bioRxiv Science⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/2021.08.18.456779

Before trilobite legs: Pygmaclypeatus daziensis reconsidered and the ancestral appendicular organization of Cambrian artiopods

Schmidt, M.·Hou, X.·Zhai, D.·Mai, H.·Belojevic, J.·Chen, X.·Melzer, R. R.·Ortega-Hernandez, J.·Liu, Y.
View original source ↗Export metadata ↓

Abstract

The Cambrian Stage 3 Chengjiang biota in South China is one of the most influential Konservat-Lagerstatten worldwide thanks to the fossilization of diverse non-biomineralizing organisms through pyritization. Despite their contributions to understanding the evolution of early animals, several Chengjiang species remain poorly known due to their scarcity and/or incomplete preservation. Here, we use micro-computed tomography to reveal in detail the ventral appendage organization of the enigmatic non-trilobite artiopod Pygmaclypeatus daziensis - one of the rarest euarthropods in Chengjiang - and explore its functional ecology and broader evolutionary significance. Pygmaclypeatus daziensis possesses a set of uniramous antennae and 14 pairs of post-antennal biramous appendages, the latter of which show an unexpectedly high degree of heteronomy based on the localized differentiation of the protopodite, endopodite and exopodite along the antero-posterior body axis. The small body size (less than 2 cm), presence of delicate spinose endites, and well-developed exopodites with multiple paddle-shaped lamellae on the appendages of P. daziensis indicate a nekto-benthic mode of life, and a scavenging/detritus feeding strategy. Pygmaclypeatus daziensis shows that appendage heteronomy is phylogenetically widespread within Artiopoda - the megadiverse clade that includes trilobites and their relatives with non-biomineralizing exoskeletons - and suggests that a single exopodite lobe with paddle-like lamellae is ancestral for this clade. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=155 SRC="FIGDIR/small/456779v1_ufig1.gif" ALT="Figure 1"> View larger version (111K): org.highwire.dtl.DTLVardef@b4ddaaorg.highwire.dtl.DTLVardef@44f686org.highwire.dtl.DTLVardef@1950095org.highwire.dtl.DTLVardef@1596739_HPS_FORMAT_FIGEXP M_FIG C_FIG Cover image: Morphological reconstruction of the non-trilobite artiopod Pygmaclypeatus daziensis from the early Cambrian (Stage 3) Chengjiang biota in south China. Artwork by Holly Sullivan (https://www.sulscientific.com/).

Source connections

Explore related subjects

paleontologyPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Schmidt, M., Hou, X., Zhai, D., Mai, H., Belojevic, J., Chen, X., Melzer, R. R., Ortega-Hernandez, J., Liu, Y.. 2021-08-19. Before trilobite legs: Pygmaclypeatus daziensis reconsidered and the ancestral appendicular organization of Cambrian artiopods. https://doi.org/10.1101/2021.08.18.456779

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Feeding experiments with Senegal bichir Polypterus senegalus provide evidence for diet-related tooth damage and dental microwear

Dental microwear is a useful tool for reconstructing jaw movements and diet in toothed vertebrates, but its application to fishes (Actinopterygii and Chondrichthyes) remains limited. This is partly due to the lack of experiments directly linking diet and microwear in these groups; only one highly-derived teleost (Actinopterygii, or ray-finned fishes) species of recent origins, the three-spined stickleback Gasterosteus aculeatus, has been subject to controlled feeding experiments. As sticklebacks are suction or ram feeders that live on macroplankton and insect larvae and do not use their dentitions for prey processing, the absence of experimental data from other fish species limits our ability to interpret dental microwear and infer diet and feeding style in a wider range of fossil and living species with various ecologies. Here we present the results of a second feeding experiment involving fishes using the basally-branching, biting, often-piscivorous ray-finned fish Senegal bichir Polypterus senegalus to evaluate whether controlled diet differences can generate detectable tooth damage and dental microwear patterns. Individuals were fed four different food items - loaches, shrimp, pellets, and mealworms - for one, two, and three months. We then examined tooth tip damage and linear microwear (scratches). Shrimp and mealworm feeding produced short scratches, whereas pellet and loach feeding produced long scratches. Most teeth exhibited apical tip damage despite the presence of a solid enameloid acrodin cap (a characteristic of ray-finned fishes), with damage being larger in loach-fed individuals and smaller in those fed with mealworms. Our results suggest a possible relationship between diet, tooth damage, and dental microwear in non-durophagous fishes which never-the-less use teeth for prey capture and processing, offering a framework for inferring diet in extinct forms with similar ecomorphology to Polypterus.

paleontology↗
bioRxiv2026

Diversity in early animal communities of the Ediacaran, Avalon assemblage

Diversity is an emergent property of macroecological and macroevolutionary processes. The Avalon assemblage preserves near-census snapshots of Ediacaran communities, enabling tests of the drivers of diversity. However, it remains unclear how alpha diversity varied among surfaces or whether variation reflected uneven sampling, abiotic context or biotic processes. We analysed diversity for 11,342 specimens across 22 surfaces and examined abiotic and biotic correlates. Despite compositional variation, most surfaces fell into four community types dominated by Fractofusus andersoni, F. misrai and/or Pectinifrons, Bradgatia, or upright fronds, with potential substructure within the upright-frond type, whereas Clapham's Pigeon Cove and Shingle Head communities, from the oldest and youngest formations, respectively, may indicate greater community differentiation near the sampled stratigraphic limits. Sampling effort varied widely, yet taxon-area curves showed richness was well captured on 12 of 22 surfaces, and Shannon and Simpson diversity remained consistent across sampling completeness and taxonomic treatments. Diversity showed no clear associations with locality or stratigraphic affiliation, but differed among community types and declined with increasing vertical segregation. Overall, these results suggest that, among the predominantly Newfoundland communities sampled, Avalon alpha diversity may have been shaped more by local community assembly and organisation than by broader geographic, environmental and temporal context.

paleontology↗
bioRxiv2026

Durophagous adaptations in a new crocodyliform from the Santonian of Hungary and a systematic reassessment of European Cretaceous atoposaurids

Atoposauridae comprises a group of diminutive, semiterrestrial, brevirostrine neosuchian crocodyliforms that represents a characteristic component of European Jurassic-Cretaceous tetrapod faunas. Although frequently evaluated within the context of crown-group Crocodylia origins, their highly contested phylogenetic relationships continue to obscure their precise role in crocodylomorph evolutionary history. Particular ambiguity surrounds the monophyly of the genus Theriosuchus - with some hypotheses inferring long-term persistence of the lineage in Mesozoic Europe, whereas others interpreting select Cretaceous species as representatives of separate, even non-atoposaurid clades (e.g. Sabresuchus spp). We describe a new, stratigraphically intermediate taxon from the Santonian of Hungary based on isolated cranial elements, consistently placed as the sister taxon of Sabresuchus (Theriosuchus) sympiestodon from the Maastrichtian of Romania by our comprehensive set of phylogenetic analyses using three separate datasets. Sabresuchus tribodon sp. nov. is either recovered within Atoposauridae (global datasets) or Paralligatoridae (ingroup analysis) and can be distinguished from all other representatives of these groups by a specialized morphology consisting of massive, thick-enameled bulbous posterior maxillary teeth ornamented with apicobasal ridges, an extremely short rostrum with a reduced number of maxillary and dentary teeth, and the significantly upturned dorsal margin of the posterior dentary and surangular. Comparable anatomical adaptations are present in ecomorphologically convergent extinct crocodyliforms whose inferred feeding ecology included durophagy. However, this complete suite of characters has not been previously documented in either atoposaurids or paralligatorids. Our systematic reassessment results in an up-to-date taxonomy of Cretaceous European atoposaurids and tentatively confirms the polyphyly of Theriosuchus, though more definitive conclusions require combining individual, differently focused datasets. We reinterpret Aprosuchus ghirai from the Maastrichtian of Romania as a junior synonym of Sabresuchus sympiestodon and the putative European notosuchian Ogresuchus furatus from the Maastrichtian of Spain as an indeterminate atoposaurid.

paleontology↗