Estimation of Age by Skull

Forensic identification from skeletal remains incorporates various parameters that conclude to identification in terms of gender, age, stature etc. Estimating the age from bone samples recovered from crime scene is a tedious task to perform. The age of a person from his skeletal remains cannot be determined absolutely, though the forensic anthropologists can estimate with certainty to which age group the bone samples belong e.g. By analysis of skull sutures, it can be said that the skull is that of an adult between 20-25 years of age, however, saying that the skull is that of a person with age of 25 years is rarely possible and if said, it has to be corroborated by various other evidences supporting the fact.

Determining the age from skeletal remains becomes important from forensic perspective as it provides the investigating agencies, the data that is important to establish the identity of the person by delimiting the area of investigation. There are numerous methods for age estimation from human bones that forensic anthropologists have been using from the past including closure of fontanels and sutures found in skull, analysis of dentition, epiphyseal fusion in long bones etc. Let us study these features in detail:

Fontanels

Fontanels are cartilagenous soft-tissues found in between the cranial bones of infant skull. They hold cranial bones in position in an infant as the cranial bones are not completely ossified in the skull of a newborn. Fontanels are of huge importance as they provide the infant skull with a great degree of flexibility that helps the infant descend through the pelvic outlet of mother.

Another significance of fontanels is that it helps the skull accommodate space for growing brain. As the infant grows, fontanels are replaced by fixed joints called sutures that ossify cranial bones in position. Generally, all fontanels are closed by 5 years of postnatal life but may remain open in case of some congenital abnormalities. Human infant skull generally has 6 fontanels:

1. Anterior fontanel (largest, present in bregmatic region)
2. Posterior fontanel (present in the occipital region, also known as lambdoidal fontanel)
3. Mastoid fontanel (two, present on either side of skull above the region of mastoid process)
4. Sphenoidal fontanel (two, present on either side of skull above sphenoid bone)

The closure time and sequence of these fontanels are listed in the table below:

Table 1 showing closure time of various fontanels

Picture showing fontanels of skull, lateral view (left) and top view (right).

Sutures

When it comes to age estimation from skeletal remains, skull is the most common structure available and used due to its structural robustness as it remains unaffected by environmental changes, mass disasters, animal interference, fire burns etc. Age estimation from skull is usually done by examination of sutures. Sutures are the joints which hold the cranial bones in position. As the infant ages through his life, sutures replace fontanels. In a skull, sutures can be seen as zig-zag lines between various cranial bones, which are initially unfused but fuse later, gradually as the age advances.

Sutures are the most common parameters used for age estimation but also the most uncertain one. Many researches have suggested that though sutures are most frequently used for age estimation they offer a wide degree of variability in closure time. This variability may be natural depending upon the environment, sex, race, nutrition etc. of a person or may be due to the presence of congenital abnormalities. It has been found that ectocranial sutures closure is variable naturally but endocranial suture closure is stable, hence, while estimating age from cranial sutures the endocranial sutures should be preferably examined. Overall, it can be said that age estimation from sutures is the easiest and simplest to carry out but involves a huge amount of risk. Let us look at various sutures found in human skull:

1. Metopic sutures: articulation of two frontal bones in the forehead region
2. Coronal suture:articulating frontal and parietal bones
3. Sagittal suture:articulating both parietal bones together
4. Lambdoidsuture:articulating parietal bones with occipital bone
5. Basilar suture: between occipital and sphenoid bone
6. Squamosal suture:between parietal and temporal bone

Other sutures that are used to estimate age:

1. Occipito-mastoid suture:between occipital bone and mastoid portion of temporal bone
2. Parieto-mastoid suture: between parietal bone and mastoid portion of temporal bone
3. Spheno-temporal suture:between temporal and sphenoid bone
4. Spheno-parietal suture:between parietal and sphenoid bone

Picture showing sutures of skull in lateral view.

Picture showing sutures of skull in posterior view.

The ectocranial and endocranial closure time of these sutures are given in the tables below:

Table 2 Endocranial closure time of major sutures of skull*

Table 3 showing closure of various skull sutures**

*the closure time of sagittal, coronal and lambdoid sutures in table 3 are ectocranial, while that of other sutures mentioned in the same table are not specified.

*the closure time of various sutures and fontanels mentioned in the tables above are based on researches conducted, these values are subject to vary.

General interpretation: A general interpretation made by analyzing the major sutures like sagittal, coronal and lambdoid suture is that if all the three sutures are not fused, the age of skull is said to be under 30 years. While, if these sutures are completely fused the age of the skull is said to be above 40 years.

In the next post, we will learn about estimation of age by bones. Happy Reading 🙂