Publications

In Press
R. Lerosey-Aubril, J. Maletz, R. Coleman, L. Del Mouro, R. R Gaines, J. Skabelund, and J. Ortega-Hernández. In Press. “Benthic pterobranchs from the Cambrian (Drumian) Marjum Konservat-Lagerstatte of Utah.” Papers in Palaeontology .
J. C Richards, K. Nanglu, and J. Ortega-Hernández. In Press. “The Fezouata Shale Formation biota is typical for the high latitudes of the early Ordovician – a quantitative approach.” Paleobiology.
K. Nanglu and J. Ortega-Hernández. In Press. “Post-Cambrian survival of the tubicolous scalidophoran Selkirkia.” Biology Letters.
Forthcoming
M. Waskom, S. R Losso, and J. Ortega-Hernández. Forthcoming. “Stuck in the mud: experimental taphonomy and computed tomography demonstrate the critical role of sediment in three-dimensional carcass stabilization during early fossil diagenesis.” Research Square. Publisher's VersionAbstract

Exceptionally preserved fossils provide critical information on the morphology and ecology of extinct organisms, but their formation remains poorly understood. Experimental taphonomy has produced critical insights that allow us to better understand preservation biases, but they typically do not reflect realistic depositional environments, employ destructive sampling, and are restricted to a two-dimensional setting. Here, we utilize micro-computed tomography to non-invasively visualize the process of decay of carcasses of the branchiopod Triops longicaudatus for a year of post-burial decay. The earliest stages of post-burial diagenesis are dynamic and produce marked differences in relative density within each of the experimental replicates affecting both the carcass and the surrounding sediment. After 64 weeks, specimens are still detectable as three-dimensional voids that capture the body in life position and external morphological features. Sediment plays a critical role in carcass stabilization and the resulting voids provide sites for mineral precipitation needed for exceptional three-dimensional fossilization.

2023
J.M. Wolfe, L. Ballou, J. Luque, V. Watson-Zink, S.T. Ahyong, J. Barido-Sottani, T.Y. Chan, K.A. Crandall, S.R. Daniels, D.L. Felder, H. Mancke, J.W. Martin, P.K.L. Ng, J. Ortega-Hernández, Palacios E. Theil, N.D. Pentcheff, R. Robles, B.P. Thoma, L.M. Tsang, R. Wetzer, A.M. Windsor, and H.D. Bracken-Grissom. 2023. “Convergent adaptation of true crabs (Decapoda, Brachyura) to a gradient of terrestrial environments.” Systematic Biology . Publisher's Version
S.R. Losso, P. Affatato, K. Nanglu, and J. Ortega-Hernández. 2023. “Convergent evolution of ventral adaptations for enrollment in trilobites and extant euarthropods.” Proceedings of the Royal Society B, 290, 2013, Pp. 20232212. Publisher's VersionAbstract

The ability to enrol for protection is an effective defensive strategy that has convergently evolved multiple times in disparate animal groups ranging from euarthropods to mammals. Enrolment is a staple habit of trilobites, and their biomineralized dorsal exoskeleton offered a versatile substrate for the evolution of interlocking devices. However, it is unknown whether trilobites also featured ventral adaptations for enrolment. Here, we report ventral exoskeletal adaptations that facilitate enrolment in exceptionally preserved trilobites from the Middle Ordovician Walcott–Rust Quarry in New York State, USA. Walcott–Rust trilobites reveal the intricate three-dimensional organization of the non-biomineralized ventral anatomy preserved as calcite casts, including the spatial relationship between the articulated sternites (i.e. ventral exoskeletal plates) and the wedge-shaped protopodites. Enrolment in trilobites is achieved by ventrally dipping the anterior margin of the sternites during trunk flexure, facilitated by the presence of flexible membranes, and with the close coupling of the wedge-shaped protopodites. Comparisons with the ventral morphology of extant glomerid millipedes and terrestrial isopods reveal similar mechanisms used for enrolment. The wedge-shaped protopodites of trilobites closely resemble the gnathobasic coxa/protopodite of extant horseshoe crabs. We propose that the trilobites' wedge-shaped protopodite simultaneously facilitated tight enrolment and gnathobasic feeding with the trunk appendages.

K. Nanglu, R. Lerosey-Aubril, J. C Weaver, and J. Ortega-Hernandez. 2023. “A mid-Cambrian tunicate and the deep origin of the ascidiacean body plan.” Nature Communications, 14, Pp. 3832. Publisher's VersionAbstract

Tunicates are an evolutionarily significant subphylum of marine chordates, with their phylogenetic position as the sister-group to Vertebrata making them key to unraveling our own deep time origin. Tunicates greatly vary with regards to morphology, ecology, and life cycle, but little is known about the early evolution of the group, e.g. whether their last common ancestor lived freely in the water column or attached to the seafloor. Additionally, tunicates have a poor fossil record, which includes only one taxon with preserved soft-tissues. Here we describe Megasiphon thylakos nov., a 500-million-year-old tunicate from the Marjum Formation of Utah, which features a barrel-shaped body with two long siphons and prominent longitudinal muscles. The ascidiacean-like body of this new species suggests two alternative hypotheses for early tunicate evolution. The most likely scenario posits M. thylakos belongs to stem-group Tunicata, suggesting that a biphasic life cycle, with a planktonic larva and a sessile epibenthic adult, is ancestral for this entire subphylum. Alternatively, a position within the crown-group indicates that the divergence between appendicularians and all other tunicates occurred 50 million years earlier than currently estimated based on molecular clocks. Ultimately, M. thylakos demonstrates that fundamental components of the modern tunicate body plan were already established shortly after the Cambrian Explosion.

L. Del Mouro, B. Becker-Kerber, V. A Janasi, de Araujo-Carvalho, B. L Waichel, E. F Lima, L. MM Rossetti, V. Cruz, M. Souza-Silva, N. Famelli, and J. Ortega-Hernández. 2023. “Organic walled microfossils in wet peperites from the early Cretaceous Paraná-Etendeka volcanism of Brazil.” Scientific Reports, 13, Pp. 15362 . Publisher's VersionAbstract

Large igneous provinces (LIPs) are major magmatic events that have a significant impact on the global environment and the biosphere, for example as triggers of mass extinctions. LIPs provide an excellent sedimentological and geochemical record of short but intense periods of geological activity in the past, but their contribution towards understanding ancient life is much more restricted due to the destructive nature of their igneous origin. Here, we provide the first paleontological evidence for organic walled microfossils extracted from wet peperites from the Early Cretaceous Paraná-Etendeka intertrappean deposits of the Paraná basin in Brazil. Wet peperites are a volcaniclastic rock formed by the interaction of lava and subaqueous sediments.The Paraná-Etendeka was formed during the Valanginian (ca. 132 Ma) as a continental flood basalt in present day South America and Namibia, and released enormous amounts of carbon dioxide, sulfur dioxide, methane and hydrogen fluoride into the atmosphere. The organic walled microfossils recovered from the Paraná-Etendeka peperites include pollen grains, spores, acritarchs, and other remains of unidentifiable organic matter. In addition to the peperites, organic walled microfossils were also found in heterolithic sandstones and interpillow sandstones. Our findings represent the first insight into the biodiversity of the Paraná Basin during the Early Cretaceous during a period of intense magmatism, and the microfossil assemblages corroborate a regional paleoclimatic transition from arid to more humid conditions that were likely induced by the volcanic activity. We corroborate the potential of wet peperite rocks as a valuable source of paleobiological data and emphasize the importance of sampling volcaniclastic units that have been traditionally considered with lower fossiliferous potential due to their igneous origin.

K. Nanglu, M. E Waskom, J. C Richards, and J. Ortega-Hernández. 2023. “Rhabdopleurid epibionts from the Ordovician Fezouata Shale biota and the longevity of cross-phylum interactions.” Communications Biology, 2, 1002. Publisher's VersionAbstract

Evidence of interspecific interactions in the fossil record is rare but offers valuable insights into ancient ecologies. Exceptional fossiliferous sites can preserve complex ecological interactions involving non-biomineralized organisms, but most of these examples are restricted to Cambrian Lagerstätten. Here we report an exceptionally preserved cross-phylum interspecific interaction from the Tremadocian-aged Lower Fezouata Shale Formation of Morocco, which consists of the phragmocone of an orthocone cephalopod that has been extensively populated post-mortem by tubicolous epibionts. Well-preserved transverse bands in a zig-zag pattern and crenulations along the margin of the unbranched tubes indicate that they correspond to pterobranch hemichordates, with a close morphological similarity to rhabdopleurids based on the bush-like growth of the dense tubarium. The discovery of rhabdopleurid epibionts in the Fezouata Shale highlights the paucity of benthic graptolites, which also includes the rooted dendroids Didymograptus and Dictyonema, relative to the substantially more diverse and abundant planktic forms known from this biota. We propose that the rarity of Paleozoic rhabdopleurid epibionts is likely a consequence of their ecological requirement for hard substrates for initial settlement and growth. The Fezouata rhabdopleurid also reveals a 480-million-year-old association of pterobranchs as epibionts of molluscs that persist to the present day.

S. R Losso, J. Thines, and J. Ortega-Hernández. 2023. “Taphonomy of non-biomineralized trilobite tissues preserved as calcite casts from the Ordovician Walcott-Rust Quarry, USA.” Communications Earth & Environment, 4, Pp. 330. Publisher's VersionAbstract
Trilobites with appendages from the Rust Formation of New York State were discovered in the 1870s and represent one of the earliest known cases of exceptional preservation of non-biomineralized tissues. The Rust Formation trilobites feature three-dimensionally preserved walking legs and delicate respiratory lamellae, but the mechanism behind their fossilization remains unknown. Here we show that after burial, carcass decay produced framboidal pyrite, while fibrous calcite precipitated on the visceral side of the body, followed by the widespread formation of sparry calcite crystal replicating non-biomineralized morphological features. Trilobites and co-occurring calcite veins show no chemical or petrographic differences, rejecting the hypothesis that exceptional preservation was caused by a local microenvironment within enrolled trilobites. These results suggest that fine-grained sediment provided support for the appendages and facilitated their fossilization through calcite replacement. Our findings carry broader implications for understanding the exceptional three-dimensional preservation of animal Paleozoic body fossils through calcite casts.
C. Zhang, Y. Liu, J. Ortega-Hernández, J. M. Wolfe, C. Jin, H. Mai, X. G. Hou, J. Guo, and D. Zhai. 2023. “Three-dimensional morphology of the biramous appendages in Isoxys from the early Cambrian of South China, and its implications for early euarthropod evolution.” Proceedings of the Royal Society B, 290, Pp. 20230335 . Publisher's VersionAbstract

 

Early euarthropod evolution involved a major transition from lobopodian-like taxa to organisms featuring a segmented, well-sclerotized trunk (arthrodization) and limbs (arthropodization). However, the precise origin of a completely arthrodized trunk and arthropodized ventral biramous appendages remain controversial, as well as the early onset of anterior–posterior limb differentiation in stem-group euarthropods. New fossil material and micro-computed tomography inform the detailed morphology of the arthropodized biramous appendages in the carapace-bearing euarthropod Isoxys curvirostratus from the early Cambrian Chengjiang biota. In addition to well-developed grasping frontal appendages, I. curvirostratus possesses two batches of morphologically and functionally distinct biramous limbs. The first batch consists of four pairs of short cephalic appendages with robust endites with a feeding function, whereas the second batch has more elongate trunk appendages for locomotion. Critically, our new material shows that the trunk of I. curvirostratus was not arthrodized. The results of our phylogenetic analyses recover isoxyids as some of the earliest branching sclerotized euarthropods, and strengthens the hypothesis that arthropodized biramous appendages evolved before full body arthrodization.

 

2022
M. Schmidt, X. G. Hou, J. Belojevic, D. Zhai, J. Mai, R. R. Melzer, J. Ortega-Hernández, and Y. Liu. 2022. “Before trilobite legs: Pygmaclypeatus daziensis reconsidered and the ancestral appendicular organization of Cambrian artiopods.” Philosophical Transactions of the Royal Society B , 377 , Pp. 20210030. Publisher's VersionAbstract

The Cambrian Stage 3 Chengjiang biota in South China is one of the most influential Konservat Lagerstatten worldwide thanks to the fossilization of diverse nonbiomineralizing 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. P. 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, endopod and exopod along the antero-posterior body axis. The small body size (less than 2 cm), presence of delicate spinose endites, and well-developed exopods with multiple paddle-shaped lamellae on the appendages of P. daziensis indicate a nekto-benthic mode of life, and a scavenging/detritus feeding strategy. P. daziensis shows that appendage heteronomy is phylogenetically widespread within Artiopoda, the megadiverse clade that includes trilobites and their relatives with nonbiomineralizing exoskeletons and suggests that a single exopod lobe with paddle like lamellae is ancestral for this clade.

P. Gilbert, K. D. Bergmann, N. Boekelheide, S. Tambutte, T. Mass, F. Marin, J.F. Adkins, J. Erez, B. Gilbert, V. Knutson, M. Cantine, J. Ortega-Hernández, and Knoll A.H. 2022. “Biomineralization: integrating mechanism and evolutionary history.” Science Advances, 8, Pp. eabl9653 . Publisher's VersionAbstract
Calcium carbonate (CaCO3) biomineralizing organisms have played major roles in the history of life and the global carbon cycle during the past 541 Ma. Both marine diversification and mass extinctions reflect physiological responses to environmental changes through time. An integrated understanding of carbonate biomineralization is necessary to illuminate this evolutionary record and to understand how modern organisms will respond to 21st century global change. Biomineralization evolved independently but convergently across phyla, suggesting a unity of mechanism that transcends biological differences. In this review, we combine CaCO3 skeleton formation mechanisms with constraints from evolutionary history, omics, and a meta-analysis of isotopic data to develop a plausible model for CaCO3 biomineralization applicable to all phyla. The model provides a framework for understanding the environmental sensitivity of marine calcifiers, past mass extinctions, and resilience in 21st century acidifying oceans. Thus, it frames questions about the past, present, and future of CaCO3 biomineralizing organisms.
S.R. Losso and J. Ortega-Hernández. 2022. “Claspers in the mid-Cambrian Olenoides serratus indicate horseshoe crab-like mating in trilobites.” Geology, 50, Pp. 897-901. Publisher's VersionAbstract

Sexual reproduction represents a fundamental aspect of animal biology, but the diversity of reproductive strategies among early Paleozoic metazoans remains obscure. Direct evidence of reproductive strategies comes from exceptionally preserved egg masses in Cambrian and Ordovician euarthropods such as waptiids and trilobites, but anatomical or behavioral adaptations for mating in these taxa are all but unknown. We demonstrate the presence of functionally specialized appendages in the mid-Cambrian (Wuliuan) Burgess Shale trilobite Olenoides serratus. New material of O. serratus preserves significantly modified and reduced endopodites underneath the seventh thoracic and first pygidial tergites. Comparison with extant euarthropods indicates that these specialized limbs are functional analogs to claspers, which are used by sexually mature males to grasp females prior to or during mating. The claspers in O. serratus were most likely used by the male to hold onto the posterior pygidial spines of the female during amplex, similar to the strategy observed in the horseshoe crab Limulus polyphemus. The new appendicular data from O. serratus provide the first direct evidence for trilobite sexual dimorphism based on the non-biomineralized ventral anatomy. Our findings illuminate the reproductive biology of trilobites and indicate that complex mating behaviors observed in extant euarthropods originated during the Cambrian explosion.

J. Ortega-Hernández, R. Lerosey-Aubril, S.R. Losso, and J. C. Weaver. 2022. “Neuroanatomy in a middle Cambrian mollisoniid and the ancestral nervous system organization of chelicerates.” Nature Communications, 13, 410. Publisher's VersionAbstract

Recent years have witnessed a steady increase in reports of fossilized nervous tissues among Cambrian total-group euarthropods, which allow reconstructing the early evolutionary history of these animals. Here, we describe the central nervous system of the stem-group chelicerate Mollisonia symmetrica from the mid-Cambrian Burgess Shale. The fossilized neurological anatomy of M. symmetrica includes optic nerves connected to a pair of lateral eyes, a putative condensed cephalic synganglion, and a metameric ventral nerve cord. Each trunk tergite is associated with a condensed ganglion bearing lateral segmental nerves, and linked by longitudinal connectives. The nervous system is preserved as reflective carbonaceous films underneath the phosphatized digestive tract. Our results suggest that M. symmetrica illustrates the ancestral organization of stem-group Chelicerata before the evolution of the derived neuroanatomical characters observed in Cambrian megacheirans and extant representatives. Our findings reveal a conflict between the phylogenetic signals provided by neuroanatomical and appendicular data, which we interpret as evidence of mosaic evolution in the chelicerate stem-lineage.

F. Saleh, R. Vaucher, M. Vidal, K. El Hariri, L. Laibl, A.C. Daley, J. C. Gutierrez-Marco, Y. Candela, D. Harper, J. Ortega-Hernández, X. Ma, A. Rida, D. Vizcaino, and V. Lefebvre. 2022. “New fossil assemblages from the Early Ordovician Fezouata Biota.” Scientific Reports, 12, Pp. 20773. Publisher's VersionAbstract

 

The Fezouata Biota (Morocco) is a unique Early Ordovician fossil assemblage. The discovery of this biota revolutionized our understanding of Earth’s early animal diversifications—the Cambrian Explosion and the Ordovician Radiation—by suggesting an evolutionary continuum between both events. Herein, we describe Taichoute, a new fossil locality from the Fezouata Shale. This locality extends the temporal distribution of fossil preservation from this formation into the upper Floian, while also expanding the range of depositional environments to more distal parts of the shelf. In Taichoute, most animals were transported by density flows, unlike the in-situ preservation of animals recovered in previously investigated Fezouata sites. Taichoute is dominated by three-dimensionally preserved, and heavily sclerotized fragments of large euarthropods—possibly representing nektobenthic/nektic bivalved taxa and/or hurdiid radiodonts. Resolving whether this dominance reflects a legitimate aspect of the original ecosystem or a preservational bias requires an in-depth assessment of the environmental conditions at this site. Nevertheless, Taichoute provides novel preservational and palaeontological insights during a key evolutionary transition in the history of life on Earth.

 

R. Lerosey-Aubril and J. Ortega-Hernández. 2022. “A new lobopodian from the middle Cambrian of Utah: did swimming body flaps convergently evolve in stem-group arthropods?” Papers in Palaeontology, 8, Pp. e1450. Publisher's VersionAbstract

Arthropods are ubiquitous in all modern habitats and yet their origin remains poorly documented. It is widely thought that their segmented and arthrodized body evolved from the annulated vermiform body of a lobopodian ancestor c. 540 Ma. This major transformation included the evolution of sclerotized and articulated appendages from annulated non-jointed limbs or lobopods. However, this scenario is complicated by the presence in many stem-group arthropods of body flaps of various origins, characteristics and functions. We describe the new lobopodian Utahnax vannieri gen. et sp. nov. from Drumian strata of the House Range in Utah. Known from an incomplete specimen, this taxon features a vermiform, annulated body flanked by pairs of swimming flaps, except in the caudal region, and a digestive system with putative glands. Extensions of the body cavity into the body flaps of Utahnax suggest that they are modified lobopods similar to the ventral body flaps of radiodonts; as such, they are not homologous to the dorsal body flaps of the stem-group arthropods Opabinia, Pambdelurion, and possibly Kerygmachela. We discuss the details of the limb anatomy of these three taxa and consider an alternative interpretation for Kerygmachela. Despite morphological similarities in radiodonts, Utahnax, and possibly Kerygmachela, our parsimony and Bayesian inference phylogenetic analyses suggest that ventral body flaps have evolved convergently in those taxa, probably accompanying a shift towards a predominantly swimming predatory lifestyle. Ecological competition with radiodonts is proposed as an explanation for the scarcity of non-radiodont swimming lobopodians in Cambrian Lagerstätten.

S. Pates, J. M. Wolfe, R. Lerosey-Aubril, A.C. Daley, and J. Ortega-Hernández. 2022. “New opabiniid diversifies the weirdest wonders of the euarthropod lower stem group.” Proceedings of the Royal Society B, 289, Pp. 20212093. Publisher's VersionAbstract

Once considered "weird wonders" of the Cambrian, the emblematic Burgess Shale animals Anomalocaris and Opabinia are now recognized as lower stem-group euarthropods. Anomalocaris and its relatives (radiodonts) had a worldwide distribution and survived until at least the Devonian, whereas - despite intense study - Opabinia remains the only formally described opabiniid to date. Here we reinterpret a fossil from the Wheeler Formation of Utah as a new opabiniid, KUMIP 314087. By visualizing the sample of phylogenetic topologies in treespace, our results fortify support for the position of KUMIP 314087 beyond the nodal support traditionally applied. Our phylogenetic evidence expands opabiniids to multiple Cambrian Stages spanning approximately five million years. Our results underscore the power of treespace visualization for resolving imperfectly preserved fossils and expanding the known diversity and spatiotemporal ranges within the euarthropod lower stem group.

M. Zhang, Y. Liu, X. G. Hou, J. Ortega-Hernández, H. Mai, M. Schmidt, R. R. Melzer, and J. Guo. 2022. “Ventral morphology of the non-trilobite artiopod Retifacies abnormalis Hou, Chen & Lu, 1989, from the early Cambrian Chengjiang biota, China.” Biology, 11, Pp. 1235. Publisher's VersionAbstract
The artiopodans represent a diverse group of euarthropods with a typically flattened dorsal exoskeleton that covers numerous pairs of biramous ventral appendages, and which are ubiquitous faunal components of the 518-million-year-old Chengjiang Lagerstätte in South China. Despite their abundance, several Chengjiang artiopodans remain poorly known, such as the large euarthropoda Retifacies abnormalis, Hou, Chen & Lu, 1989, which is distinguished by the presence of mesh-like ornamentation on its dorsal exoskeleton. Although only a few ventral details were described in a single study in 25 years, it has been frequently featured in phylogenetic analyses that explore the relationships between Cambrian euarthropods. Here, we employ micro-CT and fluorescent microphotography to investigate the exceptionally preserved ventral morphology of R. abnormalis and explore its phylogenetic implications through maximum parsimony and Bayesian inference. Detailed morphology revealed here better supports R. abnormalis as a sister group to the diminutive artiopod Pygmaclypeatus daziensis, also known from Chengjiang, and strengthens the close relationship of these taxa that have been suggested by previous studies as early-branching representatives of Trilobitomorpha. Cephalic appendages suggest this animal might be a scavenger, possibly feeding on soft-bodied organisms. Different pairs of pygidial appendages suggest an anamorphic post-embryonic ontogeny, which adds to the understanding of the developmental mode of Cambrian artiopods, and further supports the statement that post-hatching segment addition occurred in the ancestor of Euarthropoda. View Full-Text
X. Zhang, Y. Liu, R. J. O'Flynn, M. Schmidt, R. R. Melzer, X. Hou, H. Mai, J. Guo, and J. Ortega-Hernández. 2022. “Ventral organisation of Jianfengia multisegmentalis Hou, and its implications for the head segmentation of megacheirans.” Palaeontology, e12624 . Publisher's VersionAbstract

 

Megacheirans, or great-appendage euarthropods, have featured prominently in discussions regarding the early evolution of the head region in total-group Euarthropoda. However, several aspects of the ventral morphology of most representatives remain incompletely known given the loss of data associated with fossil compression, coupled with the rarity of some of these taxa. Here, we describe the ventral aspect of head organization of the jianfengiid megacheiran Jianfengia multisegmentalis using micro computed-tomography, and explore its evolutionary significance. The head consists of a pair of stalked eyes, a pair of great appendages, and four pairs of biramous appendages, all covered by a dorsal head shield. The rostral portion of the head bears a median projection, which we interpret as an anterior sclerite akin to that observed in several other Cambrian euarthropods. The anterior sclerite in J. multisegmentalis articulates with robust stalks with rounded projections in a more adaxial position, and bears the compound eyes. Critically, the ventral side of the head of J. multisegmentalis features a prominent lobe-shaped hypostome/labrum complex located immediately behind the great appendages, and between the first pair of biramous appendages. This situation is consistent with that observed in Leanchoilia illecebrosa and suggests a conserved, and possibly ancestral, pattern of a six-segmented head (eyes, great appendages and four biramous limb appendages) with a hypostome/labrum complex for Megacheira. The existence of the hypostome/labrum complex in J. multisegmentalis falsifies the hypothesis that the anterior projections on the head of jianfengiids might be homologues of the euarthropod labrum.

 

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