Ptychodus Agassiz, 1834

Genus Ptychodus Agassiz, 1834

Type species. Ptychodus schlotheimii Agassiz, 1834 ( nomen oblitum), senior synonym of Ptychodus latissimus Agassiz, 1835 ( nomen protectum). See Giusberti et al. (2018).

Diagnosis. See Vullo et al., (2024: p. 3).

Ptychodus decurrens Agassiz, 1838

( Figs. 1A–EII View Fig , J–LI, 3–8).

Selected synonyms list (for the complete list, see “Additional file 2” in supplementary material):

p.1752 Dentem seu palatum piscis Ostracionis; Brückmann: p. 116; pl. 5, fig. 4 (non fig. 4).

p.1752 “ipsum dentem exemtum petrefactum”; Brückmann: p. 120; pl. 6, fig. 4.

1835 Ptychodus decurrens Ag. ; Agassiz: p. 54 ( nomen nudum).

*vp.1838 Ptychodus decurrens Agass. ; Agassiz: atlas vol. 3, pl. 25b, figs. 1, 68 (non figs. 3–5).

vp.1838 Ptychodus polygyrus Agass. ; Agassiz: atlas vol. 3, pl. 25b, fig. 21 (non figs. 4-8, 10, 11).

1839 Ptychodus decurrens Agass. ; Agassiz: vol. 3; p. 154.

vp.1839 Ptychodus polygyrus Agass. ; Agassiz: atlas vol. 3, pl. 25, fig. 9 (non figs. 4–8, 10, 11).

v1850 Ptychodus decurrens ; Dixon: p. 362; pl. 30, fig. 7, 8; pl. 31, fig. 1; pl. 32, fig. 5.

v1850 Ptychodus depressus new; Dixon: p. 363; pl. 31, fig. 9.

v1850 Ptychodus Oweni new; Dixon: p. 364; pl. 31, fig. 2.

1887 P. decurrens ; Woodward: p. 123; pl. 10, figs. 2–10, 13.

1893 Ptychodus levis , sp. nov.; Woodward: p. 192; pl. 5, figs. 5, 6.

1902 Ptychodus decurrens var. multiplicatus nov. var.; Leriche: p. 96; pl. 2, fig. 20.

v1904 Ptychodus decurrens ; Woodward: p. 133; text fig., p. 134; pl. 15, figs. 1–5.

v1912 Ptychodus decurrens Agassiz ; Woodward: p. 239; text fig. 70 on p. 226; text fig. 71 on p. 227; text fig. 76 on p. 241, text fig. 77 on p. 243; pl. 51, pl. 52 (non syn.).

1973 Ptychodus decurrens Agassiz L. 1835 var. decurrens nov. var.; Herman: atlas, pl. 2, fig. 1.

1977 Ptychodus decurrens Agassiz L. 1835 ; Herman: p. 49; text fig., p. 52 (non syn.).

1977 Ptychodus oweni Dixon F. 1850 ; Herman: p. 53; text fig., p. 53.

2008 Ptychodus decurrens Agassiz, 1835 ; Müller: p. 62; pl. 1, 2.

p.2016 Ptychodus sp. ; Hoffman: p. 743; figs. 3.7–9, 14 (non figs. 3.1–6, 7–13).

2019 Ptychodus decurrens Agassiz, 1838 ; Brignon: p. 6, figs. 1, 5C.4, D.4, 8B.5, 8D, 18C, 44, 51C (middle figure), 52B–E, 54 (bottom figure, p. 70), 57 (three middle figures), 58A, B.

2020 Ptychodus decurrens Agassiz, 1835 ; Hamm: p. 26; figs. 37–48.

v2024 P. decurrens ; Vullo et al.; p. 3, fig. 2d.

Type series. Te eight isolated teeth from southern England illustrated by Agassiz (1838: pl. 25b, figs. 1–8; see Fig. 1E–LI View Fig ) and assigned to Ptychodus decurrens . According to the ICZN (1999: art. 74), we designate herein the lectotype of P. decurrens Agassiz, 1838 in order to fix and clarify the taxonomic identity of the species (see below).

Lectotype. NHMUK PV OR 5449 ( Fig. 3 View Fig ) is an isolated tooth from the “Mantell collection” housed in the Natural History Museum, London and it is designated herein as lectotype. Te specimen corresponds to the tooth originally illustrated by Agassiz (1838) on plate 25b, figs. 8, 8’

( Fig. 1L View Fig ; see also Brignon, 2019: p. 70). NHMUK PV OR 5449 ( Fig. 3 View Fig ) has a massive crown with symmetric outline, deep posterior sulcus and bulgy occlusal surface. Te anterior protuberance is broken on the left side (see Fig. 3A View Fig ). Fifteen thin ridges cross the tooth occlusal surface. Te ends of the ridges reach the marginal zone where they taper off and branch out to the edges of the tooth crown (see Fig. 3A, AII View Fig ). Te ridges merge with thin wrinkles on the marginal areas composing a fine reticulation. Te marginal ornamentation also includes rare granules mostly occurring on the anterior side (see Fig. 3A View Fig ). Te root of NHMUK PV OR 5449 is broken. In lateral view ( Fig. 3A,AII View Fig ), the outline of its crown is tilted anteriorly. In posterior view ( Fig. 3AIV View Fig ), the raised central area of the tooth crown has a large base and a rounded top.

Paralectotypes. Te remaining seven specimens of the original type series figured by Agassiz (1838: pl. 25b, figs. 1–7; see Fig. 1E–KI View Fig ) have to be considered as paralectotypes since they were originally syntypes of Ptychodus decurrens Agassiz, 1838 , together with the selected lectotype NHMUK PV OR 5449 ( Fig. 3 View Fig ; see ICZN, 1999; arts. 73.2.2, 74.1.3 and recommendation 74F; see also Brignon, 2019). However, three of these specimens (see Fig. 1G–II View Fig ) are clearly assignable to other species ( P. altior Agassiz, 1835 and P. mammillaris Agassiz, 1835 ; see also Amadori et al., 2019b). Among the teeth originally figured by Agassiz (1838), those in Fig. 1E, J–LI View Fig exhibit all the typical characters of P. decurrens (see “Diagnosis”, below) and, therefore, they have to be considered belonging to the species. Te major morphological differences between them concern the general shape of their crown. Most of these specimens exhibit a transversally elongated dental crown (e.g., Fig. 1E, K View Fig ). In contrast, MHNN FOS. 474 ( Fig. 1J View Fig ) is quite squared (see also Brignon, 2019: fig. 52D, E). Only one tooth ( Fig. 1K View Fig ) has a relatively flat occlusal surface (see Fig. 1KI View Fig ), while the others show bulged crowns (see Fig. 1EI,EII View Fig ,JI,LI).

Emended Diagnosis. A Ptychodus species with square to rectangular tooth crowns crossed by thin and transversally elongated ridges; the lateral ends of the ridges reach the occlusal marginal area where they taper off and branch out to the edge of the tooth crown. Occlusal ornamentations with lateral loops and posterior ramifications may occur, but they are rare. Fine wrinkles arranged in an irregular reticulation pattern cover the poorly developed marginal areas. Granules are mostly limited to the anterior occlusal surface. Dental crowns are bulged at the centre of the lower dentition, while the distal areas consist of flat teeth. Upper dentition with flat or slightly convex teeth. Lower symphyseal teeth are more symmetrical and transversely elongated than lateral teeth. Central tooth rows are juxtaposed with each other, while the more distal ones show slight imbrication. Tooth size, bilateral symmetry and number of ridges decreasing mesiodistally across the dentition with the only exception of the upper symphyseals that are small and transversely compressed. Distalmost teeth are transversally elongated and almost triangular in shape.

Referred material. Te articulated dentition CNHM 9350 from the Upper Cretaceous of Dalmatia (southern Croatia) housed at the Croatian Natural History Museum in Zagreb. Two tooth sets ( NHMUK PV OR 47904 and NHMUK PV OR 39125) and fourteen isolated teeth ( MNHN.F.CTE221, MHNN FOS. 474, NHMUK PV OR 28342, NHMUK PV OR 28348, NHMUK PV OR 28349, NHMUK PV OR 40541, NHMUK PV OR 49855, NHMUK PV P 51, NHMUK PV P 1385, NHMUK PV P 2688, NHMUK PV P 5449, NHMUK PV P 6524, NHMUK PV P 9029a and NHMUK PV P 9718) from England and an isolated tooth ( MGL 6263) from France. Te tooth set NHMUK PV OR 39125 consist of five detached teeth labelled here “ NHMUK PV OR 39125a– e”. Te tooth set NHMUK PV OR 47904 consists of four teeth embedded in three matrix blocks labelled here “ NHMUK PV OR 47904a–c”. See Table S 1 in “Additional file 1” (supplementary material), for details of the specimens.

Occurrences and ages. Te calcareous nannofossil assemblage of the matrix associated with CNHM 9350 contains rare and poorly preserved specimens. However, the presence, although very rare, of Quadrum gartneri and the absence of Eiffellithus eximius s.s., suggests the UC7 Zone ( Burnett, 1999). Te UC8 zone, however, cannot be ruled out because of the rare presence of Lucianorhabdus , which first appears just below the base of E. eximius . Hence, the data suggest a Turonian age for these specimens. Tis refutes the earlier hypothesis of a more recent age, i.e., Campanian ( Murray et al., 2016) for CNHM 9350.

NHMUK PV P 9029a and NHMUK PV OR 39125 come from the Cenomanian lower Chalk (see Friedmann et al., 2016) of southern England (Woodward, 1889, 1893, 1912). NHMUK PV P 6524 and NHMUK PV P 51 come from the late Cenomanian Holaster subglobosus Zone (see Friedmann et al., 2016) of southern England (Woodward, 1889, 1893, 1912). Unfortunately, no information on the age of the other English specimens could be obtained. Te isolated tooth MGL 6263 comes from the late Cenomanian Actinocamax plenus Zone (see Friedmann et al., 2016) of Upper France. See Table S 1 in “Additional file 1” (supplementary material), for details of the specimens.

Description of the new tooth plate. Specimen CNHM 9350 ( Figs. 4 View Fig , 5 View Fig ) consists of a tooth set (75 teeth in total), which is still embedded in a matrix slab, and its counterpart (imprint; Fig. 4A, B View Fig ). Among these teeth, 44 are still arranged with each other in their natural position, forming a dental plate (see Figs. 4 View Fig , 5 View Fig ). In addition, 31 teeth together with several tooth fragments and dental imprints are scattered on the slab around the articulated dental plate ( Figs. 4 View Fig , 5 View Fig ). Most of the teeth display rectangular crowns crossed by 8–11 thin, occlusal ridges (e.g., Fig. 4C View Fig ); the smallest teeth have a triangular (e.g., “3c” in Fig. 4D View Fig ) or oval (e.g., “f1, g1” in Fig. 4E View Fig ) shape and a lower number of ridges (four to six; see also Fig. 4D, E View Fig ). Te dental crown is bulgy in the teeth placed at the centre of the dental plate ( Fig. 4F View Fig ). Lateral teeth have a less high crown and those placed in the distal areas of the plate are completely flat (see Fig. 4F View Fig ). Across the whole dental plate, the occlusal ridges on the teeth reach the lateral crown margins with their branching ends ( Fig. 4C–E View Fig ). Tin wrinkles and granules cover the anterior marginal area of the tooth crown. Te central teeth are abraded on their occlusal surface especially at the anteriormost area of the plate (see Fig. 4A, C View Fig ). Te roots of the teeth are embedded in the matrix and, therefore, not observable.

Redescription of the comparison material. Specimens NHMUK PV OR 28348 ( Fig. 6A, AI View Fig ), NHMUK PV OR 28349 ( Fig. 6B View Fig ) and NHMUK PV OR 47904b ( Fig. 6E View Fig ) are isolated teeth with a rectangular, transversally elongated crown. Nine to eleven transversal ridges cross their occlusal crown surface. Teir anterior margin shows no protuberance, while the posterior one has a shallow sulcus. Teir occlusal surfaces are almost flat. Te ridges branch at their ends, reaching the lateral margins of the crown. Te ridges in NHMUK PV OR 28348 are damaged in the central area of the crown, while they exhibit a slight occlusal abrasion on the left side (see Fig. 6 AI View Fig ). Te crown of NHMUK PV OR 47904b ( Fig. 6E View Fig ) is markedly abraded on the right side. Te marginal area of NHMUK PV OR 28348 ( Fig. 6A, AI View Fig ), NHMUK PV OR 28349 ( Fig. 6B View Fig ) and NHMUK PV OR 47904b ( Fig. 6 AI View Fig ) is covered by fine wrinkles on the anterior and posterior tooth margins. Te tooth roots of NHMUK PV OR 28348 and NHMUK PV OR 28349 are not preserved. Te two teeth associated in NHMUK PV OR 47904c ( Fig. 6F View Fig ) are almost identical to NHMUK PV OR 28348 ( Fig. 6 AI View Fig ). Both teeth have eight occlusal ridges. Te anteriormost ridges on one of the teeth in NHMUK PV OR 47904c ( Fig. 6F View Fig ) form a small loop on the right crown side. Specimens NHMUK PV OR 40541 ( Fig. 6C View Fig ) and NHMUK PV OR 47904a ( Fig. 6D View Fig ) are very similar to NHMUK PV OR 28348 ( Fig. 6 AI View Fig ) and NHMUK PV OR 28349 ( Fig. 6B View Fig ), but their crown is squared and crossed by 13–15 ridges. Te tooth roots of NHMUK PV OR 40541 and NHMUK PV OR 47904a–c still are embedded in matrix and therefore not accessible. Specimens NHMUK PV P 6524 ( Fig. 6G–GII View Fig ) and NHMUK PV P 51 ( Fig. 6H–HII View Fig ) are two small rectangular teeth with well-developed anterior protuberances and slightly raised occlusal surfaces. Specimen NHMUK PV P 6524 has a symmetrical outline (see Fig. 6GI View Fig ). Most of the crown surface of NHMUK PV P 6524 and NHMUK PV P 51 is markedly abraded (see Fig. 6HII View Fig , GII). Fine ridges (?eight to nine) with branching ends are still recognisable on their occlusal surface. Te marginal area is covered by fine wrinkles. Specimens NHMUK PV OR 39125a–d

( Fig. 6I–L View Fig ), NHMUK PV OR 28342 ( Fig. 6N View Fig ), NHMUK PV OR 49855 ( Fig. 6Q View Fig ), NHMUK PV P 1385 ( Fig. 6S View Fig ), NHMUK PV P 9029a ( Fig. 6R View Fig ) and NHMUK PV P 9718

( Fig. 6P View Fig ) have squared crowns with rounded margins. Te anterior protuberance is poorly developed and the posterior sulcus is shallow. Specimens NHMUK PV OR 39125a-d ( Fig. 6I–L View Fig ), NHMUK PV OR 28342 ( Fig. 6N View Fig ) and NHMUK PV P 9029a ( Fig. 6R View Fig ) display flat occlusal surfaces, while a bulgier crown characterizes NHMUK PV OR 49855 ( Fig. 6Q View Fig ), NHMUK PV P 1385 ( Fig. 6S View Fig ) and NHMUK PV P 9718 ( Fig. 6P View Fig ). Irregular, thin ridges (four to ten) with branching lateral ends cross the top tooth surface. Te anteriormost ridges are quite transversal, while the rearmost ones are interrupted and branching on the posterior crown edge. Te rearmost ridges of NHMUK PV OR 49855 ( Fig. 6Q View Fig ) form a sort of fold in the centre of the tooth crown. Tin wrinkles cover the marginal areas. Specimens NHMUK PV OR 39125e ( Fig. 6M, MI View Fig ) and NHMUK PV P 2688 ( Fig. 6O–OII View Fig ) have symmetrical and transversally elongated crowns similar to NHMUK PV P 6524 ( Fig. 6GI View Fig ) with seven to eight occlusal ridges. In lateral view ( Fig. 6OII View Fig ), the outline of the crown of NHMUK PV P 2688 is perpendicular to the tooth base, while it is tilted anteriorly. Te ridges in NHMUK PV OR 39125e ( Fig. 6M View Fig ) and NHMUK PV P 2688 ( Fig. 6O View Fig ) branch posteriorly as in NHMUK PV OR 39125a–d ( Fig. 6I–L View Fig ). Specimens NHMUK PV OR 39125e and NHMUK PV P 2688 show a bulgy occlusal surface at the centre of their tooth crown (see Fig. 6MI,OI View Fig ). Rare, coarse granules are randomly scattered between the central ridges and marginal wrinkles of NHMUK PV OR 39125a–e ( Fig. 6I–MI View Fig ) and NHMUK PV OR 28342 ( Fig. 6N View Fig ). In posterior view ( Fig. 6JI View Fig ), the tooth root of NHMUK PV OR 39125b is thick and bilobate with a shallow antero-posterior sulcus. Te roots of NHMUK PV OR 39125a, NHMUK PV OR 39125c–e, NHMUK PV OR 28342, NHMUK PV OR 49855, NHMUK PV P 1385, NHMUK PV OR 5449, NHMUK PV P 9029a, NHMUK PV P 9718 and NHMUK PV P 2688 are not preserved or not accessible. Specimen MNHN.F.CTE221 ( Fig. 7A–AII View Fig ) is an isolated tooth with thirteen occlusal ridges very similar to those observed on NHMUK PV P 1385 ( Fig. 6S View Fig ), but its ornamentation lacks any posterior branching. In lateral view ( Fig. 7AII View Fig ), MNHN.F.CTE221 exhibits a bulgy dental crown tilted anteriorly; conversely, its posterior side is perpendicular to the tooth base. Specimen MGL 6263

( Fig. 7B–BII View Fig ) has a rectangular and bulgy crown with seventeen occlusal ridges similar to those on the crown of NHMUK PV P 6524 ( Fig. 6GI View Fig ), NHMUK PV OR 39125e

( Fig. 6M View Fig ) and NHMUK PV P 2688 ( Fig. 6O View Fig ). None of the ridges of MGL 6263 branch posteriorly; the ridges are abraded at the centre of the occlusal surface (see Fig. 7B View Fig ). Although the posterior corner of the right tooth edge in MGL 6263 is broken, its crown exhibits a quite regular and symmetric outline (see Fig. 7B View Fig ). Te tooth roots of MNHN.F.CTE221 and MGL 6263 are not preserved (see Fig. 7AII View Fig ,BII).

Remarks. All the specimens described here exhibit the typical ornamentation of Ptychodus decurrens Agassiz, 1838 with branching ridges on the edges of the tooth crown. However, their degree of branching can vary between teeth and / or between lateral margins of a single tooth. For examples, the branching at the end of the occlusal ridges is less pronounced on the left side in NHMUK PV OR 28348 (see Fig. 6 AI View Fig ) and on both sides in NHMUK PV OR 47904b–c (see Fig. 6F View Fig ). Te lower symphyseal teeth are well known to be the largest in any species of Ptychodus Agassiz, 1834 . Conversely, small, narrow teeth characterise the upper dentition of both cuspidate and un-cuspidate species (see Amadori et al., 2020 a, 2022a; Hamm, 2020; Shimada, 2012; Woodward, 1912). In particular, Woodward (1887) described an articulated dentition of Ptychodus decurrens Agassiz, 1838 preserving both upper and lower teeth still in natural position. Te specimen clearly shows lower teeth characterised by bulgy crowns, while the upper ones have more flattened occlusal surfaces (see also Woodward, 1912: text fig. 76). Tis pattern of dignathic heterodonty was observed already in various other un-cuspidate species of Ptychodus (e.g., P. latissimus , P. mediterraneus and P. polygyrus ; Amadori et al., 2020 a, 2020b; Hamm, 2020; Woodward, 1912). Te dental plate CNHM 9350 ( Figs. 4 View Fig , 5 View Fig ) clearly preserves several lower teeth of Ptychodus decurrens Agassiz, 1838 that are still arranged in natural position. Tis crushing plate was undoubtedly placed in the lower jaw due to the presence of the largest teeth placed across the symphyseal row (e.g., “m2–m6” in Fig. 4C View Fig ). Te first published drawings of isolated specimens of P. decurrens depict lower teeth probably belonging to the symphyseal (e.g., Fig. 1B, C View Fig ) and lateral (e.g., Fig. 1A, D View Fig ) rows. Te type series of P. decurrens ( Fig. 1E– LI View Fig ) includes both lower ( Fig. 1E, EI, J, JI, L, LI View Fig ) and upper

( Fig. 1K, KI View Fig ) teeth. Among the isolated specimens redescribed here, the tooth NHMUK PV OR 5449 ( Fig. 3 View Fig ) was

(See figure on next page.)

Fig. 6 View Fig Disarticulated teeth from the Upper Cretaceous of England assigned here to Ptychodus decurrens Agassiz, 1838 . The specimens are figured in occlusal ( A–J, K–M, N, O, Q–S), anterior ( J I, M I), posterior ( O I) and lateral ( J II, O II) views. A, A I isolated tooth NHMUK PV OR 28348; B upper lateral tooth NHMUK PV OR 28349; C isolated tooth NHMUK PV OR 40541; D associated tooth NHMUK PV OR 47904a; E associated tooth NHMUK PV

OR 47904b; F associated teeth NHMUK PV OR 47904c; G–G II isolated tooth NHMUK PV P 6524; H–H II isolated tooth NHMUK PV P 51; I, I I associated tooth NHMUK PV OR 39125a; J–J II associated tooth NHMUK PV OR 39125b; K associated tooth NHMUK PV OR 39125c; L associated tooth NHMUK

PV OR 39125d; M–M I associated tooth NHMUK PV OR 39125e; N isolated tooth NHMUK PV OR 28342; O–O II isolated tooth NHMUK PV P 2688; P isolated tooth NHMUK PV 9718; Q isolated tooth NHMUK PV OR 49855; R isolated tooth NHMUK PV 9029a; S isolated tooth NHMUK PV P 1385.

Arrows indicates occlusal tooth wear. Scale bars equal 10 mm ( A–G I, H, H I, I–S) and 5 mm ( G II, H II)

originally placed within the symphyseal row of the lower dentition, based on its bulgy tooth crown with symmetrical outline (see also Woodward, 1889: p. 139). Te bulgy, symmetrical teeth NHMUK PV P 6524 ( Fig. 6G–GII View Fig ), NHMUK PV OR 39125e ( Fig. 6M, MI View Fig ), NHMUK PV P 2688 ( Fig. 6O–OII View Fig ) and MGL 6263 ( Fig. 7B–BII View Fig ) belong to the same tooth row. Te bulgy teeth NHMUK PV P 51

( Fig. 6H–HII View Fig ), NHMUK PV P 9718 ( Fig. 6P View Fig ), NHMUK PV OR 49855 ( Fig. 6Q View Fig ), NHMUK PV OR 39125a–d

(Fig. I–L), NHMUK PV OR 28342 ( Fig. 6N View Fig ), NHMUK PV P 1385 ( Fig. 6S View Fig ) and MNHN.F.CTE221 ( Fig. 7A–AII View Fig ) were originally arranged within lateral areas of the lower dental plate. Based on their asymmetrical crowns and flat occlusal surfaces, NHMUK PV OR 28348 ( Fig. 6A– AI View Fig ), NHMUK PV OR 28349 ( Fig. 6B View Fig ), NHMUK PV OR 40541 ( Fig. 6C View Fig ), NHMUK PV OR 47904a–c ( Fig. 6D–F View Fig ) and NHMUK PV P 9029a ( Fig. 6R View Fig ) are identified here as upper lateral teeth. In general, lateral teeth with a more transversally elongated crown (e.g., NHMUK PV OR 28348, NHMUK PV OR 28349, NHMUK PV OR 47904bc) seem to be arranged close to the symphyseal row in un-cuspidate species (e.g., P. decurrens and P. mediterraneus ; see Woodward, 1912: pl. 51, fig. 9; Amadori et al., 2020 a: fig. 6).

Tooth abrasions observed on the lower crushing plate CNHM 9350 (see Fig. 5 View Fig ) indicate that the processing of prey items in Ptychodus decurrens Agassiz, 1838 occurred mostly at the centre of the dentition, as already hypothesised for other un-cuspidate species of Ptychodus (e.g., P. mediterraneus ; see Amadori et al., 2020 a). In particular, “functional teeth” (sensu Shimada, 2012) were limited to centre of the anterior portion of the crushing plates (see Amadori et al., 2020 a). A similar tooth abrasion pattern also occurs in other articulated specimens of P. decurrens (e.g., Woodward, 1912: text fig. 76).