Dalmanites, Clarke, 1890

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 : 1-2

Clarke (1890) originally described Dalmanites maecurua among other trilobites from the Maecuru and Ererê formations of the Amazon Basin, with ages varying from late Eifelian to early Givetian. The material from the Maecuru Formation (late Eifelian) was

1 Division of Paleontology, American Museum of Natural History ([e-mail]).

2 Museu Nacional/Universidade Federal do Rio de Janeiro, Departamento de Geologia e Paleontologia (vmedina@ acd.ufrj.br) .

collected in 1876 by the Imperial Geological Commission, from several localities along the Maecuru River , north of the Teaupixuna rapids, in the state of Pará. Additional material was collected in the same area, by the Orville Adalbert Derby Expedition, conducted by Petrobras in 1986 .

Clarke (1900: 15) proposed Synphoria as a subgenus of Dalmanites , for his new species Dalmanites (Synphoria) stemmatus from the Oriskany fauna, Lower Devonian of New York State. He considered that the Brazilian species Dalmanites maecurua was closely related to that form as he included it in the same subgenus as Dalmanites (Synphoria) maecurua though he did not comment on the assignment ( Clarke, 1900: 68). Delo (1935) reviewed the phacopid trilobites and divided the family Dalmanitidae into two subfamilies: Dalmanitinae Reed, 1905 , and Synphoriinae Delo, 1935 . He considered the Synphoriinae to be characterized by more or less complete distal fusion and elevation of L2 and L 3 in the glabella, the reduction of S1 and S2 to submesial pits, and the presence in some forms of spines, denticles, or crenulations on the cephalon and pygidium. He also elevated Synphoria to generic status.

In the classification of Richter et al. (1959), the subfamily Synphoriinae was not recognized as valid and Synphoria was placed in the subfamily Dalmanitinae . However, Lespérance and Bourque (1971) resurrected the Synphoriinae and Lespérance (1975) subsequently elevated it to family status ( Synphoriidae ), characterized inter alia by the fusion of L2 and L3. Lespérance recognized two subfamilies within Synphoriidae : the Synphoriinae and the Trypaulitinae.

Campbell (1977) accepted Lespérance’s (1975) subdivision of the Synphoriidae into the Synphoriinae and Trypaulitinae, but modified his concept of the family by rejecting the distal coalescence of L3 and L2 as diagnostic and arguing that this feature is widespread throughout the Dalmanitoidea . New criteria proposed by Campbell for recognizing the Dalmanitinae , Synphoriinae , and Trypaulitinae included the spacing of the cephalic apodemes (i.e., the gap between the occipital and S1 apodemes and between S1 and S2); the development of the cephalic borders and doublures; the presence or absence of a genal spine and an epiborder furrow; the thoracic and pygidial architecture, especially the morphology of the pleural furrows and the tips of the thoracic pleurae; and the position of the pygidial apodemes. Thus, according to Campbell (1977), diagnostic features of the Synphoriinae are: gap between S1 and S2 more than 1.5 times that between the occipital apodeme and S1; S1 slightly oblique to the sagittal line and S2 tends to be equidimensional in dorsal view (the shape of the apodeme in S2 produces the transversally short furrow); cephalic border narrow, convex, and poorly defined; lateral parts of the cephalic doublure correspondingly narrow and rather evenly rolled, or with a slight vincular furrow; genal spine (if present) short, lacking an epiborder furrow, tending to be oval in cross section; thoracic pleurae have a wide (exsag.) and wellrounded posterior pleural band, a thin anterior band, and pleural furrow not dominating; pygidial pleurae have well-developed anterior and posterior bands, and the posterior band does not fade toward the border; pygidial apodemes discrete and positioned away from the axial furrow.

Holloway (1981) revised some Silurian dalmanitaceans from North America and also supported this concept of the family Synphoriidae . His diagnosis of the subfamily Synphoriinae was adapted from Campbell’s (1977) work with slight modifications to accommodate stratigraphically earlier (Silurian) taxa. The modifications included the shape of the cephalic border (flattened dorsally but rolled downward and inward along the outer margin) and the shape of the pleural tips on the thoracic segments (which can be rounded, pointed, or deflected backward into a spine).