First Record of Conifer Wood from the Cañadón Asfalto Formation (Early-Middle Jurassic), Chubut Province, Argentina

Abstract

Abstract.A new fossil conifer wood -Brachyoxylon currumilii sp. nov.-is described from the Lower-Middle Jurassic of Chubut Province (Argentina). The specimens were collected at a locality where the Cañadón Asfalto Formation is exposed, in the vicinity of the Cerro Cóndor village. The studied wood is characterized by mixed pitting in radial tracheid walls (predominantly uniseriate), araucarioid cross fields, low uniseriate rays and the absence of resin canals. The use of transmitted light and epifluorescence microscopy together with SEM imaging allowed the identification of additional characters such as the presence of pitting with torus-margo and compression wood. These characters are discussed in terms of their systematic relevance. On these grounds, the systematic affinity of the studied wood is discussed and linked to the extinct conifer family Cheirolepidiaceae, one of the dominant plant groups during the Jurassic and Cretaceous in Patagonia.Keywords. Fossil wood. Mesozoic. Patagonia. Brachyoxylon. Cheirolepidiaceae. Resumen. PRIMER REGISTRO DE LEÑO DE CONIFERA DE LA FORMACIÓN CAÑADÓN ASFALTO (JURÁSICO TEMPRA-NO-MEDIO), PROVINCIA DE CHUBUT, ARGENTINA. Se describe una nueva especie de madera fósil de conífera, Brachyoxylon currumilii sp. nov., del Jurásico Inferior a Medio de la provincia de Chubut, Argentina. Los especímenes estudiados fueron coleccionados en una localidad donde aflora la Formación Cañadón Asfalto, en las cercanías de la aldea de Cerro Cóndor. Los troncos, estudiados, se caracterizan por el punteado radial de las traqueidas de tipo mixto, predominantemente uniseriado, campos de cruzamiento de tipo araucarioide, radios uniseriados bajos y ausencia de canales resiníferos. La observación bajo MEB y microscopio con luz transmitida y epifluorescencia permitió además la identificación de caracteres tales como la presencia de torus-margo en las punteaduras y estructuras de leño de compresión. Ambos caracteres son discutidos en relación a su relevancia sistemática. Sobre esta base, se discute la afinidad sistemática de la madera estudiada, la cual posee rasgos que la vincularían con la familia de coníferas extintas Cheirolepidiaceae, uno de los grupos de plantas dominantes durante el Jurásico y Cretácico de Patagonia.Palabras clave. Madera fósil. Mesozoico. Patagonia. Brachyoxylon. Cheirolepidiaceae.

Gravitropisms and reaction woods of forest trees – evolution, functions and mechanisms

“…The fossil record for reaction wood in gymnosperms is also fragmentary and inconclusive, although compression wood is commonly found in gymnosperm fossil woods beginning from at least the late Cretaceous and early Cenozoic (Blanchette et al, 1991;Chapman & Smellie, 1992;Wheeler & Lehman, 2005), and in one report from the early-middle Jurassic (Bodnar et al, 2013). However, extant gymnosperm lineages also provide insights.…”

Occurrence of Brachyoxylon Hollick et Jeffrey from the Lower Cretaceous of Zhejiang Province, southeastern China

“…nov. Being different from the new species from China, Brachyoxylon currumilii from the Lower-Middle Jurassic of Argentina bears scanty and diffuse axial parenchyma (Bodnar et al 2013). Another Argentina species, Brachyoxylon baqueroensis differs from the new species by having distinct annual rings, triseriate radial pits, and a higher number of cross-field pits (Vera and Césari 2015).…”

“…Generally, the co-occurrence of Brachyoxylon wood and leaf fossils of Cheirolepidiaceae in the Lower Cretaceous Guantou Formation further implies that the fossil wood genus Brachyoxylon may be systematically referable to the conifer family Cheirolepidiaceae. Fossils of Brachyoxylon have been widely documented from both the boreal and Gondwana regions range from the Permian to the Late Cretaceous (Philippe et al 2004a;Bodnar et al 2013). Palaeogeographically, Brachyoxylon is much more common in boreal areas (e.g., the United States, Tunisia, Japan, Cambodia, Thailand, France and Romania) than in Gondwana region (Philippe et al 2004a;Bodnar et al 2013).…”

“…Since Philippe et al (2014) proposed that a wood specimen which has "japonicum" type of radial tracheid pitting should display at least 10% of its radial tracheid pit total number being biseriate-opposite, the radial tracheid pitting of the wood studied in this paper does not belong to the "japonicum" type. Only three morphogenera of petrified wood have been defined to have mixed radial tracheid pitting and cross-fields with cupressoid oculipores, i.e., Brachyoxylon Hollick et Jeffrey, Zonaloxylon Grauvogel-Stamm et al and Protocupressinoxylon Eckhold (Philippe and Bamford 2008;Bodnar et al 2013). However, only Brachyoxylon is characterized by having araucarioid cross-field pits, which are contiguous and/or compressed and alternately arranged oculipores.…”

“…Even recently, a new species Brachyoxylon baqueroensis Vera et Césari was described from the Lower Cretaceous in Patagonia (Vera and Césari 2015). A comprehensive and detailed comparison between 17 species of Brachyoxylon was given in Bodnar et al (2013). It is noted that among those listed Brachyoxylon species, five species (i.e., B. brachyphylloides Torrey Philippe et al) are characterized by having tangential tracheid pitting and/or traumatic resin ducts (Table 1).…”