Aguaditaspis, Randolfe & Rustán & Bignon, 2022

Randolfe, Enrique A., Rustán, Juan José & Bignon, Arnaud, 2022, New dalmanitid trilobite taxa from the Lower Devonian of Argentina: comments on spinosity in endemic taxa from southern high paleolatitudes, Comptes Rendus Palevol 21 (2), pp. 17-38 : 24-25

Aguaditaspis n. gen.

( Figs 5; 6)

urn:lsid:zoobank.org:act:3F3AFB54-4B5D-44BD-BE22-592CD7BF5DFE

TYPE SPECIES. — Aguaditaspis mediaspina n. sp.

TYPE LOCALITY. — Quebrada de Talacasto, San Juan Province, Argentina.

ETYMOLOGY. — From Quebrada de las Aguaditas, the type locality in San Juan Province to the southwest of Jáchal city ( Argentina), and the Greek end meaning shield, as usual in trilobites.

OCCURRENCE. — Lochkovian-Pragian, lower muddy part of the Talacasto Formation, Quebrada de las Aguaditas, San Juan Province and Sierra de las Minitas, La Rioja Province, Argentina.

DIAGNOSIS. — Dalmanitid with strongly impressed glabellar furrows, nearly contacting axial furrows. S1 and S2, posterolaterally directed, with short tr. and deep apodems adaxially, with convex projections of glabellar lobes protruding them from behind. S1 slightly concave forward. S2 nearly straight. L1 elongated tr., L2 subrectangular and L3 subtriangular (broadest abaxially and acute adaxially). Tall palpebral area with very shallow and broad exsag. palpebral furrow anteriorly. Eye socle furrow deep and broader exsag. Robust subocular ridge. Anterior branch of facial suture cuts subocular ridge, dividing space between subocular ridge and eye socle furrow in a librigenal and a cranidial portion. Wide tr., exsag. postocular area. Lateral border furrow broad tr. anteriorly, fading posteriorly without contacting posterior border furrow. Very shallow epiborder furrow. Deep and wide exsag. posterior border furrow. Pygidium subtriangular with 18-24 axial rings, most anterior ones usually bearing postero-sagital spines dorsally or inflations variably developed. Well-defined pygidial pleurae, anterior ones evenly wide exsag., five posterior ones progressively straighter, broader tr. and effaced distally. Pygidial interpleural furrows weakly impressed. Pleural furrows broad and deep, with anterior slope steeper than posterior one, posteriormost five somewhat sinuous and variably in width and depth each.

REMARKS

This genus is based on a new combination of characters and some derived characters. Particularly distribution, orientation, width and depth of cephalic furrows are unique. A convex projection of cephalic lobes forward into the glabellar apodems, as reported in detail on the S2 of Dalmanitoides , from the Lower Devonian of Southwestern Gondwanan basins ( Rustán & Vaccari 2012), is a character often overlooked in dalmanitid descriptions. In Aguaditaspis n. gen., a similar convex projection is particularly clear on S1. However, the only known cephalon is an internal mold (CEGH-UNC 27418, Fig. 5A, B), so that some features of these external characters might be slightly different than described herein. A subocular ridge is a character also overlooked in many dalmanitid descriptions. However, in Aguaditaspis n. gen. the facial suture cuts this robust subocular ridge, in a particular and rare case ( Fig. 5A). Median spines or inflations variably developed in several pygidial axial rings is a character extremely unusual in dalmanitids. This derived character may also include single median spines on thoracic axial rings or even in the occipital ring, but the available material is insufficiently preserved to asses this ( Fig. 5E, F, L). The area corresponding to the five posteriormost pleurae in the pygidium is distinctive in terms of its expression, orientation, course, width and depth of furrows. The furrows are not strictly sinuous but somewhat irregular, even in internal molds ( Fig. 5E, F, M, N).

Aguaditaspis n. gen. shares characters of both subfamilies, Synphoriinae and Dalmanitinae ( Holloway 1981), challenging their taxonomic recognition. Particularly, a cephalic epiborder furrow, a pygidium with more than twelve axial rings and a steeply inclined anterior slope of pleural furrows, are related to Dalmanitinae. In turn, a weakly defined cephalic and pygidial border, and the sagittal distance between S1 and S2 apodems 1.5 times than distance between S1 and SO apodems, belong to Synphoriinae diagnosis. The shape of the hypostome of Aguaditaspis n. gen. is similar to some synphoriinines as Lygdozoon , but having a very shallower maculae.