The Space-Time Relationship of Taxonomic Diversity and Morphological Disparity in the Middle Jurassic Ammonite Radiation ⁎ Sébastien Moyne A, , Pascal Neige B
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Palaeogeography, Palaeoclimatology, Palaeoecology 248 (2007) 82–95 www.elsevier.com/locate/palaeo The space-time relationship of taxonomic diversity and morphological disparity in the Middle Jurassic ammonite radiation ⁎ Sébastien Moyne a, , Pascal Neige b a Centre de Sédimentologie-Paléontologie and FRE CNRS 2761, Université de Provence, Bâtiment de Sciences Naturelles, Case 67, Place Victor Hugo, F-13 331 Marseille cedex 3, France b Centre des Sciences de la Terre and UMR CNRS 5561 Biogéosciences, Université de Bourgogne, 6 bd Gabriel, F-21000 Dijon, France Received 9 May 2006; received in revised form 17 October 2006; accepted 24 November 2006 Abstract The Middle Jurassic ammonite radiation (from the late Aalenian to the end of the mid-Bathonian) is traced using combined analyses of morphological disparity and taxonomic diversity. The global signals of disparity and diversity are compared. These signals are then broken down by paleogeographical provinces to detect any heterogeneity in the radiation. An examination of the global signals reveals three biodiversity crises (discordances between signals) where morphological disparity grows while taxonomic diversity declines. The subdivision of the signals indicates the radiation was heterogeneous between provinces: the global signal is an aggregate of signals from each province. The three biological crises have different paleogeographical signatures: the first is visible in a few provinces only while the other two are visible in most provinces. First-order crises can be distinguished from second-order ones by studying the number of paleogeographical provinces affected. © 2006 Elsevier B.V. All rights reserved. Keywords: Paleogeography; Morphological disparity; Taxonomic diversity; Ammonites; Jurassic 1. Introduction groups of taxa with equal diversity may display very different morphological variability. Therefore, taxonom- Taxonomic diversity is generally used to characterize ic diversity analyses have been supplemented exten- the evolutionary history of clades and particularly sively over the last decade by morphological disparity extinctions and radiations. It may be used both to detect analyses for various taxa (e.g. Wills et al., 1994; Foote, major biological crises (Sepkoski, 1981; Sepkoski and 1999; Ciampaglio et al., 2001; Navarro et al., 2005), Hulver, 1985) and to help model the diversification of particularly because the combined use of taxonomic different biological groups (Benton, 2001). Although diversity and morphological disparity signals can only interesting in itself, taxonomic diversity has proved a lead to a better understanding of macroevolutionary poor proxy for morphological variability (see Foote processes (Wills, 2001). 1993a; Neige et al., 1997; Neige 2003). Indeed, two Interestingly, the geographical aspects of diversity/ disparity relationships have come in for a little study. ⁎ Corresponding author. This is probably because studies have concentrated on E-mail address: [email protected] (P. Neige). analysing large macroevolutionary patterns covering 0031-0182/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2006.11.011 S. Moyne, P. Neige / Palaeogeography, Palaeoclimatology, Palaeoecology 248 (2007) 82–95 83 long time spans and under the assumption that the long-standing use of morphometrics for ammonites, phenomena under study (e.g. radiations, crises) were which ensures a robust quantification of shape and fundamentally worldwide. There is a presupposition, disparity (see Raup, 1967; Dommergues et al., 1996; then, that observing diversity/disparity relationships Neige et al., 2001; Korn and Klug, 2003; Navarro et al., independently for several paleogeographical areas will 2005). The second is the wealth of knowledge paleontol- add nothing to our understanding of the radiations and ogists have of these creatures because they are abundant crises involved. This may be true, but only if large within Jurassic marine outcrops and also because they macroevolutionary patterns are independent of any have been extensively studied and figured for biostrati- environmental context. Most studies of large-scale graphical purposes. biological radiations generally present just one global diversity (or disparity) signal over time for the 2. The radiation in a global context considered taxa. They fail to take account of paleogeo- graphical homogeneity or heterogeneity. Some studies, Middle Jurassic ammonites are found worldwide in though, have shown that a radiation may be paleogeo- the three great oceanic realms (Tethyan, Pacific and graphically heterogeneous. Miller (1997a,b) reported Boreal). To trace the geographical variations in diversity that diversification patterns during the great Ordovician and disparity, 16 paleogeographical provinces have been radiation varied between provinces. A study of bivalve individualized (Fig. 1). This subdivision is derived from radiation for the same period (Babin, 1993) identified that proposed by Dommergues et al. (2001) for the the geographical shifting of the diversification as a Lower Jurassic and modified for the needs of the Middle major process. These observations indicate that a Jurassic (Moyne et al., 2004). Present-day geographic radiation cannot be described from a global signal units belonging to the paleogeographic provinces are alone. A global signal is an aggregate measure of described in Table 1. These provinces are defined by information compiled from signals from different their fauna and geology (see Dommergues et al., 2001). paleogeographical provinces. It has to be dissected to The studied period (late Aalenian to mid-Bathonian) be properly interpreted, and in particular to determine is subdivided into 15 biozones in the Tethyan Realm whether or not a radiation occurs uniformly worldwide. (Contini et al., 1997; Rioult et al., 1997; Mangold and This pilot study computes and compares signals of Rioult, 1997). This zonation is available for the Western taxonomic diversity and morphological disparity. These Tethys only and it has been correlated with parallel signals are divided between provinces to determine scales established in other countries (Krymholts et al., whether paleogeography needs be taken into account if a 1988; Hillebrandt et al., 1992; Callomon, 1994; Enay biological radiation is to be understood in a global and Mangold, 1994; Hillebrandt, 2001). All results context. presented in this study refer to the 15 biozones of the The data used are for the Middle Jurassic ammonite scale proposed for the Tethys. This period covers a total radiation, which was marked by substantial faunal span of 8 Ma (Gradstein et al., 2004, but which may be turnover of the Ammonitina sub-order near the Aale- extended to 15 Ma in reference to Odin and Odin, 1990). nian/Bajocian boundary. A single super-family went forth Unfortunately, there are no radiometric data for this and multiplied giving rise to all the groups that dominated period for accurate time calibrations. The results are the Late Jurassic (House, 1985; Page, 1996). The exact therefore presented here with a relative biostratigraphic relationships between these groups are hard to understand scale. and many phylogenies have been proposed (see Moyne and Neige, 2004 for a recent review). This key period has 2.1. Fluctuation of taxonomic diversity over time already been studied, but only for its taxonomic diversity (O'Dogherty et al., 2000; Sandoval et al., 2001, 2002; The faunal turnover at the Aalenian/Bajocian Moyne et al., 2004). Those studies show that taxonomic boundary is marked by a large increase in the number diversity was at its lowest in the Aalenian and then surged of Ammonitina species: some 80 species for each during the Bajocian. In this paper, we study all groups of biozone of the Aalenian versus 179 species in the the Ammonitina from the late Aalenian to focus on faunal Laeviuscula Zone (Fig. 2). Species diversity peaks at the turnover. We then trace the radiation until the end of the end of the early Bajocian and then remains high until the mid-Bathonian. All species belonging to the Ammonitina onset of the Bathonian (Zigzag Zone). Thereafter sub-order from the late Aalenian (Bradfordensis Zone) to species diversity plummets, recovering slightly at the the end of the mid-Bathonian (Bremeri Zone) are covered. start of the mid-Bathonian. It remains at the same level Two factors facilitate the study of this radiation. One is the until the end of the mid-Bathonian, at which point, 84 S. Moyne, P. Neige / Palaeogeography, Palaeoclimatology, Palaeoecology 248 (2007) 82–95 Fig. 1. Location of the 16 paleogeographical provinces (A–P) from the end of the Aalenian to the Bathonian (Middle Jurassic). Letters refer to provinces named and defined in Table 1 (Paleogeographical reconstruction compiled from data of Owen, 1983; Scotese, 1991, 1997; Thierry et al., 2000; Vrielynck and Bouysse, 2001). diversity dwindles to the level recorded during the (Fig. 2). An initial increase in diversity at the end of the Aalenian. Aalenian stabilizes in the Lower Bajocian. Genus diversity Genus diversity follows a roughly similar pattern of peaks in the late Bajocian before falling off rapidly during fluctuation to species diversity over the same period of time the early Bathonian and remaining low thereafter. Table 1 Name and description of the 16 paleogeographical units used in the analysis (see main text for further explanations) No Name Description A Northern Mediterranean Threshold Austroalpine outcrops of Italy,