730


Journal of Paleontology 92(4):713–733


Estes (1981) noted that N. robustus is apparently less derived than other known species, and differs more from at least the extant species than those species do from each other. While T. miocenica was placed with other species of Taricha, its exact placement within the group is uncertain, possibly because it relies entirely on our vertebral characters; analyses including N. robustus and N. crassus face a similar problem. As such, we suggest a reexamination of the three “vertebrae-only” North American taxa because we did not investigate those taxa personally when assigning character states. We furthermore suggest the addition of extant taxa Notophthalmus meridionalis and Notophthalmus perstriatus to future analyses that look to investigate North American taxa specifically, especially when including fossil taxa. Clearly, the current state of unconstrained morphological analyses struggle with Notophthalmus overall; the addition of all species and species-level characters may improve the resolution in future studies. We also suggest deeper investigation into the vertebral


characters of the Salamandridae overall because the current state of characters may not necessarily explain the morphological similarities and differences within the group. We were unable to address this in our current study, and were also unable to code some of our original characters for non-North American taxa, because of insufficient specimen availability to account for possible variation. Future studies should build on our current analysis and incorporate more data, as available, while studying multiple individuals of each taxon. Overall, we find support for T. oligocenica, T. lindoei, and


T. miocenica as members of the Taricha group with a long history of >32 Ma. The curious and consistent placement of N. robustus warrants a reexamination of the taxon and the character states assigned to it, and we recommend the same for the remaining North American taxa (including the questionable taxon N. slaughteri) for the sake of confirming their morphol- ogies. Improving the characters and character states for the vertebrae and ribs of salamandrid phylogenies should also be a priority for future analyses; other characters, such as the single geographic character, may also be possible to improve on when advancing these studies.


Functional morphology


Discussion.—The overall impression of Taricha oligocenica is that of a sturdy or robust, moderate-to-large-sized newt with a mosaic of defensive adaptions present in the Salamandridae. First is the frontosquamosal arch, which consists of an ante- romedial projection from the squamosal and a posterolateral projection from the frontal that has been considered a defensive adaptation in the family Salamandridae (Naylor, 1978a; Brodie, 1983; Duellman and Trueb, 1986), the function of which is to lessen injury during predatory attack by increasing the skull’s resistance to crushing. The frontosquamosal arch also increases the difficulty of swallowing for predators similar to Thamno- phis, which attempt to swallow their prey headfirst (Brodie, 1968a, 1983; Naylor, 1978a; Duellman and Trueb, 1986), or predators such as Lithobates and some fishes, which also attempt to swallow their prey whole (Brodie, 1968a; Naylor 1978a). Although not all salamandrids possess a complete, bony arch (some exhibit a narrow gap, or no frontosquamosal arch),


extant Taricha involve the heavy ossification of different parts of the skeleton in T. oligocenica, specifically the trunk region. As Naylor (1978a) has pointed out, only newts with complete bony frontosquamosal arches possess expanded spine tables on the vertebral neural crests (examples include Notophthalmus, Cynops, and Tylototriton; Brodie, 1983; Duellman and Trueb, 1986). Although not all newts with bony arches possess extensive sculpture on these expansions, others may vary in degree of sculpture even within an individual, such as in Taricha (Naylor, 1978a, 1978b; Brodie, 1983; this study). These expansions are most likely defensive in nature (Naylor, 1978a; Brodie, 1983; Duellman and Trueb, 1986) because they have no muscle attachments and form interlocking series along the usually vulnerable spine of these salamanders. The amount of protection provided by these expansions likely differs by how extensively they cover the spine (Van Frank, 1955). Taricha oligocenica stands out in that its expansions are as extensive and sculptured as those of extant Tylototriton and Echinotriton, perhaps even more so, as the spine tables of those taxa narrow anteriorly, while T. oligocenica has somewhat rectangular expansions (Van Frank, 1955, Estes, 1981; this study). The elongate epipleural rib processes of T. oligocenica and


this structure is only found in the Salamandridae (Wake and Özeti, 1969; Naylor, 1978a; Duellman and Trueb, 1986). The ridges and grooves of the frontosquamosal arch, continuous with the relatively robust and rigid skull seen in salamandrids (compared to other salamanders), effectively strengthen the skull, especially when resisting lateral pressure, such as that experienced when being swallowed by predators, including bullfrogs and snakes (Naylor, 1978a). Additionally, the paired arches can form a protective shelf over the eyes of newts; this shelf can also be observed when these newts swallow or take a defensive posture (Brodie, 1977). As mentioned above, the extensive pitting of the skull and frontosquamosal arches of T. oligocenica is beyond that of living members of Taricha, but less than found in Echinotriton or Tylototriton. The most glaring differences between T. oligocenica and


T. lindoei are here proposed to provide a defensive role similar to the epipleural processes of Tylototriton. Like Tylototriton, T. oligocenica and T. lindoei possess singular, robust processes, directed dorsally and distally, on somewhat elongate (beyond the length of a simple rod) ribs, both of which terminate in blunt ends (Nussbaum and Brodie, 1982; Brodie et al., 1984; Heiss et al., 2009). Unlike in Echinotriton, Pleurodeles, and possibly fossil salamanders such as Chelotriton (Marjanović and Witzmann, 2015; Schoch et al., 2015), which possess even longer, pointed ribs, often with one or more pointed epipleural processes that function to pierce the skin and inject toxins into predators if compressed, these structures are unlikely to have protruded through the skin, and may have been used for muscle attachment and to apply pressure to toxin-containing granular gland clusters (risen on the skin of Tylototriton) when compressed without piercing the skin or to help project toxin- concentrated parts of the body towards potential antagonists. The increased muscle attachment and overall robustness of the structures could also have provided extra resistance against crushing forces when attacked. Unfortunately, testing this latter hypothesis would involve significant biomechanical testing, which is beyond the scope of this study. It should also be noted


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