Redescription of Aigialosaurus dalmaticus Kramberger, 1892, a Cenomanian mosasauroid lizard from Hvar Island, Croatia

Abstract

Redescription of the type and only specimen of Aigialosaurus dalmaticus (BSP 1902II501), an "aigialosaurian" squamate from the Cenomanian-Turonian of Hvar, Croatia, and, at the time of collection, the Italian island of Lesina, indicates that previous reviews of the specimen include erroneous anatomical interpretations. The type specimen presents a new and unique pelvic anatomy: the ilium of A. dalmaticus is an elongate element with well-developed anterior and posterior iliac processes. A scenario is presented for mosasaurid pelvic evolution, whereby the anteriorly elongate and dorsally directed ilium of mosasauroids is not derived from the forward rotation of the posterior iliac process, but rather the reduction of that process and the elaboration of the anterior iliac process. Recent phylogenetic analysis of Mosasauroidea finds A. dalmaticus to be the sistergroup to Opetiosaurus bucchichi and all other mosasaurids and "aigialosaurs." We examine the character state assignments for A. dalmaticus in that study and refute those assignments owing to the absence of preservation of all four characters states found to separate A. dalmaticus from O. bucchichi. Résumé: Une nouvelle description du spécimen type et unique spécimen connu d'Aigialosaurus dalmaticus (BSP 1902II501), un squamate « aigialosaure » du Cénomanien-Turonien de Hvar (Croatie) et, au moment de son pré-lèvement, de l'île italienne de Lésina, indique que les examens antérieurs de ce spécimen comprennent des interpréta-tions anatomiques erronées. Le spécimen type présente une anatomie pelvienne nouvelle et unique : l'ilium d'A. dalmaticus consiste en un élément allongé comportant des processus iliaques antérieurs et postérieurs bien développés. Un scénario d'évolution du pelvis des Mosasauridés est présenté selon lequel l'ilium antérieurement allongé et dorsalement orienté des mosasauroïdes n'est pas dérivé de la rotation vers l'avant du processus iliaque postérieur, mais plutôt de la réduction de ce processus et de l'élaboration du processus iliaque antérieur. Une analyse phylogénétique récente des Mosasauroïdés établit qu'A. dalmaticus est le groupe-frère d'Opetiosaurus bucchichi et de tous les autres mosasaurides et « aigialosaures ». La présente étude se penche sur les attributions des états des caractères pour A. dalmaticus et les réfute en raison de la non-préservation de tous les états des caractères, au nombre de quatre, qui distinguent A. dalmaticus d'O. bucchichi. [Traduit par la Rédaction] Dutchak and Caldwell 1834

The First Freshwater Mosasauroid (Upper Cretaceous, Hungary) and a New Clade of Basal Mosasauroids

“…The ilium (Figures 4V, 7O−P) is robust with a long posterior blade, a well-developed acetabular face, a well-developed ventral facet for the ischium and a spoon-shaped preacetabular process that overlapped the pubis. This process is similar to that seen in many extant lizards and the mosasauroids Aigialosaurus dalmaticus [3] and Tethysaurus nopcsai (LM, personal observation) and represents the plesiopelvic condition [3], [4].…”

“…As far as we know, Pannoniasaurus had a primitive vertebral column, a posteriorly oriented ilium and an elongated humerus with a distal epiphysis, all most similar to aigialosaurs [3], [43]. These suggest that P. inexpectatus had an overall aigialosaur-like postcranial morphology (including plesiopelvia and plesiopedia).…”

“…That character list and taxon-character matrix originates from a previous work [32], with characters deleted/added/modified through later studies [2], [3]. In order to make it easier for the reader to follow the changes made through that series of studied, the character list (See Appendix S2) was recompiled by quoting almost word-by-word from the original character list of Bell [32] and including all changes made by later studies [3], [4].…”

“…The adaptive radiation into aquatic environments by the long extinct squamate clade commonly known as mosasauroids (mosasaurs and aigialosaurs), resulted in the evolution of paddle-like limbs (hydropedality) [2] and modified hips (hydropelvia) [3], [4], a laterally compressed and downturned tail for swimming [5], modifications to the middle-ear osteology [6], [7], and a progressive increase towards gigantism within different subclades [6]. It is therefore an excellent example of a major secondarily aquatic transition in vertebrate evolution, and the only one of its kind among squamates [8].…”

Skin of the Cretaceous mosasaur Plotosaurus : implications for aquatic adaptations in giant marine reptiles

“…A similar concentration of keeled scales is present on the dorsal surface of P. kornhuberi (Caldwell & Dal Sasso 2004;Caldwell 2006), and in modern sea snakes and sea kraits. In a paper describing the pelvis and tail of a basal mosasauroid, Smith & Buchy (2008) noted that whereas derived mosasaurs have keeled body scales, aigialosaur-grade forms do not (although keel-less scales, in fact scales of any kind, are only known from the belly region of one taxon, Carsosaurus marchesetti; Gorjanović-Kramberger's (1892) assertion of the presence of scales in Aigialosaurus dalmaticus was not confirmed by Dutchak & Caldwell (2006) and is refuted here).…”