CC BY
0
FULL COMMUNICATIONS
PALAEONTOLOGY
Type material of Trochodendroides richardsonii (Heer) Krysht. (Cercidiphyllaceae) from the Atanikerdluk (Paleocene, Greenland)
Anastasia Zolina and Lina Golovneva
Komarov Botanical Institute, Russian Academy of Sciences,
ul. Professora Popova, 2, Saint Petersburg, 197022, Russian Federation
Address correspondence and requests for materials to Anastasia Zolina, azolina@binran.ru
Abstract
Type material of Trochodendroides richardsonii (Heer) Krysht. from the Paleocene Atanikerdluk locality, Greenland, was restudied based on the original collection stored in the National Museum of Ireland, Dublin. This work allowed us to reveal the main diagnostic features of this species facilitating an emended diagnosis. Photos of the lectotype and syntypes are presented for the first time. The restudy of the collections stored in Dublin, Saint Petersburg and Stockholm shows that T. richardsonii was distributed in the early Paleocene in Greenland and Svalbard. The revision of T. richardsonii type material allows us to distinguish this species from the other species of the genus Trochodendroides Berry with similar morphology.
Keywords: Trochodendroides, Cercidiphyllaceae, Paleocene, O. Heer, Atanikerdluk, Greenland, Svalbard
Introduction
Citation: Zolina, A. and Golovneva, L. 2023. Type material of Trochodendroides richardsonii (Heer) Krysht. (Cercidiphyllaceae) from the Atanikerdluk (Paleocene, Greenland). Bio. Comm. 68(4): 297-306. https://doi.org/10.21638/ spbu03.2023.409
Authors' information: Anastasia Zolina, PhD, Researcher, orcid.org/0000-0002-5860-2501; Lina Golovneva, Dr. of Sci. in Biology, Chief Researcher, Head of the Botanical Museum, orcid.org/0000-0002-0202-9515
Manuscript Editor: Pavel Skutschas, Department of Vertebrate Zoology, Faculty of Biology, Saint Petersburg State University, Saint Petersburg, Russia
Received: August 31, 2023;
Revised: October 7, 2023;
Accepted: October 9, 2023.
Copyright: © 2023 Zolina and Golovneva. This is an open-access article distributed under the terms of the License Agreement with Saint Petersburg State University, which permits to the authors unrestricted distribution, and self-archiving free of charge.
Funding: The study was supported by the Russian Science Foundation, project no. 23-77-01087.
Ethics statement: This paper does not contain any studies involving human participants or animals performed by any of the authors.
Competing interests: The authors have declared that no competing interests exist.
Family Cercidiphyllaceae is currently regarded as belonging to the order Saxi-fragales (Angiosperm Phylogeny Group, 2016). It includes only one extant genus Cercidiphyllum Siebold et Zucc. and two species: C.japonicum Sieb. et Zucc. and C. magnificum (Nakai) Nakai (Fu and Endress, 2001), that are distributed in Japan and China. Extinct representatives of Cercidiphyllaceae are significantly more diverse, represented by several genera.
The dispersed fossil leaves from the Cretaceous and Paleogene are assigned to the genus Trochodedroides Berry (1922). The type species, T. rhomboidea (Lesq.) Berry, was described from the Cenomanian deposits of Dakota Formation, USA (Lesquereux, 1874; Berry, 1922). Recently more than fifty species of this genus have been described (Golovneva and Alekseev, 2010). Members of Trochodedroi-des have simple leaves with actinodromous venation and a crenate or dentate margin. Many species are characterized by significant morphological variability (Golovneva and Alekseev, 2010; Golovneva, Alekseev, Gnilovskaya, and Yudova, 2017).
The earliest occurrences of Trochodendroides come from the early-middle Albian in North America and Northeastern Asia (Golovneva and Alekseev, 2010; Golovneva et al., 2021). Different species of Trochodendroides were an important component of the Late Cretaceous and Paleogene floras from middle and high latitudes of Northern Hemisphere (Budantsev, 1983; Crane, 1984; Philippova and Abramova, 1993; Golovneva, 1994; Golovneva and Alekseev, 2010; Golovneva, Alekseev, Gnilovskaya, and Yudova, 2017). The latest Trochodendroides are known from the late Eocene (Budantsev and Golovneva, 2009). Fossil leaves from the Oligocene associated with Cercidiphyllum infructescences usually are included in the extant genus Cercidiphyllum (Jahnichen, Mai, and Walther, 1980; Manchester and Meyer, 1987; Kovar-Eder, Meller, and Zetter, 1998). But this name has
also been used for dispersed leaves from more ancient deposits from the Paleocene (Brown, 1932; Iljinskaja, 1974a; Chandrasekharam, 1974; Budantsev, 1983).
Leaves of Trochodendroides are associated with dispersed follicular fruits and infructescences, assigned to the genus Jenkinsella Reid et Chandler (Golovneva and Alekseev, 2017). Earlier these fructifications were also described under a wide range of extinct and extant generic names: Nyssidium Heer, Leguminosites Lesq., Berrya Knowlton, Trochodendrocarpus Krysht., Kenella Samylina, and Joffrea Crane et Stockey (Heer, 1870; Lesquereux, 1873, 1878; Schmalhausen, 1890; Hollick, 1936; Knowlton, 1930; Kryshtofovich, 1958; Iljinskaja, 1974b; Samylina, 1976; Crane, 1984; Crane and Stockey, 1986). Staminate inflorescences associated with Trochodendroides leaves were referred to the genus Alasia (Go-lovneva, 2006).
The investigation of associated reproductive structures as well as the cuticular features of Trochodendroides leaves reveals their similarity to living representatives of Cercidiphyllaceae (Golovneva and Alekseev, 2010) despite the presence of oblique fiber bundles in the Cretaceous and Paleogene fruits that are lacking in extant Cercidiphyllum.
Earlier the Trochodendroides leaves were usually assigned to the modern genus Populus L. In particular, O. Heer (1868, 1870) described several species of Trochodendroides under the name Populus in his classic works on the Paleogene flora of Greenland. Subsequently, Heer's names were widely used for the description of other Arctic floras. However, other paleobotanists interpreted Heer's species in various ways because they were only known from drawings. The original material from Greenland has never been revised.
The present study is devoted to a revision of Tro-chodendroides richardsonii (Heer) Krysht. type material. Initially it was described from the Paleocene deposits of Atanikerdluk, West Greenland (Fig. 1), under the name Populus richardsonii Heer (1868). Later Kryshtofovich (1958) transferred this species to the genus Trochodendroides. The lectotype was chosen by I. Iljinskaja (1971) based on the drawing in Heer's monograph. A detailed diagnosis of this species is absent and no photos of original material have ever been published.
Material and methods
Type material of Trochodendroides richardsonii comes from the locality Atanikerdluk along the southern coast of the Nuussuaq peninsula, West Greenland (Fig. 1). Fossil leaves were collected by Lieutenant Philip Howard Colomb, who served as a mate of the HMS "Phoenix" during the Arctic Expedition of 1854. This ship supplied the search for the Franklin expedition that had been lost in 1847.
Lieutenant Colomb and the captain of "Phoenix" Sir Edward Augustus Inglefield visited the Atanikerdluk site on July 7, 1854. On return to England Captain Inglefield donated his collection to the Geological Survey in London. The plant fossils from Colomb's collection were transferred to the Royal Dublin Society on November 24, 1854. Now these fossils are stored in the National Museum of Ireland in Dublin (NMING).
The material is preserved as leaf impressions in side-ritic shales. Most of the leaves are represented only by fragments (Fig. 2). According to modern data, plant fossils from Colomb's collection come from the Quikavsak Formation (Zolina, Manchester, and Golovneva, 2021) that consists of fluviatile conglomerates, sandstones and shales (Dam et al., 2009). Its thickness is 70-180 m. The age of these deposits was considered as the Danian (Dam et al., 2009).
Leaf architectural terminology follows that of "Manual of Leaf Architecture" (Ellis et al., 2009). Photographs of the specimens were made using Sony RX100II camera at low angle illumination. The plant drawings were completed using a graphics tablet Wacom Intuos Pro. The geographic place names in Greenland used in this paper are in modern Greenlandic orthography (after Dam et al., 2009).
Systematics
Class Magnoliopsida Family Cercidiphyllaceae Genus Trochodendroides, Berry, 1922 Trochodendroides richardsonii (Heer) Krysht. (Figs. 3-6)
Trochodendroides richardsonii (Heer) Kryshtofovich, 1958, p. 97, pro parte quoad combination. — Budantsev, 1983, pl. 14, fig. 6, 8. — Budantsev and Golovneva, 2009, p. 105, text-fig. 10, pl. 16, fig. 1-4. Populus richardsonii Heer, 1868, S. 98, pro parte quoad Taf. 4, Fig. 3-5. — Heer, 1869, S. 468, pro parte quoad Taf. 44, Fig. 8a,b. — Heer, 1870, S. 54, pro parte quoad Taf. 10, Fig. 9-11. Cercidiphyllum richardsonii (Heer) Seward et Edwards, 1941, pro parte quoad combination. — Iljinskaja, 1971, p. 1632. — Iljinskaja, 1974a, p. 124, pro parte quoad text-fig. 77, 1, 2. Cercidiphyllum arcticum auct. non (Heer) R. W. Brown, in Koch, 1963, p. 47, pro parte quoad pl. 17, fig. 1-3.
Original diagnosis (Heer, 1868): foliis suboricula-tis, basi leviter emarginatis, margine profunde crenatis, 5-7 nervis, asnervis primariss lateralibus erectis, valde flexuosis ramosis.
Diagnosis emended: Leaves ovate, widely ovate or widely elliptical with acute or slightly attenuate apex and slightly cordate or truncate base; margin crenate; teeth
Fig. 1. Type locality of Trochodendroides richardsonii (Heer) Krysht. in West Greenland.
Fig. 2. Original illustration of leaves described by Heer (1868, Taf. IV) under the name Populus richardsonii Heer and the corresponding specimen numbers in the National Museum of Ireland collection.
Fig. 3. Trochodendroides richardsonii (Heer) Krysht., the Quikavsak Formation, West Greenland: A — spec. F19203/1, lectotype, figured by Heer, 1868, Taf. IV, Fig. 3a, general view; B — spec. F19203/3, syntype, figured by Heer, 1868, Taf. IV, Fig. 5b; C, D — spec. F19203/2, syntype, figured by Heer, 1868, Taf. IV, Fig. 3b: C — leaf apex, D — margin details; E — lectotype margin details, enlarged from A. Scale bar is 1 cm.
simple, regular, large, 3-5 mm in height and 3-6 mm in width, with obtuse or rounded apices and biconvex sides, innervated by thin central vein; venation 3-5 nervous, arena between inner lateral veins usually triangular in shape.
Lectotype (Fig. 3A, E; Fig. 4a): Spec. F19203/1, National Museum of Ireland, Greenland, locality Atanikerdluk, the Quikavsak Formation, the lower Paleo-cene. Iljinskaja (1971) designated the drawing in Heer's monograph (Heer, 1868, Taf. 4, Fig. 3a) as the lectotype of the species. The place of storage of type material and specimen number of lectotype were first indicated by Budantsev and Golovneva (2009).
Syntypes: National Museum of Ireland, Dublin, Colomb collection, specimens F19203/2, F19203/3.
Heer (1868) depicted ten leaves of Populus richardsonii from Atanikerdluk. Eight of them have survived in the collection of National Museum of Ireland. Two specimens, figured in Taf. 4, Fig. 4 and Taf. 15, Fig. 1c, are missing. Some leaves from Collomb collection (Heer, 1868, Taf. 4, Fig. 5a, c, d, Taf. 6, Fig. 7, 8) are fragments without clear diagnostic features. Since there are other species of Trochodendroides in the Atanikerdluk flora (Budantsev, 1983; Budantsev and Golovneva, 2009), we do not include these dubious fragments in the type material of Populus richardsonii. As syntypes, we consider
Fig. 4. Drawings of Trochodendroides richardsonii (Heer) Krysht., the Quikavsak Formation, West Greenland: a — spec. F19203/1, lectotype, figured by Heer, 1868, Taf. IV, Fig. 3a; b — spec. F19190/2; c — spec. F19203/2, syntype, figured by Heer, 1868, Taf. IV, Fig. 3b; d — spec. F19213A/1; e — spec. F19177/2; f — spec. F19203/3, syntype, figured by Heer, 1868, Taf. IV, Fig. 5b.
only the two almost complete leaves with clearly specific diagnostic characters (Fig. 2; Fig. 3B, C).
Other specimens: In addition to the published material, there are several leaves of Populus richardsonii in the Colomb collection that were not depicted in Heer (1868): spec. F19177/2, F19190/2, F19213A/1.
Besides, we attribute to Trochodendroides richard-sonii the following specimens that were revealed during the re-examination of the original materials from Spitsbergen.
Spitsbergen, the Firkanten Formation, the Danian, collection of the Komarov Botanical Institute of the Russian Academy of Sciences, Saint Petersburg: spec. BIN 952-1-4/14, BIN 951-1-6: spec. 1, 20, 46, 52, 54, 56, 62; Swedish Museum of Natural History, spec. S051864
Description: Leaves are simple, petiolate. Lamina is ovate, widely ovate or widely elliptical, 5-11 cm in length and 5-10 cm in wide, with acute or slightly attenuate apex and slightly cordate or truncate base. Margin is crenate. Teeth are simple or rarely compound, regu-
larly spaced, large (3-5 mm in height and 3-6 mm in width), with convex apical and basal sides. Tooth apex is obtuse or rounded. Sinuses between teeth are acute or rounded, triangular.
Venation is actinodromous, with 3-5 primary veins. Midvein is straight, running to the leaf apex, producing 2-5 alternately arranged secondary veins in the upper one-third of the lamina. Inner lateral veins are thin, curving, connecting with lower secondary veins extending from the midvein. Sometimes inner lateral veins terminate in large teeth. The area between inner lateral veins is usually triangular in shape, sometimes elliptical.
Outer lateral primary veins (if present) are thinner than inner primaries and diverging from the midvein at a wider angle. Secondary veins arising from the midvein and basiscopic branches of inner and outer lateral primaries form series of brochidodromous loops near the margin. Teeth are innervated by thin veins that diverge from loops near the margin. Tertiary veins form irregular connections between the primaries and secondary
Fig, 5. Leaves of Trochodendroides richardsonii (Heer) Krysht. from the Firkanten Formation, Spitsbergen: A— spec. BIN 952-1-6/56; B — spec. BIN 952-1-4/19; C — spec. BIN 952-1-6/55; D — spec. BIN 952-1-6/52. Scale bar is 1 cm.
branches. Quaternary veins are very thin, forming an orthogonal network.
Discussion
The species Populus richardsonii was described by O. Heer (1868) from the Paleocene Atanikerdluk locality in West Greenland. In the same monograph Heer also referred a leaf from Spitsbergen (locality Kohleberg) to this species. A study of plant fossils in the Swedish
Museum of Natural History showed that the leaf from Spitsbergen (Svalbard) actually belongs to the species of Zizyphoides colombii (Budantsev and Golovneva, 2009; Zolina, Manchester, and Golovneva, 2021). Thus, the type material of P. richardsonii comes from a single locality (Atanikerdluk, Greenland) and from a single collection (Colomb collection, 1854).
In the following year Heer (1869) assigned to Populus richardsonii several additional leaves from the same locality (Atanikerdluk), collected by E. Whymper in
Fig. 6. Drawings of Trochodendroides richardsonii (Heer) Krysht. from the Firkanten Formation, Spitzbergen: a — spec. BIN 952-1-6/69; b — spec. BIN 952-1-4/19; c — spec. F19203/2; d — spec. 952-1-6/54. Scale bar is 1 cm.
1867. Three of them (Heer, 1869, Taf. 44, Fig. 7, 9; Taf. 55, Fig. 3) are represented by fragments without clearly diagnostic features. So, we attribute to Populus richardsonii only two of those leaves (Heer, 1869, Taf. 44, Fig. 7, 9).
In 1870 Heer again described Populus richardsonii from Spitsbergen, locality Cap Staratschin (Heer, 1870). We also considered this material as belonged to Populus richardsonii, although not all specimens have clearly diagnostic features (see Systematics).
We also attribute to T. richardsonii several specimens from the localities Festningsodden (synonym of Cap Staratschin), Kolfjellet, and Barentsburg, based on the examination of Spitsbergen collections from the Ko-marov Botanical Institute of the Russian Academy of
Sciences and the Swedish Museum of Natural History (Fig. 5, 6). All of these localities now are referred to the Paleocene Firkanten Formation (Budantsev and Golovneva, 2009).
A. Seward and W. Edwards (1941) transferred the species P richardsonii to extant Cercidiphyllum based on the material from East Greenland. We doubt that these leaves really belong to this species, although we have not been able to re-examine the original material. Since the modern genus Cercidiphyllum appears in the fossil records with condensed rather than racemose infructes-cences only from the Oligocene (Jahnichen, Mai, and Walther, 1980; Manchester and Meyer, 1987; Kovar-Ed-er, Meller, and Zetter, 1998), we consider the application
of the generic name Cercidiphyllum to the Paleocene species to be questionable without additional evidence.
The combination Cercidiphyllum richardsonii (Heer) Seward et Edwards was used also by I. Iljinskaja (1971, 1974a), who designated the lectotype of Populus richardsonii based on Heer's drawings.
B. Koch (1963) described leaves of Populus richardsonii from the Paleocene Agatdalen Formation of Greenland as Cercidiphyllum arcticum (Heer) R. W. Brown. Under this name Brown (1939) united different species from the Cretaceous and Paleogene. The basionym of Cercidi-phyllum arcticum is Populus arctica Heer, which now is considered as a junior synonym of type species of the genus Zizyphoides Seward at Conway — Z. colombii (Heer) Seward et Conway (Zolina, Manchester, and Golovneva, 2021). Therefore, the use of the name Cercidiphyllum arct-icum is currently invalid (Golovneva and Alekseev, 2017; Zolina, Manchester, and Golovneva, 2021).
A. Kryshtofovich (1958) transferred Populus richard-sonii to the genus Trochodendroides, because these leaves were significantly different from those of extant Populus (Salicaceae). The genus Trochodendroides united extinct species, with leaves similar to those of Trochodendreceae and Cercidiphyllaceae (Berry, 1922). We consider Trochodendroides richardsonii to be the most appropriate name for the species that was initially described as Populus richardsonii. However, the specimens attributed by Kryshto-fovich to Trochodendroides richardsonii from the territory of Northeastern Russia are currently assigned to another species of Trochodendroides: T. deminii Yudova et Golovn. (Golovneva, Alekseev, Gnilovskaya, and Yudova, 2017).
Thus, it is confirmed that Trochodendroides richardsonii was distributed in the early Paleocene at Greenland and Spitsbergen.
The name Trochodendroides richardsonii was also used later by many authors for different leaves from the Cretaceous and Paleogene floras (Herman and Lebedev, 1991; Philippova, 2001; Shczepetov et al., 2020). The revision of all these numerous findings is beyond the scope of this paper, since in many cases this requires a re-examination of the original materials.
Trochodendroides richardsonii has the greatest resemblance to T. amurensis (Krysht. ex Iljinsk.) Iljinsk., T. deminii, and T. bidentata Vassilevsk. et Golovn. All of these species are characterized by ovate shape and cre-nate margin with large teeth that have rounded apex and biconvex sides.
Trochodendroides amurensis comes from the Paleo-cene Tsagayan Formation, Amur Region, Russia (Krysh-tofovich and Baikovskaya, 1966; Iljinskaja, 1974c). It differs from T. richardsonii by smaller and more frequent teeth and by narrower laminas. Leaves of T. amurensis are characterized by an elliptical area between inner lateral veins, while those of T. richardsonii have a triangular area in this position.
The species T. deminii was described from the Turonian-Coniacian Chingandzha Formation, NorthEast of Russia (Yudova and Golovneva, 2014). Later, Golovneva, Alekseev, Gnilovskaya, and Yudova (2017) recorded it in the late Albian-early Turonian Krivorech-enskaya Formation (Anadyr River basin), the Coniacian Tylpegyrgynay and Poporechnaya formations (Pekulney Ridge), the Coniacian Valizhgen Formation (Cape Kon-glomeratovy), the Coniacian Amka Formation (Ulya River basin), the lower Campanian Upper Bystrinskaya Formation (Cape Valizhgen, Northwestern Kamchatka), and in the Maastrichtian Kakanaut Formation (Koryak Upland). This species is distinguished from T. richardso-nii by smaller and narrower leaf blades and by smaller and narrower teeth. T. deminii also has an elliptical area between inner lateral veins.
Leaves of T. bidentata from the Maastrichitian-Danian part of the Rarytkin Formation are similar with leaves of T. richardsonii by large leaf blades with truncate to cordate base and acute or attenuate apex, and also in the triangular area between inner lateral veins. But T. bi-dentata differs by large double teeth.
Besides Populus richardsonii, Heer (1868) described two other species of the genus Populus from Atanikerdluk; P. zaddashii Heer and P. arctica. The first species differs by a dentate margin with small frequent acute teeth. P. arctica is distinguished from P. richardsonii by an entire, undulate, crenate or irregularly dentate margin. In addition, teeth of P. arctica are innervated by thin loops, while those of T. richardsonii are innervated by a vein that terminates in the tooth apex.
Berry's (1926) transfer of P. arctica to the genus Trochodendroides and species Trochodendroides arctica (Heer) Berry was followed in many Cretaceous and Paleogene floras (Seward and Conway, 1935; Kryshtofov-ich and Baikovskaya, 1966; Krassilov, 1976; Budantsev, 1983; Budantsev and Mokhov, 1986; Golovneva, 1994; Manchester, Chen, Geng, and Tao, 2005; Budantsev and Golovneva, 2009). However, the type material of T. arctica should be assigned to the genus Zizyphoides of the family Trochodendraceae (Crane, Manchester, and Dil-cher, 1991; Zolina, Manchester, and Golovneva, 2021).
Conclusion
In result of the re-examination of the Trochodendroides richardsonii type material, the emended diagnosis of this species was provided and the photos of lectotype and syntypes were presented for the first time. The analysis of findings of this species in Arctic floras showed that T. richardsonii was best documented only in the early Paleocene in Greenland and Spitsbergen. Other records of this species in the Cretaceous and Paleogene floras need careful reconsideration in light of a more detailed comparison with the type material.
Acknowledgements
We are grateful to Nigel Monaghan and Matthew Parker for their help at work in the National Museum of Ireland and Dr. Steven Manchester and Dr. Sergey Snigirevsky for helpful comments.
References
Angiosperm Phylogeny Group. 2016. An update of the Angio-sperm phylogeny group classification for the orders and families of flowering plants: APG IV. Botanical Journal of the Linnean Society 181(1):1-20. https://doi.org/10.1111/ boj.12385
Berry, E.W. 1922. The flora of Woodbine Sand at Arthur Bluff. United States Geological Survey professional paper 129-G:153-180. https://doi.org/10.3133/pp129G Berry, E. W. 1926. Tertiary floras from British Columbia. Geological Survey of Canada Bulletin 42:91-116. https://doi. org/10.4095/105011 Brown, R.W. 1939. Fossil leaves, fruits and seeds of Cercidiphyllum. Journal of Paleontology 13:485-499. Budantsev, L.Yu. 1983. History of the Arctic flora of the Early Cenophytic epoch. 156 pp. Nauka Publ., Leningrad. (In Russian)
Budantsev, L.Yu. and Golovneva, L.B. 2009. Fossil flora of Arctic II. Palaeogene flora of Spitsbergen. 400 pp. Mara-fon Publ., Saint Petersburg. (In Russian) Budantsev, L.Yu. and Mokhov, Е. Р. 1986. Morphological variability and taxonomy of leaves of the genus Trochodendroides in Early Eocene flora of West Kamchatka; pp. 1927 in L.Yu. Budantsev (ed.). Problem of palaeobotany. Nauka Publ., Leningrad. (In Russian) Chandrasekharam, A. 1974. Megafossil flora from the Genesee Locality, Alberta, Canada. Palaeontographica, Abt. B 147(1-3):1-41.
Crane, P.R. 1984. A re-evaluation of Cercidiphyllum-like plant fossils from the British early Tertiary. Botanical Journal of the Linnean Society 89:199-230. https://doi. org/10.1111/j.1095-8339.1984.tb02196.x Crane, P.R., Manchester, S.R., and Dilcher, D.L. 1991. Reproductive and vegetative structure of Nordenski-oldia (Trochodendraceae), a vesselless dicotyledon from the Early Tertiary of the Northern hemisphere. American Journal of Botany 78:1311-1344. https://doi. org/10.1002/j.1537-2197.1991.tb12599.x Crane, P. R. and Stockey, R.A. 1986. Morphology and development of pistillate inflorescences in extant and fossil Cer-cidiphyllaceae. Annals of the Missouri Botanical Garden 73:382-393. https://doi.org/10.2307/2399118 Dam, G., Pedersen, G.K., S0nderholm, M., Midtgaard, H.H., Larsen, L.M., N0hr-Hansen, H., and Pedersen, A.K. 2009. Lithostratigraphy of the Cretaceous-Paleocene Nuussuaq Group, Nuussuaq Basin, West Greenland. Geologic survey of Denmark and Greenland Bulletin 19:1171. https://doi.org/10.34194/geusb.v19.4886 Ellis, B., Daly, D., Hickey, L.J., Johnson, K., Mitchell, J., Wilf, P., and Wing, S. 2009. Manual of leaf architecture. 201 pp. Cornell University Press, New York. https://doi. org/10.1079/9781845935849.0000 Fu, D. Z. and Endress, P. K. 2001. Cercidiphyllaceae; p. 126 in Z.Y.Wu and P.H.Raven (eds.). Flora of China. Missouri Botanical Garden Press, St. Louis, 6. Golovneva, L. B. 1994. Maastrichtian-Danian floras of the Koryak Upland. Proceedings of the Komarov Botanical Institute 13:1-147. (In Russian) Golovneva, L.B. 2006. Alasia, gen. nov. — male inflorescences, associated with Trochodendroides
leaves(Cercidiphyllaceae). Botanicheskii Zhurnal 91(12):1898-1906. (In Russian) Golovneva, L.B. and Alekseev, P. I. 2010. The genus Trocho-dendroides Berry in the Cretaceous floras of Siberia. Pa-laeobotany 1:120-166. https://doi.org/10.31111/palaeo-botany/2010.1.120 (In Russian) Golovneva, L.B. and Alekseev, P.I. 2017. Taxonomy and morphological diversity of infructescences Jenkinsella co-occurred with Trochodendroides leaves in the Cretaceous and Paleogene. Palaeobotany 8:92-121. https:// doi.org/10.31111/palaeobotany/2017.8.92 Golovneva, L. B., Alekseev, P. I., Gnilovskaya, A.A., and Yudo-va, D.A. 2017. The genus Trochodendroides (Cercidiphyl-laceae) in the Cretaceous flora of Noth-East of Russia. Palaeobotany 8:122-179. https://doi.org/10.31111/pal-aeobotany/2017.8.122 (In Russian) Golovneva, L., Bugdaeva, E., Volynets, E., Sun, Y., and Zolina, A. 2021. Angiosperm diversification in the Early Cretaceous of Primorye, Far East of Russia. Fossil Imprint 779(2):231-255. https://doi.org/10.37520/fi.2021.017 Heer, O. 1868. Flora fossilis arctica. Die fossile Flora der Polarländer, Vol. 1. Druck und Verlag von Friedrich Schult-hess, Zurich. https://doi.org/10.5962/bhl.title.52346 Heer, O. 1869. Contributions to the fossil flora of North Greenland, being a description of the plants collected by Mr. Edward Whymper during the summer of 1867. Philosophical Transactions of the Royal Society of London 159:445488. https://doi.org/10.1098/rstl.1869.0016 Heer, O. 1870. Die Miocene Flora und Fauna Spitzbergens. Kongliga Svenska Vetenskaps-Akademiens Handlingar 8(7):1-98.
Herman, A.B. and Lebedev, E.L. 1991. Cretaceous stratigraphy and flora of Northwestern Kamchatka. Transactions of the Geological Institute 468:1-189. Hollick, A. 1936. The Tertiary floras of Alaska. United States
Geological Survey professional paper 182:1-185. Iljinskaja, I.A. 1971. About Trochodendroides arctica and T. richardsonii. Botanicheskii Zhurnal 56(11 ):1632-1633. (In Russian)
Iljinskaja, I.A. 1974a. Cercidiphyllum Siebold et Zucc.; pp. 124128 in A. L.Takhtajan (ed.). Magnoliophyta Fossilia URSS, Vol. 1. Nauka Publ., Leningrad. (In Russian) Iljinskaja, I.A. 1974b. Nyssidium Heer;pp. 123-124 in A. L. Takhtajan (ed.). Magnoliophyta Fossilia URSS, Vol. 1. Nauka Publ., Leningrad. (In Russian) Iljinskaja, I.A. 1974c. Trochodendroides Berry; pp. 115-122 in A. L. Takhtajan (ed.). Magnoliophyta Fossilia URSS, Vol. 1. Nauka Publ., Leningrad. (In Russian) Jähnichen, H., Mai, D.H., and Walther, H. 1980. Blätter und Früchte von Cercidiphyllum Siebold et Zuccarini im mitteleuropäischen Tertiär. Schriftenr. Geol. Wiss. 16:357399.
Knowlton, F. H. 1930. The flora of the Denver and associated formations of Colorado. United States Geological Survey professional paper 155:1-135. https://doi.org/10.3133/ pp155
Koch, B.E. 1963. Fossil plants from the Lower Paleocene of the Agatdalen (Angmartussut) Area, Central Nugssuaq Peninsula, North-West Greenland. Meddelelser om Gr0nland 172:1-120. https://doi.org/10.34194/bullggu. v38.6572
Kovar-Eder, J., Meller, B., and Zetter, R. 1998. Cercidiphyllum crenatum (Unger) R.W.Brown in der kohleführenden Abfolge von Oberdorf, N Voitsberg, Steiermark. Mitteilungen der Abteilung für Geologie und Paläontologie am Landesmuseum Joanneum 2:239-263. Krassilov, V.A. 1976. Tsagayan flora of Amur region. 92 pp. Nauka Publ., Moscow. (In Russian)
Kryshtofovich, A.N. 1958. Fossil floras of Penjin Bay, Tastakh Lake and Rarytkin Range. Transaction of Botanical Institute 8(3):74-121. (In Russian) Kryshtofovich, A.N. and Baikovskaya, T.N. 1966. The Upper Cretaceous Tsagayan flora of Amur region; pp. 184-320 in P.A.Baranov, A.L.Takhtajan and T.N.Baikovskaya. (eds.). Selections of A.N.Kryshtofovich. Nauka Publ., Leningrad. (In Russian) Lesquereux, L. 1873. Enumeration and description of fossil plants from the Western Tertiary formations. Description of species of fossil plants from the Cretaceous of Kansas. Annual report. United States Geological and Geographical Survey of the Territories: 371-427. Lesquereux, L. 1874. Contributions to the fossil flora of the Western Territories. Part I. Cretaceous flora. United States Geological and Geographical Survey of the Territories 6:1-136. https://doi.org/10.5962/bhl.title.7726 Lesquereux, L. 1878. Contributions to the fossil flora of the Western Territories. Part II. The Tertiary flora. United States Geological and Geographical Survey of the Territories 7:1-366. Manchester, S. R., Chen, Z., Geng, B., and Tao, J. 2005. Middle Eocene flora of Huadian, Jilin Province, Northeastern China. Acta Palaeobotanica 45(1):3-26. Manchester, S.R. and Meyer, H.W. 1987. Oligocene fossil plants of the John Day Formation, Fossil, Oregon. Oregon Geoly 49:115-127. Philippova, G.G. 2001. Stratigraphy and age of terrestrial deposits of Central and West Chukotka. Russian Journal of Pacific Geology 20(1):85-99. (In Russian) Philippova, G.G. and Abramova, L.N. 1993. The Late Cretaceous flora of Northaestern Russia. 348 pp. Nedra Publ., Moscow. (In Russian)
Samylina, V.A. 1976. Cretaceous flora of the Omsukchan.
206 pp. Nauka, Leningrad. (In Russian) Schmalhausen, J. 1890. Wissenschaftliche Resultate der von der Kaiserlichen Akademie der Wissenschaften zur Erforschung des Janalandes und der Neusibirischen Inseln in der Jahren 1885 und 1886 ausgesandten Expedition. Abtheilung II.Tertiäre pflanzen der Insel Neusibirien. Mémoires de l'Académie Impériale des Sciences de St.-Pé-tersbourg. VII Sér. 37(5):1-22. Seward, A.C. and Edwards, W.N. 1941. Fossil Plants from East Greenland. Annals and Magazine of Natural History, Series 11 8(45):169-176. https://doi.org/10.1080/037454 81.1941.9727962 Seward, A.C. and Conway, V. 1935. Fossil plants from Kingi-tok and Kagdlunguak, West Greenland. Meddelelser om Gr0nland 93:1-41. Shczepetov, S.V., Herman, A.B., Tikhomirov, P.L., Moi-seev, A. V., Sokolov, S. D., and Hayasakae, Y. 2020. On the age of the Buor-Kemus flora of North-Eastern Asia based on data from non-marine Cretaceous in Eastern Chukotka. Stratigraphy and Geological Correlation 28:429-444. https://doi.org/10.1134/S0869593820040085 Yudova, D. A. and Golovneva, L. B. 2014. The genus Trochodendroides Berry in the Chingandzha flora of Northeastern Russia. Palaeobotany 5:60-72. https://doi.org/10.31111/ palaeobotany/2014.5.60 (In Russian) Zolina, A.A., Manchester, S.R., and Golovneva, L.B. 2021. Typification of the genus Zizyphoides Seward et Conway (Magnoliophyta, Trochodendraceae). Acta Palaeobotan-ica 61 (2):1 23-135. https://doi.org/10.35535/acpa-2021-0007
