Journal of Paleontology, 92(4), 2018, p. 546–567 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.145


Coniferous wood of Agathoxylon from the La Matilde Formation, (Middle Jurassic), Santa Cruz, Argentina


Adriana C. Kloster,1 and Silvia C. Gnaedinger2


1Área de Paleontología, Centro de Ecología Aplicada del Litoral, Consejo Nacional de Investigaciones Científicas y Técnicas (CECOAL-CCT CONICET Nordeste-UNNE). ⟨klosterdri@gmail.com⟩ 2Área de Paleontología, Centro de Ecología Aplicada del Litoral, Consejo Nacional de Investigaciones Científicas y Técnicas (CECOAL-CCT


CONICET Nordeste-UNNE), Facultad de Ciencias Exactas y Naturales y Agrimensura, Universidad Nacional del Nordeste (FaCENA-UNNE). Casilla de Correo 291, 3400 Corrientes, Argentina ⟨scgnaed@hotmail.com⟩


Abstract.—In this contribution, four species of Agathoxylon are described from the La Matilde Formation, Gran Bajo de San Julián and central and south-western sectors of Santa Cruz Province, Argentina. Agathoxylon agathioides (Kräusel and Jain) n. comb., Agathoxylon santalense (Sah and Jain) n. comb., Agathoxylon termieri (Attims) Gnaedinger and Herbst, and the new species Agathoxylon santacruzense n. sp. are described based on a detailed description of the secondary xylem. In this work, it was possible to construct scatter plots to elucidate the anatomical differences between the fossil species described on quantitative anatomical data. Comparisons are made with other Agathoxylon species from Gondwana. These parameters can be used to discriminate genera and species of wood found in the same formation, as well as to establish differences/similarities between other taxa described in other formations. Some localities contain innumerable “in situ” petrified trees, which allowed us to infer that these taxa formed small forests, or local forests, or small forests within a dense forest, which is a habitat coincident with the extant Araucariaceae.


Introduction


Sediments of the La Matilde Formation crop out in several areas of Santa Cruz province (Argentina), some localities containing “in situ” silicified trees, with many fallen and fragmented exam- ples (DeBarrios et. al., 1999).The geological and paleontological characteristics of the La Matilde Formation have already been described by several authors (e.g., Delhaes, 1913; Frenguelli, 1933; Feruglio, 1949; Stipanicic and Reig, 1957; Spalletti et al., 1982; Panza and Irigoyen, 1995; Panza, 1998). Sediments of the La Matilde Formation crop out in diverse


sectors of the province of Santa Cruz: the central-eastern sector: Cañadón de La Matilde, where the type locality is situated (Criado Roque, 1953; Stipanicic and Reig, 1957; Panza, 1984, 1995, 1998); the central sector, the best known from a paleonto- logical point of view, comprising, among other localities, the “Monumento Natural Bosques Petrificados de Jaramillo” (Jaramillo Petrified Forest National Park) (Panza, 1982, 1995, 1998); the central and south-western sector (Bajo El Puma and estancia Manantial Espejo, among other localities) (Panza, 1986; De Barrios, 1989; Panza and Marín, 1996; Panza and Cobos, 1998); and the Gran Bajo de San Julián sector comprising local- ities such as Laguna del Molino, Laguna del Carbón, Mina del Gobierno, Mina La Pareja and Puesto Raspuzzi, among others (Panza and De Barrios, 1989; Panza and Irigoyen, 1995). Herbst et al. (1995) found new outcrops containing large


quantities of petrified logs in the Gran Bajo de San Julián sector, which show the same characteristics as those from the north of


the province (i.e., forests with in situ petrified trunks and rolled trees). These localities are found in the Estancia El Mineral (Laguna La Guadalosa), Estancia Meseta Chica (Barda Blanca, Cerro Conito, northern part), and Estancia La Silvita (Laguna del Carbón) (Figs. 1, 2). Anatomical descriptions of Osmundalesmacrofossils and leaf


impressions of the orders Equisetales, Osmundales, Bennettitales, and Coniferales have been made from these outcrops (Feruglio, 1951; Archangelsky and de la Sota, 1962; Herbst, 1977, 2003; Baldoni, 1981, 1990; Herbst and Salazar, 1999). In addition, also from this formation, petrified cones (Spegazzini, 1924; Calder, 1953;Menéndez, 1960; Stockey, 1977, 1978; Stockey and Taylor, 1978), as well as silicified fungi (Singer and Archangelsky, 1957) andwood, Agathoxylon matildense (Zamuner and Falaschi, 2005), have been described from the well-known “Jaramillo Petrified Forests,” including areas such as Cerro Madre e Hija and Cerro Cuadrado, among others. In previous studies of the xyloflora from the Gran Bajo de


San Julián sector, taxa of the order Coniferales were described: Protelicoxylon Philippe and Herbstiloxylon Gnaedinger, related to members of the Cupressaceae; Circoporopitys Gnaedinger, two new species of Podocarpoxylon Gothan, and Circoporoxylon Kräusel, belonging to the Podocarpaceae; and Planoxylon Stopes, of the group Protopinaceae. Specimens of PrototaxoxylonKräusel andDolianiti of the order Taxales, andGinkgomyeloxylon tanzanii Giraud and Hankel of the order Ginkgoales, also have been described (Gnaedinger and Herbst, 2006; Gnaedinger, 2007a, b, 2012).


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