Asaphellus sp. 2

Arcerito, Facundo René Meroi, Waisfeld, Beatriz & Balseiro, Diego, 2015, Diversification of Asaphellus Callaway, 1877 (Asaphidae: Trilobita) during the Tremadocian in South West Gondwana (Cordillera Oriental, Argentina), Geodiversitas 37 (2), pp. 131-150 : 146

Asaphellus sp. 2

( Fig. 7A, B )

MATERIAL. — Two pygidia CEGH-UNC 25763, 25764.

OCCURRENCE AND AGE. — Horizon DLA 28. Lower part of the Rupasca Member, Quebrada del Arenal, K. teiichii Zone, Santa Rosita Formation, Santa Victoria Group, middle Tremadocian (Tr2).

DESCRIPTION

Pygidium semicircular, 60% wider than long, gently convex with a well-defined, flat border of uniform width. Axis defined by narrow and well impressed axial furrows, about 18% of maximum pygidial width, raised above pleural fields, increasingly elevated above pleurae posteriorly, tapering backwards and funnel shaped, with rounded posterior tip, terminating in advance of border furrow; three anterior axial rings barely visible. Broad (tr.) and gently convex pleural field, with faint indication of 3-4 pleural furrows, inner part gently convex (tr.), steeply sloping down to border abaxially. Inner margin of doublure subparallel to the pygidial margin.

REMARKS

Asaphellus sp. 2 resembles A. catamarcensis (as revised herein) mainly in the definition of the axis and in being well raised above pleural field. However, the pygidial outline is 61% wider than long, the axis is more parallel-sided, the border is wider, and the doublure widens posteromedially (lying well in advance of the posterior tip of the axis).

The well-defined and raised pygidial axis and the evenly wide border clearly distinguish this material from A. stenorhachis and A. isabelae n. sp. The latter occurs in the same beds in the Quebrada del Arenal. Also, Asaphellus sp. 2 differs from A. kayseri (Kobayashi, 1937) ( Waisfeld & Vaccari 2003) in a poorly segmented axis and pleural field, and a wider border.

The Argentinean material resembles Asaphellus ? sp. from the Saint-Chinean Formation, lower Tremadocian, Montagne Noire ( Vidal 1996), however, Asaphellus sp. 2 exhibits a narrower border and doublure. Also, Asaphellus sp. 2 is close to Asaphellus sp. 1 (herein) and A. verus ( Zhou & Fortey 1986, Upper Yehli Formation,Tremadocian, Hebei province, China), however, Asaphellus sp. 2 differs from both in a more marked, more convex, and less funnel-shaped axis. In addition, the doublure is subparallel to the border in Asaphellus sp. 2 , instead of slightly subtriangular as in Asaphellus sp. 1 .

Figures

FIG. 7. — A, B, Asaphellus sp. 2, pygidia in dorsal view: A, CEGH-UNC 25763; B, CEGH-UNC 25764; C-F, Asaphellus sp. 1, CEGH-UNC 25765-25768; C, pygidium, latex cast, dorsal view, CEGH-UNC 25765; D, pygidium, dorsal view, CEGH-UNC 25766; E, pygidium, dorsal view, CEGH-UNC 25765; F, pygidium and thorax, dorsal view,CEGH-UNC 25767;G, A. isabelae n. sp., articulated juvenile, latex cast, dorsal view,CEGH-UNC 25762. Scale bars: A-F, 0.5 cm; G, 0.25 cm. All specimens come from the Quebrada del Arenal, Santa Rosita Formation, Santa Victoria Group: A, B, G, from DLA 28; C, E, from DLA 25; D, F, from DLA 20.