Journal of Systematics and Evolution 47 (2): 93–102 (2009) doi: 10.1111/j.1759-6831.2009.00007.x Male spike strobiles with Gnetum affinity from the Early Cretaceous in western Liaoning, Northeast China 1,2Shuang-Xing GUO* 3Jin-Geng SHA 4Li-Zeng BIAN 5Yin-Long QIU 1(Department of Palaeobotany and Palynology, Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China) 2(Laboratory of Biodiversity and Biogeography, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650204, China) 3(State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China) 4(College of Earth Sciences, Nanjing University, Nanjing 210093, China) 5(Department of Ecology & Evolutionary Biology, The University Herbarium, University of Michigan, Ann Arbor, MI 48109-1048, USA) Abstract A fossil with Gnetum affinity was found in the Jianshangou Member (Barremian Age) of the Yixian Formation (Lower Cretaceous Epoch) of the Jehol Group in western Liaoning, northeastern China. The single fossil specimen is represented by both elongate-cylindrical male spike strobiles which borne within a nodal bract of cauliflorous branch. The spike strobiles have apparent nodes, invisible internodes, and numerous verticillate involucral collars. The microsporangiate units within involucral collars are not seen. The male spike strobiles with verticillate involucral collars occur exclusively in Gnetum; hence, the fossil strobiles are attributed to a new taxon, Khitania columnispicata gen. & sp. nov., being closely related to Gnetum. The general isotopic dating suggests an age of Barremian, ca. 125–122 million years (Myr) ago for the Jianshangou Member. The palaeoecological and palaeoclimatic inference based on the compositions of flora and fauna, and lithological characters of the fossil locality suggests that the fossil plants grew in a subtropical mesophytic forest and under a warmer climate. The remains of male spike strobiles are the first record of gnetalean macrofossil. It documents the evolution of the distinct gnetoid morphology and indicates a wider range of distribution of Gnetaceae in the Early Cretaceous than present day. Key words biogeography, Early Cretaceous, Gnetum affinity, male spike strobiles, northeastern China. Gnetales represent one of the four extant gym- Ginkgo, conifers, Gnetales, angiosperms) at both nospermous lineages (Kramer & Green, 1990) and morphological and molecular levels, one solution have become critical in the recent debate on relation- would be to search for fossil evidence to reconstruct ships between gymnosperms and angiosperms the evolutionary course of divergent morphology of (Donoghue & Doyle, 1999). In contrast, they have a these lineages (Doyle & Donoghue, 1987). Some very poor fossil record in comparison with other close morphological affinity to Ephedra and lineages of seed plants (Crane, 1996). While earlier Welwitschia pollen grains were ever found from the classic studies and cladistic analyses of morphology Katrol Formation (Upper Jurassic) of Kutch, India suggested that they might be related to angiosperms (Mathur & Mathur, 1965). Since then till a few years (Arber & Parkin, 1908; Crane, 1985; Doyle & ago, reports of gnetalean fossils, particularly of mac- Donoghue, 1986; Nixon et al., 1994), recent molecular rofossils, were still extremely scarce (Crane & phylogenetic studies often placed them with conifers Upchurch, 1987; Osborn et al., 1993; Crane, 1996; (Goremykin et al., 1996; Winter et al., 1999; Bowe et Won & Renner, 2006). Over the last several years, al., 2000; Chaw et al., 2000; Frohlich & Parker, 2000; however, several papers have been published on Gugerli et al., 2001; Magallon & Sanderson, 2002; macrofossils of Ephedraceae (Guo & Wu, 2000; Burleigh & Mathews, 2004), although it could not be Rydin et al., 2004, 2006; Yang et al., 2005), completely ruled out that they may be sister to all Welwitschiaceae (Rydin et al., 2003; Dilcher et al., other extant seed plants (Rydin et al., 2002). To move 2005), and Gnetales (Wang, 2004). To date, no mac- out of the current dilemma of debate on the seed plant rofossil of Gnetum has been reported. phylogeny, which mostly stems from a large amount In this study, we report a gnetalean fossil that has of divergence among the five extant lineages (cycads, two male spike strobiles, from the Jianshangou Mem- ber of the Yixian Formation in Liaoning Province, northeastern China in the Lower Cretaceous Series. ——————————— Received: 28 December 2007 Accepted: 31 July 2008 The fossil specimen consists of two male strobiles that * Author for correspondence. E-mail: <[email protected]>. have microsporangiate axes with nodes, invisible 94 Journal of Systematics and Evolution Vol. 47 No. 2 2009 internodes, and nodal whorled bracts on spike to form abundant in the number of specimens (Chen, 1999; fused verticillate involucral collars. Such male stro- Chang, 1999; Guo & Wu, 2000; Sun et al., 2001, biles are similar to those of extant Gnetum, and they 2002; Chang et al., 2003; Ji et al., 2004; Li, 2005; occur only in Gnetum and not in any other living or Dilcher et al., 2007). extinct plants. The fossil strobiles probably belong to According to the recent isotopic dating, the geo- an extinct species in relation to Gnetum. The locality logical age of the Yixian Formation is the early Early of the fossil occurrence is situated in the mid-latitude Cretaceous, between 135–120 million years (Myr) (lat. 41º12´N), whereas all modern Gnetum species are (Zhang et al., 2004) or 127–125 Myr (Zhang et al., growing in the low latitude (Kramer & Green, 1990) 2004). The Jianshangou Member is the lower part of in both of the Northern and Southern Hemispheres. the Yixian Formation attributed to Barremian Age, Discovery of this Gnetum-related fossil hence sug- between 125–122 Myr (Swisher et al., 2002; Zhang et gests that gnetoid plants had more extensive distribu- al., 2006; Chen et al., 2006). tion in the Early Cretaceous than today. Attempts were made to collect more fossil specimens of gnetoid from the same bed of the same locality and from other contemporary strata at differ- 1 Material and methods ent localities, but with no success so far. Effort was also made to extract pollen grains in situ from the The fossil material is a single specimen with two strobiles, but it failed. The fossil specimen was photo- male spike strobiles in light brown-yellowish impres- graphed using a stereo microscope, Nikon SMZ 1500 sion, which was collected from the section of eastern system. hillside of Huangbanjigou to western hillside of Jianshangou Villages (41º12′ N, 119º22′ E) in the Jianshangou Member of the Yixian Formation of the 2 Results Jehol Group in Beipiao County, Liaoning Province, northeastern China. The Jianshangou Member is the Systematics lower part of the Yixian Formation, which is divided Division – Gnetophyta Takhtajan 1986 into 11 beds with a total thickness of 34.4 m. Occur- Class – Gnetopsida Steward 1983 rence of fossil plants is very abundant and they are Order – Gnetales Pearson 1929 mostly concentrated in the beds # 6 and 8 (3.5 and 2.5 Family – Gnetaceae Lindley 1834 m thick, respectively). The lithological characters of Genus – Khitania Guo, Sha, Bian & Qiu, gen. the Jianshangou Member consist of grayish-white/ nov. grayish-yellow/black thick-bedded muddy siltstone, Etymology: Khitan is the name of an ancient eth- volcanic rocks, and volcaniclastic sedimentary rocks nic tribe that once inhabited the Liaohe Valley in (Sun et al., 2001). The fossil specimen described here Liaoning Province, northeastern China. was preserved in the bed # 8. Generic diagnosis: Two elongate-cylindrical The Yixian Formation is extensively distributed male spikelike strobiles (microsporangiate axes), in four counties of Yixian, Beipiao, Lingyuan and which with two invisible peduncles borne within a Zhaoyang in western Liaoning. It consists of a set of cupular bract of swollen node on cauliflorous branch. late Mesozoic terrestrial volcanic lava, volcaniclastic Male strobiles with many nodes and invisible inter- rock and lacustrine sedimentary rock with less fluvial nodes, and numerous verticillate annular involucral rock. It includes six fossiliferous strata with abundant collars, which formed by the fusion of verticillate animal and plant fossils. The protists and animals bracts on nodes of spike, involucral collars close include dinoflagellates, conchastracans, ostracods, arrangement, margin entire or somewhat undulation. shrimps, insects, spiders, bivalves, gastropods, fishes, Microsporangiate units (sessile male “flowers”) within reptiles, amphibians, dinosaurs, tortoises, crocodiles, involucral collars indiscernible, their number and birds, and primitive mammals. The plant taxa include arrangement unknown (probably one row or two in Bryophyte, Lycopodiatae, Equisetatae, Filicatae, arrangement). Pteridospermae, Bennettitales, Czekanowskiales, Khitania columnispicata Guo, Sha, Bian & Qiu, Ginkgoales, Coniferae, Gnetales, and Angiospermae. gen. et sp. nov. Among the fossil plants, Coniferae are the most Fig. 1: left; 2: A–F abundant in the number of genera and species. Next Etymology: Column (from Latin columna) means are Filicatae, Bennettitales, Czekanowskiales, and cylinder; spicata (from Latin spicatus) represents a Ginkgoales. Ephedraceae of Gnetales is also very strobile. GUO et al.: A fossil with Gnetum affinity from China 95 Fig. 1. Comparison of male spike strobiles