Paronychodon sp.

Torices, Angelica, Currie, Philip J., Canudo, Jose Ignacio & Pereda-Suberbiola, Xabier, 2015, Theropod dinosaurs from the Upper Cretaceous of the South Pyrenees Basin of Spain, Acta Palaeontologica Polonica 60 (3), pp. 611-626 : 615-619

? Paronychodon sp.

Fig. 3Q .

1991 Euronychodon portucalensis Antunes and Sigogneau-Russell, 1991: 118–119 , fig. 15A.

2001 cf. Euronychodon sp. ; López-Martínez et al. 2001: 49, 51, fig. 9B, C, D.

2004 cf. Euronychodon sp. ; Torices et al. 2004: 72–73.

Material.—Three teeth (MPZ98/76–78) from Blasi 2B (Tremp Formation, late Maastrichtian) ( Fig. 3Q ; SOM: Table 1).

Description.— Paronychodon teeth are relatively tall, elongate and curve gently ( Currie et al. 1990). Usually, the posterior carina is more or less straight and the anterior one is convex in lateral view, but both carinae can be convex. The enamel is sometimes folded, and three or more longitudinal ridges appear on one or both flanks of the teeth. Denticles are never present ( Currie et al. 1990).

Three teeth from Blasi 2B are referred to? Paronychodon sp. They have similar measurements and morphological characteristics to the ones described as Coelurosauria indet. They are small, and their heights are less than 3 mm, their FABL varies between 1.21 and 1.49, and their basal widths range between 0.60 and 0.84. They lack denticles on their anterior and posterior carinae, but longitudinal ridges can be observed on the labial and lingual sides of their crowns.

Discussion.— Paronychodon is an enigmatic theropod taxon that has teeth ornamented with longitudinal ridges ( Canudo and Ruiz-Omeñaca 2003). The position of this genus within Theropoda is uncertain. There is no clear reason to assign it to Dromaeosauridae , as Antunes and Sigogneau-Russell (1991) tentatively suggested. On the other hand, the assignment of Paronychodon (as a nomen dubium) to Troodontidae by Osmólska and Barsbold (1990) and Makovicky and Norell (2004), is probably based on the slight constriction between crown and root; this is insufficient because this character can be found in other theropods ( Zinke and Rauhut 1994), in toothed birds ( Currie 1987), and in some other vertebrates, such as crocodyliforms. Rauhut and Zinke (1995) suggested that Paronychodon teeth can be attributed to Pelecanimimus , but this seems unlikely ( Rauhut 2002). Rauhut (2002) proposed that they could belong to birds. The longitudinal ridges in Paronychodon teeth have been attributed to growth abnormalities ( Currie et al. 1990). Other authors consid- er them normal and refer “paronychodontids” to primitive maniraptoriform theropods, as close relatives of troodontids, ornithomimosaurs, or even birds ( Zinke and Rauhut 1994; Csiki and Grigorescu 1998; Rauhut 2002).

Teeth from our sample are similar to Paronychodon lacustris from the Upper Cretaceous of North America that have been classified as Paronychodon lacustris ( Currie et al. 1990) and group together perfectly ( Fig. 4 ). They are also similar to a Portuguese tooth classified as Euronychodon portucalensis ( Antunes and Sigogneau-Russell 1991) . Other similar teeth have been identified as cf. Paronychodon or cf. Euronychodon in French, Romanian, and Spanish sites.

North American teeth of Paronychodon are indistinguishable from Euronychodon , so it is probable that Euronychodon is a synonym ( Rauhut 2002). Pyrenean teeth previously classified as cf. Euronychodon ( Torices et al. 2004) are therefore renamed here as? Paronychodon .

Statistically, these teeth grouped consistently in all three discriminant analyses. Although one specimen grouped with indeterminate coelurosaurians because of similar size, its assignment is certain because of the presence of longitudinal ridges in its enamel ( SOM: Table 2) .

Family indet.

Genus Richardoestesia Currie, Rigby, and Sloan, 1990

Type species: Richardoestesia gilmorei Currie, Rigby, and Sloan, 1990 ; Dinosaur Provincial Park; Campanian.

? Richardoestesia sp.

Fig. 3D–L .

2003 Dromaeosauridae indet. 4; Torices 2002: 141.

2004 cf. Dromaeosauridae morphotype 8; Torices et al. 2004: 73. 2004 cf. Dromaeosauridae indet. 4; Torices et al. 2004: 73.

2005 Maniraptoriformes indet.; Canudo et al. 2005: 34.

Material.—Four teeth (MPZ98/72–74, 2004/7) from Blasi 2B (Tremp Formation, late Maastrichtian); sixty-four isolat- ed teeth (MCNA 14566–14621) from Laño (lateral equivalent of Sedano Formation, upper Campanian–lower Maastrichtian); two teeth (DPM-MON-T5, T9) from Montrebei Tremp Formation, upper Campanian–lower Maastrichtian); two teeth (DPM-VIR4-T6, T7) from Vicari 4 (Tremp Formation, upper Campanian) ( Fig. 3D–L ; SOM: Table 1).

Description.— Richardoestesia specimens are small theropod teeth (crown height between 1.4 and 5.1 mm, FABL between 1 and 5.1 mm, and basal width between 0.4 and 2.2 mm) with posterior denticle densities between 6 and 11.4 denticles/mm. Sixteen of the sixty four specimens have anterior denticles that are smaller than the posterior ones, and with densities between 8.1 and 16.3 anterior denticles/mm. Denticles are small and rectangular. In some of the teeth, it is possible to see that the posterior denticles are tilted slightly towards the apices of the teeth, which is characteristic of the genus Richardoestesia .

The morphologies of the teeth have great variability, from teeth with convex anterior borders and concave posterior borders to teeth with convex anterior borders and straight posterior borders. In some teeth, both edges are slightly convex, and the teeth resemble isosceles triangles.

The four specimens of Richardoestesia from the Blasi 2B site have almost straight (slightly biconvex) carinae, and compressed basal sections (basal widths are about half their FABLs). The tips of three of the teeth are broken and one of them is slightly worn, and their roots are not preserved. Their denticles are rectangular.

The two specimens from Montrebei have convex anterior borders and straight posterior ones. They are compressed lateromedially and their basal widths are nearly half of the corresponding FABLs. The tips show wear that in DPM-MON-T5 affects the anterior carina, and there is some breakage affecting the posterior carina in both teeth. The density of posterior denticles ranges from 7.8 to 9 denticles/mm. The morphology of each denticle is rectangular. Only DPM-MON-T9 has denticles on the anterior carina that are smaller than the posterior ones; the density is 11.5 anterior denticles/ mm. The morphology of each anterior denticle is also rectangular in lateral view, but the denticles are only found on the apical half of the carina.

The material from Vicari 4 consists of one entire tooth, and the apex of another. The complete tooth has a convex anterior carina and a concave posterior one in lateral view. Both teeth are laterally compressed with basal widths that are about half of the FABLs. Posterior denticle density is 9.5 denticles/mm. The morphology of each denticle is rectangular, and some of them (including DPM-VIR4-T7) do not show any wear.

The 56 teeth of Laño constitute most of the Richardoestesia sample. They consist of complete teeth and fragments that retain only the middle parts of the teeth, the apices, or the posterior carinae. They all have denticles on the posterior carinae, with densities between 6.5 and 11.4 denticles/mm. In sixteen of the specimens, anterior denticles are also present, with densities between 8.1 to 16.3 denticles/mm. The shape of each posterior denticle is rectangular, and in some cases a slight tilt toward the apex of the tooth can be observed. The morphology of each anterior denticle is also rectangular, but its overall size is much smaller than an equivalent posterior denticle. The morphologies of the tooth crowns cover the three types: (i) biconvex teeth; (ii) teeth with convex anterior carinae and straight posterior ones; and (iii) teeth with convex anterior carinae and concave posterior ones. Those with strongly concave posterior borders are usually lower in height than those with straight edges, which are more elongate vertically. The lower heights suggest that this morphology may represent posterior maxillary or posterior dentary teeth.

Teeth identified as Richardoestesia in the Royal Tyrrell Museum of Palaeontology (Drumheller, Canada) collections were measured. The height varies from 2.5 to 10.8 mm, the FABL varies between 1.37 and 4.67 and basal width ranges from 0.66 to 2.83 mm. Denticle densities vary from 5 to 12.5 posterior denticles/mm, and 5 to 10 anterior denticles/mm when anterior denticles are present. Each of these measurements overlap perfectly with those of the Pyrenean sample ( Figs. 4 and 5 ).

Discussion.—The morphologies and measurements of many Spanish specimens fall within the ranges of variability of teeth from North America that are identified as Richardoestesia ( Currie et al. 1990) ( Figs. 4 and 5 ). Richardoestesia gilmorei was described by Currie et al. (1990) on the basis of a pair of lower jaws containing a replacement tooth. Isolated teeth were assigned to this species based on the characteristics of the denticles, particularly their small size. Richardoestesia denticles are the smallest seen in any of the small theropods from the Upper Cretaceous. Usually they do not have anterior denticles, but when present, they are even tinier than the posterior denticles.

In Richardoestesia collections from the Late Cretaceous of Canada and the USA, various researchers ( Currie et al. 1990; Baszio 1997; Sankey et al. 2002) have observed two different morphologies: (i) tall and straight teeth, and (ii)

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shorter and curved teeth. Currie et al. (1990) considered the possibility that these two morphologies represent positional variation along the dental series, with the straighter ones coming from the anterior parts of the jaws. However, they also alluded to the possibility that the two morphotypes represented two different taxa. Baszio (1997) preferred the latter option, and he distinguished the straight teeth as a distinct species ( Richardoestesia sp. ) that Sankey (2001) named Richardoestesia isosceles . The latter paper also recognizes differences in the morphologies of the denticles between Richardoestesia gilmorei and Richardoestesia isosceles . The denticles of Richardoestesia isosceles are more square and lack interdenticular spaces ( Sankey et al. 2002). Although Richardoestesia gilmorei and Richardoestesia isosceles form two distinct morphological groups, they are not distinguishable from each other when considering variables such as crown height and FABL. In principle, the differences in the general morphology of the tooth that Baszio (1997) used to distinguish Richardoestesia sp. teeth from those of Richardoestesia gilmorei are not sufficient proof because morphological variability within even a single theropod jaw can be remarkable (Smith 2005, Reichel 2010). Company et al. (2005) proposed that Richardoestesia isosceles might be a ziphodont crocodyliform.

Teeth identified as cf. Richardoestesia have been recovered from the Upper Jurassic of Portugal, the Lower Cretaceous of Spain ( Zinke 1998; Rauhut 2002) and the Upper Cretaceous of Romania ( Codrea et al. 2002; Weishampel et al. 2010). The measurements and morphological characteristics of the teeth and their denticles are also perfectly compatible with those in the Spanish sample from the Upper Cretaceous.

A tooth from L’Abella in the Upper Cretaceous of the Pyrenees was referred to as Richardoestesia -like ( Prieto-Márquez et al. 2000). This tooth has a FABL of 3.1 mm and a posterior denticle density of 7 denticles/mm. The anterior edge is broken, so it is impossible to know whether or not it possessed anterior denticles. The denticles are rectangular. It is a taller tooth (15.3 mm) than the rest of the specimens assigned to the genus (the average height is 4.9 mm) ( Fig. 5 ). In the discriminant analysis performed, this tooth is clearly isolated by its height from both the North American and Pyrenean samples (SOM: Table 2), which suggests it might be a new taxon.

Figures

Fig. 3. Theropod dinosaurs teeth from upper Campanian–Upper Maastrichtian, Spain. A.?Pyroraptor olympius Allain and Taquet, 2000, DPM-MON-T1, Montrebei. B, C.?Dromaeosauridae indet. B. MPZ2004/6, Blasi 2B. C. DPM-FON6-T2, Fontllonga 6. D–L.?Richardoestesia sp., Laño. D. MCNA 14610. E. MCNA 14607. F. MCNA 14606. G. MCNA 14608. H. MCNA 14609. I. MCNA 14611. J. MCNA 14568. K. MCNA 14607. L. MCNA 14619. M–P. Coelurosauria indet. M. DPM-MON-T6, Montrebei. N. DPM-MON-T3, Montrebei. O. MPZ98/80, Montrebei. P. MPZ98/82, Blasi 2B. Q.?Paronychodon sp., MPZ98/76, Blasi 2B.All lateral views. Scale bars 1 mm.

Fig. 4. Principal component analysis of the South Pyrenees Basin sample and the Royal Tyrrell Museum of Palaeontology sample; a chart displaying two first principal components, PC1 and PC2.

Fig. 5. Bivariate analysis comparing height (in mm) against posterior denticles per millimeter,?Dromaeosauridae,?Pyroraptor olympius, and?Richardoestesia from the South Pyrenees area are compared against a sample of Dromaeosaurus, Saurornitholestes, Richardoestesia, and Troodon from the collections of the Royal Tyrrell Museum of Palaeontology, the Richardoestesia-like tooth from the site of Suterranya, Catalonia, Spain (Prieto-Márquez et al. 2000) and Pyroraptor olympius Allain and Taquet, 2000 from Provence (Ronan Allain, personal communication 2013).