Material.—Tooth (IGS-MJ-0001) from Upper Jurassic (Oxfordian), Švédské šance (Brno-Slatina), Czech Republic.

Description

The tooth (IGS-MJ-0001) is labiolingually compressed, its apical third is slightly oriented linguodistally, and carinae are located on the mesial and distal faces of the tooth crown. Thus, IGS-MJ-0001 most likely represents a lateral tooth (Fig. 4). The moderate labiolingual compression, slight tooth crown curvature, and lingually slightly displaced mesial carina might suggest that the tooth was positioned in the anterior half of the right maxilla or left dentary. The tooth is almost complete. Only a basal part of the tooth crown on the distal half of the tooth and an apical part of the tooth base are missing (Fig. 4A). The loss of part of the tooth base, however, apparently occurred after the discovery of the material because the rock with the fossil has clearly been broken off.

Denticles.—The denticles are chisel-shaped, non-inclined (Fig. 5), and present on both carinae. However, the mesial carina bears fully developed denticles only in its apical half. Approximately in the center of the mesial carina the denticles start to reduce in height. In the basal third of tooth crown, then, the denticles are completely missing. The distal carina is not wholly preserved, yet, due to the fact that the denticles do not appear to reduce their size, and the serrations on distal carinae are usually more strongly developed (D'Amore 2009), it is likely that the denticles were present along its whole length.

The density of denticulation, which was measured per 5 mm because the CBL exceeds 7 mm, is similar on both carinae. The density within the apical third of the mesial carina is 15 denticles per 5 mm. The density changes in the middle section to 17 denticles per 5 mm. The basal third of the mesial carina lacks denticles. As in the mesial carina, the serration density on the distal carina was counted only on the apical third and the center (in both cases the density is equal to 15 denticles per 5 mm), as the basal third of the distal carina is not preserved. The average serration density on the mesial carina (MAVG) is 16 denticles per 5 mm, and on the distal carina (DAVG) 15 denticles per 5 mm. However, it should be noted that the serration density in the basal third of the distal carina is impossible to calculate, because this part is absent, so it is possible that DAVG might not be accurate (the same applies for the DSDI parameter).

In addition to these parameters, attention was paid to the height and width of denticles. Normally, these measurements are not taken into account, but here they are mentioned because they could be considered in the future. This data, especially the height of denticles, could be affected by taphonomy or preservation. And, indeed, some denticles must be treated as unmeasurable. Nevertheless, the majority of denticles do not bear any traces of damage.

On the mesial and distal carinae the width of denticles is approximately the same and irregularly varies between 200 and 350 μm. This is congruent with similar serration density on both carinae. However, there are differences in denticle heights. On the mesial carina, the height of measurable denticles is 100–200 μm, whereas the denticles on the distal carina are higher (200–400 μm). These differences are consistent with the trend in Theropoda (D'Amore 2009).

Enamel structures.—No significant enamel structures, except the denticles on the carinae, are developed. Interdenticular sulci and caudae, and longitudinal ridges and grooves, are absent (Figs. 4, 5). It is possible to notice very fine mesiodistally oriented irregular “wrinkle-like strips” on the labial and lingual sides of the tooth crown, but whether these structures represent enamel wrinkles in the traditional sense remains uncertain. The tooth crown bears apparent irregularities accompanied by cracked enamel, which are interpreted as deformations. These subtle structures might be taphonomic.

Measurements.—see Table 1.

Comparisons.—In order to find the most probable phylogenetic position of the Moravian theropod, the tooth was compared to several taxa representing different theropod clades. The primary reference material consisted of a set of data published by Smith et al. (2005), which was modified on the basis of Smith and Lamanna (2006), and Ősi et al. (2010). Isolated tooth crowns from the Kimmeridgian of Germany (Lubbe et al. 2009) were also taken into account, but this material differs in several important features; particularly, the high serration density in relation to the size of the teeth is characteristic for some dromaeosaurids, to which these teeth belong. Likewise, the samples from the Cenomanian of Morocco described by Richter et al. (2012) might be easily distinguished from IGS-MJ-0001 as well.

Within the above-mentioned data set (SOM, Supplementary Online Material available at  http://app.pan.pl/SOM/app59-Madzia_SOM.pdf), IGS-MJ-0001 is almost indistinguishable from the teeth of basal tetanurine theropods from the Santonian of Hungary, and “M. dunkeri” from the Barremian of England and “M. pannoniensis” from the Campanian of Austria, which are also basal tetanurines (Ősi et al. 2010). The teeth are almost identical in terms of measured characters and their mutual ratios, as well as the density, shape and extent of the denticles. However, some differences can be observed in the ornamentation of the enamel. In the Hungarian tetanurines and “M. dunkeri” the enamel is clearly wrinkled (Ősi et al. 2010), whereas in IGS-MJ-0001 this feature is probably absent (see above). Nevertheless, the degree of enamel ornamentation in basal members of Tetanurae is relatively variable. For example, in contrast to the teeth of carcharodontosaurid allosauroids, which are characterized by very well developed enamel wrinkles that are especially prominent adjacent to the carinae (e.g., Brusatte et al. 2007), the teeth of some ziphodont megalosauroids lack the wrinkles completely (e.g., Benson 2010b). The distribution of complexes of interdenticular sulci/caudae is equally variable within clades (Benson 2010b; Benson et al. 2010), as well as in single jaws, as noted by Benson (2009) in an individual maxilla or dentary of the megalosauroid Megalosaurus. On the other hand, some other theropods, such as the abelisaurid Majungasaurus, show a more conservative pattern (see below).

There are several similarities with abelisaurid ceratosaurs, whose dental anatomy is, despite many fossils, relatively poorly studied (Smith 2007). Their teeth resemble the dentitions of some basal tetanurines in many ways; especially in the parameters of tooth crowns, such as CBL and CBW, crown shape, and denticle density (Smith 2007; Canale et al. 2009). However, it seems that in most taxa the enamel is at least partially ornamented; i.e., the denticles are usually followed by the complexes of interdenticular sulci/caudae (e.g., Benson et al. 2010). For example, although the teeth of Majungasaurus crenatissimus (Smith 2007) are generally similar to IGS-MJ-0001 in size, shape, and serration density, they differ in other important aspects: their mesial carinae are serrated along their whole length, and the denticles on both carinae are accompanied by the complexes of interdenticular sulci/caudae.

Comparisons to other theropod clades.—Comparisons of the tooth from Švédské šance to other theropods is problematic, because thorough descriptions of theropod teeth have been provided only for limited number of taxa (e.g., Smith 2005, 2007; Dal Sasso and Maganuco 2011), and because the Moravian material is limited. Nevertheless, this tooth is confidently distinguished from basal theropods, basal ceratosaurs, and noasaurids. At the base of the tetanurine branch of Averostra sensu Ezcurra (2006), significant differences are evident in the case of the clades Spinosauridae and Carcharodontosauridae. Within the Coelurosauria, then, it seems unlikely that the tooth belongs to a member of Maniraptoriformes (for phylogenetic relationships among Theropoda see SOM: fig. 1).

Basal theropods, such as coelophysoids, can be distinguished from IGS-MJ-0001 on the basis of the size and shape of the tooth crowns, and higher serration density (Smith et al. 2005). The tooth crowns of basal ceratosaurs, such as Ceratosaurus, have also different parameters (for measurements see SOM: fig. 2). Other dissimilarities between the Moravian sample and Ceratosaurus include, for example, the presence of longitudinal ridges and grooves on the enamel of Ceratosaurus (Madsen and Welles 2000).

Assignment to Noasauridae appears to be improbable as well. If IGS-MJ-0001 was positioned in the anterior half of the jaws, as hypothesized above, it can be clearly distinguished from Masiakasaurus knopfleri in that it lacks the longitudinal ridges (cf. Carrano et al. 2002). Moreover, IGSMJ-0001 has lower denticle density, its serrated mesial carina does not extent to the cervix dentis, and differs in tooth crown shape (cf. Carrano et al. 2002; Smith et al. 2005; Lindoso et al. 2012).

It is also probably not a spinosaurid because it lacks the clearly visible complexes of longitudinal ridges/grooves seen on the labial and lingual faces of the tooth crown of Cretaceous (e.g., Mateus et al. 2011) and Upper Jurassic (Buffetaut 2012) spinosaurids. Further, IGS-MJ-0001 differs from Carcharodontosauridae in the development of tooth crown ornamentation, which is characteristically wrinkled near the carinae (Brusatte et al. 2007).

It is unlikely that IGS-MJ-0001 belongs to Coelurosauria, but there is a few ziphodont clades that could be considered. Although early tyrannosauroids were present in Europe during the Late Jurassic (e.g., Rauhut 2003; Benson 2008; Rauhut et al. 2010; Brusatte and Benson 2013), knowledge of their dental anatomy is limited (e.g., Zinke 1998; Rauhut et al. 2010). Among early tyrannosauroids, IGS-MJ-0001 can be compared to proceratosaurids. It clearly differs from the teeth of Proceratosaurus bradleyi in its larger size, less inclined apical third of the tooth crown and considerably lower denticle count per 5 mm on both carinae (cf. Rauhut et al. 2010). It is similar to Kileskus aristotocus in terms of CBL, CBR, and CBW (cf. Averianov et al. 2010), but the denticle count of the latter is unavailable. The serration density of IGS-MJ-0001 resembles teeth of the Early Cretaceous proceratosaurid Sinotyrannus kazuoensis, but these are larger (cf. Ji et al. 2009). For now, treating IGS-MJ-0001 as a possible early tyrannosauroid would be unsupported. Although many similarities to more derived tyrannosauroids (e.g., Smith et al. 2005; Smith 2007; Brusatte et al. 2011b, 2012) may be noted, such as similar size, shape and serration density, the tooth crowns in all of the better known advanced tyrannosauroids have relatively well developed ornamentation. These include the enamel wrinkles and distinctive complexes of interdenticular sulci/caudae. Late Jurassic compsognathids have generally smaller teeth that possess higher density of denticulation and this is restricted to the distal carinae (Dal Sasso and Maganuco 2011).

Basal Alvarezsauroidea can be excluded too based on comparisons to the earliest known alvarezsauroid, Haplocheirus sollers, which has very small teeth that are serrated only distally (Choiniere et al. 2010; Han et al. 2011). Teeth of advanced alvarezsauroids (the Alvarezsauridae) are minute and simplified (e.g., Longrich and Currie 2009).

Among ziphodont maniraptoriforms, IGS-MJ-0001 can be safely distinguished from Paraves in terms of tooth crown morphology, size, and serration density. For example, the teeth of paravian coelurosaurs are often smaller than IGSMJ-0001 and more strongly inclined (e.g., Hwang et al. 2002; Smith et al. 2005; Norell et al. 2009; Lü et al. 2010; Turner et al. 2012). The denticle density is usually higher (Smith et al. 2005; Lubbe et al. 2009; Ősi et al. 2010) and in some paravians (Troodontidae), the tooth crowns are separated from the bases by distinctive constrictions (e.g., Holtz et al. 1998; Lü et al. 2010), a feature that is absent in IGS-MJ-0001.