Description. The assemblage of teeth of Archaeolamna ex. gr. kopingensis shows very varied morphologies, revealing strong monognathic and weak dignathic heterodonty (see above), as well as some ontogenetic and probable sexual heterodonty. Within the tooth assemblage, most of the teeth are reasonably small, with a small number of larger teeth (as used in the dentition reconstruction) and a very small minority of teeth that are at least 50% larger than average. The very largest teeth differ from others in that there are commonly strong but short and irregular longitudinal folds at the base of the labial face of the crown, especially prominent in teeth from posterolateral positions. Larger teeth of all anterior and anterolateral tooth positions appear to be present in both a robust and a gracile morph. These have the same overall shape but the main cusp and the root lobes of the gracile morph are considerably more slender than in the robust morph. The main cusp of the gracile teeth is also somewhat longer for the width of the tooth than in the robust morph. By analogy with some modern lamniforms and carcharhiniforms, it is probable that the gracile morph represents teeth of adult male individuals, whilst the robust morph represents females and immature individuals.
Anterior teeth have a main cusp that is rather higher than the root and a single pair of slightly divergent lateral cusplets. The main cusp is robust and tapers steadily to a point. In lower anterior teeth and presumed first upper anterior teeth, the main cusp is straight and vertical, becoming inclined in some upper anterior teeth (file two) and curved in others (file three). The lateral profile of the main cusp shows a very slight sigmoidal curvature. In all anterior teeth the lateral cusplets on anterior and posterior sides of the tooth are of similar size, and are rather higher than wide. The crown unites the main and lateral cusplets at the base on the labial side, but not on the lingual face, where a narrow neck is present at the base of each of the cusps. The labial face of the cusps is faintly convex, but commonly flat or slightly concave at the base of the main cusp. The lingual face of all cusps is strongly convex, giving them a rather semicircular cross-section. A well-defined cutting edge is continuous across all cusps. The root is bulky and strongly ‘V’ shaped. The root is somewhat asymmetrical in all anterior teeth, with the asymmetry varying with tooth position. The root lobes form an internal angle of 90 degrees or less, depending on jaw position. Root lobes are oval in cross-section, largely compressed antero-distally, but in the posterior lobe this may be twisted towards the lingual side. The terminations of the root lobes are variable in shape, ranging from smoothly rounded to sharply pointed, but are never strongly flattened. The linguo-basal base of the root is not strongly flattened. There is a rather inflated root lingual boss, and in the centre of this is either a single well-developed foramen or a cluster of up to four small foramina. In a small proportion of smaller teeth, the main foramen is within a short but deep groove.
Lower parasymphyseal teeth are very variable but are essentially modified anterior teeth. There appears to be a morphological continuum between first lower anterior teeth and highly modified and stunted parasymphyseal teeth. It is, therefore, likely that the dentition at the front of the lower jaw is less clearly defined than in other lamniforms. The crown of lower parasymphyseal teeth differs from that of other anterior teeth largely in being smaller relative to the root and less symmetrical, with lateral cusplets often being better formed on one side of the tooth than the other, or even absent on one or both sides. The root is antero-distally compressed with a very well-developed lingual boss. Root lobes are short and rarely of close to equal length; in many of the smaller teeth, only a single root lobe is fully developed.
Presumed upper parasymphyseal teeth vary in shape but the majority are relatively symmetrical; other teeth are of similar overall morphology but are distorted and show greater asymmetry. These are less abundant than lower parasymphyseal and upper intermediate teeth and may not have been present in all individuals: there is considerable variation in the presence of these small teeth between individuals of many extant lamniforms (CJU, pers. obs.). The main cusp is robust and rather triangular, although in some of the more asymmetrical teeth, the basal part may be parallel sided. Lateral cusplets are short, triangular, robust and slightly divergent. The shape of the root is rather variable, probably related to whether there were one or more teeth within this jaw position. In the more symmetrical teeth, the root is clearly ‘V’ shaped and relatively robust. The root lobes show very little tapering and have an internal angle of about 80 degrees. There is a swollen lingual region but not as enlarged as in most anterior teeth, and the root lobes are oval in cross-section without a well-defined linguo-basal face of the root. In the remainder of the teeth from this proposed position, the root is more compressed antero-posteriorly, creating a larger lingual bulge. The root lobes are short and not often well defined, comprising considerably less than half of the height of the root.
Upper intermediate teeth are common within the assemblage, and it is, therefore, likely that several files of these were present in the jaw. They are symmetrical and have an erect and triangular main cusp flanked by a pair of slightly divergent cusplets. In respects other than size, the crown of these teeth resembles that of lower anterior teeth. The root is strongly ‘V’ shaped and has an internal angle of 90 degrees or less. The root comprises about half of the height of the tooth. The root is variably compressed labiolingually. In some teeth, the root lobes are oval in cross-section with a slightly flattened linguo-basal root base, whereas in other teeth the linguo-basal face of the root is very flattened, even including the region directly below the main cusp. This flattening extends to the root lobes, which are about twice as wide as they are thick. The lingual foramen is present but very small. In addition, there are a very small number of probable upper intermediate teeth that are small and squat. A triangular main cusp is compressed labiolingually and flanked by a pair of lateral cusplets that are similar in shape to those of lower lateral teeth. The lingual face of the crown is wide at the base and is either smooth or ornamented with irregular wrinkles similar to those seen in other teeth. The lingual face of the crown is smooth other than a very well-developed neck.
Upper lateral and posterior teeth all have a similar morphology, varying largely in their size and the height of the cusps. The first upper lateral tooth has a morphology somewhat intermediate between that of the anterior teeth and the remaining lateral teeth. The main cusp is robust and has a smooth curve along both anterior and posterior edge. In all but in the smallest posterior teeth, the main cusp is of similar height to the root. The axis of the main cusp forms an angle of about 60 degrees with the base of the tooth. There is a single pair of robust lateral cusplets of similar size to each other which are slightly higher than wide. These are slightly divergent, but in more posterolateral teeth, the posterior lateral cusplet is often more erected than the main cusp. In the most posterior teeth, the anterior cusplet may be reduced or incipient. The labial face of the crown is smooth and slightly convex, although on some very large teeth and some posterolateral teeth, small vertical wrinkles may be present just above the crown-root junction. The three cusps are united by a narrow basal strip of enameloid on the labial side of the tooth, but not on the lingual side. There, a very prominent neck is present at the base of each of the cusps. The lingual face of the cusps is smooth and strongly convex. There is a well-developed cutting edge across all of the cusps. The root of upper lateral teeth is bulky and quite symmetrical, and the rather stubby root lobes form an internal angle of 90–100 degrees. The outer edge of the anterior root lobe continues from the edge of the main cusp, with a rounded termination. The labial face of the root slopes gently away from the base of the crown, and there is no labial crown overhang. The linguo-basal face of the root is slightly flattened, with no clear edge to the face. The lingual boss is large and rounded, with one or sometimes two or three foramina at the apex. In some smaller teeth, a very short but deep groove is present. Some small foramina are seen on the upper parts of the root labial face, but are rarely conspicuous.
Lower lateral teeth are very close to symmetrical, with the exception of the probable first lower tooth, which is very similar in shape to the third anterior tooth, and the smaller posterolateral teeth. The main cusp is straight and quite short, with slightly concave outer edges. There is a single pair of relatively large lateral cusplets, that are higher than wide. The base of the lateral cusplets is in line with the base of the main cusp, as opposed to being some way down the outer edge of the root lobes as in teeth from other positions in the jaw. The outer edge of the cusplets overhangs the root slightly, and in some posterolateral teeth this projection develops into an additional incipient cusplet. The labial face of the crown is very slightly convex to almost flat, and has no ornament in the vast majority of teeth. The basal edge of the enameloid on the labial side is gently arched, as opposed to the strong curvature on other teeth. The lingual face of the cusps is smooth and strongly convex, with a well-developed neck at the base of each of the cusps. In posterior teeth, the main cusp is strongly inclined as in the upper teeth, and upper and lower teeth can only be differentiated by the shape of the root. The root of lower lateral teeth is far more ‘square’ than on teeth from other positions; viewed lingually, the top of the root is only slightly arched upwards, and the edges of the root lobes are almost vertical below the outer edges of the lateral cusplets, giving a very sharp angle between these edges. The inner edges of the root lobes form a smooth semicircle in most teeth, becoming more angular in posterior teeth. The root lobes themselves have rounded terminations and are somewhat flattened labiolingually. The labial face of the root smoothly curves away from the crown, with a slight recess below the base of the main cusp. The linguo-basal face of the root is large, making up almost all of the root that can be seen in lingual view, and relatively flat. There is a distinct but not sharply angled edge to this face. The lingual boss projects slightly, giving a narrow horizontal shelf below the cusps. There are one or more foramina at the apex of the lingual boss, and in some smaller teeth these are opened out to form a short but distinct groove. Small foramina are present towards upper part of the labial face of the root, but are small and irregularly distributed.
Discussion. Archaeolamna is known from the Albian to Maastrichtian and appears to have had a virtually global distribution (see Siverson 1996). Of these occurrences, the majority of records relate to Archaeolamna kopingensis (Davis, 1890), although stratigraphical variations suggest that this may represent a group of closely related taxa rather than a single species. In addition to A. kopingensis s.l., A. haigiSiverson, 1996 from the Cenomanian of Australia and A. kopingensis judithensisSiverson, 1992 from the Campanian of the USA (the latter probably deserving of specific rank) are known.
Despite the very high degrees of heterodonty present, it is possible to make general comparisons between the Archaeolamna kopingensis s.l. specimens described here and from other populations. Albian specimens from Europe (Biddle 1993) are typically rather gracile and possess a poorly formed nutritive groove in most or all teeth. Albian specimens from Australia (Siverson 1997) are similar, but the nutritive groove is restricted to smaller teeth. Archaeolamna kopingensis s.l. specimens from the Cenomanian of Australia (Siverson 1996) and probably France (Vullo et al. 2007), as well as younger occurrences, lack a nutritive groove and possess weak folds on the labial face of the larger teeth. The specimens described here are therefore most similar to those from the Australian Albian, differing only in the possession of weak ornament on the labial face of a small number of the very largest and most posterior teeth. Although there are slight differences between different populations of A. kopingensis, it has not been possibly to produce a reliable set of criteria for separating species within what almost certainly represents a complex of morphologically similar taxa.
Within the ‘mid’ Cretaceous, A. kopingensis s.l. is widespread but not global in occurrence. It is common at this site and elsewhere in the Cenomanian of central Canada (SC, pers. obs.) as well as in Colorado (Shimada et al. 2006). It is also present in western Europe (e.g. Biddle 1993; Vullo et al. 2007; CJU, pers. obs.), Russia (CJU, pers. obs. of specimens mislabelled as other species) and Australia (Siverson 1996, 1997). Despite this, it has not been recorded in Texas (e.g. Welton and Farish 1993; Cappetta and Case 1999) or elsewhere in areas associated with Tethys. It, therefore, appears to have been a temperate water inhabitant, present in both Northern and Southern Hemispheres.