Lusitanisuchus mitracostatus, (SEIFFERT, 1970)

Guillaume, Alexandre R D, Moreno-Azanza, Miguel, Puértolas-Pascual, Eduardo & Mateus, Octávio, 2020, Palaeobiodiversity of crocodylomorphs from the Lourinhã Formation based on the tooth record: insights into the palaeoecology of the Late Jurassic of Portugal, Zoological Journal of the Linnean Society 189 (2), pp. 549-583 : 566-570

LUSITANISUCHUS MITRACOSTATUS ( SEIFFERT, 1970)

( FIGS 11–13 )

Referred material: MG26081 (IPFUB Gui Croc 7505); MG28911 (IPFUB Gui 75 6.03); (IPFUB Gui Croc 7516); MG26103 (IPFUB Gui Croc 8002); (IPFUB Gui Croc 8009).

Locality, horizon and age: Guimarota Mine (Leiria, Portugal); Alcobaça Formation; Kimmeridgian.

Description

Anterior premaxillary and maxillary teeth ( Fig. 11 ): IPFUB Gui Croc 8009 has three teeth preserved, whereas the other specimens have only one preserved. Because they are incomplete, the position in the tooth series cannot be determined. The root is exhibited in MG26103. Their height ranges from 1.014 mm to 2.373 mm and their width from 0.608 mm to 0.882 mm, with an H/W ratio from 1.668 to 2.690. The teeth are conical, with a broad, pointed apex. They do not seem compressed, suggesting a subcircular cross-section, with a faint constriction at the base of the crown. The teeth are weakly posteriorly curved. Both distal and mesial margins seem to exhibit a faint carina with no denticles observed. The enamel on both labial and lingual surfaces is covered by subparallel ridges converging toward the apex, forming basiapical striations ( Seiffert, 1973; Schwarz & Fechner, 2004; pers. obs.).

Dentary teeth ( Figs 12 , 13 ): Three teeth are preserved in MG28911 and three more alveoli without teeth are preserved. However, their position cannot be determined because the dentary is not completely preserved. MG26081 is almost complete, with two teeth preserved in the last positions. The previous two alveoli do not preserve teeth; then two more teeth are preserved, with one broken. The most anterior alveoli are not preserved. The root is exhibited in one tooth in MG28911. The height of the teeth ranges from 0.703 mm to 1.215 mm and their width from 0.54 mm to 0.993 mm, with an H/W ratio from 1.200 to 1.392. The teeth are spatulate, with a sagittate (arrowheadshaped) to truncate (straight and horizontal) apex, similar to a human incisor. They are labiolingually compressed, and there is a faint constriction visible at the base of the crown. Both labial and lingual surfaces are planar, and the edge of the apex is sharp. The enamel on both lingual and labial surfaces is covered by ridges forming basiapical striations, extending toward the apex to form vertical false denticles. These denticles are irregular in size; the lateralmost ones are small and barely visible, whereas the centralmost one is pointing outward from the apex, forming a small tip. No denticles are observed on the distal and mesial carinae of the teeth. In the lower part, ridges form parallel basiapical striations, but in the upper part, the central ridges converge toward the small tip of the apex, whereas the lateralmost striations have a flabelliform distribution and extend toward the margins and the edge of the apex, forming small lateral denticles ( Seiffert, 1973; Schwarz & Fechner, 2004; pers. obs.).

Remarks: The conical morphotype of the premaxillary and anterior maxillary teeth in Lusitanisuchus mitracostatus is commonly observed in Crocodylomorpha. Their overall shape and the ornamentation of the enamel are similar to teeth of morphotype 7, attributed to goniopholidids and usually associated with generalist feeding behaviour ( Buffetaut & Ford, 1979; Schwarz & Salisbury, 2005; Lauprasert et al., 2011; Salisbury & Naish, 2011; Puértolas-Pascual et al., 2015b), even though they are smaller and broader, as shown by their H/W ratios. The conical teeth of L. mitracostatus can also be compared with teeth of morphotype 2, attributed to atoposaurids, showing a similar shape and proportion, but the labial basiapical ridges in morphotype 2, when present, are more strongly marked than in L. mitracostatus . Material with better exposed teeth will enable us to confirm the difference between these two morphotypes.

The morphology of the dentary teeth differs from that observed in other mesoeucrocodylians ( Schwarz & Fechner, 2004), including atoposaurids, despite the similarornamentationsuggestingaparticularecological specialization. This morphology also differs from the molariform teeth characteristic of bernissartiids: the edge of the apex is sharper in Lusitanisuchus mitracostatus and comprises small denticles, whereas it is blunt and smooth in bernissartiids, the enamel in bernissartiids is more ornamented and some teeth observed in L. mitracostatus have a more pointed apex than is observed in Bernissartiidae . Not being multicuspids, they also differ from the spatulate teeth observed in Simosuchus and Uruguaysuchus ( Buckley et al., 2000) and they differ from those observed in Acynodon by being less broad and more labiolingually compressed ( Buscalioni et al., 1997; Martin, 2007; Delfino et al., 2008; Blanco et al., 2020). Given the preservation of the dentaries, no substantial difference could be observed in the tooth series between anterior and posterior teeth.

Figures

Figure 11. A–B, Lusitanisuchus mitracostatus left premaxilla–maxilla MG26103 (IPFUB Gui Croc 8002) in labial (A) and lingual (B) views with enlargements and schematic drawings of one tooth to illustrate tooth morphology. C, Lusitanisuchus mitracostatus right maxilla (IPFUB Gui Croc 8009) in labial view with enlargement and schematic drawing of one tooth to illustrate tooth morphology. Scale bar for the general views (left) is 1 cm, scale bar for enlargements and drawings (right) is 2 mm for A and B and 1 mm for C.

Figure 12. Lusitanisuchus mitracostatus left dentary MG26081 (IPFUB Gui Croc 7505) in labial (A), lingual (B), apicolabial (C) and apicolingual (D) views, with enlargements and schematic drawings of three teeth (from anterior to posterior: a, b and c) to illustrate tooth morphology. Scale bar for the general views (left) is 1 cm. Scale bar for the enlargements and drawings (right) is 1 mm.

Figure 13. Enlargement of the teeth of the Lusitanisuchus mitracostatus dentary MG28911 (IPFUB Gui 75 6.03) (from anterior to posterior: a and b) and schematic drawings to illustrate tooth morphology, in labial (A), lingual (B) and apicolingual views (C, D). Scale bar is 1 mm.