Hostname: page-component-78c5997874-m6dg7 Total loading time: 0 Render date: 2024-11-04T21:46:56.826Z Has data issue: false hasContentIssue false
  • English
  • Français

Ancient Basidiomycota in an extinct conifer-like tree, Xenoxylon utahense, and a brief survey of fungi in the Upper Jurassic Morrison Formation, USA

Published online by Cambridge University Press:  11 April 2023

Aowei Xie Open the ORCID record for Aowei Xie [Opens in a new window] ,
Carole T. Gee  and
Ning Tian
Aowei Xie*
Affiliation:
Institute of Geosciences, Division of Paleontology, University of Bonn, Nussallee 8, 53115 Bonn, Germany ,
Carole T. Gee*
Affiliation:
Institute of Geosciences, Division of Paleontology, University of Bonn, Nussallee 8, 53115 Bonn, Germany , Huntington Botanical Gardens, 1151 Oxford Road, San Marino, California 91108, USA State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
Ning Tian
Affiliation:
College of Palaeontology, Shenyang Normal University, Shenyang 110034, China
*
*Corresponding authors.
*Corresponding authors.
Rights & Permissions [Opens in a new window]

Abstract

Although the well-known Upper Jurassic Morrison Formation has yielded abundant fossil plants for nearly a century, relatively little is known about fossil fungi and their ecological relationships to the Morrison flora. The first mention of fungal decay in fossil wood was briefly made over three decades ago, and since then, a few more reports of fungal decay associated with Morrison plants have been published. However, up to now, detailed data on the fossil fungi themselves have not been given from the Morrison Formation. Here we describe in detail well-preserved fossil mycelia in a silicified log of Xenoxylon utahense Xie et Gee, 2021 from the Upper Jurassic Morrison Formation at Miners Draw, Blue Mountain, near Vernal in northeastern Utah, USA. The fungal hyphae are variable in form, ranging from straight to slightly curved to highly coiled to tubular; they measure ~1.53 μm in diameter and possess clamp connections, septa, and occasional bifurcations. The occurrence of clamp connections typical of living Basidiomycota indicates a taxonomic affinity to this division of fungi. On the basis of the patterns of wood decay in the Xenoxylon log, the fossil fungi are interpreted here as pertaining to saprotrophic, white-rot wood fungi. These fossil mycelia represent a new record of ancient Basidiomycota from the Upper Jurassic Morrison Formation and provide further evidence for plant–fungus interactions in Jurassic terrestrial ecosystems.

Type
Articles
Information
Journal of Paleontology , Volume 97 , Issue 3 , May 2023 , pp. 754 - 763
Check for updates
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
Copyright © The Author(s), 2023. Published by Cambridge University Press on behalf of The Paleontological Society

Introduction

Interactions between terrestrial plants and fungi can be traced back to the Early Devonian times, ca. 400 million years ago (Stubblefield et al., Reference Stubblefield, Taylor and Beck1985; Taylor et al., Reference Taylor, Krings and Taylor2015). One of the oldest occurrences was described by Kidston and Lang (Reference Kidston and Lang1921) as fungi in the shoot cortex of Aglaophyton major (Kidston and Lang) Edwards, Reference Edwards1986 from the Lower Devonian Rhynie Chert in Scotland. However, fossil fungi in terrestrial plants are relatively poorly known throughout geological history. The scarcity of reports on plant–fungus interactions is likely due to the inconspicuous fungal decay patterns in ancient plants, the microscopic size of many fungi, and the type of preservation in fossil plants.

Fungal remains have been found associated with various types of plant preservation, ranging from leaf impressions and compressions to permineralized material. On impressions, it is extremely difficult to ascertain evidence of plant–fungus interactions, although various spots on some fossil leaves have been interpreted as fungal decay (e.g., Unger, Reference Unger1841; Meschinelli, Reference Meschinelli1898). Compressions of both conifer and angiosperm foliage, however, have yielded evidence of multicellular epiphyllous fungi (e.g., Dilcher, Reference Dilcher1963, Reference Dilcher1965; Alvin and Muir, Reference Alvin and Muir1970; Iglesias et al., Reference Iglesias, Zamuner, Poire and Larriestra2007; Ding et al., Reference Ding, Sun, Wu and Li2011; Bannister et al., Reference Bannister, Conran and Lee2016; Maslova et al., Reference Maslova, Sokolova, Kodrul, Tobias, Bazhenova, Wu and Jin2020). Permineralized plant remains have also yielded good fossil evidence of plant–fungus interactions (Taylor et al., Reference Taylor, Krings and Taylor2015). In recent years, there has been an increasing awareness of fossil fungal remains, especially of wood-decay fungi in silicified woods (e.g., Pujana et al., Reference Pujana, García Massini, Brizuela and Burrieza2009; Césari et al., Reference Césari, Busquets, Méndez-Bedia, Colombo, Limarino, Cardo and Gallastegui2012; García Massini et al., Reference García Massini, Falaschi and Zamuner2012; Harper et al., Reference Harper, Bomfleur, Decombiex, Taylor, Taylor and Kring2012, Reference Harper, Taylor, Kring and Taylor2016; McLoughlin and Strullu-Derrien, Reference McLoughlin, Strullu-Derrien, Kear, Lindgren, Hurum, Milàn and Vajda2016; Sagasti et al., Reference Sagasti, García Massini, Escapa and Guido2019; Tian et al., Reference Tian, Wang, Zheng and Zhu2020; Gee et al., Reference Gee, Xie and Zajonz2022).

Here we report on permineralized wood with structurally preserved fungal hyphae in an Upper Jurassic log that was discovered in the Morrison Formation at Miners Draw in northeastern Utah, USA. The fossil log had recently been recognized as a new species of the enigmatic, conifer-like genus of Xenoxylon, X. utahense Xie et Gee, by Xie et al., Reference Xie, Gee, Bennis, Gray and Sprinkel2021. The fungal decay patterns evident in the fossil wood, the structure of the fossil mycelia, and possible affinity of the ancient fungi are described and discussed here. Our finding sheds new light on plant–fungus interactions in the Morrison ecosystems during Late Jurassic times.

Materials and methods

Evidence of fungal decay and the fungal remains themselves were found in a specimen of wood collected from a silicified log from the Upper Jurassic Morrison Formation in Miners Draw on Blue Mountain, about 30 km southeast of Vernal in Utah, USA (Fig. 1). At this site, the fossil wood-bearing strata occur as a series of light greenish-gray to brownish-gray, silty to very fine-grained sandstone with an exposed thickness of ~10 m (Fig. 2; Gee et al., Reference Gee, Sprinkel, Bennis and Gray2019; Sprinkel et al., Reference Sprinkel, Bennis, Gray and Gee2019). Stratigraphically, the strata pertain to the Salt Wash Member of the Upper Jurassic Morrison Formation, which represents a fluvial–lacustrine sedimentary environment at Miners Draw (Sprinkel et al., Reference Sprinkel, Bennis, Gray and Gee2019).

Figure 1. Map of fossil locality (triangle) bearing the fossil log of Xenoxylon utahense in Miners Draw near Vernal (solid circle), Utah (dark gray in inset), USA, superimposed on the outcrops of the Upper Jurassic Morrison Formation (black). Morrison outcrop base map courtesy of Kenneth Carpenter.

Figure 2. Lithostratigraphic column of the Upper Jurassic Morrison Formation in Miners Draw near Vernal, Utah, USA. Legend: (1) mudstone; (2) siltstone; (3) sandstone; (4) conglomeratic sandstone; (5) conglomerate; (6) silty sandstone; (7) covered and not measured outcrop; (8) fossil log. Section modified after Sprinkel et al. (Reference Sprinkel, Bennis, Gray and Gee2019).

Wood thin sections of the type specimen of Xenoxylon utahense (FHPR catalog number FHPR 11386, field specimen number 091119-8, thin sections of BMT-001b) were reinvestigated for fossil fungal remains in the wood tissue. The wood decay and fungal remains were studied with a Leica DM2500 compound photomicroscope (Leica Microsystems, Wetzlar, Germany) and subsequently measured and photographed with the aid of ImageAccess easyLab 7 software (Version 1992–2007, iMagic, Glattburg, Switzerland).

Repositories and institutional abbreviations

Remnants of the wood specimens of Xenoxylon are deposited at the Utah Field House of Natural History State Park Museum (FHNHM), Utah, USA, under FHPR catalog number FHPR11386. Thin sections are housed and logged into the system at the University of Bonn in Bonn, Germany, as BMT-001a, BMT-001b, and BMT-001c.

Results

Tree host

The fossil log at Miners Draw area was previously recognized as Xenoxylon utahense Xie et Gee by Xie et al., Reference Xie, Gee, Bennis, Gray and Sprinkel2021, an extinct gymnosperm that may pertain to the extinct family Miroviaceae (cf. Nosova and Kiritchkova, Reference Nosova and Kiritchkova2008; Philippe et al., Reference Philippe, Thévenard, Nosova, Kim and Naugolnykh2013). Xenoxylon utahense is a conifer-like wood dominated by tracheids and ray parenchyma that lacks axial parenchyma and resin canals. Tracheid pitting on radial walls is mostly uniseriate and strongly flattened. Crossfield pitting is fenestriform. Ray cells are mostly uniseriate, occasionally biseriate, homocellular, parenchymatous, with smooth and unpitted horizontal and end walls.

Wood decay and fungal body fossils

In transverse section (Fig. 3.1–3.4), the tracheids show various stages of wood decay, such as the decomposition of the middle lamella and tracheid cell walls, as well as the separation of the individual cell wall layers. In areas with less decay (Fig. 3.2, marked LD, 3.3), some parts of the cell walls remain more intact (Fig. 3.3, white arrows) while other areas of the cell walls within the same tracheids show greater degradation (Fig. 3.3, red arrows). In zones with more decay (Fig. 3.2, marked MD, 3.4), the cell walls and middle lamella are almost completely disintegrated. In radial section, large, irregularly shaped zones of decay appear as decolored bands or patches (Fig. 3.5, 3.6). In these decolored zones, only the faint outlines of tracheid walls may be preserved, and the circular bordered pits on the radial walls of the tracheids can no longer be observed (Fig. 3.6). Fungal remains occur in abundance in these tracheids (Fig. 3.7, red arrow).

Figure 3. Specimen BMT-001b. Thin-section micrographs in transverse (1–4) and radial (5–7) sections of tree host Xenoxylon utahense Xie et Gee in Xie et al., Reference Xie, Gee, Bennis, Gray and Sprinkel2021 from the Upper Jurassic Morrison Formation in Miners Draw, Utah, USA. (1) Overview of wood, showing several growth rings. (2) Close-up of (1) (area within red rectangle) showing details of the wood decay at different degrees of decay. LD = area with less decay; MD = more decay. (3) Close-up of (2) showing details in the area of less decay. Some parts of the cell walls remain more or less intact (white arrows), while other areas of the cell wall of the same tracheids are nearly completely degraded (red arrows). (4) Close-up of (2) showing extremely advanced disintegration of the tracheid cell walls in the area with more decay. (5) Overview of wood, in which the decolored zones appear as irregularly shaped bands or patches. (6) Close-up of (5) showing details of the decolored zones; the tracheid pitting on radial walls can no longer be observed in the decolored zone. (7) Close-up of (6) showing details of the fungal hyphae in the decolored tracheids (red arrow).

In radial section, the abundant fungal remains are represented by well-preserved mycelia composed of fungal hyphae. The fungal hyphae run more or less vertically through the tracheids (Fig. 4.1–4.7) but can also pass through the crossfields (Fig. 4.8), which illustrate that the hyphae had penetrated into the cell walls of the ray parenchyma. In the tracheid lumina, the fungal hyphae can be straight, lightly curved (Fig. 4), or highly coiled (Fig. 5.1, 5.2, 5.8, white arrow). The diameter of the hyphae ranges from 1.21 to 2.09 μm and measures 1.53 μm on average. The hyphae are tubular in morphology and smooth-walled (Figs. 4, 5). The crosswalls of the hyphae, also known as septa, can be observed in some hyphae and are located near bifurcations (Fig. 5.3, arrowheads). A large number of typical clamp connections are present in the hyphae (Fig. 4.2, 4.3, red arrows; Fig. 5.4–5.9, red arrows). Bifurcations occur in some hyphae, sometimes in conjunction with a clamp connection (Fig. 5.4, 5.5, arrows).

Figure 4. Specimen BMT-001b. Thin-section micrographs in radial section of Xenoxylon utahense with fungal hyphae. (1) Fungal hyphae passing through tracheid lumina. (2) Fungal hyphae growing along the tracheid walls, with a typical basidiomycetous clamp connection (red arrow). (3) Close-up of (2) highlighting the clamp connection (red arrow). (4) Fungal hyphae growing in the lumen of a tracheid. (5) Abundant fungal hyphae in tracheids (red arrow). (6) Close-up of (5) showing details of hyphae. (7) Another view of fungal hyphae, here in neighboring tracheids. (8) Fungal hyphae penetrating the crossfields between rays and tracheids.

Figure 5. Specimen BMT-001b. Thin-section micrographs in radial section of Xenoxylon utahense with fungal remains. (1, 2) Highly coiled fungal hypha. (3) Septum (between arrowheads) in a fungal hypha. (4–7) Typical basidiomycetous clamp connections (red arrows), which are sometimes associated with a bifurcation of the hyphae. (8) Highly coiled fungal hyphae (white arrow) and clamp connection (red arrow). (9) A typical clamp connection (red arrow).

Discussion

In the Xenoxylon utahense wood from Miners Draw under investigation here, there are multiple lines of evidence for fossil fungal decay (Figs. 3–5). On the tissue level, the preservation of the fossil wood is locally variable in its degree of decay. Particularly in radial section, the zones of decay are evident as irregularly positioned and shaped, decolored bands or patches (Fig. 3.5). In the decolored zones, the decay can be so advanced that only the faint outlines of the tracheid walls are preserved, and the outlines of the circular bordered pits can no longer be observed (Fig. 3.6). On the cellular level, there is also differential decay. In the areas showing less decay, some parts of the cell walls remain mostly intact, while other parts are more highly degraded (Fig. 3.1–3.3). In areas with cells with greater decay, there are varying degrees of decomposition of the middle lamina and tracheid cell wall (Fig. 3.3, 3.4).

Even more telling is the concrete and abundant evidence of the ancient fungus in the form of well-preserved mycelia (Figs. 3.7, 4, 5). The mycelia are represented by hyphae that not only extend through the tracheid cells but also pass through the crossfields into the ray parenchyma cells (Fig. 4.8). The hyphae are similar in their size and general morphology, although they can be straight, lightly curved, or highly coiled (Figs. 3.7, 4, 5).

While it is natural to expect some diagenesis to have affected wood preservation after 150 million years, it is the patchy and differential decoloration and decay in the wood tissue, along with the plenitude of fungal body fossils in the tracheid cells, that strongly point to ancient fungi as a major source of decay in this Xenoxylon tree. In living trees, selective delignification in wood and the cellular decomposition of the middle lamina and tracheid walls are strong indicators of white-rot fungi (Blanchette, Reference Blanchette1991; Schwarze et al., Reference Schwarze, Engels and Mattheck2000; Schwarze, Reference Schwarze2007). Similar patterns of decay in fossil woods have also been attributed to white-rot fungi, such as examples from the Upper Devonian of North America (Stubblefield et al., Reference Stubblefield, Taylor and Beck1985; Taylor et al., Reference Taylor, Krings and Taylor2015), uppermost Permian of China (Wei et al., Reference Wei, Gou, Yang and Feng2019), Paleozoic and Mesozoic of Antarctica (Stubblefield and Taylor, Reference Stubblefield and Taylor1985, Reference Stubblefield and Taylor1986; Harper et al., Reference Harper, Taylor, Kring and Taylor2016), Jurassic of the Tibetan Plateau (Xia et al., Reference Xia, Tian, Philippe, Yi, Wu, Li and Shi2020), Upper Jurassic of the western United States (Gee et al., Reference Gee, Xie and Zajonz2022), Lower Cretaceous of northeastern Brazil (dos Santos et al., Reference dos Santos, Guerra-Sommer, Degani-Schmidt, Siegloch, de Souza Carvalho, Mendonca Filho and de Oliveira Mendonça2020) and northeastern China (Tian et al., Reference Tian, Wang, Zheng and Zhu2020), and Eocene of southern Argentina (Pujana et al., Reference Pujana, García Massini, Brizuela and Burrieza2009).

In recent wood that has been decayed by white rot, it has been observed that the fungal hyphae growing in the lumina of the tracheids produce decay enzymes that degrade the secondary wall of the tracheids during an early stage of simultaneous rot (Schwarze et al., Reference Schwarze, Engels and Mattheck2000; Schwarze, Reference Schwarze2007). Then, in a later stage, the primary and secondary walls of the tracheids, as well as the middle lamella, are partially broken down, which results in the tracheid wall being thinner, and individual tracheid cells become slightly separated from one another (Schwarze et al., Reference Schwarze, Engels and Mattheck2000; Schwarze, Reference Schwarze2007). These characters are well developed in the decayed areas of the Xenoxylon wood from the Morrison Formation, which show tracheids with the colonization by fungal hyphae and these various types of cell-wall alterations, including the local removal of the middle lamella, decomposition of the secondary wall of tracheids, and cell-wall separation. Hence, the sequence of damage observed in recent white-rot decay suggests that the wood decay in the Xenoxylon tree was preserved after it had reached an advanced stage of simultaneous white rot.

Probable affinity of the fungus in Xenoxylon utahense.—In general, the morphology of sexual reproductive organs is essential to the taxonomic identification of extant fungi. However, due to the scarcity of reproductive organs in fossil fungi and paleomycological studies, the systematic identification of fossil fungi is extremely difficult. Thus, the recognition of other diagnostic structural features has been recognized as a practical approach to identifying certain ancient fungi. For example, the structural character of clamp connections—a hyphal protrusion during cell division to maintain the binucleate (dikaryon) condition—is commonly used to identify fossil Basidiomycota in the absence of sexual reproductive structures (Krings et al., Reference Krings, Dotzler, Galtier and Taylor2011; Taylor et al., Reference Taylor, Krings and Taylor2015).

In the Xenoxylon wood from Miners Draw area, the affinity of the white-rot fungus to the Basidiomycota is strongly supported by the clamp connections and septa in the hyphae. The occurrence of fungal hyphae with clamp connections in silicified wood is not unusual in the fossil record. The oldest fossil record of fungal hyphae with clamp connections comes from the Carboniferous fern rachis Botryopteris antiqua Kidston, Reference Kidston1908 in France (Krings et al., Reference Krings, Dotzler, Galtier and Taylor2011), although molecular clock analysis suggests that the first Basidiomycota originated during the Cambrian (Berbee and Taylor, Reference Berbee, Taylor, McLaughlin, McLaughlin and Lemke2001; Oberwinkler, Reference Oberwinkler2012). Similar clamp connections have also been described from the Carboniferous of North America (Dennis, Reference Dennis1969, Reference Dennis1970), Lower Permian of North China (Wan et al., Reference Wan, Yang, He, Liu and Wang2017), Triassic of Antarctica (Stubblefield and Taylor, Reference Stubblefield and Taylor1986; Osborn et al., Reference Osborn, Taylor and White1989), Jurassic of southwestern China (Feng et al., Reference Feng, Wei, Wang, Chen, Shen and Yang2015), Jurassic of Argentina (Gnaedinger et al., Reference Gnaedinger, García Massini, Bechis and Zavattieri2015; García Massini et al., Reference García Massini, Escapa, Guido and Channing2016), Lower Cretaceous of northeastern China (Hsü, Reference Hsü1953; Tian et al., Reference Tian, Wang, Zheng and Zhu2020), Cretaceous of Mongolia (Krassilov and Makulbekov, Reference Krassilov and Makulbekov2003; Zhu et al., Reference Zhu, Li, Xie, Tian and Wang2018), and Miocene of Argentina (Greppi et al., Reference Greppi, García Massini, Pujana and Marenssi2018).

Up to now, only three morphogenera have been established within fossil Basidiomycota on the basis of mycelia: Palaeancistrus Dennis, Reference Dennis1970, Palaeofibulus Osborn, Taylor, and White, Reference Osborn, Taylor and White1989, and Palaeosclerotium Rothwell, Reference Rothwell1972. The first genus, Palaeancistrus, is defined by septate fungal hyphae with clamp connections along with branching at mostly right angles (Dennis, Reference Dennis1970). The second genus, Palaeofibulus, is characterized by hyphal filaments with incomplete clamp connections (Osborn et al., Reference Osborn, Taylor and White1989). The third genus, Palaeosclerotium, is recognized by fungal sclerotia, which are branched septate hyphae (Rothwell, Reference Rothwell1972). However, when Singer (Reference Singer1977) reexamined the type specimen of Palaeosclerotium, he suggested that Palaeosclerotium shared affinities with the extant Ascomycota, an assessment that agrees with the conclusions of Dennis (Reference Dennis1976). In the wood of Xenoxylon from the Morrison Formation described here, the occurrence of fossil mycelia with septate fungal hyphae and typical clamp connections best corresponds to the morphological features of Palaeancistrus.

Plant–fungus interactions in the Morrison Formation

Abundant fossil plants have been reported from the Upper Jurassic Morrison Formation for nearly a century (e.g., Lutz, Reference Lutz1930); however, little is known from the ecological interactions between the Morrison plants and fungi. The first account of fossil fungi in a published paper is a short note referring to fungal remains observed in Morrison wood that neither included any illustrations (Tidwell, Reference Tidwell1990) nor was followed up by a more detailed treatment.

White-rot decay similar to that described here in the Xenoxylon utahense wood has been recently described in the wood of a giant tree of Agathoxylon hoodii (Tidwell and Medlyn) Gee et al., Reference Gee, Sprinkel, Bennis and Gray2019 from the Upper Jurassic Morrison Formation in Rainbow Draw near Dinosaur National Monument in Utah (Gee et al., Reference Gee, Xie and Zajonz2022). The Rainbow Draw wood site is located only ~18 km in a straight line from the Miners Draw wood site; these fossil localities are considered stratigraphically equivalent to one another (Sprinkel et al., Reference Sprinkel, Bennis, Gray and Gee2019), although different wood genera occur at each site (Xie et al., Reference Xie, Gee, Bennis, Gray and Sprinkel2021; Gee et al., Reference Gee, Xie and Zajonz2022). In the wood of the Agathoxylon log from Rainbow Draw, variable degrees of white-rot decay can be observed in neighbor cells. While the cell wall of a tracheid can appear seemingly intact, uniform, and dark in color, the cell walls of neighboring tracheids can appear to have lost color in only one small section or in the entire wall. In this particular Agathoxylon log, a sequence of events was reconstructed whereby the weakened and decomposed areas of wood tissue decayed by fungi facilitated the boring of large-diameter, vertical galleries by insects, most likely by beetle larvae (Gee et al., Reference Gee, Xie and Zajonz2022).

More evidence for plant–fungus interactions in the Morrison Formation was described by Tidwell et al. (Reference Tidwell, Britt and Ash1998) as abundant small and star-shaped decayed areas in fossil conifer woods from the Mygatt–Moore Quarry (MMQ) in Colorado that is similar to damage caused by modern brown rot. In this case, it was commented that the fungus in MMQ woods is similar to Stereum sanguionolentum (Albertini and Schwein ex Fries) Fries, Reference Fries and Fries1838 of the extant Stereaceae (Tidwell et al., Reference Tidwell, Britt and Ash1998).

Beyond microscopic evidence of fungal decay, macroscopic characters have also been used to understand the relationship between plants and fungi in the Upper Jurassic Morrison Formation. For example, small to large cavities measuring 1–5 cm in diameter found in the heartwood of a fossil conifer wood from the Morrison Formation were subsequently interpreted as the infestation of the tree by fungi (Hasiotis, Reference Hasiotis2004). However, the maker of these cavities may still be open to interpretation because similar cavities can also be produced by beetles (e.g., Ponomarenko, Reference Ponomarenko2003; Naugolnykh and Ponomarenko, Reference Naugolnykh and Ponomarenko2010; Feng et al., Reference Feng, Wang, Rößler, Ślipiński and Labandeira2017; Gee et al., Reference Gee, Xie and Zajonz2022).

Thus, the new plant–fungus interaction described here in Xenoxylon utahense wood offers us additional evidence for understanding the complex network of interrelationships in the Upper Jurassic. However, for a deeper and more comprehensive knowledge of trophic interactions in Morrison ecosystems, further discoveries and research are needed. Other ecological interactions between Morrison plants and fungi, for example, mutualism, have not been documented; up to now, only saprotrophic or possible parasitic wood-decay fungi have been reported (Tidwell, Reference Tidwell1990; Tidwell et al., Reference Tidwell, Britt and Ash1998; Gee, Reference Gee2015; Gee et al., Reference Gee, Xie and Zajonz2022).

Wood decay patterns and saprophytic fungi

In general, fungi are associated mainly with plants in three types of ecological interactions: parasitism, mutualism, and saprophytism (Newsham et al., Reference Newsham, Fitter and Watkinson1995). Compared with parasitism and mutualism, saprophytism is the most common plant–fungus interaction (Schwarze et al., Reference Schwarze, Engels and Mattheck2000; Schmidt, Reference Schmidt2006) and plays a significant role in carbon recycling in ancient ecosystems (Stubblefield and Taylor, Reference Stubblefield and Taylor1988; Taylor, Reference Taylor and Archangelsky1993; Taylor and Krings, Reference Taylor and Krings2010; Taylor et al., Reference Taylor, Krings and Taylor2015; Tian et al., Reference Tian, Wang and Jiang2021). For example, a fossil record of plant–fungus interactions from the Upper Devonian in Indiana, USA, was interpreted as saprophytism on the basis of wood-decay structures (Stubblefield et al., Reference Stubblefield, Taylor and Beck1985).

In regard to saprotrophs, extant wood-decay fungi are separated into three primary types in modern woods according to their pattern of degradation process in wood: brown rot, white rot, and soft rot (Schwarze et al., Reference Schwarze, Engels and Mattheck2000; Schwarze, Reference Schwarze2007; Taylor et al., Reference Taylor, Krings and Taylor2015), although some wood-decay fungi may also feed on living plants as parasites. Brown-rot and soft-rot fungi usually destroy the thick middle layer (S2) of secondary cell wall of the tracheids first, whereas white-rot fungi, which are the only fungal group known to be capable of decomposing wood lignin, generally bleach the wood tissue by degrading lignin, cellulose, and hemicellulose (Blanchette, Reference Blanchette1991; Schwarze et al., Reference Schwarze, Engels and Mattheck2000). From the degradation sequence of wood polymers, two major patterns have been recognized in white rot: selective delignification and simultaneous rot (Adaskaveg and Gilbertson, Reference Adaskaveg and Gilbertson1986; Rayner and Boddy, Reference Rayner and Boddy1988). Simultaneous rot occurs mainly in broad-leaved trees and seldom in conifers, while selective delignification occurs in both broad-leaved trees and conifers (Blanchette, Reference Blanchette1991; Schwarze et al., Reference Schwarze, Engels and Mattheck2000; Schwarze, Reference Schwarze2007) and is characterized by a selective initial degradation of lignin and hemicellulose in the cell walls of tracheids. This initial stage is then followed by degradation of cellulose in the cell walls (Schwarze et al., Reference Schwarze, Engels and Mattheck2000).

Conclusions

The occurrence of ancient Basidiomycota in an extinct conifer-like tree, Xenoxylon utahense, is described from the Upper Jurassic Morrison Formation at the Miners Draw area near Vernal in northeastern Utah. The fungal decay pattern is characterized by decolored, irregularly shaped zones or patches in the fossil wood, removal of the middle lamella, decomposition of the secondary wall in the tracheids, and separation of the tracheid wall layers, features that are characteristic of decay patterns observed in extant white rot. Abundant, well-preserved fungal hyphae with typical clamp connections in the tracheids of the Xenoxylon wood are morphologically similar to those of the fossil white-rot genus Palaeancistrus. This new discovery represents a new Upper Jurassic record of the Basidiomycota in Utah, offers further evidence for paleomycological diversity in the Morrison Formation, and sheds greater light on plant–fungus interactions in Late Jurassic terrestrial ecosystems.

Acknowledgments

We thank M.B. Bennis and D.E. Gray, Utah Field House of Natural History State Park Museum, for guiding us to the fossil site; S. Sroka, Utah Field House of Natural History State Park Museum, for logistical support; Y.D. Wang, Nanjing Institute of Geology and Palaeontology, CAS, for help in the field; K. Carpenter for the outcrop base map in Figure 1; D.A. Sprinkel, Azteca Geosolutions, for the use of Figure 2; M. Liesegang, RMS Foundation, for helpful discussion; Editor E. Currano, Associate Editor A. Sagasti (both Journal of Paleontology), and an anonymous reviewer for their constructive criticism and invaluable advice. Financial support from the China Scholarship Council for the doctoral studies of A.X. (CSC no. 201804910527) is gratefully appreciated. Fieldwork funding from Open Funding grant no. 193101 from the State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS) State Grant to C.T.G. also supported this study. This is contribution no. 44 of the DFG Research Unit FOR 2685 “The Limits of the Fossil Record: Analytical and Experimental Approaches to Fossilization.”

References

Adaskaveg, J.E., and Gilbertson, R.L., 1986, In vitro decay studies of selective delignification and simultaneous decay by the white rot fungi Ganoderma lucidum and Ganoderma tsugae: Canadian Journal of Botany, v. 64, p. 1615–1629.CrossRefGoogle Scholar
Alvin, K.L., and Muir, M.D., 1970, An epiphyllous fungus from the Lower Cretaceous: Biological Journal of the Linnean Society, v. 2, p. 55–59.CrossRefGoogle Scholar
Bannister, J.M., Conran, J.G., and Lee, D.E., 2016, Life on the phyllophane: Eocene epiphyllous fungi from Pikopiko Fossil Forest, Southland, New Zealand: New Zealand Journal of Botany, v. 54, p. 412–432.CrossRefGoogle Scholar
Berbee, M.L., and Taylor, J.W., 2001, Fungal molecular evolution: gene trees and geologic time, in McLaughlin, D.J., McLaughlin, E.G., and Lemke, P.A., eds., The Mycota VIIB: Systematics and Evolution: Berlin, Springer-Verlag, p. 229–245.CrossRefGoogle Scholar
Blanchette, R.A., 1991, Delignification by wood-decay fungi: Annual Review of Phytopathology, v. 29, p. 381–403.CrossRefGoogle Scholar
Césari, S.N., Busquets, P., Méndez-Bedia, I., Colombo, F., Limarino, C.O., Cardo, R., and Gallastegui, G., 2012, A late Paleozoic fossil forest from the southern Andes, Argentina: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 333, p. 131–147.CrossRefGoogle Scholar
Dennis, R.L., 1969, Fossil mycelium with clamp connections from the Middle Pennsylvanian: Science, v. 163, p. 670–671.CrossRefGoogle ScholarPubMed
Dennis, R.L., 1970, A Middle Pennsylvanian basidiomycete mycelium with clamp connections: Mycologia, v. 62, p. 578–584.CrossRefGoogle Scholar
Dennis, R.L., 1976, Palaeosclerotium, a Pennsylvanian age fungus combining features of modern ascomycetes and basidiomycetes: Science, v. 192, p. 66–68.CrossRefGoogle ScholarPubMed
Dilcher, D.L., 1963, Eocene epiphyllous fungi: Science, v. 142, p. 667–669.CrossRefGoogle ScholarPubMed
Dilcher, D.L., 1965, Epiphyllous fungi from Eocene deposits in western Tennessee, USA: Palaeontographica Abteilung B, v. 116, 54 p.Google Scholar
Ding, S.-T., Sun, B.-N., Wu, J.-Yu, and Li, X-.C., 2011, Miocene Smilax leaves and epiphyllous fungi from Zhejiang, East China and their paleoecological implications: Review of Palaeobotany and Palynology, v. 165, p. 209–223.CrossRefGoogle Scholar
dos Santos, Â.C.S., Guerra-Sommer, M., Degani-Schmidt, I., Siegloch, A.M., de Souza Carvalho, I., Mendonca Filho, J.G., and de Oliveira Mendonça, J., 2020, Fungus–plant interactions in Aptian tropical equatorial hot arid belt: white rot in araucarian wood from the Crato fossil Lagerstätte (Araripe Basin, Brazil): Cretaceous Research, v. 114, n. 104525, https://doi.org/10.1016/j.cretres.2020.104525.Google Scholar
Edwards, D.S., 1986, Aglaophyton major, a non-vascular land-plant from the Devonian Rhynie Chert: Botanical Journal of the Linnean Society, v. 93, p. 173–204.CrossRefGoogle Scholar
Feng, Z., Wei, H.B., Wang, C.L., Chen, Y.X., Shen, J.J., and Yang, J.Y., 2015, Wood decay of Xenoxylon yunnanensis Feng sp. nov. from the Middle Jurassic of Yunnan Province, China: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 433, p. 60–70.CrossRefGoogle Scholar
Feng, Z., Wang, J., Rößler, R., Ślipiński, A., and Labandeira, C., 2017, Late Permian wood-borings reveal an intricate network of ecological relationships: Nature Communications, v. 8, n. 556, https://doi.org/10.1038/s41467-017-00696-0.CrossRefGoogle ScholarPubMed
Fries, E.M., 1838, Stereum sanguionolentum (Alb. & Schw. ex Fr.) Fr. in Fries, E.M., Epicrisis Systematis Mycologici: seu synopsis hymenomycetum: Uppsala, p. 549.Google Scholar
García Massini, J.L., Falaschi, P., and Zamuner, A., 2012, Fungal–arthropod–plant interactions from the Jurassic petrified forest Monumento Natural Bosques Petrificados, Patagonia, Argentina: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 329, p. 37–46.CrossRefGoogle Scholar
García Massini, J.L., Escapa, I.H., Guido, D.M., and Channing, A., 2016, First glimpse of the silicified hot spring biota from a new Jurassic chert deposit in the Deseado Massif, Patagonia, Argentina: Ameghiniana, v. 53, p. 205–230.CrossRefGoogle Scholar
Gee, C.T., 2015, Conifer Paleobiodiversity in the Late Jurassic Morrison Formation, USA, and Implications for Sauropod Herbivory [Habilitationsschrift]: Bonn, Universität Bonn, 304 p.Google Scholar
Gee, C.T., Sprinkel, D., Bennis, M.B., and Gray, D.E., 2019, Silicified logs of Agathoxylon hoodii (Tidwell et Medlyn) comb. nov. from Rainbow Draw, near Dinosaur National Monument, Uintah County, Utah, USA, and their implications for araucariaceous conifer forests in the Upper Jurassic Morrison Formation: Geology of the Intermountain West, v. 6, p. 77–92.CrossRefGoogle Scholar
Gee, C.T., Xie, A., and Zajonz, J., 2022, Multitrophic plant–insect–fungal interactions across 150 million years: a giant Agathoxylon tree, ancient wood-boring beetles and fungi from the Morrison Formation of NE Utah, and the brood of an extant orchard mason bee: Review of Palaeobotany and Palynology, v. 300, n. 104627, https://doi.org/10.1016/j.revpalbo.2022.104627.CrossRefGoogle Scholar
Gnaedinger, S., García Massini, J.L., Bechis, F., and Zavattieri, A.M., 2015, Coniferous woods and wood-decaying fungi from the El Freno Formation (Lower Jurassic), Neuquén Basin, Mendoza Province, Argentina: Ameghiniana, v. 52, p. 447–467.CrossRefGoogle Scholar
Greppi, C.D., García Massini, J.L., Pujana, R.R., and Marenssi, S.A., 2018, Fungal wood-decay strategies in Nothofagaceae woods from Miocene deposits in southern Patagonia, Argentina: Alcheringa, v. 42, p. 427–440.CrossRefGoogle Scholar
Harper, C.J., Bomfleur, B., Decombiex, A., Taylor, E.L., Taylor, T.N., and Kring, M., 2012, Tylosis formation and fungal interactions in an Early Jurassic conifer from northern Victoria Land, Antarctica: Review of Palaeobotany and Palynology, v. 175, p. 25–31.CrossRefGoogle Scholar
Harper, C.J., Taylor, T.N., Kring, M., and Taylor, E.L., 2016, Structurally preserved fungi from Antarctica: diversity and interactions in late Palaeozoic and Mesozoic polar forest ecosystems: Antarctic Science, v. 28, p. 153–173.CrossRefGoogle Scholar
Hasiotis, S.T., 2004, Reconnaissance of Upper Jurassic Morrison Formation ichnofossils, Rocky Mountain Region, USA: paleoenvironmental, stratigraphic, and paleoclimatic significance of terrestrial and freshwater ichnocoenoses: Sedimentary Geology, v. 167, p. 177–268.CrossRefGoogle Scholar
Hsü, J., 1953, On the occurrence of a fossil wood in association with fungous hyphae from Chimo of East Shantung: Acta Palaeontologica Sinica, v. 1, p. 80–86. [in Chinese and English]Google Scholar
Iglesias, A.R.I., Zamuner, A.B., Poire, D.G., and Larriestra, F., 2007, Diversity, taphonomy and palaeoecology of an angiosperm flora from the Cretaceous (Cenomanian–Coniacian) in southern Patagonia, Argentina: Palaeontology, v. 50, p. 445–466.CrossRefGoogle Scholar
Kidston, R., 1908, On a new species of Dineuron and of Botryopteris from Pettycur, Fife: Earth and Environmental Science Transactions of The Royal Society of Edinburgh, v. 46, p. 361–364.CrossRefGoogle Scholar
Kidston, R., and Lang, W.H., 1921, On Old Red Sandstone plants showing structure, from the Rhynie Chert Bed, Aberdeenshire. Part V. The Thallophyta occurring in the peat-bed; the succession of the plants throughout a vertical section of the bed, and the conditions of accumulation and preservation of the deposit: Transactions of the Royal Society of Edinburgh, v. 52, p. 855–902.CrossRefGoogle Scholar
Krassilov, V.A., and Makulbekov, N.M., 2003, The first finding of Gasteromycetes in the Cretaceous of Mongolia: Paleontological Journal, v. 37, p. 439–442.Google Scholar
Krings, M., Dotzler, N., Galtier, J., and Taylor, T.N., 2011, Oldest fossil basidiomycete clamp connections: Mycoscience, v. 52, p. 18–23.CrossRefGoogle Scholar
Lutz, H.J., 1930, A new species of Cupressinoxylon (Goeppert) Gothan from the Jurassic of South Dakota: Botanical Gazette, v. 90, p. 92–107.CrossRefGoogle Scholar
Maslova, N.P., Sokolova, A.B., Kodrul, Т.M., Tobias, A.V., Bazhenova, N.V., Wu, X-K., and Jin, J.-H., 2020, Diverse epiphyllous fungi on Cunninghamia leaves from the Oligocene of South China and their paleoecological and paleoclimatic implications: Journal of Systematics and Evolution, v. 59, p. 964–984.CrossRefGoogle Scholar
McLoughlin, S., and Strullu-Derrien, C., 2016, Biota and palaeoenvironment of a high middle-latitude Late Triassic peat-forming ecosystem from Hopen, Svalbard archipelago, in Kear, B.P., Lindgren, J., Hurum, J.H., Milàn, J., and Vajda, V., eds., Mesozoic Biotas of Scandinavia and Its Arctic Territories: Geological Society, London, Special Publications, v. 434, p. 87–112.Google Scholar
Meschinelli, A., 1898, Fungorum Fossilium Omnium Hucusque Cognitorum Iconographia, 31 Tabulis Exornata, Volumen Unicum: Vicetiae, Typis Aloysii Fabris, 144 p.Google Scholar
Naugolnykh, S.V., and Ponomarenko, A.G., 2010, Possible traces of feeding by beetles in coniferophyte wood from the Kazanian of the Kama River Basin: Paleontological Journal, v. 44, p. 468–474.CrossRefGoogle Scholar
Newsham, K.K., Fitter, A.H., and Watkinson, A.R., 1995, Multifunctionality and biodiversity in arbuscular mycorrhizas: Trends in Ecology & Evolution, v. 10, p. 407–411.CrossRefGoogle ScholarPubMed
Nosova, N.V., and Kiritchkova, A.I., 2008, First records of the genus Mirovia reymanówna (Miroviaceae, Coniferales) from the Lower Jurassic of western Kazakhstan (Mangyshlak): Paleontological Journal, v. 42, p. 1383–1392.CrossRefGoogle Scholar
Oberwinkler, F., 2012, Evolutionary trends in Basidiomycota: Stapfia, v. 96, p. 45–104.Google Scholar
Osborn, J.M., Taylor, T.N., and White, J.F. Jr., 1989, Palaeofibulus gen. nov., a clamp-bearing fungus from the Triassic of Antarctica: Mycologia, v. 81, p. 622–626.CrossRefGoogle Scholar
Philippe, M., Thévenard, F., Nosova, N., Kim, K., and Naugolnykh, S., 2013, Systematics of a palaeoecologically significant boreal Mesozoic fossil wood genus, Xenoxylon Gothan: Review of Palaeobotany and Palynology, v. 193, p. 128–140.CrossRefGoogle Scholar
Ponomarenko, A.G., 2003, Ecological evolution of beetles (Insecta: Coleoptera): Acta Zoologica Cracoviensia, v. 46, p. 319–328.Google Scholar
Pujana, R.R., García Massini, J.L., Brizuela, R.R., and Burrieza, H.P., 2009, Evidence of fungal activity in silicified gymnosperm wood from the Eocene of southern Patagonia (Argentina): Geobios, v. 42, p. 639–647.CrossRefGoogle Scholar
Rayner, A.D.M., and Boddy, L., 1988, Fungal Decomposition of Wood: Its Biology and Ecology: Chichester, John Wiley.Google Scholar
Rothwell, G.W., 1972, Palaeosclerotium pusillum gen. et. sp. nov.: a fossil eumycete from the Pennsylvanian of Illinois: Canadian Journal of Botany, v. 50, p. 2353–2356.CrossRefGoogle Scholar
Sagasti, A.J., García Massini, J.L., Escapa, I.H., and Guido, D.M., 2019, Multitrophic interactions in a geothermal setting: arthropod borings, actinomycetes, fungi and fungal-like microorganisms in a decomposing conifer wood from the Jurassic of Patagonia: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 514, p. 31–44.CrossRefGoogle Scholar
Schmidt, O., 2006, Wood and Tree Fungi. Biology, Damage, Protection, and Use: Heidelberg, Springer, 334 p.Google Scholar
Schwarze, F.W.M.R., 2007, Wood decay under the microscope: Fungal Biology Reviews, v. 21, p. 133–170.CrossRefGoogle Scholar
Schwarze, F.W.M.R., Engels, J., and Mattheck, C., 2000, Fungal Strategies of Wood Decay in Trees: Berlin, Springer, 185 p.CrossRefGoogle Scholar
Singer, R., 1977, An interpretation of Palaeosclerotium: Mycologia, v. 69, p. 850–854.CrossRefGoogle Scholar
Sprinkel, D.A., Bennis, M.B., Gray, D.E., and Gee, C.T., 2019, Stratigraphic setting of fossil log sites in the Morrison Formation (Upper Jurassic) near Dinosaur National Monument, Uintah County, Utah, USA: Geology of the Intermountain West, v. 6, p. 61–76.CrossRefGoogle Scholar
Stubblefield, S.P., and Taylor, T.N., 1985, Fossil fungi in Antarctic wood: Antarctic Journal of the United States, v. 20, no. 5, p. 7–8.Google Scholar
Stubblefield, S.P., and Taylor, T.N., 1986, Wood decay in silicified gymnosperms from Antarctica: Botanical Gazette, v. 147, p. 116–125.CrossRefGoogle Scholar
Stubblefield, S.P., and Taylor, T.N., 1988, Recent advances in palaeomycology: New Phytologist, v. 108, p. 3–25.CrossRefGoogle ScholarPubMed
Stubblefield, S.P., Taylor, T.N., and Beck, C.B., 1985, Studies of Paleozoic fungi. IV. Wood decaying fungi in Callixylon newberryi from the Upper Devonian: American Journal of Botany, v. 72, p. 1765–1774.CrossRefGoogle Scholar
Taylor, T.N., 1993, The role of late Paleozoic fungi in understanding the terrestrial paleoecosystem, in Archangelsky, S., ed., XII Congrès International de Géologie du Carbonifère-Permian (Buenos Aires): Comptes Rendus, p. 147–154.Google Scholar
Taylor, T.N., and Krings, M., 2010, Paleomycology: the rediscovery of the obvious: Palaios, v. 25, p. 283–286.Google Scholar
Taylor, T.N., Krings, M., and Taylor, E.L., 2015, Fossil Fungi (first edition): London, Elsevier, 398 p.Google Scholar
Tian, N, Wang, Y.D., Zheng, S., Zhu, Z.P., 2020, White-rotting fungus with clamp-connections in a coniferous wood from the Lower Cretaceous of Heilongjiang Province, NE China: Cretaceous Research, v. 105, n. 104014, https://doi.org/10.1016/j.cretres.2018.11.011.CrossRefGoogle Scholar
Tian, N., Wang, Y.D., and Jiang, Z.K., 2021, A new permineralized osmundaceous rhizome with fungal remains from the Jurassic of western Liaoning, NE China: Review of Palaeobotany and Palynology, v. 290, n. 104414, https://doi.org/10.1016/j.revpalbo.2021.104414.CrossRefGoogle Scholar
Tidwell, W.D., 1990, Preliminary report on the megafossil flora of the Upper Jurassic Morrison Formation: Hunteria, v. 2, p. 1–11.Google Scholar
Tidwell, W.D., Britt, B.B., and Ash, S.R., 1998, Preliminary floral analysis of the Mygatt–Moore Quarry in the Jurassic Morrison Formation, west-central Colorado: Modern Geology, v. 22, p. 341–378.Google Scholar
Unger, F., 1841, Chloris Protogaea: Beiträge zur Flora der Vorwelt: Leipzig, Engelmann, 150 p.Google Scholar
Wan, M.L., Yang, W., He, X.Z., Liu, L.J., and Wang, J., 2017, First record of fossil basidiomycete clamp connections in cordaitalean stems from the Asseliane–Sakmarian (lower Permian) of Shanxi Province, North China: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 466, p. 353–260.CrossRefGoogle Scholar
Wei, H.-B., Gou, X.-D., Yang, J.-Y., Feng, Z., 2019, Fungi–plant–arthropods interactions in a new conifer wood from the uppermost Permian of China reveal complex ecological relationships and trophic networks: Review of Palaeobotany and Palynology, v. 271, n. 104100, https://doi.org/10.1016/j.revpalbo.2019.07.005.CrossRefGoogle Scholar
Xia, G., Tian, N., Philippe, M., Yi, H., Wu, C., Li, G., Shi, Z., 2020. Oldest Jurassic wood with Gondwanan affinities from the Middle Jurassic of Tibetan Plateau and its paleoclimatological and paleoecological significance: Review of Palaeobotany and Palynology, v. 281, n. 104283, https://doi.org/10.1016/j.revpalbo.2020.104283.CrossRefGoogle Scholar
Xie, A., Gee, C.T., Bennis, M.B., Gray, D., and Sprinkel, D.A., 2021, A more southerly occurrence of Xenoxylon in North America: X. utahense Xie et Gee sp. nov. from the Upper Jurassic Morrison Formation in Utah, USA, and its paleobiogeographic and paleoclimatic significance: Review of Palaeobotany and Palynology, v. 291, n. 104451, https://doi.org/10.1016/j.revpalbo.2021.104451.CrossRefGoogle Scholar
Zhu, Z.P., Li, F.S., Xie, A.W., Tian, N., and Wang, Y.D., 2018, A new record of Early Cretaceous petrified wood with fungal infection in Xinchang of Zhejiang Province: Acta Geologica Sinica, v. 92, p. 1149–1162. [in Chinese with English abstract]Google Scholar
Figure 0

Figure 1. Map of fossil locality (triangle) bearing the fossil log of Xenoxylon utahense in Miners Draw near Vernal (solid circle), Utah (dark gray in inset), USA, superimposed on the outcrops of the Upper Jurassic Morrison Formation (black). Morrison outcrop base map courtesy of Kenneth Carpenter.

Figure 1

Figure 2. Lithostratigraphic column of the Upper Jurassic Morrison Formation in Miners Draw near Vernal, Utah, USA. Legend: (1) mudstone; (2) siltstone; (3) sandstone; (4) conglomeratic sandstone; (5) conglomerate; (6) silty sandstone; (7) covered and not measured outcrop; (8) fossil log. Section modified after Sprinkel et al. (2019).

Figure 2

Figure 3. Specimen BMT-001b. Thin-section micrographs in transverse (1–4) and radial (5–7) sections of tree host Xenoxylon utahense Xie et Gee in Xie et al., 2021 from the Upper Jurassic Morrison Formation in Miners Draw, Utah, USA. (1) Overview of wood, showing several growth rings. (2) Close-up of (1) (area within red rectangle) showing details of the wood decay at different degrees of decay. LD = area with less decay; MD = more decay. (3) Close-up of (2) showing details in the area of less decay. Some parts of the cell walls remain more or less intact (white arrows), while other areas of the cell wall of the same tracheids are nearly completely degraded (red arrows). (4) Close-up of (2) showing extremely advanced disintegration of the tracheid cell walls in the area with more decay. (5) Overview of wood, in which the decolored zones appear as irregularly shaped bands or patches. (6) Close-up of (5) showing details of the decolored zones; the tracheid pitting on radial walls can no longer be observed in the decolored zone. (7) Close-up of (6) showing details of the fungal hyphae in the decolored tracheids (red arrow).

Figure 3

Figure 4. Specimen BMT-001b. Thin-section micrographs in radial section of Xenoxylon utahense with fungal hyphae. (1) Fungal hyphae passing through tracheid lumina. (2) Fungal hyphae growing along the tracheid walls, with a typical basidiomycetous clamp connection (red arrow). (3) Close-up of (2) highlighting the clamp connection (red arrow). (4) Fungal hyphae growing in the lumen of a tracheid. (5) Abundant fungal hyphae in tracheids (red arrow). (6) Close-up of (5) showing details of hyphae. (7) Another view of fungal hyphae, here in neighboring tracheids. (8) Fungal hyphae penetrating the crossfields between rays and tracheids.

Figure 4

Figure 5. Specimen BMT-001b. Thin-section micrographs in radial section of Xenoxylon utahense with fungal remains. (1, 2) Highly coiled fungal hypha. (3) Septum (between arrowheads) in a fungal hypha. (4–7) Typical basidiomycetous clamp connections (red arrows), which are sometimes associated with a bifurcation of the hyphae. (8) Highly coiled fungal hyphae (white arrow) and clamp connection (red arrow). (9) A typical clamp connection (red arrow).