Revision of Ordovician chitinozoan Lagenochitina esthonica sensu lato: morphometrics, biostratigraphy and paleobiogeography

Abstract

Lagenochitina esthonica is a globally distributed chitinozoan in Early to Middle Ordovician rocks. It is regarded as an index species for the early Floian in North America and has a stratigraphically constrained range in other regions. Lagenochitina esthonica is distinguished from other chitinozoans by a distinct flexure, a nearly rounded-square chamber, and a cylindrical neck with a flaring collar. However, since the first description of the species in the 1950s, it has included two varieties: a relatively short form with a test length ~400 μm, and a slender form usually longer than 600 μm. In order to revise the taxonomy of the L. esthonica group, we carried out a statistical morphometric study of a large collection of well-preserved specimens from the Baltic region where the taxon was first established. Additionally, the stratigraphic and geographic distribution of both forms was analyzed based on available occurrence data. The results show that the short form occurs in the upper Tremadocian to lower Dapingian, whereas the slender form is mostly reported from the lower and middle Darriwilian. Both forms are identified on Baltica; the short form has also been reported from Laurentia and South China, whereas the other is known also from Avalonia and Gondwana. The morphological distinction, together with differences in stratigraphic and spatial ranges, suggest that the two forms represent separate species: the original stout L. esthonica, based on the morphology of the holotype, and the slender L. megaesthonica n. sp., described herein. The updated taxonomy enhances the stratigraphic and biogeographic usefulness of lagenochitinids globally.UUID: http://zoobank.org/ec49166e-2a8d-4941-8723-f023853c5a7e.

Peri-Gondwanan acritarchs and chitinozoans from the Lower–Middle Ordovician Lashkarak Formation in the Alborz Mountain Ranges, northern Iran: regional stratigraphical significance and palaeogeographical implications

“…This taxon has been recorded from numerous localities, including Middle Ordovician, the Hope Shales (Darriwilian), England (Jenkins 1967), Florida, USA (Andress et al 1969), and France (Paris 1981, 1990); middle–late Darriwilian, Hanadir Shale Member of the Qasim Formation, the Arabian Peninsula (McClure 1988; Al-Hajri 1995; Le Hérissé et al 2007), Turkey (Paris et al 2007), Libya (Combaz and Poumot 1962; Abuhmida and Wellman 2017), and the Upper Shale Member of the Zardkuh Formation in the High Zagros Mountains, southern Iran (Ghavidel-Syooki et al 2011b; Ghavidel-Syooki 2021, 2023). The co-existing chitinozoan taxa of this biozone are Lagenochitina megaesthonica (Liang et al 2022) and Conochitina chydaea (Jenkins 1967). Lagenochitina megaesthonica is restricted to the lower and middle Darriwilian in Baltica, Avalonia, and Gondwana (Liang et al 2022).…”

“…The co-existing chitinozoan taxa of this biozone are Lagenochitina megaesthonica (Liang et al 2022) and Conochitina chydaea (Jenkins 1967). Lagenochitina megaesthonica is restricted to the lower and middle Darriwilian in Baltica, Avalonia, and Gondwana (Liang et al 2022). Iranian specimens of the genus Lagenochitina are similar to Lagenochitina esthonica s.l.…”

“…Paris 1981Subfamily LAGENOCHITININAE Paris 1981Genus Lagenochitina Eisenack 1931 emend. Paris et al 1999 L. megaesthonica Liang et al 2022 (Plate 7, figure 11)Subfamily CYATHOCHITININAE Paris 1981Genus Cyathochitina Eisenack 1955 emend. Paris et al 1999 C. campanulaeformis (Eisenack 1931) (Plate 6, figures 3, 7; 18, 19). C. calix (Eisenack 1931) sensu Paris 1981 (Plate 6, figures 1, 5; 2, 6) C. protocalix Paris 1981 (Plate 6, figures 10, 14) C. varennensis Paris 1981 (Plate 6, figures 4, 8; Plate 7, figures 12, 16) C. gerdkuhensis sp.…”

On future directions of Ordovician chitinozoan research

“…The holotypes are kept in many different institutions worldwide and some holotypes have been lost or broken due to various reasons and circumstances. Recently, a case study of a revision of the widely distributed and well-known Lagenochitina esthonica has been carried out (Liang et al 2022), providing an example of how to solve such issues. The most important part of the work is that the materials are from the same area and stratigraphic level as the lost holotype.…”