Graptolites from the Rhuddanian-Aeronian boundary interval (Silurian), Prague Synform, Czech Republic

Abstract

Forty-five graptolite species belonging to nineteen genera collected from loose rocks in the field at Všeradice and assigned to the upper vesiculosus, cyphus, triangulatus and lower pectinatus biozones of late Rhuddanian and early Aeronian age are described and discussed.

Paramonoclimacis sidjachenkoi (Obut & Sobolevskaya) and the evolution of the streptograptid thecal aperture in the Silurian (Graptolithina, Monograptidae)

“…However, the above‐mentioned genera show some variable degree of dorsal curvature. A considerable degree of dorsal curvature is typical of Coronograptus cyphus (see Štorch ) and related taxa. The genus Streptograptus (Fig.…”

“…The genus Pseudopernerograptus Wang in Wang et al ., is based on species of the Monograptus revolutus group of late Rhuddanian age. Štorch () included the species referred to Pseudopernerograptus by Wang et al . () in an emended genus Pernerograptus , but was apparently not aware of the genus Pseudopernerograptus , as he did not discuss this taxon.…”

“…The differentiation of the genera Pernerograptus and Pribylograptus is often difficult due to the poor preservation of flattened material and the often delicate and very slender proximal ends. Whereas Pernerograptus has proximal thecae with apertural hooks, retreating mesially and leaving lateral lappets and dorsal hoods grading into simple distal apertures (Štorch ), the genus Pribylograptus bears lateral apertural lappets proximally, grading to simple thecae distally in some species (Loydell ; Lukasik & Melchin ), but does not have hooked proximal thecae. Thus, the main difference is the lack of an apertural hood or hook in proximal thecae in Pribylograptus , but the taxa also differ in their general tubarium shape.…”

Retiolitine graptolites from the Aeronian and lower Telychian (Llandovery, Silurian) of Arctic Canada

“…It has long been recognized that the earliest known Silurian retiolitine graptolites occur in the mid-Llandovery Aeronian Stage (e.g., Elles and Wood, 1908;Bouček and Münch, 1944;Obut and Sobolevskaya, 1968;Lenz and Melchin, 1987a;Melchin, 1989;Štorch, 1998). Most previous studies that document Aeronian retiolitine faunas, however, report only a single genus, Pseudoretiolites.…”

“…A detailed study of the mid-Aeronian strata in the Czech sequence by Štorch (1998) showed that P. perlatus commonly occurs in the L. convolutus Zone, but that it also occurs rarely in the underlying Pribylograptus leptotheca and Demirastrites simulans zones (= Rastrites orbitus Subzone of Arctic Canada). Other species of Pseudoretiolites, such as P. decurtatus Bouček and Münch, 1944, and P. tianbaensis Ge, 1990 from China, first occur in most studies no lower than the L. convolutus Zone (e.g., Obut and Sobolevskaya, 1967;Štorch, 1998;Ge, 1990), or in the lowest Telychian Spirograptus guerichi and Spirograptus turriculatus zones (e.g., Bouček and Münch, 1944;Münch, 1952;Chen, 1984), although Lenz and Melchin (1987a) and Melchin (1989) Kozłowska-Dawidziuk, 2004, fig. 1), the previously known occurrence data summarized here point to the fact that this genus appeared within the lower Aeronian, but not at its base, and was relatively common in at least the mid and upper Aeronian globally.…”