Granadocephalus, Carvalho & Edgecombe & Smith, 2003

Carvalho, Maria Da Gloria Pires De, Edgecombe, Gregory D. & Smith, Legrand, 2003, New Calmoniid Trilobites (Phacopina: Acastoidea) from the Devonian of Bolivia, American Museum Novitates 3407, pp. 1-18 : 14-16

Granadocephalus , new genus

DERIVATION OF NAME: Combination of type locality ( Villa Granado , Cochabamba Department) and ‘‘cephalon’ ’.

TYPE SPECIES: Granadocephalus hannibali , n. gen. and sp .

REFERRED SPECIES: Monotypic.

DIAGNOSIS: Cephalon moderately convex (tr.), subsemicircular in outline; ventral margin with moderate anterior arch. Profile of glabella evenly curved, steepening anteriorly; frontal lobe not distinctly separated from rest of glabella; posterior median impression weakly developed. Axial furrow moderately impressed, divergent especially from S2, with small, rounded fossular depression near anteromedial corner of palpebral lobe. Glabellar furrows not reaching axial furrow on internal mold; S3 lightly impressed, narrow, faintly sinuous; S2 shallow but deeper than S3, weakly directed backward at its inner tip; S1 deeper, weakly concave anteriorly, direct­ ed anteromedially; S0 with strongly convex anterior margin. L3 and L2 not inflated; L1 about two­ thirds length (exsag.) of L2. L0 slightly shortened abaxially. Anterior section of facial suture not transecting anterolateral corner of glabella. Palpebral area slopes downward abaxially, lying entirely below interocular fixigena; palpebral furrow weak. Librigenal field relatively strongly pitted. Posterior cephalic border furrow straight. Entire cephalon covered by very fine granular ornament on internal mold.

DISCUSSION: We were hesitant to create a new genus and species on the basis of such a limited sample. However, the material displays a unique combination of characters within the Calmoniidae (e.g., ventral margin with moderate anterior arch; a peculiar convex [sag.] profile of the glabella; PMI weakly developed; distinctive shape and development of the glabellar furrows and lobes; anterior section of the facial suture does not transect the frontal lobe; visual surface low, lying entirely below the interocular fixigena) that does not permit it to be placed in any of the described calmoniid genera. We consider that the pygidium and the cephalon included here belong to a single species. Both were collected at the same locality and stratigraphic level, they correspond in size, the pygidium has appropriate proportions of the axis and pleurae relative to the cephalon, they have similar depth and width of the pleural furrows on the thorax (fig. 6E) and pygidium (fig. 6F), and the pygidium cannot be assigned to any other calmoniid taxon. Still, since the association of the pygidium is not certain, the generic diagnosis is restricted to cephalic characters.

The affinities of Granadocephalus are difficult to determine. Of suprageneric groups identified in previous work (Eldredge, 1979; Eldredge and Ormiston, 1979; Eldredge and Braniša, 1980), Granadocephalus lacks the diagnostic characters of either the Probolops group or the Malvinella subgroup, and membership in the Calmonia group is most probable. In the Metacryphaeus group, the only obvious comparison is with the topologically primitive genus Plesioconvexa Lieberman, 1993 , which has an evenly convex glabellar profile reminiscent of Granadocephalus (compare Plesioconvexa praecursor in Lieberman, 1993: fig. 3.8 with G. hannibali , here fig. 6C). However, Plesioconvexa , like other members of the Metacryphaeus group, has much deeper incision of S2 and S3 than does Granadocephalus . In Plesioconvexa , S2 has the characteristic transverse, apodemal impression shared by other members of the Metacryphaeus group. Furthermore, Plesioconvexa , and indeed all members of the Metacryphaeus group except for deeply nested, highly modified taxa such as Vogesina , has a much deeper palpebral furrow than does Granadocephalus . Character states such as light impression of S2 and S3, the former being weakly convex forward and the latter sinuous, as well as a shallow palpebral furrow, are shared by Granadocephalus and members of the Calmonia group. These similarities, however, may be primitive characters for Calmoniidae . Eldredge and Braniša (1980) noted that axial morphology of the Calmonia group displays conservative characters for Calmoniidae , whereas the various genera of that group are more variable in their features of the exoskeletal margin (e.g., genal spines, thoracic pleural spines, pygidial marginal spines). The state of these characters is not known for Granadocephalus .

Granadocephalus hannibali , new species

Figure 6A–G

DERIVATION OF NAME: The species name expresses our appreciation to Dr. Joseph T. Hannibal (Cleveland Museum of Natural History), who has made significant contributions to the knowledge of Bolivian paleontology, and who collected the holotype .

DIAGNOSIS: As for genus.

TYPES: Holotype: internal mold of cephal­ on with a few displaced, articulated thoracic segments, MHNC 8131 (cast AMNH 47150) (fig. 6A–E). Paratype: internal mold of pygidium, MHNC 9451 (fig. 6F, G). Both from the Icla Formation, layer of Francovichia branisi (Emsian, inferring equivalence to layer of F. branisi sensu Wolfart (1968) in the Belén Formation in the Altiplano), on a hillside 5 km east of Villa Granado, Cochabamba Department, Bolivia, near the highway leading from Aiquile to Santa Cruz de la Sierra.

DESCRIPTION: The cephalon is moderately arched (tr.), subsemicircular in outline. Its maximum width is 45 mm (across the pos­ terior border) and its sagittal length is 30 mm. The ventral margin is moderately arched anteriorly, with at least two pairs of low, widely spaced protuberances. The anterior cranidial border is uniformly narrow, set off by a sharp anterior cranidial border furrow. The anterior cephalic border is also narrow, especially medially. The axial furrow is moderately impressed, moderately wide, divergent forward especially from S2, with a small, rounded fossular pit situated opposite S3 (exsag.) and near the anteromedial corner of the eye. The anterior section of the facial suture circumscribes the frontal glabellar lobe, passing around its anterolateral corner without transecting it. Glabellar length (sag.) is 25 mm (excluding S0) and its maximum width is 27 mm. In longitudinal profile, the glabella is curved, without a break in slope between the frontal lobe and S0 medially; the frontal lobe is steepest anteriorly. The glabellar median region is almost flat (tr.). The posterior median impression (PMI) is weakly developed as a faint elongate groove that extends back nearly opposite the inner tips of S3. The three pairs of glabellar furrows are not connected with the axial furrow. S3 is narrow, lightly impressed, and faintly sinuous; S2 is shallow but deeper than S3, weakly convex anteriorly, in part by a gentle posterior curvature at its inner tip; the overall course of S2 is approximately transverse, effacing well inward of the axial furrow; S1 is deeper impressed as gently concave, anteromedially directed apodemal grooves, abruptly shallowing distally, at most faint immediately adjacent to axial furrow. S0 is well developed, with a strongly convex anterior margin and a gently convex posterior margin, such that S0 is longest sagittally; medial part of S0 moderately deep, distal part incised as faintly concave apodemal grooves that parallel apodemes in S1. L2 and L3 lack independent inflation; L3 is wedge­shaped, expanded distally; L2 is more conspicuous than L3, and slightly narrowed medially. L1 is about two­ thirds the length (exsag.) of L2. L0 is of even length across much of its width, with slight shortening distally, behind the apodemal part of S0; its width is 15 mm. The gena is subtrigonal, moderately convex. The palpebral area slopes downward laterally to the border furrow. The eye, though not well preserved, is relatively small, with the visual surface about 8 mm long and not elevated, lying entirely below the interocular fixigena; midlength of the palpebral furrow is opposite S2, its posterior edge opposite the posterolateral corner of L2. The anterior edge of the palpebral lobe is very close to the axial furrow, but the distance between them increases posteriorly such that the posterior edge of the eye is equidistant between the axial furrow and the posterior cephalic bor­ der furrow. The librigenal field slopes steeply down to the lateral cephalic border furrow, with the field bearing numerous strong pits. The lateral border of the cephalon and the genal angle are not preserved. The posterior cephalic border furrow is narrow, deep, and transverse; its anterior margin is straight. The posterior border gradually widens (exsag.) distally, more strongly widening distal to the fulcrum. The cephalon is ornamented with fine granulation, which is especially dense on the glabella.

Only an internal mold of a laterally incomplete pygidium is known. The axial furrow is shallow, narrow, and rather strongly converging posteriorly. The axis appears to be slightly wider than the inferred width of the pleurae (excluding marginal spines, if present). In lateral view the axis is gently raised above the pleural field. Five axial rings are strongly developed, plus parts of a sixth. The first two rings are moderately arched anteriorly and the succeeding ones are more gently arched. Medially the rings are widely separated from each other, with a pseudoarticulating half ring in the first two ring furrows; these rings are shortest sagittally and distinctly spatulate distally. Apodemal pits are developed in the distal parts of the ring furrows. The axis terminates far in advance of the posteromedian margin of the pygidium, with the postaxial region defined by a change in convexity rather than distinct impression of the axial furrow posteromedially. Five pleurae are preserved on the right side, but only parts of four are present on the left. The pleurae are gently arched (tr.), the ribs lengthening abaxially; the anteriormost ribs are gently and evenly curved laterally, but the last ones bend back more abruptly. The first interpleural furrow is narrow but sharply impressed, the succeeding furrows are simi­ larly narrow, but shallow; the fourth is the last discernible interpleural furrow on the internal mold. The pleural furrows are deep and relatively wide, maintaining their impression to the inner edge of the doublure. The lateral and posterior margins are not preserved, though the even outer margin of the doublure beneath the fourth and fifth ribs suggests that marginal spines or lappets were probably lacking on those segments at least.