Istria on the Internet - Paleontology

A Vertebrae of a Large Sauropod Dinosaur from the Lower Cretaceous of Croatian Istria (Croatia)
(Una vertebra di un grande dinosauro sauropode del Cretaceo inferiore dell'Istria (Croazia)

Fabio M. Dalla Vecchia

Abstract

A large vertebra from the late Hauterivian - early Barremian (Early Cretaceous) site of Valle/Bale (Istria, Croatia) is bere described. T bis rather odd specimen is identified as a dorsal vertebra of a large somphospondylian sauropod. It once more demonstrates that large dinosaurs w ere living on the Adriatic-Dinaric Carbonate Platfonn during Hauterivian-Barremian times.

Riassunto

Viene descritta una grande vertebra proveniente dal sito di età Hauteriviano superiore - Barremiano inferiore (Cretaceo inferiore) di Valle/BaIe (Istria. Croazia). Questo esemplare. in vero piuttosto in usuale. viene identifìcato come una vertebra dorsale di un sauropode somfospondilo. Esso è una ulteriore dimostrazione del fatto che grandi dinosauri vivevano sulla piattaforma carbonatica Adriatico-Dinarica durante 1 'intervallo H a uteriviano-Barremiano.

Key words (Parole chiave): Sauropoda, Cretaceo inferiore, Istria.

Introduction

The late Hauterivian-early Barremian site or Valle/BaIe has been described in several papers (BOSCAROLLI et al., 1993; DALLA VECCHIA, 1994; 1998a, b; 1999; 2000; TUNIS et al., 1994; DINI et al., 1998; BOSCAROLLI & DALLA VECCHIA, 1999). This site has furnished many fragmentary bones mainly belonging to sauropod dinosaurs (DALLA VECCHIA, 1998a), but also theropods are represented (DALLA VECCHIA, 1998b).

I describe here a relatively complete vertebra or a large dinosaur which was not reported in previous papers and has been figured only in DALLA VECCHIA (2000). The specimen was originally conglobated in the limestone matrix (fig. 1) and has been prepared mechanically and chemically (ronnic acid, diluted at 5% and burrered with calcium triphosphate) at the laboratories or the Museo Paleontologico Cittadino or Monfalcone (figs.2-3). After the preparation the specimen with a weight of several kilograms and a neural made of a very delicate network of thin bone laminea, has become particularly fragile.

The specimen has been given back to the authorities of the Municipality of Valle/Bale after their request, on March 2nd, 2001. I fear that the fragile bone will be seriously damaged as occurred to the complete cervical vertebra WN-V1 described by DALLA VECCHIA (1998a, figs. 1-2; 1999, figs. 1-10) when exposed in a room of the town ha1l of Valle/Bale. Thus, I wi1l figure here the specimen in detai1 to the future advantage of the intemational paleontologica1 community .The ridundance in the photographical documentation is useful in this sense. Our experience with published photos of the bones of the Istrian dinosaurs suggests that slight changes in perspective, lighting and focusing can avoid the reader to misinterpret the structures visible in the photographs.

Also the holotype of Histriasaurus boscarollii and two theropod remains described in DALLA VECCHIA (1998b, pp. 356-357; here figured in appendix) are under the care of the Municipality ofVa1le/Bale.

Description

The specimen is a complete centrum with most of the neural arch (figs 4-7). Both centrum and neural arch are anteroposteriorly crushed.

As initial statement, I need to say that I identify this vertebra as a sauropod vertebra because of large size, likeliness to other vertebml material found in the same site and because most of the bones found in the site belong to sauropods (cf. DALLA VECCHIA, 1998a). The pre1iminary comparison with the sauropod vertebrae described in 1iterature (e.g. HATCHER, 1901, 1903; GILMORE, 1936; JANENSCH, 1950; McINTOSH, 1990a,b; SALGADO et al., 1997) and observed directly in many museum co1lections in USA and South America makes the identification as caudal vertebra of a sauropod as unlikely. The cervicals of sauropods are opisthocolelous and the dorsals can be opisthocolelous, amphiplatyan or slightly amphicoelous (the latter conditions are common in the rear half of the series) (MCINTOSH, 1990a,b; BONAPARTE,1999).

The centrum of the vertebra here described has a deeply concave cotyle and a convex condyle and should be considered opisthocoelous, with the concave face posterior and the convex anterior.

The cotylar surface is perfect1y preserved, while the middle-lower surface of the condyle is partly weathered away (figs. 7-8). The outline of the articular faces is e1liptical, much wider than high, like in the anterior dorsal vertebrae of Tendaguria tanzaniensis (BONAPARTE et al., 2000, figs. 11-13,15). The width of the posterior articular face is 335 mm, the height is 195 mm. The anterior face is wider, at least 355 mm. The cotylar surface is fmely spongy (fig. 8); the spongious cavities becomes higher and higher moving inside the centrum. The anteroposterior compression of the centrum caused the collapse of the cavities in proximity of the anterior articu1ar surface, but some of them (the 1argest) can be seen in the right side and in the anterior part of the ventral side of the centrum (figs. 8-9). The centrum has been anteroposteriorly shortened by compression, thus now it is at maximum on1y 130 mm long. However, also considering the shortening due to compression, the length was probably not higher than 20 cm, as suggested by the compressed and thrust structures visible near the ventral margin of the right and left lateral side (figs. 12-14). Thus, the centrum was rather short (figs. 10-13).

The ventral face is nearly flat, with a relatively shallow, medial longitudinal depression (fig. 10). The lateral faces are deformed by compression. A large pleurocoel was present in the ventml half (figs. 12-14). It is bordered ventrally and dorsally by thick bars of bone (lip-like margins). The ventral bar of bone seems to reach a lateral projection of the anteroventral part of the centrum which could be a parapophyseal stalk (figs. 7, 10, 14, 18). Unfortunately, this projection has been weathered in both left and right sides.

The steep surface of the posterior half of the centrum (from the posterior edge to the middle) suggests that the shape of the centrum was spool-like or even sandglass-shaped (figs. 12-13, 15).

The neural arch was a highly laminar structure. Laminae, rod-like structures and articular surfaces have all been compressed and mangled in a way that it is very difficult to recognize their original shape and position (figs. 11-13, 16-19). All the structures of the neuraI arch have been drawn up anteroposteriorly.

The articular surfaces are easily identifiable because of their spongy aspect in contrast with the smooth surface of the other parts of the vertebra. The present position of the identified articular surfaces appears to be very odd and is due to the extreme compression. Structures very similar to the prezygapophyses of the specimen MPCM-V4 (see DALLA VECCHIA, 1998a, fig. 11; DALLA VECCHIA, 1999, figs. 39, 41-42) are present at the top ofthe preserved part ofthe neuraI arch (figs. 3, 7, 11, 16-18). If the identification as prezygapophyses is correct, their relative position suggests that the Ieft and part of the right side of the anterior part of the neural arch rotated of 90° and is crushed against the right posterior side of the neural arch (see figs. 67, 12, 18, 20), facing posteriorly. The right side of the anterior part of the neuraI arch is crushed but remained in its originaI position.

The two wide, vertical articular surfaces preserved at the base and in the middle of the posterior side ofthe neuraI arch (figs. 5-7, 15, 20-21) are probably accessory hypantraI articular faces and origina1ly they faced anteriorly. The left one (according to the originaI position) is less crushed than the other. The articular surface is 70 mm high and about 40 mm wide. From its upper part a thin lamina starts directed dorsolaterally to border laterally the wide hypantrum. A thick bony bar begins on its right side and is laterally directed ending against the dorsal margin of a thick lamina descending probably from the left prezigapophysis (figs. 5- 7, 15, 2a-21). This part is nearly "fused" agai1st the right transverse proccess, and it is hard to identify its actual margins.

Between and above the two vertical articular surfaces there is the hypantral depression which widens dorsally and is crossed by a horizontal very thin lamina (figs. 6-7, 2a-21).

Neither the opening for the neural channel nor the pedicels of the neural arch are visible, suggesting that the compression has obliterated the first and compressed the seconds. However, the compression cannot have been so strong in the dorsoventral plane, suggesting that the opening was smal1 and the pedicels short.

Several transversal (i.e. perpendicular to the long axis of the centrum) bony laminae build the laterally projecting transverse process (figs. 7, 13, 16-18, 19). They are thick proximally and become thinner distally (laterally).

Discussion

The shortness of the centrum and the structure of the neural arch (pattem of laminar structure, shape of the articular surfaces etc. ) suggest it is a dorsal vertebra more than a cervical one. The possible presence of parapophyses at the anteroventral comer of the centrum would suggest it is an anterior dorsal, possibly the first anterior dorsal because in other dorsals the parapophyses is placed higher. However, the prezigapophyses are here unusually high in the neural arch for an anterior dorsal and anterior dorsals lack the hyposphene-hypantrum complex (see HATCHER, 1901, 1903; GILMORE, 1936; JANENSCH, 1950; McINTOSH, 1990a,b; BONAPARTE,1999).

The "cellular" structure of the centrum is at present considered a diagnostic feature of the clade Somphospondyli according to WILSON & SERENO (1998). I suspect it is a characteristic widespread in the more inclusive clade Titanosauriformes, but this needs a confirmation and the taxonomical relationships among Sauropoda are far to be established.

The "cellular" centrum and neural arch, and a structure of the latter made of several thin laminae are characteristics of all the presacral centra found at Valle/Bale site, with the exception of the dorsal vertebra of Histriasaurus boscarolli (DALLA VECCHIA, 1998a; 1999).

It is probable that a peculiar titanosauriform with odd dorsal vertebrae is preserved in the limestone of the Vale/BaIe site. For size comparison, in Tendaguria tanzanensis considered about 20 m long (BONAPARTE et al., 2000, p. 47), the anterior dorsal A has a posterior articular face which is 390 mm wide and 248 mm high (ibidem, p. 49). This is a further confmnation that large dinosaurs were living on the Adriatic-Dinaric Carbonate Platform during Hauterivian-Barremian times.

Acknowledgements

My thanks go mainly to Dario Boscarolli, who found the specimen, and to Maurizio Tentor who helped me in many aspects during the realization of this note. I thank Jose Bonaparte, Ruben Martinez, Jorge Calvo, Leonardo Salgado, Sebastian Apesteguia, and Rodolfo Coria for support and access to the collections under their care in Argentina; Alexander Kellner, Diogenes Campos and Jose Suarez for the support in Brazil; Alexander Kellner for help at the American Museum ofNatural History ofNew York, and Mary Dawson for her support at The Carnegie Museum, Pittsburgh.

References

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Source:

Fabio M. Dalla Vecchia, "A Vertebra of a Large Sauropod Dinosaur from the Lower Cretaceous of Istria (Croatia), Una vertebra di un grande dinosauro sauropode del Cretaceo inferiore dell'Istria (Croazia)", Natura Nascosta, Number 22, Anno 2001, pp. 14-33.

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