Fossil specimens collected from float material are usually considered less desirable for paleontological study than those collected in situ. The purpose of this study is to demonstrate that with accurate measurement and appropriate analytical techniques useful conclusions may be drawn about specimen populations, even when the samples have been obtained from active mines and quarries where operations do not permit careful in situ collecting.

The distal edge of upper teeth of the fossil shark Hemipristis serra is coarsely serrate with the serrations having a well-defined termination before reaching the tip of the tooth (see Figure 1). Purdy et al. (2001, p. 142) observed that "Hemipristis seems to increase in size through its evolutionary history...But is this size increase an evolutionary change?" Examination of collections of teeth from the Yorktown Formation (early Pliocene), the Pungo River Formation (early – middle Miocene), and the Belgrade Formation (late Oligocene – early Miocene) of eastern North Carolina supports this observation and also suggests that the ratio (unserrated tip length) / (total edge length) decreases toward the Recent. To quantify these observations a graphics program was developed which provides quick and precise measurement of the necessarily rather small dimensions.

The goal of this study is to offer evidence of a possible phyletic change in Hemipristis serra upper lateral teeth which took place during the Miocene and early Pliocene. This particular change (of teeth becoming larger and more completely serrated) is difficult to confirm because it is also an ontogenic change. Several references make similar claims regarding selachian teeth but the present paper uses a statistical model to assess phyletic change in H. serra. Leriche (1936) states a general principle: "Lorsqu'une éspèce franchit plusieurs étages successifs, on voit généralement sa taille s'accroître à mesure que l'on s'élève dans ce groupes d'étages. C'est la «loi d'augmentation de taille dons les rameaux phylétiques» énoncée par Depéret (1907, p. 199-210)." ("When a species crosses several successive stages you generally see an increase in its size as you rise through that group of stages. This is the 'law of augmentation of size given by the phyletic branches' enunciated by Depéret."). He then mentions several species which reflect this principle, including "Odontaspis" macrota (= Striatolamia macrota), "Odontaspis acutissima" (= Carcharias taurus), "Oxyrhina" hastalis (= Isurus/Cosmopolitodus hastalis), and "Carcharodon" megalodon (= Carcharocles megalodon). Depéret's "law" is a variation of a similar principle, today known as Cope's law. Applegate (1986) states that Baja California Hemipristis teeth between the middle Oligocene and the late Miocene show a gradual increase in size but offer no evidence for this claim. The landmark paper by Naylor and Marcus (1994) lays a foundation for tracking phyletic change in the various Carcharhinus species, an enormously ambitious undertaking. Ward and Bonavia (2001), in a brief outline of an argument for considering Carcharocles to be a chronospecies, describe much more qualitatively the phyletic changes in Carcharocles teeth between the Eocene and Pliocene epochs.