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The first Miocene fossils of Lacerta cf. trilineata (Squamata, Lacertidae) with a comparative study of the main cranial osteological differences in green lizards and their relatives
Abstract
We here describe the first fossil remains of a green lizardof the Lacerta group from the late Miocene (MN 13) of the Solnechnodolsk locality in southern European Russia. This region of Europe is crucial for our understanding of the paleobiogeography and evolution of these middle-sized lizards. Although this clade has a broad geographical distribution across the continent today, its presence in the fossil record has only rarely been reported. In contrast to that, the material described here is abundant, consists of a premaxilla, maxillae, frontals, parietals, jugals, quadrate, pterygoids, dentaries and vertebrae. The comparison of these elements to all extant green lizard species shows that these fossils are indistinguishable from Lacerta trilineata. Thus, they form the first potential evidence of the occurrence of this species in the Miocene. This may be also used as a potential calibration point for further studies. Together with other lizard fossils, Solnechnodolsk shows an interesting combination of survivors and the dawn of modern species. This locality provides important evidence for the transition of an archaic Miocene world to the modern diversity of lizards in Europe. In addition, this article represents a contribution to the knowledge of the comparative osteological anatomy of the selected cranial elements in lacertid. This study gives special emphasis to the green lizards, but new data are also presented for related taxa, e.g., Timon lepidus, Podarcis muralis or Zootoca vivipara. Although the green lizards include several cryptic species for which determination based on isolated osteological material would be expected to be difficult, our comparisons show several important morphological differences.
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The amphisbaenian and anguimorph fossil lizards from the late Miocene (MN 13) Solnechnodolsk locality (southern European Russia) are described. Amphisbaenians are represented only by isolated vertebrae of which more precise allocation is difficult. The anguine material shows the presence of at least two taxa which are described from this area for the first time: Anguis cf. rarus and Ophisaurus cf. spinari. The A. rarus was previously known only from the early Miocene of Germany. Ophisaurus spinari has a broad stratigraphic range – from the early and middle Miocene of Central Europe, with the last occurrence documented from the late Pliocene of Italy. However, no record was known from the late Miocene, which would show an important part of the story. The parietal of A. cf. rarus forms the first evidence of its survival to the end of the Miocene by its shifting to south areas of Eastern Europe, together with O. spinari. The Solnechnodolsk material is evidence of a broad spatial and/or temporal distribution of both these anguine taxa and the parietal of Anguis unambiguously documents the presence of this taxon in Russia already in the late Miocene. The thermophilic forms in Solnechnodolsk are represented by monitor lizards (Varanus).
The best-preserved material of Dracaenosaurus croizeti, an almost complete and previously unpublished skull with a few associated postcranial bones (stylopodium, zeugopodium, and cervical vertebra), is described. The material comes from the locality of Cournon, a late Oligocene site in south-central France. Micro-computed tomography applied to this specimen revealed previously unknown internal osteological characters. Among lacertids, this taxon represents a notable phenomenon: it is an extreme durophagous specialist. Many of the newly observed cranial character states reflect the lifestyle of this lizard, because animals with a hard-shelled diet display a specialized cranial morphology associated with more massive cranial muscles. One unique character for Lacertidae is observed: the parietal-supraoccipital contact is formed by a ventrally deep parietal crest that fits into a bifurcate ascending process of the supraoccipital. In fact, such a connection represents the opposite to the connection in modern members of Lacertidae. Phylogenetic analysis recovered Dracaenosaurus inside Gallotiinae, a clade that would consist of the mainly Oligocene genera Pseudeumeces and Dracaenosaurus, the Miocene genus Janosikia, and the extant Psammodromus and Gallotia. Our study supports previous phylogenetic results and provides an example of the achievement of large size in mainland members of the stem of Gallotia, previously exemplified by Janosikia and Pseudeumeces. The extreme amblyodonty of Dracaenosaurus also confirms the view that herbivory in Gallotia is derived and may be the result of insularity.
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Citation for this article: Čerňanský, A., A. Bolet, J. Müller, J.-C. Rage, M. Augé, and A. Herrel. 2017. A new exceptionally preserved specimen of Dracaenosaurus (Squamata, Lacertidae) from the Oligocene of France as revealed by micro-computed tomography. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1384738.
We describe a new lizard taxon, Stefanikia siderea gen. et sp. nov., from the early-middle Eocene locality of Messel in Germany based on a nearly complete skeleton, which we studied using μCT methods. It shares many characters with the Eocene taxon Eolacerta, which is broadly distributed in the Eocene of central and Western Europe, but is much smaller and shows several important anatomical differences. The new discovery sheds light on the paleodiversity of these lizards in the Eocene of Europe, and the new family name Eolacertidae is proposed to encompass Eolacerta and Stefanikia. The relationships of Eolacerta have been intractable. Our phylogenetic analyses confirm that Eolacertidae is a member of the clade Lacertiformes and provide strong support for a sister-group relationship to Lacertidae. In some places, skin impressions are preserved, displaying the body scalation. As such, the exquisitely preserved specimens of Eolacertidae from Messel provide new insight into the morphology and ecology of lizards on the stem of Lacertidae, Europe’s dominant group of living reptiles.
http://zoobank.org/urn:lsid:zoobank.org:pub:DFD01563-A913-4286-B64B-E0912474FD08
We describe the first juvenile specimen of an eolacertid lizard. The material comes from one of the most important Eocene localities, the Messel Pit in Germany. The new specimen provides unique information on the early ontogeny of Eolacerta, the largest known lizard from Messel, with a maximum snout-vent length greater than 30 cm and a mass approaching 1 kg. The specimen described here, with a SVL of 11.3 cm and an estimated mass of 21 g, can be allocated more precisely to Eolacerta robusta based on the co-occurrence and the combination of following features: (1) the nasal process of premaxilla is long; (2) position of lacrimal (being more anteriorly located in Stefanikia siderea); (3) the postorbital process of jugal is broad; (4) the ratio of the anterior and posterior region of the frontal between the sulcus interfacialis; (5) a mid-parietal constriction of the parietal table is present; (6) the interparietal shield broadens anteriorly; (7) the transverse sulcus is straight anteriorly. The incipient character of the parietal constriction and the slightly lower number of maxillary teeth (28 vs. 30–32 in adults) are consistent with a juvenile animal. Very important is evidence for the presence of pterygoid dentition (pointed teeth arranged in a single line) and the absence of palatine dentition. Ceratobranchial I is observed for the first time for this species, and its shape and length are very similar to those of Lacertidae. There are 27 presacral vertebrae in the juvenile, as in adults. In the juvenile specimen, ventral keel on the centrum is present in all vertebrae. The ventromedial portion of the ischium is well preserved here and gives information on the exact shape of this portion, at least in juvenile form. The scalation, as far as it is preserved, is similar to that of Stefanikia, except that the rectangular subdigital scales are longer in comparison with their width, and therefore have a broader appearance.
Timon is a large-sized lacertid lizard genus with a peculiar current distribution around the Mediterranean. Six species form three distinct clades, which are geographically separated from each other. These clades inhabit the Iberian Peninsula, France and the north-western coast of Italy (Timon lepidus and T. nevadensis); the North-African part of the western Mediterranean Basin (T. pater and T. tangitanus); and the Middle East, without connection to the Mediterranean (Turkey, Syria, Iraq and Iran; T. kurdistanicus and T. princeps). Fossil occurrences are known, but are mostly restricted to the current geographical range, with some possible exceptions from Corsica, Sicily, Malta and south-eastern Italy, none of which has yet been assessed in detail. Herein, we describe fossils from the Pleistocene of Monte Tuttavista (Sardinia, Italy), which have previously been attributed to Lacerta sp. Inclusion of these fossils into a phylogenetic matrix of lacertid lizards shows that they are instead referable to Timon. It represents the first fossil occurrence of this genus from Sardinia and confirms earlier reports of a wider distribution of the genus until the late Pleistocene. The local extinction of the genus on Sardinia seems to coincide with the appearance of predators specialized to capture small prey and with strong climatic fluctuations.
Aim
The Aegean Sea constitutes a major biogeographic barrier between the European and Asian continents and several models of diversification in the Aegean have been documented. Here, we test three of those models for the Aegean green‐lizards (Lacerta trilineata–pamphylica group): Vicariance versus Overland Dispersal versus Island Stepping‐stone Dispersal. We investigate these hypotheses and complement our knowledge on the impact of the Aegean Barrier on east Mediterranean taxa.
Location
Aegean Sea, east Mediterranean.
Taxon
Lacerta lizards.
Methods
We analysed ddRAD loci (double‐digest restriction‐site‐associated DNA) to estimate species‐trees under coalescent models and maximum likelihood trees using concatenation. We performed hierarchical population structure analyses and inferred ancestral distribution‐areas. We also sequenced the complete cytochrome b gene and produced a time‐calibrated mtDNA gene‐tree to conduct a critical comparison with previous studies.
Results
Aegean green‐lizards diverged into four main groups in parallel during the Late Pliocene with distributions to the East and West of the Aegean. The Eastern group includes Lacerta pamphylica and East Aegean L. trilineata, while the Western group contains the Central Cyclades populations and the remaining populations of the Balkan Peninsula. The Aegean green‐lizards’ ancestor occurred in Anatolia, while the West lineage ancestor occurred in the Central Cyclades islands, revealing a dispersal between the two regions. The radiations of all major green‐lizard groups, including trilineata+pamphylica, occurred in parallel in the Late Pliocene.
Main Conclusions
In contrast to previously suggested biogeographical hypotheses for the group, based on mtDNA, the Island Stepping‐stone Dispersal scenario is strongly supported. Green lizards offer a rare paradigm of diversification in the Aegean, where populations largely expanded their geographical distribution and crossed the Aegean Barrier using the central Aegean islands as stepping stones.
Lizards were and still are an important component of the European herpetofauna. The modern European lizard fauna started to set up in the Miocene and a rich fossil record is known from Neogene and Quaternary sites. At least 12 lizard and worm lizard families are represented in the European fossil record of the last 23 Ma. The record comprises more than 3000 occurrences from more than 800 localities, mainly of Miocene and Pleistocene age. By the beginning of the Neogene, a marked faunistic change is detectable compared to the lizard fossil record of Palaeogene Europe. This change is reflected by other squamates as well and might be related to an environmental deterioration occurring roughly at the Oligocene/Miocene boundary. Nevertheless, the diversity was still rather high in the Neogene and started to decrease with the onset of the Quaternary glacial cycles. This led to the current impoverished lizard fauna, with the southward range shrinking of the most thermophilic taxa (e.g., agamids, amphisbaenians) and the local disappearance of other groups (e.g., varanids). Our overview of the known fossil record of European Neogene and Quaternary lizards and worm lizards highlighted a substantial number of either unpublished or poorly known occurrences often referred to wastebasket taxa. A proper study of these and other remains, as well as a better sampling of poorly explored time ranges (e.g., Pliocene, Holocene), is needed and would be of utmost importance to better understand the evolutionary history of these reptiles in Europe.
A reexamination of the holotype frontoparietal of Pelobates praefuscus Khosatzky, 1985 from the Pliocene of Moldova and an investigation of newly referred frontoparietal reveal previously unknown characters for this species. P. praefuscus, considered a synonym of Pelobates fuscus, is regarded here as a separate species. It differs from P. fuscus in the presence of frontoparietal-squamosal contact and medial position of the foramen arteriae occipitalis and from all extant Pelobates in having the arteria orbitonasalis open posteriorly. The last character, previously known only in early Miocene Pelobates, is shown to be present in late Miocene and early Pliocene congeners, whereas in late Pliocene–Pleistocene congeners, the posterior part of the arteria orbitonasalis generally is covered ventrally by bone.
The new locality of Çeştepe in the Kazan Basin, 45 km NNW of Ankara, yielded the remains of three species of reptiles (cf. Lacerta sp., Anguinae indet. and Varanus sp.) and an ochotonid lagomorph, Ochotona mediterranensis Suata Alpaslan, 2009. The latter species suggests an early Pliocene age (MN14). The fossil layer is included in the Sinap Formation that delivered abundant remains of Mio-Pliocene mammals in the southern part of the basin, but in the northern part of the basin Çeştepe is currently the unique fossil site. The age assigned by the fauna led to revise the stratigraphy of sedimentary formations in the Çeştepe area, previously confusing because of the various lithostratigraphic unit names and ages given in previous work. The taxa described in this note are still poorly known in Turkey. Varanus has been previously reported from Çalta, a locality 16.3 km SW to Çeştepe in the same basin, and O. mediterranensis from Iğdeli in the Sivas Basin. Although represented by a few taxa, the Çeştepe faunule shows Eurasian affinities.