Fossil Amphibians Research Articles

A review of the Late Miocene herpetofauna of the Keinar locality of Moldova

Small fossil amphibians and reptiles from the Late Miocene of the Keinar locality of Moldova are reviewed for the first time. The following taxa are described: Mioproteus caucasicus, Chelotriton sp., Latonia sp., Pelobates sp., Pelophylax sp., “Colubrinae” indet., Natrix sp., two Vipera spp. (“Vipera aspis complex” and “Oriental vipers complex”), and Squamata indet. Among them, Pelobates sp. exhibits the characters which occur in the Early–Late Miocene (presence of both pit-and-ridge and pustular sculptures of the frontoparietal bone) and in the Pliocene (short frontoparietal–squamosal contact) members of the genus; this combination is not observed in any other Pelobates species. The viperid snake of the “Vipera aspis complex” is recorded from Moldova for the first time.

Extended Lissamphibia: a tale of character non-independence, analytical parameters and islands of trees

The age, content and inter-order relationships of crown Lissamphibia remain a debated topic in vertebrate systematics. Recent phylogenetic analyses of fossil amphibians were used to propose an extended Lissamphibia, with Anura and Caudata nested in Dissorophoidea and with Gymnophiona nested in Stereospondyli, but this hypothesis was not supported by subsequent studies on updated matrices. In a parsimony context, the extended Lissamphibia hypothesis was shown to result from the effects of large island bias on the majority-rule consensus, which masked the presence of topologies supporting the restricted Lissamphibia hypothesis, with all extant orders nested in Dissorophoidea or in Stereospondyli. Re-analysing this dataset, taking into account the presence of inapplicable and polymorphic character states and revising the scores for logically non-independent characters, shows that the phylogenies inferred from the morphological data matrix used to propose the extended Lissamphibia hypothesis are not robust to changes in analytical parameters and that great care should be taken when analysing fossil amphibian datasets. With the set of most parsimonious trees inferred from the unrevised matrix used to propose the extended Lissamphibia hypothesis, I also demonstrate that the phenomenon of large island bias extends to phylogenetic networks, but not to topology-based tests of taxonomic instability that do not rely on split-frequencies.

New paleoecological inferences based on the Early Pleistocene amphibian and reptile assemblage from Dmanisi (Georgia, Lesser Caucasus)

Dmanisi (Georgia) is one of the oldest Early Paleolithic sites discovered out of Africa. In addition, it is the best site to understand the first Homo deme out of Africa and the first hominin occupation of Central to Western Eurasia. It has produced more than 40 hominin remains, including several very informative skulls, found in direct association with faunal remains and numerous lithic artifacts. To date, fossil amphibians and reptiles are one of the few proxies that have been used to propose quantitative climate reconstructions for the time where the hominins were living at Dmanisi. The aim of the present study is to review and amplify the previous paleoclimatic interpretation given by Blain et al. (2014), with an enhanced methodology using geographic information system and based on uncertain distribution area-occupied distribution area discrimination technique. This procedure permits to approach to a more precise common species distribution area and then using the WorldClim v. 2.1 climate database to propose for the first time monthly reconstructions for temperature and rainfall, in addition to annual parameters. The same technique is used to infer dominant ecoregions through the study area and potential tree coverage. Dmanisi climate is newly reconstructed as warm and semi-arid, similar to the present-day Mediterranean climate. New estimates however suggest warmer temperatures than previously reconstructed, together with a slightly higher but much more irregular amount of rainfall. The aridity indexes suggest a six months dry period, from May to October. Associated regional paleoenvironment is mainly characterized by Mediterranean forests, woodlands, and scrub, and the potential tree coverage is around 25%, that is, much less forested than today. New estimates agree with the ‘Iberian’ hominin ecological model, and with other proxies (large mammals, small mammals and archaeobotanical remains) that indicate a period of increased aridity contemporaneous with human occupations of the site.

On Defining and Finding Islands of Trees and Mitigating Large Island Bias.

How best can we summarize sets of phylogenetic trees? Systematists have relied heavily on consensus methods, but if tree distributions can be partitioned into distinct subsets, it may be helpful to provide separate summaries of these rather than relying entirely upon a single consensus tree. How sets of trees can most helpfully be partitioned and represented leads to many open questions, but one natural partitioning is provided by the islands of trees found during tree searches. Islands that are of dissimilar size have been shown to yield majority-rule consensus trees dominated by the largest sets We illustrate this large island bias and approaches that mitigate its impact by revisiting a recent analysis of phylogenetic relationships of living and fossil amphibians. We introduce a revised definition of tree islands based on any tree-to-tree pairwise distance metric that usefully extends the notion to any set or multiset of trees, as might be produced by, for example, Bayesian or bootstrap methods, and that facilitates finding tree islands a posteriori. We extract islands from a tree distribution obtained in a Bayesian analysis of the amphibian data to investigate their impact in that context, and we compare the partitioning produced by tree islands with those resulting from some alternative approaches. Distinct subsets of trees, such as tree islands, should be of interest because of what they may reveal about evolution and/or our attempts to understand it, and are an important, sometimes overlooked, consideration when building and interpreting consensus trees. [Amphibia; Bayesian inference; consensus; parsimony; partitions; phylogeny; Chinlestegophis.]

First occurrence of brachyopid temnospondyls in Southeast Asia and review of the Mesozoic amphibians from Thailand

Abstract. The non-marine Mesozoic sedimentary rocks of Thailand, which consist of the Indochina block and the Sibumasu block, have yielded several terrestrial and aquatic vertebrate fossils, but only few amphibian remains have been reported. Here, we present an overview on the Thai amphibian palaeo-diversity based on the literature, re-examination of published material, new findings, and unpublished material. Thai amphibian fossil remains are assigned to Stereospondyli (Cyclotosauridae, Plagiosauridae, and Brachyopoidea) and Anura and were discovered from four formations, ranging from the Upper Triassic to Lower Cretaceous of Thailand. The occurrence of Brachyopidae in Thailand, which are related to Chinese forms, supports the previous hypothesis of physical connections between the Indochina blocks and the Sibumasu block during the Mesozoic era.

Enigmatic amphibians in mid-Cretaceous amber were chameleon-like ballistic feeders.

Albanerpetontids are tiny, enigmatic fossil amphibians with a distinctive suite of characteristics, including scales and specialized jaw and neck joints. Here we describe a new genus and species of albanerpetontid, represented by fully articulated and three-dimensional specimens preserved in amber. These specimens preserve skeletal and soft tissues, including an elongated median hyoid element, the tip of which remains embedded in a distal tongue pad. This arrangement is very similar to the long, rapidly projecting tongue of chameleons. Our results thus suggest that albanerpetontids were sit-and-wait ballistic tongue feeders, extending the record of this specialized feeding mode by around 100 million years.

Ancient amphibians preserved in amber

Paleontology Extant amphibians are represented by three fairly simple morphologies: the mostly hopping frogs and toads, the low-crawling salamanders, and the limbless caecilians. Until the early Pleistocene—and for more than 165 million years—there was another group, the albanerpetontids. We know little about this group because amphibian fossils are poorly preserved, and previous specimens from this group are both rare and mostly badly damaged. Daza et al. describe a set of fossils preserved in amber showing that this group was unusual both in their habitat use (they may been climbers) and their feeding mode, which appears to have been convergent with the ballistic feeding now seen in chameleons (see the Perspective by Wake). Science , this issue p. [687][1]; see also p. [654][2] [1]: /lookup/doi/10.1126/science.abb6005 [2]: /lookup/doi/10.1126/science.abe7826

Hierarchical biota-level and taxonomic controls on the chemistry of fossil melanosomes revealed using synchrotron X-ray fluorescence

Fossil melanosomes, micron-sized granules rich in melanin in vivo, provide key information for investigations of the original coloration, taxonomy and internal anatomy of fossil vertebrates. Such studies rely, in part, on analysis of the inorganic chemistry of preserved melanosomes and an understanding of melanosome chemical taphonomy. The extent to which the preserved chemistry of fossil melanosomes is biased by biotic and abiotic factors is, however, unknown. Here we report the discovery of hierarchical controls on the inorganic chemistry of melanosomes from fossil vertebrates from nine biotas. The chemical data are dominated by a strong biota-level signal, indicating that the primary taphonomic control is the diagenetic history of the host sediment. This extrinsic control is superimposed by a biological, tissue-level control; tissue-specific chemical variation is most likely to survive in fossils where the inorganic chemistry of preserved melanosomes is distinct from that of the host sediment. Comparative analysis of our data for fossil and modern amphibians reveals that most fossil specimens show tissue-specific melanosome chemistries that differ from those of extant analogues, strongly suggesting alteration of original melanosome chemistry. Collectively, these findings form a predictive tool for the identification of fossil deposits with well-preserved melanosomes amenable to studies of fossil colour and anatomy.

Plio-Pleistocene Amphibians and Reptiles from Central Turkey: New Faunas and Faunal Records with Comments on their Biochronological Position Based on Small Mammals

Abstract Small fossil vertebrates from several Pliocene and Pleistocene localities in Central Anatolia (Turkey) are reviewed. Data on small mammals represent assemblages from the early Pliocene (MN 14: Nasrettinhoca 1, 2 and Hamamkarahisar A, B), and late Pliocene (MN 16: Hoyhoytepe 1, 2, 3 and Mercan 1); Early Pleistocene (MN 17: Mercan 2), and Middle Pleistocene (MQ 1/MQ 2: Yenişarbademli). The biochronology related characters of arvicolines Promimomys, Mimomys, Microtus, Lagurus and Clethrionomys are briefly discussed. Data on the systematics of fossil amphibians and reptiles is also described from these localities. The early Pliocene (MN 14) assemblages significantly add to knowledge on the herpetofaunal composition of this stratigraphic level, which until now was poorly characterized in Turkey. Remains of Pelobatidae, Bufonidae, Ranidae, Amphisbaenia and Natricinae are reported for the first time from the MN 14 biozone of Turkey. Palaeobatrachus from Mercan 1 extends the temporal range of this group in the Eastern Mediterranean into the late Pliocene. The described remains of amphibians and reptiles from Turkey span a considerable stratigraphic range from the early Pliocene to the Middle Pleistocene (time interval of about 5 Ma) and partly fill a gap in the palaeoherpetofaunal record of the Eastern Mediterranean.

The effect of geographic range and climate on extinction risk in the deep-time amphibian fossil record

Geographic range is of crucial importance concerning the extinction risk of species. However, our understanding of how the influence of this trait on extinction risk has varied through Earth history and across different climate regimes is still rather unexplored. This is especially true for taxa that are currently of strong interest in conservation biology, displaying a strong mismatch between paleontological studies and modern efforts to quantify the extinction risk of threatened species. We herein calculated a continuous measure for the connection of geographic range and extinction risk in the deep-time amphibian fossil record. Furthermore, we evaluated the impact of climate on this connection, using two climate proxies derived from oxygen isotope data (global relative temperature change and variations in the latitudinal temperature gradient). We show that geographic ranges tended to be larger during times of comparatively small latitudinal temperature gradients. Moreover, the strength of geographic range influencing extinction risk fluctuated temporally, but remained positive at all times. The variation in range size impact on extinction risk showed a strong connection with the latitudinal temperature gradient. Our findings indicate that geographic range persists as a factor influencing species’ extinction risk through all times. However, geographic range seemed less important during times of higher environmental variability. Reasons might be the restriction of species ranges due to environmental constraints, causing ranges to become more similar and therefore lose relative importance in buffering for extinction risk, while other factors gain in importance. Simultaneously, similar ranges might be more prone to alteration by e.g. conservation biases (related to sedimentary deposition and fossilization) in relation to their real range size, resulting in a smaller signal-to-noise ratio, potentially affecting the correlation strength. We show that trait-extinction risk dynamics can vary in their intensity, and that specifically the observed impact of geographic range on extinction risk can vary with climatic changes.

Tissue-specific geometry and chemistry of modern and fossilized melanosomes reveal internal anatomy of extinct vertebrates

Recent discoveries of nonintegumentary melanosomes in extant and fossil amphibians offer potential insights into the physiological functions of melanin not directly related to color production, but the phylogenetic distribution and evolutionary history of these internal melanosomes has not been characterized systematically. Here, we present a holistic method to discriminate among melanized tissues by analyzing the anatomical distribution, morphology, and chemistry of melanosomes in various tissues in a phylogenetically broad sample of extant and fossil vertebrates. Our results show that internal melanosomes in all extant vertebrates analyzed have tissue-specific geometries and elemental signatures. Similar distinct populations of preserved melanosomes in phylogenetically diverse vertebrate fossils often map onto specific anatomical features. This approach also reveals the presence of various melanosome-rich internal tissues in fossils, providing a mechanism for the interpretation of the internal anatomy of ancient vertebrates. Collectively, these data indicate that vertebrate melanins share fundamental physiological roles in homeostasis via the scavenging and sequestering of metals and suggest that intimate links between melanin and metal metabolism in vertebrates have deep evolutionary origins.

Fossil amphibians and reptiles from the Neogene locality of Maramena (Greece), the most diverse European herpetofauna at the Miocene/Pliocene transition boundary

Fossil amphibians and reptiles from the Neogene locality of Maramena (Greece), the most diverse European herpetofauna at the Miocene/Pliocene transition boundary

Fossil amphibians and reptiles from Tegelen (Province of Limburg) and the early Pleistocene palaeoclimate of The Netherlands

Few Quaternary herpetofaunas have been recovered from The Netherlands. Among these, the one coming from the early Pleistocene site of the Russel-Tiglia-Egypte pit near Tegelen is of particular interest, because it is the type locality of the recently described, last western European palaeobatrachid anuran, Palaeobatrachus eurydices. The large number of fossil remains of amphibians and reptiles found in the pit are representative of a very diverse fauna, including at least 17 taxa: Triturus gr. T. cristatus, Lissotriton sp., Pelobates fuscus, Bufo bufo, Bombina sp., Pelophylax sp., Rana sp., Hyla gr. H. arborea, Pelodytes sp., Mauremys sp., Lacerta sp., Lacertidae indet., Anguis gr. A. fragilis, cf. Pseudopus sp., “colubrines” indet., Natrix natrix and Vipera sp. Emys orbicularis, previously reported from a different Tegelen pit, is not present in this assemblage. Palaeoclimatic conditions reconstructed based on the herpetofaunistic association indicate a humid subtropical climate (Cfa according to the Köppen-Geiger classification of climates) for Tegelen during the TC5 section of the Tiglian, with low, but fairly regular rainfalls during the year. Mean annual temperature was 13.4 ± 0.3 °C and mean annual precipitation was 542 ± 50 mm. Moreover, three dry months were present during summer and early autumn, resulting in a much drier climate than the one present at Tegelen today. Nevertheless, the occurrence of the water-dwelling P. eurydices suggests the persistence of suitable permanent water bodies during the whole year, and the survival of this taxon in this part of Europe might have been allowed by the generally humid climate.

Common occurrence of Sharpey\u2019s fibres in amphibian phalanges

Sharpey’s fibres are known mainly as providing anchorage between tooth and the periodontal ligament but they occur also in other types of bones. In the postcranial skeleton these fibres are usually present at the muscle or tendon attachment sites. They were reported in all major groups of extant vertebrates, as well as in putative lissamphibian ancestors—temnospondyls and lepospondyls. However, it was recently stated that their presence was very rarely described in extant amphibians. In limbs, they were reported predominantly from proximal bones. They have not yet been reported from phalanges, which are the most commonly sectioned amphibian bones. Here, we describe phalangeal histology of nine species representing most major clades of lissamphibians. These results show that Sharpey’s fibres occur commonly in lissamphibian phalanges. In shaft, they are radially oriented and occur in the periosteal bone, at sites of tendon attachment. They can also occur in the metaphysis and contact the cartilage. This may provide a basis for foot muscle reconstructions in fossil amphibians.

New palaeoenvironmental and palaeoclimatic reconstructions for the Middle Palaeolithic site of Cuesta de la Bajada (Teruel, eastern Spain) inferred from the amphibian and squamate reptile assemblages

In the eastern Iberian Peninsula, the archaeological site of Cuesta de la Bajada (Teruel, Spain) has produced some of the earliest evidence of Middle Paleolithic stone tool traditions together with evidence of equid and cervid carcasses defleshed by hominins. Based on the numerical age of 317-240 ka derived from OSL, ESR and AAR dating methods for the lower part of the Cuesta de la Bajada sedimentological sequence (level CB3), as well as the biochronological inferences for the small and large mammal associations, the site can be attributed to Marine Isotope Stage (MIS) 8 or the end of MIS 9. As amphibians and reptiles have precise environmental and climatic requirements and do not differ at species level from the extant herpetofauna of the Iberian Peninsula, they can contribute to the reconstruction of the landscape and climate. In this paper, the fossil amphibians and squamate reptiles from Cuesta de la Bajada are studied for the first time. The mutual ecogeographic range and habitat weighting methods were applied to the herpetofaunal assemblages to estimate quantitative data for the landscape and climate reconstructions. The climate is shown to have been colder and wetter than today in the interior of eastern Spain, with mean annual temperature up to 2.5 °C lower and mean annual precipitation slightly higher than at present. The monthly climatic reconstruction shows differences in the distribution of precipitation over the course of the year, with more abundant precipitation from late autumn to spring (i.e. from October to May), and more or less similar precipitation to today during the summer months (July and August). This suggests there was stronger rainfall seasonality between winter and summer than currently occurs. The paleoenvironmental reconstruction based on the herpetofaunal assemblage depicts a poorly forested (15–20%) patchy landscape with a large representation of dry meadows and scrubland habitats together with well-evidenced aquatic habitats. These reconstructions are consistent with other proxies recovered at Cuesta de la Bajada (pollen, small and large mammals) as well as other European MIS 8–9 paleoclimatic records. We can thus correlate levels CB2 and CB3 with the later part of MIS 8 (265-257 ka) or with a humid fluctuation within the MIS9b (303-290 ka). It is also possible to provide a new description of the environmental and climatic conditions that occurred in inner Spain during a cold period of the late Middle Pleistocene.

Contradicting habitat type-extinction risk relationships between living and fossil amphibians.

Trait analysis has become a crucial tool for assessing the extinction risk of species. While some extinction risk-trait relationships have been often identical between different living taxa, a temporal comparison of fossil taxa with related current taxa was rarely considered. However, we argue that it is important to know if extinction risk-trait relations are constant or changing over time. Herein we investigated the influence of habitat type on the persistence length of amphibian species. Living amphibians are regarded as the most threatened group of terrestrial vertebrates and thus of high interest to conservationists. Species from different habitat types show differences in extinction risk, i.e. species depending on flowing waters being more threatened than those breeding in stagnant sites. After assessing the quality of the available amphibian fossil data, we show that today's habitat type-extinction risk relationship is reversed compared to fossil amphibians, former taxa persisting longer when living in rivers and streams, thus suggesting a change of effect direction of this trait. Neither differences between amphibian orders nor environmentally caused preservation effects could explain this pattern. We argue this change to be most likely a result of anthropogenic influence, which turned a once favourable strategy into a disadvantage.

Fossil amphibians and reptiles from Plakias, Crete: A glimpse into the earliest late Miocene herpetofaunas of southeastern Europe

Fossil amphibians and reptiles from the earliest late Miocene (early Tortonian, MN 9) of Plakias (Crete, Greece) are described in this paper. Most of the material is fragmentary, precluding precise taxonomic assignment. Nevertheless, the herpetofauna of Plakias is here shown to be diverse, comprising at least six different taxa: an alytid anuran, a crocodilian, two turtles (a pan-trionychid and a geoemydid) and two squamates (an amphisbaenian and a colubroid snake). The crocodilian material represents the first such fossils described from Greece and furthermore, one of the latest occurrences of this group in Europe. The pan-trionychid and the geoemydid represent the oldest occurrences of these groups in Greece and further add to their scarce Miocene record from this country. The first description of a fossil amphisbaenian from Greece is also provided. The new specimens from Plakias add to our knowledge of the Miocene herpetofaunas of southeastern Europe.

Smith Woodward's contributions on fossil tetrapods

Abstract Although primarily a pre-eminent palaeoichthyologist, Arthur Smith Woodward's research and publications ranged across all major tetrapod groups: nevertheless, his contributions in this area have generally been overshadowed by involvement in the ‘Piltdown Man’ affair. Smith Woodward published on fossil amphibians, every major group of reptiles and on mammals. Most of the new taxa he named remain valid, a testament to his wide knowledge and understanding of fossil vertebrates beyond his principal speciality, although some of these have now been extensively revised. He travelled widely in Europe and the Americas, resulting in some of the earliest work on Gondwanan Cretaceous reptiles. Several of his taxa revealed the existence of previously unknown groups (e.g. notosuchian crocodiles) or provided important character data that have fuelled various phylogenetic debates (e.g. snake and tyrannosauroid origins). His influence extended beyond his own scientific efforts to incorporate his role as a senior administrator, supporting the acquisition of significant reptile specimens for the collection, and as an educator, producing articles for museum visitors and the general public.

Chemical, experimental, and morphological evidence for diagenetically altered melanin in exceptionally preserved fossils

In living organisms, color patterns, behavior, and ecology are closely linked. Thus, detection of fossil pigments may permit inferences about important aspects of ancient animal ecology and evolution. Melanin-bearing melanosomes were suggested to preserve as organic residues in exceptionally preserved fossils, retaining distinct morphology that is associated with aspects of original color patterns. Nevertheless, these oblong and spherical structures have also been identified as fossilized bacteria. To date, chemical studies have not directly considered the effects of diagenesis on melanin preservation, and how this may influence its identification. Here we use time-of-flight secondary ion mass spectrometry to identify and chemically characterize melanin in a diverse sample of previously unstudied extant and fossil taxa, including fossils with notably different diagenetic histories and geologic ages. We document signatures consistent with melanin preservation in fossils ranging from feathers, to mammals, to amphibians. Using principal component analyses, we characterize putative mixtures of eumelanin and phaeomelanin in both fossil and extant samples. Surprisingly, both extant and fossil amphibians generally exhibit melanosomes with a mixed eumelanin/phaeomelanin composition rather than pure eumelanin, as assumed previously. We argue that experimental maturation of modern melanin samples replicates diagenetic chemical alteration of melanin observed in fossils. This refutes the hypothesis that such fossil microbodies could be bacteria, and demonstrates that melanin is widely responsible for the organic soft tissue outlines in vertebrates found at exceptional fossil localities, thus allowing for the reconstruction of certain aspects of original pigment patterns.

Ericek, a new Pliocene vertebrate locality in the Çameli Basin (southwestern Anatolia, Turkey)

The Cameli Basin in southwestern Anatolia preserves a sequence of fossiliferous sediments that record the Pliocene and early Pleistocene faunal development in the area. Here, we present the fauna of Ericek, a locality near the bottom of the sequence. The locality is rich in fish remains, particularly pharyngeal teeth of the cyprinids Barbus, Carassius and Capoeta, but also includes rare tooth-bearing bones of a possible cobitid and gobiid. The abundant fish remains agree with the geological interpretation that the Ericek sediments were deposited in a palaeolake. That interpretation is further supported by the abundance of mollusc fossils. The gastropod fauna is dominated by Pseudamnicola, Valvata and other freshwater prosobranch taxa. The dominance of prosobranch taxa over freshwater pulmonate species indicates a well-oxygenated lake environment. A range of aquatic, swamp and terrestrial tetrapod taxa are also represented. The amphibian fauna, documented mainly by anuran skull and postcranial bones and by a single salamander jaw, is consistent with a lacustrine setting for Ericek. Notable among the amphibian fossils are two jaws that may document the second record of palaeobatrachid frogs from Anatolia. Reptiles are represented by a few, incomplete vertebrae of colubroid and indeterminate snakes. Micromammal molars suggest the presence of a forested environment surrounding the palaeolake. Muridae are represented by three species, of which Apodemus cf. dominans is the most abundant. The shrew Asoriculus is the second most abundant species, which argues for a humid palaeoenvironment. The co-occurrences of the vole Mimomys occitanus and of the murids Orientalomys cf. similis and Rhagapodemus cf. primaevus indicate a late MN 15 age for the fauna, at an estimated age of 3.4 Ma.