Skull Identification - Index and the Non-Index Traits - Lab Report Example

Skull Identification - Index and the Non-Index Traits Skull identification entails the observation of the index traits and the non-index (physical) traits. An index is derived by comparing two measured portions of the skull to show the proportion of a proportion in relation to another. In the identification of a type of fossil skull we can first we can start by referring to the index traits (quantitative analysis) to narrow down the selection then use the physical observable traits (qualitative analysis) or any other special additional traits to make the identification. There are three indexes normally used in the identification; index of the supra-orbital height (uv/tv), index of the index of nuchal area height (tw/tv) and the index of condylar position (xy/xz). The positions of t, u, v, w, x, y and z are shown on the various figures of the specimens given. The indexes of the nuchal area height and the condylar position utilize an area of plane called the Frankfurt plane which is a line passing through the top of the ear opening from the bottom of the eye socket. The index of supra-orbital height is a measure of the height of the skull that is above the eyes for the various skulls to be identified. Indirectly it is a representation of the cranial height and also a measure of the dimension and complexity of the cerebrum. To obtain this index the distances uv and tv are measured for the skulls to be identified and compared with the values for the known specimens. The index of nuchal area height is a measure of the position and the height of the foramen magnum relatively in the skull. It enables the determination of the uprightness of the posture of a skull and thus of the fossil as whole. It is determined by measuring the distances tw and tv and finding their ratio. These ratios for the fossil skulls to be identified are compared to the ratios of the known specimens during the identification. The index of the condylar position is a measure used to show how straight a hominid stood. It is used to determine the extent backwards or forwards to which the occipital condyles (projections arising from the bottom of skull connecting the skull to the neck) are. In the identification, the names of the specimens C, D, E, F, G, H and B are given in the chart and any reference made in this report should be counterchecked in the chart. Mystery Skull #1 The mystery skull #1 has the values of the three indexes discussed above recorded as 65, 23 and 90 respectively. The skulls were first grouped with reference to the index of supra-orbital height and the specimens D, F, G, H, I and B whose scientific names are given in chart 1 were found to the potential identities of the mystery skull. The recorded values for the supra-orbital values were 70, 58, 58, 70, 66 and 70 respectively which were close to the mystery skull’s values of 65. The observation was then narrowed down to the index of nuchal area height and only three specimens (F, G and I) bore a resemblance to our mystery specimen with recorded values of 21, 23 and 12 referenced against the mystery specimen’s value of 23. A reference was then made to the index of the condylar position and we only remained with G and I (Homo erectus and Archaic Homo sapiens respectively). In order to separate the two specimens the non-index characteristics were observed and the physical traits of the specimens that match the ones of the mystery skull #1 were noted. Homo erectus has thick eyebrow projections while that is not the case for Homo sapiens. In this case the mystery skull is similar to the Homo sapiens. it is also observed that the specimen G has a protruding face when compared to both specimen I and our mystery skull #1. A look at the shape of the eye orbits suggest that our mystery skull is skull of a Homo sapiens since skull of a Homo erectus has square eye orbits while the mystery skull both has oval eye orbits which is the case for Homo sapiens. The height of the nasal orbit is also shorter for the Homo erectus when compared to the height for Homo sapiens and the mystery skull #1. The taxonomic status of Mystery Skull #1 is Archaic Homo sapiens (specimen I). The reasons are as stated above in our discussion. Mystery Skull #2 The index characteristics; index of supra-orbital height, index of nuchal area height and the index of the condylar position of the mystery skull #2 are recorded in the chart 1 as 71, 37 and 44. A review of the index characteristics of the known specimens recorded in chart 1 was made and various matches made to single out the identity of our given specimen. The matching specimens with almost the same index of supra-orbital height as our mystery specimen were D, H, I and B with the values recorded at 70, 70, 66 and 70 respectively and matched against the value of 71. The classification was further narrowed down to the index of nuchal area height and three specimens matched our specimen’s value. These were specimens D, H and B with values of 38, 37 and 40. Lastly the index of condylar position was reviewed for the above three specimens and only one specimen matches the mystery skull’s specification by mere proximity of the value. This was specimen D (Australopithecus africanus). There was no need to perform a physical characteristics review since we had narrowed down the selection to one specimen and thus the identity of mystery skull #2. Looking at the physical traits of the specimen D there is a close resemblance with the fossil of the Australopithecus africanus. Mystery skull #2 is definitely the skull of an Australopithecus africanus because it has the close resemblance to the human like species in comparison to earlier species like Australopithecus afarensis. It has a smaller brow ridge and flat smoothly sloping forehead area and upright posture The taxonomic status of Mystery Skull #2 is Australopithecus africanus (specimen D). The reasons are as stated above in our discussion. Newly Found Skull In the classification of the newly found skull, the same procedure as before was carried out by first looking at the index characteristics then the non-index characteristics. First the index of supra-orbital height for the various known specimens given was compared to the value recorded for the newly found skull and the specimens that match the descriptions grouped for further review. The index of supra-orbital height for the newly found skull recorded at 51 was compared with the values for the specimens and it was found that specimens C, E, F and G matched this value closely at 49, 51, 58 and 58 respectively. A reference was then made to the index of the nuchal area to further narrow down the list. All the specimens were still found to match the 23 index of nuchal area recorded for the newly found skull at 30, 16, 21 and 23 respectively for specimens C, E, F and G. Then with reference to the index for condylar position for the newly found skull, it was found that two out of the four specimens matched the value of the newly found skull which was recorded at 57. The values for two remaining specimens E and F were 58 and 51 respectively. In order to determine from the two specimens which one is our newly found skull a comparison of physical characteristics of each was observed and compared with the physical traits of the newly found skull. The only distinguishable feature that was in the newly found skull and the one for Australopithecus robustus was the protruding sharp edged cheek bone while for the specimen F it was protruding but rounded when viewed from the front. The newly found skull has protruding eye brows as is the case for the Australopithecus robustus. They foreheads are also not pronounced compared with other hominids. It has forehead with flat area and not visible from front view. The skull has an upright posture. The taxonomic status of Newly Found Skull is Australopithecus robustus (specimen E). The reasons are as stated above in our discussion. The table below summarizes the classification. Specimen Identity Distinguishing Physical Characteristics Mystery Skull #1 Archaic Homo sapiens (I) Non-protruding face, non-thick eyebrow projections, oval eye orbits Mystery Skull #2 Australopithecus africanus (D) More human-like cranial features (visible forehead, smoothly sloping forehead area and upright posture) Newly Found Skull Australopithecus robustus (E) protruding sharp edged cheek bones, protruding eye brows, forehead with flat area and not visible from front view, upright posture Work Cited Brown, Robin C. Florida's Fossils: Guide to Location, Identification, and Enjoyment. Sarasota, Fla: Pineapple Press, 2008. Print. Holman, J A. Fossil Salamanders of North America. Bloomington: Indiana University Press, 2006. Print. Read More