caa a22 4500 388017414 CHVBK 20180307124914.0 cr unu---uuuuu 161130e199801 xx s 000 0 eng 10.1017/S0022336000024045 doi S0022336000024045 pii (NATIONALLICENCE)cambridge-10.1017/S0022336000024045 Internal structure of Cambrian Conodonts [Elektronische Daten] [K. J. Müller, I. Hinz-Schallreuter] Based on material of the Upper Cambrian of Sweden the internal structure of proto-, para- and euconodonts has been investigated. The protoconodontids Gapparodus and Gumella show some special development of the median unit of the skeletal tissue. In Gapparodus, long, parallel-running lamellae suggest a continuous growth, even of previously secreted lamellae, until their eventual outcropping. In Gumella the fibrous median layer decreases considerably during growth until its complete reduction, which coincides with the disappearance of the posterior wall. Paraconodonts also produced several specialities in their mode of growth. Elements with lateral processes such as Proacodus and Serratocambria developed by allometric growth. The lamellae are much more widely spaced in the process than in the main cusp to attain the required length of the former. In Serratocambria additional lamellae are inserted in the process. Thin sections of tricuspidate westergaardodinids reveal paraconodontid growth with lamellar remains in the tip of the median denticle, which are isolated from the growth lines in the lateral denticles. Based on this observation a hypothetical growth model explains the lamellar development as a result of stress and strain. The Ordovician euconodontid Chosonodina clearly shows white matter and is thus unrelated, but homeomorphic to Westergaardodina. Cambropustula from the lower Upper Cambrian is the oldest euconodont yet but it lacks white matter. The latter was an evolutionary novelty, which progressively developed in the euconodont line. The systematic position of conodonts is briefly discussed; the studied material cannot contribute to the hypothesis of neural crest derived skeletal tissue. Copyright © The Paleontological Society Müller K. J. Paläontologisches Institut der Universität Bonn, Nussallee 8, D-53115 Bonn aut Hinz-Schallreuter I. Naturhistorisches Forschungsinstitut, Museum für Naturkunde, Institut für Paläontologie, Invalidenstraße 43, D-10115 Berlin aut Journal of Paleontology Cambridge University Press 72/1(1998-01), 91-112 0022-3360 72:1<91 1998 72 JPA https://doi.org/10.1017/S0022336000024045 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1017/S0022336000024045 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Müller K. J. Paläontologisches Institut der Universität Bonn, Nussallee 8, D-53115 Bonn aut NATIONALLICENCE 700 1- Hinz-Schallreuter I. Naturhistorisches Forschungsinstitut, Museum für Naturkunde, Institut für Paläontologie, Invalidenstraße 43, D-10115 Berlin aut NATIONALLICENCE 773 0- Journal of Paleontology Cambridge University Press 72/1(1998-01), 91-112 0022-3360 72:1<91 1998 72 JPA CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-cambridge