Amazonaspis, Carvalho & Fonseca, 2007

Carvalho, Maria Da Gloria Pires De & Fonseca, Vera Maria Medina Da, 2007, The Trilobite ‘‘ Dalmanites’ ’ maecurua Clarke, 1890 (Middle Devonian, Amazon Basin, Brazil) and the New Genus Amazonaspis (Synphoriidae), American Museum Novitates 3591, pp. 1-16 : 3-6

Amazonaspis , new genus

TYPE AND ONLY SPECIES: Dalmanites maecurua Clarke, 1890 , from the Upper Lontra Member , Eifelian, Maecuru Formation, Pará State, Brazil .

DIAGNOSIS: Glabella wide, with sculpture of coarse tubercles. Frontal lobe rhombic in outline, moderately inflated, glabellar furrows reaching axial furrows; S1 very close to occipital ring and oblique, S2 subparallel to S1, inner ends of S3 and S1 joined by shallow longitudinal depression separating inflated L2 and L3 from depressed medial part of glabella. Anterior branch of facial suture running outside frontal glabellar lobe, parallel to preglabellar furrows. Anterior cephalic border increasing slightly in length (sag., exsag.) medially, margin without spines or crenulations. Pygidium with 16–17 axial rings, first three weakly convex (tr.); first four interpleural furrows weakly impressed, subsequent ones line-like; 11 wide and welldeveloped pleural furrows; narrow border; median keel or mucro absent.

ETYMOLOGY: In reference to the Amazon Basin, where the type species occurs, together with the feminine Greek word aspis, ‘‘shield’’.

STRATIGRAPHIC RANGE: Eifelian, Middle Devonian.

REMARKS: Clarke (1890) did not provide a diagnosis for maecurua and his description was based upon a syntype series that consists only of a few disarticulated specimens. Although the available material is fragmentary and many morphological details are not very clear, some statements about the affinities of the species can be made. Amazonaspis displays at least some of the cranidial characters of synphoriinids, which include: distance between the cephalic apodemes S1 and S2 more than 1.5 times the gap between the occipital and S1 apodemes (these apodemes are more nearly equidistant in dalmanitinids); S1 directed obliquely forward adaxially; S2 also oblique; L2 and L3 inflated above the median part of the glabella adjacent to them; genal spine lacks a longitudinal furrow. In addition, the pygidium of Amazonaspis lacks a well-defined border; the apodemes are discrete and isolated from the axial furrow; and the pleural furrows are deep and wide (although it is not clear whether these are symmetrical in cross section). It is concluded that the Amazonian material can be placed within the family Synphoriidae rather than the Dalmanitidae .

Comparison of Amazonaspis with Synphoria: As Clarke (1900) recognized, Amazonaspis maecurua and Synphoria stemmata are very similar, particularly in the general shape of the frontal glabellar lobe (with a large and rounded anterior margin); the smooth curvature of the posterior cephalic border toward the blunt and rounded genal spines; the smooth occipital ring, without a central spine or tubercles; and the third and second glabellar lobes, which have similar ornamentation. The pygidial margins are also similar, with a slight outward curvature terminating posteriorly at a rounded angle, which does not form a mucro or spine; furthermore, the axis does not reach the posterior margin of the pygidium.

Despite these similarities, these two species differ in a number of characters: the axial furrows are shallower in A. maecurua ; glabellar lobes L3 and L2 are not fused abaxially in A. maecurua ; S2 and S3 are wider (tr.) and touch the axial furrows in A. maecurua ; the occipital furrow is distinct in both species, deep and almost transverse in Synphoria stemmata , but slightly convex forward medially in A. maecurua ; the central area of the glabella in A. maecurua bears tubercles but is smooth in S. stemmata ; the anterior cephalic margin of A. maecurua lacks crenulations like those of S. stemmata , and the pygidium includes 10–11 axial rings and 10–11 pleural furrows in S. stemmata against 16–17 axial rings and 13 pleural furrows in A. maecurua .