Palaeocambarus licenti (Van Straelen, 1928)

Audo, Denis, Kawai, Tadashi, Letenneur, Charlène & Huang, Diying, 2023, Crayfishes from the Jehol biota, Geodiversitas 45 (24), pp. 689-719 : 694-698

Palaeocambarus licenti (Van Straelen, 1928)

( Figs 1A ; 2B, C ; 3 ; 4C, D ; 5-8 ; 10-13 )

Astacus licenti Van Straelen, 1928b: 133-138 , pl. 1, figs 1-2. — Imaizumi 1938: 173-176, pl. 23, figs 1, 2, 4-6, 11.

Astacus spinirostrius Imaizumi, 1938: 176-178 , pls 12, 23, figs 9, 10, 12, 13.

Cricoidoscelosus aethus Taylor, Schram & Shen, 1999: 130-135 , figs 3, 7, 8. — Schram & Shen 2000: 416-418, pl. 1. — Shen et al. 2001: figs 1c, 2a, 3a, 3b. — Shen 2008: figs 62-65. — Schweitzer et al. 2010: 32. — Crandall & De Grave 2017: 616, 636. — Bell et al. 2020: 1023-1030, n. syn.

Palaeocambarus licenti – Taylor et al. 1999: 122-130, figs 2, 4-6. — Shen et al. 2001: figs 1a, 1b, 2b, 2c, 3c. — Shen 2008: figs 66- 67. — Schweitzer et al. 2010: 32. — Bracken-Grissom et al. 2014: 465. — Crandall & De Grave 2017: 616, 631. — Bell et al. 2020: 1026. — Xing et al. 2020: fig. 4.

TYPE LOCALITY AND HORIZON. — Barremian (c. 125 Ma; Lower Cretaceous) of Yixian Formation, Lingyuan, Liaoning province, China ( Swisher et al. 1999).

TYPE MATERIAL. — Holotype of Astacus licenti by original designation (Van Straelen, 1928) not found, probably lost.

NEOTYPE. — NIGP-126342, herein designated ( Fig. 5 ) .

DESCRIPTION. — See Appendix 1.

EXAMINED MATERIAL. — 106 specimens from NIGPAS collections and three from Tohoku University collections: NIGP-DYH-3-6, NIGP-Shen-1 ( Figs 6 A-C), Shen-2-3 ( Fig. 1B ), Shen-4-6, Shen-11-20, Shen-22-23 ( Fig. 3E, F ), Shen-26 ( Fig. 2A, B ), Shen-29, Shen-32-36, Shen-38-39; Shen-40 ( Fig.2C ), Shen-42, Shen-47, Shen-50-56, Shen-58, Shen-62, Shen-64, Shen-66-68, Shen-71, Shen-a-b-c, Shen-f-g-h, Shen-GM1 ( Fig. 6D , see also Appendix 3), Shen-RT132 ( Fig. 13C ), Shen-RT141, Shen-145, one specimen from Shen where the number “53” is crossed, NIGP-126337 (holotype of C. aethus , Figs 1A ; 3 A-D), 126338-126347, 126353 ( Fig.12B, C ), 126354 ( Figs 13A, B ), 126366, new unpublished specimens in NIGP collections: NIGP-175159 ( Fig. 7 ), 175159 ( Fig. 7 ), and research specimens without collection number herein numbered sp1-31 (sp11: Fig.12A ), Tohoku-U-57254, U-57267 and U-57272 ( Fig. 8 ; see also Appendix 6 ).

REMARK ON THE TYPE

The original type material of Palaeocambarus licenti consists of three specimens, one holotype (“type”, Van Straelen 1928b: Fig. 1 ), and two paratypes (only one originally illustrated). This material was supposedly initially housed in the Huangho Paiho Museum ( Tianjin, China). Enquiries were made to try to locate this material again, but were unsuccessful as the specimens do not appear to be in Tianjin Natural History Museum (successor to the Huangho Paiho Museum listed by Van Straelen 1928b) nor in the Royal Belgian Institute of Natural Sciences (where Van Straelen used to work). For this reason, and in order to preserve nomenclatural stability, we herein designate the specimen NIGP-126342 as the neotype of P. licenti . This specimen preserves well the rostrum, first pereiopod, epistome, parts of the tailfan and even what is possibly the annulus ventralis, all of which are important for taxonomy. Besides, Van Straelen (1928b) indicates that the now lost holotype and paratypes come from the south-west of Moukden (present day Shenyang). No outcrops of the Yixian Formation are known in the immediate vicinity of Shenyang, suggesting that the type material came from further southeast of the city. Although the exact origin of the type material cannot be determined precisely, it may correspond to Chaoyang. From this point of view, the neotype NIGP-126342 from Lingyuan most likely comes from a relatively similar outcrop.

COMMENTS

Number of species in Jehol biota

To date, three separate species of crayfishes from the Jehol biota have been described. To justify the second species, A. spinirostrius, Imaizumi (1938) argued that it differed from A. licenti by the presence of dorsal spines on the rostrum (lacking in A. licenti ), possibly the shape of cervical groove, the absence of spine on gastric region (present in A. licenti ), trigonal s2 tergopleuron (?) (more rounded in A. licenti ) and uropodal exopodite shorter than endopodite (inverse in A. licenti ). These characters were rejected by Taylor et al. (1999) who suggested they mostly represent variations in preservation. We agree with this view, as for instance, the spines dorsal to the rostrum are indeed actually part of the supraorbital carina, on the side of rostrum. Similarly, the relative sizes of the uropodal exopod and endopod appear different in different specimens due to incomplete preservation of the distal part of these structures, or different orientations of the specimens in the sediment. However, we do not agree with Taylor et al. (1999), or Shen et al. (2001) that C. aethus can be distinguished from P. licenti . As explained above, the diagnostic characters of Cricoidoscelosidae , which are the same as those distinguishing A. aethus from P. licenti are, in our opinion extremely common within crayfishes or misinterpreted. For these reasons, we do not find any compelling characters allowing for the distinction of the three species described from the Jehol biota so far.

Nevertheless, due to the large number of available specimens, the relatively large distribution area where they are found, and the often highly endemic nature of many crayfish species ( Crandall & Buhay 2008), it would not be impossible to have multiple species in the Jehol biota, especially as species may co-occur ( Alda & Kawai 2022). We therefore performed a linear morphometric analysis based on measurements of as many specimens as possible, including type material of Astacus spinirostrius Imaizumi, 1938 , and Cricoidoscelosus aethus Taylor, Schram & Shen, 1999 trying to find variations that could help characterize separate species. Results are given in table 2. As shown out of the eight elements studied, only the relative length of the pleon compared to that of uropodal exopod does not have a normal distribution: the distribution is asymmetrical but not bimodal ( Fig. 9 ). A bimodal or multimodal distribution could have hinted at the presence of multiple species in our sample. While the present results cannot exclude the possibility of having multiple species, the parameter distribution is herein attributed to intraspecific variation and variations in preservation. As a result, we cannot at present consider there are more than one species of crayfish in Jehol biota. If more than one species is indeed present, the differences between species are likely mostly obfuscated by fossilisation. We thus herein consider A. spinirostrius Imaizumi, 1938 and C. aethus Taylor, Schram & Shen, 1999 to be more recent synonyms of P. licenti (Van Straelen, 1928) .

Due to the aforementioned diagnostic characters, Palaeocambarus and Cambaroides are probably closely allied and forming a monophyletic group. A detailed comparison of Palaeocambarus to Cambaroides is complicated due to the flattened preservation of fossil specimens. It however appears that specimens of Palaeocambarus differ from of all species of Cambaroides (based on data from Kawai et al. 2003, 2013, 2016; Kawai & Min 2005; Kawai & Barabanshchikov 2022; and observations of C. dauricus and C. japonicus from MNHN-IU collections) by a longer acumen of the rostrum, larger spines on postorbital carina and on median line in the cephalic area. For these reasons, and since no detailed phylogeny of the species of Cambaroides including Palaeocambarus licenti are available, we do not consider the two genera as synonym at present ( Table 1 ).

Figures

FIG. 1. — Pleopods of different decapod crustaceans, fossil and extant: A, B, Palaeocambarus licenti (Van Straelen, 1928b) seen in ventral view (A, holotype of Cricoidoscelosus aethus Taylor, 1999, NIGP-126337) and lateral view (B, specimen NIGP-Shen-2), both from the Early Cretaceous of China; C, pleopod 4 of a female Cambaroides dauricus (MNHN-IU-2022-4077, extant, Mandchuria);D, Austropotamobius llopisi (Vía, 1971) (female? – specimen MUPA-LH-14011), from the Early Cretaceous of Spain; E, Palaeobenthesicymus libanensis (Brocchi, 1875) (specimen MNHN.F.A30607) from the Santonian of Lebanon; F, female Polycheles typhlops Heller, 1862 (MNHN-IU-2022-4080, extant, New Caledonia). Photographs: D. Audo. Scale bars: A, C, 1 mm; B, D, E, F, 5 mm.

FIG. 2. — Comparison of epistomes in fossil and extant crayfishes: A, B, epistome of P. licenti (NIGP-Shen-26), photo (A) and interpretative line-drawing (B); C, epistome of P. licenti (NIGP-Shen-40);D, epistome of a female Cambaroides dauricus (Pallas, 1972) (MNHN-IU-2022-4077, extant, Mandchuria);E, Cambarus bartonii (Fabricius, 1798) (MNHN-IU-2022-4074, extant, Philadelphia, United States); F, Astacus astacus (Linnaeus, 1758) (MNHN-IU-2022-4069, extant, Nissi, Greece). Photos of fossil specimens in cross-polarized light. Abbreviations: a1, antennula; a2.ba, antennal basipodite; a2.cx, antennal coxa; epi, epistome; uo, urinary orifice (nephropore). Photographs: D. Audo. Scale bars: 2 mm.

FIG. 3. — Ischial hooks in P. licenti: A-D, on specimen NIGP-126337 (holotype of Cricoidoscelosus aethus), ventral view in cross-polarized light (A) and interpretative line-drawing (B); C, D, detailed view of the base of P2-P4 (th5-th7) (C), and interpretative line drawing (D) – note that C and D are aligned horizontally for convenience;E, F, on specimen NIGP-Shen-22,detail of the ischium of P4 (th7). Abbreviations: a1, antennula;a2, antenna; ba, basipod;cx, coxa;epi, epistome; ex, uropodal exopod; go, male gonopod; isc, ischium; md, mandible; me, merus; mxp3, maxilliped 3 (thoracopod 3); P1-P5, pereiopods 1-5 (thoracopod 4-8); pl3, pleopod 3; r, rostrum; s2, pleonite 2; sc, scaphocerite. Photographs: A, D. Audo; C, E, D.-Y. Huang. Scale bars: A, B, 20 mm; C-F, 2 mm.

FIG. 4. — Sexual dimorphism: A, B, Cambaroides dauricus(AS11,extant,Mandchuria) male (A) and female (B); C, D, possible annulus ventralis in Palaeocambarus licenti (Van Straelen, 1928) specimen NIGP-126342 from the Early Cretaceous of China, photograph (C) and interpretative line-drawing (D); E, annulus ventralis in Cambarus bartonii (Fabricius,1798) (AS90,extant, Philadelphia,United States);Abbreviations: av, annulus ventralis;av?, potential annulus ventralis; gp♀, female gonopore; gp♂, male gonopore; pl1-2♂, pleopods 1-2 (male gonopods). Photographs: D. Audo. Scale bars: A, B, E, 5 mm; C, D, 2 mm.

FIG. 5. — Neotype of Palaeocambarus licenti (Van Straelen, 1928), specimen NIGP-126342: ventral view in cross-polarized light (A) and interpretative line-drawing (B). Abbreviations: a2, antenna; av?, potential annulus ventralis; dt; digestive tract; epi, epistome; ex, uropodal exopod; mxp3, maxilliped 3 (thoracopod 3); o, eye; P1-P5, pereiopods 1-5 (th4-th8); r, rostrum; s2-s5, pleonites 2-5; sc, scaphocerite. Photograph: D. Audo. Scale bars: 20 mm.

FIG. 6. — Palaeocambarus licenti (Van Straelen,1928): three well preserved specimens NIGP-Shen-1,both in left-lateral view,in cross-polarized light (A), interpretative line drawing (B) and close-up of the cephalic area of one of the right crayfish in NIGP-Shen-1 (C), visualisation in Meshlab of the inverted surface volume of NIGP-Shen-GM1 from the photogrammetric model, with Minnaert shader (D). Abbreviations: a, branchiocardiac groove; b, antennal groove; d, gastro-orbital groove; dt, digestive tract; e1e, cervical groove;e1e (os), cervical groove (opposite side); ex, uropodal exopod; o, eye; P1, pereiopod 1; po (d), postorbital carina (dorsal part); po (v), postorbital carina (ventral part); pr, postrostral carina; r1, acumen (distal part) of rostrum; r2, proximal part of rostrum; s1-s6, pleonites 1-6; sc, scaphocerite; su, subdorsal carina; t, telson. Photograph and photogrammetric model: D. Audo. Scale bars: A, B, 20 mm; D, 10 mm.

FIG. 7. — Palaeocambarus licenti (Van Straelen,1928),specimen NIGP-175159 with well-preserved ornamentation of first pereiopod (thoracopod 4). Photograph: D.-Y. Huang. Scale bars: 20 mm.

FIG. 8. — Syntype of Astacus spinirostrius (synonym of P. licenti), ventral view in cross-polarized light (A) and interpretative line-drawing (B), Abbreviations:a1, antennula:a2, antenna;en, uropodal endopod;epi, epistome;ex, uropodal exopod;go, male gonopod;md, mandible;mxp3, maxilliped 3 (th.3);P1-P5, pereiopods 1-5 (th. 4-8); s2-s6, pleonites 2-6; sc, scaphocerite; t, telson. Photograph: D. Audo. Scale bars: 20 mm.

FIG. 10. — Scientific reconstructions in dorsal view of Palaeastacus licenti (Van Straelen, 1928b). Drawing: C. Letenneur (UMR 7207 CR2P).

FIG. 11. — Scientific reconstructions in lateral view of Palaeastacus licenti. Drawing: C. Letenneur (UMR 7207 CR2P).

FIG. 12. — Eyes and gastroliths: detail of the eye of spec11 (A) and specimen with gastroliths NIGP-126353, whole specimen in dorsal view, in cross-polarized light (B) and close-up of the gastroliths imprint, in cross-polarized light (C). Photographs: D. Audo. Scale bars: A, 1 mm; B, 20 mm; C, 10 mm.

FIG. 13. — Two types of preservation: A, B, NIGP-126354,a possible fossil corpse (A) as shown by the presence of an infilled proctodeum (B); C, fossilized moult NIGP-Shen-RT132 (C) as shown by the disconnection of the cephalothorax shield, thinness of the exoskeleton and lack of fossilized soft-parts. Photographs: D. Audo. Scale bars: 10 mm.

APPENDIX 6. — Specimens without registration numbers used in the study, continued from previo us figures. Scale bars: 10 mm.

FIG. 9. — Distribution of pleon length to uropodal exopod length ratios.