Taimyria triassica NAUGOLNYKH et MOGUTCHEVA, 2022

Naugolnykh, Serge V. & Mogutcheva, Nina K., 2022, Taimyria Gen. Nov., A New Genus Of Evolutionary Advanced Gymnosperms From Triassic Of The Taimyr Peninsula, Siberia, Russia, Fossil Imprint 78 (2), pp. 432-444 : 435-437

Taimyria triassica NAUGOLNYKH et MOGUTCHEVA sp. nov.

Text-figs 2–11

H o l o t y p e. 4287/6, holotype figured here in Textfigs 2a, 3–10.

P l a n t F o s s i l N a m e s R e g i s t r y N u m b e r.

PFN003027.

R e p o s i t o r y. Monographic Department of the State Darwin Museum, Moscow, Russia .

During the study, the collection was kept in the Geological Institute of Russian Academy of Sciences (Moscow, Russia).

D e r i v a t i o n o m i n i s. From Triassic period.

Ty p e l o c a l i t y. The Tsvetkov Cape locality, Taimyr, Siberia, Russia; Lower Triassic, Induan.

D i a g n o s i s. Same as for the genus.

D e s c r i p t i o n. Macromorphology. The specimen studied is represented by four megastrobili (marked by arrows on Text-fig. 2 ) preserved on one bedding surface. There is a thick axis on one side of the specimen (Ax in Text-fig. 2 ). The four megastrobili are located on both lateral side of the Ax axis, with two on each side. Therefore, one can suppose that the megastrobili were arranged on a fertile branch in pinnate order, or forming a pinnate frond-like structure. Two megastrobili are preserved almost completely. Since the actual attachment of the megastrobili to the same branch (Ax) is not clearly visible, only one of the strobili is selected as a holotype ( Text-fig. 2a ). Two other strobili preserved on the other side of the branch are not complete and show their basal parts only.

The most well-preserved strobilus (holotype) is of more or less cylindrical shape ( Text-fig. 2a ). It is about 61 mm long and 15 mm wide. The base of the strobilus is not visible. Second strobilus, which is also preserved almost completely, is very similar to the holotype, but somewhat narrower, 72 mm long and 12 mm wide.

Each strobilus consists of densely arranged seed-bearing megasporangiate discs attached to the common axis in spiral order and forming well-pronounced parastichy ( Text-figs 3a, b , 4a, b ). Each observed parastichus on one side of the strobilus has three seed-bearing discs. Thus, one complete cycle should include six discs. The holotype has eleven parastichy. The second, narrower megastrobilus has fourteen parastichy. Thus, each strobilus has more than seventy seedbearing discs.

The possible fertile branch axis near the basal parts of the strobili is 7 mm wide and 80 mm long at visible part ( Text-fig. 2 , Ax). The surface of the axis is covered by very fine longitudinal ribs and furrows.

The seed-bearing discs are distinctly asymmetrical, ca. 5 × 9 mm in dimensions ( Text-figs 2a , 3a , 4a, b ). The long axes of the disc shields are oriented horizontally, and perpendicular to the main axis of the strobilus. This feature makes the present fossil different in comparison with other similar peltasperm female reproductive organs. The functionally upper or abaxial surface of the seed-bearing disc is smooth or slightly folded. Peripheries of the discs are entire-margined generally, but some discs bear six to eight unclear lobes about 1 × 2 mm in dimensions. Some discs demonstrate a flattened protective limb of about 2 mm wide at outer periphery of the lobes, making the disc semi-closed. This limb covers the seed base ( Text-fig. 4b ).

Cuticle preparations taken from the holotype show well-visible seed scars ( Text-figs 3c , 4c ). The seed scars are ovoid, 300 µm long and 200 µm wide on average. Size and shape of the seed scars well correspond to the size and shape of the chalazal base of the seeds. Judging from the material in hand, the seed scars were orientated along the radial directions of the seed-bearing disc.

The seeds are disposed beneath the seed-bearing disc and directly attached to the adaxial surface of the discs ( Text-fig. 4b ). The seed cuticles were extracted during the maceration of the discs ( Text-figs 8–10 ).

The seeds are platyspermic, very small (according to the seed size ranking scale proposed by Artjushenko 1990). Seed are ovoid, 1.7–2.0 mm long and 1.0– 1.2 mm wide, widest at the middle or lower one-third ( Text-figs 8–10 ). The seeds are narrowed at the apical micropylar end. The seed peripheries are slightly flattened. The seed coat (spermoderm) is smooth, without distinct sculpture. The seed scarlet is about 300 µm in diameter, ellipsoidal to round, central in relation to the ventral side of the seed, somewhat impressed, surrounded by weakly developed ring-shaped uplifting ( Text-figs 8b , 9a ). The main axis of the seeds is straight to slightly curved. Since the seeds lack sarcotestal wings, we can conclude that the original plant had rather limited dispersal ability (authochorous or barochorous).

Very similar seeds, but considerably larger, were described as “ Cordaicarpus ” uralicus KH.R.DOMBR. from the lower Permian (Kungurian) deposits of the Cis-Urals ( Dombrovskaya 1976). It was suggested that these seeds were produced by the peltasperm plant with the fronds Permocallipteris retensoria (ZALESSKY) NAUGOLNYKH and the seed-bearing discs Peltaspermum sp. ( Naugolnykh and Kerp 1996, Naugolnykh 2014). Seeds of this type were found later in natural connection to the seed-bearing discs of Peltaspermum petaloides NAUGOLNYKH ( Naugolnykh 2016: 86, text-fig. 35A, B, D, pl. XXIX, 6).

Discovery of the present specimen, bearing seeds in natural connection to the seed-bearing discs similar to other representatives of Peltaspermales , supports the initial idea that these seed forms belong to the peltasperms ( Naugolnykh and Kerp 1996).

Epidermal-cuticular structure. The cuticles are relatively thick.The cell outlines are indistinctly pronounced.

The most well-preserved cell structure is observed on the adaxial cuticles, especially around the seed scars, where the cells are clearly visible and well-expressed in the cuticle relief ( Text-figs 3c , 4c , 8–10 ).

The common epidermal cells are elongate, mostly of prolonged rectangular outlines, rarely more isometric. Average size of the cells is 40 × 70 µm. Radial cell walls are undulated to slightly curved. The straight cell walls are present as well. The periclinal cell walls are fairly smooth. The common epidermal cells form distinct rows radially disposed around the seed scars ( Text-figs 3c , 4c ). The cells become more isometric in the distance of 500–600 µm from the seed scar. Occasionally the papillae are joined into a common uplifting with weak extrusion ( Text-fig. 7 ). Similar cutinization of the stomata is known for some other representatives of the order Peltaspermales (e.g., Naugolnykh 2005: figs 12–14, 16, 17). In very rare cases, a crescent-shaped uplifting is developed instead the papillae. Common cells of the abaxial surface of the seed-bearing discs are of isometric outlines, round to polygonal, with average size 50 × 60 µm.

Figures

Text-fig. 2. Taimyria triassica NAUGOLNYKH et MOGUTCHEVA gen. et sp. nov., a – holotype 4287/6. Lateral female cones marked by orange arrows; main axis bearing lateral cones marked “Ax”. Scale bar 1 cm.

Text-fig. 3. Taimyria triassica NAUGOLNYKH et MOGUTCHEVA gen. et sp. nov., holotype 4287/6. a: morphology of female cone; b: position of seed-bearing discs forming parastichous lines; c: seed scar structure. Scale bar 1 cm (a, b), 100 µm (c).

Text-fig. 4. Taimyria triassica NAUGOLNYKH et MOGUTCHEVA gen. et sp. nov., holotype 4287/6. a: line drawing explaining female cone morphology after holotype; b: suggested reconstruction showing arrangement and vascularization of seed-bearing discs (left), and section through seed-bearing discs exhibiting seed attachment and marginal limb structure (right); c: seed scar structure (after Textfig. 3c), 1 – subepidermal and epidermal tissues under the cuticle, 2 – coaly tissues of mesophyll. Oval form at seed scar center is possible exit of conducting strand. Locality: Tsvetkov Cape; Lower Triassic, Induan; Keshin Formation. Scale bar 1 cm (a, b), 100 µm (c).

Text-fig. 5. Taimyria triassica NAUGOLNYKH et MOGUTCHEVA gen. et sp. nov., holotype 4287/6. a–d: epidermal-cuticular structure of upper surface of seed-bearing capsule. Locality: Tsvetkov Cape; Lower Triassic, Induan; Keshin Formation. Scale bar 100 µm (a, c, d), 50 µm (b).

Text-fig. 6. Taimyria triassica NAUGOLNYKH et MOGUTCHEVA gen. et sp. nov., holotype 4287/6. Epidermal-cuticular structure of upper surface of seed-bearing capsule. a–c, e–g: cuticles of upper surface of seed-bearing capsule, b – detail of (a), notice small white spot at picture center, which could be interpreted as scar of small monocellular trichome; d: conducting strand going to seed scar. Locality: Tsvetkov Cape; Lower Triassic, Induan; Keshin Formation. Scale bar 200 µm (a, c, d, g), 100 µm (e, f).

Text-fig. 7. Taimyria triassica NAUGOLNYKH et MOGUTCHEVA gen. et sp. nov., holotype 4287/6. Line drawing of epidermal cuticle of upper surface of seed-bearing disc showing stoma. Locality: Tsvetkov Cape; Lower Triassic, Induan; Keshin Formation. Scale bar 100 µm.

Text-fig. 8. Taimyria triassica NAUGOLNYKH et MOGUTCHEVA gen. et sp. nov., holotype 4287/6. Structure of seed extracted from seedbearing capsule. a, b: general morphology; c–e: detailed cellular structure. Locality: Tsvetkov Cape; Lower Triassic, Induan; Keshin Formation. Scale bar 1 mm (a, b; same scale for both figures), 100 µm (c–e).

Text-fig. 9. Taimyria triassica NAUGOLNYKH et MOGUTCHEVA gen. et sp. nov., holotype 4287/6. Structure of seed extracted from seed-bearing capsule. a: general morphology; b, c: detailed cellular structure. Locality: Tsvetkov Cape; Lower Triassic, Induan; Keshin Formation. Scale bar 1 mm (a), 100 µm (b, c).

Text-fig.10. Taimyria triassica NAUGOLNYKH et MOGUTCHEVA gen. et sp. nov., holotype 4287/6. a–f: seeds extracted from seed-bearing capsule. Locality: Tsvetkov Cape; Lower Triassic, Induan; Keshin Formation. Scale bar 1 cm.

Text-fig. 11. Taimyria triassica NAUGOLNYKH et MOGUTCHEVA gen. et sp. nov. Suggested reconstruction of fertile shoot. Scale bar 1 cm.