Ediacaran skeletal metazoan interpreted as a lophophorate
Authors:
Zhuravlev et al
Abstract:
While many skeletal biomineralized genera are described from Ediacaran (635–541 million years ago, Ma) strata, none have been suggested to have an affinity above the Porifera–Cnidaria metazoan grade. Here, we reinterpret the widespread terminal Ediacaran (approx. 550–541 Ma) sessile goblet-shaped Namacalathus as a triploblastic eumetazoan. Namacalathus has a stalked cup with radially symmetrical cross section, multiple lateral lumens and a central opening. We show that the skeleton of Namacalathus is composed of a calcareous foliated ultrastructure displaying regular concordant columnar inflections, with a possible inner organic-rich layer. These features point to an accretionary growth style of the skeleton and an affinity with the Lophotrochozoa, more specifically within the Lophophorata (Brachiopoda and Bryozoa). Additionally, we present evidence for asexual reproduction as expressed by regular budding in a bilateral pattern. The interpretation of Namacalathus as an Ediacaran total group lophophorate is consistent with an early radiation of the Lophophorata, as known early Cambrian representatives were sessile, mostly stalked forms, and in addition, the oldest known calcareous Brachiopoda (early Cambrian Obolellida) and Bryozoa (Ordovician Stenolaemata) possessed foliated ultrastructures.
A group of scientists from Okinawa Institute of Science and Technology Graduate University (OIST), Nagoya University, and the University of Tokyo decoded the first lingulid brachiopod genome, from Lingula anatina collected at Amami Island, Japan. The paper published in Nature Communications presents the results of their analysis of over 34,000 genes comprising the L. anatina genome and shows that despite Lingula's reputation as a "living fossil" its genome is actively evolving.
Adaptive strategies and environmental significance of lingulid brachiopods across the late Permian extinction
Authors:
Posenato et al
Abstract:
Linguliform brachiopods are traditionally considered a conservative group which seems to pass through the late Permian extinction without any significant loss, and even appear to thrive immediately after the extinction peak. In the Southern Alps, lingulids are very common in the post-extinction Mazzin Member (early Induan) of the Werfen Formation. Sparse occurrences are also known in the overlying Siusi and Gastropod Oolite members (late Induan and early Olenekian in age respectively). The recent discovery of well preserved specimens from a pre-extinction bed of the Bellerophon Formation (Changhsingian) has permitted a detailed comparative analysis, mostly based on the interior characters, preserved in the lingulid succession from across the extinction beds. The following effects on the lingulid populations have been analysed: i) change in taxonomic assessment; ii) adaptive strategies during the surviving and recovery phases; iii) environmental proxy connected with the killing mechanisms of the late Permian extinction.
The pre-extinction individuals belong to Lingularia? cf. smirnovae Biernat and Emig, a species that is characterized by large-sized shells with a short lophophoral cavity. The post-extinction populations belong to different species and, probably, even to a different genus. The first post-extinction population (early Induan), with small-sized shells and long lophophoral cavity, has been referred to Lingularia yini (Peng and Shi). It records the most severe effects of the late Permian extinction on the marine ecosystems. The late Induan – Olenekian Lingularia borealis (Bittner), with large sized shells and long lophophoral cavity, appears during the first phase of the Triassic biotic recovery.
The main adaptive strategies of Lingularia yini, in comparison with the Permian species, include: i) shell miniaturization; ii) increasing of the lophophoral cavity surface (respiratory surface); iii) increasing of shell width/length ratio. These modifications are interpreted as adaptations towards warming and hypoxia, two main killing mechanisms of the marine biota. The recovery species Lingularia borealis maintains a large lophophoral cavity, indicating an adaptation towards predominant low oxygenated bottom marine waters.
The appearance and the great abundance of Lingularia yini in the Mazzin Member (early Induan) represents a proxy of dysaerobic conditions, which determined the appearance of the second phase of the Lilliput biota, characterized by the definitive disappearance of the rhynchonelliform brachiopods and calcareous algae in the Southern Alps.
First record of Podichnus in orthide brachiopods from the Lower Ordovician (Tremadocian) of NW Argentina and its relation to the early use of an ethological strategy
Authors:
Santos et al
Abstract:
Well preserved etchings from the pedicle attachment of brachiopods occur on orthide brachiopod shells from Lower Ordovician (Tremadocian) of NW Argentina. Under the name Podichnus conicus isp. n. this trace fossil is interpreted as a fixichnia produced by the attachment of brachiopod pedicles upon hard substrates. The trace is characterized by an irregular and asymmetrical cluster of circular pits. Each individual pit has a typical conical shape and presents the external mean diameter/length ratio close to 1. The occurrence of P. conicus isp. n. in the Tremadocian is the oldest record of this ichnogenus, and points to orthide brachiopods as Podichnus producers for the first time. The presence of this structure provides new information regarding colonization of biogenic hard substrates during the Early Ordovician and an adaptive strategy of its use by orthide brachiopods.
