Tilicrassatella ponderosa ( Philippi, 1887 )

Devries, Thomas J., 2016, Fossil Cenozoic crassatelline bivalves from Peru: New species and generic insights, Acta Palaeontologica Polonica 61 (3), pp. 661-688 : 671-673

Tilicrassatella ponderosa ( Philippi, 1887)

Fig. 8A− C.

1887 Crassatella ponderosa sp. nov.; Philippi 1887: 166, pl. 38: 5, 5a.?1887 Venus medinae sp. nov.; Philippi 1887: 115, pl. 17: 1.

?1974 Crassatella medinae ( Philippi, 1887) ; Frassinetti 1974: 49, fig. 11. 1979 Crassatella ponderosa Philippi, 1887 ; Tavera 1979: 83, pl. 15: 35. 2003 Eucrassatella ponderosa ( Philippi, 1887) : DeVries and Frassinetti 2003: pl. 2: 3.

Type material: Lectotype, adult right valve with hinge partially obscured, herein designated: SGI. PI. 468, Navidad , Chile, L (95), H 76 . Paralectotype, herein designated: SGI. PI. 4750, L (55), H (43). These type designations formalize unpublished notations on museum labels, most likely written by Juan Tavera. Paralectotypes: SGI. PI. 4749 and SGI. PI. 4751, unpublished designations of Juan Tavera , are not fragments of T. ponderosa , a fact noted on the museum labels by the late Daniel Frassinetti of the Museo de Historia Natural in Santiago, Chile . Type locality: Navidad, Chile.

Type horizon: Navidad Formation, lower or middle Miocene.

Material.— UWBM 101843, B8314, L (76.7), H (70.5), T 25.4; UWBM 101844, B8328, L (59.8), H 58.3, T 21.6; UWBM 101845, B8332, H (29.6). Other specimens from B8315 (internal casts). Additional material from central Chile includes specimens from Maitenlahue ( SGO. PI. 5517) and Rapel (Sven Nielsen, personal communication 2015), all from the Navidad Formation.

Emended diagnosis.— Tilicrassatella with shell posteriorly produced and strongly inflated.

Description.—Shell to 90 mm long, elongate-ovate, inflated, beak about one-third of length from anterior end, L:H ratio 1.3, T:H ratio 0.3, maximum inflation posterior to beak. Anteriodorsal and posteriodorsal profiles straight or slightly concave. Anterior and ventral margins rounded, posterior margin bluntly truncate, moderately produced. Rounded primary posterior ridge diverging 15°, weak secondary posterior ridge 5° from posteriodorsal margin. Lunule cordate, wider than escutcheon; both about half the length of respective margins. Beak prosogyrate. Umbo rounded, prosogyrate, with closely spaced commarginal ribs. Remainder of exterior with irregular commarginal growth lines. Resilifer extending nearly to vmHP. Left anterior cardinal tooth thick, wedge-shaped, inclined anteriorly 30°, separated from beak by lunule. Left posterior cardinal tooth narrow, wedge-shaped, straight, nearly orthocline. Right anterior pseudocardinal tooth short, narrow, inclined anteriorly 70°, joining cardinal tooth with lunule. Right cardinal tooth thick, wedge-shaped, inclined anteriorly 10°. Right posterior pseudocardinal tooth lamellar, diverging 20° from cardinal tooth, passing resilifer anteriorly. Inner ventral margin crenulate.

Remarks.—Like specimens of Crassatella rafaeli , those of Tilicrassatella ponderosa have closely spaced commarginal ribs on the umbo. Specimens of T. ponderosa differ from those of T. torrens sp. nov. by their anterior inflation and markedly inequilateral valves, resulting in a steeply descending anteriodorsal margin. The only known specimen of T. sanmartini is more elongate and less rostrate posteriorly and its resilifer is directed in a mostly posterior direction. An anterioventral fragment of a juvenile left valve of T. ponderosa ( UWBM 101845) shows no evidence of ventral crenulations. A paired Miocene specimen of about 43 mm length ( SGO. PI. 115), previously termed Crassatella medinae ( Philippi, 1887) by Frassinetti (1974) and recently photographed by Leonardo Pérez (Universidad Austral de Chile, Valdivia), may be a juvenile example of T. ponderosa . Small specimens with exposed hinge plates are needed to make such a determination.

Stratigraphic and geographic range.—Chattian to Burdigalian, Chilcatay depositional sequence, East Pisco Basin, south-central Peru. Uppermost Chattian, basal Camaná Formation, southern Peru ( Vega and Marocco 2004). Lower to lower middle Miocene, Navidad Formation, Chile.