Land plants

An extensive literature documents the lack of a major extinction/turnover of the terrestrial macroflora and microflora at the TJB (e.g. Orbell 1973; Schuurman 1979; Pedersen and Lund 1980; Fisher and Dunay 1981; Brugman 1983; Niklas et al. 1983; Knoll 1984; Ash 1986; Traverse 1988; Edwards 1993; Cleal 1993a, b; Kelber 1998; Hallam 2002; Tanner et al. 2004; Lucas and Tanner 2004, 2007b; Galli et al. 2005; Ruckwied et al. 2006; Kuerschner et al. 2007). Thus, for example, Ash (1986) reviewed the global record of megafossil plants and concluded that changes across the TJB boundary primarily involved seed ferns, in particular, the loss of the families Glossopteridaceae, Peltaspermaceae, and Corystospermaceae (also see Traverse 1988). This accords well with the global compilations at the species and family levels that show no substantial extinction at the TJB (Niklas et al. 1983; Knoll 1984; Edwards 1993; Cleal 1993a, b).

An exception to prevailing thought was McElwain et al. (1999), who claimed a significant macrofloral extinction at the TJB in East Greenland, although previously, Harris (1937) and Pedersen and Lund (1980) interpreted the same data to indicate species range truncations at a depositional hiatus. The TJB in East Greenland is marked by the transition from the Lepidopteris floral zone to the Thaumatopteris floral zone, with few species shared by both zones. The former is characterized by the presence of palynomorphs including Rhaetipollis, while the latter contains Heliosporites (Pedersen and Lund 1980), and although extinction of some species across the transition between the two zones is evident, many species occur in both zones. Thus, no catastrophic extinction is documented and, at most, the floral turnover in East Greenland is nothing more than a local event, as no similar event is documented elsewhere (Hallam and Wignall 1997; Tanner et al. 2004).

The palynological record provides no evidence for mass extinction at the TJB. Thus, Fisher and Dunay (1981) demonstrated that a significant proportion of the Rhaetipollis germanicus assemblage that defines the Rhaetian in Europe (Orbell 1973; Schuurman 1979) persists in lowermost Jurassic strata. Indeed, a study of the British Rhaeto-Liassic by Orbell (1973) found that of 22 palynomorphs identified in the Rhaetipollis Zone, only 8 disappeared completely in the overlying Heliosporites Zone. These authors, as well as Brugman (1983) and Traverse (1988), have concluded that floral turnover across the TJB was gradual, not abrupt. Kelber (1998) also described the megaflora and palynoflora for Central Europe in a single unit he termed "Rhaeto-Liassic," and concluded there was no serious disruption or decline in plant diversity across the TJB.

More recently, Kuerschner et al. (2007) documented in detail the transitional nature of the change in palynomorphs in the Kossen and Kendelbach formations in the Tiefengraben section (Northern Calcareous Alps). They describe a Rhaetipollis-Limbosporites zone, correlative with the C. mars hi i ammonoid zone, in which Corollina (both torosa and meyeriana) is abundant. The overlying Rhaetipollis-Porcellispora zone, in which R. germanicus disappears near the top, contains a Corollina peak, but also contains Triassic foraminifera. The succeeding Trachysporites-Porcellispora zone marks a decline in Corollina and the disappearance of Ovalipollis pseudolatus. The overlying Trachysporites-Heliosporites zone is characterized by the maximum abundance of H. reissingeri. These authors suggest that the Triassic-Jurassic boundary in this section can be placed within the Trachysporites-Porcellispora zone, which corresponds to Schuurman's (1977, 1979) Phase 4, or between it and the Trachysporites-Heliosporites zone, which corresponds to Phase 5 of Schuurman (1977, 1979).

Nevertheless, profound palynomorph extinction at the TJB has been argued from the Newark Supergroup record in eastern North America (Olsen and Sues 1986; Olsen et al. 1990; Fowell and Olsen 1993; Olsen et al. 2002a, b) (Fig. 7). Notably, the palynomorph taxa used to define the TJB in the European sections (Rhaetipollis germanicus and Heliosporites reissingeri: Orbell 1973) are not present in the Newark Supergroup basins, so placement of the palynological TJB in these basins was initially based on a graphic correlation of palynomorph records (Cornet 1977). More recent work identified the TJB in the Newark by a decrease in diversity of the pollen assemblage, defined by the loss of palynomorphs considered typical of the Late Triassic, and dominance by several species of the genus Corollina, especially C. meyeriana (Cornet and Olsen 1985; Olsen et al. 1990; Fowell and Olsen 1993; Fowell et al. 1994; Fowell and Traverse, 1995).

This change has either been equated to the TJB or, most recently, referred to as the "T-J palynofloral turnover" (Whiteside et al. 2007). But, as Kozur and Weems (2005: 33) well observed, "there are no age-diagnostic sporomorphs or other fossils to prove that this extinction event occurred at the Triassic-Jurassic boundary." Kuerschner et al. (2007) further concluded that the Newark palynological event most likely represents an older, potentially early Rhaetian event, a conclusion shared by Kozur and Weems (2005, 2007) and by Lucas and Tanner (2007b).Thus, the palynological turnover in the Newark preceded the TJB and was a regional event, not a global mass extinction. There is no evidence of a global mass extinction of land plants at the TJB.

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