Intraspecific Variability and Problematic Dimorphism in the Early Cretaceous (Valanginian) Ammonite Saynoceras verrucosum (d'Orbigny, 1841)

Abstract

The population of Saynoceras verrucosum (d'Orbigny) from the Polish basin (Wa̧awal section, central Poland) shows no significant intraspecific variability. Dimorphism has not been found in this population. Statistical analyses of material from the shallow epicratonic Polish basin and the relatively deep Vocontian basin (southeastern France) indicated two populations. Forms from the Polish basin are somewhat more inflated and smaller than forms from the Vocontian basin.

Ammonoid Intraspecific Variability

“…Similar size-at-age variation might have existed in ammonoids, and could be reflected in differences in adult size of fossil ammonoid populations at the same locality and age (e.g., Ivanov 1971a, 1975: microconchs, macroconchs andmegaconchs;Matyja 1986: miniconchs, microconchs and macroconchs: compare Klug et al 2015, over evolutionary time (Hewitt and Hurst 1977;Dzik 1990a;Landman et al 2008) as well as interpopulational differences in adult size between different regions and/or paleoenvironments (Kummel 1948;Vogel 1959;Wendt 1971;Mancini 1978;Elmi and Benshili 1987;Stevens 1988;Courville and Thierry 1993;Mignot 1993;Mignot et al 1993;Matyja and Wierzbowski 2000;Reboulet 2001;Urlichs 2004Urlichs , 2012Ploch 2007;Landman et al 2008). It should be noted, however, that it can be hard to disentangle intra-and inter-annual environmental factors due to the inherent time-averaging each shell assemblage (fossil population) has gone through (compare Sect.…”

“…The studies of Matyja (1986Matyja ( , (1994 and Ivanov (1971aIvanov ( , 1975 are therefore open to scrutiny as they did not use the proper quantitative methods and have a low sample size (compare Callomon 1988: Davis et al 1996. Several authors have reported intraspecific differences in adult size of populations deriving from different regions and/or paleoenvironments (Elmi and Benshili 1987;Mignot 1993;Mignot et al 1993;Reboulet 2001;Urlichs 2004;Ploch 2007;Landman et al 2008). Many of these studies have suggested a correlation between miniaturization and a locally confined paleogeographic and/or paleoenvironmental context (e.g., Elmi and Benshili 1987;Mignot 1993;Mignot et al 1993;Olóriz et al 2000;Urlichs 2004;Ploch 2007).…”

“…Several authors have reported intraspecific differences in adult size of populations deriving from different regions and/or paleoenvironments (Elmi and Benshili 1987;Mignot 1993;Mignot et al 1993;Reboulet 2001;Urlichs 2004;Ploch 2007;Landman et al 2008). Many of these studies have suggested a correlation between miniaturization and a locally confined paleogeographic and/or paleoenvironmental context (e.g., Elmi and Benshili 1987;Mignot 1993;Mignot et al 1993;Olóriz et al 2000;Urlichs 2004;Ploch 2007). Such a relationship has been particularly supported by comparative studies on Tethyan populations of Jurassic ammonites from small basins in the northwest European platform (e.g., Elmi and Benshili 1987;Mignot 1993;Mignot et al 1993).…”

“…Reboulet (2001) reported that representatives of several Valanginian ammonoid species in the deeper water facies of the Vocontian basin were smaller than their counterparts in the shallow water facies in the Provence Platform, which he attributed to a decrease in growth rate under conditions of higher hydrostatic pressure as well as lower water temperature and nutrient supply in the basinal areas. Ploch (2007) reported that specimens of Saynoceras verrucosum from the deeper Vocontian basin were smaller than those from the shallower epicratonic Polish basin, which she attributed to their isolation and differences in depth or temperature. Landman et al (2008) investigated differences in body size of the Late Cretaceous Hoploscaphites nicolletii over time and between geographically separated contemporary populations.…”

“…Some authors have not only reported intraspecific differences in size (discussed in more detail above in Sect. 9.7), but also differences in shell morphology and/ or ornamentation between different paleoenvironments (Dietl 1978;Tintant 1980;Courville and Thierry 1993;Jacobs et al 1994;Diedrich 2000;Ploch 2007; Wilmsen and Mosavinia 2011). Potentially, this link between shell form and environment might also be related to differences in growth rates and development between localities Reboulet 2001).…”