Fig 1.
A range of measurements made on 323 intact mandibles of African elephants.
The lateral surface of a bisected mandible showing attempts to describe the position of the foramen mentale (h,i,j,k,l) and measurements of the length of the jaw (m,n,o,p). Note the mandible has been rocked forward from its centre of gravity in an attempt to maintain consistency in measurement between animals. None of these measurements proved to be useful in determining a stable reference point.
Fig 2.
Demonstrates age estimation in the African elephant using the Age Reference Line.
A straight line is drawn from Point A at the base of the mandibular foramen to Point B at the most distal point of molar occlusal wear. A line is drawn or vizualised along the ridge of the medial mandible (Line C). The two lines intersect at the red dot, Point D, which has been termed the Age Reference Point (ARP). A measurement of 10 cm is made from this point passing centrally through the distal molar. In this example 10 cm is marked as the distance from ARP (Point D) to the yellow line at E. This yellow line at E is termed the Age Reference Line (ARL). In this example the ARL falls on the 7th lamella (L) of the 4th molar. By reference to this ARL in Table 1 the elephant’s age can be estimated as 11.5 years. The green arrow at the mesial end of the mandible marks the mesial end of the dental alveolus, named the ‘crest’.
Fig 3.
Placement of the Age Reference Point (ARP; red dot) and Age Reference Line (ARL; yellow line) on jaws of varying ages.
A) Near-term fetus M1_–1.6 cm. B) A female at M3L5 (age 4 y). C) A female at M4L3 (age 7.5 y). D) A female at M5L6 (age 22 y). E) A male at M6L8 (age 40 y). F) A female at M6 + 2.3 cm (age 67 y). The dashed line (in B and C) marks the full extent of the medial ramus ridge, which is used to identify the ARP. The scalple handle indicates the placement of a foramen mentale on the lateral surface of the mandible.
Fig 4.
A mandible of an aged female African elephant.
The white arrow/red dot marks the Age Reference Point (ARP) and the yellow line marks the Age Reference Line (ARL). The remnant of the tooth in the right mandible had rotated as shown. Grid = 1cm2.
Table 1.
Molar progression table relating age to Age Reference Line.
Fig 5.
The Age Reference Line (ARL) ranking, showing the molar progression stage associated with data from previous ageing studies [3, 10].
Plateaus can be seen in the graph because some lamellae move through more quickly than others, particularly the smaller ones at each end of molars, and some lamellae may not pass the ARL in occlusal wear (eg M6L1).
Table 2.
Measurements from the Age Reference Point to the mesial end of the dental alveolus made on African elephants in Zimbabwean populations.
Table 3.
Mandible width of African elephants within Zimbabwe.
Fig 6.
Placement of foramena mentale.
(A) Placement of foramena mentale (FM) in the mandibles of two African elephants. Pictures of the left mandible are flipped horizontally to enable a comparative view of both sides of the mandible. i) Note the very small posterior FM on the right mandible compared to the left. ii) Note the variation in placement of the FM. (B) Variation in foramen mentale placement and ageing in African elephants using the FM technique. Both right mandibles of the two elephants (i and ii) have a similar Laws age but they show an age difference of 5 years when using the FM technique.
Fig 7.
The ranking of African elephant mandibles using the Age Reference Point (ARP) and Age Reference Line (ARL) to denote molar progression, occlusal view.
A) Four jaws at rank M5L8, i and iv are females and ii and iii males. B) Four jaws at rank M6L5, i and ii are male mandibles, ii and iv are female mandibles. NB The L1 of M6 is often not visible in early occlusal wear (just visible in ‘iv’) but can be identified on tooth extraction. C) Two jaws (i male and ii female) at M6L8, and two jaws (iii male and iv female) at M6 + 1cm. Yellow line = ARL.
Fig 8.
Examples of molars of African elephants at different Age Reference Line stages.
Green squares indicate the seventh lamellae (L7). A) three molars at stage M4L7 (molar 4 lamella 7), B) three molars at M5L7, and C) three molars at M6L7. All show similar development, but not necessarily wear, in each tooth at each stage.
Fig 9.
A comparison of the typical development (not necessarily occlusal wear) of molar teeth of African elephants at different lamellae numbers according to the position of the Age Reference Line.
Molars are aligned with mesial end to the left with the smaller molar at the top, progressively getting larger downward. Red dots indicate the lamellae number (L), which is 10 cm mesial from the Age Reference Point (See Fig 2). A) M5 (top) and M6 (bottom) at L2. M5 tends to come into wear first on L1. Due to space restrictions, M6 tends to emerge into wear from underneath the final lamellae of M5, it therefore most commonly wears first on either L2 or L3. B) M4, M5 and M6 at L3. The root base is much longer in M5 than M4, M5 is also longer and deeper. When comparing M5 and M6, M6 is typically showing first wear on L2 or L3. In M6 the lamellae also tend to taper to a smaller size whereas M5 tends to have a convex distal end. C) M5 and M6 at L4 (no M4 available). Note the convex distal end of M5 compared with the tapered end of M6. D) M4, M5 and M6 at L5.
Fig 10.
A comparison of the typical development (not necessarily occlusal wear) of molar teeth of African elephants at different lamellae numbers according to the position of the Age Reference Line.
Molars are aligned with mesial end to the left with the smaller molar at the top, progressively getting larger downward. Red dots indicate the lamellae number (L), which is 10 cm mesial from the Age Reference Point (See Fig 2). E) M4, M5 and M6 at L6. F) M4, M5 and M6 at L7. G) M4, M5 and M6 at L8. H) M4, M5 and M6 at L9.
Fig 11.
A comparison of the typical development (not necessarily occlusal wear) of molar teeth of African elephants at different lamellae numbers according to the position of the Age Reference Line.
Molars are aligned with mesial end to the left with the smaller molar at the top, progressively getting larger downward. Red dots indicate the lamellae number (L), which is 10 cm mesial from the Age Reference Point (See Fig 2). I) M5 and M6 at L10. J) M6 at L11 The foremost part of this tooth is broken off and a wooden wedge is seen below the tooth. K) M6 at L12.