Journal of Paleontology, 92(4), 2018, p. 713–733 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.85
A redescription and phylogenetic analysis based on new material of the fossil newts Taricha oligocenica Van Frank, 1955 and Taricha lindoei Naylor, 1979 (Amphibia, Salamandridae) from the Oligocene of Oregon
John J. Jacisin III,1* and Samantha S.B. Hopkins2
1Department of Ecosystem Science and Management, Texas A&M University, College Station, Texas 77840, U.S.A. ⟨
jjjacisin3@tamu.edu⟩ 2Department of Earth Sciences, University of Oregon, Eugene, Oregon 97403-1272, U.S.A. ⟨
shopkins@uoregon.edu⟩
Abstract.—Complete body fossils of salamanders are relatively rare, but provide critical information on the evolutionary roots of extant urodele clades. We describe new specimens of the fossil salamandrids Taricha oligocenica Van Frank, 1955, and Taricha lindoei Naylor, 1979, from the Oligocene Mehama and John Day formations of Oregon that illustrate aspects of skeletal morphology previously unseen in these taxa, and contribute to our understanding of population-level variation. Morphological analysis of these specimens supports the classification of T. oligocenica and T. lindoei as two different species, distinct from extant Taricha. Parsimony-based, heuristic analysis of phylogeny using 108 morphological characters for 40 taxa yields different results from a phylogenetic analysis that excludes four taxa known only via vertebrae. Our smaller analysis generally agrees with molecular phylogenies of the family Salaman- dridae, but with poorer resolution for molgin newts, especially between Taricha and Notophthalmus. The analysis including all taxa produced polytomies mostly related to complications from several fossil taxa. The presence or absence of dorsally expanded, sculptured neural spine tables on trunk vertebrae, an important character in past descrip- tions of fossil salamandrids, appears to be either homoplastic within the Salamandridae, or requires an expansion of characters or character states. Taricha oligocenica and T. lindoei are separate species of an at least 33 million-year-old clade, but their relationships with each other and extant North American salamandrids remain unclear with current levels of morphological data. Salamandrid research requires additional morphological data, particularly for the vertebrae and ribs, to better resolve salamandrid evolutionary history through morphological characters.
Introduction
The pre-Pliocene fossil record of North American newts (Salamandridae, Tarichina) is sparse, especially west of the Rocky Mountains, yet it extends far back into the Oligocene (32–33 Ma). Previous morphological comparisons with extinct and extant North American salamanders recognized at least two species of fossil salamanders from Oregon’s early Oligocene deposits: Taricha oligocenica of the Mehama Formation in western Oregon (Van Frank, 1955), and Taricha lindoei of the John Day Formation in eastern Oregon (Naylor, 1979). Van Frank’s T. oligocenica and Naylor’s T. lindoei are found in beds assigned to the Rupelian Stage (30–33 Ma; early Oligocene; dates by Retallack et al., 2000, 2004), suggesting correspon- dence with the Orellan NALMA of the early Oligocene for T. oligocenica and T. lindoei (Albright et al., 2008). Naylor (1982) described another Taricha specimen from the early Oligocene (32–33Ma) GumbootMountain strata in Washington, but to genus only. Farther east, vertebrae from a third species, Taricha miocenica, have been uncovered in Montana’s late Oligocene (Arikareean; 24–26Ma) Middle Cabbage Patch Beds (Tihen, 1974; Rasmussen, 1977; Rasmussen and Prothero,
* Corresponding author
2003), while fossil trackways from the lateMiocene of California and the late Miocene of Kansas have also been identified as Taricha (Peabody, 1959; Holman, 2006). Although we did not examine any fossils of T. miocenica in this study, Tihen (1974) proposed the grouping of T. oligocenica and T. miocenica into the subgenus Palaeotaricha (not recognized in the latest classifica- tions; Estes, 1981; Holman, 2006; Dubois and Raffaëlli, 2009). If the latest classifications are correct, then T. miocenica would represent one of the two occurrences of Taricha (along with the KansasMiocene trackways) east of the RockyMountains. Several previously described, partial to nearly complete
skeletons from Oligocene localities in the John Day and Mehama formations of Oregon represent excellently preserved, post–metamorphic individuals of the genus Taricha, also known as Pacific (or Western) newts (Van Frank, 1955; Naylor, 1979; Holman, 2006; Fremd, 2010; McClaughry et al., 2010). Additional undescribed specimens include fossils from new localities near Gray Butte, Oregon and Lyons, Oregon, and a large individual from Goshen, Oregon. This study examines the new specimens and redescribes previously examined material. We also investigate the evolutionary relationships of the family Salamandridae in North America, because the migration of salamandrids to North America and their subsequent divergence into the genera Taricha and
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