Jacisin and Hopkins—Fossil newts from the Oligocene of Oregon


that epipleural processes are present throughout fossil and extant salamandrids (and even other salamanders) to some extent, with various types and levels of functionality (Nussbaumand Brodie, 1982; Brodie et al., 1984; Marjanović and Witzmann, 2015). It is therefore difficult to project the function of epipleural processes in fossil Taricha with complete confidence outside of their similarity to those of extant Tylototriton verrucosus. The skin of all newts is toxic and sometimes fatal to


potential predators; it is especially potent in the genus Taricha (Wakely et al., 1966; Brodie, 1968a, 1968b; Brodie et al., 1974; Hanifin, et al., 2004). Given the phylogenetic bracketing of T. oligocenica and T. lindoei with other toxic newt species (including both North American genera), the fossil species were also likely to have been toxic, although it is impossible to discern how potent the toxins actually were in these organisms. Naylor (1978a) was the first to propose a connection between the frontosquamosal arch and newt toxins on the basis that it is decidedly advantageous if an organism with toxic (not to mention distasteful) skin secretions also has defensive mechan- isms that allow it to survive and decrease injury from predators experiencing the poison. In a now-famous encounter, one bullfrog (Lithobates catesbeiana) voluntarily ate an individual of T. granulosa (Brodie, 1968a). The defensive advantages of a robust, hardy body and toxic skin secretions became clear when the frog died within ten minutes and the newt emerged unscathed shortly after (Brodie, 1968a). While the toxicity of the fossil newts in this study is unknown, the skeleton of T. oligocenica in particular is more armored than that of T. granulosa (Van Frank, 1955), and is likely able to resist easy consumption from predators, as seen in extant Taricha (Brodie, 1968a, 1977; Naylor, 1979).


Conclusions


Our four phylogenetic analyses provided mixed results when compared to the molecular phylogenies of Zhang et al. (2008) and Pyron (2014), yet consistently nested Taricha oligocenica, Taricha lindoei, Taricha miocenica, and Notophthalmus robustus within a clade of North American newts. Future studies should attempt to find additional osteological characters for all fossil and extant species of North American newts for better resolution of morphological analyses, particularly for Notophthalmus, which appears to be problematic in morpholo- gical analyses. Unfortunately, the morphological characters in this analy-


sis did not resolve the positions of the fossil taxa relative to extant species of the genus, so their exact classification within the North American clade is uncertain. The use of muscular and behavioral characters does not help resolve fossil species, while a lack of species-level osteological characters, the presence of homoplasy in some potential characters, and the possibility of cryptic species complicate the ability of our analyses to discriminate between taxa. A detailed morphological study of T. oligocenica and


T. lindoei supports their classification as separate species more similar to Taricha than to any other known genus of newt. As in the phylogenetic analysis, this conclusion suggests that the genus Taricha has deep roots into at least the early Oligocene, where ancestors to living species may have diverged


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32–33 Ma. Functionally, T. lindoei is similar to, though possibly smaller than, all extant taxa, and existed in a seasonal temperate environment similar to the environments in which Pacific newts are found today. Taricha oligocenica, on the other hand, represents a large, robust newt that was considerably more armored than extant Taricha, and lived in a milder climate nearer to the Oligocene coast. Because we did not directly examine any specimens of


Taricha miocenica or of fossil Notophthalmus outside of published literature (Tihen, 1974; Estes, 1981; Holman, 2006), it is of particular importance to examine and compare these fossils in detail with additional fossils of Taricha and Notophthalmus, along with skeletons of extant members of these genera, to examine their evolutionary relationships with modern North American salamandrids. The fact that T. miocenica and all fossils of Notophthalmus are only pre- served as isolated vertebrae (Tihen, 1974; Estes, 1981) enhances the difficulty of such determinations, and our analyses and observations indicate further development of vertebral char- acters is clearly required. Despite the complications, only by performing such studies can we hope to draw concrete conclu- sions on the phylogenetic positions North American fossil newts relative to each other and to extant Taricha and Notophthalmus.


Acknowledgments


We thank E. Davis (UOMNCH), G. Retallack (UOMNCH), J. Samuels (East Tennessee State University), P. Holroyd (UCMP),K. Padian (UCMP), andD.Wake (UCMVZ) for access to the specimens under their care. We are grateful to E. Davis (UOMNCH),G.Retallack (UOMNCH), J. Samuels (ETSU), and the past and presentmembers of theHopkins-Davis Lab and other students from the University of Oregon for productive discourse and support. Special thanks to E. White (UOMNCH), for con- tributing line drawings for Figures 1 and 5, and N. Famoso (JODA), for photographs in Figures 1, 2.1, 7.2, and 7.3.We give credit to the Museum of Comparative Zoology and Harvard University for permission to use copyrighted material to help make the line drawings in Figure 5.We also thank the editor and reviewers of this paper for their contributions to the quality of this work, particularly D. Marjanović for his insight on non-North American newts. Finally, we acknowledge funding from a Geological Society of America graduate student research grant, the University of Oregon Thomas Condon Fellowship, and the UCMP Doris O. and Samuel P. Welles Research Fund for making this research possible.


Accessibility of supplemental data


Data available from the Dryad Digital Repository: http://dx.doi. org/doi:10.5061/dryad.8m9t1


References Albright, L.B. III, Woodburne, M.O., Fremd, T.J., Swisher, C.C. III, MacFadden, B.J., and Scott, G.R., 2008, Revised Chronostratigraphy and Biostratigraphy of the John Day Formation (Turtle Cove and Kimberly members), Oregon, with Implications for Updated Calibration of the Arikareean North American Land Mammal Age: The Journal of Geology, v. 116, p. 211–237.


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