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| Lunataspis borealis Lamsdell, Isotalo, Rudkin & Martin, 2022 |
Abstract
Horseshoe crabs as a group are renowned for their morphological conservatism punctuated by marked shifts in morphology associated with the occupation of non-marine environments and have been suggested to exhibit a consistent developmental trajectory throughout their evolutionary history. Here, we report a new species of horseshoe crab from the Ordovician (Late Sandbian) of Kingston, Ontario, Canada, from juvenile and adult material. This new species provides critical insight into the ontogeny and morphology of the earliest horseshoe crabs, indicating that at least some Palaeozoic forms had freely articulating tergites anterior to the fused thoracetron and an opisthosoma comprising 13 segments.
Keywords: Xiphosura, Lunataspis borealis, development, ontogeny, Sandbian
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| Lunataspis borealis sp. nov. specimens and interpretive drawings. (a) ROM IP 64616. (b) ROM IP 64617. (c) ROM IP 64618. (d) Interpretive drawing of ROM IP 64616. (e) Interpretive drawing of ROM IP 64617. (f) ROM IP 64618. Grey indicates preservation of organic cuticular material. All scale bars = 1 mm. Abbreviations: AN, axial node; CL, cardiac lobe; CN, cardiac node; FT, free tergites; LE, lateral eye; MR, marginal rim; OR, ophthalmic ridge; PT, pretelson. |
Systematic palaeontology
Chelicerata Heymons, Reference Heymons, 1901
Xiphosura Latreille, Reference Latreille, 1802
Xiphosurida Latreille, Reference Latreille, 1802
Lunataspis Rudkin, Young and Nowlan, Reference Rudkin, Young and Nowlan, 2008
Lunataspis borealis sp. nov.
Holotype. ROM IP 64616 (Fig. 1a, d), complete adult specimen in dorsal view preserving the dorsal prosomal carapace, thoracetron, postabdomen and telson.
Localities and horizon. Upper Member of the Gull River Formation, Simcoe Group, Upper Ordovician (Late Sandbian), in Kingston, Ontario, Canada (44° 15′ 52.7″ N, 76° 29′ 46.3″ W).
Diagnosis. Lunataspis with cardiac node positioned at base of cardiac lobe; lateral eyes located along middle of prosomal carapace length.
Etymology. The species name borealis is Latin for ‘northern’ and refers to the northerly latitude from which the species is known.
James C. Lamsdell, Phillip A. Isotalo, David M. Rudkin and Markus J. Martin. 2022. A New Species of the Ordovician Horseshoe Crab Lunataspis. Geological Magazine. First View, 1-5. DOI: 10.1017/S0016756822000875
