Uncalcified Red Algae

The most exquisitely preserved, early uncalcified red algae, some of which may be distantly related to the Corallinales, were discovered in the Neoproterozoic (~600 Ma) Doushantuo Formation at Weng'an, South China (Xiao et al., 2004, and references therein). The fossils are phosphatized and thus possess cellular preservation. They are particularly interesting because they help bridge the stratigraphic and evolutionary gap between the earliest rhodophyte fossils and the calcified red algae described from younger strata. The most distinctive feature of the phosphatized Doushantuo algae described by Xiao et al. (2004) is their filamentous construction or cell fountain

FIGURE 4.52 Section of Karpathia sphaerocellulosa thallus (Paleocene). Bar = 300 pm. (From Bassi et al., 2005.)

architecture. Thalli of Wengania globosa are broadly spherical, nodular, or irregular, 70-750 pm in diameter in thin section, and display a simple pseudoparenchymatous construction (FIG. 4.53) , in which cortex and medulla are not differentiated. The thalli consist of cuboidal cells that form regular files, radiating outward and branching toward the thallus margin. In W. exquisita, cell files are less regularly arranged, whereas in the third species, W. minuta, regular cell files are absent (Xiao, 2004). Similar simple thalli are formed by Thallophycoides pholeatus and Gremiphyca corymbiata ( FIG. 4.54 ). These thalli may be lobed, however, with the most profound lobation occurring in G. corymbiata. Thalli of Thallophyca ramosa and T. corrugata (FIG. 4.55) display a complex pseudoparenchy-matous construction, in which there is a clear differentiation into an inner medulla and outer cortex (FIG. 4.56), with cortical cells either smaller than the medullary cells or arranged differently, and clustered cell islands interpreted as reproductive cells (Y. Zhang et al., 1998). The pseudoparenchyma is arrayed as upward diverging splays of filaments or cell fountains. Diverging filaments form fan-shaped lobes separated by deep invaginations. Particularly striking are cylindrical, cell-lined invaginations that resemble conceptacles. Thalli of Paramecia incognata are millimeter-sized nodules characterized by cortex-medulla differentiation, thallus compartmentalization (FIG.

4.57), and absence of well-developed invaginations (FIG.

4.58). Xiao et al. (2004) stated that the complex pseudoparenchymatous thalli of Thallophyca and Paramecia display features resembling those seen in some Paleozoic members of the Corallinales, and thus these forms may be interpreted as stem group corallinaceans. They are clearly different from the crown group corallines, however, in that they are not calcified in life (Xiao and Knoll, 1999).

Neoproterozoic Plants

Thallophyca corrugata (Neoproterozoic). Bar = 100 pm. (From

FIGURE 4.53 Simple pseudoparenchymatous thallus of Xiao et al., 2004; courtesy S. Xiao.) Wengania globosa (Neoproterozoic). Bar = 50pm. (From Xiao et al., 2004; courtesy S. Xiao.)

Thallophyca corrugata (Neoproterozoic). Bar = 100 pm. (From

FIGURE 4.53 Simple pseudoparenchymatous thallus of Xiao et al., 2004; courtesy S. Xiao.) Wengania globosa (Neoproterozoic). Bar = 50pm. (From Xiao et al., 2004; courtesy S. Xiao.)

Pseudoparenchymatous Green Algae
FIGURE 4.54 Gremiphyca corymbiata showing simple pseudoparenchymatous, lobed thallus (Neoproterozoic) Bar = 100 pm. (From Xiao et al., 2004; courtesy S. Xiao.)

Another genus of anatomically preserved multicellular algae from the Doushantuo Formation is Sarcinophycus (Xiao and Knoll, 1999; Xiao, 2004). It differs from the previously detailed Doushantuo algae in that the thalli lack the cell fountain architecture and possess marginal protuberances

Calcified Algae
FIGURE 4.56 Detail of complex pseudoparenchymatous thallus of Thallophyca corrugata (Neoproterozoic). Bar = 100pm. (From Xiao et al., 2004; courtesy S. Xiao.)

(FIGS. 4.59,4.60). The systematic affinities of Sarcinophycus remain uncertain. Paratetraphycus giganteus (Z. Zhang, 1985) is yet another multicellular alga-like organism from the Doushantuo Formation. Although initially assigned to the cyanobacteria (Chroococcaceae-like coccoids; Z. Zhang, 1985), certain features have been noted that are reminiscent of extant bangiomorphic red algae (Y. Zhang et al., 1998;

Classification Algae
FIGURE 4.57 Detail of thallus of Paramecia incognata showing compartmentalized clusters (arrow) of larger, probably reproductive cells (Neoproterozoic). Bar = 100 pm. (From Xiao et al., 2004; courtesy S. Xiao.)

Saunders and Hommersand, 2004). Paratetraphycus gigan-teus has been reported from the Meso-Neoproterozoic (middle Riphean) in the southern Urals (Sergeev and Lee, 2006).

Some of the earliest compression fossils indicative of diverse, marine uncalcified macroalgal floras come from the Neoproterozoic of South China. These morphotypes, such as Doushantuophyton (centimeter-sized thallus fragments composed of erect, repeatedly forking branches) (FIG. 4.61), Konglingiphyton (centimeter-sized dendritic thalli), and Miaohephyton (millimeter-sized dichotomously branched thallus fragments characterized by horizontal constrictions), suggest affinities with the Rhodophyta. Other genera, such as Enteromorphites (centimeter-sized, branched thalli

FIGURE 4.58 Complex parenchymatous thallus of Paramecia incognata (Neoproterozoic). Bar = 100pm. (From Xiao 2004; courtesy S. Xiao.)

attached to the substrate by a holdfast) (FIG. 4.62), Gesinella (centimeter-sized, lanceolate or strap-shaped thalli with a basal holdfast), and Yemaomianiphyton (centimeter-sized tuft-like thalli composed of a strong holdfast and forked or unforked erect branches), have been interpreted as either red, green, or brown algae (Steiner, 1994). It has also been interpreted as fragmentary specimens of Enteromorphites (Xiao et al., 2002). A detailed study on the holdfast structures formed by some of the Neoproterozoic macroalgae from China and their paleoenvironmental implications has recently been published by Wang and Wang (2006). The assignment of Miaohephyton to the red algae has been questioned by Xiao et al. (1998), who suggested that this form may represent a brown alga with possible affinities in the order Fucales. Enteromorphites siniansis is an organism composed of several forked hollow tubes <17 mm long that arise from a basal holdfast. It was initially interpreted as being structurally similar to the extant green alga Enteromorpha (Ulvales) (Zhu and Chen, 1984), but Steiner

Neoproterozoic
FIGURE 4.59 Sarcinophycus radiatus showing radiating packets of cells (Neoproterozoic) Bar = 100|im. (From Xiao and Knoll, 1999; courtesy S. Xiao.)
FIGURE 4.61 Doushantuophyton lineare. (Redrawn from Steiner, 1994.)
Calcified Algae
FIGURE 4.62 Enteromorphites intestinalis thallus. (From Xu, 2001.)

(1994) noted that this structure may also resemble various red and brown algae. Enteromorphites intestinalis from the Early Cambrian Chengjiang Biota in southeastern China is a considerably larger (>7cm high) form, composed of hollow unbranched tubes that were attached to the substrate by a basal rhizoidal cell or tubular proliferations (Xu, 2001b).

Paradelesseria sanguinea is a Delesseria- or Phycodrys -like red alga from the Chengjiang Biota (Xu, 2004). The thallus is composed of leaf-like, lanceolate, or oblanceo-late and petiolate blades <90mm long that are attached to a subcylindrical, nodose stipe (FIG. 4.63). Two other enigmatic organisms from the Chengjiang Biota that have been variously interpreted as algae are Longfengshania cordata, a small thallus (2 cm high) composed of a bladelike distal portion and a hollow, stalk-like proximal portion (FIG. 4.64) , and Plantulaformis sinensis (1 cm high), a cotyledon-like thallus composed of a two-parted distal blade and hollow, stalk-like proximal portion (FIG. 4.65) (Xu, 2002). Hofmann (1985a) suggested that Longfengshania may represent algae with possible affinities in the red or brown algae. Z. Zhang (1988), however, interpreted Longfengshania as an early

FIGURE 4.63 Reconstruction of Paradelesseria sanguinea. (From Xu, 2004.)

bryophyte. Another diverse early algal flora has been reported from the Middle Cambrian Kaili Biota in Guizhou Province, China (Yang et al., 2001). This flora consists of more than 20 genera, 5 of which have tentatively been assigned to the red algae, Palaeocodium , Paraamphiroa , Wahpia , Dalyia , and Bosworthia. Thalli of Paraamphiroa siniansis are <1.5 cm high and composed of a main branch that distally produces a cluster of second-order, bi- or trifurcating branches, each consisting of uncalcified joints and calcified, cylindrical segments. This alga is believed to represent the earliest fossil evidence for a calcified red alga (Yang and Zhao, 2000).

Dalyia has also been reported from the Middle Cambrian Conasauga Formation in northwestern Georgia (USA) where it co-occurs with several putative green algae (Schwimmer and Montante, 2007), and from the Middle Cambrian Burgess Shale in British Columbia, Canada (Walcott, 1919), along with a second red alga, Waputikia ramosa ( FIG. 4.66 ). The latter differs markedly from other Precambrian and Cambrian algae as it displays a more complex morphology in the form of a central axis interrupted by large branches,

Green Algae Fossil
FIGURE 4.64 Reconstruction ofLongfengshania cordata. (From Xu, 2002.)
Green Algae Fossil
FIGURE 4.66 Suggested reconstruction of Waputikia ramosa. (From Briggs et al., 1994.)

FIGURE 4.65 Reconstruction of Plantulaformis sinensis. (From Xu, 2002.)

which in turn bear a profusion of smaller branches and terminal filaments (Briggs et al., 1994).

Several extant red algae possess morphologies that are similar to the Late Ordovician alga Manitobia patula. In this form, the laminar thallus divides in a single plane, with each segment further divided into three, nearly uniform segments. The margin of the thallus is entire, and the apex of each segment typically truncated (Fry, 1983). Three macroscopic Devonian algae occur in marine rocks in New York (Fry and Banks, 1955). Drydenia (FIG. 4.67) consists of elliptical laminae (8.5 cm long) that are basally attached to a narrow stipe terminating in a branching holdfast. In Hungerfordia (FIG. 4.68), also recorded from the Late Devonian of South Africa (Hiller and Gess, 1996), the lamina is highly dichoto-mous with the distal segments lobed. Specimens of Enfieldia are circular (5.0 cm in diameter), with the outer margin lobed, and characterized by distinct reticulations. Both Drydenia and Hungerfordia have been compared with existing red and brown algae; Enfieldia is more difficult to position systematically, perhaps representing a thalloid liverwort.

Dichota Algae
FIGURE 4.67 Drydenia foliata (Devonian). Bar = 4cm. (From Fry and Banks, 1955.)

The genus Perissothallus (FIG. 4.69) comprises several types of uncalcified macroalgae from Late Pennsylvanian and Early Permian freshwater environments of North America and Europe. The thallus consists of repeatedly dichotomizing, erect cylindrical branches that radiate from a small holdfast (Krings et al., 2007d). Vegetative reproduction occurs in the form of secondary thalli produced on prostrate branches. Striking similarities in basic structure exist between Perissothallus and members of the extant marine red algal genus Scinaia (Nemaliales), but the fossils superficially resemble species of the extant genera Codium (green algae) and Dictyota (brown algae). Another putative late Paleozoic red alga consists of a central axis with nodes of lateral appendages (FIG. 4.70 ).

Bassonia hakelensis is a Cenomanian (Late Cretaceous) marine fossil from the Haqel fish beds in Lebanon that

Fossil Algae
FIGURE 4.68 Dichotomous thallus of Hungerfordia dichotoma (Devonian). Bar = 2.5cm. (From Fry and Banks, 1955.)
Fossil Green Algae
FIGURE 4.69 Perissothallus showing branches radiating from holdfast (Pennsylvanian). Bar = 1 cm.

appears as a compressed, irregularly branched thallus, <20.0 cm long (Basson, 1972; Krings and Mayr, 2004). The thallus is more or less monopodially organized and attached to the substrate by a circular holdfast (FIG. 4.71). At irregular intervals, the main long shoot produces second-order long shoots. Numerous determinate short shoots bearing spine-like outgrowths (?trichoblasts) extend from the long shoots and give the whole thallus a spiny appearance. The basic morphology of the spine-bearing short shoots of B. hakelensis closely resembles the extant red alga Pithyopsis tasmanica (Ceramiales) that occurs along the coasts of southern

Litografias Eva Reptil
FIGURE 4.70 Grateloupia sp. (Permian). Bar = 2 cm.

Australia and Tasmania (Krings and Mayr, 2004). Another red alga from the Haqel fish beds is Delesserites lebanensis (Basson, 1981). This compressed, Delesseria- like thallus is ~9.5 cm long and includes several blades that radiate from a common stipe (FIG. 4.72). Nothing is known about the holdfast or reproductive organs of this alga.

The early Oligocene Haeringiella multifidiformis (FIG. 4.73- is characterized by a bladelike thallus attached to the substrate by a disk-like holdfast (Krings and Butzmann, 2005). The thallus is formed of a central axis that produces irregularly shaped lateral branches. Branches in the proximal portion of the thallus are closely spaced or clustered

Red Algae Fossil
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