Dipteridaceae

Kustatscher, Evelyn, Dellantonio, Elio & Van Konijnenburg-Van Cittert, Johanna H. A., 2014, The ferns of the late Ladinian, Middle Triassic flora from Monte Agnello, Dolomites, Italy, Acta Palaeontologica Polonica 59 (3), pp. 741-755 : 746-748

? Dipteridaceae indet.

Fig. 4C, D.

Material.— MGP 194/2 A – B, 194/103, 196/41, frond fragments, Monte Agnello, Dolomites, N-Italy, early late Ladinian.

Description.— Frond fragments are up to 110 mm long and 70 mm broad. Pinnae arise alternately at c. 6 mm distance from a rachis of about 4 mm width (e.g., MGP 194/2 A; Fig. 4D) The pinna fragments are 60 mm long and 10 mm wide, with a deeply incised lamina ( MGP 194/2 B; Fig. 4 C). The lobes with a rounded apex are 3.5–7 mm long and—separat- ed by sinuses— 2.5–4 mm deep but the incisions never reach the midrib. The midrib is thick (~ 1 mm). The basal part of the pinnae and the rachis are characterized by longitudinal striae ( MGP 194/2 A; Fig. 4D). Each lobe has a distinct secondary vein; tertiary veins are indistinct in the lamina ( MGP 194/2 B; Fig. 4 C 2).

Discussion.— These specimens show several characters of the Dipteridaceae , such as the partly pedate frond organization. But most of the pinnae are arranged pinnately, and no tertiary venation is visible that might render an assignment to this family possible. Dipteridaceae are characterized by a pedate (palmately dissected) frond arrangement with pinnae dissected to a certain degree, and it is the only fern family occurring in the Mesozoic in which all members are characterized by reticulate venation (see e.g., Wagner 1979). This is in contrast to some Phlebopteris species that show occasional anastomoses, but no completely reticulate venation.

Fig. 4. Fern remains from the tuff layer in the basal part of “explosion breccia” (late Ladinian, Middle Triassic) of Monte Agnello, Dolomites, N-Italy. → A. Phlebopteris fiemmensis sp. nov., young frond ( MGP 181/57 A). B. Thaumatopteris sp. , pinnae fragment ( MGP 63/80). C, D.? Dipteridaceae indet.

C. Frond fragment ( MGP 194 /2 B) ( C 1 ), detail of pinnae with secondary venation ( C 2 ). D. Frond fragment with striate attachment area of the pinnae ( MGP 194 /2 A) . E, F. Chiropteris monteagnellii sp. nov. E. Holotype , most complete frond fragment ( MGP 194 /8 A) . F. Paratype , frond fragment with clear net venation ( MGP 194 /95 B). Scale bars 10 mm, except E 5 mm.

It is an important fern family during the Late Triassic to Cretaceous with several genera (e.g., Clathropteris , Dictyophyllum , Thaumatopteris , Camptopteris , Hausmannia , Goeppertella ) occurring worldwide ( Tidwell and Ash 1994; Collinson 1996). The present material shows some resemblance to Dictyophyllum with its deeply divided lateral pinna segments and to the narrower pinnae of Camptopteris ( Nathorst 1906) . It might even be an aberrant specimen of Thaumatopteris or Goeppertella . But as long as no specimens with a clear venation have been found, the material cannot be attributed to a family or genus.