Reptiles extintos : Acynodon es un género extinto de aligatórido. Inicialmente fue considerado como perteneciente a la familia Alligatoridae,1 pero posteriormente ha sido reclasificado como un globidonto, constituyendo el globidonto más antiguo y primitivo conocido,2 con restos fósiles encontrados en Francia, España, Italia, y Eslovenia.
Acynodon aparece por primera vez en el Campaniense inferior dentro del Cretácico Superior, y desapareció durante la extinción masiva ocurrida en el límite K-T.El cráneo de Acynodon es extremadamente brevirostral, teniendo un hocico pequeño y ancho en comparación con otros aligatoroides.3
Su dentición es apomorfa con grandes dientes parecidos a molares y ausencia de dientes caniniformes en los huesos maxilar ydentario. Supuestamente esta condición se debe a una adaptación alimentaria hacia presas con fuertes caparazones.2 Lososteodermos de Acynodon poseen una distintiva doble quilla.
In 1997, Buscalioni et al. erected the new taxon Acynodon iberoccitanus on the basis of an isolated maxilla from the late Campanian or early Maastrichtian of Laño (Spain; Text-fig. 1). That species is characterized, among other features, by isodont maxillary teeth (absence of caniniform maxillary teeth), with the exception of a few molariform teeth placed at the back of the tooth row. A few other cranial skeletal elements from Laño were referred to A. iberoccitanus. Buscalioni et al. (1997) also referred some isolated teeth from the Maastrichtian of Quintanilla del Coco, Spain, to a second species, Acynodon lopezi. A complete description of the cranial anatomy of A. iberoccitanus was provided recently by Martin (2007) on the basis of relatively well-preserved remains from the late Campanian–early Maastrichtian of France at Massecaps (Martin and Buffetaut 2005), Quarante and Fox-Amphoux (figured by Vasse 1993; and mentioned as a member of Acynodon by Buscalioni et al. 1997).
Figure TEXT-FIG. 1.. The fossil record of the genus Acynodon is limited to eight Upper Cretaceous localities. Key: 1, Acynodon lopezi, Quintanilla del Coco, Spain (Maastrichtian; Buscalioni et al. 1997); 2, A. iberoccitanus, Laño, Spain (late Campanian–early Maastrichtian; Buscalioni et al. 1997); 3, Acynodon sp., Blasi 2, Arén, Spain (late Maastrichtian; López-Martínez et al. 2001); 4, A. iberoccitanus, Massecaps, Cruzy, France (late Campanian–early Maastrichtian; Martin and Buffetaut 2005; Martin 2007); 5, A. iberoccitanus, Quarante, France (late Campanian–early Maastrichtian; Martin 2007); 6, A. iberoccitanus, Fox-Amphoux, France (‘Rognacian’; Martin 2007); 7, Acynodon adriaticus, Villaggio del Pescatore, Duino-Aurisina, Italy (Santonian–Campanian; this paper); 8, cf. Acynodon sp., Fântânele, Ha?eg Basin, Romania (Maastrichtian; Martin et al. 2006).
Isolated teeth from the late Maastrichtian of the Spanish Pyrenees were explicitly referred to Acynodon (López-Martínez et al. 2001), whereas others from the approximately coeval site of Fântânele in Romania were tentatively referred to cf. Acynodon sp. (Martin et al. 2006).
Morphologically similar teeth are not rare in the European Late Cretaceous fossil record, but, in most cases are conservatively identified only to the rank of order (Debeljak et al. 2002). All the information so far available for Acynodon comes from the above-mentioned localities and concerns the cranial osteology only; no postcranial elements have been found in clear association with the cranial material so far described.
Since its original description, the phylogenetic relationships of Acynodon have been a topic of discussion. Buscalioni et al. (1997, 1999) concluded that Acynodon is closely related to Albertochampsa, Brachychampsa and Stangerochampsa, the North American short-snouted forms that they regarded as members of the Alligatoridae. Later, Brochu (1999, 2001a, b, 2003) considered Acynodon as representing an early member of the first alligatorine radiation in Europe. The phylogenetic analysis by Martin (2005, 2007) proposed, for the first time on the basis of a character matrix, that Acynodon is a basal globidontan alligatoroid.
We describe cranial and postcranial crocodylian remains from the Upper Cretaceous of Villaggio del Pescatore, north-eastern Italy. Buffetaut et al. (2001) and Dalla Vecchia et al. (2005) had previously mentioned or briefly described these remains as putative alligatoroids, but Delfino and Buffetaut (2006) recognized them as referable to the genus Acynodon. Although the bones are not completely isolated from the embedding rocky matrix (in order to keep all the skeletal elements in connection), the Italian materials provide a considerable amount of new information on the morphology of Acynodon, which allows a reconsideration of the interrelationships of the genus among basal alligatoroids.
Geological setting
- Top of page
- Abstract
- Geological setting
- Materials and methods
- Systematic Palaeontology
- Taxonomic remarks and phylogenetic relationships
- Discussion
- Conclusions
- Acknowledgments
- References
- Appendix
- Supporting Information
The crocodylian remains described here come from laminated carbonates cropping out in Villaggio del Pescatore, Duino-Aurisina Municipality (Text-fig. 1). These blackish laminated carbonates, interbedded with thick breccia beds, were formerly referred to the late Santonian (Tarlao et al. 1994; Buffetaut and Pinna 2001; Dal Sasso 2001; Dalla Vecchia 2001, 2003a, b; Nicosia et al. 2005; Dalla Vecchia and Buffetaut 2006), but Arbulla et al. (2001, 2006) proposed a wider chronological interval of Santonian–Campanian on the basis of pollen and foraminifers found within the stratigraphic succession. Dalla Vecchia (2006, p. 7) recently expressed doubts about those chronological allocations and suggests that the site is ‘most probably younger than previously supposed and work is in progress to better define its age’, but no reasons were given for this statement.
The site yielded several macrofossils of plants, crustaceans, fishes, pterosaurs, crocodylians, and hadrosauroid dinosaurs (Buffetaut and Pinna 2001; Buffetaut et al. 2001; Dalla Vecchia 2002, 2006; Dalla Vecchia et al. 2005; Delfino and Buffetaut 2006). The depositional setting has been defined as possibly corresponding to a narrow anoxic trough, markedly sloping, facing southward, and open inside a supratidal environment of the carbonate platform influenced by fresh water and marine influx; the fossiliferous laminated carbonates may have been deposited in a time interval ranging from 4000 to 10,000 years (Arbulla et al. 2001, 2006).
Institutional abbreviation. ACAP-FX, Association Culturelle, Archéologique et Paléontologique de l’Ouest Biterrois (Cruzy)-Fox-Amphoux collection; MCSNT, Museo Civico di Storia Naturale di Trieste.
Abbreviations used in the text-figures. a, angular; at, atlas; br, branchial; ch, choana; co, coracoid; cr, cervical rib; d, dentary; ec, ectopterygoid; f, frontal; h, humerus; if, incisive foramen; j, jugal; l, lacrimal; itf, infratemporal fenestra; mtc, metacarpal; mx, maxilla; n, nasal; na, naris; os, osteoderm; p, parietal; pa, palatine; ph, phalanges; pfr, prefrontal; pmx, premaxilla; po, postorbital; pob, postorbital bar; pr, prezygapophysis; pt, pterygoid; ptw, pterygoid wing; q, quadrate; qj, quadratojugal; r, radius; rc, radial carpal; ret, retroarticular process; sc, scapula; sp, splenial; sq, squamosal; stf, supratemporal fossa; sub, suborbital fenestra; sur, surangular; t, tooth; u, ulna; uc, ulnar carpal; up, ungual phalanx.
Materials and methods
- Top of page
- Abstract
- Geological setting
- Materials and methods
- Systematic Palaeontology
- Taxonomic remarks and phylogenetic relationships
- Discussion
- Conclusions
- Acknowledgments
- References
- Appendix
- Supporting Information
The specimens described here, as well as all other crocodylian remains from Villaggio del Pescatore, were completely preserved in blocks of laminated carbonates. The skeletal materials have been removed partly by acid preparation, with the result that the specimens are now exposed on slabs. Therefore, the skeletal elements of the larger specimen described here are partly embedded in the rocky matrix: the entire dorsal and left lateral surfaces, and part of the ventral surface of the skull and lower jaws are visible (Text-fig. 2). The miniatures with cranial and postcranial elements, shown in some of the figures, serve to illustrate the general relationships of the skeletal elements at an earlier stage of preparation.
Figure TEXT-FIG. 2.. Acynodon adriaticus sp. nov. Photos and line drawings of the holotype, MCSNT 57248 in dorsal view. Dashed lines identify the position of sutures less ambiguous than those represented by a dotted line. Scale bar represents 1 cm.
Systematic Palaeontology
- Top of page
- Abstract
- Geological setting
- Materials and methods
- Systematic Palaeontology
- Taxonomic remarks and phylogenetic relationships
- Discussion
- Conclusions
- Acknowledgments
- References
- Appendix
- Supporting Information
CROCODYLIA Gmelin, 1789 EUSUCHIA Huxley, 1875 ALLIGATOROIDEA Gray, 1844 ACYNODON Buscalioni et al., 1997
Acynodon adriaticus sp. nov. Text-figs 2–7
Figure TEXT-FIG. 3.. Acynodon adriaticus sp. nov. Photos and line drawings of the holotype, MCSNT 57248 in ventral view. Scale bar represents 1 cm.
Figure TEXT-FIG. 4.. Acynodon adriaticus sp. nov. Detail of the left quadrate and retroarticular process of the holotype, MCSNT 57248 in dorsal view. Arrows ‘a’ and ‘b’ point to the quadrate spine and retroarticular spine, respectively. Scale bar represents 1 cm.
Figure TEXT-FIG. 5.. Acynodon adriaticus sp. nov. Details of the tooth row of the holotype, MCSNT 57248. A, left anteroventral view of the rostrum with detail of the anterior dentition, with arrows indicating first premaxillary tooth (‘a’) and first maxillary tooth (‘b’). B, left lateral view with arrows indicating first premaxillary tooth (‘a’), first (‘b’), fourth (‘c’) and sixth (‘d’) maxillary teeth. C, posterior crushing tooth row. The dashed curve underlines the extent of the arch above the largest tooth. Areas of interest are located on the lateral view of the skull. Scale bar represents 1 cm.
Figure TEXT-FIG. 6.. Acynodon adriaticus sp. nov. Photos and line drawings of the right forelimb of the holotype, MCSNT 57248. The proximal end of the humerus is not represented. The arrow indicates a probable healed pathology. Scale bar represents 1 cm.
Figure TEXT-FIG. 7.. Acynodon adriaticus sp. nov. Photos and reconstruction of the paravertebral shield of the paratype, MCSNT 57032. A, the entire slab showing the osteoderms and the ribs. B, detail of double-keeled (left parasagittal row) osteoderms; the three selected osteoderms have been digitally isolated from the surrounding osteoderms. C, proposed schematic reconstruction of the paravertebral shield; the dashed line represents the midline; the arrow indicates the cranial direction; a lateral parasagittal row of accessory osteoderms, not represented in the reconstruction, could be present on each side. Scale bars represent 1 cm.
Derivation of name. From ‘sinus adriaticus’, the Latin name for the Adriatic Sea, on the shore of which the site of Villaggio del Pescatore is located.
Type specimen. MCSNT 57248 comprises a complete skull with lower jaws, part of the hyoid apparatus and pectoral girdle, right forelimb, the first 10 vertebrae, some ribs, and several dorsal osteoderms.
Paratype. MCSNT 57032 consists of associated osteoderms and ribs.
Type locality and age. Villaggio del Pescatore, Duino-Aurisina municipality, Trieste Province, Friuli Venezia Giulia, Italy (45°46′43′′N, 13°35′19′′S). The fossiliferous laminated carbonates are Late Cretaceous in age, either late Santonian or Santonian–Campanian (see Geological Setting section).
Diagnosis. Acynodon adriaticus differs from A. iberoccitanus and A. lopezi in the following set of characters: absence of interorbital ridge; postorbital bar extremely short and blunt with postorbital and jugal almost touching; presence of a sagittal ridge on the parietal (slightly extending to the interorbital area); dorsal surface of squamosal smooth; frontal and parietal have a concave dorsal surface; rim of the supratemporal fenestra thickened; palatines slender and sagittally grooved; palatopterygoidal suture far from the caudal angle of the suborbital fenestra; medial quadrate condyle hooked; very elongate suborbital fenestra extending anteriorly to the level of the fifth or sixth maxillary alveolus and posteriorly to the level of the largest maxillary alveolus (the penultimate alveolus); maxillary edge downturned and arched the level of the largest maxillary alveolus; posterior molariform teeth smooth, without mesiodistal apical crests horseshoe-like or simply tall.
Remarks. Due to the fact that the retroarticular region is not preserved in any known specimen of A. iberoccitanus, it is not possible to consider the presence of an anteriorly directed spine on the medial margin of the retroarticular process of MCSNT 57248 as an autapomorphy of A. adriaticus. However, the peculiar morphology of the medial margin of the quadrate condyle that characterizes the latter is likely linked to the shape of the retroarticular process and suggests that the spine may not have been present in A. iberoccitanus.
A minor diagnostic character, which could be partly influenced by the deformation of the skull, is represented by the rather acute lateral profile of the snout of A. adriaticus when compared in dorsal view with the more rounded shape of A. iberoccitanus (compare Text-fig. 2 with Martin 2007, figs 1 and 3).
Finally, the paravertebral osteoderms of A. adriaticus exhibit two keels. The number of keels, however, is unknown in the other species of Acynodon. Thus, the presence of two keels is an ambiguous diagnostic character because it may diagnose the genus Acynodon or a group within the genus. Only the recovery and description of postcranial remains referable to A. iberoccitanus and A. lopezi will help to resolve this uncertainty.
Description
The skeletal elements are preserved in anatomical connection; the neck vertebrae form a marked bend of nearly 90 degrees (as in another crocodylian specimen, MCSNT 57031). The skull is partly deformed and several sutures are not visible, but the general morphology is well-preserved. The major effect of the deformation seems to be the shortening of the right side of the skull. Moreover the lateral side of the right maxilla and jugal are slightly ‘verticalized’ due to lateromedial compression. The skull is 15.5 cm long (as measured from the tip of the snout to the level of the posterior edge of quadrate condyles), c. 12.5 wide (as measured across the quadratojugals), approximately triangular in shape, and characterized by a distinctly short rostrum (the area anterior to the orbits is only 6.5 cm long, approximately as long as the skull table). The quadrate condyles do not project from the lateral profile of the skull, which reaches its maximum width at the level of the quadratojugals, producing a bulging aspect. The relatively acute shape of the snout is minimally affected by the deformation as indicated by its symmetry. The outline of the skull cannot be described as festooned either in dorsal or lateral view. Ridges or bosses are not developed on the snout or at the anterior corner of the orbits. The interorbital ridge (the ‘spectacle’) is absent. The skull table has almost parallel lateral margins in dorsal view, with well developed and pointed squamosal prongs (at least the left one that is not broken and not significantly deformed); in posterior view, it is only slightly concave. A weak but distinct sagittal ridge is present on the skull table: it is more developed posteriorly to the supratemporal fenestrae but it is visible anteriorly at least up to the interorbital region. The skull table is concave between the supratemporal fenestrae (some degree of deformation cannot be excluded, but the symmetry of this concavity suggests that it is natural). With the exception of the area posterior to the infratemporal fenestrae, the external surface of the skull is ornamented with irregular ridges delimiting furrows and pits. The lateral and ventral surfaces of the lower jaw shows the same pattern.
Cranial fenestrae and openings. The external naris is small and irregularly rectangular in shape; its rim is modestly ridged but the posterior sector, delimited by the nasals, is slightly collapsed ventrally as compared to the surrounding premaxillae. It is not clear whether the naris had a median septum or not. Although dorsoventral compression may have modified the general shape of the snout, it seems likely that the anterior margin of the naris is placed ventrally to the posterior margin and that therefore the naris is anterodorsally oriented. The incisive foramen, partly hidden by the dentary, is moderately large and is situated far from the premaxillary tooth row. The orbits are proportionally small, and are asymmetric due to the deformation; their rim is nearly flush with the skull surface because a modest upturning of the rim is visible in the lateral sector of the left orbit, close to the postorbital bar. The supratemporal fenestrae are almond-shaped and small relative to the skull table. The posttemporal fenestrae are small and approximately horizontal. The foramen magnum and occipital condyle are slightly shifted to the left due to compression; both are small. The condyle, not visible in dorsal view and with an evident sagittal furrow, is c. 9 mm wide and 5 mm tall. The infratemporal fenestrae are very small (each is less than half the size of the orbit) but, due to the fact that the posterior margin is slightly eroded, their original size was even smaller. The quadratojugals probably formed the posterior angle of the infratemporal fenestrae. The suborbital fenestrae are fairly small as compared with a modern alligatorid, but relatively large as compared with A. iberoccitanus. Their well-preserved, notched, posterior rims reach the level of the midpoint of the largest maxillary alveolus. The anterior rim cannot be seen with confidence, but it seems that it reached the level of the fifth or sixth maxillary alveolus. The secondary choana is small, subcircular (but slightly distorted by compression), and does not have a neck or a septum. It is located in the posterior area of the palate, c. 6 mm from the posterior edge. The choana opens in the posterior sector of the pterygoids. Two faint lineations departing in posterolateral direction from the choana do not seem to be fractures or sutures between skeletal elements.
In the lower jaw, the perfectly preserved left lateral side clearly indicates that the external mandibular fenestra is not present.
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