Alessandro Palci

A new basal mosasauroid from the Cenomanian (U. Cretaceous) of Slovenia with a review of mosasauroid phylogeny and evolution

Abstract A new genus and species of basal mosasauroid reptile from the Cenomanian (Upper Cretaceous) of Slovenia, previously referred to as the “Trieste aigialosaur,” is described. The new taxon is known from only a single specimen including a well-preserved postcranial skeleton and parts of the skull (i.e., left quadrate, left surangular-prearticular complex, and left angular and splenial). Morphological characters of the quadrate and postcranial skeleton distinguish this new taxon from other basal mosasauroids such as Aigialosaurus dalmaticus, Aigialosaurus (=Opetiosaurus) bucchichi and Carsosaurus marchesettii. Cladistic parsimony analysis of a taxon character matrix composed of 135 characters and 31 terminal taxa resulted in the recovery of 12 equally parsimonious cladograms of 351 steps (CI = 0.48, HI = 0.52, and RI = 0.73). From these cladograms we present a phylogenetic hypothesis on the interrelationships of mosasauroids. Species assigned to Aigialosaurus form the basalmost mosasauroid clade. The new genus described here is reconstructed with Carsosaurus marchesettii in a clade that is the sistergroup to the following clade: (Haasiasaurus ((Halisaurinae, (Tethysaurus nopcsai (Yaguarasaurus columbianus, Russellosaurus coheni)) (Russellosaurina)))); the “Dallas aigialosaur,” Dallasaurus turneri, is found to be the basal-most mosasaurine. Arguments supporting the importance of pelvic evolution to the aquatic adaptations of mosasaurs are given along with a discussion of recent hypotheses of limb evolution in mosasauroids.

Vestigial forelimbs and axial elongation in a 95 million-year-old non-snake squamate

A new species of 95-million-year-old snake-like marine lizard, Adriosaurus sp. nov., shows complete loss of the manus and zeugopodium in association with elongation of the axial skeleton. The fossil was collected during the 19th century from Upper Cenomanian-aged (Upper Cretaceous) platy limestone quarries located near Komen, Slovenia (Fig. 1) (Jurkovšek et al., 1996; Cavin et al., 2000), and remained in collections at the Museo Civico di Storia Naturale in Trieste, Italy (MSCNT) until recent preparation revealed its unique anatomy (Fig. 2A; MCSNT 7792). The Komen squamate fauna includes the fully limbed adriosaur type species, Adriosaurus suessi, a number of undescribed adriosaurs, acteosaurs, eidolosaurs, and at least two taxa of aigialosaurs. The anatomy of this new species of Adriosaurus is informative regarding evolution within adriosaurs, but more importantly, when examined within the context of a resolved phylogeny of all squamates, illuminates broader evolutionary patterns of limb reduction and axial elongation within Squamata. In this study, we examine the transformation of the limb and axial skeleton using the phylogenies that find adriosaurs to be the sister taxon to snakes within a clade of pythonomorph squamates (e.g., Caldwell and Lee, 1997; Lee and Caldwell, 1998; Lee and Caldwell, 2000; Rage and Escuillié, 2000; Caldwell and Dal Sasso, 2004; Caldwell and Lee, 2004; Pierce and Caldwell, 2004). Despite the large number of claimed falsifications of the pythonomorph hypothesis (e.g., Zaher and Rieppel, 1999; Tchernov et al., 2000; Rieppel et al., 2003; Apesteguia and Zaher, 2006), the balance of these studies (excepting Rieppel and Zaher [2000] and Vidal and Hedges [2004]) have presented hypotheses of the ingroup relationships of snakes or have been focused on problems of character similarity without presenting an alternative snake sistergroup hypothesis and thus are of no comparative value for this study. Rieppel and Zaher’s (2000) phylogeny, produced by analysis of a selected subset of Lee’s (1998) characters and taxa, is also problematic for our purposes because they found amphisbaenians and dibamids, usually allied with lacertoids and scincids, respectively, to form a clade with snakes nested within Anguimorpha. Rationalizing amphisbaenians and dibamids as anguimorphs is problematic and so we have excluded the Rieppel and Zaher (2000) phylogeny. The molecule-based analysis of squamate phylogeny by Vidal and Hedges (2004) was ostensibly a falsification of the pythonomorph hypothesis. However, as was shown by Lee (2005), the empiricism of a total evidence analysis (taxa and characters) is the only suitable manner for inserting fossil taxa into a phylogenetic analysis. We follow Lee’s (2005) phylogeny as opposed to Vidal and Hedges’ (2004) inductive inference of the phylogenetic relationships of fossil snakes and mosasaurs. Therefore, we examine the evolutionary patterns and processes of squamate limblessness and axial elongation using the phylogenies produced by parsimony analysis of the morphology and/or molecules of fossil and modern squamates (e.g., Caldwell and Lee, 1997; Lee, 1997; Caldwell, 1999; Lee and Caldwell, 2000; Lee, 2005). We also discuss the phylogenetic distribution of limb reduction and elongation characters for snakes and lizards as they relate to the genetics of limb and body axis development in squamates (Cohn and Tickle, 1999; Weins and Slingluff, 2001; Adrianens et al., 2002; Shapiro, 2002; Sanger and Gibson-Brown, 2004).

The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution

The previous oldest known fossil snakes date from ~100 million year old sediments (Upper Cretaceous) and are both morphologically and phylogenetically diverse, indicating that snakes underwent a much earlier origin and adaptive radiation. We report here on snake fossils that extend the record backwards in time by an additional ~70 million years (Middle Jurassic-Lower Cretaceous). These ancient snakes share features with fossil and modern snakes (for example, recurved teeth with labial and lingual carinae, long toothed suborbital ramus of maxillae) and with lizards (for example, pronounced subdental shelf/gutter). The paleobiogeography of these early snakes is diverse and complex, suggesting that snakes had undergone habitat differentiation and geographic radiation by the mid-Jurassic. Phylogenetic analysis of squamates recovers these early snakes in a basal polytomy with other fossil and modern snakes, where Najash rionegrina is sister to this clade. Ingroup analysis finds them in a basal position to all other snakes including Najash.

A new genus and subfamily of mosasaurs from the Upper Cretaceous of northern Italy

ABSTRACT A new genus and two new species of mosasaurs are described from five specimens collected during quarrying operations in the ‘Lastame’ lithotype located in the mountains of northern Italy just to the north of Verona (lower Turonian—lower Santonian). These mosasaurs share some anatomical characters with the North American taxon Russellosaurus coheni, but the presence of distinctive features suggests placement into two new species within a new genus (e.g., forked distal tip of suprastapedial process of quadrate; suture between maxilla and premaxilla extends to point above third tooth position [cf. second in Russellosaurus]). We conducted two phylogenetic analyses of the Mosasauroidea (37 ingroup taxa, 131 characters), the first one with equally weighted characters and the second after successive weighting in order to reduce homoplastic noise and amplify the signal in the data. The first analysis (equal weights) resulted in 96 most parsimonious trees, whereas the second produced a single shortest tree. Both analyses consistently placed the new genus as the sister taxon to Russellosaurus, and these two taxa were placed together with Yaguarasaurus, in a clade that is the sister group of the Tethysaurinae (Tethysaurus and Pannoniasaurus). A new clade of mosasaurs, the Yaguarasaurinae, is here defined as comprising the most recent common ancestor of Russellosaurus, Romeosaurus, and Yaguarasaurus, and all of its descendants. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Giant taxon-character matrices: quality of character constructions remains critical regardless of size

Giant morphological data matrices are increasingly common in cladistic analyses of vertebrate phylogeny, reporting numbers of characters never seen or expected before. However, the concern for size is usually not followed by an equivalent, if any, concern for character construction/selection criteria. Therefore, the question of whether quantity parallels quality for such influential works remains open. Here, we provide the largest compilation known to us of character construction methods and criteria, as derived from previous studies, and from our own de novo conceptualizations. Problematic character constructions inhibit the capacity of phylogenetic analyses to recover meaningful homology hypotheses and thus accurate clade structures. Upon a revision of two of the currently largest morphological datasets used to test squamate phylogeny, more than one‐third of the almost 1000 characters analysed were classified within at least one of our categories of “types” of characters that should be avoided in cladistic investigations. These characters were removed or recoded, and the data matrices re‐analysed, resulting in substantial changes in the sister group relationships for squamates, as compared to the original studies. Our results urge caution against certain types of character choices and constructions, also providing a methodological basis upon which problematic characters might be avoided.

Emended diagnosis and phylogenetic relationships of the Upper Cretaceous fossil snake Najash rionegrina Apesteguía and Zaher, 2006

ABSTRACT The fossil snake Najash rionegrina, from the Cenomanian—Turonian (Upper Cretaceous) of Argentina, is reinterpreted after examination of the type and referred material. The current diagnosis is emended in the light of important considerations that cast doubt on the attribution of type and referred specimens (a braincase, a quadrate, and two dentary/lower jaw fragments) used to systematize this taxon. Alternative interpretations of the anatomy of the sacrum and hind limbs are proposed. Following the reevaluation of the anatomy of the type specimen and the removal from this taxon of the above-mentioned referred material, the phylogenetic position of N. rionegrina was tested in a series of maximum parsimony analyses that included all groups of extant snakes, all best-known fossil snakes (i.e., Pachyrhachis, Haasiophis, Eupodophis, Madtsoiidae, and Dinilysia), and alternative outgroups. Regardless of the outgroup used to polarize the character-state transformations, our phylogenetic analyses found no support for the hypothesis that Najash rionegrina occupies a position as the most basal snake. Depending on the outgroup, Najash is placed (1) in a position basal to all living snakes, but more derived than other fossil forms (most notably Pachyrhachis, Eupodophis, and Haasiophis); or (2) as the most basal representative of a clade of fossil snakes that is the sister group of living snakes; or (3) as the most basal representative of a clade of fossil snakes that is located between the Scolecophidia and the Alethinophidia. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Redescription of Acteosaurus tommasinii von Meyer, 1860, and a discussion of evolutionary trends within the clade Ophidiomorpha

ABSTRACT Redescription of the Upper Cretaceous marine squamate Acteosaurus tommasinii von Meyer, 1860, notes at least 10 cervical vertebrae, 27 dorsal vertebrae, an absence of pachyostosis on the vertebrae and ribs, overall limb reduction where the forelimbs are smaller than the hind limbs, a flattened pubic bone with a square pubic process and subrectangular descending ramus, small postzygapophyses on the trunk vertebrae, long and narrow neural spines on the caudal vertebrae, and posteroventrally positioned, unfused haemal arches on the caudals. Cladistic analysis of Acteosaurus and other marine squamates, including mosasauroids, dolichosaurs, pontosaurs, Adriosaurus, and Aphanizocnemus, and living and fossil snakes (Dinilysia, Yurlunggur, Eupodophis, Haasiophis, Pachyrhachis, Scolecophidia, Macrostomata, and Anilioidea) resulted in three most-parsimonious trees of 280 steps (C.I. = 0.59, R.I. = 0.81, R.C. = 0.48). All recovered tree topologies found support for the monophyly of the clade Ophidiomorpha, inclusive of Dolichosauridae (Dolichosaurus, Coniasaurus), Pontosaurus, Aphanizocnemus, Adriosaurus, Acteosaurus, and Ophidia. Acteosaurus is found to be a basal ophidiomorph and the sister taxon to the Ophidia.

Reevaluation of the anatomy of the Cenomanian (Upper Cretaceous) hind-limbed marine fossil snakes Pachyrhachis, Haasiophis, and Eupodophis

ABSTRACT New anatomical observations and reinterpretations of previously identified structures have resulted in new taxonomic diagnoses for the fossil hind-limbed marine snakes Pachyrhachis problematicus, Eupodophis descouensi, and Haasiophis terrasanctus. Among the most important conclusions of our study are the following: Haasiophis and Eupodophis show no evidence of possessing a laterosphenoid; Pachyrhachis and Eupodophis do retain a jugal; Haasiophis, like Eupodophis, has chevron bones in the caudal region; Haasiophis has a large number of unfused intercentra along the anterior portion of the precloacal column; the dentary of Pachyrhachis has numerous mental foramina (at least four); Pachyrhachis has at least one sacral vertebra with unfused sacral ribs. To test the effect of our new observations on the phylogenetic relationships of snakes, we ran three phylogenetic analyses using alternative outgroups to polarize the character transformations. The ingroup consisted of all well-preserved fossil snakes from the Cretaceous, the madtsoiids, and taxa that are representative of all major groups of extant snakes. The analyses yielded a series of most parsimonious trees that placed Pachyrhachis, Eupodophis, and Haasiophis either as a series of stem taxa at the base of the radiation of snakes (two analysis), or as members of a clade of fossil snakes that are the sister group of all living alethinopidians (one analysis).

A new species of marine ophidiomorph lizard, Adriosaurus skrbinensis, from the Upper Cretaceous of Slovenia

ABSTRACT A new species of the genus Adriosaurus Seeley, 1881, Adriosaurus skrbinensis, is described and diagnosed by the following unique features: presence of 30 dorsal vertebrae; much larger body size than that of A. suessi and A. microbrachis (about 60% larger); forelimbs much more reduced than the hind limbs, i.e., with a humerus/femur ratio of only 0.40; parietal foramen lying on the suture line between frontal and parietal; and anterior margin of the parietal convex anteriorly. Further features observed in A. skrbinensis, but obscured or poorly preserved in other adriosaurs, include intercentra articulating with (not fused or sutured to) cervical vertebrae; presence of high, rectangular neural spines on caudal vertebrae; very long chevron bones articulated to posterior ventral margin of caudal vertebrae; pubic bone with well-developed square anterior process and distinct pubic foramen. This new fossil suggests variability in the dorsal vertebrae count of Adriosaurus, ranging between 28 and 30. Similar to what has been observed in living scincids and anguids, there seems to be a direct relationship between axial elongation and shortening of the humerus in Adriosaurus. Cladistic analysis resulted in one shortest cladogram that places A. skrbinensis as the sister taxon to A. suessi.

Primary homologies of the circumorbital bones of snakes

Some snakes have two circumorbital ossifications that in the current literature are usually referred to as the postorbital and supraorbital. We review the arguments that have been proposed to justify this interpretation and provide counter‐arguments that reject those conjectures of primary homology based on the observation of 32 species of lizards and 81 species of snakes (both extant and fossil). We present similarity arguments, both topological and structural, for reinterpretation of the primary homologies of the dorsal and posterior orbital ossifications of snakes. Applying the test of similarity, we conclude that the posterior orbital ossification of snakes is topologically consistent as the homolog of the lacertilian jugal, and that the dorsal orbital ossification present in some snakes (e.g., pythons, Loxocemus, and Calabaria) is the homolog of the lacertilian postfrontal. We therefore propose that the terms postorbital and supraorbital should be abandoned as reference language for the circumorbital bones of snakes, and be replaced with the terms jugal and postfrontal, respectively. The primary homology claim for the snake “postorbital” fails the test of similarity, while the term “supraorbital” is an unnecessary and inaccurate application of the concept of a neomorphic ossification, for an element that passes the test of similarity as a postfrontal. This reinterpretation of the circumorbital bones of snakes is bound to have important repercussions for future phylogenetic analyses and consequently for our understanding of the origin and evolution of snakes. J. Morphol. 274:973–986, 2013.