Illuminating the richness of the ascidian fossil record: a new exceptionally diverse assemblage of ascidian spicules from the Middle Miocene of Bosnia and Herzegovina
Magdalena Łukowiak, Oleg Mandic, Anna Omalecka, Mădălina‐Elena Kallanxhi, Stjepan Ćorić, Patrick Grunert
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Abstract
Ascidians, or sea squirts, are sac‐like sessile tunicates commonly found in modern seas. Although the oldest ascidians, or at least ascidian‐like tunicates, are mid‐Cambrian in age, the quality of the ascidian fossil record is extraordinarily poor. It mostly consists of isolated finds or low‐diversity assemblages, often represented by mineral spicules. Our study reports the world's most diverse assemblage of ascidian spicules, originating from the Middle Miocene Bogutovo Selo near Ugljevik, Bosnia and Herzegovina. This material includes 31 spicule types, with four assignable to species (Lissoclinum cf. perforatum, Polysyncraton cf. bilobatum, Didemnum cf. vexillum and D. cf. leopardi) and 10 to genera, all belonging to aplousobranchiate ascidians. Comparing our findings with those of two other studies that use modern biological nomenclature, our assemblage shows a closer resemblance to the distant Eocene Australian assemblage than to the Miocene ascidians from Eastern Paratethys. This suggests the persistence of a once‐homogeneous and widely distributed Eocene fauna into the Miocene, while the Eastern Paratethyan basin developed an endemic fauna after the isolation of Eastern Paratethys from the open sea. Some taxa of our assemblage currently inhabit the Mediterranean Sea. The discovery of one species in distant South African waters suggests that tectonic and environmental changes during the Late Miocene, including the closure of the Gibraltar Strait and prior disconnection from the Indian Ocean, may have limited its survival to remote refugia. The study underscores the importance of including spicules in reconstructing ascidian faunas in the geological past, an area that has been surprisingly understudied.
期刊介绍:
Papers in Palaeontology is the successor to Special Papers in Palaeontology and a journal of the Palaeontological Association (www.palass.org). The journal is devoted to the publication of papers that document the diversity of past life and its distribution in time and space.
Papers in Palaeontology is devoted to the publication of papers that document the diversity of past life and its distribution in time and space. As a sister publication to Palaeontology its focus is on descriptive research, including the descriptions of new taxa, systematic revisions of higher taxa, detailed biostratigraphical and biogeographical documentation, and descriptions of floras and faunas from specific localities or regions. Most contributions are expected to be less than 30 pp long but longer contributions will be considered if the material merits it, including single topic parts.
The journal publishes a wide variety of papers on palaeontological topics covering:
palaeozoology,
palaeobotany,
systematic studies,
palaeoecology,
micropalaeontology,
palaeobiogeography,
functional morphology,
stratigraphy,
taxonomy,
taphonomy,
palaeoenvironmental reconstruction,
palaeoclimate analysis,
biomineralization studies.