The paper presents the results of a comparative morphological study of fossil remains of leafy shoots of lycopsids of Middle Jurassic deposits of the Irkutsk Basin. They prove the presence of four species of the genus Lycopodites: L. tenerrimus, L. trichiatus, L. baikalensis and L. subulifolius. Dichotomously branched stems of L. tenerrimus are covered with pairwise connivent, small lanceolate phyloids. The phyloids are slightly narrowed at the bases, with narrow, blunt or slightly subacute apices. Shoots of L. trichiatus branch dichotomously; rarely the branching resembles a sympodial one. Small (3–3.5×1 mm) phyloids of elongated triangular shape are distichously located on stems. The bases of phyloids are wide; the apexes are subacute. A distinct midrib can be observed in many phyloids. L. baikalensis is represented by thin (0.5 mm wide) stems. They branch dichotomously two or three times at an angle of 40–45°. Sickle-curved phyloids are distichously arranged on stems. The apices of phyloids are subacute; the bases are wide, running down the stem. Stems of L. subulifolius dichotomously branch at a sharp angle; phyloids are very thin, almost filiform, with sharp awl-shaped apices, located on the stem in a compressed spiral. One of the striking differences between these species is the structure of phyloids: phyloids of L. tenerrimus are lanceolate, phyloids of L. trichiatus are triangular elongated, phyloids of L. baikalensis are sickle-curved and these of L. subulifolius are very thin, almost filiform, with sharp awl-shaped apices. The structure of phyloids allows conveniently distinguishing these species even by small fragments of shoots. The presence of isophilic shoots and liguleless phyloids in these species, as well as the absence of phyloid at the branching area of shoot suggest that the studied specimens belong to the Lycopodiales order. Species of Lycopodites nicanicus, L. falcatus, L. scanicus, and L. teilhardi are significantly differ from the Irkutsk lycopsids by four-row arrangement of phyloids and their differentiation into lateral and dorsal ones. Table 2 shows a comparison of the Irkutsk lycopsids with other representatives of the genus Lycopodites which possess the isophilic shoots. The table shows that the species L. baikalensis is the most similar to the species Lycopodites prynadae, known from the Lower Cretaceous sediments of the Far East region. The rest species of the lycopsids have such a different shoot structure (see Table 2) that they do not need comments. The distribution of L. subulifolius and L. baikalensis species is confined to the Middle Jurassic sediments of the Irkutsk Basin. Species of L. tenerrimus and L. trichiatus are found outside the Irkutsk Basin: in the Jurassic deposits of Western Siberia (Kuznetsk Basin), Yakutia (Lena Basin) and Tuva (Ulugkhem Basin). Due to the rare occurrence, the lycopsids of the Irkutsk Basin are of little use for reliable stratigraphic constructions. They may be of greater interest for paleoecological and phytogeographic reconstructions.

Frolov Andrey Olegovich, Candidate of Sciences (Geology), Research Scientist, Institute of the Earth’s Crust SB RAS, 128, Lermontov st., Irkutsk, 664033, Russian Federation, e-mail: frolov88-21@yandex.ru 

Mashchuk Irina Mikhailovna, Candidate of Science (Geology), Senior Research Scientist, Institute of the Earth’s Crust SB RAS, 128, Lermontov st., Irkutsk, 664033, Russian Federation, Associate Professor, Irkutsk State University, 1, K. Marx st., Irkutsk, 664003, Russian Federation, e-mail: samaropsis@yandex.ru

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fossil lycopsids, Lycopodites, Early and Middle Jurassic, Irkutsk Basin

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