Hattoria 11: 13–21. 2020 Discovery of a simple thalloid liverwort Metzgeriites kujiensis (Metzgeriaceae), a new species from Late Cretaceous Japanese amber Tomoyuki KATAGIRI1 & Hisao SHINDEN2 1 Hattori Botanical Laboratory, Obi 6–1–26, Nichinan, Miyazaki 889–2535, Japan 2 Kuji Kohaku Co., Ltd., Kokuji-cho 19–156–133, Kuji, Iwate 028–0071, Japan Author for correspondence: Tomoyuki KATAGIRI, [email protected] Abstract An extinct liverwort species Metzgeriites kujiensis T.Katag., sp. nov. is described from the Late Cretaceous (Santonian, ca. 85 Ma) amber from the Kuji district, northern Honshu, Japan. It is characterized by thalloid plants with a distinct midrib and lamina, narrow thalli of 0.6–0.8 mm wide, regularly 1-pinnate ramification pattern, and presence of discoid branches. The new species represents the first record of the liverwort family Metzgeriaceae (Metzgeriales, Marchantiophyta) from the Late Cretaceous from East Asia. Introduction Kuji amber is the largest amber deposit in Japan and one of the most important sources for the reconstruction of terrestrial ecosystems in the Late Cretaceous East Asia continental margin, especially for revealing fauna and flora for microscopic species such as insects and bryophytes. In spite of its importance in paleontology and evolutionary biology and of their potential abundance with over 800 insect inclusions, few studies have been conducted on amber from the deposit. For its insect inclusions Kawakami et al. (1994) studied 23 specimens of fossil insects and Fursov et al. (2002) reported a fossil species of Mymarommatidae, an extremely rare family of microscopic hymenopteran insects. Recently, Nakamine & Yamamoto (2018) discovered a remarkable new genus and species of thorny lacewing (Neuroptera, Rhachiberothidae) and stressed the importance of the insect inclusions in Kuji amber. The discovery of a moss Muscites kujiensis T.Katag. inclusion by Katagiri et al. (2013) also provided valuable information on the Late Cretaceous bryoflora and demonstrated the importance of the Japanese amber for revealing the evolutional history of bryophytes in East Asia. In the present study we describe a new species of fossil liverwort preserved in the Late Cretaceous Kuji amber, the first evidence of a fossilized liverwort shoot found in Kuji amber and only the second record of a bryophyte from the Late Cretaceous bryoflora in Japan. The new species also represents the first record of the liverwort family Metzgeriaceae (Metzgeriales, Marchantiophyta) from the Late Cretaceous from East Asia. 13 Materials and Methods Geological setting: The fossil described here is from the late Cretaceous Tamagawa Formation of the Kuji Group, which is distributed in the vicinity of Kuji City in Iwate Prefecture, northern Honshu, Japan. The Tamagawa Formation of the Kuji Group has been estimated to be 83–90 Ma (Umetsu & Kurita 2007; Katagiri et al. 2013; Uno et al. 2018). Based on carbon isotope stratigraphy and U–Pb radiometric dating, Arimoto et al. (2018), recently showed that the upper part of the Tamagawa Formation, with abundant ambers occurring in the coaly mudstone, is dated to the middle Santonian, ca. 85.9±0.7 Ma. Technical methods: The ground and polished amber piece of ca. 25×18×6 mm and weighing 1.66 g, which is housed in the herbarium of the Hattori Botanical Laboratory (NICH), was originally mined from Horinai Mine (40°09′01″N,141°44′08″E) in Kokuji-cho, Kuji City in July 2018. It had been selected for decorations and has been subjected to heat and pressure treatment to enhance the properties of the amber. The inclusion containing a single shoot was investigated using a Leica M205C stereomicroscope equipped with a Nikon DS-Fi3 digital camera. In order to enhance contrast and avoid cast shadows, a Leica LED3000RL LED ring light and a Leica TL5000 Ergo LED transmitted light base were used. Taxonomy Metzgeriites kujiensis T.Katag., sp. nov. Figs. 1 & 2 Diagnosis: Species of Metzgeriites with a distinct midrib and lamina. The species is similar to Metzgeriites yuxianensis X.W.Wu & B.X.Li, but differs by having narrow thalli of 0.6–0.8 mm wide, a regularly 1-pinnate ramification pattern, and the presence of discoid branches. Type: JAPAN. Honshu. Iwate Pref., Kuji City, Kokuji-cho. Inclusion in amber mined from the Horinai Mine (40°09′01″N, 141°44′08″E) in July 2018. Tamagawa Formation. Late Cretaceous (Santonian; approximately 85 Ma). Kuji Kohaku H1 (holotype: NICH-497606). Description: Plant thalloid, dorsiventral, differentiated into midrib and lamina, 11 mm long and 2.0–4.0 mm wide including branches, regularly 1-pinnately branched at an angle of 45–75°, without ventral branches (Fig. 1). Thallus thin, lingulate, 1.0–2.0 mm long, (0.4–)0.6– 0.8 mm wide, with midrib 0.2–0.3 mm wide, without hairs on both dorsal and ventral surfaces, without ventral scales or mucilage hairs; margin linear, entire; apices obtuse to rounded (Fig. 2A–C). In the middle of the plant discoid branches ca. 1.0 mm in length and width with retuse or emarginate apices are present (Fig. 2E). These can be sexual branches or gemmae, but detailed morphology not preserved. Rhizoids smooth, present on ventral part of the main thallus lamina (Fig. 2D). Gemmae unknown. Reproductive structures and sporophytes unknown. Etymology: The species epithet refers to the type locality. [Japanese name: Kuji- futamatagoke] Systematic position: Phylum: Marchantiophyta Stotler & Crand.-Stotl.; Class: Jungermanniopsida Stotler & Crand.-Stotl.; Order: Metzgeriales Chalaud; Family: Metzgeriaceae H.Klinggr.; Genus: Metzgeriites Steere 14 Figure 1. Metzgeriites kujiensis T.Katag. A: Amber inclusion. B: Plant from dorsal view. C: Plant from ventral view. All photographed from NICH-497606, holotype. Taxonomic changes Metzgeriites Steere, Amer. Midl. Naturalist 36: 306. 1947. ＝Metzgerites X.W.Wu & B.X.Li, Acta Palaeontol. Sin. 31: 276. 1992; nom. illeg., later homonym (Turland et al. 2018, Art. 53.2) Metzgeriites barkolensis X.W.Wu (Turland et al. 2018, Art. 55.4) ≡Metzgerites barkolensis X.W.Wu, Acta Palaeontol. Sin. 35: 69. 1996. 15 Figure 2. Metzgeriites kujiensis T.Katag. A–B: Branches from dorsal view. C: Apical part of shoot from dorsal view. D: Part of main thallus from ventral view, showing a rhizoid arrowed. E: Median part of main thallus from dorsal view, showing discoid branches. All photographed from NICH-497606, holotype. 16 Metzgeriites exhibens X.W.Wu & B.X.Li (Turland et al. 2018, Art. 55.4) ≡Metzgerites exhibens X.W.Wu & B.X.Li, Acta Palaeontol. Sin. 31: 277. 1992. Metzgeriites multifidus P.C.Wu (Turland et al. 2018, Art. 55.4) ≡Metzgerites multifidus P.C.Wu, Acta Geol. Sin. 91: 1548. 2017. Metzgeriites multirameus G.Sun & Shao L.Zheng (Turland et al. 2018, Art. 55.4) ≡Metzgerites multiramea G.Sun & Shao L.Zheng, Early angiosperms and their associated plants from western Liaoning, China 180. 2001. Metzgeriites yuxianensis X.W.Wu & B.X.Li (Turland et al. 2018, Art. 55.4) ≡Metzgerites yuxianensis X.W.Wu & B.X.Li, Acta Palaeontol. Sin. 31: 276. 1992. Discussion The epiphytic simple thalloid liverwort genus Metzgeria Raddi has a worldwide distribution and is a main component of the family Metzgeriaceae (Metzgeriales) which includes three genera: Metzgeria, Steereella Kuwah. with two species (Kuwahara 1973, 1986), and Vandiemenia Hewson with one species (Furuki & Dalton 2008). Recent molecular phylogenetic studies have suggested that Metzgeriaceae/Metzgeriales originated in the Permian, 285 Ma, and its crown group diversification took place in the Cretaceous, followed by Cenozoic radiations (Cooper et al. 2012; Laenen et al. 2014; Bechteler et al. 2019). In spite of the extant diversity of Metzgeria/Metzgeriaceae with ca. 100 species worldwide Table 1. Fossil species in the family Metzgeriaceae. The species originally described under the genus Metzgerites, which is here considered to be a later homonym of Metzgeriites, were shown with an asterisk (*). Species name Period Country Reference Metzgeriothallus sharonae Middle Devonian USA Hernick et al. (2007) Hernick, Landing & Bartowski Metzgeriothallus metzgerioides (J.Walton) Late Carboniferous England Walton (1928), R.M.Schust. Schuster (1981) Metzgeriites glebosus (T.M.Harris) Early Jurassic Greenland Harris (1931), Steere Steere (1947) Metzgeriites barkolensis X.W.Wu* Middle Jurassic China Wu (1996) Metzgeriites exhibens X.W.Wu & B.X.Li* Middle Jurassic China Wu & Li (1992) Metzgeriites yuxianensis Middle Jurassic China Wu & Li (1992) X.W.Wu & B.X.Li* Metzgeriites multirameus Late Jurassic China Sun et al. (2001) G.Sun & Shao L.Zheng* as M. multiramea Metzgeriites infracretaceus (Saporta) Early Cretaceous Portugal Saporta (1894), Oostend. Oostendorp (1987) Metzgeriites multifidus P.C.Wu* Early Cretaceous China Guo et al. (2017) Metzgeriites kujiensis T.Katag. Late Cretaceous Japan present study 17 (Söderström et al. 2016), fossil records of Metzgeria/Metzgeriaceae are extremely limited. They include two species of Metzgeriites Steere, five species of Metzgerites X.W.Wu & B.X.Li, and two species of Metzgeriothallus R.M.Schust. See Table 1 for details. The fossil-genus Metzgeriites was originally proposed by Steere (1947) for the thalloid fossil liverworts, based on the family Metzgeriaceae with the characters of the “Order Jungermanniales Anacrogynae”. He included only M. glebosus (T.M.Harris) Steere [≡ Hepaticites glebosus T.M.Harris] (Harris 1931) from the Early Jurassic. The second genus Metzgerites X.W.Wu & B.X.Li [type: M. yuxianensis X.W.Wu & B.X.Li] was proposed by Wu & Li (1992) for fossil plants with the character of extant species of Metzgeria. The species of Metzgerites have all been known from the Jurassic to Cretaceous in China. However, we consider the genus Metzgerites should be treated as a later homonym of Metzgeriites Steere [type: M. glebosus] (Steere 1947) because both have been applied to fossil plants with the character of extant species of Metzgeria/Metzgeriaceae and are sufficiently alike to be confused (Turland et al. 2018, Art. 53.2).