End-Triassic Nonmarine Biotic Events

S. G. Lucas and L. H. Tanner End-Triassic nonmarine biotic events

Journal of Palaeogeography, (2015), 4, (4): 331-348 (00083) doi: 10.1016/j.jop.2015.08.010

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Biopalaeogeography and palaeoecology End-Triassic nonmarine biotic events Spencer G. Lucasa, *, Lawrence H. Tannerb a New Mexico Museum of Natural History, 1801 Mountain Road NW, Albuquerque, New Mexico 87104-1375 USA b Department of Biological Sciences, Le Moyne College, 1419 Salt Springs Road, Syracuse, NY 13214 USA

Received 1 July 2015; accepted 18 August 2015 Available online

KEYWORDS Abstract The Late Triassic was a prolonged interval of elevated extinction rates and low Triassic-Jurassic origination rates that manifested themselves in a series of extinctions during Carnian, Norian boundary, and Rhaetian time. Most of these extinctions took place in the marine realm, particularly af- mass extinction, fecting radiolarians, conodonts, bivalves, ammonoids and reef-building organisms. On land, land plants, the case for a Late Triassic mass extinction is much more tenuous and has largely focused on East Greenland, tetrapod vertebrates (amphibians and reptiles), though some workers advocate a sudden end- tetrapods, Triassic (TJB) extinction of land plants. Nevertheless, an extensive literature does not identify Newark Supergroup, a major extinction of land plants at the TJB, and a comprehensive review of palynological CAMP volcanism records concluded that TJB vegetation changes were non-uniform (different changes in different places), not synchronous and not indicative of a mass extinction of land plants. Claims of a substantial perturbation of plant ecology and diversity at the TJB in East Greenland are indicative of a local change in the paleoflora largely driven by lithofacies changes resulting in changing taphonomic filters. Plant extinctions at the TJB were palaeogeographically localized events, not global in extent. With new and more detailed stratigraphic data, the perceived TJB tetrapod extinction is mostly an artifact of coarse temporal resolution, the compiled correlation effect. The amphibian, archosaur and synapsid extinctions of the Late Triassic are not concentrated at the TJB, but instead occur stepwise, beginning in the Norian and extending into the Hettangian. There was a disruption of the terrestrial ecosystem across the TJB, but it was more modest than generally claimed. The ecological severity of the end-Triassic nonmarine biotic events are relatively low on the global scale. Biotic turnover at the end of the Triassic was likely driven by the CAMP (Central Atlantic Magmatic Province) eruptions, which caused significant environmental perturbations (cooling, warming, acidification) through outgassing, but the effects on the nonmarine biota appear to have been localized, transient and not catastrophic. Long-term changes in the terrestrial biota across the TJB are complex,

* Corresponding author. E-mail address: [email protected]. Peer review under responsibility of China University of Petroleum (Beijing). http://dx.doi.org/10.1016/j.jop.2015.08.010. 2095-3836/Copyright © 2015, China University of Petroleum (Beijing). Production and hosting by Elsevier B. V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 332 S. G. Lucas and L. H. Tanner

diachronous and likely climate driven evolutionary changes in the context of fluctuating background extinction rates, not a single, sudden or mass extinction.

1 Introduction (Schoene et al., 2010; Fig. 1). Correlation of nonmarine and marine biochronology in The biodiversity crisis at the end of the Triassic (Tri- the Late Triassic-Early Jurassic remains imprecise. Here, assic-Jurassic boundary: TJB) has long been identified as we primarily rely on the correlations based on tetrapod bi- one of the “big five” mass extinctions of the Phanerozoic ostratigraphy and biochronology (land-vertebrate faunach- (Sepkoski, 1982). However, during the last decade, we have rons) advocated by Lucas (1998, 2008, 2010b), Lucas et questioned this identification of a severe and sudden biotic al. (2007a, 2012) and Lucas and Tanner (2007b) (Fig. 1). decline at the TJB (Hallam, 2002; Lucas and Tanner, 2004, Many Late Triassic megafossil plant localities can be di- 2008; also see Tanner et al., 2004). Instead, our thesis is that the Late Triassic was a prolonged (approximately 30‑million-year-long) interval of elevated extinction rates and low origination rates that manifested themselves in a series of discrete extinctions during Carnian, Norian and Rhaetian time. Most of these extinctions took place in the marine realm, particularly affecting radiolarians, conodonts, bivalves, ammonoids and reef-building organisms (Lucas and Tanner, 2008). On land, the case for a Late Triassic mass extinction is much more tenuous and has largely focused on tetrapod vertebrates (amphibians and reptiles), though some workers advocate a sudden end-Triassic extinction of land plants as well. Here, we focus on the Late Triassic record of land plants and terrestrial tetrapods to demonstrate that they do not document a sudden or a severe end-Triassic extinction. From a palaeogeographical point of view, the nonmarine fossil record identifies some local extinctions across the TJB, but no global mass extinction.

2 Late Triassic-Early Jurassic timescale

We use the standard global chronostratigraphic timescale for the Late Triassic-Early Jurassic compiled by Ogg (2012a, 2012b), but modified with regard to some recent data and analyses of its radioisotopic calibration (Lucas et al., 2012; Ogg et al., 2014; Wotzlaw et al., 2014) (Fig. 1). The base of one of the three Late Triassic stages (Carni- an) has an agreed on GSSP (global stratotype section and point), and the base of the Norian stage will be defined by a conodont datum that is close to the traditional ammonoid- based boundary (Balini et al., 2010; Krystyn et al., 2007; Lucas, 2010a, 2013b; Orchard, 2010, 2013, 2014). The favored definition of the Rhaetian base has as its primary signal the LO (lowest occurrence) of the conodont Misikella posthernsteini. At present, the only fully published GSSP candidate for the Rhaetian base is the Stein- bergkogel section near Hallstatt, Austria (Krystyn et al., 2007). However, Giordano et al. (2010) concluded that the LO of Misikella posthernsteini is actually younger at Steinbergkogel than it is in the section they studied in the Lagronegro basin in southern Italy, so the Italian section may become the GSSP location. The GSSP defined for the TJB (base of Jurassic System = base of Hettangian Stage) Figure 1 Correlation of the Late Triassic-earliest Jurassic stand- is correlated by the lowest occurrence of the ammonoid ard global chronostratigraphic scale (sgcs) to tetrapod biochro- Psiloceras spelae (Hillebrandt et al., 2013). The best nu- nology based on land-vertebrate faunachrons (lvfs). See text for merical calibration places this boundary close to 201.4 Ma sources. End-Triassic nonmarine biotic events 333 rectly related to this tetrapod-based biochronology (e.g., placement. Thus, for example, Sha et al. (2011, 2015) re- Lucas, 2013a). Palynostratigraphic correlations in much of cently placed the TJB in nonmarine strata of the Junggur this interval are discussed in a comprehensive way by Cirilli Basin in northwestern China using palynomorphs and non- (2010) and Kürschner and Herngreen (2010). Conchostracan marine bivalves that cannot be unambiguously correlated biostratigraphy for the Late Triassic-Early Jurassic also can with precision to any other TJB section. be tied directly to the tetrapod biostratigraphy and bio- More problematic are nonmarine sections where the TJB chronology (Kozur and Weems, 2005, 2007, 2010; Lucas et can only be approximated, and that approximation sepa- al., 2011, 2012; Weems and Lucas, 2015). rates very different nonmarine fossil assemblages that dif- An extremely important point is that correlation of Late fer in age by many millions of years. A good example of Triassic nonmarine biochronology to the standard global this is provided by the study of the tetrapod record in the chronostratigraphic scale is achieved primarily by cor- Gondwana basins of India by Bandyopadhyay and Sengupta relation to the Germanic basin section, where marine in- (2006). This record has an obviously Late Triassic tetrapod tercalations and other data provide a reasonably precise assemblage (with phytosaurs, aetosaurs, etc.) of likely No- cross-correlation to the marine Upper Triassic sections in rian age in the lower Dharmaram Formation, overlain hun- Austria and Italy (Kozur and Bachman, 2005, 2008; Kozur dreds of meters higher by the clearly Jurassic (likely Sine- and Weems, 2010; Lucas, 2010a, 2010b). For the Lower Ju- murian), dinosaur-dominated tetrapod assemblage of the rassic, nonmarine-marine correlation tiepoints exist (e.g., Kota Formation. All that intervenes are two undescribed Lucas, 2008), but are constrained in much less detail than tetrapod taxa — a sphenodontian and a plateosaurid dino- is the Upper Triassic record. saur — from the upper Dharmaram Formation. Lucas and Magnetostratigraphy also provides some service to cor- Huber (2003) suggested these fossils are likely Late Triassic relation of nonmarine and marine strata across the TJB, in age, but Bandyopadhyay and Sengupta (2006) assigned but not the precision always needed. The Rhaetian-early them a Hettangian age. They then claimed the Gondwana Hettangian interval is a time of dominantly normal po- basin record shows a substantial turnover in tetrapods at larity, and each section studied reveals from two to four the TJB, even though the two assemblages in India that short intervals of reversed polarity in the dominantly nor- are comparable across that boundary are likely Norian and mal Rhaetian-Hettangian multichron (e.g., Hounslow and Sinemurian in age, and thus separated by at least 6 million Muttoni, 2010; Hounslow et al., 2004; Lucas and Tanner, years, invalidating their conclusion. 2007b; Lucas et al., 2011; Marzoli et al., 2004). Correlation Another example comes from the work of Pieńkowski et of these short reversals to each other is not straightforward al. (2011, 2014) in Poland, where late Norian tetrapod body and forces a reliance on biostratigraphic or chemostrati- fossils are compared to Hettangian(?) footprint assemblag- graphic inferences to provide precise correlations within es and show a change from diverse, dicynodont‑ and ar- the Rhaetian-Hettangian multichron (for example, see Lu- chosaur-dominated faunas to dinosaur-dominated footprint cas and Tanner, 2007b, Fig. 7). faunas. Dinosaur-dominated footprint faunas, however, are Incorrect placement of the TJB boundary in the Newark also known from the Late Triassic (e.g., Lucas, 2007), so Supergroup long confounded nonmarine-marine correla- the comparison of the Polish Norian bone and Hettangian(?) tions and gave the impression of a significant extinction footprint records does not necessarily reflect biotic turno- of plants and tetrapods at the TJB (see discussion below). ver across the TJB. However, well supported and now well accepted correlation of the TJB in the Newark section (Cirilli et al., 2009; Kozur and Weems, 2005, 2007, 2010; Lucas and Tanner, 2007b; 3 TJB terrestrial record Olsen et al., 2011, 2015; Whiteside et al., 2010) moves the boundary upward stratigraphically to a level well removed It is fair to say that only seven places on Earth have from any evidence of a sudden biotic turnover. a record of non-marine TJB fossil plants and tetrapods of Correlation of nonmarine strata to the now defined TJB sufficient extent, diversity and stratigraphic density to be in marine strata is achieved by some workers using either relevant to evaluating a TJB extinction: (1) Chinle-Glen palynostratigraphy or carbon isotope stratigraphy. How- Canyon Group succession of the American Southwest; (2) ever, palynostratigraphy does not unambiguously identify Newark Supergroup strata of the eastern seaboard of North the boundary in many sections (Bonis and Kürschner, 2012; America from Nova Scotia to the Carolinas, and including Bonis et al., 2009; Pieńkowski et al., 2011). And, many rift basin deposits of Morocco in North Africa; (3) Jameson nonmarine carbon isotope records rely on too few data Land in eastern Greenland; (4) European records inside and points to convincingly identify the carbon-isotope excur- outside of the Germanic basin, particularly in Germany, the sions recognized in marine sections across the TJB or pro- United Kingdom and Italy; (6) northwestern Argentina; and duce records with such high noise levels as to defy correla- (7) the Karoo basin of South Africa (Fig. 2). tion (e.g., McEwain et al., 1999). Recent examples of such Today, and (based on actualism) during the TJB inter- problematic carbon-isotope-based correlations of the TJB val, much terrestrial diversity is accounted for by monerans in nonmarine strata include Gómez et al. (2007) in Spain, and arthropods. Yet, the monerans have virtually no fos- Whiteside et al. (2010) in the USA, Pieńkowski et al. (2011, sil record, and the record of arthropods across the TJB is 2014) in Poland and Hesselbo et al.’s (2002) carbon-isotope essentially nonexistent for many groups. Arthropod groups curve in East Greenland, discussed below. that have relatively good TJB fossil records, such as ostra- Nevertheless, such considerations do not deter some cods and conchostracans, show no significant extinction at workers from precise placement of the TJB in nonmarine the TJB (e.g., Kozur and Weems, 2010). Insects also have sections where few if any data exist to support precise a fossil record that shows no evidence of a diversity crash 334 S. G. Lucas and L. H. Tanner

Figure 2 Principal localities that are referred to in the text where the nonmarine Triassic-Jurassic boundary interval has a dense fossil record: A = Argentina, C= Chinle basin, American Southwest, G = Germanic basin, J = Jameson Land, East Greenland, K=Karoo basin, South Africa and N=Newark Supergroup basins. across the TJB (Grimaldi and Engel, 2005; Labandeira and Traverse, 1988). Most reviews identify only the extinction Sepkoski, 1993). Indeed, Grimaldi and Engel (2005, p. 73) of peltasperms, a clade of seed ferns, at the TJB. Global concluded, “there seems to have been little differentia- compilations at the species and family levels show no sub- tion between insect faunas of the Late Triassic and Early stantial plant extinction at the TJB (Cleal, 1993a, 1993b; Jurassic.” Edwards, 1993; Knoll, 1984; Niklas et al., 1983). A recent Plant diversity across the TJB is based on a much be‑ analysis by Cascales-Miñana and Cleal (2012: 76-77) con- tter fossil record, both in the form of megafossil plants cluded that “the changes observed in the plant fossil record and their microfossil “proxies,” the palynomorphs (sporo- in the Late Triassic Series are mainly reflecting an ecologi- morphs). The record of terrestrial fossil vertebrates across cal reorganization of the terrestrial habitats weeding-out the TJB is comparable in quality to the plant record, and it some of the families of less adaptable plants that had filled shows no evident extinction of freshwater fishes (McCune the newly available niches during Triassic times, rather and Schaeffer, 1986; Milner et al., 2006). Supposed TJB than a global ecological crisis on the scale of that seen at tetrapod extinctions focus on three principal groups: tem- the end of Permian times.” nospondyl amphibians, some archosaur taxa and some syn- Some data do reveal local turnover of paleofloras across apsid taxa. These records have been evaluated using both the TJB. A good example is a study of Swedish benettital- body fossils (bones and teeth) and trace fossils (footprints). eans that documented restriction of two species to the Rhaetian followed by five species restricted to the Hettan- gian. However, this is not considered by its authors, Pott 4 Land plants and McLoughlin (2009: 117), as anything more than a “moderate taxonomic turnover,” and it is a palaeogeographically local event. 4.1 Overview Contrary to prevailing thought, McElwain and collaborators (Bacon et al., 2013; Belcher et al., 2010; Mander et An extensive literature does not identify a major extinc- al., 2010, 2012; McElwain and Punyasena, 2007; McElwain tion of land plants at the TJB (e.g., Ash, 1986; Brugman, et al., 1999, 2007, 2009) claim significant changes in the 1983; Burgoyne et al., 2005; Cascales-Miñana and Cleal, megaflora at the TJB in East Greenland (Fig. 3). Accord- 2012; Cleal, 1993a, 1993b; Edwards, 1993; Fisher and Du- ing to these workers, these encompass a sudden change nay, 1981; Galli et al., 2005; Hallam, 2002; Kelber, 1998; from high diversity Late Triassic plant communities to lower Knoll, 1984; Kuerschner et al., 2007; Lucas and Tanner, diversity and less taxonomically even Early Jurassic com- 2004, 2007b, 2008; McElwain and Punyasena, 2007; Niklas munities. This is the only location where a case has been et al., 1983; Orbell, 1973; Pedersen and Lund, 1980; Ruck- made for a major turnover in the megaflora at the TJB, wied et al., 2008; Schuurman, 1979; Tanner et al., 2004; but we question whether the data support recognition of End-Triassic nonmarine biotic events 335

Figure 3 Measured secion of Triassic-Jurassic boundary interval of Kap Stewart Group in East Greenland showing distribution of megafossil plants and published carbon-isotope curve. The lithologic column is modified from McElwain et al. (2007) and shows megafossil plant beds using their scheme (1, 1.5, 2, etc.) followed by the scheme used by Harris (1937) in parentheses (Equisetites, A, B, etc.). The carbon isotope curve is from Hesselbo et al. (2002). 336 S. G. Lucas and L. H. Tanner a megafloral crisis in East Greenland of more than local the Astartekløft section is the well documented (in marine palaeogeographic significance. sections) negative excursion in carbon then it is not the TJB, but instead a point in the Rhaetian (e.g., Hillebrandt 4.2 Plant extinctions in East Greenland et al., 2013; Lucas et al., 2007b; Mander et al., 2013; Ruhl et al., 2010). Thus, all the events McElwain and collabora- The Astartekløft section of the Primulaev Formation of tors associate with the TJB actually preceded it. the Kap Stewart Group in Jameson Land, East Greenland The chemostratigraphic correlation proposed by Hes- (Fig. 3) apparently encompasses the TJB and records the selbo et al. (2002) relies on the presence of an unconform- transition from the Lepidopteris floral zone to the Thau- ity at 47 m in the Astartekløft section. Questions should matopteris floral zone, with few species shared by both be raised about the nature of this unconformity and the zones (Harris, 1937). The former is characterized by the temporal magnitude of the hiatus it represents, as well as presence of palynomorphs, including Rhaetipollis, while the associated substantial change in lithofacies (Fig. 3). the latter contains Heliosporites (Pedersen and Lund, Indeed, we note that most of the megafossil plant assem- 1980), and although extinction of some species across the blages below that level are from mudrock-dominated inter- transition between the two zones is evident, many species vals, whereas almost all of those above that level are from occur in both zones. Thus, Harris (1937: 76) emphasized sandstone (Fig. 3). According to McElwain et al. (2007, p. that “real mixing” of the two floral zones occurs over a 551), the mudrock likely represents floodplain deposits of 10 m interval (Fig. 3), and “this is real mixing….the two mainly autochthonous plants, whereas the sandstones rep- sets of plants will be seen on the same bedding plane and resent channel and splay deposits that also include alloch- they continue to be found together from top to bottom, of thonous plants. However, in evident contradiction to parts one of these beds….” Therefore, the data and analyses of of their text and measured stratigraphic section, McElwain Harris (1937) and Pedersen and Lund (1980) did not iden- et al. (2007, table 1) identify all the plant localities up tify an abrupt change in the land plants across the TJB in through their bed 5 as coming from “sheet splay” deposits, Jameson Land. Furthermore, what species turnover looks the plants from bed 6 as from a coal swamp (though no coal abrupt in this section was attributed by Harris (1937) and is present in the section at Astartekløft) and their plant Pedersen and Lund (1980) to species range truncations at a beds 7 and 8 as coming from abandoned channels. In the depositional hiatus, an unconformity also recognized in the absence of more data (e.g., detailed lithologic descriptions Astartekløft section by Dam and Surlyk (1993) and Hesselbo of the plant-bearing strata) and an actual sedimentological et al. (2002) (Fig. 3). analysis of the plant-bearing beds, we are not able to re- In contrast, in this section McElwain and collaborators solve these evident contradictions in the study of McElwain claim: (1) a sudden, 85% drop in species diversity at the et al. (2007). TJB (based on megafossil plants but not reflected in the Instead, it seems evident that the section at Astartekløft palynomorph record); (2) a decrease in the relative abun- embodies a major lithofacies change at an unconformity, dance of common plant species at the TJB; (3) a change from a mudstone‑ and sheet-sandstone-dominated deposi- in leaf physiognomy to larger and rounder leaves; (4) an tional system to a thick, channel-sandstone-dominated sys- increase in charcoal indicative of wildfire at the TJB; and tem (Fig. 3). On face value, it preserves two taphofloras in (5) an increase in chemical damage to sporomorphs at the different lithofacies, and this raises the possibility that at TJB. They see all but possibly the last of these as indicative least some of the apparent floral change inferred by McEl- of a “super greenhouse” caused by CAMP (Central Atlantic wain and collaborators is due to the change in the depo- Magmatic Province) eruptions. sitional system (lithofacies). Assuming the TJB is present We question, though, the validity of the placement of in this section near the 47 m level, the megafossil plant the TJB in the Astartekløft section. McElwain and collabo- assemblages across the TJB are clearly not “isotaphonom- rators place it at about the 47 m level of this section, bas- ic” (as claimed by McElwain et al., 2007), so they are not ing that placement on the carbon isotope record published strictly comparable to each other in terms of composition, by Hesselbo et al. (2002) (Fig. 3). This record shows an diversity and relative abundance. apparent, but modest (~2 ‰), negative excursion beginning According to McElwain and collaborators, a substantial at about the 45 m level. We note that this “excursion” co- perturbation of plant ecology and diversity is preserved incides with an unconformity of unknown duration. Hence, at the TJB in East Greenland. We suggest that the data the relationship of the isotopic trend above this hiatus to they present are indicative of a palaeogeographically lo- the missing, underlying strata is undetermined. Moreover, cal change in the paleoflora largely driven by lithofacies the general isotopic trend for this section bears little simi- changes resulting in changing taphonomic filters. No cata- larity to the published isotope stratigraphy for sections of strophic land plant extinction is documented and, at most, putative identical age. the floral turnover in East Greenland is nothing more than Nevertheless, Hesselbo et al. (2002) assumed that the a palaeogeographically local event, as no similar, coeval base of the excursion represents the “initial isotope excur- event is documented elsewhere (Hallam and Wignall, 1997; sion” and that the remainder records the “main isotope Lucas and Tanner, 2008; Tanner et al., 2004). Furthermore, excursion” seen in marine sections that cross the TJB (e.g., whatever happened to the megaflora in East Greenland, it Ruhl et al., 2010). Therefore, the intervening section with happened very late in the Triassic, not at the TJB. a more positive isotopic trend (spanning 4 m at St. Audrie’s Bay in England) is conveniently missing, so we regard Hes- 4.3 Plant microfossils selbo et al.’s (2002) correlation as tenuous at best. Further- more, if the initial negative excursion at the ~ 45 m level in Like the megafossil plant record, the palynological re- End-Triassic nonmarine biotic events 337 cord provides no evidence for a mass extinction of land indicate vegetation changes that are non-uniform (differ- plants at the TJB (Bonis and Kürschner, 2012). Decades ago, ent changes in different places), not synchronous and not Fisher and Dunay (1981) demonstrated that a significant indicative of a mass extinction of land plants. They attrib- proportion of the Rhaetipollis germanicus assemblage that uted these changes to climate change driven by CAMP vol- defines the Rhaetian in Europe (e.g., Orbell, 1973; Schuur- canism that produced a warmer climate and stronger mon- man, 1979) persists in lowermost Jurassic strata, and this soonal flow across Pangea, which developed drier interiors remains the case (e.g., Bonis and Kürschner, 2012; Bonis et and wetter coastal regions. As they well put it, “…instead al., 2009; Cirilli, 2010; Kürschner and Herngreen, 2010). of a major and globally consistent palynofloral extinction Brugman (1983) and Traverse (1988) thus concluded that event, the TJB is characterized by climate-induced quan- floral turnover across the TJB was gradual, not abrupt. titative changes in the sporomorph assemblages that vary Kelber (1998) described the megaflora and palynoflora for regionally in magnitude and composition” (Bonis and Kür- Central Europe in a single unit he termed “Rhaeto-Liassic,” schner, 2012: 256). In summary, there is no evidence of a and concluded there was no serious disruption or decline in global mass extinction of land plants at the TJB. plant diversity across the TJB. More recently, Kuerschner et al. (2007) and Bonis et al. (2009) documented the transi- tional nature of the change in palynomorphs across the TJB 5 Tetrapods in the Northern Calcareous Alps of Austria (also see Hille- brandt et al., 2013), and the palynomorph record in East Greenland also does not document an abrupt TJB extinction 5.1 Overview (Mander et al., 2010, 2013). Nevertheless, profound palynomorph extinction at the The idea of a substantial nonmarine tetrapod extinction TJB was long identified in the Newark Supergroup record in at the TJB began with Colbert (1949, 1958), and has been eastern North America by Olsen and collaborators (Cornet, more recently advocated by Olsen et al. (1987, 1990, 2002a, 1977; Cornet and Olsen, 1985; Fowell and Olsen, 1993; Ols- 2002b). Nevertheless, Weems (1992), Benton (1994), Lucas en and Sues, 1986; Olsen et al., 1990, 2002a, 2002b). Their (1994), Tanner et al. (2004) and Lucas and Tanner (2004, work identified the TJB in the Newark section by a decrease 2007b, 2008) rejected this conclusion. in diversity of the plant microfossil assemblage, defined by Colbert (1958) concluded that the temnospondyl am- the loss of palynomorphs considered typical of the Late Tri- phibians, a significant component of many late Paleozoic assic, followed by dominance of the palynoflora by several and Early-Middle Triassic tetrapod assemblages, under- species of the genus “Corollina” (= Classopollis), especial- went complete extinction at the TJB. However, these tem- ly C. meyeriana (Cornet and Olsen, 1985; Fowell and Olsen, nospondyls are only a minor component of Late Triassic 1993; Fowell and Traverse, 1995; Fowell et al., 1994; Olsen tetrapod assemblages, being of low diversity and relatively et al., 1990). They thus placed the TJB in the Newark sec- small numbers in most stratigraphic units (e.g., Hunt 1993; tion at the base of the Classopollis meyeriana palynofloral Long and Murry, 1995). Moreover, current data demonstrate zone (Fig. 4). These workers attached considerable impor- the disappearance of most of the temnospondyls — capi- tance to a peak abundance of trilete spores at this level, tosaurids, metoposaurids and latiscopids — at or just be- which they termed a “fern spike” (Cornet and Olsen, 1985; fore the Norian-Rhaetian boundary, and only one family ex- Fowell and Olsen, 1993; Fowell et al., 1994; Whiteside et tinct at the end of the Triassic (plagiosaurids) (Milner, 1993, al., 2007). Although not present in all of the Newark basins 1994; Schoch and Milner, 2000). Late Triassic temnospondyl (e.g., Cirilli et al., 2009), an increase in trilete spores has extinctions thus largely preceded the TJB. been noted in some European sections, where the acme To Colbert (1958), the bulk of the TJB tetrapod extinc- zone is referred to as the Triletes Beds (Kuerschner et al., tion was in the disappearance of the “thecodonts.” These 2007; Ruhl et al., 2010; van de Schootbrugge et al., 2009). “thecodonts” were more recently referred to as the cruro- As noted by van de Schootbrugge et al. (2009), however, tarsans (phytosaurs, aetosaurs and rauisuchians), though occurrences of a fern-dominated flora at the level of this that name is no longer advocated by the latest cladistic apparent palynological turnover are limited strictly to the analysis (Nesbitt, 2011). Phytosaurs, aetosaurs and raui- Northern Hemisphere. suchians are the only members of Colbert’s “thecodonts” This palynofloral change has been referred to as the “T-J to have a substantial Norian or younger fossil record based palynofloral turnover” (Whitesideet al., 2007) or the “Pas- on current data. Other groups of thecodonts that have saic palynofloral event” (Lucas and Tanner, 2007b). But, as been portrayed by some as going extinct at the TJB either Kozur and Weems (2005: 33) well observed, “there are no lack Rhaetian records (for example, the Ornithosuchidae: age-diagnostic sporomorphs or other fossils to prove that von Baczko and Ezcurra, 2013) or have so-called Rhaetian this extinction event occurred at the Triassic-Jurassic records of problematic age, such as records from British boundary.” Indeed, Kuerschner et al. (2007) concluded that fissure-fill deposits (e.g., Fraser, 1994). the Newark palynological event most likely represents an A non‑“thecodont” group that did go extinct during the older, potentially early Rhaetian event, a conclusion shared Rhaetian is the Procolophonidae (Fig. 5). However, procolo- by Kozur and Weems (2005, 2007, 2010) and by Lucas and phonids were a group of low diversity by Norian time, and Tanner (2007b). Thus, the palynological turnover in the many of their so-called Rhaetian records are from British Newark preceded the TJB (Fig. 4) and was a palaeogeo- fissure fills (e.g., Fraser, 1994). The tetrapod taxa from graphically regional event, not a global mass extinction. these fissure fills are mostly endemic taxa of no biochrono- Bonis and Kürschner (2012) provided a comprehensive logical significance or cosmopolitan taxa with long strati- review of TJB palynological records to conclude that they graphic ranges. As Lucas and Hunt (1994: 340) noted, “a 338 S. G. Lucas and L. H. Tanner

Figure 4 Biostratigraphic correlation of the Newark Supergroup section from the Late Triassic through the Triassic-Jurassic boundary. Note unconformities indicated by missing conchostracan zones. Modified from Kozur and Weems (2010), Lucas et al. (2012) and Weems and Lucas (2015). single age should not necessarily be assigned to the fossils difficult to test. We accept that it documents phytosaur from one fissure and....individual fossils from the fissures persistence into the earliest Jurassic, contradicting the may range in age from middle Carnian to Sinemurian.” We longstanding assumption of their extinction at the TJB. thus regard as problematic the precise age of many of the There are no demonstrable aetosaur or rauisuchian Triassic tetrapod fossils from the British fissure fills. body fossils in Rhaetian strata (Desojo et al., 2013; Lucas, Phytosaur fossils are known from Rhaetian-age strata in 2010b; Nesbitt et al., 2013), though Nesbitt et al. (2013) the Newark section, the Glen Canyon Group and the Ger- mentioned a possible Early Jurassic rauisuchian from south- manic basin (e.g., Lucas and Tanner, 2007a; Olsen et al., ern Africa, based on a single snout fragment that they also 2002a, 2002b; Stocker and Butler, 2013). A Lower Jurassic stated may be of a large crocodylomorph. Aetosaur and phytosaur record has been documented by Maisch and Ka- rauisuchian body fossil records thus suggest their extinc- pitzke (2010). This is an unabraded snout fragment found tion before Rhaetian time. in the lowermost Jurassic pre-planorbis beds (Neophyllites Nevertheless, the footprint ichnogenus Brachychirothe- zone) at Watchet in England. Stocker and Butler (2013) ex- rium is known from Rhaetian strata, and Lucas and Heckert pressed skepticism about the stratigraphic provenance of (2011) argued that an aetosaur was the trackmaker. Note this record, and it may be a reworked fossil, a possibility that Smith et al. (2009) reported what they identified as End-Triassic nonmarine biotic events 339 chirothere tracks from the Lower Jurassic Elliot Forma- et al., 1987, 1990, 2002a, 2002b; Szajna and Silvestri, tion of Lesotho in southern Africa, but as Klein and Lucas 1996; Silvestri and Szajna, 1993) (Fig. 5). However, a close (2010) noted, these tracks differ from chirothere footprints examination of all Triassic tetrapod taxa known from the in significant ways and are more likely large crocodylo- Newark Supergroup identifies only three body-fossil taxa morph tracks. The available stratigraphic data thus sug- (indeterminate phytosaurs, the procolophonid Hypsogna- gest a three-step extinction of the “crurotarsans” — first, thus and sphenodontians) in the youngest Triassic strata, rauisuchians by the end of the Norian, second, aetosaurs which are strata of Rhaetian age (Huber et al., 1993; Kozur (based on the footprint ichnogenus Brachychirotherium) by and Weems, 2010; Lucas and Huber, 2003). Recent collect- the end of the Rhaetian and third, phytosaurs in the early ing has not changed that, and only a few fragmentary tetra- Hettangian (Fig. 6). pod fossils are known from the Newark extrusive zone and Synapsids of the Late Triassic are dicynodonts and cy- are not age diagnostic (Lucas and Huber, 2003; Lucas and nodonts (e.g., Abdala and Ribeiro, 2010; Lucas and Hunt, Tanner, 2007b). 1994; Lucas and Wild, 1995). Most Late Triassic dicynodont The McCoy Brook Formation, which overlies the only records are Carnian, with a couple of post-Carnian records CAMP basalt of the Fundy basin in Nova Scotia, yields a as young as late Norian (Dzik et al. 2008; Lucas, 2015; Lu- tetrapod assemblage generally considered Early Jurassic in cas and Wild, 1995; Szulc et al., 2015). The Late Triassic age by vertebrate paleontologists (Fedak et al., 2015; Lu- cynodont record is more extensive, especially in Gond- cas, 1998; Lucas and Huber, 2003; Lucas and Tanner, 2007a, wana. Traversodontids have a relatively diverse record in 2007b; Olsen et al., 1987; Shubin et al., 1994). However, the Carnian-Norian and a single Rhaetian record (note that this assemblage could straddle the marine-defined TJB the Gondwana cynodont-bearing strata assigned a Rhaetian given that Cirilli et al. (2009) demonstrated that at least age by Abdala and Ribeiro, 2010 are actually Norian: Lucas, the lowermost McCoy Brook strata (lower part of Scots Bay 2010b). Trithelodontids cross the TJB, and a problematic Member) are Rhaetian. group of tooth-based taxa, the “dromatheriids,” disappears Indeed, very recently, Sues and Olsen (2015) and Fedak in the Rhaetian (Lucas and Hunt, 1994). Note, though, that et al. (2015) have assigned a latest Triassic (Rhaetian) age the origin and diversification of mammaliaforms, which to an assemblage of vertebrate fossils from the “fish bed” likely include the “dromatheriids,” began in the Late Tria‑ in the Scots Bay Member of the McCoy Brook Formation ssic (e.g., Newham et al., 2014). On present evidence, a TJB that includes the crocodylomorph Protosuchus and the tri- synapsid extinction is thus of a handful of taxa, with most tylodont Oligokyphus. These two taxa are known only from taxa extinct by Rhaetian time, but others crossing the TJB. Jurassic strata elsewhere (e.g., Lucas and Tanner, 2007a), and their assignment to the Rhaetian is based on inferred 5.2 Newark tetrapod record cyclostratigraphic correlations (Sues and Olsen, 2015), not on direct association with Triassic fossils. Therefore, we The recent case for a mass extinction of tetrapods at question the age assignment of the “fish bed” to the Trias- the TJB has relied heavily on the Newark Supergroup re- sic, though we also note that if correctly assigned a Rhae- cord of tetrapod fossils (e.g., Olsen and Sues 1986; Olsen tian age, it pushes the temporal record of Protosuchus and

Figure 5 Stratigraphic ranges of tetrapod footprint ichnogenera and body fossil taxa across the Late Triassic (Rhaetian) Passaic palynofloral event in the Newark section. Modified and updated after Olsen et al. (2002a). 340 S. G. Lucas and L. H. Tanner of Oligokyphus back into the Triassic, thus diminishing the the result of a rapid (thousands of years) evolutionary re- apparent turnover in tetrapod taxa across the TJB. sponse by the theropod survivors of a mass extinction and Because the Newark body fossil record of tetrapods is referred to it as “ecological release” (Olsen et al., 2002a: sparse across the TJB and inadequate to evaluate a po‑ 1307). They admitted that this can be invalidated by the ssible tetrapod extinction, the tetrapod footprint record description of Dilophosaurus-sized theropods or diagnostic in the Newark Supergroup has been used as a proxy (e.g., Eubrontes tracks in verifiably Triassic-age strata. Olsen and Sues, 1986; Olsen et al., 2002a,2002b; Szajna Indeed, tracks of large theropod dinosaurs assigned to and Silvestri, 1996). However, detailed stratigraphic study Eubrontes (or its possible synonym Kayentapus) are known of the Newark footprint record indicates nothing more than from the Triassic of Australia, Africa (Lesotho), Europe moderate turnover in the footprint assemblage at a within- (Great Britain, France, Italy, Germany, Poland-Slovakia, Rhaetian stratigraphic level below the lowest CAMP basalt Scania) and eastern Greenland, invalidating the “ecologi- sheet (Fig. 5). Similar changes in tetrapod footprint assem- cal release” hypothesis (Bernardi et al. 2013; Lucas et al., blages are also known from the Chinle Group-Glen Canyon 2006b; Niedźwiedzki, 2011). A detailed review of these re- Group section of the American Southwest and from the Ger- cords indicates Carnian, Norian and Rhaetian occurrences manic Basin (e.g., Lucas et al., 2006a; Lucas, 2007). of tracks that meet the definition of Eubrontes established The footprint turnover in the Newark section (Fig. 5) is by Olsen et al. (1998). Also, theropods large enough to supposedly the disappearance of four ichnogenera in the have made at least some Eubrontes-size tracks have long uppermost Passaic Formation, and the appearance of three been known from the Late Triassic body-fossil record (e.g., ichnogenera at that datum (Olsen et al., 2002a, 2002b). The Langer et al., 2009). Thus, the sudden abundance of these ichnogenera that disappear represent phytosaurs (Apatopus: tracks in the Newark Supergroup cannot be explained sim- Klein and Lucas, 2013), aetosaurs (Brachychirotherium: Lu- ply by the rapid evolution of small theropods to large size cas and Heckert, 2011) and tanystropheids (Gwynnedichni- following a mass extinction. The concept of a sudden ap- um: Lucas et al., 2014). There are single Newark records of pearance of Eubrontes tracks due to “ecological release” Procolophonichnium (procolophonid: Baird, 1986) just beat the TJB thus proposed by Olsen et al. (2002a, 2002b) can low the turnover level and a single record of Ameghinichnus be abandoned. (mammaliaform: de Valais, 2009) above the level. According to Olsen et al. (2002a, 2002b), the ornithis- 5.3 Conclusions chian dinosaur footprint ichnogenus Anomoepus first appears at this level, but a later detailed review of the ich- With new and more detailed stratigraphic data, the long nogenus by Olsen and Rainforth (2003) indicated that the perceived TJB tetrapod extinction looks mostly like an ar- lowest stratigraphic record of Anomoepus is stratigraphi- tifact of coarse temporal resolution, the compiled corre- cally higher, in the Newark extrusive zone (Fig. 5). The lation effect of Lucas (1994). Thus, Colbert (1958) knew, crocodylomorph footprint ichnogenus Batrachopus appears and we still know, that Late Triassic tetrapod assemblages at the turnover level, but there are older Triassic body in Laurussian locales are dominated by phytosaurs, with fossil records of crocodylomorphs (Klein and Lucas, 2010; lesser numbers of aetosaurs, rauisuchians and dinosaurs. Nesbitt et al., 2013). Olsen et al. (2002a, 2002b) showed Some Gondwanan Late Triassic assemblages are cynodont the prosauropod-dinosaur-footprint ichnogenus Otozoum (mostly traversodontid) and rhynchosaur dominated. In appearing in the upper Passaic Formation, but a later revi- contrast, well known Early Jurassic tetrapod assemblages sion of the ichnogenus by Rainforth (2003) established its are dinosaur dominated, with lesser numbers of crocodylo- stratigraphically lowest record as Jurassic, in the Newark morphs and cynodonts (tritylodontids), and no phytosaurs, extrusive zone (Fig. 5). The lacertoid footprint ichnogenus aetosaurs or rauisuchians. But, the former are Norian, and Rhynchosauroides has its last Newark record in the upper the latter are Sinemurian age assemblages, separated in Passaic Formation, but this ichnogenus has Jurassic records time by at least 6 million years. elsewhere (Avanzini et al., 2010). Given the lack of evidence for TJB plant and arthropod Thus, what the Newark tetrapod footprint and body-fos- extinctions, what could have caused a TJB tetrapod extinc- sil record show is the local extinction of phytosaurs (they tion? Aetosaurs, some of the cynodonts and all of the dicy- have a younger record elsewhere), aetosaurs, tanystrop- nodonts perceived of as suffering extinction are inferred heids and procolophonids (this may be the level of their herbivores, whereas the phytosaurs and rauisuchians are global extinction). That is the extent of the turnover in inferred predators. Given that many herbivores — notably tetrapod taxa it documents, and the turnover level in the the prosauropod dinosaurs — continue through the TJB, a Newark is at a Rhaetian horizon, not at the TJB (Fig. 5). sudden trophic collapse of vertebrate communities on land Part of the footprint turnover in the Newark section is cannot be supported. Instead, the extinctions of tetrapods the local lowest occurrence of the theropod footprint ich- during the Late Triassic appear to be a prolonged series of nogenus Eubrontes (as defined by Olsen et al., 1998, i.e., events that began in the Norian and extended into the Het- tridactyl theropod pes tracks longer than 28 cm). For dec- tangian (Fig. 6). ades, much was made of this record of Eubrontes. Thus, Olsen and Galton (1984) concluded that the lowest occurrence of Eubrontes marks the base of the Jurassic, and 6 Ecological severity Olsen et al. (2002a, 2002b) later argued that the sudden appearance of Eubrontes in the “earliest Jurassic” strata of McGhee et al. (2004, 2013) argued that mass extinc- the Newark Supergroup indicates a dramatic size increase tions need to be evaluated not just as biodiversity crises in theropod dinosaurs at the TJB. They interpreted this as (crashes), but also in terms of their ecological severity. In End-Triassic nonmarine biotic events 341 their scheme of ecological severity, they considered the tal volume ejected during the initial eruptive episode (Mar- TJB nonmarine extinction to be in their category I or IIa. zoli et al., 2011). Category I means that ecosystems before the extinction The total duration of the CAMP eruptions has been esti- were replaced by new ecosystems post-extinction, whereas mated at ~600 ky by cyclostratigraphy (Olsen et al., 1996). category IIa means that the extinctions caused permanent The initial estimate of the size of the province, by McHone loss of major ecosystem components. Clearly, as we have and Puffer (1996), was ~2.3 × 106 km2, but Deckart et al. pointed out earlier (Lucas and Tanner, 2008), this is a gross (1997) and Marzoli et al. (1999) extended the boundaries of overestimate of the ecological significance of whatever ex- the province to include all areas near the rift margin con- tinctions took place on land across the TJB. taining mafic intrusions of approximately correlative age, McGhee et al. (2004) concluded that the TJB involved a ultimately outlining an area of 11 × 106 km2. Defining the rapid ecological replacement of Triassic mammal-like rep- vast potential aerial extent of CAMP led to an erupted lava tiles and rhynchosaurs by dinosaurs. However, the strati- volume calculation of ~2 × 106 km3, similar to the volume graphically highest rhynchosaurs are Revueltian (early- calculated for the Deccan Traps. As noted by Tanner et al. middle Norian), and the group was largely gone by the end (2004), however, this calculation entails the assumption that of the Carnian (Hunt and Lucas, 1991; Lucas et al., 2002; the entire area was covered by lava to an average depth of Spielmann et al., 2013). Late Norian dicynodonts are now hundreds of meters. Even in the Newark basin, however, known (Dzik et al., 2008; Szulc et al., 2015) and document where the entire erupted thickness is preserved, the total a small presence in the post Carnian, unless a putative thickness varies widely, from ＞ 1 km to as little as tens of Cretaceous record (with problematic provenance) from meters. Therefore, we regard this assumption as untenable. Australia is verified (Thulborn and Turner, 2003). The other It is widely acknowledged that floral and faunal turnover principal group of Late Triassic mammal-like reptiles, the at the end of the Triassic was likely driven by the CAMP cynodonts, were of low diversity after the Carnian-Norian eruptions, which caused a significant environmental per- (Abdala and Ribeiro, 2010; Lucas and Hunt, 1994). Dino- turbation through outgassing (e.g., Belcher et al., 2010; saurs appeared as body fossils in the Carnian and began to Blackburne et al., 2013; Bonis et al., 2009; Haworth and diversify substantially in some parts of Pangea by the late Raschi, 2014; Ruhl et al., 2010; Schoene et al., 2010; van Norian (e.g., Langer, 2014; Langer et al., 2009). de Schootbrugge et al., 2009; Tanner et al., 2004). Atten- Thus, the ecological severity of the end-Triassic tetra- tion has focused largely on the potential for greenhouse pod extinction is relatively low (Category IIb on the McGhee warming produced by the outgassed CO2 (Berner and Beer- et al., 2004 classification), and the plant extinctions do not ling, 2002; McElwain et al., 1999; Steinthorsdottir et al., look like they were ecologically severe either (see above). 2011), but many of these studies ignore the constraints of Clearly, there was no substantial disruption of the terres- the likely volume of erupted lava and gas content. Yapp and trial ecosystem (excluding some local perturbations) across Poths (1996), for example, estimated a catastrophic 18‑fold the TJB. increase in atmospheric CO2 across the TJB, whereas Tan- ner et al. (2001) calculated a much more modest increase (of several hundred ppm), and more recently, Steinthors- 7 The role of CAMP volcanism dottir et al. (2011) calculated a CO2 doubling (by 2000 to 2500 ppm). The tremendous divergence in the published

In the marine realm, the end-Triassic drop in diversity estimates of atmospheric CO2 loading from CAMP outgassing was selective but notable for the rapid loss of specific taxa, stems from the different approaches used to generate the such as conodonts, radiolarians, infaunal bivalves and am- calculations. McElwain and collaborators (e.g., McElwain et monoids, suggesting physical processes that strongly affect- al., 1999; Steinthorsdottir et al., 2011) rely primarily on the ed ocean bioproductivity (Tanner et al., 2004). For many stomatal response of plants to elevated CO2 levels, while years, the hypothesis was advanced that the extinctions others (Cleveland et al., 2008; Schaller et al., 2012; Tan- were associated with a single catastrophic cause, specifi- ner et al., 2001) utilize the isotopic composition of pedo- cally, the Manicouagan bolide impact, the remnant crater genic carbonates. These approaches also yield diverging of which spans ~ 70 km in southern Quebec, Canada (Olsen estimates for the pre-eruption atmospheric composition, et al., 1987, 2002a, 2002b). However, this hypothesis was knowledge of which is essential to determining the warming firmly disproved by radioisotopic dating of the Manicouagan effects of CAMP outgassing. Thus, there is as yet no agree- structure, which showed that the impact occurred ~ 14 Ma ment on the mass of CO2 released by the CAMP eruptions, prior to the TJB (Hodych and Dunning, 1992; Onoue et al., much less agreement on the climatic consequences. 2012; Ramezani et al., 2005). Tanner et al. (2004, 2007) drew attention to the lack of

Subsequently, attention on the TJB “extinctions” has fo- consideration of the effects of SO2 outgassing by the CAMP cused primarily on the environmental effects of the erup- eruptions, and further demonstrated that high atmospheric tion of the flood basalts of the Central Atlantic Magmatic SO2 loading also can force changes in plant stomatal fre- Province (CAMP). Formerly, the onset of CAMP eruptive ac- quency, an effect eventually noticed by other workers (Ba- tivity was assumed to post-date the TJB (Whiteside et al., con et al., 2013). The environmental effects of large sulfur 2007), but it is now well-established that these eruptions emissions during prolonged flood basalt eruptions are not span the boundary (Cirilli et al., 2009; Kozur and Weems, clear, but the formation of H2SO4 aerosols, which in addition 2005, 2007, 2010; Lucas and Tanner, 2007b). Within the ba- to causing acidic precipitation, are known to increase at- sins of the Newark Supergroup, the eruptions proceeded in mospheric opacity and result in reduced short-wave radiant three main episodes, separated by eruptive hiatuses during heating, causing global cooling (Sigurdsson, 1990). Fluorine which sediments accumulated, with the majority of the to- and chlorine volatile emissions during the CAMP eruptions 342 S. G. Lucas and L. H. Tanner

Figure 6 Some biotic events across the Triassic-Jurassic boundary. also would have contributed to the acidification of surface and low origination rates in many biotic groups (e.g., Bam- waters and terrestrial environments (Guex et al., 2004; Lu- bach et al., 2004; Kiessling et al., 2007; Lucas and Tanner, cas and Tanner, 2008; van de Schootbrugge et al., 2009). 2008). Most of the evidence for this comes from the marine Thus, a temporary loss of phytoplankton productivity biota, with multiple Late Triassic, and often substantial in marine surface waters is an entirely reasonable conse- extinctions of radiolarians, conodonts, bivalves, ammo- quence of the CAMP eruptions. The subsequent “trickle- noids and reef-building organisms. In the marine realm, down” effects through the marine trophic system are clear, these events are: (1) early-middle Carnian boundary (the even without climate change. Primary producers would “Carnian crisis”), which included major extinctions of cri- have been most profoundly affected by the changes in wa- noids (especially the Encrinidae), echinoids, some bivalves ter chemistry, but higher level consumers would also have (scallops), bryozoans, ammonoids, conodonts and a major felt ecological pressure, although perhaps less strongly. The change in the reef ecosystem; (2) a substantial extinction compounding effects of climate change-rapid, short-term of conodonts, ammonoids and some bivalves (especially cooling forced by H2SO4 aerosols and slower, longer-term pectinids) at the Carnian-Norian boundary; (3) within and warming driven by CO2 - would have exacerbated the envi- at the end of the Norian, when there are several extinc- ronmental stresses on the ecosystems. Thus, floral and fau- tion events that had a particularly profound effect on cono- nal turnover at the end of the Triassic was likely driven by donts, marine bivalves and ammonoids; and (4) a final set the CAMP eruptions, which caused significant environmen- of stepwise extinctions, particularly of ammonoids and tal perturbations (cooling, warming, acidification) through conodonts, within and at the end of the Rhaetian. (e.g., outgassing, but the effects on the nonmarine biota appear Flügel, 2002; Hallam, 1995; Hornung et al., 2007; Johnson to have been palaeogeographically localized, transient and and Simms, 1989; Lucas and Tanner, 2008; Schäfer and Fois, not catastrophic. 1987; Tanner et al., 2004) On land, plant and tetrapod extinctions were much less dramatic. Within the Carnian most workers envision a hu- 8 End Triassic nonmarine biotic events mid phase (or “pluvial”) as a possible cause of some turnover of terrestrial taxa, at least in Europe (e.g., Hornung The Late Triassic was a time of elevated extinction rates et al., 2007; Rigo et al., 2007; Simms and Ruffell, 1989, End-Triassic nonmarine biotic events 343

1990), though this has been disputed (e.g., Visscher et al., 9. Bandyopadhyay, S., Sengupta, D. P., 2006. Vertebrate faunal 1994). There is an end-Carnian event in the terrestrial tet- turnover during the Triassic-Jurassic transition: An Indian rapod record, with some evolutionary turnover across the scenario. New Mexico Museum of Natural History and Science Carnian-Norian boundary (Benton, 1986, 1991, 1993; Lucas, Bulletin, 37, 77-85. 1994). Extinctions on land closer to the TJB look even less 10. Belcher, C. M., Mander, L., Rein, G., Jervis, F. X., Haworth, significant. The amphibian, archosaur and synapsid extinc- M., Hesselbo, S. P., Glasspool, I. J., McElwain, J. C., 2010. Increased fire activity at the Triassic/Jurassic boundary in tions of the Late Triassic are not concentrated at the TJB, Greenland due to climate-driven floral change. Nature Geo- but instead occur stepwise, beginning in the Norian and science, 3, 426-429. extending into the Jurassic (Fig. 6). Changes in the land 11. Benton, M. J., 1986. More than one event in the Late Triassic plants are complex, diachronous and likely climate driven mass extinction. Nature, 321, 857-861. evolutionary changes over background extinction rates, not 12. Benton, M. J., 1991. What really happened in the Late Trias- a serious extinction or set of extinctions. sic? Historical Biology, 5, 263-278. We conclude that no significant extinction took place on 13. Benton, M. J., 1993. Reptilia, in: Benton, M. J., (Ed.), The land at the TJB. Indeed, the idea of a single mass extinc- Fossil Record 2. Chapman and Hall, London, pp. 681-715. tion on land at the TJB has led to a search for the cause 14. Benton, M. J., 1994. Late Triassic to Middle Jurassic extinc- of the “mass extinction” and drawn attention away from tions among continental tetrapods: Testing the pattern, in: what were actually a series of biotic events that took place Fraser, N. C., Sues, H-D., (Eds.), In the Shadow of the Dino- throughout the Late Triassic (Fig. 6). Research should now saurs. Cambridge University Press, Cambridge, pp. 366-397. 15. Bernardi, M., Petti, F. M., Porchetti, S. D., Avanzini, M., 2013. focus on these multiple extinctions and their causes, not Large tridactyl footprints associated with a diverse ichnofau- on a single extinction event. Perhaps the most interesting na from the Carnian of the Southern Alps. New Mexico Mu- question not yet addressed by most researchers is why a seum of Natural History and Science Bulletin, 61, 48-54. prolonged (at least 30 million years) interval of elevated 16. Berner, R. A., Beerling, D. J., 2007. Volcanic degassing neces- extinction rates occurred during the Late Triassic. sary to produce CaCO3 undersaturated ocean at the Triassic- Jurassic boundary. Palaeogeography, Palaeoclimatology, Pal- aeoecology, 244, 368-373. Acknowledgements 17. Blackburn, T J., Olsen, P. E., Bowring, S. A., McLean, N. M., Kent, D. V., Puffer, J., McHone, G., Rasbury, E. T., Et-Touha- We are grateful to Baas van de Schootbrugge for encour- mi, M., 2013. Zircon U-Pb geochronology links the end-Triassic aging us to publish this article. We also thank Professor Li, extinction with the Central Atlantic Magmatic Province. Sci- Jin-Geng Sha, Shu-Zhong Shen and two anonymous review- ence, 340, 941-945. 18. Bonis, N. R., Kürschner, W. M., 2012. Vegetation history, di- ers for their helpful reviews of this article. versity patterns, and climate change across the Triassic/Ju- rassic boundary. Paleobiology, 38, 240-264. References 19. Bonis, N. R., Kürschner, W., Krystyn, L., 2009. A detailed palynological study of the Triassic-Jurassic transition in key sections of the Eiberg basin (Northern calcareous Alps, Austria). 1. Abdala, F., Ribeiro, A. M., 2010. Distribution and diversity Review of Palaeobotany and Palynology, 156, 376-400. patterns of Triassic cynodonts (Therapsida, Cynodontia) in 20. Brugman, W. A., 1983. Permian-Triassic Palynology. State Uni- Gondwana. Palaeogeography, Palaeoclimatology, Palaeo- versity Utrecht, Utrecht, pp. 1-121. ecology, 286, 202-217. 21. Burgoyne, P. M., van Wyk, A. E., Anderson, J. M., Schrire, 2. Ash, S., 1986. Fossil plants and the Triassic-Jurassic bounda- B. D., 2005. Phanerozoic evolution of plants on the African ry, in: Padian, K. (Ed.), The Beginning of the Age of Dinosaurs. plate. Journal of African Earth Sciences, 43, 13-52. Cambridge University Press, Cambridge, pp. 21-30. 22. Cascales-Miñana, B., Cleal, C. J., 2012. Plant fossil record 3. Avanzini, M., Pinuela, L., Garcia-Ramos, J. C., 2010. First re- and survival analysis. Lethaia, 45, 71-82. port of a Late Jurassic lizard-like footprint (Asturias, Spain). 23. Cirilli, S., 2010. Uppermost Triassic-lowermost Jurassic pa- Journal of Iberian Geology, 36, 175-180. lynology and palynostratigraphy: A review, in: Lucas, S. G., 4. Bacon, K. L., Belcher, C. M., Haworth, M., McElwain, J. C., (Ed.), The Triassic timescale. Geological Society, London,

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