Contents ABSTRACT 5 GENUS DREPANOISTODUS 25 D. suberectus, subsp. A, n. subsp. 25 INTRODUCTION 5 GENUS HISTIODELLA 25 OBJECTIVES 5 H. donnae, n. sp. 25 PROCEDURES 5 GENUS JUANOGNATHUS 26 FIGURED SPECIMENS 6 J. hayesi, n. sp. 26 COMMENTS ON TAXONOMY 6 J. jaanussoni 26 PREVIOUS WORK 7 J. variabilis 27 FAUNAL EVALUATION 8 CORRELATION 9 J.? n. sp. 1 27 GENUS LOXODUS 27 SYSTEMATIC PALEONTOLOGY 10 L. bransoni s.f. 27 GENUS ACANTHODUS 10 GENUS MACERODUS 28 A. lineatus s.f. 10 dianae 28 A. uncinatus s.f. 10 GENUS MICROZARKODINA 28 A. sp. s.f. 10 M. ? cf. M. marathonensis 28 GENUS ACODUS 10 GENUS OELANDODUS 29 A. delicatus 10 O.cf. O.costatus 29 A. deltatus deltatus 12 O.cf. O.elongatus 29 A. oneotensis s.f. 12 GENUS OEPIKODUS 30 A.? russoi 13 O. communis 30 A. triangularis 13 O.? n. sp. 31 GENUS A. sp. A s.f. 14 OISTODUS 31 A. sp. indet. 14 O. forceps s.f. 31 GENUS ACONTIODUS 14 O. gracilis s.f. 32 A. iowensis s.f. 14 A. propinquus s.f. 14 O.cf. 0. inaequalis s.f. 32 O. n. sp. 32 A. aff. A. propinquus s.f. 14 A. staufferi s.f. 15 O. cf. 0. lanceolatus 33 GENUS CLAVOHAMULUS 15 O. ? lecheguillensis, n. sp. 33 C. densus s.f. 15 O. mehli s.f. 33 C. lemonei, n. sp. 15 O. cf. O. multicorrugatus 35 C. n. sp. A 16 O. cf. O. parallelus s.f. 35 O. cf. O. pseudoramis s.f. 35 GENUS CORDYLODUS 16 O. aff. O. selenopsis s.f. 35 C. angulatus s.f. 16 C. intermedius s.f. 17 O. ? cf. O. ? striolatus 35 C. lindstromi s.f. 17 O. vulgaris s.f. 35 O. sp. s.f. 36 C. rotundatus s.f. 18 GENUS CRISTODUS, N. GEN. 18 O. sp. 1 s.f. 36 O. sp. 2 s.f. 36 C. loxoides, n. sp. 18 GENUS DISTACODUS 19 GENUS ONEOTODUS 36 D. expansus s.f. 19 O. gracilis s.f. 36 GENUS DREPANODUS 19 O. simplex s.f. 36 D. aff. D. amoenus s.f. 19 O. cf. 0. variabilis s.f. 36 D. arcuatus s.f. 19 O.? sp. A s.f. 37 ?D. cf. D. arcuatus s.f. 20 O.? sp. B s.f. 37 D. concavus s.f. 20 GENUS PALTODUS 37 D. cf. D. conulatus s.f. 20 P. bassleri 37 D. ? gracilis s.f. 20 P. comptus s.f. 37 D. pandus s.f. 20 P. spurius s.f. 37 D. parallelus s.f. 21 P.? sweeti s.f. 38 D. cf. D. planus s.f. 21 P.? sp. s.f. 38 D. proteus s.f. 21 P. n. sp. s.f. 38 D. pseudoconcavus, n. sp. s.f. 21 GENUS PA RACORDY LODUS 38 D. sculponea s.f. 22 P. gracilis 38 D. toomeyi s.f. 22 GENUS PROTOPANDERODUS 39 D. aff. D. sp. 3 of Serpagli (1974) s.f. 22 P. asymmetricus s.f. 39 D. sp. s.f. 22 P. elongatus 39 D. n. sp. 1 s.f. 22 P. gradatus 39 D. n. sp. 2 s.f. 24 P. cf. P. gradatus 39 D. n. sp. 3 s.f. 24 P. leei, n. sp. 39 D. n. sp. 4 s.f. 24 P. leonardii 40 D.? n. sp. 5 s.f. 24 P. longibasis 40 D. n. sp. 6 s.f. 24 P. cf. P. rectus 40 D. n. sp. 7 s.f. 25 P.? n. sp. 1 s.f. 40 P. ? n. sp. 2 s.f. 41 iv GENUS R EUTTERODUS 41 S. pseudoquadratus s.f. 50 R. andinus? 41 S. aff. S. pseudoquadratus s.f. 50 R. borealis, n. sp. 41 S. quadraplicatus s.f. 50 GENUS SCANDODUS 42 S. rex s.f. 50 S. aff. S. flexuosus s.f. 42 S. rex paltodiformis 51 S. furnishi s.f. 42 S. sexplicatus s.f. 51 S. aff. S. furnishi s.f. 42 S. sulcatus s.f. 51 S. cf. S. furnishi s.f. 42 S. triplicatus s.f. 52 S. aff. S. mysticus s.f. 44 S. variabilis s.f. 52 S. cf. S. pipa s.f. 44 S. n. sp. 1 s.f. 52 S. n. sp. 1 s.f. 44 S. n. sp. 2 s.f. 52 S. n. sp. 2 s.f. 44 GENUS S PATHOGNATHODUS 53 S. n. sp. 3 s.f. 45 "?S. sp." s.f. 53 S. n. sp. 4 s.f. 45 GENUS T RIANGULODUS 53 GENUS S COLOPODUS 45 T. cf. T. brevibasis 53 S. abruptus, n. sp. s.f. 45 GENUS U LRICHODINA 53 S. acontiodiformis, n. sp. 46 U. abnormalis s.f. 53 S. acontiodiformis angularis, n. subsp. s.f. 46 U. deflexa s.f. 55 S. bolites, n. sp. 46 U. wisconsinensis s. f. 55 S. cornutiformis s.f. 47 U. n. sp. 1 s.f. 55 S. emarginatus s.f. 47 U. n. sp. 2 s.f. 55 S. filosus s.f. 47 U. n. sp. 3 s.f. 56 S. filosus xyron, n. subsp. s. f. 47 New Genus A of Sweet and others, 1971 56 S. floweri, n. sp. 47 New Genus A, n. sp. A 56 S. gracilis 48 New Genus B, n. sp. s.f. 57 S. kelpi, n. sp. s.f. 48 REFERENCES 58 S. parabruptus, n. sp. s.f. 49 PLATES 1-28 61 S. aff. S. parabruptus, n. sp. s.f. 49 S. carlae, n. sp. s.f. 49 INDEX 119 TABLE 1—Distribution and abundance of conodonts recovered from the Scenic Drive section in back pocket FIGURES 1—Isopach map of El Paso Group 5 2—Map of southern end of Franklin Mountains showing location of sampled section 6 3—Chart showing subdivisions used by various workers for the El Paso Group in westernmost Texas 7 4—Acanthodus lineatus—Drepanodus proteus (views) 11 5—Drepanodus aff. D. sp. 3 of Serpagli—Oistodus n. sp. (views) 23 6—Oistodus? lecheguillensis n. sp.—Protopanderodus? n. sp. 2 (views) 34 7—Scandodus aff. S. flexuosus—Scolopodus parabruptus n. sp. (views) 43 8—Triangulodus cf. T. brevibasis—Ulrichodina deflexa (views) 54 5 Abstract Samples were taken at 20-ft (6-m) intervals through a 1,345-ft (410-m) section of the El Paso Group (Lower Ordovician) in the southern Franklin Mountains of westernmost Texas and southern New Mexico as part of a detailed study of the conodonts of that unit. The succession is predominantly dolostone in the lower part and limestone in the upper part of the section. All of the 1-kg samples processed yielded conodonts. More than 16,500 conodont elements were recovered, and preservation of the conodonts ranges from poor to good. Altogether, 145 species are described and/or discussed taxonomically. The conodonts are distributed among 30 genera, of which Cristodus is new. Of the 145 species, 41 are discussed in terms of multielement taxonomy, and 104 are discussed in form tax- onomy. New species named herein include: Clavohamulus lemonei, Cristodus loxoides, Drepanodus pseudoconcavus s. f. , Histiodella donnae, Juanognathus hayesi, Oistodus? lecheguillensis, Protopanderodus leei, Reutterodus borealis, Scolopodus abruptus s.f., Scolopodus acontiodiformis, S. acontiodiformis angularis, S. bolites, S. filosus xyron, S. kelpi, S. parabruptus, S. carlae, and S. floweri. The conodonts range in age from early (but not earliest) to late Canadian. North American conodont Fauna C is represented in the lowermost beds of the El Paso Group in west Texas. Diagnostic conodonts of Fauna D appear between 180 ft (55 m) and 300 ft (91.5 m) above the base of the section. Elements of Fauna E appear abruptly at 839 ft (255.7 m). Fauna 1 is represented in the uppermost El Paso; diagnostic elements of this fauna appear between 1,140 ft (347.5 m) and 1,300 ft ( 396.2 m) above the section base. Correlation by means of conodonts is discussed, and the El Paso faunal sequence is compared with faunas from Lower Ordovician conodont- bearing successions in the United States and abroad. Introduction Conodonts of Early Ordovician age are as yet quite Procedures poorly known , especially considering the relatively widespread occurrence of rocks of that age. Lindström ( Samples of 2-3 kg were taken at approximately 20-ft ( 1971) and Ethington and Clark (1971) have summar- 6.1-m) stratigraphic intervals along a section measured ized the knowledge of Early Ordovician conodonts of across the El Paso Group in the southern Franklin Europe and North America. Contributing to the paucity Mountains in westernmost Texas in May 1973 (Fig. 1). of definitive studies of Early Ordovician conodonts, at The thickness was measured across strike using Brunton least in North America, is the widespread occurrence compass and Jacob's staff. The measured section (Fig. 2) through this interval of dolostones that are difficult to is just south of the section described by Cloud and disaggregate. Sections that yield to acidizing techniques Barnes (1948). I measured 1,345 ft (410 m) of El Paso and that are partly to nearly continuous through the along the traverse. This thickness is greater than the ap- Lower Ordovician do exist, and several of these sections proximate 1,000 ft (305 m) given by Richardson (1909) are presently the objects of intense conodont study. and less than the 1,590 ft (485 m) measured by Cloud In North America, important sequences of this age and Barnes (1948). Kottlowski (1963, p. 16) stated that " being studied are those of the Great Basin; the Arbuckle in the southern Franklin Mountains, the El Paso Group of southern Oklahoma; the Canadian Rocky Limestone is 1,355 or 1,590 feet thick (Cloud and Mountains; the northern and central Appalachians; the Canadian Arctic; and the El Paso Group of western Texas, New Mexico, and Arizona.