Revision of existing classification of fossil insect feeding traces and description of new ichnotaxa from Middle Jurassic sediments of Eastern Siberia (Russia)

This paper revises the existing system of formal classification by Vialov and Vasilenko for fossil plants involving insect feeding and oviposition. The classification of these fossil traces has been amended and supplemented in accordance with the requirements of the International Code of Zoological Nomenclature. The following nomenclatural combinations are made: Insectophagichnata (Vialov) Enushchenko and Frolov, comb. et stat. (classis) nov., Phagolignichnidina (Vialov) Enushchenko and Frolov, comb. et stat. (subordo) nov., Phagophytichnidina (Vialov) Enushchenko and Frolov, comb. et stat. (subordo) nov. Fossil traces of these interactions were found and illustrated for Mesozoic insects and leafes of Ginkgo tapkensis from Middle Jurassic sediments of the Irkutsk Coal Basin in Eastern Siberia, Russia. The examined traces consist of ovipositions (traces of insect egg laying), galls (traces of insect caused teratologies) and epidermal punctures (traces of piercing and sucking). The following ichnotaxa are described and illustrated: Paleoovidinae Enushchenko and А. Frolov, ichnosubfam. nov., Paleoexoovoidinae Enushchenko and Frolov, ichnosubfam. nov., Sugophytichninae Enushchenko and А. Frolov, ichnosubfam. nov., Sugophytichnida pertusura Enushchenko and Frolov, ichnogen. et ichnospec. nov., Paleoovidus vasilenkoi Enushchenko and А. Frolov, ichnospec. nov., Paleoexoovoida ovoidea Enushchenko and А. Frolov, ichnogen. et ichnosp. nov., Paleogallus vialovi Enushchenko and Frolov, ichnospec. nov. Punctures of the leaf epidermis probably belong Mesozoic cicadas of the Palaeontini, which dominate the adjacent strata of the studied location. The extremely low occurrence of interaction between insects and plants in these Jurassic deposits of Eastern Siberia have ichnotaxonomic importance for understanding the functioning of Jurassic terrestrial paleoecosystems.

The first discovery leaves of angiosperms in the Middle Jurassic deposits in Eastern Siberia

There is fossil of linear whole-marginal leaves with parallel venation in the Middle Jurassic (Aalenian) sediments of the Irkutsk Coal Basin, were found. During the study of cuticle preparations it was found that leaves were steam-bearing, has anastomoses between veins, anomocytic stomata and the diamond-shaped main cells of the epidermis. Such a combination of characters is widespread in modern monocotyledonous and is absent among fossil as well as modern sporeals and gymnosperms plants. We have every reason to believe that we have found unique structures of leaves characteristic of monocotyledons. This find is the oldest among the herbaceous angiosperms of the Jurassic period, such as Yuraherba and Yukhaniya, and the first found in Siberia.

Sorosaccus sibiricus Prynada (Ginkgoales) from the Middle Jurassic deposits of the Irkutsk Coal Basin, Eastern Siberia

New findings of pollen cones of Sorosaccus sibiricus Prynada were studied in detail from the Aalenian—Bajocian Prisayan Formation of two localities in the Irkutsk coal basin (Ust’-Baley and Vladimirovka). Specimens of S. sibiricus previously described from Ust’-Baley (Heer, 1876) were reexamined. It was revealed that S. sibiricus differs from other species of Sorosaccus in a shape of the apical (free from the microsporangia) part of the microsporophylls. Microsporophylls of S. sibiricus consist of a petiole and a wide-oval distal lamina with acute apex, commonly bending upward. The lamina was often folded and became lanceolate, linear, or fan-shaped with uneven to toothed margin. Microsporangia (6—8) are oval in outline, helically attached to the petiole. Pollen grains were extracted from S. sibiricus microsporangia for the first time. They are oval to boat-shaped in outline, monosulcate and differ from other known Sorosaccus pollen grains by the verrucate surface of the exine. The diagnosis of the species Sorosaccus sibiricus is emended.

Leafy shoots and pollen cones of conifers from the Middle Jurassic deposits of the Irkutsk Coal Basin

Among the numerous remains of the Jurassic conifers in the Irkutsk Coal Basin, several types of leafy shoots are distinguished. One type is characterized by the leaves with numerous veins. These remains were described as Podozamites irkutensis N. Nosova et Kiritch. (Nosova et al., 2017). The leaves of other types have a midvein. These leafy shoots are attributed to several taxa: Marskea sp. nov. (in press), Elatocladus falcatus (Heer) Prynada, E. heeriana N. Nosova et Kiritch., sp. nov., Elatocladus sp. and Pagiophyllum sp. Elatocladus falcatus (Heer) Prynada, 1962 (=Elatides falcata Heer, 1976) was described from the deposits of the lower subformation of the Prisayan Formation (the Aalenian) of the Ust’-Baley locality. An epidermal structure of the Elatocladus falcatus leaves is unknown. Here we designate the lectotype for E. falcatus. We have studied the leaf epidermal structure of the leafy shoots from the upper subformation of the Prisayan Formation (the Aalenian-Bajocian) in the localities Topka and Vladimirovka. Based on the morphological and epidermal features, we describe a new species Elatocladus heeriana. The shoots of E. heeriana have with helically arranged leaves. The leaves are sessile and dorsoventrally flattened, linear, lanceolate to falcate, with the tip curving toward the apex of the stem, with the broad and decurrent base and acute apex. The leaves are hypostomatic. They are characterized by straight to undulating anticlinal cell walls of the abaxial epidermis near the leaf edge and base. Stomata are arranged in two narrow bands, orientated transversely to irregularly. Subsidiary cells of the stomatal complexes are without papillae. Rare fragments of the Pagiophyllum sp. shoots were found in the deposits of the upper subformation of the Prisayan Formation (the Aalenian–Bajocian) in the localities Olkha and Vladimirovka. Their leaves are falcate, with a median keel on the abaxial side. The bad preservation of the cuticle did not allow us to study the epidermal pattern in details. Stomata are arranged in the bands, orientated irregularly. Subsidiary cells of the stomatal complexes are without papillae. One pollen cone (microstrobilus), attached presumably to the E. heeriana shoot, and several detached pollen cones of Schidolepium gracile Heer (1880) were found. The pollen cones are elongated, with numerous imbricate, helically arranged and dorsoventrally flattened microsporophylls. Sterile part of the microsporophyll expands to the distal lamina with acute apex. Some microsporophylls near the cone base are oval with rounded apex. The numerous microsporangia are visible in the apical part of the mature pollen cone, but a distal lamina of the microsporophylls often is indistinct here. Microsporangia (5–7 per microsporophyll) are elongated, fusiform. Pollen grains are spherical, nonsaccate, with the rugulate-perforate surface, apertures are invisible. The emended diagnosis is provided for the type species S. gracile, as well as the lectotype is designated.