Hsiou et al., 2010 - Colombophis

Hsiou et al., 2010 - Colombophis

(Parte 1 de 4)

Reappraisal of the south American Miocene snakes of the genusColombophis, with description of a new species

ANNIE S. HSIOU, ADRIANA M. ALBINO, and JORGE FERIGOLO

Hsiou, A.S., Albino, A.M., and Ferigolo, J. 2010. Reappraisal of the South American Miocene snakes of the genus Colombophis, with description of a new species.Acta Palaeontologica Polonica55 (3): 365–379.

A redescription of the extinct snake genus Colombophis is presented, on the basis of new specimens from the late Mio− cene of southwestern Brazilian Amazonia, and those previously reported for the middle Miocene of Colombia and Vene− zuela.The reappraisal of Colombophis allows the recognition of a new species,C. spinosus sp. nov. The revised diagnosis of the genus is based on the midtrunk vertebrae, distinct from those of other snakes mainly in the features of the neural arch, position and shape of the neural spine, inclination of the zygapophyses, shape of the centrum, and development of the haemal keel. The affinities of Colombophis with “Anilioidea” are still unresolved; it is distinguished from all known extinct and extant “anilioids” due to its great vertebral size and the frequent presence of paracotylar foramina. The poste− rior paired apophyses of the haemal keel in some vertebrae, and the high neural spine of C. spinosus also contrast signifi− cantly with the “anilioid” genera, making the allocation of the genus into this probably paraphyletic group not well sup− ported. Here, we recognizedColombophisas a basal alethinophidian of uncertain relationships.

Keywords:Serpentes, Alethinophidia,Colombophis, Miocene, South America.

Annie S. Hsiou [anniehsiou@gmail.com] and Jorge Ferigolo [jorge.ferigolo@fzb.rs.gov.br], Seção de Paleontologia, Museu de Ciências Naturais, FZB−RS, Av. Salvador França,1427, CEP: 90690−0, Jardim Botânico, Porto Alegre,Rio Grande do Sul, Brazil; Adriana M. Albino [aalbino@mdp.edu.ar], CONICET, Departamento de Biología, Universidad Nacional de Mar del Plata, Funes 3250, 7600 Mar del Plata, Argentina.

Received 21 September 2009, accepted 23 February 2010, available online 25 February 2010.

Introduction

Colombophis was a medium−size to large genus of snake, hitherto represented exclusively by the type species Colom− bophis portai Hoffstetter and Rage, 1977, based on about 40 midtrunk vertebrae recovered from the middle Miocene Villavieja Formation (Fish Bed) at the Los Mangos locality, near La Venta, Colombia. In spite of its relatively large size, Colombophis was considered belong to the “Anilioidea” (Hoffstetter and Rage 1977), a probably paraphyletic group of alethinophidian snakes. Later, Hecht and LaDuke (1997) recognized some additional incomplete vertebrae from the same area, but they did not describe or discuss the morphol− ogy of the genus. More recently, Head et al. (2006) referred a single vertebra from the middle Miocene of the Socorro For− mation (Venezuela) to Colombophis cf. C. portai. New spec− imens from the late Miocene of the Solimões Formation, southwestern Brazilian Amazonia, increase the knowledge of the vertebral morphology of Colombophis. Reviewing all the available material assigned to this genus and evaluating the intracolumnar and intrageneric variation, allows us to recognize a new species of Colombophis and to evaluate the taxonomic allocation of the genus into the “Anilioidea”.

Institutionalabbreviations.—AMU−CURS, Colección Alcal− día de Urumaco, Rodolfo Sánchez, Urumaco, Venezuela; IB,InstitutoButantan,SãoPaulo,Brazil;IGM,INGEOMINAS −Instituto Nacional de Investigaciones en Geociências, Minería y Química, Museo Geológico, Bogotá, Colombia; MCN.D., Coleção Didática de Herpetologia, Museu de Ciên− ciasNaturaisda Fundação Zoobotânica do Rio GrandedoSul, Porto Alegre, Brazil; MPNHN, Muséum National d’Historie Naturelle, Paris, France; MZUSP, Museu de Zoologia, Uni− versidaded eS ãoP aulo,S ão Paulo, Brazil; UFAC−PV, Cole− ção de Paleovertebrados, Laboratório de Pesquisas Paleonto− lógicas, Universidade Federal do Acre, Rio Branco, Brazil.

Otherabbreviations.—cl,centrumlength;coh,condyleheight; cow,condyle width; cth, cotyle height; ctw, cotyle width; h, to− tal height of vertebra; naw, neural arch width at interzyga− pophyseal ridge; nch, neural canal height; ncw, neural canal width; nsh, neural spine height; po−po, width across post− zygapophyses; pr−pr, width across prezygapophyses; pr−po, distance between pre−and postzygapophysesof the same side; prl, prezygapophysis length; prw, prezygapophysis width; zh, zygosphene height; zw, zygosphene width; SALMA, South American Land−MammalAge.

doi:10.4202/app.2009.1111Acta Palaeontol. Pol.5 (3): 365–379, 2010

Material and methods

The material comes from the middle Miocene of Colombia (La Victoria and Villavieja formations) and Venezuela (Up− per Member of Socorro Formation), and from the late Mio− cene, southwestern Brazilian Amazonia (Solimões Forma− tion) (Fig. 1).

The La Venta Fauna of Colombia is one of the most con− spicuousCenozoic vertebrate paleofaunasin South America.It originates from Honda Group beds including the La Victoria and the Villavieja formations, in the Magdalena River Valley, between the eastern and central Andes Mountains of south− western Colombia (Guerrero1997).The vertebrate faunafrom these formations belongs to the Laventan SALMA (South American Land−MammalAge), middle Miocene (Madden et al. 1997). The holotype of the species Colombophis portai Hoffstetter and Rage, 1977, recognized among the remains from La Venta fauna,was not available for this study because thewhereaboutsofthespecimensatMPNHNarecurrentlyun− known (Jean−Claude Rage, personal communication 2008). More recently, new specimens of Colombophis from the La Victoria and the Villavieja formations were collected during the Duke University−INGEOMINASexpeditions to the upper Magdalena River Valley between 1985 and 1991 (Madden et al. 1997). Part of this material was published by Hecht and LaDuke(1997)andis nowstoredatIGM.Oneof us (A)had the opportunity to reanalyze the squamate material from this collection and found discrepancies regarding the collection numbersofthespecimensandthetaxonomicassignmentspub− lishedbyHechtandLaDuke(1997).Moreover,differentboxes generally contain more than one specimen, including remains corresponding to more than one taxon, under the same collec− tion number. Due to the discrepancies mentioned above and the fact that it was not possible to know exactly which speci− menswerestudiedbyHechtandLaDuke(1997),thecollection numbers of IGM are distinguishedherein by addition of nu− merals betweenparentheses.Theyshould notbe consideredas the same numbersof the published specimens.

The specimen from northwestern Venezuela comes from the Upper Member of the Socorro Formation, which crops out in the Falcón Basin, close to the Urumaco Municipality. It is only one vertebra, referred previously to Colombophis cf. C.portaiby Head etal.(2006) and stored atAMU−CURS. Based on numerous previous studies of foraminifera and palynomorphs, a middle Miocene age was proposed for the Socorro Formation (Sánchez−Villagra and Aguilera 2006).

According to the mammal fauna, the localities in the

Solimões Formation insouthwestern Brazilian Amazonia are referred to the Huayquerian SALMA, which would corre− spond to the late Miocene (Cozzuol 2006; Latrubesse et al. 2007) or even to the Montehermosan SALMA (late Mio− cene/Pliocene) (Latrubesse et al. 1997). In addition, Latru− besse et al. (2007), largely based on palynological data ob− tained in typical mammal fossil localities, proposed a late Miocene age for the fossils from the Solimões Formation.

The snake specimens collected from this formation are stored at UFAC−PV.

Among “Anilioidea”, the comparative material used here in the review of Colombophis includes postcranial specimens of the extant species Anilius scytale (IB 40251, MZUSP 14572, 14573, and 14574). Data from the literatureas well as figures of Cylindrophis ruffus from Ikeda (2007) were also used. The vertebrae of Uropeltidae and Anomochilus are un− known by us due to the difficulties of obtaining comparative material of these taxa, so that data from the literature were used (Lee and Scanlon 2002). The osteological nomenclature and measurements follow Auffenberg(1963), Hoffstetter and Gasc (1969), and Rage (1984, 1998). The inclination of the prezygapophyses was taken considering the horizontal plane at the floor of the neural canal. The systematic arrangement follows Lee and Scanlon (2002). The measurements are ex− pressed in millimeters.

Systematic paleontology

Squamata Oppel, 1811 Serpentes Linnaeus, 1758 Alethinophidia Nopsca, 1923

GenusColombophisHoffstetter and Rage, 1977

Type species: Colombophis portai Hoffstetter and Rage, 1977, Los Mangos locality, near La Venta, middle Miocene, Colombia.

Includedspecies.—Colombophis portai Hoffstetter and Rage, 1977 and Colombophis spinosus sp. nov.

Emended diagnosis.—Fossil snake with midtrunk vertebrae characterized by the following combination of character states: mediumtolargesize;clearlydepressedneuralarch,notvaulted in posterior view;shallow median notch of the posterior border of the neural arch; long dorsal surface of the neural arch, smooth or even concave, extending from the anterior edge of the zygosphene to the neural spine; neural spine reduced to a tubercle or relatively high and circular in outline, always re− stricted to the posterior end of the neural arch; zygapophyses prominent and strongly inclined above the horizontal plane, reaching the level of the zygosphene roof; prezygapophyseal process short; variable presence of paracotylar foramina; paradiapophyses weakly divided or even indistinct; centrum notmarkedlywidenedanteriorly;haemalkeelbroad,indistinct, and often only posteriorly developed, with the usual presence of two small and divergent apophysesmore or less differenti− ated;and subcentralforaminaplacedcloseto the sagittalplane of the centrum, variably enlarged, reducedor absent.

Stratigraphic and geographic range.—Middle to late Mio− cene, Colombia, Venezuela, and Brazilian Amazonia.

Colombophis portaiHoffstetter and Rage, 1977 Figs. 2–5; Table 1.

1977 Colombophisportai HoffstetterandRage,1977:174–179,fig.4. 1997Colombophis portai; Hecht and LaDuke 1997: 95–96.

Holotype: MNHN. VIV 6, one midtrunk vertebra.

Type locality: Los Mangos,near La Venta,Departamento de Huila, Co− lombia; Fish Bed, Villavieja Formation, middle Miocene.

Emended diagnosis.—Colombophis portai differs from C. spinosus sp. nov. by its midtrunk vertebrae longer than broad, with a very low neural spine, resembling a tubercle and circu− lar in outline in dorsal view; thin to moderate zygosphene; anterolaterally orientated prezygapophyses; and undivided paradiapophyses.

Description.—Most of the vertebrae are fragmented and con− sist of isolated neural arches, centra, and other very incom− doi:10.4202/app.2009.1

HSIOU ET AL.—MIOCENE SNAKES FROM SOUTH AMERICA 367

Tropic of Capricorn Brazil

Colombia Venezuela

Honda Bogotá

Neiva Villavieja

La Victoria

Urumaco Caracas

Magdalena

River

Orinoco

River 10

200 km

Manuel Urbano

Feijó Tarauacá

Assis Brasil Purus River Iaco

River

Acre River

(Parte 1 de 4)

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