the trunk and limbs. Oreopithecus thus seems to have been more adapted for suspension than was either Sivapithecus or Rudapithecus (Hills, 1992).

Ramapithecus: Ramapithecus was considered a possible human ancestor on the basis of the reconstructed jaw and dental characteristics of fragmentary fossils. The first Ramapithecus fossil (fragments of an upper jaw and some teeth) were discovered in 1932 in fossil deposits in the Sivalik hills of Northern India. Ramapithecus represented the first step in the evolutionary divergence of humans from the common hominid stock that produced modern apes and humans. Identifying features are:-

1.  Incisors and canines are smaller in relation to molar.

2.  Absent of molar cusps.

3.  Upper jaw is shortened & does not protrude forward but is long vertically.

4.  Palate is arched & wider from behind than the front.

5.  Face is short & deep, suggestive of not used teeth as weapon.

6.  He used hands for hunting & defense i.e. Ramapithecus was probably an erect biped with hands free.

Fig-1: Fragments of Upper teeth of Ramapithecus compared with Man and Ape

(Source: www.googleimage.com)

Australopithecines: Most fossil hominids back to 2 million years ago, and perhaps just beyond, are more closely related to modern humans than they are to chimpanzees and belong to our own genus, Homo. The earlier part of the lineage has been allocated to several fossil species, of which Homo erectus and Homo habilis are the two best known. Compared with the African apes, most of all these forms of Homo have a relatively large brain, relatively reduced chewing (or molar) teeth and limb bones that are, except in points of detail, like those of modem Homo sapiens. However, there are at least four, and perhaps five, species of hominid that lack the expanded brain, the reduced molar teeth and the skeletal features of Homo. They antedate or overlap with the earliest representatives of Homo, and are known collectively as the australopithecines (Hills, 1992).

Fig-3: Species of Australopithecines

(Source Link: www.googleimage.com)

Types of Australopithecines: Australopithecines are conventionally split into two groups on the basis of their body types –

1.  The gracile (more lightly built) and

2.  Robust (more ruggedly built) forms.

The robust australopithecines can be divided into at least two species of the genus Paranthropus: P. robustus from southern Africa and. P. boisei from eastern Africa. The name Australopithecus (‘southern ape’) is then reserved for the two gracile australopithecine taxa: A. africanus from southern Africa and A. afarensis from eastern Africa. Paranthropus is here used as a separate genus for the robust australopithecines.

Table-1: Two -schemes for tire-nomenclature and taxonomy of Australopithecines

Australopithecines are classed as hominids rather than pongids because, like Homo. The features included reduced canine teeth and their limbs were substantially adapted for bipedal walking. However, their brains-were relatively small and details of the brain fissures were different from those of later hominids. Moreover, although australopithecine limb bones could resist the loads and stresses of upright stance and locomotion, they did so without having the characteristic shape of the Homo pelvis and thigh bone (femur).

Fig-4: Distinguishing Features of Australopithecines

(Source: Cambridge Encyclopedia of Human Evolution)

History and context of the fossil discoveries: It is not easy identifying the Features that mark the human genus Homo, as the group contains not just all living people but our closest fossil relatives as well. Moreover, many features that distinguish humans are behavioral, and leave no fossil evidence. It is very difficult judging whether a particular kind of early human had developed a language, society or art, and other features that can be recognized in fossils are usually used to infer these attributes.

Southern African australopithecines: The first australopithecine fossil was found-in southern Africa in 1924 in a cave that was exposed at the Buxton Limeworks, which is close to Taung, hear Kimberley. The Taung cave, like those at the other australopithecine sites in southern Africa, was formed as expansions of water channels that ran through the limestone. Once the caves started forming, they developed openings onto the ground surface, through which soil and debris, including bone, was washed in.

Eastern African australopithecines: Australopithecine fossils from eastern Africa are found very different geological circumstances. The first fossil discovered at Garusi in Tanzania, a site that is now included in the Laetoii site complex. More than 40 years elapsed between that first discovery and the re-exploration of the area by Mary Leakey, which resulted in the’ discovery of fossils that make up part of the collection attributed to Australopithecus afarensis, now considered to be a gracile australopithecine species distinct from A africanus. Three views predominate about the relationship between the australopithecines and Homo. In the first scheme, A. afarensis is the common ancestor of two lineages, one leading to Homo, the other leading via A. africanus to P. robustus and P. boisei. The second scheme also sees A. afarensis as ancestral to A. africanus, but it has the latter as the common ancestor of two lineages, one being Homo and the other leading to, and including, and the robust australopithecines. A third scheme has fewer supporters, but it may prove to be more durable than the others. In this arrangement, the australopithecines and Homo share a common ancestor, which has not yet been found in the fossil, record. Two lineages result from such an ancestor. One leads to the robust australopithecines via A: afarensis; the other leads, via A. africanus, to Homo. These and other differences in our perceptions of hominid relationships, however, still owe as much to disagreements about methodology as to differences in interpretations of the fossils themselves (Hills, 1992).

Early Humans: A large brain has usually been the single most important feature, although on its own this may be an unreliable guide to membership of the genus Homo. In early fossils; body size must also be taken into account to give an idea of relative brain size; if this were not done, some small-bodied and small-brained early humans might not qualify as human at all. Most members of the genus Homo do have a brain volume of more than 700 milliliters (ml), considerably larger than that of the largest robust australopithecine or living ape. To house a brain of such a size, the human cranial ‘ vault is large in relation to the face, and the face is tucked under the vault more than is the case in early apes or hominids. Other diagnostic features of humans include the-presence of a prominent nose (as represented by raised bone Surfaces around the nasal opening) and a bony spine at the centre of the base of the nasal opening. These characteristics are further reflected in various measurements of the face. The base of the human skull is short and well flexed or folded up. Such distinctive features may be related to the development of language and the remodeling of the throat to give a lower position for the voice box. The jaws of humans are also notable, because the bone of the lower jaw is rather thin and there may be a vertical front to the jaw or even a bony prominence – a chin. The teeth, and in particular the last of the cheek teeth, are small. Tooth eruption is slow compared with that in apes and early hominids.

Homo habilis: In the early 1960s, stone tools were found scattered among hominid bones close to the site where A. boisei had been unearthed. Because of its association with tools, this early human was called Homo habilis, meaning “handy man.” The distinguishing features are:

• Brain volume of about 680 cubic centimeters, larger than the australopithecine range of 400 to 550 cubic centimeters.
• Small in stature, with arms longer than legs (Hills, 1992).

Fig-5: Two hominid skulls of Homo habilis

(Source: Cambridge Encyclopedia of Human Evolution)

Fig-6: Reconstruction of large and small Homo habilis skulls

(Source: Cambridge Encyclopedia of Human Evolution)

Homo erectus: Homo erectus was a lot larger than Homo habilis—about 1.5 meters tall. It had a large brain, about 1000 cubic centimeters and walked erect. Its skull had prominent brow ridges and, like modern humans, a rounded jaw.

Java man: A Dutch doctor and anatomist named Eugene Dubois unearthed a skull cap and a thighbone in 1891. He informally called Java man, for three reasons: 1. The structure of the thigh bone clearly indicated that the individual had long, straight legs and was an excellent walker. 2. The size of the skull cap suggested a very large brain, about 1000 cubic centimeters. 3. Most surprisingly, the bones seemed as much as 500,000 years old, judged by other fossils Dubois unearthed with them (Hills, 1992).

Fig-7: Homo erectus skull

(Source: www.mhhe.com)

Homo neanderthalensis: Neanderthals, Homo neanderthalensis, lived in Europe and the Near East from 200,000 to 28,000 years ago. They were thick-boned with a larger brain, they buried their dead, and they made hunting tool.

Fig-8: Reconstructed skulls of two Neanderthals showing distinguishing features

(Source: Cambridge Encyclopedia of Human Evolution)

Modern Humans: The first modern humans were anatomically distinct from neanderthals with their less –prominent brow ridges, higher, shorter and more rounded skulls,shorter lower jaws with a bony chin and a less robust skeleton.they also had a hip bones od modern type, suggesting that the hip joints functional like those of modern people. Three species of modern man are- Cro-Magnon, Grimaldi and chancelade.

Cro-Magnon remains are representative of the earliest anatomically modern human beings. However, the skull of Cro-Magnon show traits that are unique to modern humans, including the tall, rounded skull with a near vertical forehead. A large brow ridge, no longer tops the eye sockets and there is no prominent prognathism of the face and jaw (http://humanorigins.si.edu).

Grimaldi: The fossil remains were found in the village Grimaldi, on the Mediterranean coastal region. Two Skulls were found i.e. of a woman (30 yrs. old) and a boy (15 yrs. old). The characters are-mastoid processes are small and supraorbital ridges are feebly developed & the forehead is well developed. Large orbits with sub-rectangular shape and broad nose with low bridge were observed. Chin is poorly developed and teeth are large. Majorities of characters show affinities with the Negroids.

Chancelade Man: Fossil remains were discovered in 1888 in a rock shelter at Chancelade, southwestern France. The skull is long and narrow measuring 19.4 cm in length and 18.75 cm in breadth and thus showing a cranial index of 70.9 (dolichocephalic). The vault is high and supraorbital ridges are slightly marked. The forehead is almost vertical while the parietal tuberosities were well marked. The mastoid processes are fully developed. The Chancelade man resembles the modern Eskimo in the following characters: short stature; large, high dolichocephalism head; elevated sagittal region; a very wide and long face; flat, prominent cheek-bones; narrow nasal aperture; powerful masticator apparatus (http://www.shareyouressays.com).

Fig-9: Specimens of the Cro-Magnon (early modern humans)

(Source: Cambridge Encyclopedia of Human Evolution)

Table-2: Distinguishing features of early human Species

Fig-10: Fossil cast of early human Species

Source Link: www.googleimage.com

(A=Archaic H. sapiens B=H. neanderthalis C= Homo sapiens sapiens D= Homo erectus E= Homo

ergaster F=Archaic H. sapiens)

Summary

The discovery of human remains more than 10,000 years old is always a cause for scientific celebration. Such finds are rare and valuable, as each new sample or technique may reveal threads of evidence in our understanding of human evolution. Consequently, there is a persistent requirement to measure, cast and sample from existing and newly discovered human bones. Cast, the positive replica (plaster, plastic, bronze etc.) made from the mold and mold is the material (usually a type of rubber) that is brushed or poured over the original to make the negative. The cast may be made from the bone or soft tissues. The fossil record shows a sequence from simple bacteria to more complicated organisms through time and provides the most compelling evidence for evolution. There are fossil casts from African, Asian, and European hominids to study the evolution i.e. Kenyapithecus, Dryopithecus, Sivapithecus, Ramapithecus, Australopithecines and early humans (Homo habilis, Homo erectus, Homo neanderthalensis & modern man are- Cro-Magnon, Grimaldi and Chancelade).

References

• Cook, J., & Ward, C. (2008). Conservation assessment of the Neanderthal human remains from Krapina, Croatia and its implications for the debate on the display and loan of human fossils. British Museum technical research bulletin, 2, 39-44.
• White, T. D., Black, M. T., & Folkens, P. A. (2011). Human osteology. Academic press.
• Alfonso, M. P., & Powell, J. (2007). Ethics of flesh and bone, or ethics in the practice of paleopathology, osteology, and bioarchaeology. Human remains: Guide for museums and academic institutions, 5-20.
• HILLS, C. (1992). The Cambridge encyclopedia of human evolution. Cambridge: Cambridge University Press.
• Fenton, C. L., Rich, P. V., Fenton, M. A., & Rich, T. H. (1989). The fossil book: a record of prehistoric life. Courier Corporation.
• Seilacher, A. (2007). Trace fossil analysis. Springer Science & Business Media.
• Tattersall, I. (1995). The fossil trail: How we know what we think we know about human evolution.
• Oxford University Press, USA.
• Etler, D. A. (1996). The fossil evidence for human evolution in Asia. Annual Review of Anthropology,25(1), 275-301.
• www.mhhe.com/biosci/genbio/raven6b/graphics/raven06b/other/raven06b_23.pdf
• http://humanorigins.si.edu/evidence/human-fossils/fossils/cro-magnon