Fig 1.
Map of Mexico with inset of northeastern Mexico and the Jurassic-Cretaceous transition at Puerto Piñones.
Salinites grossicostatum specimens described here originate from a shaly limestone of the latest Tithonian “Kossmatia-Durangites-Salinites Beds” (cf. [12]), respectively the uppermost Crassicollaria Zone [8]. Locality map after [13]. Puerto Piñones: N25°02.719’/W101°03.396’.
Fig 2.
Size-frequency histogram for Salinites grossicostatum.
Specimens were collected from a single layer of the uppermost Tithonian La Caja Formation at Puerto Piñones. D = diameter.
Fig 3.
Representative specimens of Salinites grossicostatum representing an ontogenetic series from juvenile (a) to mature (i).
(a) CPC-1405; (b) CPC-1406; (c) CPC-1407; (d) CPC-1408; (e) CPC-1409; (f) CPC-1410; (g) CPC-1411; (h) CPC-1412; (i) CPC-1413; scale bars = 10 mm.
Fig 4.
Early ontogenetic internal shell development and measurements of Salinites grossicostatum based on four median sections.
(a) CPC-1217, with sketch to the right (a2) to illustrate internal shell structures; (b) CPC-1214; measurements are provided in mm.
Fig 5.
Apertural height (ah) versus shell diameter (D) for two micro- and two macroconchs (CPC-1214–1217).
Note that apertural height is illustrated logarithmically. The regression lines indicate a change in growth at the primary constriction and that allometric growth is higher during post-embryonic stages than before.
Fig 6.
Measurements of the siphuncle in five specimens.
The upper plot illustrates the ratio between siphuncular diameter [DS] versus shell diameter [D]; the lower plot figures the siphuncular diameter versus apertural height at the plane of coiling [ah]. To the right, high-resolution scans illustrate the siphuncle; (a) longitudinal median section of CPC-1228; (b) transversal section through the plane of coiling in CPC-1214. Black arrows indicate position of the siphuncle; scale bars = 2.5 mm.
Fig 7.
Plot of shell diameter [mm] versus septum number for five specimens.
Sexual dimorphism is indicated between septum numbers 25 and 30 by a considerably higher growth increase in macroconchs.
Fig 8.
Ratio between septal angle versus septal number for four mature specimens and one juvenile (CPC-1231).
Specific correlative septal “events” are marked by dashed lines. D = diameter at the last septum.
Fig 9.
Sutural ontogeny of Salinites grossicostatum.
(a) CPC-1218; (b) CPC-1219; (c) CPC-1220.
Fig 10.
First occurrence of characteristic ornamentation patterns in Salinites grossicostatum.
In macroconchs, the spiral groove, the serration of the keel and the apophysis appear at larger diameters.
Fig 11.
Ontogenetic reconstruction of Salinites grossicostatum based on external and internal characteristics.
Sexual dimorphism and four major stages are recognized: embryonic, neanic, juvenile and mature. The diameter indicates the first occurrence of characteristic modifications.