A New Limulid (Chelicerata, Xiphosurida) from the Late Cretaceous (Cenomanianeturonian) of Gara Sbaa, Southeast Morocco

Cretaceous Research 106 (2020) 104230

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Cretaceous Research

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Short communication A new limulid (Chelicerata, Xiphosurida) from the Late Cretaceous (CenomanianeTuronian) of Gara Sbaa, southeast Morocco

* James C. Lamsdell a, , Jessica N. Tashman b, 1, Giovanni Pasini c, Alessandro Garassino d a Department of Geology and Geography, West Virginia University, 98 Beechurst Avenue, Brooks Hall, Morgantown, WV, 26506, USA b Department of Geology, Kent State University, 221 McGilvrey Hall, Kent, OH, 44242, USA c Via Alessandro Volta 16, 22070, Appiano Gentile, Como, Italy d Department of Earth and Biological Sciences, Loma Linda University, Loma Linda, CA, 92350, USA article info abstract

Article history: Two specimens of a new species of horseshoe crab, Mesolimulus tafraoutensis sp. nov., are described from Received 24 April 2019 the Late Cretaceous (CenomanianeTuronian) Gara Sbaa Lagerstatte€ of southeast Morocco. These most Received in revised form likely represent juveniles, as suggested by their small size and possession of a number of characteristics, 13 August 2019 such as short genal spines, that are characteristic of modern juvenile horseshoe crabs. Despite this, the Accepted in revised form 28 August 2019 development of the prosomal keel into a broader cardiac ridge and the scalloped lateral margins of the Available online 3 September 2019 cardiac lobe clearly place these specimens within Mesolimulus. A further characteristic, the occurrence of only two tubercles on the thoracetron pleural ridges, marks Mesolimulus tafraoutensis sp. nov. as a Keywords: Horseshoe crabs distinct species. As Mesolimulus resolves phylogenetically as a total group limulid outside of the crown Limulidae group, the new discovery indicates that stem-lineage limulids persisted into the Cretaceous and co- Mesolimulus existed with crown-limulids as they underwent their major radiation. Lagerstatte€ © 2019 Elsevier Ltd. All rights reserved. North Africa Ontogeny

1. Introduction specimens retained under open nomenclature, xiphosurids have a low standing diversity over the majority of their evolutionary history. As aquatic chelicerates with a fossil record that stretches back to Xiphosurids (and xiphosurans, inclusive of supposed horseshoe the Ordovician (Rudkin et al., 2008; Van Roy et al., 2010), xiphosurids crabs without a fused thoracetron, in general) attained the peak of are easily recognisable in the fossil record on account of their broad, their diversity during the Carboniferous when bellinurines invaded semicircular prosomal carapace (which lends them their common and diversified within non-marine coal swamp habitats (Lamsdell, misnomer, ‘horseshoe crab’) and fused opisthosomal thoracetron. 2016), a trend that has persisted even with the realisation that Their comparatively featureless dorsal carapace morphology, how- Palaeozoic synziphosurines are not true horseshoe crabs (Lamsdell, ever, means that differentiating xiphosurid species is more difficult 2013; Selden et al., 2015) and that a number of bellinurine species than recognising their existence. Numerous reports of xiphosurids represent different ontogenetic stages of a single species and thus are remain in open nomenclature (e.g., Ewington et al., 1989; Hauschke synonyms (Haug et al., 2012). Nevertheless, throughout the rest of et al., 1992; Hauschke and Wilde, 2008; Krause et al., 2009; Haug the Palaeozoic, and into the recent, it has been rare for more than et al., 2012), a problem that is further compounded by the un- three or four xiphosurid species to co-occur globally. Even today, certainties regarding the monophyly of several genera, with Paleo- when sampling is presumably more reliable than in the geological limulus Dunbar, 1923 and Limulitella Størmer, 1952 in particular past, only four species of horseshoe crab are known (Lamsdell, in serving as wastebasket assignments for Palaeozoic and Mesozoic press). All four extant species resolve within the clade Limulidae, species, respectively (Lamsdell, 2016). Even accounting for which can trace its origins into the Triassic (Lamsdell and McKenzie, 2015). Two of the three modern genera also have fossil records extending into the Mesozoic: Tachypleus syriacus (Woodward, 1879), from the Late Cretaceous (Cenomanian) of Lebanon, resolves phylo- * Corresponding author. genetically as a crown-group Tachypleus Leach, 1819 (Lamsdell and E-mail address: [email protected] (J.C. Lamsdell). 1 Current address: Science Department, Jackson College, 2111 Emmons Road, McKenzie, 2015), while Limulus Müller, 1785 is represented in the Jackson, Michigan 49201, USA. Late Cretaceous (Maastrichtian) by Limulus coffini Reeside and Harris, https://doi.org/10.1016/j.cretres.2019.104230 0195-6671/© 2019 Elsevier Ltd. All rights reserved. 2 J.C. Lamsdell et al. / Cretaceous Research 106 (2020) 104230

1952 from Colorado, USA. Older occurrences purportedly of Limulus chondrichthyan Haimirichia amonensis (Cappetta and Case, 1975) from the Late Jurassic (Tithonian) of Poland (Kin and Błazejowski,_ (see Vullo et al., 2016). The only other vertebrate recorded from the 2014) most likely represent specimens of the closely related genus locality, an indeterminate lizard, is no longer available for study Crenatolimulus Feldmann et al., 2011 (Tashman, 2014), which is (Martill et al., 2011). otherwise known solely from the type species, C. paluxyensis Numerous arthropods, including hymenopteran and orthop- Feldmann et al., 2011 from the Early Cretaceous (Albian) of Texas, teran insects and decapod and isopod crustaceans, form the bulk of USA. the invertebrate biota (Garassino et al., 2008; Martill et al., 2011), Two other xiphosurids are known from the Cretaceous; how- although rare free-living crinoids are also present (Garassino et al., ever, their exact phylogenetic affinities are currently uncertain. 2008), as is some plant material. The decapod crustaceans in Casterolimulus kletti Holland et al., 1975, from the Maastrichtian of particular have been the subject of study (Garassino et al., 2008) North Dakota, USA, is known from a single large prosomal carapace. and include the penaeoid Cretapenaeus berberus Garassino et al., Originally assigned to the Limulidae, it has recently been suggested 2006, the astacideans Amazighopsis cretacica Garassino and to belong instead to the morphologically aberrant clade Austro- Pasini, 2018 and Glyphea garasbaaensis Garassino et al., 2008, the limulidae (Lamsdell, 2016). However, this results in a long temporal anomurans Galathea sahariana Garassino et al., 2008, Muelleristhes gap between the genus Casterolimulus Holland et al., 1975 and the africana (Garassino et al., 2008) and Cretagalathea exigua Garassino other austrolimulids, and it is currently uncertain to which clade (if et al., 2008, as well as the brachyuran Marocarcinus pasinii Guinot either) Casterolimulus belongs, although a close relationship has et al., 2008. Moreover, isopods have recently been the subject of been suggested with another Cretaceous xiphosurid, Victalimulus study and been assigned to the sphaeromatid Unusuropode castroi Riek and Gill, 1971 (Lamsdell, in press). Victalimulus mcqueeni Riek Duarte and Santos, 1962 (Corbacho et al., 2018). Rare limulids have and Gill, 1971, from the Aptian of Victoria, Australia, is a limulid that previously been noted (Garassino et al., 2008), but these remain currently resolves in a polytomy with Limulus and a clade undescribed and are the focus of the present contribution. Much of comprising species assigned to the genera Carcinoscorpius Pocock, the above-mentioned material was collected during field research 1902 and Tachypleus (Tachypleinae) (Lamsdell, 2016). It is there- carried out in October 2006 by one of the authors (G.P.) in collab- fore at present unclear whether or not these two species represent oration with the Department of Invertebrate Paleontology of the crown-group limulids (and in turn crown-group xiphosurids) as do Museo di Storia Naturale di Milano. the other Cretaceous species. In consequence, it is unclear whether The co-occurrence of terrestrial (plant, insect and reptile) forms crown-limulids radiated during the Cretaceous alongside remnants and marine fish and crustaceans indicates that the lagoon experi- of the limulid stem-lineage, or whether the former had completely enced at least some continental influence. Horseshoe crabs are replaced the stem-lineage during the Jurassic. known to be able persist for some time in non-marine salinities Here, we describe a new species of limulid from the Late (Sekiguchi and Shuster, 2009) and have successfully invaded non- Cretaceous Gara Sbaa Lagerstatte€ of southeast Morocco. The speci- marine environments a number of times over their evolutionary mens show morphological characteristics indicative of the genus history (Lamsdell, 2016, in press), and so cannot be used, as has Mesolimulus, which resolve phylogenetically as total-group limulids been done in the past (e.g., Holland et al., 1975), as an indicator of outside of the crown group. The new discovery indicates that stem- fully marine conditions. However, the occurrence of free-living lineage limulids did indeed persist into the Cretaceous and co- crinoids and the ammonite genus Neolobites (G. Pasini, pers. obs., existed with crown-limulids as they underwent their major 2006) provides a good gauge of marine salinity, and suggest that radiation. salinities were close to normal marine conditions.

2. Geological setting 3. Material and methods

The Gara Sbaa Lagerstatte€ is a spatially restricted laminated The two limulid specimens that form the basis of the current Plattenkalk located in southeastern Morocco along the ‘Hamada des study originate from a 60e70 cm section of sublithographic lami- Kem Kem’, close to the Algerian border (Garassino et al., 2008; nated limestones occurring in the 180-cm-thick strata of the Gara Martill et al., 2011), 26 km south-southwest of the village of Sbaa Lagerstatte€ . The specimens are preserved partially com- Tafraout. The Gara Sbaa Lagerstatte€ overlies the Cenomanian fluvial pressed, exhibiting folding and wrinkling but retaining some three- siliciclastics of the Kem Kem Beds which are famous for their dimensional relief. Both specimens retain some remnants of the dinosaur body fossils and trackways (Sereno et al., 1996; Dal Sasso original cuticle preserved as a white calcareous layer. This layer is et al., 2005; Ibrahim et al., 2014a, b) and represents a marine split between the part and counterpart of each specimen and transgression, marked by the appearance of the ammonite genus fluoresces under ultraviolet light. Both specimens are housed in the Neolobites Fischer, 1882, and transition to a shallow restricted car- palaeontological collections of the Museo di Storia Naturale di bonate lagoon environment (Cavin et al., 2010; Martill et al., 2011). Milano, Italy (MSNM). The strata are late Cenomanianeearly Turonian in age and yield a diverse vertebrate and invertebrate biota that has occasionally been 4. Systematic palaeontology referred to as the ‘Agoult assemblage’ (Cavin et al., 2010). The biota has largely gained interest for its diverse fish fauna (Murray et al., Xiphosura Latreille, 1802 (¼ Merostomata Dana, 1852) 2013), including the macrosemiid Agoultichthys chattertoni Xiphosurida Latreille, 1802 Murray and Wilson, 2009, the pycnodontid genus Pycnodus Agassiz, Limulina Richter and Richter, 1929 1833, the ichthyodectids Ichthyodectes bardacki Cavin, 1997 and Limuloidea von Zittel, 1885 Cladocyclus Agassiz, 1841, the clupeid Diplomystus Cope, 1877, the Limulidae von Zittel, 1885 (¼ Mesolimulidae Størmer, 1952) sorbinichthyid Sorbinichthys africanus Murray and Wilson, 2010, Genus Mesolimulus Størmer, 1952 the clupavid Lusitanichthys africanus Cavin, 1999, the dercetid Rhynchodercetis Arambourg, 1943, the aspidorhynchid Belonosto- Type species. Limulus walchi Desmarest, 1822, from the Late Jurassic mus Agassiz, 1834, the enchodontid Saurorhamphus Heckel, 1850,as of Germany, by original designation. well as several indeterminate acanthomorphs (Cavin et al., 2010; Other species. Mesolimulus crispelli Vía, 1987 (Middle Triassic, Martill et al., 2011; Murray et al., 2013) and the lamniform Spain), Mesolimulus (?) sibericus Ponomarenko, 1985 (Late Jurassic, J.C. Lamsdell et al. / Cretaceous Research 106 (2020) 104230 3

Siberia) and Mesolimulus tafraoutensis sp. nov. (early Late Creta- and prosomal carapace lateral margin, extending to level of cardiac ceous, Morocco). lobe anterior margin before becoming effaced. Lateral eyes reniform, Emended diagnosis. Limulid with prosoma wider than long; cardiac 2.5 mm long and 1 mm wide, positioned midway along ophthalmic lobe narrow with scalloped margins, parallel sided with keel ridge. Short (1 mm) upwardly directed ophthalmic spines located at developed into median cardiac ridge with rounded cross section, posterior of ophthalmic ridges. Lateral margin of prosomal carapace flanked by deep furrows; thoracetron wider than long, bearing with narrow marginal rim extending onto proximal portion of genal apodemal pits; thoracetron margins bearing five moveable and six spines. Occipital bands depressed, extending from posterior fixed spines; lateral ridge running along fulcrum (modified after ophthalmic ridges to anterior of genal spines. Genal spines short, Størmer, 1952). extending 7 mm beyond prosomal carapace posterior, narrowing Remarks. Of the species previously included within the genus Mes- evenly distally from width of 7 mm proximally. olimulus, only the holotype of Mesolimulus walchi, along with Mes- Thoracetron 15 mm long, 25 mm wide anteriorly narrowing to olimulus crispelli and the newly described Mesolimulus tafraoutensis 7 mm wide posteriorly. Free lobes project dorsally from thoracetron sp. nov., can be assigned with any certainty. Other species previously surface, bearing short terminal spine. Axial region of thoracetron considered to belong to Mesolimulus are now recognised as repre- 5 mm wide at broadest point, with keel. At least four apodemal pits sentatives of the extant genera Tachypleus or Limulus (Lamsdell and flank thoracetron axis. Marked subaxial ridges converging posterior McKenzie, 2015). Mesolimulus (?) sibericus, currently retained run along thoracetron length, in line with ophthalmic ridges. Two within the genus with some question, is known from a single spec- short spines or nodes are located along the subaxial ridges towards imen that, like Mesolimulus tafraoutensis sp. nov., is most likely a their posterior. Pleural region 3 mm wide, demarcated from rest of juvenile. Mesolimulus (?) sibericus appears to possess the broad car- thoracetron by clear furrow. Outline of fixed spines present but diac ridge that characterises Mesolimulus; however, the cardiac lobe poorly preserved, with attachment points for moveable spines in may lack the scalloped margins present in other species. Further- between; however, moveable spines have disarticulated and are more, the ophthalmic ridges may not be effaced anterior to the not preserved, so the number of moveable and fixed spines is un- cardiac lobe, which would preclude the species from Mesolimulus. certain. Telson insertion 5 mm wide, terminal pleura 3 mm long, However, that particular specimen is rather poorly illustrated and 3 mm wide at base. restudy is required before its generic assignment can be ascertained. MSNM i26843 (paratype). Part and counterpart of prosomal carapace and partial thoracetron in dorsal view. Maximum preserved Mesolimulus tafraoutensis sp. nov. length of specimen 31 mm, incomplete posteriorly, maximum Figs. 1, 2 preserved width 33 mm. Prosomal carapace 20 mm long, 33 mm 2008 Indeterminate xiphosuran; Garassino et al., fig. 5A. wide, preserving remains of original cuticle as pale coating that LSID: urn:lsid:zoobank.org:act:4B2CFC32-F89F-421E-927A- fluoresces under ultraviolet light (Fig. 2C, D). Anterior and lateral 47B7DB230577 portions of carapace showing wrinkles and folds from compression. Type material. MSNM i26844 (holotype), part and counterpart of Cardiac lobe located centrally on carapace, 11 mm long and 6 mm wide at base, narrowing anteriorly with scalloped lateral margins prosomal carapace and thoracetron in dorsal view (Fig. 1). MSNM i26843 (paratype), part and counterpart of prosomal carapace and faintly preserved. Broad keel, developed into cardiac ridge, extending along length of cardiac lobe. Faint raised triangular area partial thoracetron in dorsal view (Fig. 2). Etymology. The specific epithet refers to the village of Tafraoute, 3 mm anterior to cardiac lobe likely indicates position of median ocelli. Ophthalmic ridges positioned midway between cardiac lobe located nearby. Locality, horizon and age. Gara Sbaa (Hamada des Kem Kem), and prosomal carapace lateral margin, extending to level of cardiac lobe anterior margin before becoming effaced. Reniform lateral southeast Morocco, CenomanianeTuronian (early Late Cretaceous). Diagnosis. Mesolimulus with semi-circular prosomal carapace; eyes, 3 mm long by 1 mm wide, located halfway along ophthalmic trunk doublure dorsally delineated by furrow; posterior margin of ridge, associated with short eye spine. Ophthalmic spines located at raised thoracetron region defined by pleural ridges narrow; pleural posterior of ophthalmic ridges, short (1 mm long) and upwardly ridges bearing only two tubercles; telson articulation at posterior of directed. Narrow (0.5 mm) lateral margin extends onto proximal thoracetron lunate, narrow. portion of genal spines. Depressed occipital bands extend from Description. MSNM i26844 (holotype). Part and counterpart of pro- posterior ophthalmic ridges to anterior of genal spines. Genal somal carapace and thoracetron in dorsal view. Maximum preserved spines short, extending 4 mm beyond prosomal carapace posterior, length of specimen 36 mm, maximum preserved width 36 mm. narrowing evenly distally from width of 5 mm proximally. Prosomal carapace 21 mm long, 36 mm wide. Carapace surface is Thoracetron with posterior and lateral margins poorly preserved. compressed and exhibits numerous wrinkles and folds; however, Visible dimensions 11 mm long, 17 mm wide. Keeled axis apparent, structures such as the cardiac lobe and ophthalmic ridges are visible, bearing large node or spine at its anterior. Free lobes just visible but while the curved suture of the prosomal doublure is visible to the left indistinct. side of the carapace anterior. The carapace itself appears to retain Remarks. The new specimens most likely represent juveniles, as < aspects of the original cuticle as a pale coating which fluoresces suggested by their small ( 40 mm) size and possession of a number under ultraviolet light (Fig. 1C, D). Margins of the thoracetron pre- of characteristics such as short genal spines that are characteristic of served with insertion points for moveable spines and telson visible, modern juvenile horseshoe crabs (Sekiguchi et al., 1988; Shuster and Sekiguchi, 2003). Despite this, the development of the prosomal keel although both spines and telson have disarticulated and are not preserved with the specimen. Cardiac lobe 10 mm long and 7 mm into a broader cardiac ridge on the scalloped lateral margins of the cardiac lobe clearly place these specimens within Mesolimulus.The wide at base, narrowing anteriorly with scalloped lateral margins, deep furrows running alongside. Broad keel developed into cardiac delineation of the thoracetron doublure dorsally by a furrow sepa- rates the new specimens, along with Mesolimulus walchi,from ridge visible running down centre of cardiac lobe. Raised triangular node likely bearing median ocelli located 3 mm anterior to cardiac Mesolimulus crispelli from the Triassic of Spain. The narrow, lunate telson articulation and possession of only two tubercles on the lobe. Ophthalmic ridges positioned midway between cardiac lobe 4 J.C. Lamsdell et al. / Cretaceous Research 106 (2020) 104230

Fig. 1. Mesolimulus tafraoutensis sp. nov., holotype, MSNM i26844. Specimen preserving prosomal carapace and thoracetron. A, C: part. B, D: counterpart. A and B imaged under normal light, C and D under ultraviolet light. The original cuticle, preserved as a calcareous coating, fluoresces under ultraviolet light. Labels in B are as follows: AK, axial keel; FL, free lobe; LE, lateral eye; MR, marginal rim; ON, ocellar node; OR, ophthalmic ridge; PR, pleural ridge; SM, scalloped margin of cardiac lobe; Tu, tubercles. The right margin of the cardiac lobe is marked by a dashed line. Scale bars equal 10 mm. pleural ridge, characteristics that are known to remain constant most obvious of these is their small size, overall length being less throughout the ontogeny of other species of Mesolimulus, differen- than 40 mm. The majority of xiphosurids in the fossil record are tiate these specimens from the Jurassic Mesolimulus walchi from small, with “giant” (>100 mm in length) species first recorded from Germany. the Carboniferous (Siveter and Selden, 1987). While the majority of extinct xiphosurid species were undoubtedly smaller than their modern counterparts, the recovery of occasionally “large” 5. Discussion (50e60 mm long) individuals among otherwise “small” (<40 mm long) species indicates that numerous forms in the fossil record are The available specimens of Mesolimulus tafraoutensis sp. nov. represented solely by subadult individuals. This can have important exhibit a number of characteristics of juvenile horseshoe crabs. The ramifications for attempts to reconstruct the phylogeny of the J.C. Lamsdell et al. / Cretaceous Research 106 (2020) 104230 5

Fig. 2. Mesolimulus tafraoutensis sp. nov., paratype, MSNM i26843. Specimen preserving prosomal carapace and partial thoracetron. A, C: part. B, D: counterpart. A and B imaged under normal light, C and D under ultraviolet light. The original cuticle, preserved as a calcareous coating, fluoresces under ultraviolet light. Labels in B are as follows: LE, lateral eye; MR, marginal rim; ON, ocellar node; OR, ophthalmic ridge; OS, ophthalmic spine; SM, scalloped margin of cardiac lobe. The right margin of the cardiac lobe is marked by a dashed line. Scale bars equal 10 mm. group. Including juveniles in phylogenies has been shown to thoracetron pleural ridge. The spines and tubercles of horseshoe destabilise analyses and result in species unknowingly represented crabs become more subdued as they mature; however, their by juvenile instars resolving more stem-ward than their placement number does not change and as such makes a good criterion for when adult material is considered (Lamsdell and Selden, 2013). distinguishing species in the fossil record. Fortunately, studies of growth series in ancient (Haug et al., 2012; Comparing size parameters of limulid congeners assumes Haug and Rotzer,€ 2018; Tashman et al., 2019) and modern growth rates can be generalised across equivalent developmental (Sekiguchi et al., 1988; Shuster and Sekiguchi, 2003) horseshoe crab stages. Because Mesolimulus walchi and Mesolimulus tafraoutensis species provide an indication of which characters vary throughout sp. nov. inhabited similar shallow lagoonal sedimentary settings ontogeny and how this information can to be taken into account (Barthel et al., 1994) and possessed morphological features which when defining species and conducting phylogenetic analyses. Short place them in the same genus, prosomal measurements were genal spines, which occur in the available type material of Meso- compared. Prosomal length and width measurements were ob- limulus tafraoutensis sp. nov., is a trait indicative of juveniles. tained from 83 specimens of Mesolimulus walchi contained in the Assignment to Mesolimulus is, however, possible due to the pres- collections of the Palaeontological Museum at Munich. Prosomal ence of two characteristics known not to be influenced by onto- width measurements ranged from 26.4 to 175.7 mm and averaged genetic changes, i.e., scalloping of the cardiac lobe lateral margin 83.5 mm (Table 1). Novitsky (2009) suggested that a specimen of and the expansion of the prosomal carapace keel into a rounded Mesolimulus walchi from Germany was a juvenile, based on cardiac ridge. A further feature, the occurrence of only two tuber- possession of a 58-mm-wide prosoma. The prosomal widths of the cles on the thoracetron pleural ridges, marks Mesolimulus tafraou- holotype and paratype of Mesolimulus tafraoutensis sp. nov. are 36 tensis sp. nov. as a distinct species from the otherwise similar and 33 mm, respectively. If growth rates and instar stages were Mesolimulus walchi, which bears three tubercles along the comparable between members of Mesolimulus walchi and 6 J.C. Lamsdell et al. / Cretaceous Research 106 (2020) 104230

Table 1 Prosomal widths (in mm) of Mesolimulus walchi from the Palaeontological Museum at Munich and Mesolimulus tafraoutensis sp. nov.

Mesolimulus tafraoutensis sp. nov. Mesolimulus walchi

33.0 26.4 28.0 29.2 43.6 50.7 53.7 53.8 54.6 55.7 36.0 56.0 56.0 57.5 59.2 59.2 59.6 61.0 64.2 64.5 65.6 66.1 66.4 66.8 67.2 67.6 67.7 67.9 68.4 68.9 69.0 70.0 70.1 70.1 74.6 75.5 75.5 76.4 76.4 77.9 78.2 79.5 79.8 81.1 84.4 84.4 85.1 85.4 86.1 86.2 86.2 86.5 88.4 89.0 91.1 92.1 94.1 94.9 95.0 97.3 97.8 99.5 99.7 100.7 100.8 100.9 103.0 103.4 103.8 104.4 108.6 108.9 111.3 112.5 113.0 113.6 114.6 114.8 116.2 118.2 125.9 130.1 132.7 132.7 175.7

Mesolimulus tafraoutensis sp. nov., then the small prosomal sizes of References the latter would indicate that the fossils represent earlier developmental stages than individuals of M. walchi with prosomal sizes Agassiz, L., 1833e1844. Recherches sur les poissons fossiles, 1e5. Imprimerie de Petitpierre, Neuchatel^ . in excess of 36 mm. Agassiz, L., 1841. On the fossil fishes found by Mr. Gardner in the province of Ceara, At Gara Sbaa, shallow-marine lagoonal sedimentary rocks and in the north of Brazil. Edinburgh New Philosophical Journal 30, 82e84. the presence of terrestrial fossils associated with Mesolimulus Arambourg, C., 1943. Note preliminaire sur quelques poissons fossiles nouveaux. Bulletin de la Societ eg eologique de France 13, 281e285. tafraoutensis sp. nov. and other marine organisms together indicate Babcock, L.E., Merriam, D.F., West, R.R., 2000. Paleolimulus, an early limuline a nearshore palaeoenvironment. Modern limulids, which have (Xiphosurida), from Pennsylvania-Permian Lagerstatten€ of Kansas and tapho- been useful taphonomic proxies for extinct species (Babcock et al., nomic comparison with modern Limulus. Lethaia 33, 129e141. 2000), are known to nurse as juveniles up to eight years (Chiu and Barthel, K.W., Swinburne, N.H.M., Conway Morris, S., 1994. Solnhofen: a study in Mesozoic paleontology. Cambridge University Press, Cambridge, 236 pp. Morton, 2004) in the shallow intertidal zone before migrating Cappeta, H., Case, G.R., 1975. Selaciens nouveaux du Certac e du Texas. Geobios 8, offshore with age. The presence of Mesolimulus tafraoutensis sp. 303e307. nov. in nearshore sedimentary rocks may likewise indicate a sub- Cavin, L., 1997. Nouveaux Teleostei du gisement du Turonien inferieur de Goulmima (Maroc). Comptes Rendus de l’Academie des Sciences, Paris, Sciences de la Terre adult developmental stage. Adults of modern Limulus are typically 325, 719e724. solitary and inhabit deeper waters on the continental shelf between Cavin, L., 1999. A new Clupavidae (Teleostei, Ostariophysi) from the Cenomanian of 6 and 18 m (Walls et al., 2002). During mating rituals, adults Daoura (Morocco). Comptes Rendus de l'Academie des Sciences, Paris, Series IIA. Earth and Planetary Science 329, 689e695. migrate to beaches, but these events only last between late spring Cavin, L., Tong, H., Boudad, L., Meister, C., Piuz, A., Tabouelle, J., Aarab, M., Amiot, R., and mid-summer each year. Because of the infrequency of adult Buffetaut, E., Dyke, G., Hua, S., Le Loeuff, J., 2010. Vertebrate assemblages from spawning events, it is more likely that the specimens of Meso- the early Late Cretaceous of southeastern Morocco: an overview. Journal of African Earth Sciences 57, 391e412. limulus tafraoutensis sp. nov. represent juveniles which inhabit Chiu, H.M.C., Morton, B., 2004. The behavior of juvenile horseshoe crabs, Tachypleus nearshore environments all year round. tridentatus (Xiphosura), on a nursery beach at Shui Hau Wan, Hong Kong. Hydrobiologia 523, 29e35. Cope, E.D., 1877. A contribution to the knowledge of the ichthyological fauna of the 6. Conclusions Green River shales. Bulletin of United States Geological and Geographical Sur- vey 3, 807e819. Corbacho,L.,Morrison,S.,Alonso,M.,2018.FirstmentionofUnsuropode castroi Mesolimulus tafraoutensis sp. nov. represents the first record of Durante & Santos, 1962 (Crustacea: Isopoda) in the Upper Cretaceous of Mesolimulus from North Africa, extending the distributional area of Gara es Sbaa^ Lagerstatte€ , south-eastern Morocco. Earth Sciences 7, e the genus and its temporal range into the Late Cretaceous. The 288 292. Dal Sasso, C., Maganuco, S., Buffetaut, E., Mendez, M.A., 2005. New information on occurrence of the species also shows unequivocally that limulid the skull of the enigmatic theropod Spinosaurus, with remarks on its size and stem taxa persisted alongside the limulid crown-group. Given that affinities. Journal of Vertebrate Paleontology 25, 888e896. crown-group limulids most likely originated prior to the Creta- Dana, J.D., 1852. United States exploring expedition during the years 1838, 1839, 1840, 1841, 1942 under the command of Charles Wilkes, U.S.N.C. 13. Crustacea, ceous, and possibly as far back as the Triassic (Lamsdell and part I. Sherman, Philadelphia, 685 pp. McKenzie, 2015), the realisation that stem- and crown-limulids Desmarest, A.-G., 1822. Les crustaces proprement dits, pp. 66e154. In: coexisted for at least part of their evolutionary history is not Desmarest, A.-G. (Ed.), Histoire naturelle des crustaces fossiles, sous les rapports zoologiques et geologiques. F.-G. Levrault, Paris/Strasbourg. completely novel. 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Garassino, A., De Angeli, A., Pasini, G., 2008. New decapod assemblage from the The authors thank two anonymous referees for their comments Upper Cretaceous (Cenomanian-Turonian) of Gara Sbaa, southeastern Morocco. fi Atti della Societa italiana di Scienze naturali e del Museo civico di Storia nat- on the manuscript and John W.M. Jagt, Associate Editor, for nal urale in Milano 149, 37e67. pointers. We also thank Giorgio Teruzzi, Museo di Storia Naturale di Garassino, A., Pasini, G., Dutheil, D.B., 2006. Cretapenaeus berberus n. gen., n. sp. Milano, Italy, for the pictures of the studied specimens. (Crustacea, Decapoda, Caridea) from the Late Cretaceous (Cenomanian) of J.C. Lamsdell et al. / Cretaceous Research 106 (2020) 104230 7

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