The first finding of a plesiosaur in Italy is reported. The specimen, a single humerus has been collected in the Argille Varicolori formation, in an outcrop close to the village of Zavattarello. Micropaleontological dating indicates a Santonian-Campanian age for the sediment enclosing the fossil. The morphology of the bone is described. -from Autho

Renesto Silvio

English

Archivio istituzionale della ricerca - Università dell'Insubria

Riv. It. Paleont. Strat. v.99 n. -t pp. 101-106 Maggio 1993A CRETACEOUS PLESIOSAUR REMAIN (REPTILIA, SAUROPTERYGIA)FROM THE ARGILLE VAzuCOLORI OF VARZI(PAVIA, LOMBARDY, NORTHERN ITALY)SIVIO RENESTOKey-zrords: Plesiosauria (Reptilia, Sauropterygia), Santonian-Cainpanian (Upper Cretaceous), Varzi(Pavia, Northern Italy).Riassunto. Si segnala il primo ritrovamento di resti di Plesiosauro in Italia. Il fossile, un omero desrroisolato, è stato rinvenuto in un affioramento delle Argille Varicolori, presso Z*attarello (Pavia). La datazionemediante metodi micropaleontologici suggerisce un' età cretacica per il sedimento (Santoniano-Campaniano).Le dimensioni ed alcune caratteristiche morfologiche dell' osso fanno ritenere che quesro appartenesse ad unesemplare giovanile, attribuibile all' ordine Plesiosauria. Il cattivo stato di conservazione impedisce una ulte-riore classificazione più dettagliata. Si può tuttavia suggerire la probabile appartenenza alla superfamigliaPliosa*roidea.Abstract. The first finding of a plesiosaur remain in Italy is reported. The specimen, a single humerushas been collected in the Argille Varicolori formation, in an outcrop close to the villa4e ol Zavattarello nearVarzi (Pavia, Lombardy, Northern Italy). Micropaleontological dating by analysis of calcareous nannofossilsindicates a Santonian-Campanian age for the sedimenr enclosing the fossil. The morphology of the bone isdescribed: available characters allow to consider the bone as belonging to a juvenile specimen and to ascribe itrc rhe Plesìosauriawirh confidence, but the poor preservation prevenÉ further reliable raxonomic assignmentat lower ranks; some clues however suggest that it may belong to the Pliosauroidea,Introduction.Plesiosaurs (Reptilia, Sauropterygia) were among the most successful and wide-spread groups of Mesozoic marine reptiles. Their remains have been collected invarious Jurassic and Cretaceous localities around the world, but no plesiosaur findingin Italy has been reported so far. In spring t992 an isolated bone has been collected byG. Bianchini, an undergraduate student in geology of the Università di Milano, duringa survey on the area of his thesis. The fossil was collected from the Argiile Varicolori- Dipartimento di Scienze della Terra dell'Università degli Studi di Milano, Via Mangiagalli 34,I20133Milano Italy.702 S. RenestoFig. 1 - Index-map of the fossil locality (asterisk).formation (Gelati et al., 1974) in an outcrop near the small village of Zavattarello (Fig.1) in the Varzi district (Pavia, Lombardy, Northern kaly). The outcrop consists o{siltous and marly shales with red, violet or green bands, densely cripped and fissu-rated. No other macrofossil has been ever collected from this formation, The analysisof calcareous nannofossils by Dr. E. Erba of the Dipartimento di Scienze della Terra,Università degli Studi di Milano, suggests a Santonian-Campanian (Upper Cretaceous)age for the sediment in which the bone was included. The morphology of the boneallows to consider it as a plesiosaur humerus, probably belonging to a juvenile in-dividual. Findings of Jurassic marine reptiles are scarce in ltaly, consisting principallyof a crocodilian and of some ichtyosaurian remains. Several cretaceous marine reptileshave been collected from many Italian localities, but findings consist of chelonians,mosasaurs, and aigialosaurids (Cigala Fulgosi et al., 1980; Leonardi, 1946; Carroll,1992) whereas no plesiosaur remain has been recorded so far, thus the finding fromZavattarello becomes important, even if the poor preservation does not allow an accu-rate taxonomic assessment. On the basis of its general outline, the bone is tentativelyconsidered as belonging to a member of the family Pliosauridae.Palaeontological descriptionClass ReptiliaSubclass Sauropterygia Owen, 1860Order Plesiosauria de Blainville. 1835Cretaceorc Plesiosaur humeru frorn ltalySuperfamily P I i o s A ît r o i d e a (Seeley, 1874)\flelles, 1943Family P I i o s a u r i d a e Seeley, 1874Pliosauridae indet.Text-fig. 2-4Material. A single humerus (Fig. 2, 3) signed as 6765 MPUM of the catalogue of the Museo Paleon-tologico Università di Milano, Dipartimento di Scienze della Terra, where the fossil is stored.Horizon and locality. Santonian-Campanian (Upper Cretaceous); Argille Varicolori (Gelati et al.,1974) near the small village of Zavanarello (Varzi, Pavia, Lombardy, Northern ltaly).Description.The humerus (Fig. 2, 3) is thick and heavy in its proximal porrion, becomingflattened and expanded distally; the anterior outline is gently convex, while the poste-rior one is concave. The bone is better preserved in its proximal portion, while themore distal one is fractured and eroded, specially at its margin. The proximal head ofthe bone shows a rounded, hemispherical articular surface for the glenoid, thecapitulum, and a stout dorsal tubercle, pierced by many foramina for blood vessels andnerves. The dorsal tubercle is separated from the capitulum only by an embayement ofthe margin of the proximal head of the humerus (Fig. 3a). According to Brown (1981),this latter character is an indicator of juveniie stage, since in adult plesiosaurs the twostructures are more distinctly divided and sometimes separated by a strip of periostealbone. Vell developed foramina are present in both the anterior and posterior marginsof the bone. On the proximal third of the ventral surface of the bone, some rugositiesare visible, testifying the insertion of the stout pectoral muscles. Two fractures crossthe shaft of the bone and the distal portion is heavily eroded, mainly in its posteriorregion, so that the distal outline of the bone cannot be restored.Systematic discussion.The taxonomic assignment of this fossil is difficult, owing both to the juvenilecondition of the specimen and to the poor preservation. The general outline of thebone and the morphology of the proximal head allow to consider this specimen asbelonging to the Plesiosauria (Brown, 1981; Romer, 1956), any further assignement tolower rank taxa is tentative however. In fact the morphology of the distal portion ofthe humerus is among the main diagnostic elements in the plesiosaur forelimb (Brown,1e8 1).According to Brown (1981) and Carroll (1988) the Plesiosauria are divided in twomain superfamilies: the short-necked, iarge-skulled Pliosauroidea and the long-necked,small-skulled Plesiosauroidea. The humerus of the Pliosauroidea is more elongated andslender than that of most Plesiosauroidea, which is frequently as large as deep. Themorphology ol ezîs MPUM is more similar ro thar of the pliosaur humeri (Fig. +).103104 S. Renestot-ldThe humerus signed as 6265 MPUM. a) Dorsal; b) ventral; c) anterior (preaxial); d) posterior(postaxial) views. Scale bar equals 5 cm.Fig. 2Cretaceots Plesiosaur hum.errc from ltalla6765 MPUM, proximal (a) and distal (b) head. Scale bar equals 5 cm..tufbIIIcBAF'io 4 Comparison among the outlines of the humeri of a plesiosauroid (A), of a pliosauroid (B), and ofspecimen 6765 MPUM (C), from dorsal view. A and B redrawn from Robinson (1925). Drawingsnot to scale.The outline of the preserved portion of the anterior margin of the bone suggests thatthis latter was not so expanded in its distal portion as can be observed in mostcretaceous and jurassic Plesiosauroidea. The Pliosauroidea consist of only one family,the Pliosauridat, with several genera both from United States and Europe (Brown,1981; Carroll, 1988; Tarlo, 1960). Attempts to ascribe specimen 6765 MPUM ro anypliosaur genera will be not reliable however, and the best thing to do is to consider ittentatively as Pliosaurilae indetermined.106 S. RenestoAchnozabdgemetza.I wish to thank Dr. G. Bianchini, Milano who found specimen 6765 MPUM. I am also deeplyindebted to Dr. E. Erba, Milano, for dating the sediment in which the bone was enclosed, to Dr. D. Brown,London for the helpful and stimulating discussions and to Prof. C. Rossi Ronchetti, Milano for criticalreading and srylistic revision of the manuscript.REFERENCESBrown D. S. (1981) - The English Upper Jurassic Plesiosauroidea (Reptilia) and a review of thephylogeny and classification of the Plesiosauria. Bull. Br. Mw. Nat. Hist. (Geol.), v. 35, pp.253-347, London.Carroll R. L. (1988) - Vertebrate Palaeontology and Evolution. V. of 698 pp., Freeman ór Co.,New York.Carroll R. L. (1992) - Aigialosaurs: Mid Cretaceous varanoid Lizards. tourn. Vm. Paleont., v. 72,pp. 66-86, Lawrence.Cigala Fnlgosi F., Kotsakis T., Massari F.,Medizza F. Er Sorbini L. (1980) - Il giacimento di S.Anna d' Alfaedo. In I Vertebrati fossili Italiani - Catalogo della Mostra, pp. 123-128, Vero-na,Gelati R., BrrzzíD., Catasta G. 6r Cattaneo P. C. (1974) - Evoluzione stratigrafica dell'Appen-nino Vogherese a Nord-Est della Val Staffora. Rio. It. Paleont. Strat., v. 80, n. 3, pp.479-574, Milano.Leonardi P. (1946) - I Mosasauri del Veneto. Cornment Pont. Acc. Scitnt., v. 10, pp. 463-486,Roma.Robiruon J. A. (L975) - The locomotion of plesiosaurs. N. Jahrb. Geol. Palaeont., Abh., v. 749,pp. 286-332, Stuttgart.Romer A. S. (1956) - The Osteology of the Reptiles. Y. of 772 pp., Univ. Chicago Press, Chi-cago.Tarlo L. B. H. (1960) - A review of the Upper Jurassic pliosaurs. Bull. Br. Mw. Nat. Hist. (Geol.),v. 4, pp. 147-789, London.'Welles S. P. (1952) - A review of the North American Cretaceous elasmosaurs. Unizt. Calif, Publ.Geol. Sc., v. 29, pp. 47-144, BerkeleyRecàaed Febraary 23, 1993; accepted Marcb 1, 1993

Cretaceous plesiosaur remains (Reptilia, Sauropterygia) from the Argille Varicolori of Varzi (Pavia, Lombardy, Northern Italy)

https://irinsubria.uninsubria.it/bitstream/11383/2153971/1/lucia%2c%2bRenesto%2b99-1.pdf

Cretaceous plesiosaur remains (Reptilia, Sauropterygia) from the Argille Varicolori of Varzi (Pavia, Lombardy, Northern Italy)

Abstract

Similar works

Full text

Available Versions

Archivio istituzionale della ricerca - Università dell'Insubria