Fossil Salamander Research Articles

Morphometric analyses of the vertebrae of Ambystoma (Tschudi, 1838) and the implications for identification of fossil salamanders.

Ambystoma (Tschudi, 1838) represents a speciose clade of salamanders that are found across much of North America. Fossils referred to Ambystoma are reported from early Cenozoic deposits and are common in Quaternary fossil deposits. Most fossils identified as Ambystoma are isolated vertebrae. Both quantitative and qualitative characters were reported as being useful for identifying fossilized vertebrae of Ambystoma below the genus level. However, there is limited information on intraspecific variation in those characters and previous studies noted intracolumnar variation which affects the utility of those characters for fossil identification. A lack of understanding of variation in modern species of Ambystoma casts uncertainty on our ability to identify fossil vertebrae confidently. We aimed to document intraspecific and intracolumnar variation in vertebral morphology among species of Ambystoma and examine the implications for fossil identification. We assembled one of the largest skeletal data sets for Ambystoma and took linear measurements on 15 species. We used 2D geometric morphometric analyses to characterize atlantal shape variation in Ambystoma. We apply those morphometric data in a case study where we identify fossil vertebrae from Hall's Cave, a Quaternary fossil locality in central Texas. We found patterns of intraspecific and intracolumnar variation that have substantial implications for fossil identification. Classification accuracies for species and clades within Ambystoma varied considerably. Overall classification accuracies based on size-adjusted measurements and 2D geometric morphometric landmarks were lower compared with classifications from non-size adjusted linear measurements. We identified fossil vertebrae from our case study as likely belonging to the tiger salamander clade within Ambystoma, but found that some fossils with lower classification probabilities are of uncertain identity. We discuss biogeographic implications for our fossil identifications and comment on challenges and next steps for advancing our understanding of morphological variation in Ambystoma.

A new hynobiid-like salamander (Amphibia, Urodela) from Inner Mongolia, China, provides a rare case study of developmental features in an Early Cretaceous fossil urodele.

A new fossil salamander, Nuominerpeton aquilonaris (gen. et sp. nov.), is named and described based on specimens from the Lower Cretaceous Guanghua Formation of Inner Mongolia, China. The new discovery documents a far northern occurrence of Early Cretaceous salamanders in China, extending the geographic distribution for the Mesozoic fossil record of the group from the Jehol area (40th–45th parallel north) to near the 49th parallel north. The new salamander is characterized by having the orbitosphenoid semicircular in shape; coracoid plate of the scapulocoracoid greatly expanded with a convex ventral and posterior border; ossification of two centralia in carpus and tarsus; and first digit being about half the length of the second digit in both manus and pes. The new salamander appears to be closely related to hynobiids, although this inferred relationship awaits confirmation by research in progress by us on a morphological and molecular combined analysis of cryptobranchoid relationships. Comparison of adult with larval and postmetamorphic juvenile specimens provides insights into developmental patterns of cranial and postcranial skeletons in this fossil species, especially resorption of the palatine and anterior portions of the palatopterygoid in the palate and the coronoid in the mandible during metamorphosis, and postmetamorphic ossification of the mesopodium in both manus and pes. Thus, this study provides a rare case study of developmental features in a Mesozoic salamander.

Polydactyly and other limb abnormalities in the Jurassic salamander Chunerpeton from China

Polydactyly and other malformations such as supernumerary limbs are relatively common in extant salamander populations. They generally result from biotic or abiotic disruption of normal regeneration following non-lethal predator or conspecific bite injury. Here, we record, for the first time, similar malformations in a fossil salamander. Fourteen specimens of the perennibranchiate Jurassic salamander Chunerpeton tianyiensis (Urodela, Cryptobranchidae), recovered from Jianping County, Liaoning Province, China, display polydactyly or abnormal phalangeal counts in one or more limbs, and two also possess supernumerary hind limbs. Polydactyly in Chunerpeton is mainly post-axial, occurring on the feet more often than the hands, and on the right side of the body more often than on the left. The extra legs also occurred on the right side of the body. Similar conditions can be observed in living salamanders, so these specimens suggest that the challenges faced by aquatic salamanders, and the developmental processes triggered in response, have changed relatively little in 160 million years.

A new fossil salamander (Caudata, Proteidae) from the Upper Cretaceous (Maastrichtian) Hell Creek Formation, Montana, U.S.A.

ABSTRACT North American Late Cretaceous salamanders are principally known by isolated atlantes and trunk vertebrae. Here I describe a new genus and species of fossil salamander, Paranecturus garbanii, gen. et sp. nov., based on these elements from the lower portions of the Hell Creek Formation (Maastrichtian), Garfield County, northeastern Montana, U.S.A. It is diagnosed by a unique combination of character states that include the presence of an alar-like process of the atlas and a groove on the posterior face of the neural arch and solid dorsal rib-bearers of the trunk vertebrae. My phylogenetic analysis of 13 caudate taxa and 23 atlantal and trunk vertebral characters recovered P. garbanii as a member of the Proteidae. P. garbanii represents the oldest fossil record of the Proteidae and demonstrates that this lineage was present before the Cretaceous-Paleogene mass extinction event. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

Taxonomic diversity, stratigraphic range, and exceptional preservation of Juro-Cretaceous salamanders from northern China

Since the late 1990s, eight localities in volcanic shale-rich lacustrine deposits of Middle Jurassic through Early Cretaceous age in northern China (western Liaoning Province, northern Hebei Province, and southern Inner Mongolia) have yielded thousands of exceptionally well-preserved salamander specimens. With 10 species published and several new taxa yet to be named and described, the fossil samples from northern China represent the most species-diverse, individually abundant, and exquisitely preserved salamander fossil assemblage known from the Mesozoic Era. The stratigraphic range of the fossil record covers a geologic time span of roughly 40–45 million years from the Middle Jurassic (Bathonian) through the Early Cretaceous (Aptian). In contrast to the well-known stem-group salamanders Karaurus and Kokartus from the Middle to Late Jurassic of Middle Asia, the Chinese record contains the earliest known crown-group salamanders, including Jurassic representatives of both Cryptobranchoidea and Salamandroidea. The Chinese Mesozoic record includes numerous examples of virtually complete larval, juvenile, young adult, and fully grown adult individuals that collectively provide key information on the life histories and developmental patterns of the earliest known crown-group salamanders. Many specimens show preservation of soft tissue structures, including body outline, eye, liver, and external gill filaments. This kind of soft tissue preservation is unusual for fossil salamanders, so the Chinese Mesozoic specimens are important for furnishing otherwise unavailable information on the life history, diversity, and ecological adaptations of early crown-group salamanders.

A neotenic salamander, Jeholotriton paradoxus, from the Daohugou Beds in Inner Mongolia

Over the past 10 years, there has been a wealth of discoveries of fossil salamanders from the Jehol Biota in northern China. These specimens have revealed many new species in addition to establishing probable divergence times and relationships among modern salamander families. Among these are numerous specimens of a neotenic species Jeholotriton paradoxus. In this study, we focused on this particular salamander species because its classification still remains enigmatic. The aim of this research was to determine the relationship of Jeholotriton with respect to other Jehol salamanders as well as modern salamander families. Although Jeholotriton has been described in previous studies, the discovery of new specimens and increasing knowledge of other Mesozoic salamanders has allowed for a more through description of the genus. Jeholotriton is known only from the Daohugou locality in Ningchen, south-eastern Inner Mongolia. It may be close to the base of the modern Urodele radiation, and might provide evidence of their transition from putative ancestors in the Permo-Triassic. We discovered that the fossil Kokartus (family Karauridae) and the living hynobiids (the most primitive group of modern salamanders) Ranodon sibiricus and Hynobius maculosus, as well as Dicamptodontidae tenebrosus all share some similarities with Jeholotriton. However, conclusive relationships could not be confidently established because of the unique combination of mature and larval characteristics in Jeholotriton. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 164, 659–668.

Jeholotriton paradoxus (Amphibia: Caudata) from the Lower Cretaceous of southeastern Inner Mongolia, China

ABSTRACT A fossil salamander is described based on specimens from a Lower Cretaceous deposit near Ningcheng, Inner Mongolia, China. Recently reported as Jeholotriton paradoxus, this form represents a neotenic salamander as indicated by larval features such as external gills, tooth-bearing coronoids, pterygoids with anteromedially oriented anterior processes, and underdeveloped maxillae, in combination with adult features such as extensive medial contact of the nasals and posteriorly directed tooth rows in the palate. This taxon is distinguished from other Mesozoic salamanders by having 15–16 presacrals, proximally expanded unicapitate ribs, vomers with large tooth patches anteriorly and longitudinal dentigerous bars posteriorly, large nasals with no anterior notch, frontals with no anterolateral extension, premaxillae with distinct alary processes, short transverse processes on the vertebrae, and phalangeal formulae of 2-2-3-2 for the manus and 2-2-3-3-2 for the pes. Including Laccotriton, Liaoxitriton, Sinerpeton and Chunerpeton, five taxa of Mesozoic salamander have now been found in China. Jeholotriton has especially well-preserved impressions of articulated skeletons, a type of preservation that is uncommon in Mesozoic strata throughout the world and provides important anatomical details of this early salamander. The great diversity of fossil salamanders from the late Mesozoic of northeastern China implies that East Asia was an important center for the early evolution of urodeles.

Enigmatic Caudata (amphibia) from the upper cretaceous of gondwana

All living and fossil salamanders known till now are primarily Laurasian and have amphicoelous or opisthocoelous vertebrae. But Cretaceous salamanders from Gondwanan continents (South America and Africa) have procoelous vertebrae. One of them, from the Maastrichtian of Bolivia, is here described as Noterpeton bolivianum gen. and sp. nov. and it is referred to a family of its own, Noterpetontidae fam. nov. It is suggested that the procoelous Gondwanan forms could represent the sister group of all the other salamanders, but no detailed phyletic study can be undertaken on the basis of the available material.

The earliest known Salamanders (Amphibia, Caudata):A record from the Middle Jurassic of England

Marmorerpeton gen. nov. represented by M. kermackisp. nov. and M. freemani sp. nov., is the earliest known genus of fossil salamander from the Upper Bathonian, Middle Jurassic of Kirtlington, Oxfordshire, England. Marmorerpeton is more primitive than any other known salamander in the absence of intravertebral spinal nerve foramina in the atlantal centrum, but in other features it resembles members of the family Scapherpetontidae, neotenous salamanders otherwise known from the Upper Cretaceous and Palaeocene. The Kirtlington herpetofauna is a unique freshwater assemblage of Middle Jurassic small amphibians and reptiles, several of which represent the earliest known occurrences of their respective groups.

A new specimen of Taricha (Amphibia: Caudata) from the Oligocene of Washington

A nearly complete fossil salamander, including part and counterpart, is referred to Taricha. The specimen is of a post-metamorphic individual and is a member of the more primitive subgenus Palaeotaricha as well as being the oldest known member of the genus. This documented congruence between age and primitiveness supports the validity of the paleontological approach to phylogenetic analysis.

Spinal nerves and their bearing on salamander phylogeny.

Examination of the vertebral columns of representatives of all families of salamanders revealed that, in contrast to the condition found in most other vertebrates, salamander spinal nerves of often pass through foramina in the vertebrae. Two kinds of spinal nerve foramina were found: those in the anterior halves of vertebrae, and those in the posterior halves. In addition, many salamanders retain intervertebral nerves. However, within each family or, in a few cases, subfamily there is a characteristic pattern of spinal nerve-vertebral relationships. The first spinal nerve of all salamanders exits through a foramen in the anterior half of the atlas. All more posterior nerves are intervertebral in the families Cryptobranchidae, Hynobiidae and Proteidae. The posterior caudal nerves exit through the posterior halves of the caudal vertebrae in the family Amphiumidae, while in the subfamilies Dicamptodontinae and Rhyacotritoninae all post-sacral nerves exit through the posterior halves of the vertebrae. All but the first three nerves exit through posterior foramina in the family Plethodontidae and the subfamily Ambystomatinae, while all but the first two nerves pass through posterior foramina in the families Salamandridae and Sirenidae. Several fossil salamanders were also examined. These showed that the amphiumid and dicamptodontine-rhyacotritonine nerve patterns had evolved by the Late Cretaceous, and the sirenid pattern had probably evolved by that time. Other Cretaceous genera associated with the Ambystomatoidea still possessed the primitive intervertebral pattern. Using spinal nerve patterns and several other previously described morphological characters, a new hypothesis of the phylogeny of recent and fossil salamanders is presented and compared to earlier proposed phylogenies of the group. A new classification of salamander families is presented.

A List of the World's Recent and Fossil Salamanders

A List of the World's Recent and Fossil Salamanders

A New Fossil Salamander from Montana and Wyoming

Lisserpeton bairdi, n. gen., n. sp., occurs in the Late Cretaceous Bug Creek local fauna of Montana. It is most closely related to the Late Cretaceous and Paleocene Scapherpeton tectum, and belongs with it in the family Scapherpetonidae. Lisserpeton is also present in the vertebrate fauna of the Lance Formation, Late Cretaceous, Wyoming, and in a number of Paleocene localities in Montana and Wyoming.

A New Genus of Fossil Salamander from North America

A new genus and species of fossil salamander, Opistho- triton kayi, from Niobrara County, Wyoming, Lance formation, Upper Cretaceous, is described. On the basis of the structure of the centrum, Opisthotriton is, at present, best regarded as a salamandrid. However, certain features of the available vertebrae exhibit peculiarities encoun- tered in this family as represented at the present time. The genus may eventually be assigned to the Plethodontidae, or to an extinct family. Most important is that the recognition of this genus and species estab- lishes the presence of the suborder Salamandroidea in the New World during the Mesozoic. An additional specimen from the Eagle Coal Mine, Bear Creek, Montana, Lower Paleocene is referred to the same genus. During the past few years several distinctive opisthocoelous sala- mander vertebrae from the Mesozoic and Cenozoic of North America have come to my attention. Comparison with other known fossil and Recent salamanders indicate sufficient dissimilarity to warrant the description of a new genus. The material constitutes one of the earlier records of fossil salamanders in the world, and provides addi- tional information regarding the composition of the urodele fauna of the Cretaceous of North America.

Trackways of Living and Fossil Salamanders, by Frank E. Peabody [Review

Trackways of Living and Fossil Salamanders, by Frank E. Peabody [Review

A New Fossil Salamander of the Genus Siren from the Eocene of Wyoming

specimens listed below, which I have examined, Smith and Taylor (1948: 99) give a number of localities for this species. Most of these have been plotted in Figure 3. Distrito Federal: Mexico (AMNH 1289); vicinity of Guadalupe (AMNH 12216-27, 13366-78). Guanajuato: Guanajuato (USMN 9891, 12684, 26155); Santa Rosa (USMN 47206). Jalisco: Teocaltiche (UIMNH 32308). Mexico: Lagunilla de Ojuelos, 5 mi. W Toluca (AMNH 55265-66). Michoacan: Tupitaro (USMN 10239 [3 specimens], 10243 [3 specimens], 10251, 1025355, 10258); Sahuayo (USMN 113735); 5 mi. NW Maravatio (UIMNH 32304-05). Puebla: Chignahuapan (USMN 21454-59). San Luis Potosi: Arriaga (LSUMZ 2520-38, 2554-55); Bledos (LSUMZ 2549-50, 4275-77, 4285); 21 km. W Illesca (LSUMZ 2317); Laguna de las Rusias (LSUMZ 5654); Presa Gonzales Santos, 10 mi. SW San Luis Potosi (LSUMZ 4303-06); Presa Prudentia (LSUMZ 5668); Presa San Jose, 4 mi. SW San Luis Potosi (LSUMZ 4307-10); Sierra San Miguel, 7500 ft. (LSUMZ 4973).