Maurotarion Alberti, 1969

Adrain, Jonathan M., 2009, New and revised species of the aulacopleurid trilobite Maurotarion from the Lower Devonian (Pragian) of Nevada, Zootaxa 2215, pp. 1-23 : 3-5

Maurotarion Alberti, 1969

= Goniopleura Hawle and Corda, 1847 (preoccupied, not replaced) = Tricornotarion Chatterton, 1971

= Branisella Přibyl and Vanėk, 1981 (preoccupied, not replaced)

Type species. Harpidella maura, Alberti, 1967 .

Other species. See Adrain and Chatterton (1995a, p. 318), with the following additions and amendments: Maurotarion chrysion n. sp., Pragian, Wenban Limestone, Nevada, USA; Otarion dongujumqinensis Nan, 1976 , Lower Devonian of Inner Mongolia, China; Forbesia euryceps M’Coy, 1876 , Yan Yean Formation, Ludlow, Australia (see Sandford [2000]; = Cyphaspis spryi Gregory, 1901 , fide Sandford [2000, p. 164]); M. fooi n. sp., Pragian, Wenban Limestone, Nevada, USA; Harpidella (Harpidella) hecate Van ĕk, Vokáč, and Hörbinger, 1992, Konĕprusy Limestone, Pragian, Czech Republic; M. isaacsoni Adrain and Edgecombe, 1996 , Belén Formation, Eifelian, Bolivia; M. legrandi Adrain and Edgecombe, 1996 , Belén Formation, Eifelian, Bolivia; Phillipsia minuscula Hall, 1876 , Schoharie Grit, Emsian, New York State, USA; M. racheboeufi Adrain and Edgecombe, 1996 , Icla Formation, Emsian, Bolivia; M. richardsoni Chatterton and Ludvigsen, 2004 , Jupiter Formation, Aeronian, Anticosti Island, Quebec, Canada; M. wenbanense n. sp., Pragian, Wenban Limestone, Nevada, USA.

Otarion pusillus Liu, 1982 , is known from an internal mold of a single incomplete and distorted pygidium. It could possibly represent a species of Maurotarion .

Harpidella (s.l.) occidentalis Owen, 1981, was assigned to Maurotarion by Adrain and Chatterton (1995a, p. 318), but should be reassigned to Harpidella .

Cyphaspis australis Ohern and Maynard, 1913 , from the Lower Devonian of Maryland, USA, may possibly represent a species of Maurotarion , but is known only from the original line drawing of a cranidium.

Harpidella (Harpidella) thomasi Clarkson and Howells, 1981 , was assigned to Maurotarion by Adrain and Chatterton (1995a), but its affinities are uncertain. The species is known from a single articulated specimen represented by counterpart molds ( Clarkson and Howells, 1981 pl. 79, figs. 1, 2). Clarkson and Howells (1981) also assigned an isolated pygidium, but expressed doubt as to whether it belonged. The pygidium is very long, with at least five axial rings, a morphology unknown in Maurotarion and unusual for an otarionine in general, aside from younger derived species of Otarion Zenker, 1833 . The pygidium possibly represents a proetid, though given the uncertainty of the affinities of thomasi , assignment to that species cannot be ruled out on present evidence. Harpidella (H.) thomasi resembles species of Maurotarion in its apparently weakly inflated cranidium lacking dorsal sculpture and in its large eye and narrow librigenal field. However, it possesses a thoracic axial spine on the sixth segment, a feature definitively absent in every species of Maurotarion for which there is available evidence. Ordovician aulacopleurids typically have a thoracic axial spine (e.g., Adrain, 2005; unpublished data). If loss of this spine is synapomorphic within Maurotarion , it is conceivable that some basal species could retain it. Harpidella (H.) thomasi is Aeronian in age, and the only older species of Maurotarion is the Rhuddanian M. messieri Adrain and Chatterton, 1995 a. Whether or not M. messieri possessed a spine is uncertain - Adrain and Chatterton (1995a, fig. 9.16–9.18, 9.24, 9.25) illustrated segments with long axial spines, but M. messieri occurs along with H. tikkaneni Adrain and Chatterton, 1995 a. All species of Harpidella s.s. (sensu Adrain and Chatterton, 1995a) for which information is available possess such a spine, and the segments likely belong to H. tikkaneni .

Diagnosis: See Adrain and Chatterton (1995a, p. 318).

Discussion: Adrain and Chatterton’s (1995a) revised concept of Maurotarion has been followed in most subsequent studies (e.g., Curtis and Lane, 1997; Edgecombe and Fortey, 2000; Sandford, 2000; Chatterton and Ludvigsen, 2004; Rustán, 2008).

With the taxa added herein, the Pragian becomes the stratigraphic stage with the highest Maurotarion species diversity, at nine. Four of these species, however, are very poorly known. Harpidella neptis Alberti, 1967 , from the “ princeps ” Limestone at Ghtira-Tal, northwest Morocco, is known from only two cranidia. It was assigned to Otarion (Maurotarion) by Alberti (1969, pl. 36, figs. 9, 10). With so little information, it is not clear that the species is actually a representative of Maurotarion . In particular, it has very narrow interocular fixigenae, with the palpebral lobes nearly abutting the glabella. The palpebral lobes are also much smaller and narrower than in typical species of the genus, and do not protrude laterally to the widest point of divergence of the anterior facial sutures. In other respects it does resemble species of Maurotarion , such as in the possession of small L1 which do not significantly protrude from the lateral outline of the glabella, and a long, flat, anterior border. More material, particularly of sclerites in addition to the cranidium, would be required to adequately assess the affinity of the species.

Harpidella (Harpidella) distincta Přibyl and Vanĕk, 1981 , from the Vinariče Limestone, and H. (H.) tantula Přibyl and Vanĕk, 1981 , from the Dvorce-Prokop Limestone, both Pragian of the Prague Basin, Bohemia, Czech Republic, were assigned to Maurotarion by Adrain and Chatterton (1995a). The former is known from a single incomplete internal mold of a cranidium ( Přibyl and Vanĕk, 1981, pl. 7, fig. 10), and the latter from five incomplete cranidia ( Přibyl and Vanĕk, 1981, pl. 7, figs. 1–5). Přibyl and Vanĕk compared the species only with each other and with their new H. (H.) kobayashii (Emsian, Czech Republic), which is known from three fragmentary cranidia ( Přibyl and Vanĕk, 1981, pl. 7, figs. 11, 12, pl. 9, fig. 8). These species are essentially uninterpretable beyond their probable status as ingroup Maurotarion .

Of the five non-Nevada species, only the late Lochkovian or earliest Pragian Bolivian M. dereimsi (Kozlowksi, 1923) is reasonably well understood (see Adrain and Edgecombe, 1996, p. 424, pl. 52, figs. 1–3, 5–9). Adrain and Edgecombe (1996) argued that M. dereimsi formed a predominantly Malvinokaffric clade with their new species M. racheboeufi (Emsian, Bolivia) and M. legrandi (Eifelian, Bolivia), and probably also with M. isaacsoni Adrain and Edgecombe, 1996 (Early Devonian, Bolivia), and Maurotarion nov. sp. A of Adrain and Edgeombe (1996, p. 426; late Emsian or younger, South Africa). They also ( Adrain and Edgecombe, 1996, pp. 420–421) considered that M. periergum was related to the M. dereimsi group. This opinion was based on the presence of inflated genal spine bases, termination of the lateral border furrow in front of the genal angle and continuation of the posterior border furrow along the genal spine, and an anterior border than is only slightly longer medially than laterally. Adrain and Edgecombe (1996, p. 422) tentatively interpreted the entire Malvinokaffric Maurotarion species group as monophyletic, and sister to M. periergum , implying an episode of Pragian invasion from lower latitudes. This scenario was challenged by the description ( Edgecombe and Fortey, 2000) of a Silurian Malvinokaffric species of Maurotarion from Bolivia. Though not well known, this species is potentially a member of the M. dereimsi group. Before further biogeographic speculation is engaged in, a formal phylogenetic analysis of the entire genus is required. Such an analysis is beyond the scope of the present paper, but the species described herein provide some of the best known morphological data available for eventual cladistic analysis.