Faunal Bone Lab
Introduction
This lab report discusses the examples of different skeletal elemental elements in three different mammals living in coastal Otago, Aotearoa (New Zealand) in the 19th century. The three species of mammal that I chose to examine are the Canis familiaris, the Oris aries, and the Arctocephalus forsteri or in their common names dogs, sheep, and fur seals. Specifically, the three elements I chose to compare between the three species are the pelvis, the humerus, and the scapula. Using these skeletal elements I will explain how it articulates and what with, how one would orient the bone, each one’s distinguishing features and how to tell various species apart. I will also discuss what the structure means for the animal it came from, such as the differences in locomotion. After general notes and more specific bone information have been covered about each bone I will discuss the implications when these bones are found in the archaeological record. Based on the condition of the bones, when they are found broken or worn, and how easily or difficult particular species or specific bones are to tell apart.
PELVIS
The pelvis, or hip bone, is the lower articulation point of the mammals’ lower spine and laterally to the hind limbs. The major difference between the fur seal and both the dog and sheep lies in the evolutionary adaptations of Pinnipeds, mammals that spend much of their lives in water. Due to this major differentiation in habitat, the form completely changes while still having the same major parts. The pelvis itself is a combination of four separate bones that fuse in mammals; the ilium, the acetabulum, the ishcium, and the pubis. Depending on which aspect is discovered in the record the bone and the species could be easy or difficult to differentiate.
Ilium
The thin to wide (moving cranially and dorsally [head to tail and back to stomach]) wing-like portions of bone on the cranial end of the pelvis are the Ilium with the rounded ends being called the iliac crest and the thinner bases connected to the acetabula region. If these cranial aspect pieces were found broken apart in an assemblage, they can be used to identify a species. On the dog (Figure 1) and the sheep (Figure 2) the wings of the ilium protrude to various amounts. The dogs’ wings are flattened leading the iliac crest to appear thin and well rounded. The sheep’s wings are large triangular shapes, extending further medially than that of the dogs’, causing the iliac crest to extend wider and appear more as an oval than the dogs’. The other major difference between the land-based species in the ilia is the extent to which the crests angle laterally, with the sheep’s angle of growth being greater than the dogs’. The fur seals’ ilia are distinct from the form of the land mammals, because (as illustrated in Figure 3) they are flattened, wide, and short in comparison with the rest of the pelvis. The iliac crests facilitate a wide opening by the medial articulation of the spine and the angle increases laterally. Like the dogs’ the crests are well-rounded due to the lack of extra wing growth, making these regions of seal and dog slightly more difficult to tell apart.
Acetabulum
These round indentations are the distal articulation points to the proximal end of the animals’ femurs. On land, animals these points will lie on the ventral side (as shown in Figure 1) to aid the animals in walking on land because the hind limbs are underneath them. This is illustrated in Figure 2 by the arrows pointing to the unseen acetabula on the underside of the sketch. However, as shaded in Figure 3 the fur seal’s acetabula are positioned on the lateral edges of the dorsal side, closer to where the spine medially articulates with the two halves of the pelvis.
Ischium and Pubis
On the caudal end of the pelvis are the Ischia and Pubis bones. The Ischia are located on the most caudally with the pubis being fused medial and cranially. The most differentiable aspects are the tubers that form on both sides laterally. On the sheep’s pelvis [shown in Figure 2] these grow a couple of centimeters and appear only a centimeter wide. In contrast, the dog’s tubers (labelled in Figure 1) only appear to extend laterally about a centimeter and are wider than the sheep’s, growing more into the base of the Ischia create a rounded edge. These tuberosity ishium are not found on the fur seal’s pelvis. Making note of the easily differentiable fur seal pelvis, the Ischia are thin and curved dorsally with their connection to the pubis being at the pubic arch where the two sides can rub against each other and the pubis leading back proximally to the acetabulum on the ventral side with the ischial foramen separating the two parts (all illustrated in figure 3). Between the two land-based mammals the differences are less apparent; the Ischia are all square-shaped and caudally connected to the pubis with the ischial foramen in between. The shape of these causes the pelvis of these two species to look like a rabbit face masquerade mask, with the ilia as the ears, the foramen as the eye holes, and the ischium as the cheek covers. The breaking of these portions may separate parts of the ‘mask’ but this general appearance would aid in differentiating the pelvis of these species of land mammals from other bones. With the fur seal, three portions are needed, including the sacrum portion of the spine. If one can therefore put the two sides of the pelvis together, like a puzzle, the species cannot be a seal.
HUMERUS
The upper arm bone articulates proximally with the distal/caudal end of the scapula and distally with the radius medially and ulna laterally. The head on the medial aspect would identify the bone as being from the left or the right side of the animal.
Head
The head is where the proximal end of the humerus medially articulates with the distal end of the scapula. Not sketched, due to the angle of the drawing, when present the head appears similar between species and can also be confused with being part of a femur because they are both the distal part of the ball and socket joint.
Greater and Lesser tubercles
The two ridges on the lateral side of the bone, next to the head are the greater and lesser tubercles, differentiated by their size and extent of protrusion. The differences between the species are shown in the illustrations below. The dog humerus (Figure 4) the greater tubercle is rounded while the sheep’s (Figure 5) is pointed upwards and laterally, and the fur seals’ (Figure 6) are widest in comparison with the rest of the bone between the other species. In the example of the fur seals’ humerus that was sketched, the element of the greater tubercle appeared as if it had been worn down, with the crest creating the most concave intertubercular groove of the bones sketched.
Shaft
The shaft of the humerus, without either the proximal or distal ends, can be mistaken for shafts of other long bones and other species. However, between the species in this report, the shapes of the shafts are a distinguishing feature of species. The dog humerus (Figure 4) is a simple cylindrical shape with less distinguished, compared to the other species, teres deltoid tuberosities and musculospiral grooves. The sheep humerus shaft has an oval shape with a wider growth area due to the extended major teres and deltoid tuberosities with a slightly concave musculospiral groove (Figure 5). The fur seal humerus shaft (Figure 6) is not a uniform shape, which distinguishes it from both other fur seal bones and other humeri, with an extended and rounded teres tuberosity and a protruding, but flat-topped deltoid tuberosity, which leads distally to the flat musculospiral groove.
Radial fossa (and Supratrochlear foramen)
Between the species the size and length of the radial fossa is indicative of which species the bone came from. Between the three examples in this report; in figure 4 the dogs’ radial fossa is the longest measuring approximately 3 centimeters, the sheep’s (Figure 5) is only about 1 centimeter and the fur seal’s (Figure 6) is about 1.5 centimeters. The most obvious difference, only found in the dog (Figure 4), is the supratrochlear foramen. The hole is only found in certain species and normally in the left humerus, making for easy identification (Gray, 1878: 212).
Humeral Condyle
The distal aspect of the humerus is called the humeral condyle, which has high variation between the three species. The differences in form are reflexive of the difference in locomotion, and the shape of the articulation with the radius and ulna. The dog’s (Figure 4) shows a couple centimeters wide base with cylindrical and softly curved bumps of the trochlea and capitulum into the flat lateral epicondyle. The sheep’s humeral condyle is wider, approximately 4 centimeters with more convex trochlea and sharp edges of the capitulum leading to the round circumference and concave face of the lateral epicondyle (Figure 5). The fur seal’s (Figure 6) humeral condyle is wider than both of the others, approximately 6 centimeters because of the greatly protruding medial epicondyle, which only grows large enough in this species to show in the angle from which I made the illustrations. The rounded cylindrical base has rounded edges next to the concave trochlea and convex capitulum.
SCAPULA
The shoulder bone connects laterally with the proximal end of the humerus and with the lateral end of the clavicle. In each of the species included in this report, the bones are millimeters in thickness, with a thinner fossa centrally located and slightly thicker surrounding edges and an elevated spine running near the length of the bone, which creates a slight corner on the proximal end called the lateral angle. The way to identify which side of the body the scapula would be on is first based on the direction of the spine since it has to face outwards and second on the direction the caudal angle is pointing because the angle is pointing dorsally/cranially, would be protruding through the skin. Based on the position of the spine separating the fossa and due to its length, the shape of the entire bone is going to change, which makes differentiating between species simple.
Glenoid Cavity
The glenoid cavity is where the head of the humerus articulates laterally/distally with the scapula. The edges of the joint are the tubercles, supraglenoid and infraglenoid, identified by which side (cranial or caudal) of the spine on which the growth is located. All of these are illustrated in Figures 7, 8, and 9. These joint ends of the scapula all appear similar to one another with insignificant differentiation in overall sizing and the only noticeable distinctions appear on the width moving into the fossa and where the spine and acromion are located.
Spine and Acromion
The major protrusion ridge on the lateral side of the scapula is called the spine. This dives the scapula into two sections and extends into the lateral angle. The acromion is a thickened growth on the distal end of the spine and is where the scapula articulates with the lateral end of the clavicle. As illustrated between Figures 7 and 9, the dogs’ acromion has a bulbous edge while the fur seals’ has a thinner relative width and longer extension canopy that reaches closer to the glenoid cavity. Illustrated in the example of the sheep’s scapula (Figure 8) the acromion was broken off, a common find in archaeological fieldwork. According to veterinarian research and photographs, the thickness of an adult sheep is similar in shape to a dog’s, likely due to their comparable lifestyle on land (Turner, 2007: 159S fig1E). In the examples illustrated below the spine locations vary greatly between species, making identification, even when broken, relatively simple. In the figures below the difference in spine position is apparent; in the dog (Figure 7) it’s located near the middle, in the sheep (Figure 8) it’s close to the cranial side, and in the fur seal (Figure 9) it’s next to the caudal side.
Overall Shape and Fossa (Supra- and Infraspinous)
Depending on the position of the spine on the scapula, the width of the fossa will change. The fossa between the spine and the caudal angle is infraspinous, and the other is supraspinous. As shown in Figure 7, the spine of the dog scapula is located in the middle of the bone, mostly dividing the scapula in half, however, the approximately right angle of the caudal angle causes the fossa and the overall shape of the bone to have a triangular shape. The lateral angle caused by the spine is obtuse, almost a straight angle, also leading to the triangular shape and larger area of the infraspinous fossa. For both of these two elements, the measurements of the caudal and lateral angles are similar to the shape of the sheep’s scapula in Figure 8. The fur seal (Figure 9) is the most distinct, having a shape similar to an angel wing. The dorsal/cranial side is extended and rounded, causing a larger area with a few ridges to strengthen the integrity of the supraspinous fossa. The seals’ acute caudal angle and its influence on the difference of area between the lesser infraspinatus and greater supraspinous fossa (Figure 9), is another major distinction between that species and the other two mammal species in this report.
CONCLUSION
In this report, I discussed three bone types: the pelvis, humerus, and scapula from three species of mammals: dogs, sheep, and fur seals, all found in Aotearoa in the 19th century. The distinctions between the elements of each species of bone have to do with the habitat in which they would have lived and, therefore, how the species is adapted to feed itself. The dog and the sheep are adapted to life on land, but their separations in form are due to their different diets; dogs hunt down meat while sheep graze on grasses. The largest differences are found in the fur seal’s pelvis shape, the size of the scapula, and the shape of the humerus because of its need for strong front flippers and flexible locomotion in the water. Because of these skeletal adaptations, if particular elements are found in the archaeological record the bones can be more easily identified. In a final way to identify similar pieces if the site is known to be a post-contact site, like the one from which these bones were found the possibility of the sheep species appears, because they were not found in Aotearoa until contact with the Europeans.
