Recent Advances in Morphometric Approaches to Covariation of Shell Features and the Complexity of Suture Lines in Late Jurassic Ammonites, With Reference to the Major Environments Colonized

Ontogeny and covariation in the Toarcian genus Osperleioceras (Ammonoidea)

“…Fractal analyses of suture lines have shown that sutural complexity correlates on a large scale with shell geometry [Oloriz et al, 1999]. Only qualitative differences were observed in Osperleioceras : sutural elements tend to be more finely fringed in involute morphotypes.…”

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

“…Westermann's points (i) and (iv) focus on technical matters concerning our morphometric data and conclusions. Here we show the results from a numerical approach conducted on variables related to those considered more relevant by Westermann (1999) for addressing the 'suture problem': (i) whorl height of phragmocones (estimated at the end-points of the suture measured), which is a parameter more closely related to sutural complexity than whorl diameter, according to partial correlation data (Oló riz & Palmqvist 1995;Pérez-Claros 1999); (ii) taxonomic grouping (at the superfamily level, since most specimens analysed belong to the Order Ammonitina); and (iii) basic planispiral shell shape, as de ned by Westermann (1996), which was presumably related to lifestyle and habitat depth of ammonites. In our approach, the only exceptions for a precise evaluation of shell strength are direct measurements of thickness of shell wall and septa, which were not available in our database, although two observations apply here: (i) the precise thickness measurement in epigenized shells is not unequivocal, nor is the speci c gravity of the shell substance (Reyment & Eckstran 1957;Reyment 1958;Heptonstall 1970;Mutvei 1975), and (ii) stress-maximum values (which are equivalent for connecting rings and the whole shell in cephalopods; Ward 1987) do not provide information about the usual/preferred stress-eld in a biological structure.…”

“…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.…”

“…The functional signi cance of uted septa and complex sutures in ammonoids has stirred debate during recent decades (for recent interpretations and controversy, see review and references in Saunders 1995;Seilacher & LaBarbera 1995;Jacobs 1996;Westermann 1996;Daniel et al 1997;Oló riz et al 1999;Lewy 2002). A persistent assumption has been that ammonoid shells are designed for resisting ambient hydrostatic pressure.…”

“…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.…”