Mid-Cretaceous coastal amber forest palaeoenvironment revealed by exceptionally preserved ostracods from an extant lineage Author Wang, He https://orcid.org/0000-0002-5822-3309 Nanjing Institute of Geology and Palaeontology Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China wanghe0701@163.com Author Matzke-Karasz, Renate https://orcid.org/0000-0002-8010-2028 Department of Earth and Environmental Sciences, Palaeontology and Geobiology, Ludwig-Maximilians-Universitaet Muenchen, Richard-Wagner-Strasse 10, 80333 Muenchen, Germany r.matzke@lrz.uni-muenchen.de Author Horne, David J. https://orcid.org/0000-0002-2148-437X School of Geography, Queen Mary University of London, Mile End Road, London E 1 4 NS, UK text Fossil Record 2022 2022-06-02 25 1 147 172 http://dx.doi.org/10.3897/fr.25.e84604 journal article http://dx.doi.org/10.3897/fr.25.e84604 2193-0074-1-147 91C70EDD7ACE492EAA7F1CE884018AE6 78E78880F4095BA2B0F947505C456D99 Sanyuania sp. Figs 14 , 15 , 16 Material. Single male specimen; BA19005-8. Dimensions. L = 245 μm , H = 116 μm , W ≈ 120 μm . Description. Carapace (Figs 14A-E , 16A, C ) small subtriangular shape in lateral view. Greatest height at 1/4 of length. Anterior margin broadly rounded. Posterior margin narrowly rounded. Dorsal margin straight, moderately sloping down from the greatest height to the posterior margin. Ventral margin straight in middle part in both valves, with slightly concave regions in the very middle, forming distinct flaps as an area of valve overlap (LV>RV) (Fig. 16A ). From posterior third, ventral margin ascending towards posterior end. Carapace in dorsal view elliptical, with posterior and anterior part compressed and central region strongly protruding. The valve's lateral surface punctate in the flat anterior and posterior marginal regions, while pitted (i.e., covered with wider and deeper depressions) in the central region and dorsally. Valves thick in cross section (Fig. 16C ). Inflated central region with distinct sulcus mid-dorsally. Inner calcified lamella wide. Central muscular scar pattern, pore morphology and detailed hinge elements not preserved. Figure 14. Microtomographic reconstruction of Sanyuania sp., based on microtomography of adult male (BA19005-8), surface rendering and soft parts of BA19005-8, surface renderings. A-E. With same scale, carapace; F-R. With same scale, soft parts. A. RV external; B. RV internal; C. LV external; D. LV internal; E. Dorsal view, anterior to left; F. A1, right; G. A1, left; H. A2, right; I. A2, left; J. Md, right; K. Md, lef; L. Mxl, right; M. Mxl, left; N. L5, right; O. L5, left; P. L6, right; Q. L6, left; R. L7, right. Soft parts almost all preserved, but with a low degree of detail. A1 (Figs 14F, G , 15A , 16D ) rod-shaped. Segmentation and setation not preserved. Figure 15. Drawings of appendages of Sanyuania sp., based on microtomography of adult male (BA19005-8). A. A1; B. A2; C. Mxl; D. HP; E. Md; F. L5; G. L6; H. L7. Scale bar: 10 µm . Figure 16. Microtomographic reconstruction of Sanyuania sp., based on data of adult male (BA19005-8), volume rendering. A. Oblique ventral view into gaping carapace with flaps for improved valve overlap (arrows); B. Mouth area from ventral, with labrum (la), labium (lb), mandible (Md) and maxillula (Mxl); C. Cross section in posterior region, with very thick and robust valves; D. Anterior body region with A1 and A2 and presumed sac of spinneret gland (highlighted); E. Mandible (highlighted); F. Soft body with L5, L6 and L7 and HP; G. HP in dorsal view (highlighted). Scale bars 100 µm ( A, C, D, F ); 10 µm ( B, E, G ). A2 (Figs 14H, I , 15B , 16D ) more robust than A1, number of segments unknown. With prominent knee between protopodite and endopodite, close to which the spinneret seta (exopodite) originates, the only preserved setation of both A2 in this specimen. Between the right A2 and the internal side of RV, a roundish, disk-shaped body is preserved, which we tentatively interpret as the sac of the spinneret gland containing the secretion (Fig. 16D ). Md (Figs 14J, K , 15E , 16B, E ) Masticatory process of coxa preserved, reaching into the oral opening, but teeth only weakly preserved. The palp's segmentation and setation not preserved. Vibratory plate not preserved. Mxl (Figs 14L, M , 15C , 16B ) Protopod with three masticatory lobes (endites 1-3) and two-segmented palp, without any claws/setae preserved; branchial plate preserved. L5 (Figs 14N, O , 15F , 16F ) Walking leg, elongate, with long endopodite consisting of indeterminate number of segments. L6 (Figs 14P, Q , 15G , 16F ) Presumed walking leg, protopodite elongate, endopod not well preserved. L7 (Figs 14R , 15H ) Walking leg, elongate protopodite and long endopodite, the latter with at least three segments. HP (Figs 15D , 16F, G ) almost triangular in shape, apically forming distinct tip, shaped like an arrowhead. Remarks. We assign the studied specimen to the genus Sanyuania within the Loxoconchidae , mainly based on shape, ornamentation and morphology of its carapace. Preserved soft parts, although with little detail, and without genus-specific features being observable, at least do not oppose this assignment. The morphology of the preserved hemipenes is clearly in line with Hartmann's (1966 : 758) description of hemipenes typical of Loxoconchinae as consisting of a voluminous capsule and a triangular, distally rounded top piece. A direct comparison of our specimens' hemipenis with that of Sanyuania segersi Savatenalinton & Martens, 2009a shows a high degree of similarity ( Savatenalinton and Martens 2009a : fig. 5A) with its triangular (arrow-head-like) distal tip on a broad, rounded main body. Regarding the shape of the carapace, as well as the flattened anterior and posterior margins, our specimen is most similar to S. cuneata Zhao & Whatley, 1992. However, the surface ornamentation of the valves with broader pits centrally and smaller ones marginally, comes closer to that of S. wangi Zhao & Whatley, 1992. None of the known Sanyuania species, however, possess the mid-dorsal sulcus featured in our specimen. Clearly our data on this single specimen are too limited for more certainty; more specimens are needed for a full taxonomic assessment. We therefore present this specimen in open nomenclature here.