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New multipodomerous appendages of stem-group euarthropods from the Cambrian (Stage 4) Guanshan Konservat-Lagerstatte.

ABSTRACT: Stem-group euarthropods are important for understanding the early evolutionary and ecological history of the most species-rich animal phylum on Earth. Of particular interest are fossil taxa that occupy a phylogenetic position immediately crownwards of radiodonts, for this part of the euarthropod tree is associated with the appearance of several morphological features that characterize extant members of the group. Here, we report two new euarthropods from the Cambrian Stage 4 Guanshan Biota of South China. The fuxianhuiid Alacaris? sp. is represented by isolated appendages composed of a gnathobasic protopodite and an endite-bearing endopod of at least 20 podomeres. This material represents the youngest occurrence of the family Chengjiangocarididae, and its first record outside the Chengjiang and Xiaoshiba biotas. We also describe Lihuacaris ferox gen. et sp. nov. based on well-preserved and robust isolated appendages. Lihuacaris ferox exhibits an atypical combination of characters including an enlarged rectangular base, 11 endite-bearing podomeres and a hypertrophied distal element bearing 8-10 curved spines. Alacaris? sp. appendages display adaptations for macrophagy. Lihuacaris ferox appendages resemble the frontal appendages of radiodonts, as well as the post-oral endopods of chengjiangocaridid fuxianhuids and other deuteropods with well-documented raptorial/predatory habits. Lihuacaris ferox contributes towards the record of endemic biodiversity in the Guanshan Biota.

SUBMITTER: Jiao DG

PROVIDER: S-EPMC8580442 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Although hyaline cartilage is widely distributed in various invertebrate groups such as sabellid polychaetes, molluscs (cephalopods, gastropods) and a chelicerate arthropod group (horseshoe crabs), the enigmatic relationship and distribution of cartilage in taxonomic groups remains to be explained. It can be interpreted as a convergent trait in animal evolution and thus does not seem to be a vertebrate invention. Due to the poor fossil record of cartilaginous structures, occurrences of mineralized fossil cartilages are important for evolutionary biology and paleontology. Although the biochemical composition of recent cephalopod cartilage differs from vertebrate cartilage, histologically the cartilages of these animal groups resemble one another remarkably. In this study we present fossil material from the late Triassic Polzberg Konservat-Lagerstätte near Lunz am See (Lower Austria, Northern Calcareous Alps). A rich Carnian fauna is preserved here, whereby a morphogroup (often associated with belemnoid remains) of black, amorphous appearing fossils still remained undetermined. These multi-elemental, symmetrical fossils show remarkable similarities to recent cartilage. We examined the conspicuous micro- and ultrastructure of these enigmatic fossils by thin-sectioning and Scanning Electron Microscopy (SEM). The geochemical composition analyzed by Microprobe and Energy Dispersive X-ray Spectroscopy (SEM-EDX) revealed carbonization as the taphonomic pathway for this fossil group. Mineralization of soft tissues permits the 3D preservation of otherwise degraded soft tissues such as cartilage. We examined eighty-one specimens from the Polzberg locality and seven specimens from Cave del Predil (formerly Raibl, Julian Alps, Italy). The study included morphological examinations of these multi-elemental fossils and a focus on noticeable structures like grooves and ridges. The detected grooves are interpreted to be muscular attachment areas, and the preserved branched system of canaliculi is comparable to a channel system that is also present in recent coleoid cartilage. The new findings on these long-known enigmatic structures strongly point to the preservation of cephalic cartilage belonging to the belemnoid Phragmoteuthis bisinuata and its homologization to the cephalic cartilage of modern coleoids.

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New multipodomerous appendages of stem-group euarthropods from the Cambrian (Stage 4) Guanshan Konservat-Lagerstatte.

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