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The Stuff We Work With


With rare exceptions, the only actual remains a Pleistocene paleontologist has to work with are bones and teeth, and these often are fragmentary. After death, which itself may be violent, remains are widely scattered and often destroyed as scavengers take their due, erosion and weathering take a toll, and physical and chemical features within the burial sediments attack. The paleontologist is faced with identification problems seldom met by neobiologists; as a result, misidentifications are not uncommon (not that neobiologists are immune from that problem). The stuff we work with is challenging and requires familiarization with anatomy and, for those of us who work with diverse faunas rather than specializing on a single taxon, an acquaintance with a broad sweep of once-living things.

This section is meant to introduce the novice to this stuff that we work with. You may never need or want to know this stuff, but if you do, it's here.

As with all disciplines, scientific or not, we have our jargon. Although this often is noted with a sneer, in practice it allows communication with one's peers (and when used excessively among those not in the discipline, thoroughly deserves the sneers). Part of the jargon is in the following pages; it is mostly repeated in the glossary along with much more.

Much of the material here is taken directly from Mammalogy on the Web, authored by myself and presented by the Centennial Museum and Department of Biological Sciences; some other material is pilfered from courses in paleontology and bioarchaeology taught by myself at UTEP. The "Stuff" section considers mostly mammals.

Figure to illustrate orientation termsSeveral terms involved in orientation are regularly used. Figure 1 shows several of the important ones. Note that the frame of reference for "proximal" and "distal" changes with the element; thus the forearm is distal to the upper arm but proximal to the wrist. In general, an item or part that is proximal is closer to the center of the body in respect to the other item or part. Biologists usually employ orientation terms in relation to anatomical structures regardless of the orientation of the organism; thus, in the upright, bipedal humans, dorsal is the side with the spinal column and the head is anterior. Other important terms not shown include "lateral" (to the side) and "medial" (toward the center).

Fig. 1. This figure of a monkey illustrates several terms used in orientation by biologists.



Diamonds may be a girl's best friend, but the nearest thing to that available to mammalian paleontologists are teeth. It's ironic, but teeth that seem so vulnerable in the mouth are the most easily and best preserved elements in fossil deposits. Furthermore, mammalian teeth tend to reveal both aspects of genetic relationships and ecological features of their owners. Unlike most other toothed vertebrates, mammalian dentitions have exact occlusal relationships that allow efficient processing of foodstuffs. To a degree, then, evolutionary changes in part of the dentition requires concomitant changes in other parts to maintain the occlusal relationships, and upper and lower dentitions are tied together functionally.

Mammalogists have an extensive terminology regarding dentition. For our purposes, only a smidgen of the terminology needs to be addressed here.

Mammals, along with some other vertebrates, have thecodont dentition; that is, the teeth are set in sockets (known as aveoli) in the jaw bones. Alveoli in the skull of Neotoma

Fig. 2. The figure is a palatal view of a fossil Neotoma (packrat). The alveoli for the paired incisors are seen at top; posteriorly, the alveoli for the three pairs of molars can be seen. Within the alveoli, the deeper spaces for the molar roots are visible. Even in the absence of teeth, the number of teeth and, often, some idea of the taxon involved is possible from the alveoli alone.

Mammals are heterodont (for the most part), primitively having incisors (I), canines (C), premolars (P), and molars (M) recognizably different from each other. By the late Cretaceous or early Cenozoic, tooth formulas had standardized to a normal maximum of 50 for marsupials and 44 for placental mammals. These numbers and the distribution of the various tooth types are recognized as the primitive tooth formulas for the two groups since apparently modern marsupials and placentals are descended from ancestors with those tooth types and numbers.

Tooth formulas are given in various ways, but once the general pattern is seen, are easily recognizable. The formulas give the numbers and kinds of teeth on one side of the upper and lower jaws. Marsupials had a primitive tooth formula of I 5/4 (that is, 5 upper and 4 lower on each jaw), C 1/1, P 3/3, and M 4/4 = 25; doubled (for the two sides) gives the total number of teeth as 50 (often given after the "=" sign rather than the number for one side). The abbreviations for the various tooth types frequently is omitted since they always are given in the same order. Thus 5/4 1/1 3/3 4/4 = 50 gives the same information.

The tooth formula for placentals is 3/3 1/1 4/4 and 3/3 = 44. Most mammals have lost teeth evolutionarily, but the remaining teeth retain the identities they would have if all teeth were present. Teeth are numbered according to the primitive formula. They are numbered from front to back with each type starting over with "1". Thus in placentals, I1/i1 I2/i2 I3/i3 C1/c1 P1/p1 P2/p2 P3/p3 P4/p4 M1/m1 M2/m2 M3/m3. Various conventions to indicate uppers and lowers are used; in the example, an upper case letter indicates an upper tooth and a lower case letter a lower tooth. Sometimes superscripts and subscripts are used and sometimes a slash behind (e.g., P4/ for upper premolar 4 and /P4 for the lower).

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