an eurypterid (adelophthalmus sp.) from a plant-rich lacustrine facies ...

Lucas, S.G., Zeigler, K.E. and Spielmann, J.A., eds., 2005, The Permian of Central New Mexico, New Mexico Museum of Natural History and Science Bulletin No. 31

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AN EURYPTERID (ADELOPHTHALMUS SP.) FROM A PLANT-RICH LACUSTRINE FACIES OF UPPER PENNSYLVANIAN STRATA IN EL COBRE CANYON, NEW MEXICO JOSEPH T. HANNIBAL1, SPENCER G. LUCAS2, ALLAN J LERNER2 AND DAN S. CHANEY3 1

Cleveland Museum of Natural History, 1 Wade Oval Drive, Cleveland, Ohio 44106; 2New Mexico Museum of Natural History and Science, 1801 Mountain Road N.W., Albuquerque, NM 87104; 3Department of Paleobiology, P.O. Box 37012 NHB, MRC-121 Smithsonian Institution, Washington, DC 20013-7012

Abstract—A large carapace (dorsal shield) of a somewhat deformed eurypterid prosoma found associated with plant specimens in Upper Pennsylvanian strata of the El Cobre Canyon Formation (Cutler Group) of El Cobre Canyon, Rio Arriba County, New Mexico, is assigned to the genus Adelophthalmus, a rare, but widespread, upper Paleozoic genus. The specimen, preserved in plant-rich layers of a gray lacustrine deposit within a sequence of red siltstones and sandstones, is a good example of an occurrence of the genus in a nonmarine context. INTRODUCTION Eurypterids are rare components of upper Paleozoic faunas. Occurrences have been documented, however, at a number of sites in the Pennsylvanian and Permian of North America, including the Pennsylvanian of western Pennsylvania (Hall, 1884); the Dunkard Group (Pennsylvanian and Permian) of southwest Pennsylvania (Scott, 1971); Mazon Creek (Desmoinesian), Illinois (Kjellesvig-Waering, 1963; Plotnick, 1997); Hamilton Quarry (Virgilian), Kansas (Dunbar, 1924; Kues, 1988); the Upper Pennsylvanian of Iowa (Schram, 1984); the Pennsylvanian and Permian of southeast Nebraska (Barbour, 1914; Dunbar, 1924, p. 199-201; see also Kues, 1988, p. 102); the Pine Shadow Member of the Atrasado Formation (Missourian) at the Kinney Brick Quarry in the Manzanita Mountains of central New Mexico (Kues, 1985); and the Red Tanks Member of the Bursum Formation (Virgilian) at Carrizo Arroyo in the Lucero uplift of central New Mexico (Kues and Kietzke, 1981). The purpose of this paper is to describe and briefly discuss Cleveland Museum of Natural History (CMNH) 13578, a specimen recently discovered in El Cobre Canyon, in northern New Mexico (Fig. 1). The specimen is assigned to the genus Adelophthalmus, a widespread, albeit rare, upper Paleozoic genus, representatives of which have been reported from central New Mexico (Kues and Kietzke, 1981; Kues, 1985) as well as Kansas (Dunbar, 1924; Kues, 1988) and other localities in North America as well as Europe (see, for example, Waterston, 1968) and Asia. Measurements, and most terminology, were adapted from Kues and Kietzke (1981). PROVENANCE The fossil described here was collected at New Mexico Museum of Natural History locality 4564, in the El Cobre Canyon Formation of the Cutler Group (Lucas and Krainer, 2005) in El Cobre Canyon, Rio Arriba County, New Mexico (sec. 9, T24N, R6E) (Fig. 1). The fossiliferous strata at locality 4564 are gray and greenish gray silty/ sandy shale of an areally restricted lacustrine deposit. These strata also yield an extensive paleoflora first noted by Smith et al. (1961). Plants collected from that level (United States National Museum locality 42120) include: Macroneuropteris scheuchzeri, Alethopteris bohemica, pteridosperm axes, Calamites sp., Sphenophyllum verticillatum, Sphenophyllum angustifolium, Pecopteris sp., Sphenopteris biturica, and Nemejcopteris feminaeformis, an assemblage typical of Late Pennsylvanian wetland floodplains (see DiMichele and Chaney, 2005, for more on the flora). The megafossil plants, palynomorphs from locality 4564 (J. Utting, written commun., 2001) and stratigraphically-equivalent vertebrate fossils such as Desmatodon, indicate a Late Pennsylvanian (probably Virgilian) age (Lucas and Krainer, 2005). Locality 4564 is part of a thick succession of red-bed siliciclastic sediment deposited in a nonmarine, fluvial setting across the Pennsylvanian-Permian boundary

FIGURE 1. Measured stratigraphic section and location map at locality 4564 in El Cobre Canyon, Rio Arriba County, New Mexico.

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FIGURE 2. Adelophthalmus sp., CMNH 13578, overall view of slab containing specimen and plant material. Eurypterid prosoma is at top of slab. Scale equals 1 cm.

(Eberth and Miall, 1991). SYSTEMATIC PALEONTOLOGY Adelophthalmus Jordan and von Meyer, 1854 Remarks: We follow Kues and Kietzke (1981, p. 712) in our usage of the genus Adelophthalmus in preference to Anthraconectes Meek and Worthen, 1868. Adelophthalmus sp. Figs. 2-6 Material: A single eurypterid specimen, CMNH 13578 (Figs. 2-6), consisting of a large, flattened, somewhat distorted, prosoma preserved in gray shale with abundant plant material, including seed ferns and pieces of wood. The shale containing the fossils is thinly bedded and slightly undulatory, so the eurypterid is preserved on a gently curving surface, and thus is not entirely in one plane. The left side of the specimen is more complete and less distorted than the right side. The cuticle of the prosoma is carbonized and crazed. Description: Carapace (dorsal shield) of prosoma broad, semicircular in outline, anterior/lateral edge convex, posterior edge slightly convex. Thin rim borders at least anterior of carapace. Margin of carapace emarginate/inflected, with unidentified feature superimposed, or possibly part of carapace folded. Length of carapace 30 mm; width 46 mm. Length-to-width ratio of carapace 0.65 mm. Large compound eyes separated by about 12 mm; lateral edge of left eye located about 12 cm from maximum width of prosoma. Lateral eyes kidney shaped (reniform), best preserved (left) eye 2.7 mm wide, 4.5 mm long using method of Kues and Kietzke (see Table 1), about 4.6 mm long measured along long axis of eye (but exact anterior boundary of eye uncertain), eyes composed of numerous facets. Left eye with raised rim. Semicircular rim on carapace, having obscure origination probably near anterolateral corner of eye, extends anteriad in arc to within 3.6 mm of anteriormost point of prosoma; rim may have defined anterior margin of raised area (glabellalike form of Kjellesvig-Waering, 1948, p. 41) in life; right section of rim somewhat irregular; rim defines areas of slightly different ornamentation. Two longitudinal lobes located between eyes, extending posteriad from semicircular rim, or at least from well anterior of eyes, to within 11 mm of carapace posterior. Lobes converge anteriad, separated by shallow depressed area posteriad. Boundary of left longitudinal lobe well defined from just anterior to interior midpoint of eye, posteriorad and then mediad, forming one-half of presumed U-shaped lateral and posterior border embracing both lobes.

FIGURE 3. Adelophthalmus sp., CMNH 13578, camera lucida drawing showing parts identified in text.

Median ocelli and ocellar tubercle not apparent. Much of carapace surface covered with scalelike (resembling imbricated shingles) to triangular ornamentation; ornamentation patchy in distribution. Largest ornament (up to 1.2 mm wide) on longitudinal lobes, this ornament scalelike, with strongly defined, raised, convex posterior borders, and with low, poorly developed, subtly convex, anterior borders; long axes of ornamentation more-or-less perpendicular to central axis of carapace. Towards posterior of lobes, and beyond, ornamentation more raised, pustulelike. Such ornament elongate, flat-topped, with concave anterior and posterior borders. Lateral ornamentation composed of smaller, sharply triangular forms (mucrones), with raised point of triangle directed away from eyes. Most triangular forms laterad to eyes less than 0.3 mm long and less than 0.3 mm wide. Triangular forms become larger (up to about 0.6 mm wide) mediad, pointed end oriented towards posterior of carapace. Scalelike ornamentation grades into triangular ornamentation in places where two types meet; both types intermixed in places. Patches of ornament located between lateral eyes and posterior carapace border ranges from rounded forms to triangular shaped forms. Ornamentation subdued between longitudinal lobes, directly behind eyes, and in two elongate regions extending anteriad from center of posterior border of carapace at about 30 degree angle. Lateral ornamentation of (?)underside of carapace (seen where carbonized cuticle flaked off) ridgelike, composed of gently curved terrace lines running more-or-less parallel to width of specimen, most less than 1 mm long, but up to 3 mm long. Medial ornamentation on (?)underside of carapace punctate anteriorly from semicircular rim to anterior of carapace. Punctae approaching 0.3 mm in width, resulting in rounded depressions, posterior to rim in glabellalike area. Edges of carapace marked with fine striae oriented parallel to rim. See Table 1 for additional measurements. Discussion: The specimen is carbonized, as are specimens described by Kues and Kietzke (1981) from Carrizo Arroyo and that described by Kues (1985) from Kinney Quarry. Because of the delicate nature of the remaining cuticle, the specimen was not whitened for photography. The prosoma is very large for the genus, about equal in width to the largest prosoma of A. luceroensis, and about equal in length to the largest specimen of A. mansfieldi reported by Kues and Kietzke (1981, text-fig. 9). The El Cobre carapace is also larger than the largest prosomas measured for A. mazonensis, A. sellardsi, and Hamilton Quarry specimens assigned to Adelophthalmus aff. A. mazonensis (Kues and Kietzke, 1981, text-fig. 9; Barry Kues, written commun., 2005). Because of the inflection on the anterior of the carapace, it is not clear if the El Cobre specimen has a triangular spur, but this cannot be

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FIGURE 5. Adelophthalmus sp., CMNH 13578, left side of specimen, showing various types of ornamentation. Scale equals 1 cm.

FIGURE 4. Adelophthalmus sp., CMNH 13578, carapace. Scale equals 1 cm.

ruled out. As with specimens from Kinney Quarry (Kues, 1985, p. 2627) and elsewhere, some of the features seen on the carapace may reflect ventral features impressed upon the dorsal side of the specimen during fossilization. The semicircular rim, for example, may reflect the ventral marginal prosomal plate (ventral shield of Kjellesvig-Waering, 1963, fig. 46, and Kues, 1985, p. 27). The distinct lateral and posterior boundary of the left longitudinal lobe, and the subrectangular structure impressed into the carapace, and obscuring the right eye, may also represent underlying features. Identification to genus level is fairly certain, but identification to a species is difficult as species belonging to the genus have generally similar dorsal anatomy and there is considerable variation in specimens that have been assigned to individual species. The El Cobre specimen shares characters with several species in the genus. The length-towidth ratio of the El Cobre carapace (circa 0.65) is extremely close to the mean ratio (0.64) of the Red Tanks specimens assigned to A. luceroensis Kues and Kietzke, 1981, and not far from the ratio (0.69) of a specimen assigned to A. luceroensis from Kinney Quarry (Kues, 1985, p. 28). It is also within the range of the Hamilton Quarry specimens (0.60-0.75) assigned to Adelophthalmus aff. A. mazonensis by Kues (1988), and is within the range of other species as well (Kues and Kietzke, 1981, table 6). The length-to-width ratio, however, must be viewed with caution as much depends on preservation (Roy Plotnick, written commun., 2005). The eye length/prosoma length ratio of the El Cobre specimen (0.15) is substantially lower than that of the Red Tanks

(mean values of 0.21 to 0.29 with larger specimens at the low end) and Kinney Quarry (0.25) specimens, but in the range of the Hamilton Quarry specimens (0.11-0.31). The ocular length/postocular length of the El Cobre specimen (0.63) is well withing the range of the Red Tanks specimens (although, as a larger specimen one might have expected it to have a larger ratio) as well as the Hamilton Quarry specimens, and near that of one of the Kinney Quarry specimens. The longitudinal lobes are roughly similar in dimensions to those of the unnamed Hamilton Quarry eurypterid (Kues, 1988, fig. 1G). The anterior groove and Ushaped lateral lobe border seen on this specimen, however, are similar to that of Adelophthalmus mansfieldi as illustrated by Hall (1884, pl. 4, fig. 2) and by Clarke and Ruedemann (1912, fig. 43). The ornamentation of the specimen is distinctive. Much of the ornamentation of the El Cobre specimen is larger than that of Adelophthalmus cf. A. wilsoni whose ornamentation Waterston (1968, p. 2) described as being minute, but coarser medially (the general pattern of the El Cobre specimen). The pointed, triangular ornamentation resembles that of the ventral shield of A. mazonensis (KjellesvigWaering, 1963, fig. 46). The flat-topped pustulose forms somewhat resemble the irregular polygonal ornamentation described for a tergite of Mycterops (?)M. blairi Waterston (1968, p. 4; plate 1, fig. 1) and Mycterops sp. (Kjellesvig-Waering, 1963, fig. 55). The presence of two major types of ornamentation, scalelike and triangular/angular, is found in other species assigned to the genus Adelophthalmus, including A.

TABLE 1 1. Measurements* in mm of CMNH (Cleveland Museum of Natural History) 13578. carapace (prosoma) length carapace width carapace length-to-width ratio distance from anterior of carapace to semicircular rim on carapace distance from semicircular rim to posterior of U-shaped border of lobes distance from posterior of U-shaped border of lobes to posterior of carapace longitudinal lobe length compound eye length (left eye) eye length/carapace length inside distance between eyes (approximate) outside distance between eyes (approximate) distance from lateral edge of carapace to left eye distance from anterior of carapace to anterior of eyes (pre-eye distance) distance from posterior of carapace to posterior of eyes (post-eye distance) ratio of pre-eye/post-eye distance ratio

30 46 0.65 3.6 15 11 >11 4.5 0.15 12 19 12 10 16 0.63

* Terminology modified from Kues and Kietzke (1981, especially text-fig. 3). Most measurements are rounded to the nearest whole mm.

37 The ocellar lobe, however, is not always preserved in the Hamilton Quarry assemblage. CONCLUSIONS

FIGURE 6. Adelophthalmus sp., CMNH 13578, detail of left side. Left eye is to the upper right. Most ornamentation is triangular (composed of mucrones). Scale equals 1 cm.

sellardsi and A. mazonensis, but the distribution of coarse vs. fine ornament on those forms differ from that of the El Cobre specimen in detail (compare, for example, Figs. 3 to 5 with fig. 1 in KjellesvigWaering, 1948). Like the Hamilton Quarry specimens assigned to Adelophthalmus (Kues, 1988, p. 100), the ornamentation is larger and semilunar between the lateral eyes, and changes shape posteriorly. As detailed above, the El Cobre specimen resembles the Hamilton quarry Adelophthalmus material in a number of ways, but it also differs in some ways. The best preserved of the Hamilton Quarry material, for instance, has an ocellar lobe, lacking in the El Cobre specimen.

This record documents the occurrence of eurypterids in El Cobre Canyon, an area where the trackways of arthropleurids, gigantic terrestrial myriapods, have also been found (Lucas et al., 2005). Eurypterids have been found with arthropleurid and other myriapod body fossils at Mazon Creek, Illinois, and Cannelton, Pennsylvania (Hannibal, 1997). Care must be taken to distinguish the two taxa. (Note the close resemblance of what Hannibal (1997, fig. 6b) described as a lobe of the rosette plate of Arthropleura to a reniform eurypterid eye.) With some exceptions (see Schram, 1984, for one), most eurypterids lived in nonmarine environments during the Late Paleozoic, and the genus Adelophthalmus has been considered to be exclusively nonmarine (Plotnick, 1997, p. 209). The specimen described here, preserved in plant-rich lacustrine layers of a redbed sequence, is a good example of such an occurrence. The El Cobre eurypterid is the first specimen from New Mexico not assigned to A. luceroensis. El Cobre was geographically distinct from the other New Mexico eurypterid localities, Kinney Quarry and Carrizo Arroyo, during the Missourian/ Virgilian, in that it was further inland and more upland than these other more shoreward New Mexico localities. The differences between the El Cobre specimen and other New Mexico specimens may have resulted from adaptation to differing habitats and to intermittent geographic isolation, as suggested by Kues and Kietzke (1981, p. 727). ACKNOWLEDGMENTS Zarko Ljuboja, Andover, Ohio, first recognized that this specimen was a eurypterid. Greg Petusky, CMNH, took the photos. Roy Plotnick, University of Illinois, Chicago, made helpful comments on an early version of the manuscript and Barry Kues, University of New Mexico, kindly reviewed a later version. Bill DiMichele, United States National Museum, identified the plant species noted. The United States Forest Service permitted work on their land. This project utilized equipment purchased by National Science Foundation Award 0216039 grant to J. Keiper and others at the CMNH.

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