Year: 1991
Type: article
Abstract: Conulariid specimens that terminate adapically in a transverse wall, or schott, have been interpreted in several ways.These interpretations have been based more on analogy with extant organisms than on evaluation of fossil material.Currently favoured interpretations are that (1) schott-bearing specimens represent individuals that were severed, in life, by currents ; (2) schott-bearing specimens were free-swimming individuals ;(3) schott-bearing specimens represent non-injured, sessile individuals that retracted the apical part of their soft body toward the oral end, as part of their normal life history.Examination of the test cavity of conulariid specimens that do not terminate in a schott, and analysis of the frequency of occurrence of schott-bearing specimens in low-versus high-energy sedimentary deposits, indicate that the most likely interpretation of schott-bearing specimens is that they represent living individuals severed by currents.Proponents of a scyphozoan affinity for conulariids have generally interpreted schott-bearing specimens as conulariid medusae, one of the alternatives not favoured by the present analysis.In spite of this, the interpretation of schott-bearing specimens as severed individuals is consistent with the hypothesis that conulariids and scyphozoans were closely related.Previous discussions of the mode of life and life history of conulariids have presented compelling evidence that conulariid specimens terminating in a narrow apex (Text-fig.1a) were sessile animals, either free-standing and attached at the apex to shell material or other substrates, or embedded in massive sponges or bryozoans (e.g.Sinclair 1948;Finks 1955 Finks , 1960;;Rooke and Carew 1983; Babcock et al. 1987;Harland and Pickerill 1987; Van Iten 1991a).Yet disagreement persists as to the nature of conulariid specimens whose apical end, now truncated some distance above the apex, terminates in a more or less smooth, generally convex transverse wall (Text-fig.1b).This structure, referred to by Kiderlen (1937) as the schott (the German word for bulkhead), was originally interpreted as one of a series of internal septae, homologous to the septae of nautiloid cephalopods (Hall 1847).Although schott-bearing specimens have been found that exhibit one or two additional schotts above the terminal one (Babcock and Feldmann 1986a; see also below), it is now agreed that the conulariid schott and nautiloid septa are not homologous structures (e.g.Werner 1966Werner , 1967;;Bischoff 1978;Grasshoff 1984; Babcock and Feldmann 1986a).More recent discussions of the nature of the conulariid schott have focused on one or more of the following three alternatives: (1) the schott was a cicatrix, produced in response to severance of the body by currents (Werner 1966(Werner , 1967)); (2) the schott was an autotomy scar, produced when the adult conulariid detached from its apical end and assumed a free-swimming mode of life (e.g.Kiderlen 1937;Boucek 1939;Termier andTermier 1949, 1953; Moore and Harrington 1956;Chapman 1966;Kozlowski 1968;Bischoff 1978;Grasshoff 1984) ; (3) the schott was a regular growth feature, produced upon attainment of a certain age (Sinclair 1948; Babcock and Feldmann 1986a).With the exceptions of Termier andTermier (1949, 1953) and Kozlowski (1968), advocates of the hypothesis that the conulariid schott was produced in response to assumption of a freeswimming mode of life interpret schott-bearing conulariids as similar to medusae of scyphozoan cnidarians, a group that has been widely regarded as the most likely candidate for an extant nearest relative of conulariids (e.g.
Author: Heyo Van Iten
Language: English
Subfield: Paleontology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2954581530