Cephalopod Aptychi from Los Loyos Limestone, Madera Group (Middle

wise not a probable candidate. Glyptosaurus sensustricto (Sullivan, 1.979)seems the most aptychifrom reasonabletaxonomic assignment based on Gephalopod tubercular arrangement and osteoderm size. LosMoyos Limestoro, Madera Group Biostratigraphic and biogeographic significance The discovery of cI. Glyptosaurusin the (MiddlePennsyluanian), BacaFormation of south-central New Mexico is significant in three ways: 1.)Glyptosaurus is a late Wasatchian-Uintan genus known from nearAlbuquerque, New Mexico Colorado, Utah, and Wyoming (Sullivan, 1979);its occurrence in the Baca Formation by Barry S. Kues,Department of Geology, University of New Mexico, Albuquerque, NM near Carthageis consistent with, though not conclusive proof of, the Bridgerian-age assignmentmade by Lucasand others (1982). Introduction sils, to discuss their relationships with the 2) Other glyptosaurs known from New Mex- cephalopod conchs in the fauna, and to pro- ico are from the San Basin and are of Aptychi are bivalved structures that prob- fuan vide a brief summary of the fauna itself, Paleoceneand early Eocene age (Sullivan, ably functioned asopercula on somecephalo- which includes some taxa not previously re- 1981);therefore, UNM BE-012 is the pods (see Yochelson,1983), although they ported from the Pennsylvanian of New Mex- youngest glyptosaur known from New Mex- have also been interpreted as cephalopod ico. Specimensmentioned and illustrated ico. 3) To our knowledge, UNM BE-012also lower jaws (Morton, 1981).Aptychi are here are in the University of New Mexico representsthe most southerly occurrenceof a known from many genera of Mesozoic Department of Geology paleontology collec- specimenthat apparently pertains to Glypto- ammonoids (Arkell, 1,957,p. L82) but are ex- tions and have been assigned UNM num- saurus. hemely rare in the Paleozoic.Only two finds bers. ACKNOWLEDGMENTS-Wethank Adrian of aptychi from the late Paleozoichave been Hunt and Donald Wolberg for field assist- reported. Closs and others (1964)noted Location and geologic setting ance in the BacaFormation, W. D. Turnbull aptychi in a unit containing the ammonoid (Field Museum of Natural History) for the Pseuilogastriocerasfrom the Permian of Utah, The assemblagereported herein was col- subloan of the Carnegie Museum Glypto- and Thompson and others (1980)described lected by the author, Kenneth Kietzke, and aptychi that, in life, were probably associated membersof a paleontology classfrom a road- saurusspecimen, and Richard Estes and firi Zidek for reading an earlier version of this with the nautiloid Lirocerasfrom the Bishop cuton theeast side of NM-I4,5.6mi (9.1km) Cap Member, Magdalena Formation (Des- south of the intersection of I-40 and NM-14 PaPer. moinesian), in Vinton Canyon, El Paso at Tijeras(Fig. 1). This Iocalityis just north of References County, Texas. The latter report is also im- the village of Cedro in the Manzano Moun- portant becauseit provides the first good cir- tains east of Albuquerque. The roadcut con- Gardner, J. H., 7910,The Carthage coal field, New Mex- ico: U.S. GeologicalSurvey, Bulletin 381,,pp. 452460 cumstantial evidence that some late sists primarily of light-brown to grayish- Lucas, S G , 1983,The BacaFormation and the Eocene- Paleozoicnautiloids may have possessed brown, sparsely fossiliferous, fissile mud- Oligocene boundary in New Mexico: New Mexico aptychi. Recently, well-preserved aptychi stones. Collections totalling approximately GeologicalSociety, Guidebook to the 34th field confer- have been discovered in the Middle Penn- 30 kg were made from severallevels within a pp ence, 787-192. sylvanian of central New Mexico, in an 2-m-thickinterval near the top of the roadcut, Lucas, S. G., Wolberg, D. L., Hunt, A , and Schoch, R M., 7982,A middle Eocenetitanothere from the Baca assemblagethat contains both ammonoid immediatelybelow a massivelimestone bed. Formation, south-central New Mexico: Journal of and nautiloid phragmocones. Theseunits are in the upper part of the Los Paleontology,v. 56, pp. 542-545 The purposeof this paper is to document Moyos Limestone (Madera Group) and are Sullivan,R. M,7979, Revisionof the Paleogenegenus in age, basedon fusulinid Glyptwaurus(Reptilia, Anguidae): American Museum a new occurrenceof these rare Paleozoicfos- IateDesmoinesian of Natural History, Bulletin,v.763, pp.7-72- -, 1981,Fossil lizards from the San Juan Basin, New Mexico;ln Lucas,S. G., Rigby, J. K., Jr., and Kues, B. S. (eds.), Advances in San Juan Basin paleontology: Uni- versity of New Mexico Press,pp 7G88 ,,Fort -, 1982,Fossil lizards from swain quarry Un- ion formation," middle Paleocene(Tonejonian), Car- bon County, Wyoming: Journal of Paleontology, v. 56, pp.9G7,0r0. Wilpolt, R. H., and Wanek, A. A., 1951,Geology of the region from Socorroand SanAntonio eastto Chupadera Sedillol Mesa, Socono County, New Mexico: U.S. Geological Suruey, Oil and Gas Investigations Map OM-121. Wilpolt, R. H., MacAlpin, A. J., Bates,R. L., and Vorpes, G.,1946, Geologicmap and stratigraphicsections of the Paleozoicrocks of Joyita Hills, Los Pinos Mountains, and northern Chupadera Mesa, Valencia, Tonance, and Socono Counties, New Mexico: U.S. Geological Survey,Oil and GasInvestigations Preliminary Map 61. BernolilloCounf y FIGURE l-Map showing aptychi locality (x) in Cedro Canyon, south of Tijeras November 1983 New Mexico Geology evidence at other localities (Myers and (1980), and the descriptive comments of ciesin the Los Moyos Limestone.Thompson McKay,1976). these authors, for the most part, are equally and others (1980)noted node fragments of Marine invertebratesare sparselybut rela- applicableto the Cedro specimens. The MetacocerasatVinton Canyon that indicated a tively evenly distributed through the aptychi smallestof the Vinton Canyon aptychi is 20 shell too large to be closed by an aptychus, horizon, and the invertebrate fossils within mm long, slightly larger than two of the three but no evidence exists for such large speci- the sampleswere examined and identified to measured Cedro specimens, but the largest mensof Metacocerasinthe Cedro assemblage. provide a general view of the fauna associ- Cedro specimen (Fig. 3) is slightly longer A full-sizedspecimen of M. cornutumhaving ated with the aptychi. than the largest Vinton Canyon specimen. a diameter of 70-90 mm would have had an Following the reasoning of Thompson and apertural diameter of approximately 30-40 Aptychi and cephalopods others (1980,pp.907-908), the Cedro aptychi mm, about the size that could have been Five aptychi and24 partial phragmocones are assignedto the form genus Cornaptychus coveredby a large aptychus. comprisethe remains of severaldifferent spe- sP. One other cephalopod in the Cedro ciesof cephalopodsin the assemblage.Com- A moderatenumber of cephalopod phrag- assemblagedeserves mention. It is the outer plete aptychi are paired structures consisting mocones were collected from the aptychi shell laver, without evidence of sutures or of right and left halves attachedat a symphy- horizon, but most were incomplete and ornamehtation, of one side of a moderately sis, but the specimensat hand are disarticu- many are poorly preserved.In all examples, large shell (UNM 5998)having a diameter of lated halves. One specimen (UNM 5991), the shells were flattened on bedding planes, 45 mm and an estimated apertural diameter however, does include both halves of an making it impossible to accuratelydetermine of about 25 mm (Fig. a). The umbilicus is aptychus still partially appressed (Fig. 2). cross-sectionalshape or apertural Propor- small and moderately deep, and the shell Eachhalf of an aptychus is roughly oval, very tions. Two ammonoid genera and at least appearsto be involute. On the basisof gener- thin shelled, has fine concentric growth lines three nautiloid genera are present in the al shell morphology, this specimen is very on the external surface, and has its apex dis- assemblage.Definite evidence of the associa- likely a nautiloid rather than an ammonoid, placedabout two-thirds of the distancealong tion, in life, of the aptychi with a particular and no observable features occur that pre- the symphysis. As noted by Thompson and cephalopod (for example, a shell preserved clude it from belonging to the Liroceratidae. others (1980),aptychi of this type superficial- with the aptychus covering its aperture) is Conceivably, the aptychi in the Cedro ly resemblebivalve mollusk shells. The three lacking; however, some speciesmay be dis- assemblagecould have come from specimens best preserved aptychi have the following missedas the possiblebearers of the aptychi of this cephalopod that were about the same dimensions:1) UNM 5991-length, t7 mm; on size considerationsalone. Both ammo- sizeor somewhat larger than the specimenat width, 9 mm; width/length, 0.53; 2) UNM noids are far too small to have borne the hand. 5996-length, 40 mm (est.); width, 19 mm aptychi. Most of the ammonoids are Anthra- (est.), width/length, 0.a8; 3) UNM 6005- coceras?,a small goniatitid having a maximum length, L8 mm; width, l.L mm; width/length, shell diameter in the Cedro assemblageof 0.61. approximately 18 mm. One fragmentary No significant differences are found be- ammonoid specimen is quite different from tween these specimensand those described Anthracoceras?in that it has fine. closelv and illustrated by Thompson and others spaced, transverse lirae covering the initiil half of the last whorl, fading to obscurity toward the aperture. Suture marks are not preserved in this specimen, but its external ornamentation resemblesthat of.Reticu- Ioceras.The

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