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1 2010

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The myth of the Triassic lytoceratid ammonite Trachyphyllites Arthaber, 1927, in reality an Early Jurassic Analytoceras hermanni Gumbel, 1861

Hoffmann R., Keupp H.

Acta Geologica Polonica

2010

Vol. 60, no. 2

219-229

The ammonoid "Trachyphyllites costatum" Arthaber (1927), based on a single specimen from an erratic boulder of presumed Late Triassic (Norian age) from Timor, (Indonesia), was originally described as a phylloceratid but later recognized as a true lytoceratid by Basse (1952) and Schindewolf (1961), and used by Wiedmann (1966a, 1966b, 1970) to support his idea of a polyphyletic origin of the post-Triassic ammonoids and of the Late Triassic roots of the lytoceratids. New collections of additional specimens and associated taxa from other erratic boulders in the type locality have confirmed observations (Tozer 1971; Krystyn 1978) that the age of the original boulder was misinterpreted, and have shown that "Trachyphyllites" is actually of Early Jurassic (Hettangian) age. An unpublished generic revision of the entire superfamily Lytoceratoidea by Hoffmann (2009) has shown that "Trachyphyllites costatum Arthaber" is a junior synonym of Analytoceras hermanni (Gumbel, 1861), a taxon thought by Wahner (1894) to be a subjective synonym of Analytoceras articulatum (J. Sowerby, 1831) We reestablish the species Analytoceras hermanni (Gumbel, 1861) for Analytoceras articulatum "Type B" (Wahner 1894), which is characterized by a wide umbilicus and a small whorl expansion rate. The morphologically distinct "Type A" (Wahner 1894) corresponds to the type species of Analytoceras, A. articulatum (J. Sowerby, 1831). A revised phylogeny of the Early Jurassic lytoceratids is presented.