Despite their ecological and evolutionary interests, the phylogeny of Asteroidea (sea stars) is still subject to debate at several taxonomic levels. In the present study, we assemble new mitochondrial genomes for 15 species, including three newly characterized families (Odontasteridae, Poraniidae, and Stichasteridae) and representing an important addition for two orders (Velatida and Spinulosida). By analysing them alongside the 31 previously available mitogenomes, we evaluate mitogenomic variation (mitogenome organization and phylogenetic relationships) within the class. Gene order and sizes were concordant with previous studies. However, an alternative initiation codon (ATT for NAD1) was found in two Pterasteridae species. Evolutionary patterns between orders provided some interesting insights (e.g. Spinulosida as the sister-group to the Valvatida + Paxillosida), but the most novel patterns were observed among families (e.g. close relationships of Stichasteridae and Paulasteriidae; close relationships of Odontasteridae and Poraniidae; Brisingidae and Freyellidae as sister-group to the Asteriidae, Paulasteridae, and Stichasteridae). Finally, we found Pterasteridae to be paraphyletic, which could lead to the incorporation of Myxasteridae within Pterasteridae. Altogether, this study confirms that mitogenomes provide valuable and cost-effective markers to complement evolutionary patterns derived from nuclear data.
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RBINS Staff Publications 2024
Danian (lower Paleocene) sequences in north-central Tunisia are dominantly composed of marls and shales but a conspicuous, indurated glauconite-bearing marker bed is associated with the P3a–P3b transition. This glauconite bed is considered to correlate with the Latest Danian Event (LDE) described from the Nile Basin in Egypt, with the ‘top Chron C27n event’ (Atlantic and Pacific Oceans) and with the ‘CIE-DS1’ (Zumaia, Spain). The LDE is thought to reflect a short period of global warming, similar to the Paleocene Eocene Thermal Maximum, but of lesser magnitude. The presence of a glauconitic bed at the P3a/P3b transition in Tunisia suggests that the sequence is condensed, which is confirmed by planktic foraminifer and nannofossil biostratigraphy, and by the absence of the typical LDE beds found in most Egyptian sections. Benthic foraminiferal assemblages were quantitatively analyzed in three sections in north-central Tunisia (Sidi Nasseur, Garn Halfaya, Elles) in order to characterize the paleoenvironmental evolution during the late Danian and compare this with sections in Egypt. The benthic foraminiferal assemblages indicate that the Tunisian sections were located along a depth- and a paleoenvironmental gradient on the shelf north of Kasserine Island. The reconstructed depth range is comparable with sections in Egypt, and encompasses middle neritic (Sidi Nasseur section) to shallow upper bathyal depths (Elles section,with up to 16% Gavelinella beccariiformis below the P3a/P3b). Like in Egypt, assemblage shifts across the P3a/P3b subzonal transition indicate shallowing and a transition to amore eutrophic paleoenvironment, characterized by relatively high abundances of buliminids and Stainforthia sp. The δ13C and δ18O records generated on well-preserved specimens of the ostracode species Bairdia failed to demonstrate the presence of the carbon isotope excursion (CIE) associated with the LDE at the base of Subzone P3b. A condensed section or a hiatus associated with the glauconite bed would explain why the CIE is not recorded in the Tunisian sections.
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