A new proteid salamander (Urodela, Proteidae) from the middle Miocene of Hambach (Germany) and implications for the evolution of the family

Abstract

Members of the urodele family Proteidae currently account for eight extant species within two genera and at least four extinct species within three genera. The clade has a clear disjunct geographical range, with the extinct Paranecturus and the extant Necturus in North America and the extinct Mioproteus and the extant Proteus in Europe and Asia. A recent phylogenetic analysis supported a Eurasian clade including both fossil and living species found east of the Atlantic Ocean. However, the finding of a new proteid salamander, herein named Euronecturus grogu, from the Miocene of western Germany sheds new light on the evolution of this family, challenging the idea of all Eurasian members of the group deriving from a single lineage separated from the North American ones at least prior to the Oligocene. This new proteid taxon is based on five isolated atlases found in late Orleanian (MN 5) sediments in Hambach 6C, and displays features that are unknown in any other proteid, such as the presence of secondary dorsal crests, small and posteriorly-directed postzygapophyses, and (in at least some specimens) a wide and deep ventral fossa between the anterior cotyles. A phylogenetic analysis recovered the new taxon in an earlybranching position within Proteidae, sister to all other proteids but the late Maastrichtian Paranecturus. It thus suggests the presence in Europe of a second proteid lineage, currently known only in the middle Miocene, that appears unrelated to the Mioproteus-Proteus clade.

Biogeographic history of Palearctic caudates revealed by a critical appraisal of their fossil record quality and spatio-temporal distribution

“…Whereas it differs from the European lineage of Mioproteus / Proteus (see below), BEXHM: 2010 16.14 shares these (and other) features with the extant North American genus Necturus , whose fossil record extends back to the late Paleocene of Canada [ 58 ]. Because of this close similarity, it is possible that BEXHM: 2010 16.14 represents an early occurrence of a proteid lineage distinct from Mioproteus / Proteus , possibly leading to the species Euronecturus grogu , recently described from the Middle Miocene of Germany ([ 59 ]; see below).…”

“…Skutschas [ 13 ] noted that the known material of Bishara backa (a partial atlas, now lost) could be referred to the family Proteidae. An additional atlas figured by Skutschas [ 13 ] bears a striking similarity with the extinct proteid Mioproteus [ 79 , 80 ], whereas it clearly differs from both Euronecturus and Necturus [ 59 ]. As such, we agree with Skutschas [ 13 ] that Bishara backa potentially represents another proteid lineage in the Cretaceous of Eurasia.…”

“…Excluding the two possible Cretaceous occurrences mentioned above, the stratigraphically oldest unequivocal occurrence of a proteid is Mioproteus gardneri (figures 1 and 4 a ). This taxon was described from the early Oligocene of Romania by Venczel & Codrea [ 80 ] and it appears to be closely related to the extant European genus Proteus [ 59 , 144 ].…”

“…Several remains referred to indeterminate species of Mioproteus have also been documented in the Czech Republic, Moldova, Kazakhstan and Russia, spanning the Early Miocene to the Early Pliocene [ 14 , 91 , 110 ]. As mentioned above, a distinct proteid genus, Euronecturus grogu , more closely related to the North American Necturus than to Mioproteus , was recently described from the Middle Miocene of Germany [ 59 ]. Orthophyia longa , from the Middle Miocene of Germany [ 123 ], should be considered a nomen dubium, representing an indeterminate proteid [ 8 , 59 ].…”

“…Mioproteus wezei was erroneously reported to be present in the Pleistocene of Poland in figure 5 of Macaluso et al . [ 59 ], but this locality (Weze II) is actually Late Pliocene in age (MN 16 according to Młynarski et al . [ 195 ] and Stefaniak [ 198 ]).…”