Jacisin and Hopkins—Fossil newts from the Oligocene of Oregon
character 71 for Tylototriton, in which the length of the trunk ribs differs between species. The unconstrained analysis with all 40 taxa produced
420 most parsimonious trees, with a length of 635 steps, a consistency index of 0.501, a retention index of 0.633, and a homoplasy index of 0.753. The strict consensus (Fig. 8) is not exceptionally well resolved, although the outgroups (Ambystoma and Dicamptodon), Salamandrinae (Salamandra and Chioglossa), Pleurodelini (Tylototriton, Echinotrition, and Pleurodeles), and Molgini (including a European and North American clade) form monophyletic groups as in molecular studies (Zhang et al., 2008; Pyron, 2014). Unfortunately, the Molgini, along with Salamandrina, form a massive polytomy in the strict consensus tree as presently coded. This polytomy includes uncertain placements of Notophthalmus viridescens and the fossil Notophthalmus crassus, as well as several European fossil taxa, Cynops, and Paramesotriton. We also retain a stepped relationship of Lissotriton species (along with Carpathotriton) and a clade including Neurergus, Ommatotriton, Triturus, and Ichthyosaura. Finally, we recovered a clade including all living and extinct species of Taricha, along with fossil species Notophthalmus robustus in our analysis. The constrained analysis of all 40 taxa produced 760 most
parsimonious trees, with a length of 667 steps, a consistency index of 0.4768, a retention index of 0.5956, and a homoplasy index of 0.7646. The strict consensus of these trees (Fig. 9) forms a large polytomy within the Salamandrinae. Within this polytomy, the strict consensus retains the entirety of the North American clade, but retains only minor parts of the Pleurodelini and European newts. Within the North American clade, the fossil species (except for N. crassus) form a polytomy alongside the group of extant Taricha species, while living N. viridescens and extinct N. crassus form a polytomy with the larger North American newt group. Our unconstrained analysis without the “vertebrae-only”
fossil taxa produced 32 most parsimonious trees, with a length of 630 steps, a consistency index of 0.503, a retention index of 0.629, and a homoplasy index of 0.751. The strict consensus tree of this analysis (Fig. 10) retains the outgroup, the Salamandrinae, and the Pleurodelini-Molgini sister groups. Within the Molgini, we have a trichotomy of extinct and extant Taricha, Notophthalmus viridescens, and all other newts within Molgini, including the fossil taxa. Within Taricha, the fossil taxa T. oligocenica and T. lindoei form a separate branch from extant species of Taricha, which have additional soft tissue and reproductive character data available. Finally, our constrained analysis without the “vertebrae-
only” fossil taxa produced 16 most parsimonious trees, with a tree length of 662 steps, a consistency index of 0.4789, a retention index of 0.5907, and a homoplasy index of 0.7628. The strict consensus tree (Fig. 11) portrays the outgroup, Salamandrina,the Salamandrinae, and a North American clade of Taricha and Notophthalmus well, but overall reduces the newts into a large polytomy, removes Pleurodeles and several fossil taxa to one step outside of the Pleurodelini, and struggles to separate the taxa into a distinct Pleurodelini-Molgini sister-group relationship. Notophthalmus viridescens forms a sister group to living and fossil species of Taricha, while the non-North American Molgini also form a single large clade with fair similarity to molecular trees.
725
Discussion.—This paper focuses on North American taxa, although our analysis enables us to make a few observations about non-North American taxa in addition to those found in Marjanović and Witzmann (2015). Both of our constrained analyses (Figs. 9, 11) form a large polytomy including the newt taxa while not recovering a monophyletic Pleurodelini, fossil Chelotriton (both the Enspel/Randeck and
MB.Am.45 specimens), and Pleurodeles. The analysis reflects a North American clade including all living and fossil North American species. Removal of the “vertebrae-only” taxa before analysis greatly reduced the number of trees (from 760 to 16), suggesting that the current status of vertebral characters in Salamandridae as a whole is insufficient to properly understand several of the taxa, perhaps because of a lack of data and/or low samples sizes, homoplasy in vertebral characters, poor description of character states, or some combination of the above. One possible example of this issue pertains to the width and dorsal sculpture of the neural crest of the vertebrae (character 61; character 61 in Marjanović andWitzmann, 2015; characters 2 and 3 in Buckley and Sanchiz, 2012). Using Taricha as an example, Venczel (2008) assigned state 0 (neural crest not expanded into spine table), whereas Buckley and Sanchiz (2012) and Marjanović and Witzmann (2015) assigned Taricha state 2 (dorsal surface of broadened spine table sculptured). Examination of extant species of Taricha (Table 1) reveals a mix of character states even within a single vertebral column. Fully mature individual skeletons typically exhibit both state 1 (unsculptured expansion of the neuropophysis into spine table) and the previously mentioned state 2, apparently across all living species in our analysis. We have coded the extant species as such. Taricha oligocenica and Taricha miocenica both appear to exhibit only state 2, though with different shapes for the spine table, while Taricha lindoei appears to exhibit state 1 as seen in some extant Taricha, although this may be an artifact of nearly two- dimensional preservation. In addition to the difference in observations even within a
single newt genus for this character, we suspect that the current list of character states is insufficient for describing the morphology of the neural crest and the spine table, when present. Taxa such as Taricha, for example, only show a broadening spine table at the posterior-most part of the neural crest (like an elongate, narrow, upside-down funnel), and may or may not exhibit sculpture, while taxa such as Echinotriton and Tylototriton have overall broader, near-triangular, extensive neural crest spine tables, and appear to exhibit sculpture throughout a mature individual’s trunk vertebrae. We suggest investigating differences of shape in the spine table in the future, and perhaps either adding these data as an additional character, or using them to better define or increase the number of character states for this character in future analyses. Other vertebral characters may similarly produce such issues, but we feel that the amount of expansion and sculpture of the neural crest exhibits the problem best. Our unconstrained analyses (Figs. 8, 10) recovered a
monophyletic Pleurodelini group, unlike in our constrained analyses; however, inclusion of all 40 taxa resulted in a massive polytomy between the Pleurodelini and various parts of what is molecularly recognized as the Molgini. Just as in the constrained analyses, the removal of “vertebrae-only” taxa
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