Have macrofossils of hornworts been detected in geological record?

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Abstract

Based on literature, the opinions on the evolution and time of the origin of hornworts are briefly summarized, and the structure of macrofossils that were referred to as hornworts is described in detail. There are no reliable macrofossils of hornworts from the Cenozoic. The majority of the seven macrofossils classified as hornworts from the Cretaceous deposits of India, in our opinion, are not true hornworts. Shuklanites deccanii most likely represents a remain of a liverwort, and the two species of Krempogonium are the “male flower” of a moss. Nothing definite can be said about the taxonomic affiliation of the three other remains basing on the descriptions and images in the original articles. Only Notothylites nirulai is most likely the remain of a hornwort, but its relationship to Notothylas is insufficiently grounded. The type specimen of Notothylacites filiformis from the Cretaceous deposits of the Czech Republic is the remains of a plant whose spores are similar to hornworts, but the general morphology of the specimen does not allow it to be attributed to hornworts; another impression, attributed to the same species, resembles an alga rather than a bryophyte. Treatment of Dendroceros victoriensis from the Early Cretaceous deposits of Australia as a member of the modern genus is unfounded, although the impressions of its paratypes (which are the thalli with sporogonia) resemble hornworts. Macrofossils of hornworts are unknown from the Jurassic, Triassic, and Paleozoic.

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About the authors

V. R. Filin

Lomonosov Moscow State University

Email: platon-anna@yandex.ru
Russian Federation, 1, Leninskie Gory, Moscow, 119991

A. G. Platonova

Lomonosov Moscow State University

Author for correspondence.
Email: platon-anna@yandex.ru
Russian Federation, 1, Leninskie Gory, Moscow, 119991

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2. Fig. 1. A macrofossil in Dominican amber. For explanations, see the text. After: Frahm, 2005, p. 140, Fig. 2, with changes. Scale bar: 1 mm.

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3. Fig. 2. Macrofossils from the cherts collected near the Mohgaon-Kalan locality, India, Upper Cretaceous: sporogonium resembling Notothylas (A, B), Shuklanites deccanii (C–E), Notothylites nirulai (F, G). A – sporogonium; B – spores and elater-like bodies; С, D – an almost radial (C) and the next (D) section in the series of successive peels of a sample; F – radial section of sample; G – a spore and a two-celled pseudoelater; for explanations, see the text. A and В – after: Gupta, 1956, p. 541, Fig. B-2 (A) and Fig. B-3 (В), with changes; С and D – after micrographs: Singhai, 1973, Plate 1-1 and Plate 1-2, respectively; E – after: Singhai, 1973, p. 173, Text-fig. 3, with changes; F, G – after: Chitaley, Yawale, 1978, p. 113, Text Figures 1 and 5, respectively, with changes. Scale bars: А, С, D – 250 µm; B, E, G – 15 µm; F – 1 mm.

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4. Fig. 3. Thalli with sporogonia of Notothylas javanica (A, B) and N. cf. orbicularis (C) in longitudinal sections. B – an enlarged portion of A. 1 – seta-like slender part of the capsule base; 2 – involucre; 3 – thallus; 4 – foot; columella was out of the section in С. Scale bars: А, С – 0.2 mm; В – 50 µm.

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5. Fig. 4. Macrofossils from the cherts collected near the Mohgaon-Kalan locality, India, Upper Cretaceous: Krempogonium mohgaoensis. A – reconstruction of the sample performed by E. Namboodiri and co-authors (after: Nambudiri et al., 2004, p. 174, Text-fig. 2, with changes); B – our interpretation of the micrograph (Nambudiri et al., 2004, p. 176, Plate 2-1); for explanations, see the text. Scale bar: 1 mm.

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6. Fig. 5. Macrofossils from the cherts collected near the Mohgaon-Kalan locality, India, Upper Cretaceous: Anthoceroites deccanii (A) and Sporollites harisii (B–D). A – our drawing based on the micrograph (Khursel, Narkhede, 2017, p. 1199, Plate-1, Fig. 5); B – schematic drawing by S. Pundkar, with changes (Pundkar, 2021, p. 28, Text Fig. 1); С, D – our drawings based on the microphotographs (Pundkar, 2021, p. 29, Plate Fig 1 (D), Fig. 5–7 (C)); for explanations, see the text. Because of the inconsistency of the sizes in descriptions and figures in the original articles, scale bars are not given.

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7. Fig. 6. Notothylacites filiformis, Czechia, Late Cretaceous (A-E), and Cladophora sericea (F). A – holotype (after: Nĕmejc, Pacltová, 1974, Plate 1-1, with changes), F. Nĕmejc and B. Pacltová indicated only one sporangium (lower left) in the photograph; B – isotype (after: Nĕmejc, Kvaček, 1975, Plate 1-1, with changes); С – drawing from the paper of V.A. Krassilov and R. Shuster (after: Krassilov, Shuster, 1984, p. 1183, Fig. 2, with changes); D, E – spores at the earlier (D) and later (E) stages of maceration (after: Nĕmejc, Pacltová, 1974, Plate 4-13 (D) and Plate 4-15 (E), with changes); F – thallus of herbarium specimen; for explanations, see the text. Scale bars: A – 5 mm, B, F – 2 mm; D, E – 20 µm.

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8. Fig. 7. Spores of Notothylas cf. orbicularis. A – intact spore; B – ultrastructure of the sporoderm portion (TEM); C – outer layer of the pseudoperisporium peeled off the spore after acetolysis; D – exosporium without pseudoperisporium after acetolysis; 1 – exosporium; 2 – lamellate pseudoperisporium, arrow – siliceous layer of pseudoperisporium. Scale bars: А – 10 µm, B – 1 µm; С, D – 20 µm.

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9. Fig. 8. Dendroceros victoriensis, Australia, Early Cretaceous (A, B) and Characiosiphonites nipanica (=Sporangioceros nipanica), Rajmahal Hills (India), Jurassic (C, D); for explanations, see the text. A, B – after: Drinnan, Chambers, 1996, р. 12, Fig. 6A, B, with changes; C – after micrographs: Sharma, Suthar, 1986, p. 272, Fig. A, C, also: Sharma et al., 2002; p. 33, Plate 1–3, 4; D – after: Sharma et al., 2002, p. 35, Fig. 15, with changes. Scale bars: A, B – 2 mm; С – 100 µm; D – 500 µm.

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10. Fig. 9. Macrofossil from Jurassic beds of Bureinsky basin. Arrows: the structures which V.A. Krassilov considered as elaters. After: Krassilov, 1967, Fig. 1.18. Scale bar: 100 µm.

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11. Fig. 10. Hypothetical stages of a psilophyte-like polysporangiate sporophyte evolution from an anthocerote-like ancestor (far left); for explanations, see the text. А – after: Smith, 1955, p. 133, Fig. 82; В – after: Ligrone et al., 2012a, p. 863, Fig. 9, p. 861, Fig. 8, and Ligrone et al., 2012b, p. 938, Fig. 1, with changes. The meristem is indicated with arrows in Fig. B.

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