Ivanites leonorae, 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 : 22-24

Ivanites leonorae n. gen., n. sp.

( Figs 3; 4)

urn:lsid:zoobank.org:act:4E9AE8A7-77D6-4E5D-B465-D4FB4EC303ED

Kasachstania ? sp. Rustán, 2016: 137; fig. 6.

TYPE MATERIAL. — Holotype. One enrolled specimen CORD-PZ 7114 ; Fig. 3B, E, H, K, M-N; and Fig. 4A, D, E, G, from Quebrada de las Aguaditas (Lochkovian-Pragian).

Paratypes. Two cephala: CEGH-UNC 12736, from Quebrada de las Aguaditas (Lochkovian-Pragian); Fig. 3C, F, I, L, O-Q; and CEGH-UNC 24430 (assigned with doubt), from Quebrada de Talacasto (Pragian); Fig. 3A, D, G, J; and one pygidium: CEGH-UNC 24424, from Loma de los Piojos (Lochkovian-Pragian); Fig. 4B, C, F, H.

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

ETYMOLOGY. — This taxon is dedicated to Irene Leonor Grunewald, EAR’s mother.

OCCURRENCE. — As for the genus.

DIAGNOSIS. — As for the genus (monospecific).

DESCRIPTION

Whole dorsal surface of carapace lacking ornamentation.

Cephalon widely parabolic in dorsal view. Cranidium with length/width index approximately 0.55, with a minimum of convexity in the anterolateral sides. Very short sag. and exsag. preglabellar area, less than 0.1% of total cranidial length sag. Shallow epiborder furrow running close to margin, narrowest in the anterior portion.

Glabella expanding tr. rather evenly forward, maximum width tr. located in the middle part of the frontal lobe, nearly equivalent to 0.6 of maximum cephalic width tr.

Glabella piriform-shaped,with axial furrows nearly straight and weakly divergent forward (approx. 16°) in the posterior part up to the junction with S3, then strongly divergent (approx.34°) up to the cephalic border, shallowest adjacent to the anterior part of the eye and deepest adjacent to S1. Shallow and delicately incised preglabellar furrow. Preglabellar field not developed.

SO nearly straight, barely sinuous laterally, very narrow sag., exsag. and shallow ( Fig. 3H). S1 nearly straight, narrow sag., exsag., shallowing laterally to fade without contacting axial furrows, incised, becoming deeper, apodemal, adaxially. Apodems slightly convex forward, located nearly at the same exsagittal distance to SO and apodems of S2. S2 nearly straight, shorter tr. than S1, shallowing and fading laterally without contacting axial furrows, apodemal adaxially. S3 anterolaterally oriented, narrowest exsag. adaxially then broadening anterolaterally, effaced adjacent to anterior part of the eye in the contact with axial furrows. LO insufficiently appreciable. L1 short exsag., subrectangular, scarcely inflated and corresponding to 10% of glabellar total length sag. L2 slightly larger sag. than L1, subrectangular and barely more inflated near the axial furrows. L3 larger exsag. than L2, rapidly expanded anterolaterally, slightly inflated near the axial furrows.

Glabellar frontal lobe dorsally oval to sub-rhombic, from slightly convex in posterior part to gently convex and sloping forwards anteriorly in lateral view, weakly inflated and convex dorsally with a slightly depressed median dorsal area subtly elongated exsag.; posteromedial impression subtly expressed.

Eye kidney-shaped in dorsal view, with posterior edge opposite of S1 and anterior edge opposite to contact between axial furrows and S3. Eye maximum length exsag. about 40% of cranidium total length sag., and maximum width tr. about 15% of cephalon total width tr., ocular surface taller in anterior part, gently convex and subvertical in general, more vertically oriented in the posterior part ( Fig. 3E). Lenses regularly ordered in 45 vertical rows with a maximum of 16 lenses, with smaller ones in lower position. Lens formula, according the most complete eye from CORD-PZ 7114, is (from anterior): 2? 7? 9? 9 11 12 13 13 14 14? 15 15? 15 16 15 15 15 15 15 15 15 15 14 14 13 12 12 12 11 11 10 10 9 9 8 8 8 7 6 6 6 6? 5? 4? 2? ( Fig. 3M).

Palpebral furrow moderately deep and strongly convex exsag., deeper anteriorly, narrower tr. and shallower backward.

Shallow and broad exsag. subocular ridge. Anterior branch of facial suture running subparallel to axial furrows, then circumscribing the glabellar frontal lobe.Posterior branch of facial suture running with a strong convexity anterolaterally from the posterior part of the eye, turning backwards and reaching lateral margin a little behind of the half exsag. of eye. Palpebral area elevated in comparison with remaining fixigenal field, slightly convex dorsally in posterior view. Postocular area moderately inclined laterally and slightly convex. Posterior border furrow in appearance deep and narrow exsag. Librigenal field narrow tr., depressed and steeply sloped downwards. Lateral border furrow broader tr. and deeper on librigenal field than on fixigenal field. Anterior border furrow indistinguishable of preglabellar furrow. Genal spine (from specimen CEGH-UNC 24430, Fig. 3G), slightly shorter than the cranidium total length sag., as wide as 10% of cephalon maximum width tr. Posterior border furrow continued into the base of the genal spine. Anterior cephalic doublure (according specimen CEGH-UNC 24430, Fig. 3J), with length sag. about 15% of total cranidium length

sag., nearly flat to barely concave with a very shallow furrow near margin. More depressed internal area about 50% of total doublure length sag., posteriorly located.

Hypostome unknown.

Thorax scarcely known ( Fig. 3N). Axis with 37% of thorax total width tr. across the most anterior segments. Median part sag. of axial rings convex anteriorly and concave posteriorly in dorsal view, lateral sides slightly convex. Axial rings more convex medially in transversal view.

Pygidium broadly subtriangular in dorsal view, with length/ width index approximately 0.8. Axial furrows nearly straight to barely convex laterally, very narrow tr. and moderately deep, diverging from sagittal plane about 6-7°. Pygidial axis narrow, approximately 25% of the maximum pygidial width tr., with a maximum of dorsal convexity tr. medially and just a barely concave profile in lateral view, with 18-20 well-defined axial rings plus a terminal piece. First pygidial eight axial rings gently elevated dorsally in the posterior part, in lateral view, then becoming nearly flat and effaced backward. Nearly first seven axial rings with convex to sub-rectangular lateral sides in dorsal view, posterior ones nearly sub-rectangular. Inter-ring furrows narrow sag., deepest laterally, effaced medially sag. Inter-ring furrows effaced sagittally in the posterior part of the axis, defining a median band of even width tr. Pleural field with 14 pleurae, narrow exsag. and deep pleural furrows, gradually less impressed backward and more posteriorly directed. Anteriormost pleurae (particularly the first seven) sinuous (slightly convex backward near axial furrow, then strongly convex forward toward fulcrum) bending backwards at fulcrum. Posteriormost pleurae becoming progressively straighter and backwardly oriented, trending to be parallel to the axis. Interpleural furrows well-impressed, incised, and symmetrical in cross-section exsag. Pleural bands and furrows progressively fading distally to efface next to pygidial margin, leaving an insinuated pygidial border. Pygidial border and distal part of pleurae steeply inclined downward. Stout caudal mucro slightly downward directed with acute dorsal convexity, tip not adequately preserved.

REMARKS

Ivanites leonorae n. gen., n. sp. resembles “ Kasachstania ” gerardoi Edgecombe & Ramsköld, 1994, a species with current uncertain generic assignment ( Randolfe et al. 2020), from the upper Silurian of Bolivia and Lower Devonian of Argentina. Ivanites leonorae n. gen., n. sp. differs in having smaller exsag. eyes, anteriorly evenly rounded glabellar frontal lobe in dorsal view (not acute), a less rounded pygidium, much narrower exsag. pygidial pleural furrows, distal part of pleural bands without elevations and depressions, delicately convex pygidial border instead of being wide tr. and concave, and distal part more depressed toward the mucro. The cephalon CEGH-UNC 24430 ( Fig. 3A, D, G, J) is assigned with doubt to I. leonorae n. gen., n. sp. Differences with other cephala of I. leonorae n. gen., n. sp. include a lower profile in lateral view, margin nearly straight in lateral and frontal view, lower eyes in appearance with less rows of lenses and frontal lobe not so convex and steeply inclined forward anteriorly. This specimen originated from sandy layers (Pragian of the Quebrada de Talacasto section), in contrast with remaining specimens of I. leonorae n. gen., n. sp. coming from nodules from the pelitic lowermost part of the Talacasto Formation (Lochkovian to Pragian from Quebrada de las Aguaditas and Loma de los Piojos sections), and thus some morphological differences might be, taphonomic, due to a slight dorso-ventral compression. This specimen is the only one preserving a genal spine and consequently its characters were not included in the diagnosis. Such genal spines, exhibiting the posterior border furrow continued in a longitudinal genal furrow, were considered typical of Dalmanitinae ( Campbell 1977).