New Cretaceous crabs (Crustacea, Brachyura) from Moscow Oblast and Dagestan (Russia): patterns in phylogeny and morphospace of the oldest eubrachyurans (Dorippoidea) *

Abstract Four new brachyuran species, assigned to two new genera and one existing genus, are recorded from Lower and Upper Cretaceous strata of Moscow Oblast (Moskovskaya Oblast) and Dagestan, Russia. Three new taxa, Personadorippe levashiensis gen. et sp. nov., Levashidromites cornutus gen. et sp. nov. and Vectis collinsi sp. nov., were recovered from Aptian strata in Dagestan; these constitute the first formal description of Cretaceous crabs from the northern Caucasus. Of these, Personadorippe levashiensis gen. et sp. nov. represents one of the oldest eubrachyuran crabs known to date, being of middle Aptian age and thus predating the late Aptian Telamonocarcinus antiquus Luque, 2014 (see Luque, 2014a) from Colombia. A single carapace of Personadorippe kalashnikovi gen. et sp. nov. constitutes the first ever record of crabs from Upper Cretaceous deposits of the Moscow region. Vectis collinsi sp. nov. represents only the third species of the genus, and the first outside the United Kingdom. The genus Vectis is reassessed and here reassigned to the Viaiidae, which now comprises three genera. Rathbunopon? atherfieldense Wright, 1997 is also transferred to Vectis. The family Longodromitidae is here restricted to six genera, inclusive of Levashidromites gen. nov., and a new diagnosis is supplied. Navarrara, previously assigned to the Longodromitidae, is reassigned to the Telamonocarcinidae. Withersella is also transferred to the Telamonocarcinidae; the genus constitutes the oldest dorippoid (and hence, currently assigned eubrachyuran) crab. Personadorippe gen. nov., here described on the basis of two new species, follows shortly after. Eodorippe connori Nyborg, Garassino, Vega and Kovalchuck, 2019 is here reassigned to Personadorippe gen. nov. Carapace tripartition and branchial condensation, i.e., the ratio between the median carapace portion and the relative distance of the branchial groove to the cervical groove, are here used as important proxy characters for reconsidering the taxonomic placement of primitive crabs. Phylogenetic analyses and assessment of phylomorphospace have revealed that the new genera described herein are part of a Jurassic–Cretaceous radiation of primitive crabs. This radiation proceeded via a high-magnitude morphological shift away from the morphology typical of Tanidromites, with subsequent expansion in all directions of morphospaces occupied.


Introduction
Despite the large areal extent of the Russia Federation, only a few Mesozoic crabs have been recorded to date (Table 1).So far, there are only a few published records of decapod crustaceans from Cretaceous strata in the Moscow area (Moscow Oblast).However, in recent years, crabs have been collected at several localities in this region; these are here formally named, described and illustrated.Ilyin (2005, p. 186, pl. 9, fig. 1) assigned a crab carapace, collected by Dr Evgenij Yu.Baraboshkin near the village of Gavrilkovo (Moscow Oblast, Dmitrovsky District, River Volgusha), to Homolopsis glabra Wright and Collins, 1972.Located near that village is a well-studied section of Lower Cretaceous sands that are referred to the Gavrilkovo Formation (Fig. 1).These levels have yielded the middle Albian zonal ammonite species Hoplites dentatus (J.Sowerby, 1821) (see Olferev, 1986).From the same strata, Dr Aleksandr S. Alekseev collected fragments of thoracic segments of decapod crustaceans in 1989, but these could not be identified in detail (Ilyin, 2005).As far as we are aware, these are the only references in the literature to Cretaceous crabs in the Moscow region.However, the website of Russian fans of palaeontology (www.ammonit.ru)includes photographs of fragmentary appendages, such as propodi and meri, of decapod crustaceans from the locality of Varavino, originating from the Cenomanian Lyaminsk Formation (Fig. 1).
Despite the vast territory of the northern Caucasus and significant outcrops of Cretaceous rocks in that area, decapod crustaceans have only rarely been recorded in the literature.Aliev and Aliev (1980) described and illustrated two new species of ghost shrimp, Protocallianassa caucasica and P. sarysuensis, from Upper Cretaceous (Coniacian) sandstones of the Lesser Caucasus, i.e., different regions of Azerbaijan and Armenia.Other records from Cretaceous levels of the Caucasus pertain to references without descriptions and/or illustrations, such as a paper by Mordvilko (1960), who noted small bivalves, conchostracans and teeth of pycnodont fishes from a particular level within Lower Cretaceous (Valanginian) limestones near Kislovodsk.In the same paper, reference is made to common finds of crab carapaces in Aptian and Albian strata of the Caucasus, but their taxonomic affiliation is not indicated.In short, the present record is the first formal description of Cretaceous crabs from the northern Caucasus.

Nikolskoye
A single carapace, here referred to Personadorippe kalashnikovi gen.et sp.nov., was collected near the village of Nikolskoye (Dmitrovsky district, Moscow Oblast) in 2011.Around 500 m to the west of Nikolskoye, there used to be a sand pit (Fig. 1CeD); excavation at this site came to a halt in 2005.Today, this pit is completely filled up and lost.Strata formerly exposed here had a complex facies structure: interspersed with sands and clays of Necrocarcinus bodrakensis Levitskiy, 1974(¼ N. labeschii (Eudes Deslongchamps, 1835;see;Ilyin, 2005, p. 198, p. 198) Crimea, Bakhchisaray district, village of Prohladnoe (Mangushsky ravine) Lower Cretaceous: upper Albian, Hysteroceras varicosum ammonite Zone; Mangush Formation Levitskiy (1974, p. 115) Necrocarcinus tauricus Ilyin and Alekseev, 1998 Crimea, Bakhchisaray district, village of Prohladnoe (Mangushsky ravine) Lower Cretaceous: upper Albian, Hysteroceras varicosum ammonite Zone; Mangush Formation Ilyin and Alekseev (1998, p. 46) Raninella yanini (Ilyin and Alekseev, 1998) Crimea glacial origin (till) were sands of Cretaceous age (Fig. 1DeE) and clayey levels of Late Jurassic age.Most likely, these Mesozoic deposits were glacially transported masses during the Pleistocene, in particular at the time of the Moscow glaciation (Astakhov, 2004).The border of the Moscow glaciation passed from the southwest to the northeast of the Moscow region, approximately halfway.The period of the Moscow glaciation coincides with glaciation of the Alps, where it is called Riess II.
In the vicinity of this locality are widely distributed deposits of a Late Cretaceous date that are included in the Lyaminsk Formation (Olferev, 1986).According to more recent stratigraphical data (Stratigraficheskaya …, 2004), the Lyaminsk Formation can be assigned to the Polpino Horizon, or lower Cenomanian.The section formerly exposed at this site attained a thickness of about 40 cm.The bottom part consisted of a condensed layer of sand with concretions and gravel, overlain by a solid sandstone level and sand in the uppermost layer of the section.
The sands of the Lyaminsk Formation are rich in a range of macrofossils (Fig. 2AeP), with the largest concentration being found in the condensed sandstone layers.The commonest fossils are shark teeth, while remains of bony fish, reptiles, decapod crustaceans and ammonites are rarer.The find of the ammonite Schloenbachiavarians (J.Sowerby, 1817) confirms the early Cenomanian age of these deposits (compare Wilmsen and Mosavinia 2010; Kennedy 2013).

Levashi
Other brachyuran carapaces (Personadorippe levashiensis gen.et sp.nov., Levashidromites cornutus gen.et sp.nov.and Vectis collinsi sp.nov.) have been recovered from Aptian deposits near the village of Levashi (Levashinsky district, northern Caucasus, Dagestan).Lower Cretaceous deposits in this region have been relatively well studied and a number of formations identified.
In the vicinity of Levashi various Aptian strata crop out, namely the lower and upper levels of a sandy-argillaceous nature, the intermediate one being essentially sandy.In the middle and upper units of this formation spherical sandy-calcareous concretions are found (Fig. 1GeK); these measure up to 2 m in diameter (Snezhko et al., 2011).It is in these concretions that decapod crustacean material is often found, including the crab carapaces here described.The collector, O. Khapisov, has informed us that these carapaces were found associated with the ammonite Parahoplites melchioris Anthula, 1899, which is a zonal species and confirms the middle Aptian age of these concretions.On this evidence, this part of the section can be correlated with the Kubina Formation (Sostoyanie … 2008).
The associated fossil fauna at Levashi is very diverse (Fig. 2ReW), including numerous ammonites, various benthic forms (bivalves, gastropods, crayfish and sometimes starfish) and rare remains of vertebrates such as fishes and marine reptiles.
Infraorder Brachyura Linnaeus, 1758Section Podotremata Guinot, 1977Subsection Dynomeniformia Guinot, Tavares and Castro, 2013Superfamily Dromioidea De Haan, 1833Family Longodromitidae Schweitzer and Feldmann, 2009a Genera included.Abyssophthalmus Schweitzer and Feldmann, 2009a, Longodromites Patrulius, 1959, Pilidromia Schweitzer, Feldmann, Lazǎr, Schweigert and Frant¸escu, 2018, Levashidromites gen. nov., Planoprosopon Schweitzer et al., 2007band Rosadromites Schweitzer, Feldmann, Rader and Frant ¸escu, 2016.Diagnosis.Carapace elongated subrectangular, longer than wide, lateral margins subparallel, slightly narrowing towards posterior margin; weakly convex transversely, nearly flat longitudinally; rostrum produced, projected, widely triangular or subtrapezoidal, anterior margin concave; fronto-orbital width equalling maximum carapace width; orbital fossae very large, appearing as welldelineated, deeply concave sockets at anterior carapace; orbits anteriorly and weakly anterolaterally directed; outer orbital spine directed anterolaterally, subtle or robust.Lateral margin subvertical, sinuous, blunt in cross section, without spines, restricted where branchial and cervical grooves notch lateral margins.Carapace areolation normally weak; deep and well-defined cervical and branchial grooves; carapace tripartite, cervical and branchial grooves well separated, branchial condensation weak; cervical groove low V-shaped to subhorizontal, notching lateral carapace margin; branchial groove well defined, subparallel to cervical groove, notching lateral carapace margin.Posterior margin wide, strongly concave.Protogastric, mesogastric, epibranchial and cardiac regions well delineated and inflated, anterior mesogastric process narrow, elongate; posterior branchial region large.Dorsal carapace surface densely granular, anterior regions usually with few tubercles.Elements other than carapace unknown (in genera here assigned to Longodromitidae).Remarks.A new diagnosis of the Longodromitidae is given above, because previous diagnoses were based on an unfortunate mix of genera.When the family Longodromitidae was erected, it contained three genera (Schweitzer and Feldmann, 2009a, p. 100), namely Longodromites, Abyssophthalmus and Planoprosopon.Here we maintain these three genera, and accept three more: Levashidromites gen.nov., Pilidromia and Rosadromites.Previous authors have included various other genera (see Table 2), with a wide variety of morphologies, rendering any diagnosis useless.In many discussions, the 'Augenrest' was used as a proxy character, or even an apomorphy.However, this feature was insufficiently diagnosed and not studied in detail and is thus in need of a thorough revision.The orbital structures of primitive crabs (Dynomeniformia) are highly variable and convergent and no apomorphy can be assigned at the present stage.The other genera assigned to the Longodromitidae by Schweitzer et al. (2017, p. 216) and Schweitzer et al. (2018, p. 320) need to be transferred to other families.The taxonomic heterogeneity of the assemblage previously described by those authors is illustrated well by the genus Navarrara Klompmaker, 2013, which is here placed in the Telamonocarcinidae (Eubrachyura; see below).Work on Glaessnerella is underway (Van Bakel and others).Longodromitids were originally included in the superfamily Glaessneropsoidea Patrulius, 1959 (Schweitzer andFeldmann, 2009a, p. 82; see also; Schweitzer and Feldmann, 2009b); as far as we are aware it has never been included into other higher taxonomic groups.The orbital structures are well developed and well defined, with large, deep fossae to accommodate the (apparently large) eyes.The lateral margins are developed, not gently rounded as in the Homolodromiidae or Glaessneropsidae, but at least the anterolateral margin is defined, often sharp and ornamented or reinforced with teeth and rims.The family Longodromitidae cannot be accommodated in the Homolodromiidae because the former have a well-developed front and orbital fossae, unlike the disposition in the latter.Moreover, longodromitids have a more condensed medium carapace portion.Here we refer the Longodromitidae to the Dromioidea, on the basis of the nature of the orbitofrontal margin and lateral carapace margins.The superfamily Glaessneropsoidea has been maintained by other authors, as based on assumed characters, in particular of the orbitofrontal margin.A review is needed to determine whether or not this superfamily is indeed valid, or that families included in it are in need of reassessment (see also Guinot, 2019).
Etymology.From Levashi, the town near which the material was discovered, and -dromites, referring to many other dromioid crabs.
Diagnosis.Carapace elongated subrectangular, longer than wide, widest at hepatic spine and posterior part of mesobranchial region, weakly convex transversely and longitudinally; rostrum produced, projected, widely triangular; fronto-orbital width corresponding to maximum carapace width; small inner orbital spine; outer orbital spine directed anterolaterally; orbits very large, appearing as concave open sockets at anterior carapace, outer orbital spines robust, pointed; lateral margin sinuous, blunt in cross section, without spines; carapace surface granular, anterior regions with few tubercles; areolation weak; deep cervical and branchial grooves, cervical groove well defined, widely U-shaped, notching lateral carapace margin; branchial groove well defined, arched, notching lateral carapace margin.Posterior margin wide, axially strongly concave; dorsal surface densely granulated; protogastric, mesogastric, epibranchial and cardiac regions well delineated and inflated; branchial region developed, wide.Remarks.Levashidromites gen.nov. is assigned to the Longodromitidae on account of having subparallel, weakly arched to subhorizontal cervical and branchial grooves; a slightly condensed epibranchial region; pronounced and well-developed, outwardly directed outer orbital spines; orbital margins with notches and teeth; large orbital fossae that occupy the entire anterior margin; a well-defined mesogastric region with wide triangular basal portion and a narrow, acute anterior mesogastric process, as well as enlarged granules/tubercles on the proto-and mesogastric regions.Levashidromites gen.nov.differs from Abyssophthalmus in having stronger, outwardly directed outer orbital teeth, a proportionally larger and wider posterior carapace as well as a waisted (hourglassshaped) overall carapace outline.The new genus can be differentiated from Longodromites in having stronger, outwardly directed outer orbital teeth, a widened posterior carapace (vs posterolateral margins converging towards posterior margin in Longodromites) and a short, acute and oblique groove on the epibranchial region.Levashidromites gen.nov.differs from Pilidromia in having stronger, outwardly directed outer orbital teeth, a conspicuously low urogastric region (vs well-developed, proportionally large and bilobed in Pilidromia) and a short, acute and oblique groove on the epibranchial region.
From Planoprosopon the new genus can be distinguished by possessing a proportionally wider carapace, also posteriorly, and stronger, outwardly directed outer orbital teeth.Finally, Levashidromites gen.nov.differs from Rosadromites in having a more strongly widened posterior branchial region and a conspicuously low urogastric region and in lacking a groove that separates the protogastric from the hepatic region.In both Levashidromites gen.nov.and Rosadromites a short, acute and oblique groove on the epibranchial region is present.Unfortunately, the entire anterior carapace margin of Rosadromites is missing from the unique type specimen, precluding comparison of the outer orbital spines or orbital construction.However, it would seem that Levashidromites gen.nov. is morphologically quite closely comparable to Rosadromites.Levashidromites gen.nov.(Aptian of Dagestan, Russia) and Rosadromites (Albian of Texas, USA) are the youngest members of the Longodromitidae which, by the mid-Cretaceous, was widely distributed geographically.Species of Planoprosopon and Abyssophthalmus appear closely similar morphologically; in fact, characters among species of both genera may overlap.Thus, a comprehensive reassessment of these two genera is needed in order to validate their status.

Figs. 4AeD, 7D
Material.The holotype is the sole specimen known to date (Museum of the World Ocean, Kaliningrad, Russia), number MWO 1 9977.Etymology.Latin cornutus, meaning 'horned', in reference to the strong outer orbital spines that render a horned appearance to the crab.

Diagnosis. As for genus.
Type locality and stratigraphical level.Near the village of Levashi, Levashinsky district (Dagestan, Russia); Kubina Formation (Lower Cretaceous, middle Aptian; Parahoplites melchioris ammonite Zone).Description.Carapace subpentagonal, longer than wide, widest at hepatic spine and posterior part of mesobranchial region, weakly vaulted transversely and longitudinally; fronto-orbital width equalling maximum carapace width; orbits wide, shallow, directed forwards, small inner orbital spine, outer orbital spine directed anterolaterally; triangular mesogastric region with axial depression, long, well-delineated, mesogastric process bordered by row of three hepatic tubercles; protogastric region bulbous with one large, central spine; deep sinuous cervical groove continuing to lateral incision; epibranchial region bulbous, covered with granules and small lateral spine; broad, well-delineated urogastric region; deep branchial groove curving anteriorly from cardiac towards epibranchial; bulbous and triangular cardiac region extending almost to posterior margin; large globular mesobranchial region regularly covered with granules; lateral margin sinuous; posterior margin wide, axially strongly concave; ventral aspects and appendages unknown.Remarks.For differences with allied forms, see the remarks above (under Levashidromites gen.nov.).
Remarks.Vectis was originally included in the Prosopidae (Homolodromioidea), but transferred to the Glaessneropsidae Patrulius, 1959 (Glaessneropsoidea) by Karasawa et al. (2011, p. 538) and Schweitzer et al. (2012, p. 22).The orbits of Glaessneropsis Patrulius, 1959 are large, well defined with well-developed, subhorizontal, notched orbital margins and distinct outer orbital spines; a completely different disposition from that seen in Vectis.The Glaessneropsidae was elevated to superfamily status, Glaessneropsoidea, by Schweitzer and Feldmann (2009a, table 1).The status and validity of this supposed superfamily are far from certain, the diagnosis given by Schweitzer and Feldmann (2009a, p. 82) having been based on plesiomorphies, and lack of an 'Augenrest', a structure sensu Schweitzer and Feldmann (2009a, p.61) which must be discussed in detail and is possibly equal to the orbit (or orbital fossa), 'false orbit' sensu Wright and Collins (1972, p. 43), 'plage orbitaire' sensu Guinot and Richer de Forges (1995, p. 303) or 'unprotected eye' sensu Breton (2009, fig. 9).Vectis and Viaiidae do not appear to be closely related to the Glaessneropsidae, and we leave the superfamily status open as incertae sedis.
Addition of Vectis to the Viaiidae is not directly obvious, but morphological comparisons have now revealed Vectis to be a basal, not distinctly modified, member of that family.Vectis shows an elongate carapace outline with a wide posterior branchial region, converging lateral margins that taper anteriorly, a single, projected and widely triangular front, oblique orbits that do not occupy the entire carapace width and do not have distinct outer orbital corners and it lacks well-defined carapace margins.The cervical groove is widely U-shaped; a distinct branchial groove notches the lateral carapace margin; there is a weak branchial condensation (branchial and cervical grooves well divided) as well as an oblique groove that subdivides the protogastric region and an oblique groove that separates the proto-and epigastric regions.In addition, the branchial groove reaches the cardiac region halfway and merges with the anterolateral cardiac region into a recurved epibranchial groove.These characters of Vectis are remniscentof Heeia and Viaia (compare Fig. 11) and differ from the carapace 'Bauplan' of the Glaessneropsidae and also of e.g., the Nodoprosopidae Schweitzer andFeldmann, 2009a (Schweitzer andFeldmann, 2009a).Guinot (2019, p. 764) hypothesised that, "… it [Vectis] might not be a podotreme crab at all", and that it could belong to the Eubrachyura.One of the features on which this hypothesis was based is the nature of the posterior carapace margin, termed 'biconvex' or 'flanged' (Guinot, 2019, p. 781).The well-defined, deep branchial groove, which notches the lateral carapace margin, is well separated from and semiparallel to the cervical groove; together, these two grooves divide the carapace into three parts with a non-condensed anterior (epi)branchial region.The presence of a large and wide posterior branchial region and the lack of well-defined carapace margins (which are completely rounded) do not favour placement in the Eubrachyura.Some majoids are reminiscent of Vectis and of the Viaiidae, in particular some taxa contained in the family Inachoididae Dana, 1851.Worthy of note is the overall resemblance to Esopus A. Milne-Edwards, 1875; this unusual majoid has recently been discussed in detail by Guinot and Van Bakel (2020).Diagnosis.See Luque (2014a).
Remarks.Navarrara, Withersella and Personadorippe gen.nov.are here included in the Telamonocarcinidae (see Fig. 6) for the first time, adding significant geological and stratigraphical data on that Early and mid-Cretaceous family of dorippoid crabs (Figure 10).Luque (2014a) included only Eodorippe and Telamonocarcinus.The Telamonocarcinidae belong "to the oldest heterotreme representatives" (Guinot, 2019, p. 288).
Navarrara was originally assigned to the Longodromitidae (included in the Glaessneropsoidea) by Klompmaker (2013, p. 154).This was done, "because it matches the diagnosis given in Schweitzer and Feldmann (2009a, p. 100) quite well".However, the diagnosis of the Longodromitidae given by those authors is so general and based on a non-monophyletic lot of genera that many Jurassic and Cretaceous crabs, now assigned to a range of families and superfamilies, could be included in that family.In order to be able to accommodate Navarrara, the diagnosis of the Longodromitidae was emended by Klompmaker (2013, p. 154).
From Appendix B (see below), it is clear that Navarrara and Longodromites, the generic type of the family, have quite different character sets (no fewer than 15 out of 19 characters are rated differently).This results in a completely different position in all possible trees (see Figs.  2011), Schweitzer and Feldmann (2011) and Klompmaker (2013, p. 173) or to the Carcineretidae (Collins et al., 1995;Fraaye, 1996;Wright, 1997;Collins, 2003).Nyborg et al. (2019, p. 134) noted that Eodorippe connori was most closely similar in shape to Withersella.
Withersella differs from Torynomma in six (out of 19) characters, as rated in Appendix B. The most prominent differences include the condensation of the anterior branchial region between the branchial and cervical grooves in Withersella and the subequal length of the anterior mesogastric process to the posterior mesogastric triangle (anterior mesogastric process elongate in Withersella).Torynomma is a podotreme crab, with the groove system subdividing the carapace into three parts.In all aspects, Withersella is different from the derived portunoid Carcineretes, some obvious differences including overall carapace shape (converging carapace margins in Withersella (vs diverging in Carcineretes), an orbital margin with several teeth and notches in Carcineretes and a substraight posterior carapace margin in Carcineretes (vs concave in Withersella).
Withersella can be placed in the Telamonocarcinidae with confidence; our cladistic analysis supports this (see Figs. 8 and 9).It appears morphologically closest to Personadorippe gen.nov.(see below).
The Telamonocarcinidae was erected, as a subfamily, by Larghi (2004), on the basis of abundant, well-preserved and complete material from the Cenomanian of Lebanon, so the dorippoid affinities of this family was proved by dorsal and ventral morphology, as well as completely preserved appendages.Guinot et al. (2013) noted that the Telamonocarcinidae showed a combination of dorippid and ethusid features, that it might not be monophyletic and probably contained the oldest known dorippoids.A cladistic analysis (see Appendices A and B) has been performed for the present paper in order to study the homology of composition and characters of the group.The condensation between the branchial and cervical grooves, subdivided anterior branchial region, long and narrow mesogastric process, subsquare carapace with widened branchial regions and wide and oblique orbitofrontal margins without distinct orbital notches form a consistent character set.The oldest records of the family are recorded herein with Withersella crepitans from the lower Aptian Deshayesites forbesi ammonite Zone   1).Thus, this family was geographically widely distributed and represented by several genera (i.e., a wide variation), suggesting a long evolutionary history, dating back to the Jurassic.
In a subsequent study, the carapace morphology of the Telamonocarcinidae should be compared in detail with that of the older (Early JurassiceEarly Cretaceous) Lecythocaridae Schweitzer and Feldmann, 2009a, a possibly basal family of dorippoids (see also Guinot et al., 2019).The Lecythocaridae Schweitzer and Feldmann, 2009a may well be eubrachyuran in nature and ancestral to the Telamonocarcinidae.The range of the Lecythocaridae is Upper Jurassic (Kimmeridgian) (Schweigert, 2018, p. 3) to Lower Cretaceous (Berriasian) (BWMvB and RHBF, pers.obs., work underway); species have been recorded from Germany, Austria, Romania and the Czech Republic (Schweigert and Robins, 2016).An important proxy character and evolutionary polarity in brachyuran macro-evolution is 'branchial condensation', occurring at intrafamilial level.The epibranchial region, i.e., the median carapace portion between the cervical and branchial grooves, is large (long) in basal forms, while it is reduced in size, or absent/ evanesced in more derived, stratigraphically younger forms.Over geological time the branchial groove shifted gradually towards the cervical groove and finally the two grooves morphed into a single groove, the cervical groove.architecture and anatomy of the respiratory system in the branchial chamber, the area between the body and carapace enclosing the gills/branchiae.The pleura, or body wall separating the gills from the body, are connected to the ventral internal ridge that is visible externally as the branchial groove.Whenever the carapace between the cervical and branchial grooves is shortened, the gill chamber is expanded proportionately.
The mechanism behind this phenomenon may be a metabolic rate increase with would have meant more oxygen extraction from sea water.Griffen and Sipos (2018) concluded that metabolic rates in brachyurans strongly increased with temperature and that their metabolism was correlated with their ecological niche, varying with both diet strategy and habitat.Branchial condensation through time can be recognised in a wide array of extinct crabs.The Palaeocorystoidea, in particular the basal group of the Necrocarcinidae and its subfamily Paranecrocarcininae (compare Van Bakel et al., 2012), have well-defined branchial grooves that are subparallel to the cervical groove, with a welldeveloped median portion of the carapace (epibranchial region), e.g., in Bellcarcinus aptiensis Luque, 2014 (Luque, 2014b, pl. 1).In the vast majority of younger forms of the Palaeocorystoidea, the branchial groove is very weak to indiscernible; if it can be traced at all, it lies close to the cervical groove.In summary, branchial condensation appears to be a good proxy character for determining the relationship of crabs and their taxonomic position, in particular whether these are podotreme or not, or occupy a basal position in their clade.Good examples are the genera Binkhorstia Noetling, 1881 and Torynomma Woods, 1953, which were included in the Torynommidae Glaessner, 1980 by several authors (Glaessner, 1980;Van Bakel et al., 2003;De Grave et al., 2009, p. 29;Schweitzer et al., 2010, p. 78).Torynomma shows a subequal division of the carapace into three portions by the branchial and cervical grooves (compare Schweitzer and Feldmann, 2011, fig.6), a basal condition typical of basal podotreme crabs.This is a completely different condition than the one seen in Binkhorstia (see Van Bakel et al., 2003, fig. 1), which shows a near-complete branchial condensation: the branchial and cervical grooves are subparallel and nearly merged.The epibranchial region in Binkhorstia is condensed, leaving only a narrow strip.These conditions demonstrate that Torynomma is a basal podotreme that occupies a completelydifferent taxonomic position from the eubrachyuran Binkhorstia.The taxonomic position of Binkhorstia will be clarified by Van Bakel et al. (in prep.).
In other groups of decapod crustaceans, branchial condensation can be observed as well.The geological record of majoids is particularly incomplete in the Cretaceous, but majoids are considered, next to the Dorippoidea, to represent the most ancient and most basal eubrachyuran crabs (see e.g., Guinot et al., 2019, p. 782;Guinot and Van Bakel, 2020).The carapace outline of majoids is usually pyriform, with a wide posterior carapace, which is comparable with the outline in the Dorippoidea.
Diagnosis.Carapace subrectangular in outline, length slightly exceeding width; gently curved in longitudinal and transverse cross sections; regions weakly vaulted; front axially sulcate; orbitofrontal margin occupying most of carapace width; orbital margin oblique, without notches; outer orbital spine short, triangular; lateral margins sinuous, blunt, without spines; carapace surface granular; cardiac region narrow, cervical groove widely V-shaped, reaching lateral carapace margin; branchial groove well defined near cardiac region.Posterior carapace margin rimmed, concave.Cheliped palm compact, fingers long, with sharp, toothed cutting margin.
Remarks.Personadorippe gen.nov.shows a character set which places it unambiguously in the Telamonocarcinidae, i.e., condensation between branchial and cervical grooves, a subdivided anterior branchial region, a long and narrow mesogastric process, a subsquare carapace shape with widened branchial regions and wide and oblique orbitofrontal margins without distinct orbital notches.The results of our cladistic analysis (see appendices A, B; Figs.8e9) confirm the close relationship with other included genera.We consider that these genera form a distinct, basal family within the Dorippoidea.Personadorippe gen.nov. is morphologically most closely similar to Navarrara and Withersella in its squarish carapace shape, overall granular carapace dorsal surface, a rather straight, oblique orbital margin with a single notch and curvature of the branchial region., 1993. 11. Eodorippe spedeni Glaessner, 1980.12. Goniochele angulata Bell, 1858.13.Goniochele cf.

Phylogenetic reconstruction, phylomorphospace and minimum spanning tree analysis
For the purpose of phylogenetic framing and quantitative morphological characterisation of the two new crab genera described herein, a set of analyses were performed.The phylogenetic analysis was performed on the matrix of 16 primitive crab genera and 19 morphological characters that describe these (character data in Appendix).The phylogenetic analysis was performed in the R computational environment (R Development Core Team, 2015), using packages 'ape 5.0' (Paradis and Schliep, 2018) and 'phangorn' (Schliep, 2010).The following matrix of contrasts was used in the parsimony analysis: The first approximate tree was found by using a random addition parsimony search.Later on, this tree was used as an input for a more effective parsimony ratchet tree search (Nixon, 1999).Finally, accelerated transformation (ACCTRAN), which assumes that most changes occurred down the tree (Felsenstein, 2004) (i.e., the expected result of an adaptive evolutionary radiation), was performed on the most parsimonious tree, yielding the most parsimonious phylogram.
Phylomorphospace analysis was performed through the following steps: i) the discrete character matrix was transformed into a distance matrix calculating Manhattan distance using R package 'vegan'; ii) principal co-ordinate analysis (PCoA) was performed on the given matrix in order to minimise the dimensionality of the data; iii) the first two PCoA co-ordinates (which explained 64 per cent and 31 per cent of variance in character data) were used for plotting the taxa; iv) finally, aphylomorphospace graph was drawn using the most parsimonious tree and projecting it onto this two-dimensional PCoAmorphospace using the package 'phytools' (Revell, 2012).Although uncertain/missing values in the taxon/character matrix could have biasing effects in the determination of morphospace occupancy (Lehmann et al., 2019), in the current data set such entries were uncommon (11 out of 304 or just 3.6 per cent), and thus should have yielded a very low bias.
Complementary to the phylomorphospace approach, the socalled minimum spanning tree method was used.This allows a better understanding of the pattern of morphological/phenetic similarities between previously known and newly described genera.First, taxa were seriated according to their pattern of distribution of character states (see palaeoecological applications in Ryan et al., 1999), thus forming the gradient from most "primitive" to most "advanced", and later on these were connected by minimum spanning tree calculated from the primary distance matrix (step (i) in phylomorphospace analysis), using function mst of the 'vegan' package (Oksanen et al., 2015).

Discussion: trends in phylogeny and morphospaces
The cladogram and phylogram that resulted from maximum parsimony analysis reveal the placement of the newly described crab genera as well as the broader context of early crab evolution (Fig. 8A, B).The genera Tanidromites and Glaessnerella assume basal positions in both diagrams, while Torynomma, Vespridromites and Levashidromites gen.nov.appear as a polytomy, sister to more advanced clades that contain Personadorippe gen.nov., which is sister to Navararra.Both phylogram and cladogram show that these two new genera belong to two distinct derived clades: Personadorippe gen.nov. is closely related to Withersella, Abysssophthalmus, Verrucarcinus and Navararra, whereas Levashidromites gen.nov.assumes a more basal, intermediate position between Vespridromites and Longodromites.
Due to the relatively low number of characters in relation to the available number of crab taxa analysed for the presented analysis, the fine subdivision and exact relationships of separate genera should be seen as preliminary.The possible use of stratigraphical distribution of taxa, in the case of a limited number of morphological characters, could be a helpful option in deciphering bifurcation paths of crab phylogeny through the use of stratocladistics (Fisher, 2008).To date, the known fossil record of the group analysed is very patchy, and many taxa are known from single localities only, which makes use of their temporal distribution rather difficult and most probably strongly affected by sampling artefacts.Therefore, significant sampling over a wide of stratigraphical intervals, geographical regions and palaeoenvironments is needed to ensure sufficient information density of the temporal distribution patterns of crab taxa, which is a pre-requisite for the use of stratocladistic methods.
The distribution of early crab taxa in the phylomorphospace (Fig. 9A) reveals distinct trends in the macroevolution of this group.Tanidromites, the most primitive taxon analysed, is clearly separated from the remainder of the taxa, and the transition to the advanced groups proceeded through a high-magnitude directional shift in morphospace (to the left side of the graph), where most of the subsequent JurassiceCretaceous diversification occurred.This pattern indicates directional shift in morphospace occupancy and morphological diversification through time (Adams and Collyer, 2019).Interestingly, it appears that, after initial diversification in the "advanced" portion of the morphospace, there was a centrifugal diversification in many directions where the genera Planoprosopon?, Longodromites and Abyssophthalmus assumed novel morphologies, and Verrucarcinus secondarily evolved a more primitive condition.The new genera, Personadorippe and Levashidromites, are located in the tight morphological cluster of derived crab taxa.However, it can be seen that Personadorippe gen.nov.sits further to the left, in a more "advanced" portion of the phylomorphospace.
The seriated positions of taxa on the circle are approximately proportional to their phylogenetic relationships, as revealed by the present analyses.However, a very uneven character of morphological similarities is exhibited by the minimum spanning tree of primitive crabs (Fig. 9B), which indicates a non-linear progression of crab morphology during macroevolution.Phenetically, Tanidromites is placed in proximity to Verrucarcinus by morphospace analysis because both taxa exhibit plenty of primitive character states.In other words, both taxa are found to be phenetically close to each other by the absence of joint derived characters.Verrucarcinus is also closely similar to Dioratiopus and Planoprosopon.This observation concurs with the distribution of taxa in the phylomorphospace, and the conclusion that during crab macroevolution there was repeated convergence and reversal in morphology to more primitive states.In the phenetic network discussed, Levashidromites gen.nov.exhibits the closest links to the relatively primitive Glaessnerella, the more advanced Planoprosopon and the more closely related, yet more derived Telamonocarcinus clade.Morphologically, the new genus Personadorippe is most closely linked to its sister taxon, the more advanced Eodorippe, and to more primitive members of the same advanced clade of Telamonocarcinus and Withersella (Fig. 9B).The overall pattern of morphospace occupation matches interpretations of opportunistic phylogenetic diffusion well, with multiple innovations and acquisitions of convergent morphologies in ecological expansion of crabs during the Mesozoic marine revolution (e.g., Vermeij, 1977;Klompmaker et al., 2015) in concert with dynamics of their main habitat: biogenic reefs (Klompmaker, 2013), which are the most diverse and complex marine environments that promote macroevolution (Kiessling et al., 2010).

Concluding remarks
The new taxa described herein from Lower and Upper Cretaceous strata of Moscow Oblast and Dagestan, Russia, are part of the JurassiceCretaceous radiation of both primitive and derived crabs.The Dorippoidea appears to be more diverse and widespread in Lower Cretaceous strata than hitherto described, and can be recognised on carapace morphology.Carapace tripartition and branchial condensation, are important proxy characters for reconsidering the taxonomic placement of primitive crabs.The families Viaiidae and Longodromitidae are revised on the basis of proxy characters; several other Mesozoic families are in urgent need of reconsideration.The phylomorphospace analysis applied here shows distinct early macroevolutionary trends and there is great potential for future exploration early brachyuran evolution.

Fig. 1 .
Fig. 1.Localities Nikolskoye (AeE) and Levashi (GeK).A, F. European part of Russia with administrative division; B. Moscow Oblast and adjacent regions; C. neighbourhood of the locality Nikolskoye; D. photograph of the cleared section Nikolskoye in 2012; E. photograph of the section Nikolskoye and its structure; G. Dagestan and adjacent regions; H. neighbourhood of the locality of Levashi; I. photograph of cleared section Levashi in 2016; K. concretions from Aptian deposits in Levashi.
8 and 9).This observation calls for a thorough re-consideration of the family diagnoses within the superfamily Homolodromioidea and in what is now called the Glaessneropsoidea.The validity of the latter needs to be tested.Withersella was earlier assigned to the family TorynommidaeGlaessner, 1980by Van Bakel et al. (2003),Schweitzer et al. (2007a,  p. 19; 2010, p. 78),Karasawa et al. (
For example: in the early Kimmeridgian Prolecythocaris hauckei Schweigert and Robins, 2016, the epibranchial condensation is less well developed than in the late Kimmeridgian Lecythocaris paradoxa (von Meyer, 1858) (compare Schweigert and Robins, 2016, fig.2A, B with C, D) and the coeval Prolecythocaris rieberi (compare Schweigert, 2018, fig.2).This change in external morphological character state raises questions about the arrangement and function of the internal brachyuran body.The branchial groove is linked to the position,
Fraaije et al. (2012, fig.4) hypothesised a transition in Triassic to Late Jurassic anomurans in which the branchial groove shifted forwards and led to a single cervical groove on the dorsal carapace in diogenid paguroids from the Upper Jurassic onwards.A similar branchial condensation occurs in other group of paguroids as well(compare Fraaije, 2014, figs.5e6).Fraaije et al. (2018) described how a huge increase in phyto-and zooplankton during the Jurassic led to a worldwide increase in meiofaunal diversity directly and indirectly triggered a radiation of many benthic groups.Increased metabolic rates in brachyurans could well have been caused by this macroevolutionary polarity and have triggered ecological specialisation such as burying, swimming and carrying foreign objects.A wide posterior branchial chamber, together with condensation (shortening) of the median portion of the carapace, can be observed in diverse basal eubrachyuran clades in the Cretaceous.Ancient eubrachyurans such as the Telamonocarcinidae (oldest occurrence: Aptian), Archaeopidae Karasawa, Kishimoto, Ohara and Ando, 2019 (oldest occurrence: Turonian) and Archaeochiapasidae Guinot, Carbot-Chanona and Vega, 2019 (occurrence: Cenomanian) have a wide posterior carapace and various gradations of branchial condensation.

Fig. 9 .
Fig. 9. A. Phylomorphospace of early crabs with projected phylogram and estimated morphologies of ancestors (internal branching points).B. Minimum spanning tree of early crabs.
Mesogastric region elongate, covering anterior half of carapace length, pinched in between epigastric elevations, with long, narrow mesogastric process, with subvertical lateral margins; posterior portion broadly subrhombic with convex posterior margin.Protogastric region suboval, bearing central tubercle; weakly differentiated from small, subrectangular hepatic region.Urogastric region slightly wider than base of mesogastric region, low, consisting of two transversely lined lobes, divided by axial depression.Epibranchial region conspicuously small, pointed triangular, positioned laterally; mesobranchial region consisting of two lobes; anterior one larger, elongated transversely, eye shaped; posterior one smaller, more axially placed, weakly delimited posteriorly.Cardiac region subpentagonal, apex pointed downwards, region bearing two anterior tubercles and a single smaller posterior tubercle.Intestinal region undefined.Metabranchial region large, rather plain, with convex lateral margin.Cervical groove narrow, acute, broadly V-shaped, best defined axially.Branchiocardiac groove short, anteriorly well defined.Branchial groove shallow, not clearly defined.Grooves enclosing mesogastric region, urogastric region and epibranchial region well developed.Carapace surface covered with granules and tubercles, cuticle not preserved.Ventral surface and appendages not preserved.Remarks.Having been collected from Cenomanian strata at Nikolskoye, this is the youngest of the two species of Personadorippe gen.nov.described herein, and it represents the most northerly occurrence of the Telamonocarcinidae to date.The areolation with the appearance of a face and the wide posterior branchial region, are typical features of this species.Personadorippe levashiensissp.nov.urn:lsid:zoobank.org:act:6607214E-5768-4080-B4AA-F3D35571EF33.Figs.3EeF, 5, 7B Material.A unique specimen, the holotype, MWO 1 9381.Etymology.The trivial name is based on the village of Levashi (Levashinsky district, Dagestan, northern Caucasus), where the type material was recovered.Diagnosis.Species of Personadorippe gen.nov.with spaced, acute granules; no tubercle on protogastric region, narrow urogastic and cardiac regions and mesogastric region stretching clearly less than half total carapace length.Type locality and stratigraphical level.Near the village of Levashi (Levashinsky district, Dagestan, northern Caucasus); Lower Cretaceous, middle Aptian strata of the Kubina Formation (Parahoplites melchioris ammonite Zone).Description.Carapace rather small (CL ¼ 22 mm), subsquare in outline, length and width subequal, widest at 20 per cent of maximum carapace length from posterior in branchial region; regions weakly inflated; carapace nearly flat in longitudinal and transverse sections.Rostrum not preserved; base of rostrum axially sulcate.Orbital margin subhorizontal, without notches, outer orbital spine broken at base, apparently well developed.Anterolateral margins subvertical, parallel; posterolateral margin subequal in length, convex all along branchial region.Posterior margin concave, inverted V-shaped, divided into two curved portions, with acute rim.Mesogastric region rather small, covering anterior half of carapace length, with acute, narrow mesogastric process, lateral margins subvertical; posterior portion broadly triangular with convex posterior margin.Protogastric region large, subrectangular, clearly separated from rather large subrectangular hepatic region.Urogastric region subequal in width than mesogastric region, widely rectangular, divided by weak axial groove.Epibranchial region small, triangular, positioned laterally; mesobranchial region consisting of two lobes; anterior one oblique; posterior one more axially placed, subtriangular.Cardiac region pentagonal, apex pointed downwards, region acutely delineated posteriorly.Intestinal region undefined.Metabranchial region large, weakly vaulted, with convex lateral margin.

Table 1
List of all Mesozoic brachyurans from Russia described to date.

Table 2
Schweigert and Frant¸escu, 2018dromitidae according to authors.Pilidromia Schweitzer, Feldmann, Laz ar,Schweigert and Frant¸escu, 2018  Planoprosopon Schweitzer, Feldmann and Laz ar, 2007  Vespridromites Schweitzer and Feldmann, 2011 [NOTE: Rosadromites is not included here; Pilidromia was added] Present paper Abyssophthalmus Schweitzer and Feldmann, 2009 Longodromites Patrulius, 1959 Pilidromia Schweitzer, Feldmann, Laz ar, Schweigert and Frant¸escu, 2018 Levashidromites gen.nov.Planoprosopon Schweitzer, Feldmann and Laz ar, 2007 Rosadromites Schweitzer, Feldmann, Rader and Frant¸escu, 2016 is known from the Cenomanian of France and the United Kingdom, while Viaia has been recorded from the upper Albianelower Cenomanian of northern Spain.Vectis is the stratigraphically oldest member of the family Viaiidae, known from Aptian deposits in southern England and Dagestan (Russia).The validity of this species must await reexamination of all type material of species of Vectis from the United Kingdom, as these co-occur in Aptian and Albian strata of the Isle of Wight with several species described from unique, partially preserved material.The trivial name honours the late Joe S.H. Collins, who added enormously to our knowledge of Cretaceous crabs.Diagnosis.Vectis with strongly inflated regions, coarse granulation, distinct and deep cervical and branchial grooves and a subtle protogastric tubercle.Carapace pyriform, well delineated, with inflated and coarsely tuberculated regions, moderately arched longitudinally, strongly convex transversely; distinctly wide posterior branchial region; downturned rostrum; posterolateral margins with coarse spines; anterolateral margins with (paired) spines and notches; deep cervical and branchial grooves; swollen epigastric regions; posterior part of mesogastric region with central furrow, mesogastric process covered with row of two large tubercles; hepatic region swollen; inflated epibranchial region; distinct, tumid pentagonal cardiac region; large intestinal region; strongly tuberculated metabranchial region.No appendages and/or ventral elements preserved.Type locality and stratigraphical level.Near the village of Levashi, Levashinsky district (Dagestan Russia); Kubina Formation (Lower Cretaceous, middle Aptian; Parahoplites melchioris ammonite Zone).Description.Pyriform carapace, well delineated with inflated and coarsely tuberculated regions, widest at middle of metabranchial region, moderately arched longitudinally, strongly convex transversely; wide, downturned rostrum with median sulcus; orbits or orbital spines not completely preserved (no description possible); substraight anterolateral margin and convex posterolateral margin; posterolateral margins with 4e5 robust spines; anterolateral margins with (paired) spines and notches; slightly concave posterior margin approximately half of maximum carapace width; deep cervical and branchial grooves running almost parallel from cardiac region to lateral notches; tumid epigastric regions covered with large central tubercle; posterior part of mesogastric region with central furrow, mesogastric process covered by two large tubercles; tumid hepatic region with at least one large tubercle; reniform, inflated epibranchial region; prominent tumid pentagonal cardiac region surrounded by broad and deep branchiocardiac groove; wide and high intestinal region covered with few variably sized tubercles separated from large inflated, strongly tuberculated metabranchial region by broad and deep groove starting from cardiac region and ending in posterolateral notch.No appendages and/or ventral elements preserved.Remarks.Vectis collinsi sp.nov.differs from the type species,V.wrighti, in a much coarser surface granulation, a narrower posterior cardiac apex with concave lateral grooves and lateral carapace margins that have strong conical spines.In addition, it has small tubercles on the proto-and mesogastric regions and carapace grooves are wider.Vectis collinsi sp.nov.shows better-developed spines and notches on the lateral carapace margin, but this may be a preservational difference since both species are known from unique type specimens only.Of Vectis caseyi, represented by a single specimen from the lower Albian of Surrey, United Kingdom, only the posterior part of the carapace is preserved.The grooves are thin and acute, and the carapace surface finely granular; these features readily differentiate it from Vectis collinsi sp.nov.Vectis echinorum from the upper Aptian of the Isle of Wight, United Kingdom, is represented by partially or poorly preserved specimens.Vectis collinsi sp.nov.differs from V. echinorum in having a coarsely granular intestinal region, a more vaulted and coarsely granular cardiac region and carapace margins with conical spines.
The new genus differs from Navarrara in having less inflated regions, an undefined intestinal region, a lack of lateral teeth and spines and of central cardiac and paired mesogastric tubercles.Personadorippe gen.nov.differsfromWithersella in having a wider cardiac region, wider posterior branchial regions (i.e., a wider posterior carapace), tubercles on anterior regions, a wider cardiac region and a straight orbital margin (vs curved in Withersella).Carapaces of Telamonocarcinus and Eodorippe are wider than long, have more oblique, converging lateral margins and a narrower cardiac region, in comparison with Personadorippe gen.nov.Eodorippe connori Nyborg, Garassino, Vega and Kovalchuck, 2019, from the Albian of Oregon, USA, appears better assigned to Personadorippe gen.nov.It differs from E. spedeni Glaessner, 1980 in having a more subsquarish carapace shape and different carapace ratios, a narrower and W-shaped posterior carapace margin, a subdivided epibranchial region and granular carapace microstructure.It was originally assigned to Eodorippe(Nyborg et al., 2019, p.  134)but described as, "It is most similar in shape to Withersella Wright & Collins, 1972 …".Eodorippe binodosa Collins, Kanie and Karasawa, 1993 is here left in Eodorippe; this species' posterior margin is shaped more like the type species, E. spedeni, and the carapace surface is less granular than in members of Personadorippe gen.nov.
groove broadly V-shaped, axially bluntly curved.Branchiocardiac groove short, anteriorly and posteriorly well defined.Branchial groove as well defined as cervical groove, angle slightly steeper, weakly curved.Grooves subdividing anterior branchial region oblique, acute, well developed.Carapace surface covered with granules, decalcified portions of cuticle preserved.Ventral surface not preserved.Right-hand cheliped preserved; palm compact, rounded, margin of carpal articulation oblique, lower margin bluntly rounded, fingers long, pollex relatively large, triangular, flat, with sharp, toothed cutting margin; dactylus slender, straight, with dorsal ridge and sharp cutting margin.Remarks.This species represents one of the oldest dorippoids, i.e., one of the earliest eubrachyurans, currently known.Only Withersella crepitans from the lower Aptian (Deshayesites forbesi ammonite Zone) of the Isle of Wight, United Kingdom, is older.Personadorippe levashiensis gen.et sp.nov.differsfromP. kalashnikovi gen.et sp.nov.(seeabove) in having a relatively shorter anterior mesogastric process in comparison to the posterior mesogastric triangle; in having a narrower cardiac region, with its posterior apex further away from the posterior carapace margin; in having a narrower urogastric region; in lacking the prominent central tubercles on the protogastric region; and in having a different groove system and subdivision in the anterior branchial region (between branchial and cervical grooves).The claw is directly associated with the carapace, placed under the carapace insitu, and can be assigned to this species with confidence.It shows a distinct morphology; fingers are longer than the palm, the flat, high fixed finger with sharply toothed cutting edge and slender untoothed dactylus.It can be compared within the Telamonocarcinidae only with Telamonocarcinus gambalatus, of which also claws are known (seeLarghi, 2004, figs.5, 6.7, 6.8).The claws of T. gambalatus have fingers that are shorter than the palm, and the claws appear more robust overall.The claw of Personadorippe levashiensis gen.et sp.nov.resembles that of extant dorippoids.