taxonID	type	description	language	source
53258785FFA81F66E79CFF67FA69FCDA.taxon	materials_examined	Type genus: Prochydorus Smirnov, 1992. Emended diagnosis: Body high, head capsule well developed, durable, covered with a head shield. Post-cephalic body covered with valves. Antenna II relatively long (length of basal segment + exopod = about half body length), both branches three-segmented, antennal formula (4 – 7) – (1) – (3) / (1) – (1) – (3). Gut not convoluted. Differential diagnosis: Unique antenna II (with lateral setae only on proximal segment of endopod) differentiates the family Prochydoridae from any other family in the known orders of the Cladocera.	en	Kotov, Alexey A. (2009): A revision of the extinct Mesozoic family Prochydoridae Smirnov, 1992 (Crustacea: Cladocera) with a discussion of its phylogenetic position. Zoological Journal of the Linnean Society 155 (2): 253-265, DOI: 10.1111/j.1096-3642.2008.00412.x, URL: https://academic.oup.com/zoolinnean/article-lookup/doi/10.1111/j.1096-3642.2008.00412.x
53258785FFA81F66E79CFF67FA69FCDA.taxon	description	2. Rostrum pointed, ventral margin of valves without setae and / or denticles 3. Body very high, mandible attached to the valve at a distance from point of joint of head and valve, antenna II short ........................................................................................................ 1. Prochydorus Smirnov, 1992 4. Body less high, mandible attached to the point of joint of head and valve, antenna II long ................................. .................................................................................................................. 2. Archeoxus Smirnov, 1992	en	Kotov, Alexey A. (2009): A revision of the extinct Mesozoic family Prochydoridae Smirnov, 1992 (Crustacea: Cladocera) with a discussion of its phylogenetic position. Zoological Journal of the Linnean Society 155 (2): 253-265, DOI: 10.1111/j.1096-3642.2008.00412.x, URL: https://academic.oup.com/zoolinnean/article-lookup/doi/10.1111/j.1096-3642.2008.00412.x
53258785FFA81F63E7D8FAAFFEC1FBD2.taxon	description	Smirnov, 1992 a: 112, figs 4 E, 8 C – E, 9 E, F, 10, 12 E, 13; Dumont & Negrea, 2002: 226 – 227. Type locality: Khotont. The northern part of Mount Ukra, 6 km west of Khotont Somon in the valley of the Orkhon, north-eastern Hangay, Arhangay Aimag, Mongolia. More than 1500 impressions of different insects were collected from this locality (Rasnitsyn & Quicke, 2002). Age: The absolute age of this locality was not estimated, but its palaeofauna consists of both Jurassic and Cretaceous taxa, and the age is estimated as near the Jurassic – Cretaceous boundary (Rasnitsyn & Quicke, 2002). Holotype: PIN, 4307 / 2024 and 2040 (impression and counter-impression). Paratypes: PIN 4307 / 2019, 2020, 2025, 2038, 2039 (counter-impression of 19). The current condition of Smirnov’s (1992 a) paratype 4307 / 2020 prevents accurate determination. Impression 4307 / 2017, also listed by the author as a paratype of P. rotundus, may belong to Archeoxus mirabilis. Other material studied: PIN 4307 / 2002, 2007, 2013, 2016, 2032 (counter-impression of 13), 2041. Diagnosis: As for the genus. Description: Body very high (height / length = 0.83 – 0.92), rounded in lateral view, dorsum regularly convex, postero-dorsal angle well defined, posteroventral portion broadly rounded. Head about 0.4 ¥ body › Figure 1. Drawings of Upper Mesozoic Prochydoridae based on SEM photographs. A, Prochydorus rotundus from Khotont, reconstruction based on a series of specimens. B, antenna II of holotype, PIN 4307 / 2040. C, specimen PIN 4307 / 2031 from Khotont, antenna II. D, Archeoxus mirabilis from Khotont, reconstruction based on a series of specimens. E, antenna II of specimen PIN 4307 / 2018. F, ‘ Archeoxus ’ vetrosus from Khotont, antenna II of holotype PIN 4307 / 2027. G, Palaeorak scherbakovi gen. nov., sp. nov. from Khasurty, holotype 5026 / 178. H, reconstruction of general view based on series of specimens. I, postabdominal claw, 5026 / 177. J, antenna II, 5026 / 179. Scale bars: 1 mm. view, postabdominal claws, antenna II and apical segment of its exopod. E, holotype PIN 4307 / 2040 (counter-impression). F, G, paratype PIN 4307 / 2019, general view and mandibles. H, paratype PIN 4307 / 2020. Scale bars: A, F, H, 1 mm; B – E, G, 0.1 mm. · length, massive, head capsule of the ‘ daphniid-type’, with head shield supplied with a distinct fornix, rostrum pointed. Valve ventral margin without denticles or setae. Postabdomen with claw supplied with minute denticles. Antenna II short. Exopod length 0.21 – 0.25 ¥ body length, its proximal segment large, longer than 2 + 3 segments. Endopod somewhat shorter than exopod, its proximal segment only somewhat longer than second segment. Antennal formula (5) – (1) – (3) / (1) – (1) – (3). A short spine on apical segment of exopod. Mandible small, mandibular joint (Figs 2 G, 3 B: maj) located on valve margin (Figs 2 G, 3 B: vam), at a distance from point where margins of head and valve come together (Figs 2 G, 3 B: phv), instead of being attached to head shield (Figs 2 G, 3 B: hsm). Length 2.0 – 2.5 mm. Comments: The animal may have been subglobular in shape, as are the extant chydorids Chydorus Rak and Indialona (Smirnov & Timms, 1983; Smirnov, 1996; Kotov, 2000).	en	Kotov, Alexey A. (2009): A revision of the extinct Mesozoic family Prochydoridae Smirnov, 1992 (Crustacea: Cladocera) with a discussion of its phylogenetic position. Zoological Journal of the Linnean Society 155 (2): 253-265, DOI: 10.1111/j.1096-3642.2008.00412.x, URL: https://academic.oup.com/zoolinnean/article-lookup/doi/10.1111/j.1096-3642.2008.00412.x
53258785FFAF1F61E64DFC45FC71F8AA.taxon	materials_examined	Type (sole) species: Palaeorak scherbakovi sp. nov. Etymology: The name of the new genus comes from Greek Palaeo (ancient), and Rak, the generic name of a chydorid with blunt rostrum and well-developed setae on the ventral margin of the valve, described by Smirnov & Timms (1983). The name Rak is derived from the Russian word (rak) for a crustacean. Diagnosis: Body moderately high, head capsule of ‘ chydorid-type’ (compressed dorso-ventrally), covered with ‘ flat’ head shield with rostrum truncated, valves with denticles and short setae along ventral margin of valves, mandible attached to point of joint of head shield and valve. Comments: The genus is probably a few million years younger than Prochydorus and Archeoxus. PALAEORAK SCHERBAKOVI SP. NOV. (FIGS 1 G – J, 5 A – H) Type locality: Khasurty. Outcrops at Khasurty River, 10 km south of Tsakir, Zakamensk District, Buryat Autonomous Republic, Asian Russia. Based on palaeofauna analysis, the Mesozoic water body represented by these sediments was reconstructed as a small mountain lake surrounded by a forest composed of different plants (D. E. Scherbakov, pers. comm.). Age: Glushkov Formation, probably, earliest Cretaceous. This recently discovered locality is poorly studied. Among fossil insects, characteristic Cretaceous taxa are more prevalent than Jurassic taxa (D. E. Scherbakov, pers. comm.). Etymology: The species is dedicated to Dr D. E. Scherbakov (PIN), who found micro-crustacean impressions on rock fragments from Khasurty. Holotype: An impression of a specimen in lateral position, 2.5 mm in length, in the collection of the Palaeontological Institute of Russian Academy of Sciences, PIN 5026 / 178. Paratypes: 97 relatively well-preserved specimens on 22 rock fragments, PIN 5026 / 89 - 177, 179 - 186 (each number is the access number for each specimen, rather than each rock fragment). Description: Body subovoid in lateral view, moderately high (height / length = 0.71 – 0.79), highest point of dorsum greatly prominent under head level, postero-dorsal angle well defined, postero-ventral angle widely rounded. Head about one-third body length, covered with a ‘ flat’ head shield, which ends proximally in a blunt rostrum. In some specimens there is a shallow depression at the posterior border of head, which may be a result of specimen deformation. The valve ventral margin is supplied with small denticles and short marginal setae (preserved only in some specimens). The postabdomen is supplied with a pair of elongated, slightly curved terminal claws, their incurved (dorsal) side armed with small denticles, but lacking a basal spine. Antenna I was not found. Antenna relatively long, about half body length or longer, its basal segment long, exopod 0.33 – 0.38 body length. Both exopod and endopods with proximal segments very long, longer than two following segments. Antennal formula (5 – 7) – (1) – (3) / (1) – (1) – (3). No spines were found on any segments. Mandibles relatively small, attached at body where head and valve join (instead of attached to the head shield in chydorids). Limbs are not distinct. Size 1.8 – 3.0 mm. Comments: In contrast to Khotont, only one fossilized cladoceran, P. scherbakovi sp. nov., was found in Khasurty.	en	Kotov, Alexey A. (2009): A revision of the extinct Mesozoic family Prochydoridae Smirnov, 1992 (Crustacea: Cladocera) with a discussion of its phylogenetic position. Zoological Journal of the Linnean Society 155 (2): 253-265, DOI: 10.1111/j.1096-3642.2008.00412.x, URL: https://academic.oup.com/zoolinnean/article-lookup/doi/10.1111/j.1096-3642.2008.00412.x
