These defects may correlate with prenatal stress to the mother (malnutrition) or perinatal stress of birth. Enamel defects are most common on canine teeth, and occur in approximately 90% of gorillas and orangutans compared to 45% of chimpanzees. Evidence from Taung and other australopithecine fossils indicates that the life history pattern of modern humans may have developed as recently as tens of thousands of years ago rather than millions (Smith 1992).Įnamel defects in deciduous teeth correlate with physiologic stress during development. Strikingly, the Taung child fossil of Australopithecus africanus demonstrates an eruption pattern more consistent with the great apes. The order of tooth eruption is also significant, with modern humans developing permanent anterior teeth significantly sooner than great apes relative to eruption of the first molar. Life history theorists theorize that long-lived, slow growing mammals offset the risk of dying before somatic maturation by reaching reproductive maturity first. Using data about dental eruption, studies by Shigehara reveal that shorter-lived mammals complete somatic development prior to sexual maturity, while longer-lived primates tend to reach sexual maturity before transition to adult dentition is completed. Paranthropus and Australopithecus africanus juveniles seem to exhibit wearing patterns consistent with early weaning, lending evidence that our life history and shortened interbirth interval may extend farther back than molar eruption suggests (Aiello 1991) later weaning species (chimpanzee and orangutans). Tooth wear characteristics are also informative, with greater wear in earlier weaning great apes (gorilla) vs. This early weaning may have allowed for a shorter inter-birth interval in our long-lived, slow growing species (Dean 2009). In contrast, humans are likely to have acquired our early weaning and extended childhood more recently in our evolutionary history. Based on the skull of the Nariokotome youth, an example of a juvenile homo erectus, it appears that the first molar eruption occurred later in chronologic age compared to australopithicus, which featured a growth history similar to that of the great apes. The ability to distinguish between a juvenile and an entirely different species is critical in assembling the fossil record. The presence of deciduous teeth has allowed anthropologists to determine the approximate age at death for a number of early hominin fossils. Their more equal size may reflect the fact that each cusp begins its initial mineralization closer together in time than permanent molar tooth cusps do. Deciduous molar teeth tend to have more pointed and, in the case of dm2, more equally sized cusps than permanent molars. This diastema is pre-canine in the upper tooth arch and post-canine in the lower tooth arch. Deciduous ape canine crowns project beyond the occlusal plane and create a space (diastema pl. Deciduous ape canines are much taller and have a concave posterior border that extends onto a distal talon or talonid, whereas human deciduous canines are narrowest at the cervix and broaden out to become widest in the mid-crown. Great ape deciduous incisors are, like their permanent counterparts, larger than human deciduous incisors.
Deciduous tooth roots are proportionately longer than permanent tooth roots relative to their crown height and deciduous molars have more widely splayed roots with little common root trunk. Deciduous tooth crowns are whiter, have larger pulp chambers, have thinner enamel, are more bulbous than permanent tooth crowns and lack a sinuous cervical margin. A successional permanent tooth develops beneath and lingual to each one. Deciduous molars are, perhaps more correctly, sometimes referred to as deciduous premolars. In all Hominids there are 20 deciduous teeth (di2: dc1: dm2 in each quadrant of the mouth). All deciduous teeth are small enough to begin to form before birth but small immature jaws cannot accommodate large permanent teeth (one reason for diphyodonty). Primates, like most eutherian mammals are diphyodont (have two generations of teeth) although some mammals have deciduous teeth that are not replaced (usually the first post-canine tooth), some have lost a few or all of their deciduous teeth, and others shed them all before birth.
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