Research Article |
Corresponding author: Dayou Zhai ( dyzhai@ynu.edu.cn ) Academic editor: Ivana Karanovic
© 2022 Qianwei Wang, David J. Horne, Jiawei Fan, Ruilin Wen, Robin J. Smith, Min Wang, Dayou Zhai.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Wang Q, Horne DJ, Fan J, Wen R, Smith RJ, Wang M, Zhai D (2022) Ilyocypris leptolinea Wang & Zhai, sp. nov., an ostracod (Ostracoda, Crustacea) from the late Quaternary of Inner Mongolia, northern China. ZooKeys 1137: 109-132. https://doi.org/10.3897/zookeys.1137.94224
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Ilyocypris leptolinea Wang & Zhai, sp. nov. is described from late Quaternary sediments in central-eastern Inner Mongolia, northern China. The new species, which has a carapace shape and pitted surface typical of the genus, is characterised by double rows of fine, densely arranged marginal ripplets, separated by an inner list, along both anterior and posterior calcified inner lamellae in the left valve. Outline analysis and Principal Component Analysis indicate that its morpho-space overlaps with I. bradyi Sars, 1890, I. japonica Okubo, 1990, and I. mongolica Martens, 1991, which have living or fossil representatives in Inner Mongolia, but it is clearly discriminated from I. innermongolica Zhai & Xiao, 2013. Judging from the relatively coarse lithology dominated by silt and sand, and the lack of accompanying brackish-water ostracods, I. leptolinea Wang & Zhai, sp. nov. may have lived in a relatively shallow freshwater lake. It perhaps can be added to the list of species that went extinct during the Quaternary, but the timing and process of extinction await further investigation.
Fossil, lacustrine sediment, marginal ripplet, new species, outline analysis, Xiaojinggou Basin
The Ostracoda genus Ilyocypris Brady & Norman, 1889, dating back to the Late Cretaceous (
Despite the above-mentioned ecological disparity and taxonomic diversity within Ilyocypris, the morphological differences between many of its species are so subtle that reliable species identification can be difficult without information of the male reproductive organs (
With the help of Scanning Electron Microscopy (SEM),
In this study we describe a new fossil species of the genus Ilyocypris, based on well-preserved material from late Quaternary sediments in Inner Mongolia of China. A variety of morphological features, such as the marginal ripplets on the anterior and posterior valve margins, inner lists, valve shape, and ornamentation on the valve surface, are described and compared with those of congeners. A discussion is given about the overlap of morpho-space of the new species with some of its congeners as visualised by outline analysis, Principal Component Analysis (PCA), and cluster analysis.
The XJG2 section (43°51'41.9"N, 116°24'57.1"E, Fig.
A digital Elevation Model showing the position of the study area (red rectangle) in central-eastern Inner Mongolia, China B digital Elevation Model showing the location of the XJG2 section C field photo of the section D lithology of the section. Red triangle indicates the result of 14C dating of gastropods from depth 139‒140 cm. See text for details.
In the field, the XJG2 section was excavated (Fig.
In the laboratory, the extraction of ostracod valves generally followed the method described by
Examined valves of Ilyocypris from XJG2 section. All the adult left valves are identified as Ilyocypris leptolinea Wang & Zhai, sp. nov. based on marginal ripplets. Others are tentatively assigned to this species. Note that all the valves of this species used for outline analysis in this study are adult left valves imaged for exterior view. Abbreviations: A, adult; A-1, last juvenile stage before adult; H, height; L, length; LV, left valve; MR, marginal ripplets; OL, outline; RV, right valve.
Specimen | Stage | RV/LV | L×H (mm) | Type designation | MR preservation | OL analysis |
---|---|---|---|---|---|---|
XJG2-021-1 | A | LV | 0.94×0.48 | paratype | yes | yes |
XJG2-136-2 | A | LV | 0.83×0.45 | / | yes | yes |
XJG2-138-2 | A | LV | 0.96×0.52 | / | yes | / |
XJG2-139-1 | A | LV | 0.82×0.42 | / | yes | / |
XJG2-153-1 | A | LV | 0.90×0.47 | / | yes | yes |
XJG2-153-2 | A | LV | 0.87×0.47 | / | yes | yes |
XJG2-153-3 | A | LV | 0.92×0.50 | / | yes | yes |
XJG2-160-1 | A | LV | 0.91×0.49 | / | yes | / |
XJG2-174-1 | A | LV | 0.98×0.53 | / | yes | yes |
XJG2-177-1 | A | LV | 0.90×0.47 | paratype | yes | yes |
XJG2-188-1 | A | LV | 1.01×0.53 | / | yes | / |
XJG2-189-1 | A | LV | 0.81×0.43 | / | yes | yes |
XJG2-190-1 | A | LV | 1.05×0.56 | paratype | yes | yes |
XJG2-192-1 | A | LV | 0.94×0.51 | / | yes | yes |
XJG2-192-2 | A | LV | 0.91×0.50 | / | yes | yes |
XJG2-192-3 | A | LV | 0.87×0.48 | / | yes | / |
XJG2-192-5 | A | LV | 0.78×0.43 | / | yes | / |
XJG2-193-1 | A | LV | 0.91×0.48 | paratype | yes | yes |
XJG2-196-4 | A | LV | 0.84×0.46 | / | yes | / |
XJG2-197-2 | A | LV | 0.90×0.48 | paratype | yes | / |
XJG2-199-2 | A | LV | 0.86×0.46 | paratype | yes | / |
XJG2-210-1 | A | LV | 0.94×0.48 | holotype | yes | yes |
XJG2-212-2 | A | LV | 0.94×0.52 | / | yes | yes |
XJG2-218-1 | A | LV | 0.78×0.42 | / | yes | / |
XJG2-228-2 | A | LV | 0.88×0.46 | paratype | yes | yes |
XJG2-192-4 | A-1 | LV | 0.70×0.39 | / | not observed due to aggregation | / |
XJG2-196-1 | A-1 | LV | 0.74×0.42 | / | yes | / |
XJG2-197-1 | A-1 | LV | 0.70×0.39 | / | yes | / |
XJG2-199-1 | A-1 | LV | 0.74×0.41 | / | yes | / |
XJG2-202-3 | A-1 | LV | 0.80×0.44 | / | yes | / |
XJG2-222-1 | A-1 | LV | 0.72×0.39 | / | yes | / |
XJG2-129-1 | A | RV | 0.91×0.47 | / | / | / |
XJG2-136-1 | A | RV | 0.93×0.50 | / | / | / |
XJG2-169-1 | A | RV | 0.87×0.48 | / | / | / |
XJG2-190-2 | A | RV | 0.90×0.49 | / | / | / |
XJG2-191-1 | A | RV | 0.83×0.45 | / | / | / |
XJG2-193-2 | A | RV | 0.90×0.47 | / | / | / |
XJG2-196-2 | A | RV | 0.88×0.47 | / | / | / |
XJG2-196-3 | A | RV | 0.95×0.50 | / | / | / |
XJG2-197-5 | A | RV | 0.83×0.46 | / | / | / |
XJG2-197-6 | A | RV | 0.90×0.49 | / | / | / |
XJG2-202-1 | A | RV | 0.86×0.46 | / | / | / |
XJG2-202-4 | A | RV | 0.85×0.45 | / | / | / |
XJG2-203-1 | A | RV | 0.85×0.45 | / | / | / |
XJG2-203-2 | A | RV | 0.86×0.45 | / | / | / |
XJG2-205-2 | A | RV | 0.85×0.45 | / | / | / |
XJG2-212-3 | A | RV | 0.82×0.44 | / | / | / |
XJG2-216-1 | A | RV | 0.99×0.53 | / | / | / |
XJG2-217-1 | A | RV | 0.86×0.47 | / | / | / |
XJG2-218-2 | A | RV | 0.87×0.47 | / | / | / |
XJG2-221-1 | A | RV | 0.81×0.45 | / | / | / |
XJG2-226-1 | A | RV | 0.88×0.47 | / | / | / |
XJG2-228-3 | A | RV | 0.79×0.43 | / | / | / |
XJG2-192-6 | A-1 | RV | 0.77×0.42 | / | / | / |
In the sample XJG2-140 (depth 139‒140 cm), a small number of well-preserved gastropods were found, which were used for 14C dating.
Pre-treatment of the dating material was done in the Laboratory Test Center, Institute of Geology, China Earthquake Administration (Beijing, China). Brush-cleaned gastropod shells were soaked in 0.1N HCl in an ultra-sonic bath until the surface layer (c. 1/3 in thickness) was eroded away. The residual was rinsed with deionised water and was then oven-dried. Approximately 20 mg of such cleaned, dried shell was dissolved with 1 ml of H3PO4 at 70 °C in an airtight reacting system with a pressure of ~ 10-2 Pa. The released CO2 was purified and was deoxidised by H2, with Fe powder as the catalyst, yielding ~ 1 mg of graphite, which was dated in a NEC 1.5SDH-1 Compact PKUAMS facility at the Institute of Heavy Ion Physics, Peking University (Beijing, China). The 14C age of the sample was calibrated using the OxCal v. 4.2 program (
In order to characterise and then to compare the shapes of different valves, outline analysis was performed, with general principles following those provided by
Principal Component Analysis (PCA) was performed on the polar-coordinate data of the fixed outlines (see above) using the software CANOCO v. 4.5 (
A total of 42 outlines of the valves of Ilyocypris were analysed (Tables
Examined valves of other species of Ilyocypris. All the specimens are adults, which can be judged from their larger sizes, wider calcified inner lamellae, and patterns of inner marginal ripplets (only applied to left valves). Additional abbreviations to those in Table
Species | Specimen number | RV/LV, int/ext | L×H (mm) | Locality | Horizon | OL analysis |
---|---|---|---|---|---|---|
I. bradyi | CC22 | LV, ext | 0.85×0.44 | Greenlands Pit, Purfleet, UK | MIS 9 (Pleistocene) | yes |
I. bradyi | CC23 | LV, ext | 0.86×0.44 | Greenlands Pit, Purfleet, UK | MIS 9 (Pleistocene) | yes |
I. bradyi | CC26 | LV, ext | 0.85×0.43 | Greenlands Pit, Purfleet, UK. | MIS 9 (Pleistocene) | yes |
I. bradyi | MTDB-3 | LV, ext | 1.06×0.55 | Marks Tey, UK | MIS 11 (Pleistocene) | yes |
I. bradyi | MTDB-5 | LV, ext | 0.98×0.51 | Marks Tey, UK | MIS 11 (Pleistocene) | yes |
I. bradyi | MTDB-13 | LV, ext | 1.04×0.55 | Marks Tey, UK | MIS 11 (Pleistocene) | yes |
I. bradyi | NHM UK PM OS 19853 | LV, ext | no data | Boxgrove, UK (cf. Whittaker and Parfit 2017) | MIS 13 (Pleistocene) | yes |
I. bradyi | NHM UK PM OS 19854 | LV, ext | no data | Boxgrove, UK (cf. Whittaker and Parfit 2017) | MIS 13 (Pleistocene) | yes |
I. bradyi | dyzoc810 | RV, ext | 0.83×0.43 | Creek Y16, Inner Mongolia, China (cf. |
extant | yes |
I. mongolica | dyzoc515 | LV, ext | 0.80×0.43 | Lake X26, Inner Mongolia, China (cf. |
extant | yes |
I. mongolica | dyzoc518 | LV, ext | 0.89×0.48 | Lake X26, Inner Mongolia, China (cf. |
extant | yes |
I. mongolica | LBM 1430009163 | LV, ext | 0.83×0.46 | Pond X36, Inner Mongolia, China (cf. |
extant | yes |
I. innermongolica | dyzoc5 | LV, int | 0.73×0.37 | Lake Hulun, China (cf. |
extant | yes |
I. innermongolica | dyzoc5 | RV, ext | 0.71×0.36 | Lake Hulun, China (cf. |
extant | yes |
I. innermongolica | dyzoc7 | LV, int | 0.76×0.42 | Lake Hulun, China (cf. |
extant | yes |
I. innermongolica | dyzoc7 | RV, ext | 0.74×0.39 | Lake Hulun, China (cf. |
extant | yes |
I. innermongolica | dyzoc8 | LV, int | 0.69×0.37 | Lake Hulun, China (cf. |
extant | yes |
I. innermongolica | dyzoc8 | RV, ext | 0.69×0.36 | Lake Hulun, China (cf. |
extant | yes |
I. innermongolica | dyzoc93 | LV, int | 0.70×0.36 | Lake Hulun, China (cf. |
extant | yes |
I. innermongolica | dyzoc93 | RV, int | 0.67×0.35 | Lake Hulun, China (cf. |
extant | yes |
I. innermongolica | dyzoc100 | LV, int | 0.74×0.37 | Lake Hulun, China (cf. |
extant | yes |
I. innermongolica | dyzoc100 | RV, ext | 0.73×0.36 | Lake Hulun, China (cf. |
extant | yes |
I. innermongolica | dyzoc114 | LV, int | 0.73×0.37 | Lake Hulun, China (cf. |
extant | yes |
I. innermongolica | dyzoc114 | RV, ext | 0.71×0.36 | Lake Hulun, China (cf. |
extant | yes |
I. japonica | LBM 1430009143 | LV, ext | 0.91×0.50 | Shiga Prefecture, Japan (cf. |
extant | yes |
I. japonica | LBM 1430009146 | LV, ext | 0.76×0.40 | Gyeongsangnam-do, South Korea (cf. |
extant | yes |
I. japonica | LBM 1430009147 | LV, ext | 0.86×0.46 | Gyeongsangnam-do, South Korea (cf. |
extant | yes |
The 240-cm thick lacustrine XJG2 section consists of clay, silt, and fine-sand fractions and contains no gravels (Fig.
The gastropod shells (laboratory dating code: CG-2021-1566) from the sample XJG2-140 in the middle part of the XJG2 section (Fig.
In addition to Ilyocypris, the fossil ostracods recovered from the XJG2 section include members of the genera Candona Baird, 1845, Cypridopsis Brady, 1867, Fabaeformiscandona Krstić, 1972 and Pseudocandona Kaufmann, 1900 (work in progress, to be published elsewhere). Valves of Ilyocypris were found between the depths of 240 cm and 20 cm. Examination of the morphologies of the left valves, including shape, ornamentation, and marginal ripplets, suggests that they belong to a new species, which is described below.
Order Podocopida Sars, 1866
Superfamily Cypridoidea Baird, 1845
Family Ilyocyprididae Kaufmann, 1900
Subfamily Ilyocypridinae Kaufmann, 1900
Genus Ilyocypris Brady & Norman, 1889
XJG2 section (43°51'41.9"N, 116°24'57.1"E, Fig.
Late Pleistocene to Holocene; holotype from 209‒210 cm depth in section, c. 70 cm below level of gastropod shells that yielded a calibrated radiocarbon date of 10,108 ± 93 calendar years before present (cal yr BP).
Holotype
: adult left valve, XJG2-210-1 (XJG2, section code; 210, sample code, corresponding to 209‒210 cm depth in section; 1, registration number), length 0.94 mm, height 0.48 mm. Paratypes: seven adult left valves, XJG2-021-1, XJG2-177-1, XJG2-190-1, XJG2-193-1, XJG2-197-2, XJG2-199-2, XJG2-228-2. All type specimens with marginal ripplets on anterior and posterior calcified inner lamellae well-preserved (Figs
Adult left valves of the ostracod Ilyocypris leptolinea Wang & Zhai, sp. nov. from the late Quaternary Xiaojinggou section of Inner Mongolia, China A–D XJG2-210-1 (holotype, 0.94 × 0.48 mm) A exterior view B interior view C interior view of the posterior part, showing the marginal ripplets D interior view of the anterior part, showing the marginal ripplets. Arrows and numerals indicate three inner lists on the calcified inner lamella E, F XJG2-206-4 E oblique-dorsal view F enlarged view of the rectangle in (E), showing the crossing pattern of the inner lists at the median part of ventral margin. Arrows and numerals indicate the three inner lists G XJG2-206-1, enlarged oblique-dorsal view of the median part of calcified inner lamella, showing the crossing pattern of inner lists H–J XJG2-199-2 (paratype) H interior view I interior view of the postero-ventral part, showing the marginal ripplets J Interior view of the antero-ventral part, showing the marginal ripplets. Arrows and numerals indicate the three inner lists. Scale bars: 200 μm (A, B, E, H); 100 μm (C, D, I, J); 50 μm (F, G).
Adult left valves of the ostracod Ilyocypris leptolinea Wang & Zhai, sp. nov. from the late Quaternary Xiaojinggou section of Inner Mongolia, China A–C XJG2-21-1 (paratype) A exterior view B interior view of the postero-ventral part, showing the marginal ripplets C interior view D–G XJG2-197-2 (paratype) D interior view E interior view of the antero-ventral part, showing the marginal ripplets and three inner lists (arrowed) F adductor muscle scars (AMS) and mandibular scars (MS) G interior view of the posterior part, showing the marginal ripplets. Scale bars: 200 μm (A, C, D); 100 μm (B, E, G); 50 μm (F).
17 adult left valves, 22 adult right valves, six A-1 juvenile left valves, and one A-1 juvenile right valve (Table
From the Greek leptos for fine, small, or subtle, and Latin linea for line or thread, referring to fine marginal ripplets on calcified inner lamellae of LV.
Adult left valves (n = 25, Fig.
Intermediate-sized Ilyocypris (length ranging from 0.78 to 1.05 mm, Table
Left valves. Intermediate-sized Ilyocypris. Valve sub-reniform in lateral view, with greatest height (antero-dorsal corner) at anterior third. Dorsal margin, i.e., section between antero-dorsal and postero-dorsal corners, nearly straight but with blunt turn immediately behind posterior sulcus due to inflation of postero-dorsal part. Anterior margin broadly rounded, with dorsal part nearly straight and more ventral parts evenly rounded. Posterior margin evenly rounded and less obtrusive. Ventral margin concave. Valve surface carrying two transverse sulci, with anterior sulcus originating from antero-dorsal corner, tapering ventrally, and terminating slightly above mid-height. Posterior sulcus wider and shorter. Adductor muscle scars situated in ovate depression immediately below posterior sulcus. Mandibular scars situated in two small depressions to antero-ventral position of adductor muscle scars. Shell surface densely covered with small pits, with those in front of anterior sulcus, between two sulci and behind posterior sulcus, smaller. Small number of tiny spines present along anterior and posterior margins in some specimens.
Interior view, anterior and posterior calcified inner lamellae comparatively wide but with anterior one slightly wider. Three inner lists present on anterior calcified inner lamella (Figs
Dorsal view (Fig.
Right valves. Shape similar to that of left valve, but dorsal margin straighter (Fig.
Ostracod valves tentatively identified as Ilyocypris leptolinea Wang & Zhai, sp. nov. from the late Quaternary Xiaojinggou section of Inner Mongolia, China A–D XJG2-203-1, adult right valve A exterior view B interior view C interior view of the antero-ventral part, showing three inner lists (arrowed) D interior view of the postero-ventral part E XJG2-193-4, right valve of A-1 juvenile, exterior view F–H XJG2-199-1, left valve of A-1 juvenile F interior view G interior view of the postero-ventral part, showing the marginal ripplets H interior view of the antero-ventral part, showing the marginal ripplets. Scale bars: 200 μm (A, B, E, F); 100 μm (C, D, G, H).
Valves of A-1 juveniles. Shape similar to that of adults but with dorsal margin more inclined (Fig.
The new species can be easily distinguished from congeners by the fineness, number, and distribution of the two rows of marginal ripplets as well as the presence of the outer-most (first) inner list in the intermediate zone that separates the two rows of marginal ripplets. Ilyocypris bradyi, for example, has fewer, thicker, and more widely spaced ripplets confined to the postero-ventral area, typically four or five in the outer row (see e.g.,
Illustrations showing the overlap of the outline morpho-spaces of five species of Ilyocypris that have living or Quaternary representatives in eastern Inner Mongolia. All outlines have been standardised for equal surface area, rotated with the antero-ventral and the postero-ventral parts resting horizontally, and with the geometric centres set at (0, 0) A outlines of 42 valves B mean outlines of the five species. Arrows indicate areas showing relatively large inter-species variability, i.e., the postero-dorsal‒posterior and the postero-ventral areas C principal Component Analysis (PCA) biplot of 42 valves based on their outline data. Coloured shaded areas indicate the morpho-spaces of the five species, cast on the two-dimensional space defined by PCA axis 1 and 2.
The dissimilarity matrices of the specimens (Tables
Average intra- (bold) and inter-species outline dissimilarity of the five species of Ilyocypris analysed in this study, based on a Fixed Outline Canberra Dissimilarity (FOCD, %) index between the specimens analysed in this study. Small numerals in parentheses indicate the number of dissimilarity values used for averaging. Species abbreviations: Ibr, I. bradyi; Iep, I. leptolinea Wang & Zhai, sp. nov.; Iin, I. innermongolica; Ija, I. japonica; Imo, I. mongolica.
Species | Iep | Ibr | Imo | Iin | Ija |
---|---|---|---|---|---|
Iep | 1.00(105) | ||||
Ibr | 1.18(135) | 0.84(36) | |||
Imo | 1.01(45) | 1.21(27) | 0.81(3) | ||
Iin | 1.49(180) | 1.14(108) | 1.58(36) | 0.83(66) | |
Ija | 1.00(45) | 0.92(27) | 0.80(9) | 1.17(36) | 0.61(3) |
Average intra- (bold) and inter-species outline dissimilarity of the five species of Ilyocypris analysed in this study, based on a Minimal Running Canberra Dissimilarity (MRCD, %) index. Small numerals in parentheses indicate the number of dissimilarity values used for averaging. Species abbreviations: Ibr, I. bradyi; Iep, I. leptolinea Wang & Zhai, sp. nov.; Iin, I. innermongolica; Ija, I. japonica; Imo, I. mongolica.
Species | Iep | Ibr | Imo | Iin | Ija |
---|---|---|---|---|---|
Iep | 0.96(105) | ||||
Ibr | 1.10(135) | 0.76(36) | |||
Imo | 0.95(45) | 1.10(27) | 0.70(3) | ||
Iin | 1.38(180) | 1.07(108) | 1.42(36) | 0.71(66) | |
Ija | 0.93(45) | 0.87(27) | 0.72(9) | 1.12(36) | 0.61(3) |
In the cluster analyses based on the two dissimilarity indices (Fig.
Cluster dendrograms of the valve outlines of Ilyocypris species based on the matrices of ‘Fixed Outline Canberra Dissimilarity’ (FOCD, with antero-ventral and postero-ventral parts of valves placed horizontally) (A) and ‘Minimal Running Canberra Dissimilarity’ (MRCD) (B) showing overlap of the morpho-spaces between congeners. The analysed Ilyocypris species are those with living or Quaternary representatives in eastern Inner Mongolia. Pink dashed rectangles indicate groups of specimens mentioned in the text. See text for details.
The above-mentioned partial-separation pattern of Ilyocypris species in the cluster dendrograms (Fig.
Based on the morphologies of valve material, we have herein erected Ilyocypris leptolinea Wang & Zhai, sp. nov. from late Quaternary lacustrine strata of Inner Mongolia. This species is best recognised by its two rows of densely arranged fine inner marginal ripplets on both the anterior and the posterior calcified inner lamellae of the left valve. Other features, such as the three inner lists, the relatively great width of the calcified inner lamella, and the node-free valve surface may also help diagnose the new species (Figs
Outline analyses indicate that although I. leptolinea Wang & Zhai, sp. nov. can be distinguished from I. innermongolica by valve shape, its morpho-space exhibits considerable overlap with other Ilyocypris species that have living/fossil representatives in Inner Mongolia, namely I. bradyi, I. japonica, and I. mongolica (Figs
The drawback of valve outline is that it is usually a continuous or semi-continuous feature that generates overlapping patterns between species (Figs
Most of the valve-shape difference among different Ilyocypris species is present in the posterior part of the valves while the shapes of the anterior parts are almost identical (Fig.
The prevalence of lacustrine sediments in the Xiaojinggou Basin indicates the existence of a lake in this area during the late Quaternary. From the lithology of the section XJG2, which is dominated by silt and sand fractions and shows a trend of becoming coarser towards the upper part (Fig.
The disappearance of I. leptolinea Wang & Zhai, sp. nov. above the depth of 20 cm in the XJG2 section may be significant, perhaps even indicative of its extinction. This species has not been reported from Quaternary sediments elsewhere or from modern habitats, and it may have been endemic to the Xiaojinggou area during the late Quaternary, with a comparatively narrow ecological niche. It would not only add to our knowledge of the animals that went extinct during the Quaternary (
This work is the first investigation of the lacustrine sediments and the ostracod fossils in the Xiaojinggou Basin, and future works will endeavour to reconstruct the palaeoenvironments of this area based on more analyses of the ostracods and other proxies. With previous palaeoenvironmental investigations in eastern Inner Mongolia focused on the three large brackish-water lakes (
Although Ilyocypris leptolinea Wang & Zhai, sp. nov. is ‘ordinary’ among the species of the genus as judged from its carapace size, shape, and not noded, pitted valve surface, the patterns of marginal ripplets and the inner lists on its left valves are unique. The erection of this species based on the observations of various features, especially the marginal ripplets and the outline analyses, could become a case study for describing new species of the genus Ilyocypris based on valve material. Judged from the lithology and accompanying ostracods in the section, I. leptolinea Wang & Zhai, sp. nov. may have lived in intermediate depth to shallow freshwater, although as an extinct species it could hardly provide independent environmental indications. The new species may add to the knowledge of extinct animals in the late Quaternary and provides basic data for studying environmental changes during this period.
This study is supported by NSFC grants 32160116 and 41902011, the Key Research Program of the Institute of Geology & Geophysics, Chinese Academy of Sciences (IGGCAS-201905), and Yunnan Provincial Grants 202101AT070158 and YNWR-QNBJ-2019-295. We thank Fangzhi Peng (Advanced Analysis and Measurement Center of Yunnan University) and Xiangtong Lei (Institute of Palaeontology, Yunnan University) for imaging the ostracod specimens. The comments from Peter Frenzel (Friedrich Schiller University Jena) and an anonymous reviewer are much appreciated.