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A New Araeoscelid Reptile, Zarcasaurus Tanyderus, from The

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A New Araeoscelid Reptile, Zarcasaurus Tanyderus, from The A newarceoscelid reptile, Zarcasaaras tanyderus, fromthe Gutler Formation (Lower Permian) of north-centralNew Mexico byDonald B. Brinknan,Curator, Tyrrell Museum of Palaeontology,Drumheller, Alberta, David S Berman,Associate Curator, Section of Vertebrate Fossils, Carnegie Museumoi NaturalHistory, Pittsburgh, PA, and DavidA. Eberth,Graduale Student, Department ol Geology, University of Toronto, Toronto, 0ntario A new genus and species of araeoscelid that Petrolacosauruswas related to the cap- skull, and are interpreted as an adaptation reptlle, Zarusaurus tanuderus, is described torhinomorphs.It alsohas been argued thlt to a specializeddiet that probably included on the basisof a partiai jaw and disarticu- Petrolacosaurusbelongs to a group of archaic protectedby a heavy exoskel- postcranial invertebrates lated elements from the Cutler mammal-likerep- importantlv this theory is ex- (Lower edaphosaursof the early eton. Most Formition Permian) of north-cen- a lower tral New Mexico. It is the first reoresenta- tile pelycosaurs(Stovall, Price, and Romer, tendedto suggestthat the absenceof tive of this family to be reported from that 1956).Most recently,a redescriptionof Pe- temporal fenestra in Araeoscelismay be the state, and it is considered closely related to trolacosaurusbv Reisz0.977 , 1981\has estab- result of a secondaryclosure. These conclu- Araeoscelis.Z. tanyderus possesses a com- lishedfirmly 6oth its positionas a primitive sions prompted a somewhat revised classi- bination of primitive and derived features diaosid and its close relationship with Ar- fication in which Araeosceliswas assignedto with respeci to Araeoscelis, indicating that aeoicelis.Previously undescribed specimens the AraeoscelidaeWilliston, 1910, and Petro- they could not have had a direct ancestor- of Araeoscelispresently under study (Reisz, lacosaurusto the PetrolacosauridaePeabody, descendant relationship. Berman,and Scott,in preparation)have pro- 1952;both families were united under the vided additionalinformation that greatlyex- suborderAraeoscelidia Williston, 1913.Other pands upon our assessmentof the generathat have been included in this sub- Introduction phylogenetic relationships of Araeoscelis,a order, but which are consideredtoo poorly The phylogeneticpositions of Araeoscelisand summary of which can be given here. Cur- known to be assignedto either famiiy, ar-e Petrolacosaurusare important to our under- rent evidenceindicates that Araeoscellsshares I(adaliosaurusCredner, 1889, and Dictybolus standingof the early diversificationof diap- a more recent common ancestorwith-that Olson, 1970. sid reptiles.Araeoscelis is a small,lightly built is, it is more closelyrelated to--Petrolacosau- The new araeosceliddescribed herc as Zar- reptile from the Lower Permianof Texasand rus than with the captorhinomorphs,and that casaurustanyderus consists of a partial, dis- Oklahoma (Vaughn, 1955;Simpson, 1979). both genera share a more recent common articulatedskeleton collected by the authors In the most recent detailed descrintion of ancestorwith eosuchiansthan with the cap- during the summer of 1982from the Cutler Araeoscelis,Vaughn (1955)concluded that it torhinomorphs. Formation (Lower Permian) near the village is bestconsidered a lizard-likeexperiment of Together, Araeoscelisand Petrolacosaurusof Arroyo del Agua in Rio Arriba County, the anapsid captorhinomorph reptiles. He representthe earliest,most primitive known north-centralNew Mexico (Fig. 1). The dis- argued that, exceptfor such featuresas the stagein theadaptive radiation of the diapsid covery was reported in a preliminary paper upper temporal fenestra,specialized denti- reptiles. This relationship is strongly sup- on the sedimentology and paleontology of tion, elongatelimbs, and elongate cervical ported by their postcranialskeletons that ex- the Lower Permianred-bed deposits of north- vertebrae,Araeoscelis resembles in most re- hibit only minor differences,but, most central New Mexico (Eberth and Berman, spectsthe primitive membersof the group. importantly, they share numerous derived 1983).Z. tanyderusrepresents the first record On the basis of better preservedearly cap- feafures.Cranial differencesbetween the two of an araeosceloidfrom New Mexico. It is torhinomorphs, Carroll (1959)agreed wiih genera,on the other hand, aremore marked. more closely related to Araeoscelisthan to Pe- Vaughn's assessment.Romer (1956, 1966, They are recognizedas providing Araeoscelistrolacosaurusand is, therefore, assigned to 1967),on the other hand, placed Araeoscelis with a more massive, sturdily constructed the Araeoscelidae. with a number of poorly known, early (Per- mian and Triassic) forms generally referred to asprotorosaurs, which he regardedas an- cestralto the sauropterygians(plesiosaurs, nothosaurs,and placodonts).The protoro- saurs,as defined bv Romer,are now believed to be a ratherdiverse assemblage of distantly related forms (Kuhn-Schnyder, 1967; Brink- man, 1981;Chatterjee, 1980; Carroll , 7981), and there is little evidenceto suggestthat Araeoscelisis closely related to any of them (Vaughn,1955). The controversyof the phylogeneticaffin- ities of Araeoscelishas seemingly been re- solved with the demonstration of its close relationship with Petrolacosaurus,a diapsid reptile of lizard-likeproportions from the Late Pennsylvanianof Kansas.Petrolacosaurus was originally describedby Peabody(1952), who believedit to be closelyrelated to the eosu- chians,the most primitive group of diapsid reptiles, with strong ties with the captorhi- nomorphs.Vaughn (1955)recognized the close similarity between Araeoscelisand Petrolaco- L--.-- saurusand even suggestedthat they may be- Iong to the same family, thereby implying FIGURE l-Locality of Zarcasnurustanyderus, Rio Arriba County, north-central New Mexico. May 1984 Nau MexicoGeology Systematicpaleontology of an ancient river svstem. The limited ex- TABLE 1-Measurements (in mm) of vertebrae of Class Rsprrlre tents of the crevasse channels suggest the Zarcasaurustanyderus gen. et sp. nov., CM 47704. 2 is the height SuborderAnaeoscrlron Williston, 1913 proximity of interchannel pond and./or marsh f. is the greatestlength of centrum, the centrum at the anterior end, 3 is the trans- Family AnaroscEuoanWilliston, 1910 environments where such channels would of width of the centrum at the anterior end, 4 Zanceseunus, new genus verse quickly lose their U-shape morphology. is the height of the centrum at the posterior end, Tvpr spnclss:Zarcasaurus tanyderus nsp. DIacNosrs-Same as for the genus. 5 is the transverse width of the centrum at the Eryuor-ocv-Refers to the Agua Sarca, a posterior end, and 5 is the length of the neural smallcreek about 3 km northwest of the type Description and comparison arch pedicle. locality;pronounced Zarca and spelledas such All of the elements assigned to the holo- Vertebra on early maps and publications (Langston, type, CM 41704,werc collected from the sur- 1es3). face and had eroded out of a single slope. Axis 2.8 3.5 7.5 DracNosrs-A small araeoscelid closely re- Although only two elements (dorsal verte- Midcervical 77.2 4.0 4.6 3.5 3.8 8.5 lated to Araeoscelisand characterized by the brae) were articulated, all the elements were Posteriorcervical 8.6 3.5 3.7 3.1 3.9 4.3 following derived features: cervical verte- found closely associated. None of the parts Dorsal 5.9 2.8 3.9 3.2 3.9 3.4 brae are longer, with central lengths exceed- is duplicated and all are of an appropriate Dorsai 5.0 3.4 3.5 3.3 4.0 3.4 ing those of the dorsals by as much as two size to have belonged to a single individual. times; absence of a prominent notch on the No bones were found associated with CM distal edge of the astragalus that separates 41704 that would indicate the presence of the articular facets for the fourth distal tarsal another form of similar size. For these rea- tentative, as is identification of the prearti- and centrale. Primitive features that distin- sons, CM 47704is considered to represent a cular-angular contact near the ventral mar- gdsh Zarcasaurusfrom Araeoscelisinclude: the single individual that probably was repre- gin of the jaw fragment. In its possession of humerus lacks ectepicondylar foramen; a sented originally by a greater part of artic- a precoronoid, Zarcasauruswould more closely supracondylar process is present on the pos- ulated skeleton. approach Araeoscelis than Petrolacosaurui. terior condyle of the femur; a concave area Lowrn 1ew-The lower jaw is represented There is no evidence of a postsplenial in Zar- of finished bone separates the lateral and me- by a short section of the left ramus just an- casaurus.The postsplenial is absent in Ar- dial articular surfaces on the proximal end terior to the adductor fossa (Fig. 2). It in- aeoscelis.but is present in Petrolacosaurusas of the tibia; the tibial facet of the astragalus cludes the posterior end of the dentary, which a moderate-sized element wedged between is convex and not developed into a ridge- includes one emptv socket and two incom- the angular and prearticular at the level of and-trough pattern. plete teeth. The more complete tooth is miss- the coronoid. ing only its tip; this is possibly a result of VnnrpnnaE-Three cervical and five dorsal Zarcasaurus tanyderus, new species wear. The tooth is stout, like those of 4r- vertebrae of varying degrees of complete- Ervrr.rorocv-Derived from the Greek tany, aeoscelis,rather than like the slender teeth of ness and fragments of centra comprise the long, and deros, neck, referring to the spec- Petrolacosaurus,though it lacks the
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