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Hopkins MJ, To R. Long-term clade-wide shifts in trilobite segment number and allocation during the Palaeozoic. Proc Biol Sci 2022; 289:20221765. [PMID: 36541173 PMCID: PMC9768642 DOI: 10.1098/rspb.2022.1765] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Arthropods are characterized by having an exoskeleton, paired jointed appendages and segmented body. The number and shape of those segments vary dramatically and unravelling the evolution of segmentation is fundamental to our understanding of arthropod diversification. Because trilobites added segments to the body post-hatching which were expressed and preserved in biomineralized exoskeletal sclerites, their fossil record provides an excellent system for understanding the early evolution of segmentation in arthropods. Over the last 200 years, palaeontologists have hypothesized trends in segment number and allocation in the trilobite body, but they have never been rigorously tested. We tabulated the number of segments in the post-cephalic body for over 1500 species, selected to maximize taxonomic, geographical and temporal representation. Analysis reveals long-term shifts in segment number and allocation over the 250-million-year evolutionary history of the clade. For most of the Palaeozoic, the median number of segments in the body did not change. Instead, the total range decreased over time and there was long-term increase in the proportion of segments allocated to the fused terminal sclerite relative to the articulated thoracic region. There was also increased conservation of thoracic segment number within families. Neither taxonomic turnover nor trends in functionally relevant defensive behaviour sufficiently explain these patterns.
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Affiliation(s)
- Melanie J. Hopkins
- Division of Paleontology (Invertebrates), American Museum of Natural History, New York, NY 10024, USA
| | - Rebecca To
- Department of Ecology and Evolution, University of Michigan Ann Arbor, MI 48109, USA
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How to Study Classification. Cladistics 2020. [DOI: 10.1017/9781139047678.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Classification. Cladistics 2020. [DOI: 10.1017/9781139047678.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Systematics Association Special Volumes. Cladistics 2020. [DOI: 10.1017/9781139047678.025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Relationship Diagrams. Cladistics 2020. [DOI: 10.1017/9781139047678.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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The Separation of Classification and Phylogenetics. Cladistics 2020. [DOI: 10.1017/9781139047678.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Beyond Classification. Cladistics 2020. [DOI: 10.1017/9781139047678.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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The Interrelationships of Organisms. Cladistics 2020. [DOI: 10.1017/9781139047678.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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How to Study Classification. Cladistics 2020. [DOI: 10.1017/9781139047678.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Modern Artificial Methods and Raw Data. Cladistics 2020. [DOI: 10.1017/9781139047678.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Further Myths and More Misunderstandings. Cladistics 2020. [DOI: 10.1017/9781139047678.022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Afterword. Cladistics 2020. [DOI: 10.1017/9781139047678.023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Systematics: Exposing Myths. Cladistics 2020. [DOI: 10.1017/9781139047678.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Essentialism and Typology. Cladistics 2020. [DOI: 10.1017/9781139047678.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Beyond Classification: How to Study Phylogeny. Cladistics 2020. [DOI: 10.1017/9781139047678.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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How to Study Classification: ‘Total Evidence’ vs. ‘Consensus’, Character Congruence vs. Taxonomic Congruence, Simultaneous Analysis vs. Partitioned Data. Cladistics 2020. [DOI: 10.1017/9781139047678.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
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What This Book Is About. Cladistics 2020. [DOI: 10.1017/9781139047678.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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How to Study Classification. Cladistics 2020. [DOI: 10.1017/9781139047678.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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The Cladistic Programme. Cladistics 2020. [DOI: 10.1017/9781139047678.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Index. Cladistics 2020. [DOI: 10.1017/9781139047678.024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Parameters of Classification: Ordo Ab Chao. Cladistics 2020. [DOI: 10.1017/9781139047678.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Monothetic and Polythetic Taxa. Cladistics 2020. [DOI: 10.1017/9781139047678.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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How to Study Classification: Consensus Techniques and General Classifications. Cladistics 2020. [DOI: 10.1017/9781139047678.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Non-taxa or the Absence of –Phyly: Paraphyly and Aphyly. Cladistics 2020. [DOI: 10.1017/9781139047678.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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Introduction: Carving Nature at Its Joints, or Why Birds Are Not Dinosaurs and Men Are Not Apes. Cladistics 2020. [DOI: 10.1017/9781139047678.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Preface. Cladistics 2020. [DOI: 10.1017/9781139047678.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Scholtz G, Staude A, Dunlop JA. Trilobite compound eyes with crystalline cones and rhabdoms show mandibulate affinities. Nat Commun 2019; 10:2503. [PMID: 31175282 PMCID: PMC6555793 DOI: 10.1038/s41467-019-10459-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Accepted: 05/14/2019] [Indexed: 01/23/2023] Open
Abstract
Most knowledge about the structure, function, and evolution of early compound eyes is based on investigations in trilobites. However, these studies dealt mainly with the cuticular lenses and little was known about internal anatomy. Only recently some data on crystalline cones and retinula cells were reported for a Cambrian trilobite species. Here, we describe internal eye structures of two other trilobite genera. The Ordovician Asaphus sp. reveals preserved crystalline cones situated underneath the cuticular lenses. The same is true for the Devonian species Archegonus (Waribole) warsteinensis, which in addition shows the fine structure of the rhabdom in the retinula cells. These results suggest that an apposition eye with a crystalline cone is ancestral for Trilobita. The overall similarity of trilobite eyes to those of myriapods, crustaceans, and hexapods corroborates views of a phylogenetic position of trilobites in the stem lineage of Mandibulata. Little is known about the internal anatomy of early eyes. Here, Scholtz and colleagues show the internal eye structures from fossils of two genera of trilobites, which support an ancestral apposition eye with crystalline cones in Trilobita and a close affinity with Mandibulata.
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Affiliation(s)
- Gerhard Scholtz
- Humboldt-Universität zu Berlin, Institut für Biologie/Vergleichende Zoologie, Philippstr. 13, 10115, Berlin, Germany.
| | - Andreas Staude
- Fachbereich 8.5 "Mikro-ZfP", BAM Bundesanstalt für Materialforschung und -prüfung, Unter den Eichen 87, 12205, Berlin, Germany.,Thermo Fisher Scientific, c/o Zuse Institut Berlin (ZIB), Takustr. 7, 14195, Berlin, Germany
| | - Jason A Dunlop
- Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstr. 43, 10115, Berlin, Germany
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Du KS, Ortega-Hernández J, Yang J, Zhang XG. A soft-bodied euarthropod from the early Cambrian Xiaoshiba Lagerstätte of China supports a new clade of basal artiopodans with dorsal ecdysial sutures. Cladistics 2019; 35:269-281. [PMID: 34622993 DOI: 10.1111/cla.12344] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/17/2018] [Indexed: 11/28/2022] Open
Abstract
We describe the exceptionally well-preserved non-trilobite artiopodan Zhiwenia coronata gen. et sp. nov. from the Cambrian Stage 3 Xiaoshiba Lagerstätte in Yunnan, China. The exoskeleton consists of a cephalic shield with dorsal sutures expressed as lateral notches that accommodate stalked lateral eyes, an elongate trunk composed of 20 tergites-the first of which is reduced-and a short tailspine with marginal spines. Appendicular data include a pair of multi-segmented antennae, and homonomous biramous trunk limbs consisting of an endopod with at least seven podomeres and a flattened exopod with lamellae. Although the presence of cephalic notches and a reduced first trunk tergite invites comparisons with the petalopleurans Xandarella, Luohiniella and Cindarella, the proportions and exoskeletal tagmosis of Zhiwenia do not closely resemble those of any major group within Trilobitomorpha. Parsimony and Bayesian phylogenetic analyses consistently support Zhiwenia as sister-taxon to the Emu Bay Shale artiopodan Australimicola spriggi, and both of them as closely related to Acanthomeridion from the Chengjiang. This new monophyletic clade, Protosutura nov., occupies a basal phylogenetic position within Artiopoda as sister-group to Trilobitomorpha and Vicissicaudata, illuminates the ancestral organization of these successful euarthropods, and leads to a re-evaluation of the evolution of ecdysial dorsal sutures within the group.
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Affiliation(s)
- Kun-Sheng Du
- Key Laboratory for Palaeobiology, Yunnan University, Kunming, 650091, China.,MEC International Joint Laboratory for Palaeoenvironment, Yunnan University, Kunming, 650091, China
| | - Javier Ortega-Hernández
- Department of Zoology, University of Cambridge, Downing Street, Cambridge, CB2 3EJ, UK.,Museum of Comparative Zoology and, Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA
| | - Jie Yang
- Key Laboratory for Palaeobiology, Yunnan University, Kunming, 650091, China.,MEC International Joint Laboratory for Palaeoenvironment, Yunnan University, Kunming, 650091, China
| | - Xi-Guang Zhang
- Key Laboratory for Palaeobiology, Yunnan University, Kunming, 650091, China.,MEC International Joint Laboratory for Palaeoenvironment, Yunnan University, Kunming, 650091, China
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Hopkins MJ. Development, Trait Evolution, and the Evolution of Development in Trilobites. Integr Comp Biol 2018; 57:488-498. [PMID: 28582534 DOI: 10.1093/icb/icx033] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Trilobites offer one of the best fossil records of any arthropod group. This is due to a number of factors, most notably the combination of (1) having inhabited areas where organisms are more likely to be buried and ultimately fossilized; and (2) having had a highly biomineralized exoskeleton more likely to survive the stresses of fossilization. This biomineralized exoskeleton was also morphologically complex, bearing traits that had ecological significance, and was present throughout postembryonic development, from larval to adult stages. Because the morphology of the exoskeleton changed gradually across molts during development, it is possible to reconstruct ontogenetic series for many species. Over the last decade, studies have documented both variation in modularity among closely related species and conserved developmental patterns among modules. In the latter case, trait evolution could still occur through modification of rates of morphological change along otherwise conserved ontogenetic trajectories. At the clade level, the pattern of expression and release of new exoskeletal segments during post-embryonic development was generally conserved across most species, but the relative timing of different segmentation events could vary, and developmental traits appear to have been relatively labile across the clade's evolutionary history. Most recently, comparative analyses indicate that the association between segmentation events and the timing of shifts in the rate of ontogenetic shape change varies across species. Despite these advances, we still know relatively little about how development constrained or contributed to trait evolution in trilobites, and almost nothing about the origin of novel traits in trilobites. A major (but removable) obstacle is the current lack of well-supported trilobite phylogenies that span higher taxonomic levels.
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Affiliation(s)
- Melanie J Hopkins
- American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA
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Abstract
Until now, the fossil record has not been capable of revealing any details of the mechanisms of complex vision at the beginning of metazoan evolution. Here, we describe functional units, at a cellular level, of a compound eye from the base of the Cambrian, more than half a billion years old. Remains of early Cambrian arthropods showed the external lattices of enormous compound eyes, but not the internal structures or anything about how those compound eyes may have functioned. In a phosphatized trilobite eye from the lower Cambrian of the Baltic, we found lithified remnants of cellular systems, typical of a modern focal apposition eye, similar to those of a bee or dragonfly. This shows that sophisticated eyes already existed at the beginning of the fossil record of higher organisms, while the differences between the ancient system and the internal structures of a modern apposition compound eye open important insights into the evolution of vision.
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Ortega-Hernández J, Esteve J, Butterfield NJ. Humble origins for a successful strategy: complete enrolment in early Cambrian olenellid trilobites. Biol Lett 2013; 9:20130679. [PMID: 24068021 DOI: 10.1098/rsbl.2013.0679] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Trilobites are typified by the behavioural and morphological ability to enrol their bodies, most probably as a defence mechanism against adverse environmental conditions or predators. Although most trilobites could enrol at least partially, there is uncertainty about whether olenellids-among the most phylogenetically and stratigraphically basal representatives-could perform this behaviour because of their poorly caudalized trunk and scarcity of coaptative devices. Here, we report complete-but not encapsulating-enrolment for the olenellid genus Mummaspis from the early Cambrian Mural Formation in Alberta, the earliest direct evidence of this strategy in the fossil record of polymerid trilobites. Complete enrolment in olenellids was achieved through a combination of ancestral morphological features, and thus provides new information on the character polarity associated with this key trilobite adaptation.
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Affiliation(s)
- Javier Ortega-Hernández
- Department of Earth Sciences, University of Cambridge, , Downing Site, Cambridge CB2 3EQ, UK
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Stein M, Budd GE, Peel JS, Harper DAT. Arthroaspis n. gen., a common element of the Sirius Passet Lagerstätte (Cambrian, North Greenland), sheds light on trilobite ancestry. BMC Evol Biol 2013; 13:99. [PMID: 23663519 PMCID: PMC3662621 DOI: 10.1186/1471-2148-13-99] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Accepted: 04/29/2013] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND Exceptionally preserved Palaeozoic faunas have yielded a plethora of trilobite-like arthropods, often referred to as lamellipedians. Among these, Artiopoda is supposed to contain taxa united by a distinctive appendage structure. This includes several well supported groups, Helmetiida, Nektaspida, and Trilobita, as well as a number of problematic taxa. Interrelationships remain unclear, and the position of the lamellipedian arthropods as a whole also remains the subject of debate. RESULTS Arthroaspis bergstroemi n. gen. n. sp., a new arthropod from the early Cambrian Sirius Passet Lagerstätte of North Greenland shows a striking combination of both dorsal and ventral characters of Helmetiida, Nektaspida, and Trilobita. Cladistic analysis with a broad taxon sampling of predominantly early Palaeozoic arthropods yields a monophyletic Lamellipedia as sister taxon to the Crustacea or Tetraconata. Artiopoda is resolved as paraphyletic, giving rise to the Marrellomorpha. Within Lamellipedia, a clade of pygidium bearing taxa is resolved that can be shown to have a broadly helmetiid-like tergite morphology in its ground pattern. This morphology is plesiomorphically retained in Helmetiida and in Arthroaspis, which falls basally into a clade containing Trilobita. The trilobite appendages, though similar to those of other lamellipedians in gross morphology, have a unique outward rotation of the anterior trunk appendages, resulting in a 'hard wired' lateral splay, different to that observed in other Lamellipedia. CONCLUSIONS The combination of helmetiid, trilobite, and nektaspid characters in Arthroaspis gives important hints concerning character polarisation within the trilobite-like arthropods. The distinctive tergite morphology of trilobites, with its sophisticated articulating devices, is derived from flanged edge-to-edge articulating tergites forming a shield similar to the helmetiids, previously considered autapomorphic for that group. The stereotypical lateral splay of the appendages of lamellipedians is a homoplastic character shown to be achieved by several groups independently.
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Affiliation(s)
- Martin Stein
- Natural History Museum of Denmark, Universitetsparken 15, DK-2100 Copenhagen, Denmark
| | - Graham E Budd
- Department of Earth Sciences, Palaeobiology, Uppsala University, Villavägen 16, SE 752 36 Uppsala, Sweden
| | - John S Peel
- Department of Earth Sciences, Palaeobiology, Uppsala University, Villavägen 16, SE 752 36 Uppsala, Sweden
| | - David AT Harper
- Department of Earth Sciences, Durham University, Science Labs, Durham DH1 3LE, UK
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Gapp IW, Congreve CR, Lieberman BS. Unraveling the phylogenetic relationships of the Eccoptochilinae, an enigmatic array of ordovician cheirurid trilobites. PLoS One 2012; 7:e49115. [PMID: 23173046 PMCID: PMC3500270 DOI: 10.1371/journal.pone.0049115] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Accepted: 10/09/2012] [Indexed: 11/18/2022] Open
Abstract
The Cheiruridae are a diverse group of trilobites and several subfamilies within the clade have been the focus of recent phylogenetic studies. This paper focuses on the relationships of one of those subfamilies, the Ordovician Eccoptochilinae. We analyze sixteen species from six genera within the traditionally defined group, using the pilekiid Anacheirurus frederici as an outgroup. To assess the monophyly of the Eccoptochilinae seven sphaerexochine species, Kawina arnoldi, Sphaerexochus arenosus, S. atacius, S. latifrons, S. mirus, S. parvus, and S. scabridus were included in the analysis as well. The results of this analysis show that the genus Eccoptochile represents a paraphyletic grade and species traditionally assigned to Parasphaerexochus and Skelipyx plot within Pseudosphaerexochus. Also, representative species of Sphaerexochinae plot within the traditionally defined Eccoptochilinae, suggesting Eccoptochilinae itself is paraphyletic. To resolve this, we propose all species of Pseudosphaerexochus be placed within Sphaerexochinae and Eccoptochilinae be restricted to a monotypic Eccoptochile clavigera.
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Affiliation(s)
- I Wesley Gapp
- Department of Geology, University of Kansas, Lawrence, Kansas, United States of America.
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