Cedarina clevensis, Adrain, Jonathan M., Peters, Shanan E. & Westrop, Stephen R., 2009

Adrain, Jonathan M., Peters, Shanan E. & Westrop, Stephen R., 2009, The Marjuman trilobite Cedarina Lochman: thoracic morphology, systematics, and new species from western Utah and eastern Nevada, USA, Zootaxa 2218, pp. 35-58 : 51-54

Cedarina clevensis n. sp.

Figs. 9 , 10

Etymology. After Cleve Creek, the type locality.

Type material. Holotype, pygidium, SUI 109011 ( Fig. 10 M, P, T, U), and paratypes SUI 109001-109010, 111860, 111861, from the Lincoln Peak Formation (Marjuman; Crepicephalus Zone ), Cleve Creek, Schell Creek Range, White Pine County, eastern Nevada, USA.

Diagnosis. Anterior border furrow weakly posteriorly deflected medially; preglabellar field about same length as anterior border; palpebral lobes long but very narrow; glabella broadest at base, tapering forward; librigena with relatively narrow field; genal spine of only moderate length, tapered to sharp point; thoracic axial spine narrow; pygidium with four fully expressed axial rings.

Description. Cranidium with glabella elongate and broad at base; axial furrows narrow and deeply incised, shallowest and bowed laterally around L1, moderately anteriorly convergent, turned without interruption to grade into anteriorly arcuate preglabellar furrow; glabella with dorsal sculpture of very fine granules; S1-S3 visible as faint impressions with suppressed granulation; L1 and L2 very weakly inflated, but slightly swollen laterally; preglabellar field about same sagittal length as anterior border; field and frontal areas with granular sculpture similar to that of glabella, set atop fine radiating series of caecal trunks; anterior sections of facial sutures strongly anteriorly divergent, maximum point of divergence just behind contact with anterior border furrow; anterior border furrow very short (sag., exsag.) and strongly incised, with only gentle anterior arc, deflected very slightly posteriorly across median portion; anterior border longest sagittally, length constrained by long, obliquely set connective sutures abaxially, with moderate dorsal inflation in sagittal profile, sculpture of fine granules on posterior region, and widely spaced fine raised lines running subparallel to margin on anterior region; preglabellar field sloped down at about 40º from plane of palpebral lobes; eye ridge prominent in small and medium-sized specimens, progressively subdued with size, set about 30º posteriorly from a transverse plane, running from anterior corner of palpebral lobe to near indistinct junction of axial and preglabellar furrows, in smaller specimens course is more transverse; eye ridge not obviously bicomposite, but forming a raised, moderately inflated ridge, separated from fixigena anteriorly and posteriorly by short (exsag.) shallow furrows; palpebral lobe long but very narrow, slightly inclined toward glabella, with sculpture of fine granules; palpebral furrow expressed only at posteriormost edge of lobe, otherwise palpebral lobe grades into interocular fixigena with no break in slope; interocular fixigena narrow, with weak dorsal inflation and granular sculpture identical to that of palpebral lobe; posterior border short proximally; posterior border furrow very short (exag.) and incised proximally; posterior projections not preserved in large specimens; LO long, only slightly longer sagittally than exsagittally, with granular sculpture similar to that on rear of median glabellar lobe; very faint median node set at ring midlength; occipital lobes weakly differentiated behind L1; glabella moderately inflated in sagittal profile, occipital ring flat.

Rostral plate and hypostome not found.

Librigena with long, narrow field, posterior portion of field broader and subtriangular; eye narrow and strongly curved, reniform, separated from field by shallow furrow; field with strong caecal sculpture of pits and ridges adaxially and radiating trunks abaxially; posterior section of facial suture indicates posterior projection was not lobate as in some other cedariids; posterior border furrow not developed on librigena, cut entirely by suture immediately above base of genal spine; lateral border furrow very narrow, deeply incised anteriorly, progressively shallower posteriorly, effaced completely just in front of and atop base of genal spine; lateral border flat, separated from ventral aspect by sharp, blade-like lateral edge, with sculpture of very fine granules and somewhat irregular, meandering and very sparsely distributed fine raised lines; raised lines more robust and more densely crowded posteriorly, and continued along dorsal aspect of genal spine; genal spine about same length as remainder of librigena, curved adaxially, flattened in same manner as lateral border, tapered rapidly to sharp tip; ventral aspect of border turned sharply under dorsal aspect to form ventrally concave furrow subparallel to lateral margin, separated from doublural sector by raised ridge; doublure turned up underneath lateral border furrow, with sculpture of closely spaced and regular fine raised lines set subparallel to inner margin; contact between rear of posterior border and genal spine sharp, angle about 90º.

Spine-bearing thoracic segment with narrow axis; articulating half ring short, slightly longer sagittally than exsagittally, separated from ring by moderately deep furrow; ring lacking dorsal sulpture; narrow and gracile median spine with base set at about midlength of ring, posterior edge of ring drawn back to form small oblique ridge on either side which merges with spine posteriorly, small furrow developed between ridge and spine; length of spine unknown, but probably would have reached past rear of pygidium; axial furrow narrow and incised, but quite shallow, running slightly obliquely; pleural region distinctly bowed, with margins describing shallow M shape; posterior pleural band about twice length (exsag.) of anterior band, both lacking sculpture; region of anterior band distal to fulcrum developed into wide, short subtriangular facet; pleural furrow short and finely incised proximally, longer and deeper distally; fulcrum set close to axis; distal pleural regions with posterior and anterior bands merged into flattened, posteriorly turned pleural spine; doublure beneath rear of ring with fine subparallel raised lines; doublure present as very short (exsag.) strip underneath rear edge of pleura, longer distally, and underlying entire pleural spine distal to termination of pleural furrow, with sculpture of relatively robust and widely spaced raised lines cutting anterolaterally across doublure.

Pygidium subtrapezoidal, with narrow axis; axis with subparallel sides, four weakly expressed rings (easiest to discern ventrally) and a transverse terminal piece and faint, subtriangular post-axial ridge; rings and ring furrows almost effaced dorsally, but short; dorsal sculpture absent from rings; axial furrows relatively deep anteriorly, becoming progressively shallower posteriorly, interrupted posteromedially by post-axial ridge; four pleural furrows expressed, but progressively weaker and more difficult to discern posteriorly; anterior edge of pleura with short facet across most of its width; anterior and posterior pleural bands subequal in length; entire pleural region lacking sculpture; interpleural furrows very weakly expressed; broad, flat border against which furrows terminate; margin and border with slight anterior inflection medially; doublure broad, underlying border, with sculpture of closely spaced fine raised lines running subparallel to margins.

Discussion. Although material is rare and somewhat fragmentary, Cedarina clevensis nevertheless becomes one of the better known members of the genus, and the first for which ventral information is available. It confirms the presence of a thoracic axial spine, indicating that this is likely the common condition for members of the genus. Juvenile cranidia ( Fig. 10 A, C; assignment to C. clevensis tentative) represent the first ontogenetic information for a member of Cedarina , showing the presence of a shallow median furrow on the preglabellar field in early ontogeny, better expression of the eye ridge, a distinct palpebral furrow that is effaced in later ontogeny, independently inflated L1, and stronger expression of the median occipital node.

Compared with C. schachti , the only other adequately known species, C. clevensis differs in the possession of a shorter preglabellar field, shorter glabella with broader base, smaller and particularly narrower palpebral lobes lacking expression of a palpebral furrow in large specimens, a shorter occipital ring, a much narrower thoracic axial spine, and a longer, more subquadrate pygidium.

Figures

FIGURE 9. Cedarina clevensis n. sp., from the Lincoln Peak Formation (Marjuman; Crepicephalus Zone), Cleve Creek, Schell Creek Range, White Pine County, eastern Nevada. Magnifications are x 15 except where noted. A, F, I, K. Cranidium, SUI 109001, dorsal, ventral, anterior, and left lateral views (CLC 70.5 T m). B-D. Cranidium, SUI 109004, dorsal, ventral, and right lateral views (CLC 67.5 T m). E. Right librigena, SUI 109007, external view, x 12 (CLC 67.5 T m). G, H, J. Right librigena, SUI 109002, external, internal, and ventrolateral views (CLC 70.5 T m). L. Right librigena, SUI 109005, external view, x 10 (CLC 67.5 T m). M. Right librigena, SUI 109003, external view (CLC 67.5 T m).

FIGURE 10. Cedarina clevensis n. sp., from the Lincoln Peak Formation Marjuman; Crepicephalus Zone), Cleve Creek, Schell Creek Range, White Pine County, eastern Nevada. All magnifications are x 15. Juvenile specimens in A-C and E are questionably assigned. A, B, E. Cranidium, SUI 111860, dorsal, right lateral, and anterior views, x 30 (CC 1). C. Cranidium, SUI 111861, dorsal view, x 25 (CC 1). D. Left librigena, SUI 109006, external view, x 10 (CLC 67.5 T m). F, G, I, J. Thoracic segment, SUI 109008, dorsal, ventral, anterior, and left lateral views (CLC 67.5 T m). H, K, N, Q. Pygidium, SUI 109009, left lateral, dorsal, posterior, and ventral views (CLC 67.5 T m). L, O, R, S. Pygidium, SUI 109010, dorsal, posterior, ventral, and right lateral views (CLC 67.5 T m). M, P, T, U. Pygidium, holotype, SUI 109011, dorsal, posterior, left lateral, and ventral views (CLC 67.5 T m).