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Revision of Dromilites bucklandii (Crustacea, Decapoda, Brachyura): Type material revealing its real identity, a junior synonym, and a new species

Barry W.M. van Bakel, Ninon Robin, Sylvain Charbonnier, and Jeff Saward

Plain Language Abstract

Dromiidae, also known as sponge crabs, is one of the earliest families of Brachyura. Known since the Late Jurassic, they are well represented during the Eocene epoch, which triggered the descriptions of well-known fossil species from deposits in South-eastern England since the mid-nineteenth century (London Clay Formation). This study is based on a simple observation: the original material that allowed the description of the Eocene crab species Dromilites bucklandii differs from all the material subsequently described as such. It actually corresponds to a rarer species, with a rather flat carapace, which has been described much later as a new species: D. simplex. Here, we demonstrate that this latter species has actually to be considered as D. bucklandii, and we create the new species D. belli to include all the fossil crabs, displaying ornamented carapaces that have been mistakenly identified as D. bucklandii for more than 150 years. We show, by providing images of historic non-figured and new well-preserved material, that these two species differ from each another, regardless of the growth stage of the carapaces.

Resumen en Español

in progress

Traducción: Enrique Peñalver (Sociedad Española de Paleontología) or Diana Elizabeth Fernández

Résumé en Français

in progress

Translator: Antoine Souron

Deutsche Zusammenfassung

Revision von Dromilites bucklandii (Crustacea, Decapoda, Brachyura): Typenmaterial offenbart seine wahre Identität, ein Juniorsynonym und eine neue Art

Einige der fossilen Krabben aus dem späteozänen London Clay waren unlängst Gegenstand einiger Revisionen, darunter die hervorragend erhaltenen dromiiden (Schwamm-) Krabben. Wir untersuchten das Originalmaterial des Typus von Dromilites bucklandii von Milne Edwards, das sich von allen nachfolgend beschriebenen Stücken zu unterschieden scheint. Der Typus von D. bucklandii ist conspezifisch mit dem sehr viel später beschriebenen D. simplex Quayle und Collins, 1981. Stücke bei denen sich nachfolgende Autoren - von denen Bell (1858) der häufigsten ist - typischerweise auf D. bucklandii beziehen, werden hier formal als die neue Art D. belli n. sp. beschrieben. Diese neue Art wird basierend auf den Abbildungen und neuen Stücken von Bell beschrieben, die eine ausgeprägte ontogenetische Variation bei der Carapax-Aeroloation aufweisen. Zur Dokumentation der ontogenetischen Variation und des Sexualdimorphismus untersuchten wir beim gesamten Material das Größenspektrum, die Variationen bei der Ornametierung und das Geschlecht (das in vielen Fällen bestimmt werden konnte, da der Abdomen erhalten war). Diese Vergleiche bauen auf der neuen Bildgebung auf, die bis dato für die Forschungsarbeit nicht zugänglich waren. Wir stellen mit dieser Untersuchung eine Beschreibung und Abbildung des Typusmaterials zur Verfügung, das von den Wissenschaftlern des Neunzehnten Jahrhunderts nur grob beschrieben war (und oft keine Abbildungen hatte). Hiermit erweitern wir unsere Kenntnis über ausgestorbene Brachyura. Wir stellen Abbildungen von allen britischen Typen von Dromilites zur Verfügung.

Schlüsselwörter: Krabben; Dromioidea; Eozän; Synonymie; Ontogenie; London Clay

Translator: Eva Gebauer

Arabic

Translator: Ashraf M.T. Elewa

 

 

FIGURE 1. Dromilites bucklandii H. Milne Edwards, 1937. 1. Lectotype MNHN.F.B21561: (London Clay, Isle of Sheppey, Kent, United Kingdom): 1a. carapace in dorsal view, 1b. carapace in frontal view, 1c. carapace coated with ammonium chloride in dorsal view, 2. Holotype NHMUK PI IC 34026 (London Clay, Highgate, London, UK; Spencer coll.) of Dromilites simplex, nov. syn. of D. bucklandii : 2a. colored dorsal view, 2b. black and white dorsal view. Scale bars equal 10 mm. Photographs: Lilian Cazes (1) and Barry van Bakel (2).

 

FIGURE 2. Dromilites belli n. sp. type series from the Ypresian of London Clay (Copenhagen Fields, London, United Kingdom). 1. Holotype NHMUK PI OR 59089 (Wetherell coll.) coated with ammonium chloride (female individual): 1a. carapace in dorsal view, 1b. carapace in frontal view, 1c. carapace in ventral view, 1d. carapace in left-lateral view; 2. Paratype NHMUK PI OR 59091 (Wetherell coll.) coated with ammonium chloride (male individual): 2a. carapace in dorsal view, 2b. carapace in frontal view, 2c. carapace in ventral view, 2d. carapace in left-lateral view. Scale bars equal 10 mm. Photographs: Philip Hurst, Natural History Museum, London.

figure 2 

FIGURE 3. Dromilites belli n. sp. type series from the Ypresian London Clay (Division B1, Kent, United Kingdom). 1. Paratype MAB.k 3583 (Seasalter, foreshore exposure) coated with ammonium chloride: 1a. carapace in dorsal view, 1b. carapace in frontal view; 2. Paratype MAB.k 3584 (Seasalter, foreshore exposure): claws; 3. Paratype MAB.k 3585 (Seasalter, foreshore exposure) (female individual): abdomen in ventral view; 4. Paratype MAB.k 3587 (Seasalter, foreshore exposure) (female individual): abdomen in ventral view; 5. Paratype MAB.k 3586 (Tankerton, foreshore exposure) (male individual): abdomen in ventral view. Scale bars equal 1cm. Photographs. Lilian Cazes (1) and Barry van Bakel (2-5).

 

 

TABLE 1. Comparative carapace lengths of both examined material of Dromilites bucklandii H. Milne Edwards, 1837 and Dromilites belli n. sp.

Carapace lengths of the examined material of Dromilites
D. bucklandii Carapace length
(in mm, excluding rostrum)
Carapace width
(in mm, excluding lateral spines)
Sex D. belli n. sp. Carapace length
(in mm)
Carapace width
(in mm, excluding lateral spines)
Sex
NHMUK PI In.61700 14.2 16.22 unknown MNHN.F.R03853 17.5 18.2 unknown
NHMUK PI In.28173 16.1 15.5 unknown MAB.k 3583 17.5 19.7 unknown
NHMUK PI IC 548 20.1 14.6 female MNHN.F.A66911 21.5 19.5 unknown
MNHN.F.B21561 21.5 21.4 unknown MNHN.F.R03854 29 27 unknown
NHMUK PI IC 34026 22.3 18.5 male NHMUK PI OR 59089 32 31.5 female
MAB.k 3590 24 21 unknown Rayner et al., 2009, p.56 33,5 31 female
Rayner et al., 2009, p.55, 'sp. 1' 26 21.5 unknown MAB.k 3586 25 23 male
      unknown NHMUK PI OR 59091 35,5 37 male

 

 

bvbBarry W.M. van Bakel. Oertijdmuseum De Groene Poort, Bosscheweg 80, 5283 WB Boxtel, the Netherlands; and Naturalis Biodiversity Center, P.O. Box 9517, 2300 RA Leiden, the Netherlands. This email address is being protected from spambots. You need JavaScript enabled to view it.

Barry van Bakel, palaeontologist and carcinologist for more than 20 years, studies fossil crabs with focus on the primitive crabs (podotremata). He is associated researcher at Oertijdmuseum De Groene Poort, and Naturalis Biodiversity Center. Comparative morphology with extant congeners and macroevolution are typical aspects of his recent work.

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nr authorNinon Robin. Muséum national d’histoire naturelle, Centre de Recherche sur la Paléobiodiversité et les Paléoenvironnements (CR2P, UMR 7207), Sorbonne Universités-MNHN, CNRS, UPMC-Paris6, 57 rue Cuvier, Case postale 48, F-75005, Paris, France. This email address is being protected from spambots. You need JavaScript enabled to view it.

Currently graduate assistant at the Muséum national d’Histoire naturelle of Paris, Ninon Robin’s research focuses on the contact associations between fossil organisms and the inferred paleosymbioses (parasitic, commensal or mutualistic). She is interested in all aspects of ancient interspecific associations, mainly involving fossil marine invertebrates, but also vertebrates and plants as host.

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scSylvain Charbonnier. Muséum national d’histoire naturelle, Centre de Recherche sur la Paléobiodiversité et les Paléoenvironnements (CR2P, UMR 7207), Sorbonne Universités-MNHN, CNRS, UPMC-Paris6, 57 rue Cuvier, Case postale 48, F-75005, Paris, France. This email address is being protected from spambots. You need JavaScript enabled to view it.

Sylvain Charbonnier, palaeontologist and curator of fossil invertebrates at the Muséum national d’Histoire naturelle, Paris, studies exceptionally preserved fossils from Konservat-Lagerstätten (La Voulte, Cerin, Hadjoula, Hakel). His palaeontological work focuses in particular on Mesozoic marine arthropods and on the reconstruction of their palaeoecosystems.

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js authorJeff Saward. 53, Thundersley Grove, Thundersley, Essex, SS7 3EB, United Kingdom. This email address is being protected from spambots. You need JavaScript enabled to view it.

Jeff Saward is a collector of Eocene London Clay crustacea from Southeast England for more than thirty years. Author and contributor to various studies and descriptions of London Clay crustacea, he’s currently a member of the Tertiary Research Group, UK, and the vice-President of Essex Rock and Mineral Society. 

 

APPENDIX

Photogrammetric reconstructions of Dromilites bucklandii H. Milne Edwards, 1837 lectotype (MNHN.F. B21561, Ypresian of the Isle of Sheppey, Kent, UK) and Dromilites belli n. sp. (MAB.k 3583, Ypresian of Seasalter, Kent, UK). Photogrammetry. Lilian Cazes. Available as an animated PDF file for download.