[Paleontology • 2026] Dianhaia heptacantha • A non-biomineralized trilobitomorph euarthropod (Trilobitomorpha: Helmetiida: Helmetiidae) with appendicular morphology from the early Cambrian Chengjiang Biota, China

 

Dianhaia heptacantha 

Zhu, Zeng, Liu & Zhao, 2026

 DOI: doi.org/10.1017/jpa.2026.10257

Abstract

Helmetiida is a major group of Trilobitomorpha and Artiopoda known from Cambrian Burgess Shale-type Lagerstätten. Phylogenetic studies have suggested that they are closely related to trilobites as their possible sister taxon. With seven genera and eight species, Helmetiida has only been found in the Burgess Shale and the Chengjiang biota. Here we describe a new helmetiid, Dianhaia heptacantha n. gen. n. sp., from the early Cambrian Chengjiang biota (Cambrian Series 2, Stage 3), Yunnan Province, South China. Dianhaia heptacantha n. gen. n. sp. possesses an anterior sclerite that is diagnostic of Helmetiida. The semicircular cephalon bears a pair of short genal spines. The thorax consists of seven tergites, each having a pair of long pleural spines and showing edge-to-edge articulation. The pygidium carries one short terminal spine and three pairs of long lateral spines. Dianhaia heptacantha n. gen. n. sp. is distinguished from other helmetiids by different numbers of thoracic tergites and pygidial spines. Computed microtomography shows that D. heptacantha n. gen. n. sp. has a pair of antennae and 13 pairs of homonomous biramous appendages. Each biramous appendage consists of a gnathobasic protopodite, seven-podomerous endopodite, and a lobate exopodite with lamellae. Phylogenetic analysis of Artiopoda resolved Dianhaia n. gen. as the sister taxon of Haifengella within Helmetiida. The discovery of this new helmetiid enriches the taxonomic diversity and appendicular morphoanatomy of Cambrian trilobitomorphs from the Chengjiang biota.

Systematic paleontology

Euarthropoda Lankester, 1904

Artiopoda Hou and Bergström, 1997

Trilobitomorpha Størmer, 1944

Conciliterga Hou and Bergström, 1997

Helmetiida Novozhilov, 1960

Helmetiidae Simonetta and Delle Cave, 1975

Included genera: Helmetia Walcott, 1918; Kuamaia Hou, 1987; Rhombicalvaria Hou, 1987; Haifengella Zhao et al., 2014.

Dianhaia heptacantha n. gen. n. sp. from the Cambrian Stage 3 Chengjiang biota, holotype NIGP 203984, part and counterpart.
(1, 2, 4–9) Part, NIGP 203984a; (1) whole specimen; (2) interpretative drawing; (4) endopodite; (5) a thoracic biramous appendage; (6) exopodite; (7) setae on the exopodite; (8) spines on the pleural spine; (9) spines on the pygidium.
(3) Counterpart, NIGP 203984b.

Scale bars represent 5 mm (1, 2), 1 mm (3, 7), 2 mm (4–6, 8, 9).

 Abbreviations: as, anterior sclerite; ce, cephalic segment; cs, cephalic shield; cw, claw; ed, endite; en, endopodite; ex, exopodite; gs, genal spine; gn, gnathobase; hy, hypostome; lm, lamella; ls, lateral spine; ps, pleural spine; pt, protopodite; py, pygidium; sp, marginal spine; ts, terminal spine; T1–7, thoracic tergite 1–7; xs, setae on exopodite.

Dianhaia heptacantha n. gen. n. sp. from the Cambrian Stage 3 Chengjiang biota, paratype NIGP 203985.
(1) Whole specimen; (2) interpretative drawing; (3) pygidial segments; (4) cephalic and anterior thoracic segments with appendages; (5) marginal spines on the pygidial pleural spine; (6) marginal spines on the pygidium; (7) whole appendage; (8) endopodite; (9) setae on exopodite. Scale bars represent: 5 mm (1, 2), 2 mm (3), 1 mm (4–9).

Abbreviations: as, anterior sclerite; en, endopodite; ex, exopodite; ls, lateral spine; ps, pleural spine; pt, protopodite; py, pygidium; sp, marginal spine; st, sternite; ts, terminal spine; T1–7, thoracic tergite 1–7; xs, setae on exopodite.

Genus Dianhaia new genus

Etymology: Derived from Dianhai, another name of the Dian Lake, which is close to the fossil locality.

Remarks: Dianhaia n. gen. has an oval anterior sclerite and tergites with edge-to-edge articulation, supporting its assignment to Helmetiida. Its well-developed segmental boundaries and several large pygidial spines indicate that it was a member of Helmetiidae (Losso et al., 2025). Different from Helmetia and Kuamaia, Dianhaia n. gen. has long pleural spines and pygidial spines that are similar to the counterparts in Rhombicalvaria and Haifengella (Hou and Bergström, 1997; Zhao et al., 2014; Losso et al., 2025). But compared with Rhombicalvaria and Haifengella, Dianhaia n. gen. has different numbers of thoracic tergites and pygidial spines, suggesting it is a separate genus.

Dianhaia heptacantha new species

Holotype: NIGP 203984a, b, part and counterpart.

Materials: Holotype (NIGP 203984a, b); paratype (NIGP 203985).

Diagnosis: The cephalic shield possesses a pair of short genal spines. The thorax comprises seven thoracic tergites with long pleural spines. The semicircular pygidium bears one very short terminal spine and three pairs of long lateral spines. Biramous appendages have an undivided long-ovate flap with marginal setae and imbricated lamellae.

Occurrence: Maotianshan Shale Member, Yu’anshan Formation, Wutingaspis–Eoredlichia trilobite Zone, Cambrian Series 2, Stage 3, Jianshan section, Kunming City, Yunnan Province, China.

Etymology: Hepta means seven in Greek. Acantha means spine in Greek. The name derives from the seven pairs of thoracic spines and seven pygidial spines in this species.

Reconstruction of the helmetiid euarthropod Dianhaia heptacantha n. gen. n. sp. from the Cambrian Stage 3 Chengjiang biota.
 (1) Dorsal view; (2) ventral view. 
 Morphology of the articular membrane and position of antennae are inferred. The number of antennal podomeres was referred from Kuamaia lata.

 

Yuyan Zhu, Han Zeng, Yao Liu and Fangchen Zhao. 2026.  A non-biomineralized trilobitomorph euarthropod (Helmetiida) with appendicular morphology from the early Cambrian Chengjiang Biota, China. Journal of Paleontology.  First View, pp. 1 - 10. DOI: doi.org/10.1017/jpa.2026.10257 [07 October 2026]

[Paleontology • 2026] Yujingia glutenotunica • Cambrian Fossils illuminate the ambulacrarian common ancestor

 

Yujingia glutenotunica 

He, Mussini, Han, Reich, Ou, Cheng & Shu, 2026 

胶膜玉净虫  |  DOI: doi.org/10.1016/j.cub.2026.08.053

Highlights: 

• A new early Cambrian ambulacrarian, Yujingia, preserves soft parts and tentacles

• Yujingia possesses pinnate appendages with filter-feeding grooves

• Phylogenetic analyses place Yujingia near the common ancestor of extant Ambulacraria

• The fossils suggest living ambulacrarians evolved from tentaculate suspension feeders

Summary

The origins of ambulacrarians, which comprise the morphologically disparate echinoderms (sea stars and their relatives) and the worm-like hemichordates, are poorly constrained, obscuring the assembly of their exceptionally disparate body plans. We describe Yujingia glutenotunica, an ambulacrarian from the early Cambrian Chengjiang biota (518 Ma). Yujingia combines a simple cylindrical body plan with a crown of specialized appendages, including pinnate arms bearing filter-feeding grooves and alternating side-branches. Phylogenetic analyses recover Yujingia within a grade of tentaculate fossils immediately basal to the last common ancestor of all modern ambulacrarians. These results suggest that ambulacrarians evolved from semi-sessile organisms with complex suspension-feeding adaptations, otherwise only found in crown-group echinoderms and tentaculate hemichordates (pterobranchs). Yujingia fills a key gap in the early deuterostome fossil record, thus challenging the conventional worm-like, pharyngeal filter-feeder models for the ambulacrarian last common ancestor and supporting unexpectedly deep origins for the echinoderm and pterobranch body plans.

Keywords: Ambulacraria, Chengjiang biota, deuterostome evolution

Systematic paleontology

Superphylum Ambulacraria

Phylum, Class, Order, Family indet.

Yujingia glutenotunica gen. et sp. nov.

Etymology: The generic name Yujingia refers to the Dharma Vessel held by Guanyin, one of the Four Great Bodhisattvas of Chinese Buddhism, in reference to the fossil’s overall shape. The specific name glutenotunica is derived from the Latin words gluten and tunica, which refers to the optically light body preserved around the visceral mass of the fossil. ...

Kaiyue He, Giovanni Mussini, Jian Han, Mike Reich, Qiang Ou, Meirong Cheng and Degan Shu. 2026. Cambrian Fossils illuminate the ambulacrarian common ancestor. Current Biology. DOI: doi.org/10.1016/j.cub.2026.08.053 [September 16, 2026]

[Paleontology • 2026] Megachelicerax cousteaui • A Chelicera-bearing Arthropod reveals the Cambrian Origin of Chelicerates

Megachelicerax cousteaui

Lerosey-Aubril & Ortega-Hernández, 2026

DOI: doi.org/10.1038/s41586-026-10284-2 

Artistic reconstruction by Masato Hattori 

Abstract

Chelicerata is a megadiverse (over 120,000 species) arthropod clade that includes familiar taxa of profound ecological and economic importance, such as scorpions, spiders and mites. Extant chelicerates share a unique anatomical character, the chelicerae—feeding first appendages terminated by a simple pincer-like chela. The fossil record of these primarily predatory animals spans almost 500 million years, suggesting a likely yet undocumented origin during the Cambrian Explosion. Artiopods4,5,6, megacheirans, habeliids and mollisoniids have been considered Cambrian stem- or crown-group chelicerates, but they all lack unequivocal chelicerae, leaving the emergence of chelicerae-bearing arthropods unclear. Here we describe Megachelicerax cousteaui gen. et sp. nov., a large soft-bodied arthropod from the middle Cambrian of Utah featuring massive three-segmented chelicerae, along with five pairs of pseudobiramous prosomal limbs with non-foliaceous exopodal rami, and plate-like lamellae-bearing opisthosomal appendages. Bayesian and parsimony phylogenetic analyses resolve Megachelicerax as a stem-group chelicerate bridging Cambrian habeliids and post-Cambrian chelicerae-bearing synziphosurines. This finding provides unequivocal evidence of large predatory chelicerates in the Cambrian, illuminates their body plan’s origin, and confirms habeliids, mollisoniids and probably megacheirans as members of total-group Chelicerata.

 

Megachelicerax cousteaui gen. et sp. nov.

Megachelicerax cousteaui. 
 Artistic reconstruction by Masato Hattori (© Harvard University).

Rudy Lerosey-Aubril and Javier Ortega-Hernández. 2026. A Chelicera-bearing Arthropod reveals the Cambrian Origin of Chelicerates. Nature.  DOI: doi.org/10.1038/s41586-026-10284-2  [01 April 2026]

[Paleontology • 2024] Sphenoecium marjumensis & Tarnagraptus cupidus • Benthic pterobranchs from the Cambrian (Drumian) Marjum Konservat-Lagerstätte of Utah, USA

Sphenoecium marjumensis  &
 Tarnagraptus cupidus 

Lerosey-Aubril, Maletz, Coleman, Mouro, Gaines, Skabelund & Ortega-Hernández, 2024

 

DOI: doi.org/10.1002/spp2.1555 

 ortega-hernandezlab.oeb.harvard.edu

 x.com/PlLife2

Abstract

Pterobranchs are rare in Cambrian strata of North America despite discoveries of more than 30 exceptionally preserved fossil biotas. Miaolingian pterobranchs from this continent typically form low-diversity and low-abundance assemblages. Here we describe an abundant pterobranch material from the Drumian Marjum Formation recently collected at the Gray Marjum Quarry in the House Range of Utah, USA. The faunule is composed of two new species: Sphenoecium marjumensis, an encrusting representative forming compact bushy colonies of more than 80 tubes with poorly developed rhizomes, and Tarnagraptus cupidus, an erect growing taxon characterized by intertwining stems and a monopodial colonial growth. Known in extant rhabdopleurids, this mode of colonial growth had hitherto never been observed in fossil pterobranchs. Its documentation in a c. 500-myr-old taxon attests to its deep origin in the evolutionary history of the group. Although the new species almost exclusively occur in the Marjum strata, this pterobranch faunule is broadly similar to those recovered from other Miaolingian Burgess Shale-type deposits of North America in terms of genus-level composition, species richness, and ecological structure. This may indicate that pterobranchs were poorly diverse components of animal communities at that time, or that they mostly thrived in more proximal shelf environments where conditions conducive to their preservation rarely developed. The common co-occurrence of taxa with fundamentally different ecomorphotypes in the Miaolingian Series of North America strongly suggests an earlier phase of morphological diversification of benthic pterobranchs during the early Cambrian, which remains insufficiently documented by fossils.

Keywords: Pterobranchia, Graptolithina, Marjum Formation, Konservat-Lagerstätten, Miaolingian, Drumian

 

Rudy Lerosey-Aubril, Jörg Maletz, Robert Coleman, Lucas Del Mouro, Robert R. Gaines, Jacob Skabelund and Javier Ortega-Hernández. 2024. Benthic pterobranchs from the Cambrian (Drumian) Marjum Konservat-Lagerstätte of Utah. Papers in Palaeontology. DOI: doi.org/10.1002/spp2.1555  ortega-hernandezlab.oeb.harvard.edu/news/back-back-publications-cambrian-ordovician-lagerstätte

  x.com/InvertebratePal/status/1806687327194087599

  x.com/PlLife2/status/1790758316098117943

  x.com/ThePalAss/status/1791479826722766987

[Paleontology • 2025] Falciscaris mumakiana • A New giant nektobenthic radiodont benthivore (Radiodonta: Hurdiidae) from the Early Ordovician Fezouata Biota in Morocco

 

Falciscaris mumakiana 

Potin, Claisse, Trébaol, Gueriau, Wu, Pates & Daley, 2025

 DOI: doi.org/10.4202/app.01278.2025 

 Researchgate.net/publication/398154837

Artwork by Alexis Trébaol

The Fezouata Shale Formation is an Early Ordovician Lagerstätte that preserved exceptionally detailed records of complex marine ecosystems, making it crucial for understanding the early evolution of animal life. It has yielded the youngest known community of radiodonts to date. This group is particularly well known from the Cambrian, with iconic representatives such as Anomalocaris, which are emblematic of the Cambrian explosion. Here we describe a new radiodont from the Fezouata Biota, Falciscaris mumakiana gen. et sp. nov. based on seven specimens of isolated frontal appendages. These appendages bear long endites with large and robust auxiliary spines, suggesting they were adapted for foraging through sediment in search of prey. The appendages of F. mumakiana gen. et sp. nov. can be relatively large compared to the majority of radiodont appendages, with endites reaching up to 11.4 cm in length, suggesting a total body size exceeding one meter for this Ordovician radiodont. In contrast, smaller specimens can be up to 10 times smaller, indicating ontogenetic stages during which the frontal appendage morphology changes little. Following the “Ordovician Plankton Revolution”, the proliferation of planktonic resources and enhanced pelagic-benthic coupling during this period likely allowed for the rise of giant suspension-feeding radiodonts, such as the Aegirocassisinae and F. mumakiana gen. et sp. nov., the new giant benthivore. In term of taxonomic diversity, benthivores radiodonts remain a minor component of radiodont diversity in the Fezouata Biota compared to the more dominant suspension feeders.

Key words: Panarthropoda, Radiodonta, Hurdiidae, gigantism, benthivores, feeding evolution, Fezouata Shale, Early Ordovician.

Superphylum Panarthropoda Nielsen, 1995 

Order Radiodonta Collins, 1996 

Family Hurdiidae Lerosey-Aubril & Pates, 2018

Hurdiid radiodont Falciscaris mumakiana gen. et sp. nov. frontal appendage, 
from the Fezouata Shale Formation, Lower Ordovician, Morocco.
YPM IP 516782a/b, holotype and paratypes 

 Genus Falciscaris nov.

Etymology: From Latin falx (genitive falcis), scythe, in recognition of the strongly curved shape of the endites tips; and Latinised Greek caris, crab, commonly used in arthropod taxonomy.

Falciscaris mumakiana sp. nov.  

 Etymology: Mûmak (plural mûmakil) is a fantasy elephant-like animal from the Tolkien universe Lord of the Rings. They are described as giant animals and are depicted in the third part of the movie trilogy as having 4 long curved tusks equipped with spines, looking like the curved and spiny endite of Falciscaris mumakiana gen. et sp. nov. 

Diagnosis.—Hurdiidae frontal appendage with at least seven podomeres: one proximal, five intermediate and one distal. Proximal podomeres rectangular, taller than long. At least six laminiform endites are present, long ones on five intermediate podomeres and a shorter one distally. Intermediate endites over twice the height of podomeres, all ending in a strongly curved, hook-like tip. Each endite bears dorsally curved auxiliary spines in at least three sizes, alternating such that spines of the same size are never adjacent.

Artistic life reconstruction of the hurdiid radiodont Falciscaris mumakiana gen. et sp. nov. 
Apart from the frontal appendages, the reconstruction is based on other related hurdiids.

by Alexis Trébaol

Gaëtan J.-M. Potin, Pénélope Claisse, Alexis Trébaol, Pierre Gueriau, Yu Wu, Stephen Pates, and Allison C. Daley. 2025. A New giant nektobenthic radiodont benthivore from the Early Ordovician Fezouata Biota in Morocco. Acta Palaeontologica Polonica. 70(4). 709-722. DOI: doi.org/10.4202/app.01278.2025 

 Researchgate.net/publication/398154837_A_new_giant_nektobenthic_radiodont_benthivore_from_the_Early_Ordovician_Fezouata_Biota_in_Morocco

[Paleontology • 2025] ?Carcinosoma aurorae • Early Ordovician Sea Scorpions from Morocco suggest Cambrian Origins and main Diversification of Eurypterida

?Carcinosoma aurorae

Van Roy, Richards & Ortega-Hernández, 2025

DOI: doi.org/10.1098/rspb.2025.2061 

Abstract

Eurypterida were a diverse clade of aquatic euchelicerates that occupied environments ranging from freshwater to fully marine and included several of the largest euarthropods on record. Although a Middle Ordovician megalograptid hitherto represented the oldest evidence of this clade, its phylogenetic position suggested an earlier history for the origin and main diversification within Eurypterida. Here, we report unequivocal eurypterid fragments from the Early Ordovician Fezouata Biota of Morocco, pre-dating the previously oldest record of this group by 12–15 million years. We describe ?Carcinosoma aurorae n. sp. based on several distinctively spinose isolated appendages diagnostic of the eurypterine clade Carcinosomatidae. This discovery demonstrates that the major morphological and ecological diversifications within Eurypterida between swimming Eurypterina and benthic crawling Stylonurina had taken place by the Early Ordovician. Furthermore, the derived phylogenetic position of carcinosomatids implies that most eurypterine clades had already diversified by that time. A cuticle patch with dense scales, reminiscent of pterygotids, likely belongs to a second eurypterid species. The remarkable diversity of euchelicerates in the Fezouata Biota indicates undocumented Cambrian origins and provides further evidence for an early eurypterid radiation centred off Gondwana. Significantly, the sister-group relationship between Eurypterida and Arachnida entails equally early arachnid origins.

Keywords: Arachnida, Cambrian explosion, Carcinosomatidae, Chelicerata, Eurypterida, Fezouata Biota, Great Ordovician Biodiversification Event, Konservat-Lagerstätte, Pterygotidae, Tremadocian

Euarthropoda Lankester, 1904 

Euchelicerata Weygoldt & Paulus, 1979 

Prosomapoda Lamsdell, 2013 

Planaterga Lamsdell, 2013 

Dekatriata Lamsdell, 2013 

Eurypterida Huxley, 1857  

Eurypterina Novojilov, 1962  

Diploperculata Lamsdell Hoşgör & Selden, 2013 

Carcinosomatoidea Størmer, 1934 

Carcinosomatidae Størmer, 1934 

Genus: ?Carcinosoma Claypole, 1890  

Isolated appendages of ?Carcinosoma aurorae n. sp. from the Early Ordovician (upper Tremadocian) Fezouata Biota of Morocco.
 (A–D) Holotype NM S 5974 consisting of a walking limb, gnathobase and four fragmentary tergites, part. (A) Overview, dry. (B) Overview, under a mixture of ethanol and propanol. (C) Details of the limb and gnathobase, dry. (D) Details of the limb and gnathobase, under a mixture of ethanol and propanol.
(E,F) Paratype MCZ.IP. 202866, consisting of nearly complete walking limb, part. (E) Dry. (F) Under demineralized water. All scale bars represent 10 mm.

?Carcinosoma aurorae n. sp.

 

Derivation of name. Genitive, from Latin, aurora, -ae, meaning ‘of the dawn’, referring to the early occurrence of this animal, making it the oldest eurypterid currently on record.

 

Diagnosis. Species of ?Carcinosoma with articulating spine pairs of unequal length on podomeres of limbs II–V , with positions of long and short spines alternating between podomeres. Gnathobases with long and slender teeth.

Peter Van Roy, Jared C. Richards and Javier Ortega-Hernández. 2025. Early Ordovician Sea Scorpions from Morocco suggest Cambrian Origins and main Diversification of Eurypterida. Proc. R. Soc. B. 292: 20252061. DOI: doi.org/10.1098/rspb.2025.2061 [12 November 2025]

 

[Paleontology • 2025] Oura megale • A large early Cambrian Deuteropod with a delta-shaped tailpiece

 Oura megale O’Flynn, Williams & Liu, 

in O’Flynn, Williams, Thomas, Hou et Liu, 2025. 

DOI: doi.org/10.26879/1547 

ABSTRACT

We describe Oura megale n. gen. n. sp., a large (ca. 14 cm long) euarthropod from the lower Cambrian Chengjiang Konservat-Lagerstätte of Yunnan Province, China. It possesses stalked, compound eyes and a possible raptorial frontal appendage (synapomorphies and symplesiomorphies of lower stem- and upper stem-group euarthropods, respectively), but in combination with deuteropodan synapomorphies (e.g., a multi-segmented head). Micro-X-ray fluorescence shows a thorax that consists of 10 comparatively long and five comparatively short segments. The terminal segment articulates with a large, delta-shaped tailpiece that may have conferred high positional manoeuvrability in the water column. The phylogenetic position of O. megale n. gen. n. sp. in the euarthropod stem may add support to the homology of raptorial frontal appendages between lower stem-group euarthropods and deuteropods.

Keywords: new genus; new species; Cambrian Chengjiang biota; euarthropod; micro-X-ray fluorescence; tailpiece

 Oura megale n. gen n. sp. (YKLP 17237).
A, photograph of ventral view. B, Fe map. C, composite line drawing. D, F1 map. E, P map. F, F1 map of head region. G, P map of head region.

 Abbreviations: l, left; r, right; A1, frontal appendage; ex.A6, exopod of 5th head limb on head segment 6; an, cephalic segment (n); as, anterior sclerite; cf, compactional fold; e, eye; es, eye stalk; exn, exopod (n); sn, sternite (n); Tn, thoracic exopod (n); tn, thoracic segment (n). Scale bars represent 20 mm.

SYSTEMATIC PALAEONTOLOGY

Phylum EUARTHROPODA Lankester, 1904

Unranked DEUTEROPODA Ortega-Hernández, 2016

Class, Order and Family incertae sedis

Genus OURA O’Flynn, Williams and Liu, new genus

Etymology. Gr. Oura, f. tail.

Remarks. Oura n. gen. is ascribed to Deuteropoda — as defined by a multi-segmented head and body arthrodization (Ortega-Hernández, 2016). Oura n. gen. bears: stalked, compound eyes, that is, a synapomorphy and symplesiomorphy of lower stem-group Euarthropoda and Deuteropoda, respectively (Ortega-Hernández, 2016, p. 11, table 4); and robust frontal appendages (FA, i.e., A1) that insert approximately one-half the length of the head behind the eye stalks and are inferred to be deutocerebral. The proximal-most three podomeres of the right-side frontal appendage (FA) are preserved, and these are morphologically like those of radiodonts and certain ‘great appendage’-bearing deuteropods.

Oura megale O’Flynn, Williams and Liu, new species

  

Etymology. Gr. Megale, large, great.

Diagnosis. Six cephalic segments. From anterior to posterior, these are: oblate spheroidal anterior sclerite to which large ovate paired stalked lateral eyes are attached; post-ocular segment with paired uniramous deutocerebral FAs; and four subsequent segments. FA antero-laterally orientated, consisting of ≥ three podomeres that bear elongate triangular spines. Thorax consists of 15 segments (anterior-most 10 comparatively long; posterior-most five comparatively short), each with one pair of presumed biramous appendages. Segment 15 articulated with large, ogival delta tailpiece.

Robert J. O’Flynn, Mark Williams, Ed Thomas, Xianguang Hou, and Yu Liu. 2025. Oura megale n. gen. n. sp., A large early Cambrian Deuteropod with a delta-shaped tailpiece. Palaeontologia Electronica. 28(3):a44. DOI: doi.org/10.26879/1547 

palaeo-electronica.org/content/2025/5687-early-cambrian-deuteropod-oura-megale

 x.com/PalaeoE/status/1977837034074210364

Plain Language Abstract:  Oura megale, a large arthropod (segmented, jointed-limbed animal), comparable in size to anomalocaridids (i.e., giant invertebrate Cambrian predators featuring mouthparts composed of a ring of plates), inhabited the Cambrian seas (approximately 518 million years ago) of south-western China. It had stalked eyes and a grasping frontal appendage, but in combination with a multi-segmented head, as we see in, for example, modern insects. Palaeontological techniques show a trunk that consists of 10 long and five short segments. The rearmost segment is associated with a large, delta-shaped tail that may have been conducive to efficient swimming. The evolutionary relationships between O. megale and other arthropods may suggest that the grasping appendage (shared by several arthropods) is inherited from a common ancestor.

[Paleontology • 2025] Nektognathus evasmithae • A fossilized ventral ganglion reveals a chaetognath affinity for Cambrian nectocaridids

 

Nektognathus evasmithae 

 Vinther, Parry, Lee, Nielsen, Oh, C. Park, Kihm, DeVivo, Harper, Nielsen & T.-Y. S. Park, 2025

DOI: doi.org/10.1126/sciadv.adu6990 

Artwork by Robert Nicholls

Abstract

Nectocaridids are enigmatic Palaeozoic animals with a controversial phylogenetic position. Previous hypotheses have placed them in their own phylum, chordates, molluscs (specifically cephalopods), or radiodont panarthropods. We describe here a nectocaridid, Nektognathus evasmithae gen. et sp. nov. from the early Cambrian (~519 million years) Sirius Passet Lagerstätte of North Greenland. Key specimens preserve paired, phosphatized arcuate structures consistent with preservation of a ventral ganglion, a feature characteristic of extant and fossil chaetognaths, including the amiskwiid Timorebestia koprii also from Sirius Passet. Nektognathus shares a gnathostomulid-like jaw apparatus, lateral fins, subterminal anus, and large antennae with Timorebestia and Amiskwia, placing nectocaridids in the chaetognath stem lineage. The complex sensory anatomy of nectocaridids, which is partially shared with other extinct amiskwiids, highlights a more dynamic predatory lifestyle much higher in the trophic food chain during early chaetognath evolution.

Nektognathus evasmithae gen et sp. nov. holotype, MGUH34956.
 (A) Image with low-angle lighting illuminated from top left, coated with magnesium oxide smoke. (B) Illuminated submerged in water under high-angle illumination. (C) EPMA carbon elemental map. (D) Interpretative drawing. (E to G) Close-up of anterior trunk region preserving the jaw apparatus. (E) Carbon elemental map featuring the outline of the jaw apparatus due to splitting of the specimen. (F) Low-angle lighting illumination coated with magnesium smoke. (G) Low-angle illumination coated with magnesium smoke with outline of jaw apparatus superimposed. (H and I) Specimen of Isoxys in the anterior section of the digestive tract, outlined in (I). (J and K) Preservation of ventral ganglion with superimposed striated musculature outlined in (K). (L and M) Digestive tract preserved by modest relief in the posterior trunk and caudal region, outlined in (M). Colors in interpretative drawing represent gut (green), ventral ganglion and nervous system (blue), jaw apparatus (red and mustard yellow), eyes (light yellow), Isoxys specimen (pink) and body outline (gray). a, antennae; cr, caudal region; fr, fin rays.

Systematic Paleontology

Spiralia Schleip, 1929

Chaetognathifera Bekkouche and Gąsiorowski, 2022

Phylum Chaetognatha Leuckart, 1854 (stem group)

Family Nectocarididae Conway Morris, 1976

Diagnosis: Dorsoventrally flattened bilaterian with lateral fins supported by fin rays. The body is divided into a distinct head and trunk. The head is narrow and bears long frontal antennae and a pair of large, lateral eyes of camera type. A jaw apparatus flanks the digestive tract in the anteriormost part of the trunk, consisting of a bilateral set of very large, subtriangular elements and a basal, anterior, median plate. The tubular gut terminates subterminally anterior to the posterior fin region. Diagnosis was emended from Conway Morris (1976).

Genera included: Nectocaris Conway Morris 1976, Nektognathus gen. nov.

Genus Nectocaris Conway Morris 1976

Genus Nektognathus evasmithae gen. et sp. nov.

Locality and horizon: The material was collected at locality 1 in Sirius Passet, 82°47.6′N, 42°13.7′W, Peary Land, North Greenland.

Etymology: Nekto (Gr) for swimming and gnatha (Gr) meaning jaw. The species name is for Professor Emeritus Eva Smith in recognition of her enduring fight for impartial justice for everyone and holding politicians accountable.

Diagnosis for species and genus: Nectocaridid with distinct, caudal fin-region lacking fin rays. The eye stalks are short or absent. Ventral ganglion forms distinct arcuate structures in the midbody that is ~25% the length of the trunk.

 

 Jakob Vinther, Luke A. Parry, Mirinae Lee, Morten Lunde Nielsen, Yeongju Oh, Changkun Park, Ji-Hoon Kihm, Giacinto DeVivo, David A. T. Harper, Arne T. Nielsen and Tae-Yoon S. Park. 2025. A fossilized ventral ganglion reveals a chaetognath affinity for Cambrian nectocaridids. Science Advances. 11(30); DOI: doi.org/10.1126/sciadv.adu6990 [23 Jul 2025]

[Paleontology • 2025] Primicaris larvaformis • A tiny Cambrian stem-mandibulate reveals Independent Evolution of Limb Ttagmatization and Specialization in early Euarthropods

Primicaris larvaformis  Zhang, Han, Zhang, Liu & Shu, 2003

in Liu, Zeng, Zhao, Y. Zhu, Li, Yin et M. Zhu, 2025. 

DOI: doi.org/10.1038/s41598-025-03544-0 

Abstract

The mandibulate euarthropods are the most speciose animal group, but the evolutionary gaps in origin of mandibulate body plan remain unresolved. Marrellomorphs, a common Paleozoic euarthropod group, had a long evolutionary history from Cambrian to Devonian. With computed microtomography, here we report the fine-scale soft-bodied morphoanatomy of the oldest marrellomorph Primicaris larvaformis, a millimeters-sized euarthropod from the ~ 518-million-year-old Chengjiang biota, China. Primicaris possesses a body plan featuring morphologically similar post-antennular biramous appendages, but also mandibulate diagnostic features including multi-segmented exopodites, a well-developed and differentiated hypostome-labrum complex, and a pancrustacean-like topological configuration of frontalmost three pairs of appendages. Phylogenetic analysis resolves Acercostraca and Marrellida as stem-Mandibulata. The undifferentiated post-antennular appendages in Primicaris suggest a possibility that the head appendages acquired a crown-mandibulate configuration before their morphological specialization in mandibulate origin. The emergence of novel appendage morphotypes in Acercostraca and Marrellida reveals that the complexity of limb tagmatization evolved independently in different Euarthropoda clades.

Keywords: Computed tomography, Limb tagmatization, Euarthropod, Mandibulate, Chengjiang biota, Cambrian explosion

Overall morphology of Primicaris larvaformis.
 (a) NIGP 200783A, optical photo, ventral view. (b, c) Juvenile specimens. (b) NIGP 200792, optical photo, ventral view. (c) NIGP 200791A, optical photo, dorsal view. (d, e) NIGP 200812 (see also in Fig. 3). (d) Optical photo, dorsal view. (e) Tomographic maximum projection image, dorsal view. (f) NIGP 200798A, optical photo, ventral view. (g) NIGP 200809A, optical photo, dorsal view. (h) NIGP 200810, optical photo, dorsal view. (i) NIGP 200813A, optical photo, ventral view. (j, k) NIGP 200799. (j) Optical photo, dorsal view. (k) SEM-EDS map of carbon. (i, m) NIGP 200817. (l) Optical photo, dorsal view. (m) SEM-EDS map of iron.

 a1–14, post-antennular appendage 1–14; ab, anterior border; an, antennule; ax, axial region; ba, base of appendage; dv, gut diverticulae; eb, eye bulge; er, eye ridge; gt, gut; ls1–11, lateral spine of dorsal shield 1–11; pl, pleural region; ps, posterior spine of dorsal shield; rg, ridge of dorsal shield; st, setae. 

Scale bars represent: 0.5 mm (a–m).

Systematic palaeontology

Phylum Euarthropoda Lankaster, 1904.

Order Acercostraca Lehmann, 1955.

Genus Primicaris Zhang, Han, Zhang, Liu and Shu, 2003

Primicaris larvaformis Zhang, Han, Zhang, Liu and Shu, 2003

Emended diagnosis: Small euarthropod with a body length less than 6 mm. Undivided dorsal shield with up to twelve pairs of lateral marginal spines and a pair of posterior spines. One pair of uniramous antennules is followed by up to 14 homonomous pairs of biramous appendages (emended from ref. 13).

 

Yao Liu, Han Zeng, Fangchen Zhao, Yuyan Zhu, Yimeng Li, Zongjun Yin and Maoyan Zhu. 2025. A tiny Cambrian stem-mandibulate reveals Independent Evolution of Limb Ttagmatization and Specialization in early Euarthropods. Scientific Reports. 15: 19115. DOI: doi.org/10.1038/s41598-025-03544-0 [31 May 2025]

[Paleontology • 2025] Mosura fentoni • Early Evolvability in Arthropod Tagmosis exemplified by A New Radiodont from the Burgess Shale

 

Mosura fentoni 

 Moysiuk & Caron, 2025

  

DOI: doi.org/10.1098/rsos.242122 

Abstract

Much diversity in arthropod form is the result of variation in the number and differentiation of segments (tagmosis). Fossil evidence to date has suggested that the earliest-diverging arthropods, the radiodonts, exhibited comparatively limited variability in tagmosis. We present a new radiodont, Mosura fentoni n. gen. and n. sp., from the Cambrian (Wuliuan) Burgess Shale that departs from this pattern. Mosura exhibits up to 26 trunk segments, the highest number reported for any radiodont, despite being among the smallest known. The head is short, with a small, rounded preocular sclerite, three prominent eyes and appendages with curving endites tipped with paired spines, altogether suggesting a nektonic, macrophagous predatory ecology. The trunk is divided into a neck, mesotrunk with large swimming flaps and multisegmented posterotrunk with tightly spaced bands of gill lamellae and reduced flaps. Detailed preservation of expansive circulatory lacunae, closely associated with the gills, clarifies the nature of similar structures in other Cambrian arthropod fossils, including Opabinia. The morphology of the posterotrunk suggests specialization for respiration, unique among radiodonts, but broadly convergent with the xiphosuran opisthosoma, isopod pleon and hexapod abdomen. This reinforces the hypothesis that multiple arthropod lineages underwent parallel diversification in tagmosis, in tandem with their initial Cambrian radiation.

Keywords: segmentation, convergence, Cambrian explosion, functional specialization, body plan, arthropod

Systematic palaeontology

 

Superphylum Panarthropoda Nielsen 1995 

Phylum Arthropoda Gravenhorst 1843

Order Radiodonta Collins 1996 

Family Hurdiidae Lerosey-Aubril & Pates 2018 

Genus Mosura n. gen.

Type species: M. fentoni n. sp., by monotypy.

Etymology: From the name of the fictional Japanese monster, or kaiju モスラ (also known as ‘Mothra’), romanized according to Hepburn style, in reference to the moth-like appearance of the animal.

 Morphological summary and artistic reconstruction.
 (a) Life reconstruction; (b) whole body, dorsal view; (c) ventral view; (d) cross-section through mesotrunk;
(e) appendage, lateral view; (f) appendage, frontal view; (g) podomere 5 from lateral and frontal views; (h) appendage, ventral view, extended; (i) appendage, ventral view, retracted.

 Abbreviations: bf, bifurcated tip of endite; br, brain; en, endite; fa, frontal appendage; fg, foregut; fl, flap; fn, frontal appendage nerve/circulatory lacuna; ip, putative inner plates of oral cone; lc, lacuna of circulatory system; le, lateral eye; lm, band of lamellae; me, median eye; mg, midgut; mo, mouth; mt, mesotrunk; ne, neck; np#, lateral eye neuropil #; oc, oral cone; on, optic nerve; os, preocular sclerite; ot, outer spine of appendage; p, phosphatized element; pd#, podomere #; pt, posterotrunk; ra, flap ray; sb, segmental boundary; tp, terminal process; ts, terminal spine of appendage. Elements shown in dashed lines (appendage podomeres, oral plates, ring-shaped brain) are uncertain and have been inferred.

Artwork by Danielle Dufault © Royal Ontario Museum.

 

Mosura fentoni n. sp.

 

Holotype: ROMIP 67995, part and counterpart, a complete specimen preserved in dorsal view (figure 2a–d).

Etymology: In honour of Peter E. Fenton, for his 40 years of service as a technician in the Invertebrate Palaeontology section at the Royal Ontario Museum, and for his unwavering friendship to both authors.

Diagnosis: Radiodont with an adult trunk region divided into a four-segmented neck, six-segmented mesotrunk and up to 16-segmented posterotrunk. Flaps of mesotrunk up to ca 60% of core segment width. Flaps of posterotrunk markedly differentiated in size, less than ca 20% of core segment width. Caudal blades absent, posterotrunk terminating in pair of small, triangular processes. Appendages with six elongate endites (ca 3.5 times podomere height) with bifurcated tips. Lateral eye stalks short, less than eye diameter.

Joseph Moysiuk and Jean-Bernard Caron. 2025. Early Evolvability in Arthropod Tagmosis exemplified by A New Radiodont from the Burgess Shale. R. Soc. Open Sci. 12: 242122. DOI: doi.org/10.1098/rsos.242122 [14 May 2025]

 

[Paleontology • 2025] Helmetia expansa Walcott, 1918 Revisited – New insights into the internal anatomy, moulting and phylogeny of Conciliterga

Helmetia expansa Walcott, 1918 

in Losso, Caron et Ortega-Hernández, 2025. 

DOI: doi.org/10.1080/14772019.2025.2468195 

 Reconstruction by Marianne Collins

Abstract

The trilobitomorphs are a megadiverse and ecologically versatile group of Paleozoic euarthropods that include the iconic trilobites, as well as non-biomineralized clades exclusively known from Konservat-Lagersttätten. The concilitergans, defined by the presence of a broad, variably effaced and flattened dorsal exoskeleton, have received comparatively little attention. This is particularly true for Helmetia expansa from the mid-Cambrian Burgess Shale (British Columbia) – the first chronologically reported species of Conciliterga, which was originally figured (based on a single specimen) by Walcott (1918). Here, we present the first comprehensive description of H. expansa based on all material available from the Burgess Shale, totalling 36 specimens housed at the Royal Ontario Museum and the Smithsonian Institution. The non-biomineralized dorsal exoskeleton is broad and flat, with a serrated margin throughout. The body consists of a cephalon with well-developed anterolateral spines, six thoracic tergites and a large pygidium bearing two pairs of lateral spines and a single terminal spine. The preserved appendages include short uniramous antennae followed by 15 pairs of homonomous and biramous limbs composed of a gracile endopodite and an exopodite with a broad lobe and thick lamellae. The digestive system consists of a straight gut tract, including a ‘J’-shaped foregut and five paired digestive glands on the anterior half of the body expressed as small and convex oblong structures with a submillimetric lamellar ultrastructure. Two specimens of H. expansa provide the first direct evidence of moulting in concilitergans. The lack of dorsal ecdysial sutures suggests a marginal moulting strategy similar to extant Xiphosura. A revised phylogeny of Trilobitomorpha supports Arthroaspis bergstroemi from the early Cambrian Sirius Passet of Greenland as the earliest branching concilitergan and prompts a new diagnosis for the clade. Our results inform the internal relationships within Conciliterga and formalize the families Helmetiidae (Helmetia, Rhombicalvaria, Haifengella and Kuamaia) and Tegopeltidae (Tegopelte, Skioldia, Saperion).

Keywords: Burgess Shale, Cambrian, Conciliterga, exceptional preservation, Helmetiida, moulting

Artiopoda Hou & Bergström, 1997

Trilobitomorpha Størmer, 1944

Conciliterga Hou & Bergström, 1997

Constituent taxa: Arthroaspis bergstroemi Stein et al., 2013; Helmetiida Novozhilov, 1960.

Order Helmetiida Novozhilov, 1960

Constituent taxa: Family Tegopeltidae Simonetta & Delle Cave, 1975; Family Helmetiidae Simonetta & Delle Cave, 1975.

Concilitergan diversity and relationships.
A, Arthroaspis bergstroemi, MGUH 30382, from the early Cambrian (Stage 3) Sirius Passet, Greenland. B, Helmetia expansa, USNM 83952, from the mid-Cambrian (Wuliuan) Burgess Shale, Canada. C, Kuamaia lata, CJHMD 00064, from early Cambrian (Stage 3) Chengjiang, China. D, Tegopelte gigas, USNM 189201, from the mid-Cambrian (Wuliuan) Burgess Shale, Canada.
E, simplified topology based on results from phylogenetic analyses herein which resolved Arthroaspis bergstroemi as an early-branching concilitergan.

 Holotype of Helmetia expansa USNM 83952, dorsal view.
A, Cross polarized light. B, Low angle light. C, Magnification of A showing cephalon. D, Magnification of A showing lamellae.

Abbreviations: cep, cephalon; anl, anterolateral spine; ant, antenna; asc, anterior sclerite; ey, eye; ex, exopodite; hyp, hypostome; lm, lamellae; mey, medial eyes; mg, midgut gland; opn, optical nerve; py, pygidium; rs, reniform structure; stn, sternite number; th, thorax.

Family Tegopeltidae Simonetta & Delle Cave, 1975

Constituent genera: Tegopelte Simonetta & Delle Cave, 1975; Skioldia Hou & Bergström, 1997; and Saperion Hou & Bergström, 1997.

...

Family Helmetiidae Simonetta & Delle Cave, 1975

Emended diagnosis: Concilitergans in which the thorax has tergites with non-effaced boundaries and well-developed pleural spines, and a pygidium with variable number of posterolateral spines and a medial terminal spine with a broad base.

Constituent genera: Helmetia Walcott, 1918; Rhombicalvaria Hou, 1987; Haifengella Zhao et al., 2014; Kuamaia Hou & Bergström, 1997.

Genus Helmetia Walcott, 1918

Type species: Helmetia expansa Walcott, 1918

 

 the Burgess Shale concilitergan Helmetia expansa.

 Reconstruction by Marianne Collins

Conclusion: 

We redescribe Helmetia expansa as one of the best-known concilitergans based on 36 specimens from the Burgess Shale. It has large anterolateral spines, a serrated margin, a six-segmented thorax and a large pygidium with two pairs of spines.

New material reveals insights into the preservation of non-biomineralized structures in H. expansa, including antennae, biramous appendages, optic structures and traces of digestive glands. Additionally, H. expansa acquired an adult exoskeletal morphology that at least doubled in size throughout ontogeny and provides rare direct evidence of moulting in a non-biomineralized Cambrian trilobitomorph.

New morphological characters and broader taxon sampling of Cambrian artiopodans clarifies the internal relationships within Conciliterga, which contains Arthroaspis bergstroemi from Sirius Passet and two major families Helmetiidae and Tegopeltidae, both represented in the Burgess Shale and Chengjiang Lagerstätten.

Sarah R. Losso, Jean-Bernard Caron and Javier Ortega-Hernández. 2025. Helmetia expansa Walcott, 1918 Revisited – New insights into the internal anatomy, moulting and phylogeny of Conciliterga. Journal of Systematic Palaeontology. 23(1); 2468195. DOI: doi.org/10.1080/14772019.2025.2468195  [04 Apr 2025]