964
Journal of Paleontology 91(5):960–967
Limulitella tejraensis new species Figures 3, 4
Holotype.—ZPAL V.46/101p (Fig. 3.1).
Type locality and horizon.—Tejra, Ouled Chebbi Formation (Anisian–early Ladinian, Middle Triassic), Medenine area, Sahara Platform, southern Tunisia.
Geographic range.—Known from the type locality only.
Diagnosis.—Prosoma with depressed occipital bands, broad at the ophthalmic ridge becoming thinner and disappearing at the genal spines. Ophthalmic ridge extends in S-shaped line from ocelli along the carapace inner edge as far as the genal angle. Posterior margin of opisthosoma lacks small spines.
Description.—Prosoma wider than long (average length 16.7mm; average width 31.1 mm), weakly to moderately vaulted. Prosomal rim uniform, narrow (Fig. 3.1, 3.3). Anterior margin semicircular, with lateral margins parallel to median axis of carapace, ending posteriorly in long acute genal spines (Fig. 3.7, 3.8). Cardiac lobe smooth, narrowing anteriorly with sinuous margin and obscure nodose anterior, extends ~50% of prosoma length, terminating anteriorly at slightly visible ocelli (Fig. 3.1, 3.3, 3.6, 3.7). Large lateral (compound) eyes posterior to midlength on well-defined ophthalmic ridges (Fig. 3.6, 3.7). Ophthalmic ridge forming rounded structure, inscribing an S-shape within an inner ridge of prosoma to genal spines (Fig. 3.2, 3.7). The genal spines curve inwardly and posteriorly along outer ridge of prosoma. Depressed occipital bands are broad at the ophthalmic ridge, becoming thinner and then dis- appearing at the genal spines (Fig. 3.1). Unsegmented opisthosoma small (average length 12.2mm;
average width, 19.1 mm), triangular, weakly to moderately vaulted in cross section (Fig. 3.4, 3.5). Axial ridge well defined (Fig. 3.5) in the anterior part, bounded by five pairs of depressed entapophoseal pits (apodemes), decreasing in size posteriorly along diagonal axial furrows. Longitudinal ridges form inner margin of opisthosomal flanks, which are separated from central part of opisthosoma by distinct pleurae. Not observed are the opisthosomal (moveable) spines. Flanks extend along S-shaped pleurae. Posterior margin relatively deep and triangular, terminating in two distinct large marginal spines. Telson triangular in cross section. Venter not preserved in specimens.
Etymology.—After the type locality.
Other material.—Five paratypes, ZPAL X.46/102; ZPAL X.46/ 103p,n; ZPAL X.46/106; ZPAL X.46/109; ZPAL X.46/120. Others specimens: ZPAL X.46/104; ZPAL X.46/105; ZPAL X.46/107; ZPAL X.46/108; and ZPAL X.46/110-119.
Discussion
Comparison of Limulitella tejraensis n. sp. with other Triassic limulines.—Triassic horseshoe crabs are considered to have a relatively poor fossil record, with only nine genera having been described: Limulitella Størmer, 1952, known from Germany (Fritsch, 1906; Hauschke and Wilde, 2008), France (Schimper, 1853; Bleicher, 1897), the Netherlands (Hauschke et al., 2009), Madagascar (Hauschke et al., 2004), and Russia (Ponomarenko, 1985); Mesolimulus Størmer, 1952 from Spain (Vía, 1987); Tachypleus Leach, 1819 (=Heterolimulus Vía Boada and De Villalta, 1966) from France; Tarracolimulus Romero and Boada, 1977 from Spain; Psammolimulus Lange, 1923 from Germany (Lange, 1923; Meischner, 1962); Yunnanolimulus Zhang et al., 2009 from south-west China (Hu et al., 2011); Paleolimulus Dunbar, 1923 from Germany (Hauschke and Wilde, 1987, 2000); and two genera described from freshwater strata of Middle Triassic age of New South Wales (Riek, 1968; Pickett, 1984): Australolimulus Riek, 1955 and Dubbolimulus Pickett, 1984. Dubbolimulus has been previously considered to be a synonym of Paleolimulus (Lamsdell, 2016). With respect to the opisthosoma, which is conspicuously smaller than the carapace, the three last genera are quite different from forms described in this paper, and some of them exhibit extremely aberrant morphologies. The opisthosomal (moveable) spines are not present on the described specimens. However, on the reconstruction of Limulitella tejraensis n. sp. we have drawn moveable spines, taking into account the morphologically closest representative of the genus, Limulitella bronnii (Schimper, 1853) from France, illustrated by Gall and Grauvogel-Stamm (1999). The morphological phylogenetic analyses recently carried
out by Lamsdell (2016) demonstrated that Limulitella is a polyphyletic genus. Of all known Triassic horseshoe crabs, Limulitella tejraensis n. sp. seems to be almost identical to the Limulitella forms from France, Germany, and Madagascar. Certainly, the morphological features of L. tejraensis are remarkably similar to those of L. bronnii (Schimper, 1853) from France, illustrated by Gall and Grauvogel-Stamm (1999; see also Röhling and Heunisch, 2010). The shape of the ophthalmic ridge, S-shaped inscribing within inner ridge of the prosoma to the characteristic genal angles are the main features that distinguish L. tejraensis n. sp. from L. bronnii. In both forms, the unsegmented opisthosoma is small with flanks extending along S-shaped pleurae and the posterior margin is significantly cleft triangularly in the posterior part, which in L. bronnii bears two shorter distinct marginal spines. The posterior margin of L. tejraensis n. sp. lacks those spines. Limulitella bronnii was described and sketched by
Figure 4. Reconstruction of Limulitella tejraensis n. sp. The movable spines are not present on the fossils.
Schimper (1853) from the early Middle Triassic (Anisian) ‘Grès à Voltzia’ Formation of eastern France, which represents an environment interpreted as a refugium for terrestrial
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