Magyarcarcinidae new family ( Crustacea : Decapoda : Goneplacoidea ) , and description of Magyarcarcinus yebraensis new species , from the Bartonian ( Middle Eocene ) of the Jaca basin , south-central Pyrenees ( Aragón , N Spain )

The discovery of Magyarcarcinus yebraensis n. sp. in Bartonian levels of the Margas de Arguís Formation (Bartonianearly Priabonian) at Yebra de Basa (Aragón, N Spain) within the Jaca basin of the central Pyrenees (Fig. 1), increases the number of described species from this formation (Artal et al., 2013; Ossó et al., 2014). The rich decapod assemblage occurring in these strata displays clear affinities with the Tethyan Eocene faunas from Italy and Hungary, in addition to a relationship with the Upper Eocene faunas from the southern part of the British Isles. M. yebraensis n. sp. is congeneric with M. loczyanus (Lőrenthey, 1898), originally ascribed by Lőrenthey (1898) as to the genus Palaeograpsus Bittner, 1875. More recently, Karasawa & Schweitzer (2004) in their revision of the latter genus, erected the genus Magyarcarcinus to accommodate M. loczyanus, and included the genus within the family Goneplacidae MacLeay, 1838. The recovered samples of M. yebraensis n. sp., both males and females, present well-preserved ventral structures, thus allowing to confirm the adscription of Magyarcarcinus to the superfamily Goneplacoidea, but evidencing at the same time the need of a new family where to accommodate this genus, and the need of a revision of its diagnosis. A detailed comparison with each of the Goneplacoidea families, and particularly with some related genera, reinforces the need for the erection of such a new family. The migration patterns of Tethyan fauna to the North Atlantic during the Bartonian transgression through the South-Pyrenean Basin, already suggested by Via (1991), is confirmed by the presence of Magyarcarcinus and its associated decapod assemblage in the Bartonian strata of the south-central Pyrenees. Treb. Mus. Geol. Barcelona, 22 (2016): 7-18


INTRODUCTION
The discovery of Magyarcarcinus yebraensis n. sp. in Bartonian levels of the Margas de Arguís Formation (Bartonian-early Priabonian) at Yebra de Basa (Aragón, N Spain) within the Jaca basin of the central Pyrenees (Fig. 1), increases the number of described species from this formation (Artal et al., 2013;Ossó et al., 2014).The rich decapod assemblage occurring in these strata displays clear affinities with the Tethyan Eocene faunas from Italy and Hungary, in addition to a relationship with the Upper Eocene faunas from the southern part of the British Isles.M. yebraensis n. sp. is congeneric with M. loczyanus (Lőrenthey, 1898), originally ascribed by Lőrenthey (1898) as to the genus Palaeograpsus Bittner, 1875.More recently, Karasawa & Schweitzer (2004) in their revision of the latter genus, erected the genus Magyarcarcinus to accommodate M. loczyanus, and included the genus within the family Goneplacidae MacLeay, 1838.The recovered samples of M. yebraensis n. sp., both males and females, present well-preserved ventral structures, thus allowing to confirm the adscription of Magyarcarcinus to the superfamily Goneplacoidea, but evidencing at the same time the need of a new family where to accommodate this genus, and the need of a revision of its diagnosis.A detailed comparison with each of the Goneplacoidea families, and particularly with some related genera, reinforces the need for the erection of such a new family.The migration patterns of Tethyan fauna to the North Atlantic during the Bartonian transgression through the South-Pyrenean Basin, already suggested by Via (1991), is confirmed by the presence of Magyarcarcinus and its associated decapod assemblage in the Bartonian strata of the south-central Pyrenees.Fig. 2. Geological sketch of the outcrop area.Modified from Mapa Geológico de España 1:50.000,sheet 210 Yebra de Basa (Montes, 1992).Fig. 2. Esquema geològic de l'àrea del jaciment.Modificat del Mapa Geológico de España 1:50.000,full 210 Yebra de Basa (Montes, 1992).Material.Type specimens of Magyarcarcinus yebraensis n. sp. are housed at Museo de Ciencias Naturales de la Universidad de Zaragoza (Spain) under the acronym MPZ.Other specimens figured for comparison are kept in the A. Ossó collection, under the acronym AO.
Geological setting.The study area is located in the Basa anticline, within the so-called Jaca basin.This basin developed an E-W orientation in a time when the Pyrenees were subjected to a S-N compression.The basin infilling began during Lutetian times, and the general depositional sequence, named "Secuencia de Jaca" (Remacha & Picart, 1991), comprises several different formations (see also Puigdefábregas, 1975).The decapod-bearing layers of this study correspond to the Margas de Arguís Formation, also known as Margas de Pamplona-Arguís Formation (Puigdefábregas, 1975).In this area, it consists of a sequence, approximately 700 meters thick, of blue-grey marls interbedded with sandstone intervals (Figs. 2, 3).
The base is defined by large scale sandstone deposits of offshore shelf facies marked by several episodes of shallowing and deepening.These deposits culminated in a relatively long transgressive episode that filled the basin.The general marine conditions of the Margas de Arguís Fm. correspond to a tectonic transgressive-regressive cycle (Toledo, 1992).It is also worth noting that these layers were affected by deltaic contributions, with important terrigenous inputs, that become totally dominant in the upper levels (see Ossó et al., 2014).
The crab remains were recovered from the lower levels of the section.According to Canudo et al. (1991), the outer shelf sediments where such decapods occur are included the Bartonian age depositional sequence, SD5, as indicated by the presence of planktonic foraminifera of the Pomeroli Biozone.Biostratigraphic and magnetostratigraphic data (Pueyo et al., 2002) establish the lower and upper limits of the Margas de Pamplona-Arguís Formation from 40.32 to 37.17 Ma, which, according the ICS ICC 2015, correspond to a Bartonian-early Priabonian age.The level where M. yebraensis has appeared consists of blue-gray marls with small associated fauna composed only of scarce nummulites, ostreids, scaphopods, and small branching bryozoans; no other decapod remains occur.However, in the underlying levels, a concentration of Portunus catalaunicus Via, 1941 and Harpactocarcinus punctulatus A. Milne-Edwards, 1862 is observed.The overlying levels have also provided abundant specimens of P. catalaunicus; both species typically occur in the Bartonian of the western Tethys sea margin.
The well preserved remains of Magyarcarcinus yebraensis n. sp., recovered in the south-central Pyrenees, permit us to enlarge the knowledge of the genus Magyarcarcinus, especially regarding the sterno-abdominal features not present, or only partially preserved, in the holotype of M. loczyanus.
The inclusion of the genus in the superfamily Goneplacoidea seems well supported by many features such as the rounded and smooth carapace with not clearly defined regions; the straight front and broad fronto-orbital margin; the sternite 7 expanded and sternite 8 not visible; the sternal sutures 2/3 complete, 4/5 and 5/6 interrupted medially, and 6/7 appearing complete; all the male abdominal somites free, somites 1-2 slightly narrower than somite 3, and with somite 3 covering the space between the coxa of P5.This array of characters seems to match perfectly with the diagnosis of Goneplacoidea (Karasawa & Schweitzer, 2006;Ng & Manuel-Santos, 2007;Castro et al., 2010).
Nevertheless, the unique combination of characters that Magyarcarcinus exhibits such as: a smooth and rounded carapace, the frontal and fronto-orbital ratios, a sternum relatively broad and not clearly ovate, the sternite 4 broad and vaulted, and suture 3/4 complete, among others, is not seen in any of the current Goneplacoidea families.Nevertheless, several of these characters are shared by many Goneplacoidea members.For instance, the deep and narrow median longitudinal groove through sternites 3/4 reaching the suture 2/3, is present in Sotoplacidae Castro, Guinot & Ng, 2010(see Castro et al., 2010).Also, the distinct sternal suture 1/2 is present in Acidopsidae Števčić, 2005Števčić, (see Castro et al., 2010)); the well-marked and complete suture 3/4 is present in several members of Progeryonidae Števčić, 2005, or Conleyidae Števčić, 2005(see Castro & Ng, 2008;Castro et al., 2010); and the markedly triangular abdomen narrowing gradually from sternite 3 to the telson is also seen in Conleyidae and in members of Goneplacidae such as Thyraplax Castro, 2007, Neogoneplax Castro, 2007or Guinoplax Castro & Ng, 2010, among others.Despite this, the particular combination of characters seen in Magyarcarcinus suggests the need to place this genus in his own family Magyarcarcinidae within Goneplacoidea.
We examine the characteristics of Magyarcarcinus, the sole member of the new family Magyarcarcinidae, with an emphasis on the ventral features in comparison to extant and extinct Goneplacoidea families (including two incertae sedis genera) and considering recent works with refined diagnosis.
Members of Progeryonidae share significant similarities with Magyarcarcinus like a well-marked male suture 3/4 (Castro & Ng, 2008), defined as "deep, laterally only" in Castro et al. (2010), and a broad triangular male abdomen with distinct sutures, being somite 3 the larger and filling the space between the coxa of P5.However, they differ from Magyarcarcinidae in having a transversally ovate carapace with at least one anterolateral tooth, a shorter fronto-orbital margin, smaller orbits with an entire supra-orbital margin, a broader thoracic sternum, the 3 rd sternite with a shallower longitudinal groove, without reaching the suture 2/3, a narrower sternite 7, and abdominal somites 3 and 4 fused or with sutures visible whereas they are completely free in Magyarcarcinidae (Crosnier, 1976;Ng & Manuel-Santos, 2007;Ng & Guinot, 1999;Ng et al., 2008;Guinot & Richer de Forges, 1981;Castro & Ng, 2008;Castro et al., 2010).
Members of family Mathildellidae Karasawa & Kato, 2003 differ from Magyarcarcinidae because, even exhibiting a smooth surface of the carapace, the regions are still distinguishable.In addition, the fronto-orbital width is narrower, despite of having a bimarginate front as in Magyarcarcinidae; the anterolateral margins are usually toothed, being entire in Magyarcarcinidae; the thoracic sternum is more ovate; the sterno-abdominal cavity reaches only the median part of sternite 4 while in Magyarcarcinidae it reaches the suture 2/3; the suture 3/4 is not well marked as in Magyarcarcinidae; the somite 3 do not fills the space between the coxa of P5 as in Magyarcarcinidae; the male abdomen is also more rectangular elongate and with sutures distinct, or somites 3 and 4 fused, whereas it is triangular and somites are completely free in the new family (Guinot & Richer de Forges, 1981;Karasawa & Kato, 2003a;Ng & Manuel-Santos, 2007;Ng et al., 2008;Castro et al., 2010).
Conleyidae Števčić, 2005 shares with the new family the poorly distinct dorsal carapace regions; the complete sternal suture 3/4, the longitudinal median groove present in sternite 4, an episternite 7 expanded laterally forming plate which covers the anterior edge of P5 coxa; a broad sternite 7, and the male abdomen with all somites free.Nevertheless, they differ from Magyarcarcinidae in having narrower fronto-orbital margin; a toothed anterolateral margin; a broader thoracic sternum; a ridge in suture 1/2, deeper suture 4/5, and absence of longitudinal median groove in sternite 3. None of these features exhibited by Conleyidae are present in Magyarcarcinidae (Ng & Ng, 2003;Ng & Manuel-Santos, 2007;Ng et al., 2008;Castro et al., 2010).
Members of Chasmocarcinidae Serène, 1964, share only some features with Magyarcarcinidae such as a straight front, or entire anterolateral margins.However, many characteristics differentiate them from Magyarcarcinus: a carapace rectangular or trapezoidal; a broader sternum; a male abdomen not entirely filling space between coxae of P5; a large portion of sternite 8 visible in ventral view with a characteristic coxo-sternal supplementary plate; and the fused male abdominal somites 3-5 (Karasawa & Schweitzer, 2006;Ng et al, 2008;Castro et al., 2010).
Beyond some shared characters as entire and sharp edged anterolateral margin or sternites 1-2 fused, forming a triangular plate, Scalopidiidae Števčić, 2005, clearly

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differs from Magyarcarcinidae in the very smaller orbits, a broader thoracic sternum in males, a longitudinal median groove not present in sternites 3 and 4, a narrower T-shaped male abdomen, or abdominal somite 2 much shorter than the somites 1 and 3 ( Števčić, 2005;Ng & Castro, 2008;Ng et al., 2008 andNg &Castro, 2013).Sotoplacidae Castro, Guinot & Ng, 2010, share only a few characters with Magyarcarcinidae such as: a smooth carapace surface, a longitudinal median groove trough sternites 3 and 4, or all male abdominal somites free.Sotoplacidae, clearly differ from the new family in having broader orbits, spiny anterolateral margins, a wider thoracic sternum, a deeper sterno-abdominal cavity; the suture between sternites 3/4 only visible laterally, a large portion of sternite 8 exposed and a notably narrower male abdomen (Števčić 2005; Ng & Castro, 2008; Ng et al.,  2008; Castro et al., 2010).
Members of Acidopsidae Števčić, 2005 exhibit a few characters in common with Magyarcarcinidae such as: relatively broad orbits, relatively narrow sternum, and several species of this family have a deep and narrow longitudinal groove through sternites 3 and 4 as in Magyarcarcinidae.But they can be easily differentiated from the new family in having characters such as different general carapace shape, the suture 3/4 is only visible laterally, a small or large portion of male sternite 8 not covered by the abdomen, the male abdomen narrower with the abdominal somites 3-5 fused and very different width and shape of somites 1-2-3, which preclude any relationship with Magyarcarcinidae (Ng, 2002;Ng et al., 2008;Castro et al., 2010;Ng & Rahayu, 2014).
Litocheiridae Števčić, 2005 exhibit a smooth dorsal surface and similar fronto-orbital margin, a broad male abdomen with all somites free, narrowing gradually from sternite 3 to telson, and somite 3 only slightly broader than sternites 1-2, characters shared with the new family.However, they clearly differ from Magyarcarcinidae in having a subquadrate carapace, the sternal suture 3/4 only visible laterally with longitudinal median groove absent and a small portion of sternite 8 exposed when male abdomen is closed, among others differences (Türkay, 1975;Castro et al., 2010;Ng et al., 2008).
Euryplacidae Stimpson, 1871 present only some dorsal similarities with Magyarcarcinidae, such as a dorsal surface smooth with regions not clearly defined.Nevertheless, differences between them are strong, for instance: a not so rounded carapace, the anterolateral margins usually toothed, the suture 3/4 is not well-marked or interrupted, the male sterno-abdominal cavity reaches only to anterior margin of sternite 4 whereas in Magyarcarcinidae it reaches the posterior margin of sternite 3, a T-shaped male abdomen remarkably narrow with somites 4-6 narrowing steeply from somite 3 to telson, and very long somite 6.The aforementioned differences discard a close relationship with Magyarcarcinidae (Castro & Ng, 2010;Ng et al., 2008;Castro et al., 2010).
Vultocinidae Ng & Manuel-Santos, 2007 present a longitudinal median groove through sternites 3 and 4 that, although shallower, is also visible in Magyarcarcinidae.But many other features of Vultocinidae, as the sculpted and subquadrate carapace with regions defined by swollen ridges and deep grooves, the ovate thoracic sternum, the broad sternite 4 with straight grooves parallel to the lateral margin, a narrower sternite 7, and a not triangular male abdomen, discard the relationship between the two families (see Ng & Manuel-Santos, 2007;Ng et al., 2008;Ng & Richer de Forges, 2009;Castro et al., 2010;Ossó et al., 2014).
Members of the fossil family Carinocarcinoididae Karasawa & Kato, 2003 also share several characters with Magyarcarcinidae, such as: a dorsal surface of carapace smooth, the front nearly straight and/or the supraorbital margin without well-marked fissures.However they display features clearly different from those of Magyarcarcinidae, which rule out the relationship between those two families, such as the relatively distinct dorsal regions, the anterolateral margins toothed, a broader thoracic sternum, the sternites 1-2 fused as equilateral triangle, more flattened sternite 4, absence of longitudinal median groove in sternite 3 which is present in Magyarcarcinidae, the suture 3/4 is only distinct by a shallow depression; as well, the male abdomen is narrower and with the abdominal somites 3-5 fused, and a portion of sternite 8 visible ventrally, which is not the case in Magyarcarcinidae (Karasawa & Fudouji, 2000;Karasawa & Kato, 2003a;Karasawa & Schweitzer, 2006).
Agostella Ossó, 2011 (Goneplacoidea, incertae sedis) from the Eocene of Spain, shares several features with Magyarcarcinus such as a convex anterior half of thoracic sternum, a swollen sternite 4 with convex lateral margins, and all male somites free.Nevertheless, it differs from Magyarcarcinus in its dorsal regions of carapace distinct and swollen, the anterolateral margins with three spines, the relatively broader thoracic sternum, the shallower longitudinal median groove through sternites 3 and 4, the suture 3/4 defined by a groove but only visible laterally, and a male abdomen not triangular (Ossó, 2011).
Emended diagnosis.Carapace small to medium sized, rounded in shape, slightly wider than long, moderately convex in both directions, dorsal surface finely granulated, dorsal regions weakly discernible; front straight, bimarginate, weak medial notch; orbits broad, slightly oblique, supraorbital margin with medial closed fissure; acute outer orbital spine; anterolateral margin entire, convex, sharp edged; posterolateral margin convex; posterior margin slightly convex.Thoracic sternum relatively broad, ovate to subrectangular; sternites 1-2 forming a plate subtriangular much wider than long; sternite 3 broad; sternite 4 broader than sternite 3, wider than long, vaulted,   (Lőrenthey, 1898) and the fossil and extant genus Carcinoplax Milne-Edwards, 1852 (Goneplacidae), most probably based on its rounded carapace with poorly defined regions, the anterolateral margins almost entire, and the straight front with a weak medial notch.Furthermore, characters as the broad thoracic sternite 7 with a posterior prolongation, all male abdominal somites free and a large vulvae in females, are shared by both genera.However, very clear differences exist: the orbits are broader in Magyarcarcinus and the anterolateral margins are usually armed in Carcinoplax while they are entire in Magyarcarcinidae; the thoracic sternum is narrower in Magyarcarcinus, with deep a median longitudinal groove across sternites 3 and 4, which is absent in Carcinoplax; the suture 3/4 is complete in Magyarcarcinus but interrupted in Carcinoplax; the male abdomen of Magyarcarcinus presents the lateral margins straight, covering the space between coxa P5, and the sternite 8 is not visible, whereas Carcinoplax presents a male abdomen with the lateral margins concave and a small portion of sternite 8 is visible (Guinot, 1969(Guinot, , 1989;;Ng & Manuel-Santos, 2007;Castro, 2007;Ng et al., 2008;Castro et al., 2010).Amydrocarcinus Schweitzer, Feldmann, Gonzales-Barba & Vega, 2002 (Goneplacidae) from the Eocene of Baja California (Mexico) presents a similar carapace aspect, moderately vaulted in both senses, smooth, with the regions poorly defined; a front straight and the anterolateral margins entire as in Magyarcarcinus; also presents a male abdomen with all the abdominal somites free and filling space between coxa P5.But it clearly differs from Magyarcarcinus by its entire supra-orbital margin, whereas in Magryarcarcinidae a close supraorbital fissure is present.Also differs in having a broader thoracic sternum, and because the medial longitudinal groove across sternites 3 and 4, present in Magyarcarcinus is absent in Amydrocarcinus; the male abdomen is more rectangular and with concave lateral margins of abdominal somites, instead of the straight margins of Magyarcarcinus (Schweitzer et al., 2002: 17-18, fig. 19;Schweitzer & Karasawa, 2004: 73-76, fig.1, 1-2).
Diagnosis.As for the genus.
Description.Carapace small to medium in size, rounded in shape, slightly wider than long, moderately convex in both senses, widest about two thirds from the posterior margin; dorsal surface apparently smooth but finely granulated; dorsal regions weakly discernible, defined by very shallow grooves.Front straight, bilobed  with weak medial notch, bimarginate, about one third of maximum width.Orbits broad, rounded, slightly oblique, supraorbital margin with closed medial fissure; acute outer orbital spine; eyestalks relatively short.Fronto-orbital margin about 80% of maximum width.Lateral margins unarmed, joining at the point of maximum width of the carapace; anterolateral margins entire, convex, sharp edged; posterolateral margins convex, posteriorly convergent; posterior margin slightly convex; slight re-entrant between posterolateral and posterior margin.Cervical groove fairly discernible medially by V-shapped scar; branchiocardiac grooves defined by scars.
Discussion.Although differences among Magyarcarcinus yebraensis n. sp. and M. loczyanus are not remarkable, in our opinion they are sufficient to establish a new species.For instance, the orbits in M. yebraensis n. sp. are broad and slightly oblique, whereas in M. loczyanus they are smaller and forward directed, and the closed supraorbital fissure is more easily discernible in M. yebraensis than in M. loczyanus.Also, the frontal margin in M. yebraensis n. sp. is clearly bilobed with a wellmarked medial notch, while it is straighter in M. loczyanus and the medial notch is not so marked.In addition, the frontal/width and fronto-orbital/width ratios are clearly different between both species.Magyarcarcinus yebraensis n. sp. has a frontal/width ratio about 0.32 and a frontoorbital/width ratio about 0.77, whereas in M. loczyanus, those ratios are 0.25 and 0.65, respectively.Regarding sternal features, the difference in width of the basis of sternite 2 is evident as well and, while in M. yebraensis n. sp. the ratio of the basis of the triangle formed by sternites 1-2 with the height is about triple, in M. loczyanus this ratio is about twice (check Lőrenthey, 1898, plate IV, fig. 6a-d;Schweitzer & Karasawa, 2004, fig. 1;this work, Figs. 4 and 6, H-J).

FINAL REMARKS
The unique combination of significant characters displayed by Magyarcarcinus, justifies the erection of a new family within the superfamily Goneplacoidea, to accommodate the new genus.Probably, the most outstanding/ relevant features distinguishing Magyarcarcinidae new family from other goneplacoids are the relatively broad male thoracic sternum, the distinct sternal suture 1/2, the sternal suture 3/4 complete, and the longitudinal median groove crossing sternites 3 and 4, which together suggest a clear basal condition of Magyarcarcinidae within Goneplacoidea, thus contributing to a better understanding of this superfamily.
The great relationship between the decapod faunas of the Late Eocene levels of the south-central Pyrenees of Spain and the coeval ones from Italy and Hungary, also confirmed by the presence of Magyarcarcinus in both areas, is noteworthy.The hypothesis proposed by Via (1991: 185, fig. 3) suggested how the Middle-Late Eocene Tethyan carcinofaunas from Hungary and Italy could have reached the southern part of the British Islands via the southern margin of the Iberian Peninsula, or through the northern way represented by the lasting South-Pyrenean Basin.Current knowledge confirms that the latter path, this is, a migration via the northern margin of the Iberian Peninsula, is the most parsimonious alternative (Domínguez & Ossó, 2016).
The Tethyan Eocene decapod fauna described by Quayle & Collins (1981)  among others, are also present in the uppermost levels of the Margas de Arguís Formation.These two evidences strongly suggest that the migration path followed by these faunas, from the Tethys sea to reach the North Atlantic ocean, was, at least, through the South-Pyrenean Basin and the Bay of Biscay, when the second Eocene relative sea level rise during the Bartonian, connected the open North Atlantic waters with the westernmost Tethyan ones (Domínguez & Ossó, 2016).