Cedarina schachti, 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 : 44-50

Cedarina schachti n. sp.

Figs. 5–8

Etymology. The species is named in honour of Robert Schacht, who collected and donated the holotype and one of the paratype specimens.

Type Material. Holotype, FMNH PE 57116, paratypes SUI 102868, 104476, and additional specimens USNM 437968, 437975, from the Weeks Formation (Marjuman; Cedaria Zone ), Weeks Canyon, northern House Range, Millard County, western Utah, USA.

Diagnosis. Frontal area and preglabellar field long; anterior border evenly anteriorly arcuate; anterior sections of facial suture strongly anteriorly divergent; palpebral lobes large; pygidium relatively narrow and long.

Description. Cephalon with sagittal length 46.6% (42.9–50.4) width across base of genal spines; cranidium with sagittal length 54.3% (49.5–59.8) maximum width across posterior fixigenae; width across anterior sections of facial suture 96.5% (89.8–103.3) width across midlength of palpebral lobes and 47.6% (45.5–50.0) width across posterior fixigenae; dorsal cephalic sculpture of fine, sparsely distributed granules on borders, prominent caecal ridges, grooves, and pits on genal fields, less well impressed and more finely pitted proximally, deeper and more radially oriented distally; fine granules on interocular fixigena, distal part of posterior fixigena, and all of glabella, and very faint small tubercles scattered over proximal posterior fixigena and rear of glabella, particularly on LO; glabella with sagittal length (including LO) 71.5% (70.0– 72.3) cranidial sagittal length and maximum width across LO 70.3% (63.2–83.4) sagittal length; glabella low, with only weak to moderate dorsal inflation, trapezoidal in outline; axial furrows with more or less straight, anteriorly convergent course, bowed out slightly around LO, in at SO, gently out around L1, and very slightly inward opposite remaining anterior part of glabella; preglabellar furrow variable from quite strongly anteriorly convex ( Fig. 8 A) to more transverse ( Fig. 6 ), contact with axial furrow at rounded angle; axial and preglabellar furrows similarly narrow and moderately incised; glabellar furrows effaced, visible distally as very slight indentations in lateral glabellar margin; L1 and L2 expressed mainly as slight swellings, L3 not obvious dorsally; SO with transverse course, very slightly bowed forward medially, very short (sag., exsag.), slightly longer sagittally, shallow laterally, deeper in middle 80%, and deepest sagittally; LO subrectangular, longer (sag., exsag.) than axial rings of anterior thoracic segments, slightly shorter exsagittally than sagittally, with dorsal sculpture of very fine granules, rear margin evenly posteriorly arcuate; preglabellar field long; anterior border longer sagittally than exsagittally owing to oblique course of long connective suture; border dorsally flattened on anterior aspect, sloped sharply towards border furrow posteriorly, lacking dorsal sculpture, anterior margin evenly anteriorly arcuate; anterior border furrow short (sag.; exsag.), relatively shallow; anterior sections of facial sutures strongly anteriorly divergent in front of palpebral lobe, bowing near anterior border furrow to run into oblique connective suture; palpebral lobes large, anteroposteriorly elongate, lacking dorsal sculpture, area around lateral margin raised; palpebral furrow expressed as break in slope; eye ridge running obliquely from anterior edge of palpebral lobe to just in front of L3 (best expressed on Fig. 6 ); interocular fixigenae narrow, lacking sculpture; rear of palpebral lobe nearly abutting glabella; posterior section of facial suture running transversely at rear of palpebral lobe, turned anteriorly to form cedariform lobe on posterior fixigena; posterior border inflated and semicylindrical, short (exsag.) near axial furrow, longer distally; posterior border furrow deep and short (exsag.); both border and border furrow deflected posteriorly near fulcrum.

Librigena with eye large and long; eye socle not obvious, but region is crushed on all available specimens; furrow separating base of visual surface from field shallow, curved subparallel with outer margin of palpebral lobe; field narrowest about 80% of distance anteriorly, wider immediately in front of eye, and much wider posteriorly at rear of eye, with moderate dorsal inflation, transected by subparallel caecal trunks, with very subdued scattered tubercles on rear part; lateral border furrow narrow, relatively shallow, edge sharply defined along contact with border, contact with field more gently sloping, furrow curved parallel with lateral margin of border; posterior border and lateral border completely confluent across posterior section of facial suture, no sutural ridges developed; lateral border flattened in dorsal aspect anteriorly, more inflated and semicylindrical posteriorly, similar in width to anterior border anteriorly, wider posteriorly to base of genal spine, border lacking dorsal sculpture; genal spine broadest just behind base, long and robust, extending nearly to ( Fig. 5 ) or just past ( Fig. 6 ) rear of pygidium, curved slightly adaxially, tapering more or less evenly to sharp, slightly outwardly turned point.

Hypostome known only from poorly preserved mold ( Fig. 7 ), maximum width anteriorly about 73 percent sagittal length; lateral margins slightly posteriorly convergent, width at rear about 85% anterior width; posterior margin deflected sharply from lateral margin, with moderate posterior curvature; hypostome was apparently quite convex.

Rostral plate unknown.

Thorax of 10 segments, with very long median axial spine on eighth; axial ring of similar length sagittally and exsagittally, with dorsal sculpture of fine granules and relatively densely distributed, very subdued tubercles; axial furrow narrow, sharply incised, deflected laterally around side of axial ring; pleural furrow prominent, deep, but quite short (exsag.), contacts axial furrow, with transversely straight course proximally, deflected and curved posteriorly distally at about fulcrum; both anterior and posterior pleural bands raised and ridge-like, with transverse row of very fine tubercles on each; posterior pleural band shorter distally; anterior and posterior bands unite distally to form laterally protruded, posterolaterally directed, pleural spine; axis of successive segments steadily reduced in width posteriorly; axis of eighth segment almost entirely occupied by base of robust spine; spine somewhat longer than distance from anterior margin of cranidium to posterior margin of pygidium, tapered gradually to sharp point; pleural spines small anteriorly, increasing in size posteriorly to reach maximum around seventh or eighth segment, those of ninth and tenth segment slightly smaller but more posteriorly directed.

Pygidium poorly known; of typical morphology for genus, micropygous, with width about three times sagittal length; apparently composed of 3–4 segments; margin complete, pleurae not extended into spines as in thorax.

Discussion. Cedarina vale Lochman, 1940 , the type species from the Bonneterre Dolomite of Missouri, is known only from tiny photographs of one cranidium, one librigena, and one pygidium in the original description. Hu (1983, pl. 1, figs. 34–38) assigned and illustrated two cranidia, a librigena, and a pygidium. These are clearly morphologically distinct from Lochman's species. Hu (1983, p. 278) recognized this, but opined that "Comparing these morphologic differences with the present studied materials, it might assume that this species has a broad morphologic varieties within the same species population." (sic) It is not clear why one would assume this, as a more likely explanation is that they are simply different taxa. Although Hu's material was collected by Lochman and was said to be ( Hu, 1983, p. 275) "from the same general area Saline Creek at Avon, Ste. Genevieve County, Missouri," (sic) no further stratigraphic information was given and whether Hu's material is from the same horizon as Lochman's is not known. Cedarina schachti differs from C. vale in the possession of an evenly forwardly arcuate anterior border, versus one with a strong posterior inflection medially. The anterior border is concomitantly shorter sagittally. The anterior sections of the facial sutures are more anteriorly divergent in C. schachti , the preglabellar field is longer, and the frontal areas occupy a larger area. The glabella is more nearly parallel sided, and relatively narrower at the base. The librigenal field of C. schachti is considerably wider. Although the pygidium of C. schachti is not well known, its outline ( Fig. 7 ) clearly shows that is is relatively narrower and longer than that of C. vale .

Cedarina alberta Lochman in Lochman and Duncan, 1944, from the Pilgrim Formation of south-central Montana, is based on inadequate material, including two poorly preserved cranidia, a nearly uninterpretable librigena, and one pygidium. Lochman and Hu (1962) subsequently assigned material from the DuNoir Limestone of Wyoming to the species. Despite the poor preservation of the type material, the Wyoming specimens do appear to be consistent with it, and this assignment is reasonable. Cedarina alberta differs from C. schachti in its much longer (exsag.) and narrower posterior fixigena, shorter preglabellar field, narrower frontal area, more forwardly tapering glabella, and narrower pygidium.

Cedarina cordillerae ( Howell and Duncan, 1939) is ostensibly the most widely distributed species. The type material is from the Pilgrim Formation in the Big Snowy Mountains of central Montana, and is poorly preserved. Lochman and Duncan (1944, pp. 89–90, pl. 17, figs. 1–10) subsequently reillustrated the holotype along with additional material. Lochman (1950, p. 347, pl. 50, figs. 20, 21) illustrated another cranidium and librigena from the Pilgrim Formation in the Little Snowy Mountains, Montana, and Hu and Li (1971, p. 171, pl. 2, figs. 1–37, text-fig. 2a–m) illustrated many specimens, including an essentially complete ontogenetic series. Material has subsequently been assigned from the Riley Formation, Texas ( Palmer, 1955, p. 727, pl. 80, figs. 8, 10), the Wasatch Mountains, Utah (Hu, 1971, p. 87, pl. 13, figs. 1–29, text-fig. 42), the Rabbitkettle Formation, Northwest Territories, Canada ( Pratt, 1992, p. 82, pl. 31, figs. 17–21), and the Deadwood Formation, South Dakota ( Stitt, 1998, p. 1038, fig. 6.14). Many of these records involve sparse, poorly preserved material, and the presence of a median occipital spine has possibly led to the identification of any Cedarina cranidia bearing such a spine as C. cordillerae . The species, its putative distribution, and the quality of the evidence comprise another example of the common phenomenon discussed by Adrain and Westrop (2005), in which inadequate, or inadequately illustrated, material from geographically widespread areas are assigned to species that are themselves poorly documented. Although the various sets of material are generally similar, the available quality and numbers of both specimens and illustrations simply preclude modern systematic evaluation. Cedarina cordillerae differs from C. schachti and all other species of Cedarina in its median occipital spine. It is similar to C. vale , and differs from C. schachti , in having a posteromedian deflection of its anterior border furrow.

Cedaria prima Lochman in Lochman and Duncan, 1944, from the Pilgrim Formation, Montana, is based on mostly flattened material. It is distinguished from C. schachti by its shorter preglabellar field, less anteriorly divergent anterior facial sutures, much more anteriorly convergent axial furrows, apparently smaller eye, and longer pygidium.

Cedarina victoria Lochman in Lochman and Duncan, 1944, from the Pilgrim Formation in the Big Snowy Mountains, Montana, is characterized by very large and long lateral extensions of the posterior fixigenae and a long librigenal field. The cranidial morphology is not evident on the material from the Wind River Mountains of Wyoming assigned to the species by Lochman and Hu (1962, p. 23, pl. 3, figs. 9–14), which seems to represent a separate species. Cedarina victoria is further distinguished from C. schachti in its narrower frontal area, longer anterior border, more forwardly positioned palpebral lobes, apparently smaller eye, and much narrower librigenal field.

Cedarina obtusans Duncan in Lochman and Duncan, 1944, from the Pilgrim Formation in the Big Snowy Mountains, Montana, is a very distinctive species, characterized by a very long anterior border and very wide anterior part of the librigenal lateral border. It further differs from all other species in the possession of a pygidium with a pair of posteriorly directed pleural spines on the first segment.

Cedarina dakotaensis Stitt, 1998 , from the Deadwood Formation, Black Hills, South Dakota, was erected on the basis of material mostly preserved as coarse molds in a sandstone. It is not clear that all of the sclerites assigned by Stitt are conspecific. One librigena ( Stitt, 1998, fig. 6.10) in particular appears to have a much longer field than either of the other examples ( Stitt, 1998, fig. 6.8, 6.12). One assigned pygidium ( Stitt, 1998, fig. 6.11) is considerably longer and narrower than the others. The holotype cranidium ( Stitt, 1998, fig. 6.6) differs from those of C. schachti in the possession of a posteromedially inflected anterior border furrow, less anteriorly divergent anterior facial sutures, smaller palpebral lobes, and longer, narrower posterior fixigenae.

Figures

FIGURE 5. Cedarina schachti n. sp., from the Weeks Formation (Marjuman; Cedaria Zone), northern House Range, Millard County, western Utah, USA. Dorsal exoskeleton lacking pygidium, holotype, FMNH PE 57116, dorsal view, x 12.

FIGURE 6. Cedarina schachti n. sp., from the Weeks Formation (Marjuman; Cedaria Zone), northern House Range, Millard County, western Utah, USA. Dorsal exoskeleton, paratype, SUI 104476, dorsal view, x 12.

FIGURE 7. Cedarina schachti n. sp., from the Weeks Formation (Marjuman; Cedaria Zone), northern House Range, Millard County, western Utah, USA. Dorsal exoskeleton (internal mold), SUI 102868, dorsal view, x 12.

FIGURE 8. Cedarina schachti n. sp., from the Weeks Formation (Marjuman; Cedaria Zone), northern House Range, Millard County, western Utah, USA. A. Anterior part of dorsal exoskeleton, USNM 437975, x 12. B. Anterior part of dorsal exoskeleton, USNM 437968, x 12.