1. Introduction

The crustacean minor fauna from the Gara Sbaa (southeastern Morocco) Cretaceous layers is still very poorly reported and known. Purpose of this study is to report two tanaidaceans (Peracarida), representing the first record from the Cretaceous of Africa.

Representatives of Peracarida inhabit many different environments mainly terrestrial, marine, freshwater, and brackish water. Tanaidacea is a peracaridan ingroup of small body sized benthic crustaceans having epifaunal (surface dwellers) or infaunal (burrowing in sediment) lifestyle, having a relatively scarce fossil record despite their massive occasional abundance at some localities (^{Malzahn, 1970}; ^{Heardet al.,2020}). Indeed, finding of fossil tanaidaceans are therefore usually isolated remains or fragmentary body parts. According to ^{Shädelet al., (2019)} “the identification of isolated parts or fragmentary fossils is challenging in various aspects and many remains of tanaidaceans are probably not recognized as such”.

Currently, there are 30 formally described fossil species of tanaidaceans, extending from the Lower Carboniferous to the Miocene (^{Shädelet al.,2019}; ^{Heardet al., 2018}). Most of these species are known from inclusions in amber of the Cretaceous (Albian to Turonian) and Neogene (^{Vonk and Schram, 2007}; ^{Sánchez-Garcíaet al., 2015}, ²⁰¹⁶, ²⁰¹⁷; ^{Heardet al., 2018}) whereas the remaining fossils come from non-amber sites. Among these, several species were described from the Lower Cretaceous layers of Hannover (Germany) (^{Schramet al., 1986}) and from Chiapas, Mexico (^{Heardet al., 2020}).

This new report represents the first fossil record of a tanaidacean from N Africa, enlarging the knowledge on their diversity and distribution during their evolutionary history.

2. Geological setting and fossil assemblage

The Gara SbaaLagerstätteis a spatially restricted laminated Plattenkalk located in southeastern Morocco along the ‘Hamada des Kem Kem’, close to the Algerian border (^{Garassinoet al., 2008}; ^{Martillet al., 2011}) 26 km south-southwest of Tafaout village. The Gara SbaaLagerstätteoverlies the Cenomanian fluvial siliciclastics of the Kem Kem Beds which are famous for their dinosaur body fossils and trackways (^{Serenoet al., 1996}; ^{Dal Sassoet al., 2005}; ^{Ibrahimet al., 2014a}, ^2014b) and represents a marine transgression, marked by the appearance of the ammoniteNeolobites^{Fisher, 1882}, and transition to a shallow restricted carbonate lagoon environment (^{Cavinet al., 2010}; ^{Martillet al., 2011}).

The strata are late Cenomanian-early Turonian in age and contain a diverse vertebrate and invertebrate biota that has occasionally been referred to as the ‘Agoult assemblage’ (^{Cavinet al., 2010}) subject of several studies for its diverse fish fauna (^{Murrayet al., 2013}). The fish assemblage shows affinities with the Middle Cretaceous ichthyofauna from South America and Lebanon, sharing taxa at generic level. Moreover, the co-occurrence of terrestrial plant and insect, with marine fish and crustaceans suggest that salinities were close to normal marine conditions (^{Martillet al., 2011}). Numerous marine arthropods as one limulid (^{Lamsdellet al.,2020}), several decapods (^{Garassinoet al., 2006}, ²⁰⁰⁸; ^{Guinotet al., 2008}; ^{Garassino and Pasini, 2018}; ^{Pasini and Garassino, 2020}), and one isopod crustacean assigned to a species previously reported from the Turonian of Brazil (^{Corbachoet al., 2018}), were previously reported form the bulk of the invertebrate Gara Sbaa biota, attesting the faunal affinities between Africa and South America.

3. Material

Two almost complete specimens, lacking first cheliped and partial pleotelson, gathered from a 60-70 cm section of sublithographic laminated limestones occurring at the 180 cm thick strata of the Gara SbaaLagerstätte. The specimens are preserved partially compressed, but retaining some three-dimensional remnants of the original cuticle preserved as a white calcareous layer. This layer is split between the part and counterpart of each specimen and fluoresces under ultraviolet light. The studied material was part of the specimens collected during field research carried out in October 2006 by one of the authors (G.P.) in collaboration with the Department of Invertebrate Paleontology of the Museo di Storia Naturale di Milano. The specimens are housed in the invertebrate paleontological collection of the Museo di Storia Naturale di Milano, Italy (MSNM).

Abbreviations:lcxp: carapace length;wcxp: carapace width;P-1-P-5: pereiopods 1-5;perxl: pereon length;perxw: pereon width;plxl: pleon length;plxw: pleon width;Pl1-Pl6: pleonites 1-6;P1-P6: pereonites 1-6;Tl: total length (excluding pleoteson).

4. Systematic palaeontology

Order Tanaidacea ^{Dana, 1849}

Suborder Apseudomorpha ^{Sieg, 1980}

Superfamily and family indeterminate

GenusAfroapseudeusnov.

Type species: Afroapseudes cretacicusn. gen., n. sp., by monotypy

Etymology: From Africa, where the specimens were collected and Apseudomorpha lineage. Gender: masculine.

Diagnosis: Body elongate, slightly narrowing posteriorly; sub-pentagonal carapace wider than long and sub-triangular rostrum; eyes rounded, apparently without peduncle; antennulae base rectangular elongate; pereon longer but narrow than carapace; pereonites similar in width and size each than other; P1-P6 with wrinkled furrows dorsally; sub-rectangular P1 and P2 with convex lateral margins and dorsolateral vaults; sub-trapezoidal P3-P6 with convex lateral margins and posterior marginal lateral process; P-1-P-2 elongate meri, slightly longer than combined carpus plus propodus with short, curved fossorial dactylus; pleon narrower than pereon and 2.8 times shorter than pereon; Pl1-Pl5 narrow than pereonites, all similar in size and shape, wider than long with acute lateral margins; elongate pleotelson narrower than Pl1-Pl5.

Afroapseudes cretacicusn. gen., n. sp.

Figures 1 and 2

Figure 1 Afroapseudes cretacicusn. gen., n. sp. MSNM i27639, holotype: part (A), counterpart (B), counterpart, UV light (C). MSNM i27090, paratype: part (D), counterpart (E), counterpart, UV light (F). Scale bar equals 2 mm. 

Figure 2. Afroapseudes cretacicusn. gen., n. sp. A) line drawing of the body. Carapace (green); pereonites 1-6 (blue); pleonites 1-5 (yellow); pleotelson (orange, partially preserved). B) line drawing of the carapace. Abbreviations - ap: anterolateral process; br: branchial region; P1: pereonite 1. 

Etymology: From the Upper Cretaceous, age of the studied specimens.

Diagnosis: as for the genus.

Holotype: MSNM i27639a, b (part and counterpart - dorsal view).

Paratype: MSNM i27090a, b (part and counterpart - in ventral view).

Material and measurements: Two specimens preserved in part and counterpart (MSNM i27639a, b (in dorsal view): lcxp: 2 mm (including rostrum); wcxp: 3 mm; perxl: 5 mm; perxw: 2.5 mm; plxl: 1.8 mm; plxw: 2 mm; Tl: 8.8 mm (excluding the pleotelson) - MSNM i27090a, b (in ventral view): lcxp: 2 mm; wcxp: 3 mm; perxl: 5.5 mm; perxw: 2.4 mm; plxl: 2 mm; plxw: 2 mm; Tl: c. 9.5 mm, (excluding the pleotelson).

Note: the following description is based on the dorsal characters preserved on the type specimen counterpart (preserving the original cuticle), whereas the ventral parts are based on the paratype part three-dimensionally preserved.

Description: Nearly complete body, elongate, flattened dorsoventrally, slightly narrowing posteriorly.

Carapace- Sub-pentagonal carapace with rounded lateral margins, wider than long; cephalic region with moderately elongate sub-triangular rostrum with wide base, terminating in an obtuse pointed tip slightly downward directed with a distal median slight longitudinal groove; rostral lateral margins slightly convex; small, rounded eyes, eye-lobes apparently not present; short anterolateral pointed triangular process frontally directed; rounded branchial regions (corresponding to the fused thoracic somites 1-2) vaulted dorsally and flattened ventrally, wider than the cephalic region; convex lateral margins of branchial regions, tapering to the anterolateral pointed process/spine; almost straight carapace posterior margin slightly sinuous; fusion of cephalon and vestigial thoracic somite1-2, indicated by pair of lateral notches, connected by a transverse concave suture; posterior half of carapace wider than pereon.

Carapace appendages- Short antennulae located laterally at the basis of both sides of rostrum; first antennular segment elongate; first cheliped not preserved with rounded basis observable in ventral view at nearly 1/3 of the posterior carapace margin length.

Pereon- Sub-rectangular pereon 2.5 times longer than carapace in dorsal view, narrower than carapace; sub-rectangular P1-P2 with a pair of dorsolateral vaults and convex lateral margins; sub-trapezoidal P3-P6 with slightly convex lateral margins and posterior marginal lateral process; P1-P6 wider than long, similar in width and size each than other, with transversally wrinkled furrows dorsally; P1-P6 flattened ventrally, smooth at the middle with a longitudinal axial furrow and with bossed, kidney-shaped structures on both the lateral sides.

Pereon appendages- Pereiopods partially preserved, exposed along the pereonites lateral sides; P-1-P-2 elongate meri, slightly longer than combined carpus plus propodus with short, curved distal fossorial-like ?dactylus (as preserved).

Pleon- Pleon narrow than pereon; nearly 2.8 times shorter than pereon; Pl1-Pl5 narrow than P1-P6; Pl1-Pl5 in dorsal view equal in size, flattened ventrally, much wider than long with lateral margins produced into acute, curved posteriorly processes convex posteriorly; pleopods not preserved.

Pleotelson- Poorly preserved; pleotelson seems elongate, narrow than Pl1-Pl5, with convex lateral sides (as preserved); uropods not observables.

Discussion: ^{Schramet al., (1986)} summarized and revised the available information on fossil Tanaidacea representing three suborders: Anthracocaridomorpha ^{Sieg, 1980} (fossil), Apseudomorpha ^{Sieg, 1980}, and Tanaidomorpha ^{Sieg, 1980} (both fossil and recent). Based on ^{Schramet al. (1986)}, the studied specimens are assigned to the Apseudomorpha ^{Sieg, 1980} for their general body features as the truly diagnostic pointed rostrum, presence of a distinct anterolateral process, pleonites produced into acute lateral processes, and the dorsoventrally flattened body, usually more flattened than in other suborders. Based on ^{Schramet al. (1986)} and ^{Heardet al. (2020)}, the fossil Cretaceous record includes only three species assigned to the Apseudomorpha,Carlclausus emersoni^{Schram, Sieg and Malzahn, 1986} (Jurapseudidae ^{Schram, Sieg and Malzahn, 1986}),Cretitanais giganteus(^{Malzahn, 1979}) (Cretatanaidae ^{Schram, Sieg and Malzahn, 1986}) andProtoapseudoides espinalensis^{Heard and Morales-Núñez, 2020} (Protoapseudoidae ^{Heard and Morales-Núñez, 2020}), the first two from Germany and last one from Mexico. For the general body features and characters of the carapace structure, we can confidently exclude that the studied specimens belong to the Cretatanaidae.Carlclaususis based on a specimen lacking the frontal carapace. Our specimens are also different fromProtoapseudoidesin shape of carapace, pereon and pleon, cephalon being longer and nearly square (except for rostrum), pereonites turning narrower posteriorly and narrower pleonites with not so acute lateral extensions.

We can simply remark thatCarlclausus emersonishows some pleonal features having several generic affinities with the studied specimens like pereonites 1 and 2 with convex lateral margins lacking projection, P3-P6 with lateral projections and short pleonites 1-5 with with lateral margins produced into acute, elongated processes as others Jurassic species ascribed to Jurapseudoideasensu^{Schramet al., (1986)}, similar also in the general carapace arrangement. At the same time, among the other younger fossil species reported to dateBarapseudes prima^{Quayle, 2016} (Apseudidae ^{Leach, 1814}) from the middle Eocene of UK, shows thoracic and pleonal generic features resembling those ofAfroapseudes cretacicusn. gen., n. sp. So, we assign hereinAfroapseudes cretacicusn. gen., n. sp. to the Apseudomorpha in having (except their notably different geological age) a different outline and ornamentation of the thorax, shape, and respective proportions of the pereonites respect to those of the most similar representatives of the Jurapseudidae and Apseudidae.

Due to the lacking of some diagnostic features of the cephalic appendages, first cheliped, telson, and uropods, we are unable to establish for the new genus the belonging superfamily and family. The morphological similarities and the shared characters with the compared families allows to suppose that the new taxon would be hypothetically considered as a possible lineage between the Jurassic and the more recent Paleogene Apseudomorpha. The question would be perhaps resolved after discovery of new fossil taxa shortening the wide fossil gape among the Jurassic to Paleogene forms.

Finally, we point out that the species is randomly gathered into the Gara Sbaa laminate layers associated with the crustaceans and fish fauna, not uncommon but usually not recognized or collected by the local diggers due their small size, mainly focused on the commercial vertebrate fish fauna; the specimens were commonly incomplete, partially imbedded in the layers and nearly impossible to prepare, or simply poorly preserved; notably the pleotelson were badly preserved or absent in all the specimens (c. twelve) observed directly on the field (G.P. per. ob., 2006).

5. Paleoenvironmental remarks

In our opinionAfroapseudes cretacicusn. gen., n. sp., may be considered as inhabit the soft sediments (perhaps with fossorial behaviors), deposited in shallow marine waters representing a marine transgression, possibly transitional to a restricted carbonate lagoon environment with temporary/seasonal supply of freshwater from the nearby land.

Due to the present scarcity of fossils records from the worldwide Cretaceous, we can only remark that the most similar environmental conditions seem to be those reported for the Albian (Lower Cretaceous) outcrops of Chiapas, Mexico, considered as “deposits accumulated within a shallow lagoon or estuary with occasional freshwater influence” (^{Vegaet al., 2006}) from whichProtoapseudoides espinalensiswas reported.