Decapod Diversity in the Mid-Cretaceous of Northern Spain

Decapod diversity in the mid-Cretaceous of northern Spain Report Molengraaff Fonds – grant to Adiël Klompmaker, 2010 Introduction During the late Albian – early Cenomanian (102-97 Ma) interval both sea level and global temperatures were high (Haq et al., 1988; Larson, 1991; Scott, 1995), while oceanic spreading rates peaked (Larson, 1991). Hence, epicontinental seas expanded markedly and the number of reefs increased worldwide (Kiessling, 2002). Reefal deposits assigned to the Albeniz Unit of the Eguino Formation (López-Horgue et al., 1996), of late Albian – early Cenomanian age, are found near Alsasua, western Navarra (northern Spain; Fig. 1). This unit overlies upper Albian siliclastic sediments and consists of two stages, documenting firstly the establishment of carbonates on a ramp and, secondly, the formation of patch reefs with marly deposits in between (López-Horgue et al., 1996). Six patch reefs have been observed over an area of some 30 square kilometers (Fig. 2). Fig. 1. A, Location of Spain in Europe. B, Location of the study area in northern Spain. C, A detailed map of the study area with the location of the Koskobilo and the Monte Orobe quarries, the latter in which a contemporaneous decapod fauna was found in the past. From these levels, numerous decapod crustaceans have already been described, in particular from the Monte Orobe patch reef (Van Straelen, 1940, 1944; Ruiz de Gaona, 1943; Via Boada, 1981, 1982; Gómez-Alba, 1989; López-Horgue et al., 1996; Fraaije et al., 2008). At a nearby locality in the Aldoirar reef, which is composed mainly of scleractinian corals, algae and a few rudistid bivalves, fieldwork was conducted during three consecutive years (2008-2010) at the disused Koskobilo quarry, from which 1 Fraaije et al. (2009) had previously recorded a paguroid anomuran. Klompmaker et al. (2011a, see attachment) recorded the first gastrodorid from the Cretaceous Period (Gastrodorus cretahispanicus), recognized in assemblages collected at this locality, and Klompmaker et al. (2011b, see attachment) added Rathbunopon obesum. Fig. 2. An overview of the patch reefs in the Alsasua area during the late Albian – early Cenomanian. The Koskobilo quarry is located in the southeastern part of the Aldoirar patch reef. Modified after López- Horgue et al. (1996, fig. 3). The purpose of this report is to provide information on the entire decapod fauna from Koskobilo, and its diversity compared to other localities in the world consisting of Cretaceous sediment yielding a rich decapod fauna. Moreover, sites within the quarry are compared to one another based on the finds of the author in the summer of 2010. Diversity in Koskobilo The total number of specimens from the Koskobilo quarry is approximately 1000 (collected in the summers of 2008-2010), of which about 250 were collected by the author during the fieldtrip in 2010. Taken together the decapod fauna of Koskobilo consists of 37 species in this single locality, many of which are new to science (see Table 1). Although not all published yet (Klompmaker et al., in prep.), it appears that the Koskobilo quarry is going to yield about twenty new species in total, and also several new genera. Numerous species have also been discovered in recent coral reefs. Abele (1974) mentioned 55 decapod species in a coral environment with six substrates, and Abele (1976) noted 55 and 37 decapod species for two localities off the Pacific coast of Panama. Table 1. The list of decapod species known from the Kokskobilo and Monte Orobe quarries. Koskobilo Monte Orobe 1 "Xanthosia" n. sp. Annieporcellana dhondtae Fraaije et al., 2008 2 Annuntidiogenes worfi Fraaije et al., 2009 Annuntidiogenes ruizdegaonai Fraaije et al., 2008 3 Caloxanthus n. sp. Distefania incerta (Bell, 1863) 4 Cretatrizocheles (n. gen.) n. sp. Distefania 'transiens' (Wright and Collins, 1972) 5 Distefania n. sp1 Eodromites grandis (Von Meyer, 1857) 6 Distefania n. sp2 Eomunidopsis navarrensis (Van Straelen, 1940) 7 Distefania incerta (Bell, 1863) Eomunidopsis orobensis (Ruiz de Gaona, 1943) 2 8 Eodromites grandis (Von Meyer, 1857) Etyxanthosia fossa (Wright & Collins, 1972) 9 Eomunidopsis n. sp. Glyptodynomene alsasuensis Van Straelen, 1944 10 Eomunidopsis navarrensis (Van Straelen, 1940) Goniodromites laevis (Van Straelen, 1940) 11 Eomunidopsis orobensis (Ruiz de Gaona, 1943) Graptocarcinus texanus Roemer, 1887 12 Etyxanthosia fossa (Wright & Collins, 1972) Homolopsis edwardsii Bell, 1863 13 galatheoid Navarradromites (n. gen.) n. sp. 14 Gastrodorus cretahispanicus Klompmaker et al. 2011 Navarrahomola (n. gen.) n. sp. 15 Glyptodynomene alsasuensis Van Straelen, 1944 Necrocarcinus labeschei (Eudes-Deslongchamps, 1835) 16 Goniodromites laevis (Van Straelen, 1940) Paragalathea multisquamata Via Boada, 1981 17 Graptocarcinus texanus Roemer, 1887 Paragalathea ruizi (Van Straelen, 1940) 18 Hispanigalathea (n. gen.) n. sp. Paragalathea straeleni (Ruiz de Gaona, 1943) 19 Hispanigalathea n. sp. Pithonoton bouvieri Van Straelen, 1944 20 Laeviprosopon n. sp1 Rathbunopon obesum (Van Straelen, 1944) 21 Laeviprosopon n. sp2 Sabellidromites scarabaea (Wright and Wright, 1950) 22 Laeviprosopon n. sp3 Viaia (n. gen.) n. sp. 23 Laeviprosopon n. sp4 Xanthosia cf. 'X. similis' (Bell, 1863) (=X. fossa?) 24 Mesotylaspis (n. gen.) n. sp. 25 Navarracaris (n. gen.) n. sp. 26 Navarradromites (n. gen.) n. sp. 27 Navarrahomola (n. gen.) n. sp. 28 Nykteripteryx (n. gen.) n. sp. 29 Paragalathea multisquamata Via Boada, 1981 30 Paragalathea ruizi (Van Straelen, 1940) 31 Paragalathea straeleni (Ruiz de Gaona, 1943) 32 Pithonoton bouvieri Van Straelen, 1944 33 Priscinachus n. sp1 34 Priscinachus n. sp2 35 Rathbunopon obesum (Van Straelen, 1944) 36 Torynomma n. sp. 37 Viaia (n. gen.) n. sp. Stratigraphic and biogeographic notes The Koskobilo fauna sheds light on the transition from Late Jurassic decapod faunas to Cretaceous faunas. Gastrodorus has only been found in Upper Jurassic sediments previously, but is now also known from the mid-Cretaceous. Surprisingly, Eodromites grandis was hitherto known only from the Late Jurassic, but is now also found in Koskobilo. Specimens of this species also represent the youngest specimens from this genus. The same applies for the four species of Laeviprosopon. Striking similarities exist between the decapod fauna from Koskobilo and the Paleocene (Danian) Fakse fauna from Denmark, possibly due to a similar depositional environment containing corals. Examples include Caloxanthus, Xanthosia, and some galatheids. 3 Many genera are new to Iberia (Spain and Portugal) and have not been encountered in Monte Orobe or were misidentified from Monte Orobe. These include (obviously) all new genera, Gastrodorus, Caloxanthus, Priscinachus and Torynomma. Koskobilo versus Monte Orobe In comparison to Monte Orobe, a patch reef in a small abandoned quarry some 4 km north of Koskobilo, the diversity in Koskobilo is markedly higher. This may be due to several factors: a) the smaller species were recognized in Koskobilo, b) possibly more collecting time in Koskobilo based on the number of specimens from Monte Orobe in the Museo Geológico del Seminario de Barcelona in comparison with the collection from Koskobilo, although a part of the collection of the Museo Geológico del Seminario de Barcelona was loaned and not returned (P. Artal, pers. comm. 2008) or c) Koskobilo contained several sites within the quarry yielding slightly different decapod faunas, possibly related to a different microenvironment, see below. Another observation is that some of the decapods appear larger in Monte Orobe (e.g. Distefania incerta and Eodromites grandis), and more decapods are preserved with a cuticle instead of internal molds in Koskobilo. Diversity in the Cretaceous This decapod diversity is unique for the Cretaceous. In fact, Koskobilo will become the richest decapod locality in the world most likely with 37 species. Table 2 shows an overview of other decapod rich localities in the world yielding at least ten species. As can be seen, the ENCI quarry in the Netherlands is second with 31 species. More species are planned to be described from this quarry though (Fraaije, pers. comm., 2011), so this locality might rival Koskobilo in the future, if no additional species will be discovered from the Koskobilo quarry. Both localities have in common that they were a coral reef. Table 3 shows the richest decapod formations from the Cretaceous with at least ten species. The Eguino Formation which includes the Koskobilo and Monte Orobe localities tops this list as well with 42 species followed by the Maastricht Formation. An interesting question is whether the peak in diversity is caused by a preservational bias or is due to ecological reasons (i.e. a natural high number of species within fossil coral reefs). A preservational bias may be considered likely as sedimentation rates are generally high in carbonate environments. Tucker (1990: p. 33-34) mentioned that ‘carbonate sediments can accumulate rapidly compared with other sedimentary rock types’. He notes sedimentation rates in the order of 0.1-6 millimeters per year for carbonate systems depending on the position within a reef. Schlager (1999) mentioned sedimentation rates from the same order of magnitude. The preservation of the decapods from Koskobilo is, however, by no means very good, which may be expected with high sedimentation rates. For example, the vast majority of the carapaces are broken and complete carapaces are uncommon. Moreover, not a single complete specimen is found with the venter, abdomen,

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