The fossil record of the mosses is less complete than that of the liverworts. Krassilov and Schuster (1984) suggested that perhaps the earliest mosses evolved rapidly into drought-tolerant forms that occupied sites where fossilization was unlikely. Nevertheless, there is some record of mosses as early as the Carboniferous (e.g., Walton, 1928). One of these is Muscites plumatus, an impression of a small leafy shoot in rocks of Mississippian age (Thomas, 1972). The axis is covered with helically arranged leaves with clasping bases. Each leaf is about 7.5 mm long and terminates in an elongate tip. Sex organs, sporophyte capsule, or rhizoids were not present. Additional species of Muscites have been described from the Pennsylvanian of France (Renault and Zeiller, 1885, 1888) and the Triassic of Africa (Townrow, 1959; Anderson, 1976).
Although there are only a few records of mosses from the Carboniferous, numerous species have been described from Permian rocks, including an extensive moss flora from Siberia (Neuburg, 1960a). From this flora of well-preserved vegetative shoots, Neuburg described six genera that she assigned to the Bryales and three to a new order, the Protosphagnales. Protosphagnum (FIG. 5.23) has leaves similar to those of the extant genus Sphagnum, except for the presence of a midrib. Ignatov (1990) has also described a diverse flora of well-preserved mosses from the Upper Permian of the Russian Platform. The dozen specimens represent remains of the gametophyte generation and include forms that are referable to the extant orders Dicranales, Pottiales, Funariales, Leucodontales, and Hypnales.
To date the best documented permineralized late Paleozoic moss comes from the Permian of Antarctica (Smoot and Taylor, 1986a). Merceria augustica consists of delicate axes < 1 mm in diameter to which are attached helically arranged leaves and numerous rhizoids (FIG. 5.24). Each leaf is unistratose and contains a thickened midrib (FIG. 5.25 ). Although no evidence of reproductive organs or sporophytes was found associated with the specimens, the shape of the leaf cells, structure of the leaf margin, and anatomy of the axes suggest affinities within the Bryales.
Megafossils of Triassic and Jurassic true mosses are relatively rare and consist almost entirely of compression specimens, although these plants are often represented in palynofloras (e.g., Zavattieri and Volkheimer, 2003).
Sphagnophyllites triassicus consists ofisolated Sphagnum-like leaves from the Triassic of India (Pant and Basu, 1978). Another Mesozoic moss is Tricostium, a small Late Jurassic-Early Cretaceous specimen from Siberia, which consists of a stem densely covered with imbricate leaves, each approximately 1.2 mm long (Krassilov, 1973a); on some leaves are elongate pores. In another form from the same area, Yorekiella, the awl-shaped leaves are two or three ranked and lack midribs.
Some of the most exquisitely preserved younger Mesozoic mosses (sporophytes and gametophytes) come from the Late Cretaceous (Santonian) of North America. Gametophytes of Eopolytrichum antiquum (Polytrichaceae) (Konopka et al., 1997) have broadly lamellate leaves densely arranged around the stem. Some specimens have male "inflorescences" in the form of conspicuous rosettes of overlapping perigonal bracts, antheridia, and clavate paraphyses. Female gametophytes have not been found. Sporophytes (FIG. 5.26) consist of oblong capsules, which are terete in cross section and somewhat flattened dorsiventrally. The capsule wall consists of bulging-mammillose exothecial cells with abruptly thinned outer periclinal walls. The operculum is rounded, and an annulus is missing. The peristome consists of a short
peristomal membrane, which originates just within the rim of the capsule. Peristomal teeth are apparently lacking, but cells in the circumference of the peristomal membrane suggest that, if this species had developed teeth, there would have been 32 peristome teeth. Stomata are restricted to the apophysis and resemble those seen in extant Polytrichaceae. Campylopodium allonense (Dicranaceae) (Konopka et al., 1998) has oblong, curved, and nodding capsules (FIG. 5.27) that display a distinct basal stomatiferous swelling. The operculum is obliquely rostrate (beaked) with a smooth, cucul-late (hood-shaped), or cone-shaped calyptra. Beneath the operculum is a peristome composed of a single cycle of 16 bifid teeth (FIG. 5.28) . The spores are spherical, 10-12pm
in diameter, and display a delicate rugose sculpture. Associated sterile gametophytes consist of leafy stem portions; fertile gametophytes have not been found.
The Cenozoic record of mosses is considerably more extensive than that of the Paleozoic and Mesozoic, and includes impression-compression specimens (FIG. 5.295.31) and amber fossils (N. Miller, 1980, 1984) (Table 5.1) . Aulacomnium heterostichoides from deep-water varved clays (Eocene) of a freshwater lake in British Columbia (Janssens et al., 1979) is an example of a well-preserved compression of a moss gametophyte. The plant is irregularly branched (FIG. 5.30) and contains helically arranged, elliptical leaves with multicellular teeth along the upper half of the margin. The cells of the upper laminal surface are regularly isodiametric and uni-papillose, whereas those of the basal surface are rectangular with slightly thicker walls. Based on an analysis of characters in existing populations of Aulacomnium, the fossil is believed to be most closely related to A. heterostichum, a living species found in eastern North America and eastern Asia.
Numerous Cenozoic mosses are preserved in amber from the Baltic, Bitterfeld (Germany), and the Dominican Republic (e.g., Frahm, 1993, 1994, 1996a, b, c, 1999a, b, 2000, 2001b, 2004a, b, 2006a, b; Frahm and Reese, 1998; Frahm and Newton, 2005) (Table 5.1) . The mosses present in the amber can either be assigned to modern species or represent fossil species belonging to modern genera; others cannot be referred to any modern species, and are therefore assigned to morphogenera such as the compression genera Dicranites (FIG. 5.31), Hypnites, and Muscites.
At least 30 genera of mosses have been recorded from Baltic and Saxon amber. Several of the moss species preserved in Baltic amber (e.g., Trachycystis flagellaris) still exist today, but their occurrence is restricted to eastern and/ or southeastern Asia. This suggests that these forms became
extinct in Europe as a result of the Quaternary climatic changes, but persisted in Asia (Frahm, 2001a). Other mosses from Baltic amber (e.g., Haplocladium angustifolium) represent species that today still occur in Europe, but are restricted to the Southern Alps as Cenozoic relicts. The inventory of mosses preserved in Dominican amber includes representatives of almost 20 genera (Frahm and Newton, 2005; Frahm,
figure 5.32 Hypnodontopsis conferta (Eocene). Bar =1.5 mm. (Courtesy J.-P. Frahm.)
2006a). Most of the species are also known today from the Neotropics, which suggests that the foundation of the neotropical moss flora was in existence as early as the Paleogene (45-25 Ma) (Frahm, 2001a).
Most mosses in amber occur as sterile gametophytes or gametophyte fragments; fertile gametophytes and sporo-phytes are comparatively rare. One fossil example of a gametophyte with attached sporophyte is Dicranites grollei from Eocene Baltic amber (Frahm, 1999b). This fossil consists of the distal portion of a stem with 14 linear leaves, each up to 1.8 mm long. The stem apex bears a twisted seta that terminates in a round, distally constricted capsule, which displays 6 (probably originally 16) short, lancet-like, undivided peristome teeth. Another example that includes gametophyte and sporophyte in organic connection is Hypnodontopsis conferta (Baltic amber) (Frahm, 2001b, 2004a). One of the specimens is a complete plant, consisting of a stem bearing numerous linear leaves and a complete sporophyte (FIG. 5.32). The seta is 1.5-2mm long, twisted, and cygneous (shaped like the neck of a swan). It terminates in a short, oval capsule with 16 longitudinal ribs. The capsule is open and displays the peristome, where the 16 peristomal teeth are fused into eight pairs. Complete plants displaying game-tophyte and sporophyte in organic connection have also been reported from Saxonian amber (e.g., Campylopodiella cf. himalayana; Frahm, 1996b).
figure 5.32 Hypnodontopsis conferta (Eocene). Bar =1.5 mm. (Courtesy J.-P. Frahm.)
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All theory, dear friend, is grey, but the golden tree of life springs ever green.
Johann Wolfgang von Goethe, Faust: The Tragedy, Part I
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