Shell features, main colonized environments, and fractal analysis of sutures in Late Jurassic ammonites

Abstract

A precise approach to the quantification of relationships between suture complexity, as measured by fractal analysis (step‐line procedure), the architecture of shells, and the main colonized environments, has been made in a set of Late Jurassic ammonites (N=507). Statistically significant differences between fractal‐dimension (Df) mean values of evolute and involute shells are interpreted as caused by differences in the surface:volume (S:V) ratio. Suture complexity is also related to the shape of whorl section. The lowest Df values correspond to subcircular whorl sections (low S:V ratio) and the highest ones to acute sections (high S:V ratio). The shape of flanks shows correlation with suture complexity. The highest values of Df are found in planulate shells and the lowest ones in whorl cross sections with convex flanks. Highly significant differences appear between Df mean values from unsculptured shells and those from ammonites with ribs and/or tubercles of medium to large size. Multivariate analysis shows a combined variation of shell features and suture complexity, resulting in a heterogeneous distribution of Df values within the ammonite morphospace, mainly according to structural (shell architecture) and ornamental (sculpture strength rather than density) factors. Finally, the data obtained on relationships between suture complexity and the colonized environments (epicontinental vs. epioceanic inhabitants) suggest that suture complexity is not primarily related to bathymetry, and/or that no major differences in habitat depths existed between epicontinental and epioceanic ammonites.

Morphostructural constraints and phylogenetic overprint on sutural frilling in Late Jurassic ammonites

“…Inspection of D f mean, minimum and maximum values reveals that there is no general trend-increase in sutural complexity for specimens gathered from swell areas in epioceanic fringes with respect to those inhabiting epicontinental shelves and inland seas. In fact, Perisphinctoidea, which is the clade best represented in the database, shows a higher mean fractal Palmqvist 1995;Oló riz et al 1997Oló riz et al , 1999 and was implicitly assumed by Westermann (1996) modifying his previous hypothesis (Westermann 1990), mainly when concerned with major ecologic distributions of Ammonitina.…”

“…1 shows the fractal dimension (D f ) values of ammonite sutures in those specimens inhabiting normal neritic-to-epeiric seas (n = 239) and epioceanic fringes (n = 41) in relation to whorl height (W h , log 10 -transformed to avoid departures from normality) corresponding to the sutures analysed (see details on the methodology used for estimating D f values in Lutz & Boyajian (1995), Oló riz & Palmqvist (1995 and Oló riz et al (1997Oló riz et al ( , 1999). …”

“…Results after using a large database (n > 500) of Late Jurassic ammonites (Oló riz & Palmqvist 1995;Oló riz et al 1997Oló riz et al , 1999 indicate that sutural complexity, as measured by the fractal dimension values of the sutures, was similar in specimens inhabiting epicontinental shelves and epioceanic plateaux. Hence, although mid-outer shelf and epioceanic environments on seamounts (and even on assumed typically 'deeper' environments, e.g.…”

“…post-mortem transport in the water column, bottom sweeping and even reworking). Many authors (including the main supporters of Buckland's theory) now consider that most ammonites were epipelagic (up to 250 m water depth) in both oceanic-epioceanic and epeiric waters (Westermann 1990(Westermann , 1996Oló riz et al 1993;Oló riz & Palmqvist 1995;Daniel et al 1997;Oló riz et al 1996Oló riz et al , 1997Oló riz et al , 1999Westermann & Tsujita 1999;Oló riz 2000;Lewy 2002). This interpretation seems to be con rmed by assumptions on the ontogenetic decrease of siphuncle strength in Ammonitina (Westermann 1971), the clade that comprises the largest part of our database.…”

Globacrochordicerasgen. nov. (Acrochordiceratidae, late Early Triassic) and its significance for stress-induced evolutionary jumps in ammonoid lineages (cephalopods)

“…Furthermore, the possible influence of facies changes recorded at the Spathian/Anisian boundary (see below) is also reduced. Indeed, several authors discussed the possible relationships between ammonoid shell shape and facies (Jacobs et al 1994;OlÕriz et al 1997;Kawabe 2003;Wilmsen & Mosavinia 2011; further references in Monnet et al 2011) but without a clear consensus. In the northern Humboldt Range, the depositional environment of strata of haugi Zone age does not significantly differ from that of the younger Anisian faunas (i.e.…”