978


Journal of Paleontology 91(5):968–980 The statocyst in Aviamysis n. gen. is apparently circular


presence of an antennal flagella, the strong lanceolate-shaped median ventral projection arising ventrally from front of the labrum and extending beyond it, similar to those of extant species such as Paramblyops brevirostris Tattersall, 1955 or Schistomysis assimilis (Sars, 1877), and the shape of the uropod exopod and the configuration of the thoracopods. Thus, assignment of Aviamysis to the subfamily Boreomysinae remains tentative. A morphological peculiarity of Aviamysis concerns the


and without any trace of internal structure, such as statolith. Strong support for an ancestral status of Boreomysinae is also seen in the non-mineralized (organic) composition of the uropodal statoliths, a trait also found in the basal taxon Rhopalophthalminae. In both subfamilies, the nearly exclu- sively non-crystalline (organic) structure of the statoliths is plesiomorphic compares with the more complex mineralized statoliths found in all other subfamilies (Ariani et al., 1993; Wittmann et al., 1993). It is noteworthy several features of Aviamysis, such as the


the Mysida origin was sometime before the Jurassic, although the question of where and when cannot yet be answered. The description of the fossil specimens of El Pinetell presented in this study strengthens the evidence for the suggestion of Taylor et al. (2001), as well as greatly extends time of the origin of this crustacean order. Moreover, the general appearance of Aviamysis n. gen. provides greater morphological diversity to the first fossil forms and, consequently, to the evolutionary history of the order Mysida. The mode of life of Aviamysis pinetellensis n. gen. n. sp.


in the Middle Triassic marine environment of the Western Tethys is an open question. Marine conditions prevailing in the Iberian region during the Triassic, especially during the whole Ladinian, included a wide diversity of coastal and depositional environments (shores, lagoons, tidal flats, reefs, etc.). Assemblage information from the Alcover unit suggests that this Triassic mysid lived in a marine shallow environment or lagoonal basin within an extended reef complex. Some features of Aviamysis pinetellensis n. gen. n. sp.


shape of the antenna. This appendix includes a sympod with three discernible segments (praecoxa, coxa, and basis), an antennal scale and a peduncle composed of three segments that supports two flagella. This structure can be considered as unique within the order Mysida because, in general, the antennal endopod takes on the form of a multi-segmented flagellum (Tattersall and Tattersall, 1951; Meland et al., 2015). A second peculiarity is derived from the 3-segmented uropodal exopod in Aviamysis: in Mysida, the uropodal exopod is divided by no more than two distal or proximal articulations. Finally, the configuration of thoracopods in Aviamysis differs from those seen in living Boreomysinae (Tattersall and Tattersall, 1951). In Aviamysis, the thoracopods are grouped in at least two different shape groups (third to fourth thoracopods with endopod elongated and robust, sixth to eighth with shorter endopods and undivided carpopropodus). By comparison, in Boreomysi- nae the endopods of the third–eighth thoracopods are all similar in shape, with the carpus distinct and propodus usually divided into two or three subsegments. The formalization of a new subfamily based on the


description of only two fossil individuals seems very hazardous, so we included it (with reservation) in the Boreomysinae. However, given the scale of time elapsed between the age of Aviamysis and the first fossils of previously known Mysida (~70 Myr), it is not impossible that this taxon will someday define a new subfamily. To do this, however, discovery and descriptions of newMysida fossils from the Triassic will be necessary.


Discussion


Taylor et al. (1998) provided a large-scale phylogenetic analysis including recent “mysidacean” and lophogastrid taxa plus fossil pygocephalomorphs. True fossils of the order Mysida have been dated as far back as Middle Jurassic time (Callovian, 163–166 Myr). These animals were well developed, very similar in appearance to the mysids of today, which led Secretan and Riou (1986) to suggest that the evolutionary stage reached by the Jurassic has not appreciably changed in the intervening time period. As suggested by Taylor et al. (2001),


suggest that this mysid could have had an epibenthic lifestyle: (1) the general body form was apparently robust; (2) the shape of the thoracopod exopods, apparently much shorter than the endopods; and (3) the short abdomen. The relatively robust thoracopod endopods also suggest a good capacity for benthic locomotion. Schram (1974) proposed that the radiation of the Peracarida


took place in the Permo-Triassic, which is the period when the first recognisable peracarid fossils appeared (Schram, 1986).


In his view, the dominant Palaeozoic peracarids were the Pygocephalomorpha, which were epibenthic. At the end of the Permian, primitive peracarids occupied refugia or went extinct and were replaced by advanced peracarids adapted to benthic strategies (Poore, 2005). In this sense, comparing the zoo- geographic distribution of extant genera with that of the fossil forms, Udrescu (1984) also hypothesized that primitive Lophogastrida were littoral-benthic forms. In contrast with the more recent interpretations of the Triassic Lophogastrida pela- gic lifestyle (Feldmann et al., 2015, 2017), data provided by the new fossil taxon described here seem to corroborate that the first Triassic representatives of the order Mysida probably had an epibenthic lifestyle and lived in a coastal benthic environment, from which they were diversified to colonize a broad range of aquatic ecosystems on Earth.


Acknowledgments


We wish to express our gratitude to F. Aguilar for providing us with the nice photographs of the holotype. Special thanks to the referees (C.E. Schweitzer and an anonymous reviewer) for improving the manuscript.


References


Ariani, A.P., Wittmann, K.J., and Franco, E., 1993,Acomparative study of static bodies in mysid crustaceans: evolutionary implications of crystallographic characteristics: The Biological Bulletin, v. 185, p. 393–404.


Beltan, L., Calzada, S., Via, L., and Villalta, F., 1989, On Ladinian biotas from northeastern Spain: Abstracts 28th International Geological Congress, Washington D.C., v. 1, p. 121–123.


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