Nilssonia sp.

Flores-Barragan, Miguel Angel & Leon, María Patricia Velasco-de, 2020, New records of Bjuvia and Nilssonia from the Permian of Mexico, Palaeontologia Electronica (a 28) 24 (3), pp. 1-17 : 8-10

Nilssonia sp.

Figure 4 A-B

Material. CFZ-MTZ266.

Locality. Carretera.

Description. Leaf pinnate (segmented) is subdivided into numerous, regular oppositely positioned segments. The leaf is 6.3 cm long and 4.7 cm wide in the middle part. It has segments with a constant width from 1 to 1.2 cm wide at the base, and the leaf apex is unknown. The distance between the segments is relatively constant at about 0.2-0.3 cm. The lamina is attached to the upper edge of rachis and is completely covered by the rachis, which can measure up to 0.3 cm in width. The venation of the segments is inserted at an angle of 80-90°. The veins can dichotomize near the base then become parallel with a density of 12 to 17 veins per cm in the proximal part to the margin.

Remarks. Segmented leaves have been reported for the Permian from different parts of the world, such as Pterophyllum cotteanaum Gutbier from the lower Permian of Germany ( Barthel et al., 2010), Pseudoctenis middridgensis Stonley from the upper Permian of England (Stonley, 1958), and/or Pseudoctenis samchokense, Kawasaki from the upper Permian of China ( Pott et al., 2010). However, in these cases, the lamina segments are laterally attached to the rachis and are not similar to the Puebla specimen ( Table 3 ). The leaf described in the present work is assigned to Nilssonia based on the leaf lamina clearly being attached to the upper edge of the rachis (Van Konijnenburg-van Cittert, et al., 2017). Nilssonia has some records for the upper Paleozoic (Tian and Zhang 1980; He et al., 1996), and the first reliable reports are from the Triassic. The species Nilssonia sturii Krasser from the upper Triassic of Austria ( Pott et al., 2007) evinces some similarity to the specimen from Mexico but differs from it by having a lower number of veins, as well as the presence of dichotomies in the Mexican specimen.

It is important to mention that the dichotomies in the veins in the genus Nilssonia are not common in species from the Northern Hemisphere, but are common in species from Gondwana ( Holmes et al., 2010). Therefore, it is not comparable to other species described for the Triassic of Europe ( Barbacka, 2001; Kustatscher and Van Konijnenburg-van Cittert, 2010).

Figures

FIGURE 4. Specimens of leaves of Cycadophytes. A) Nilssonia sp. Specimen CFZ-MTZ266, the arrow indicates an area in which it is observed how the leaf covers the rachis. B) Parallel and dichotomous venation of Nilssonia sp. C) Parallel venation of Taeniopteris lentriculiformis, specimen CFZ-MTZ330. D) Specimen of Taeniopteris lentriculiformis. E) Taeniopteris crassinervis, specimen CFZMtz-713. F) Parallel and dichotomous venation of Taeniopteris crassinervis. Symbols: m, leaf margin; r, rachis; the arrows indicate the areas with dichotomous venation. Scale. A, D-F 1 cm, B and C 0.5 cm.