A new Middle Triassic (Ladinian) trilophosaurid stem-archosaur from Germany increases diversity and temporal range of this clade

Abstract

We report the first trilophosaurid stem-archosaur from Central Europe, Rutiotomodon tytthos gen. et sp. nov., from the Middle Triassic (Ladinian) Erfurt Formation of Baden-Württemberg (Germany). It is currently known from two jaw fragments with distinctive teeth. The labiolingually wide but mesiodistally narrow maxillary and dentary teeth each have a large labial cusp from which an occlusal ridge extends lingually to a small lingual cusp. A mesial and a distal cingulum extend between the labial and lingual cusps. The mesial and distal faces of the labial cusp each bear three prominent, lingually curved apicobasal ridges (arrises). A referred partial dentary has an edentulous, expanded symphysis similar to the mandibular ‘beak' in Trilophosaurus buettneri . A review of Coelodontognathus ricovi , from the Lower Triassic (Olenekian) of southwestern Russia, supports its referral to Trilophosauridae rather than Procolophonidae. Based on this reassessment and the new material from the Middle Triassic, the temporal range of trilophosaurids now spans nearly the entire Triassic Period, from the Olenekian to the Rhaetian. Trilophosaurids present craniodental features that indicate omnivory or herbivory with limited oral food processing. They were more diverse in terms of dental structure (and presumably diet) than previously assumed.

New specimen and redescription of Anisodontosaurus greeri (Moenkopi Formation: Middle Triassic) and the spatiotemporal origins of TrilophosauridaeCitation for this article: Foffa, D., Nesbitt, S. J., Kligman, B. T., Butler, R. J., & Stocker, M. R. (2023) New specimen and redescription of Anisodontosaurus greeri (Moenkopi Formation: Middle Triassic) and the spatiotemporal origins of Trilophosauridae. Journal of Vertebrate Paleo

“…2A, 3A, 6A, B). Similar rows of nutrient foramina can be seen on a horizontal ridge of bone on the dentary of Variodens inopinatus (NHMUK PV R36850; Chambi-Trowell et al, 2021), ventral to the anterior portion of the tooth row of Coelodontognathus ricovi (PIN 4137/127; Sues & Schoch, 2023), in Trilophosaurus buettneri (TMM 31025-5;TMM 31025-125;Spielmann et al, 2008), and in Azendohsaurus madagaskarensis (Nesbitt et al, 2015:fig. 7F).…”

“…7F). Unfortunately, we cannot determine how far anteriorly the series of foramina continues in UCMP 37804, and there is no visible horizontal ridge on the lateral surface of the dentary, unlike those reported on the dentary of Coelodontognathus ricovi (PIN 4137/127; Sues & Schoch, 2023), Variodens inopinatus (NHMUK PV R36850), and Tricuspisaurus thomasi (NHMUK PV R6106) (Chambi-Trowell et al, 2021;Skinner et al, 2020). It is impossible to determine whether such a ridge was present in life in UCMP 37804 because of poor preservation (Figs.…”

“…The NEXUS file of the full data matrix is available on Morpho-Bank (http://morphobank.org/permalink/?P4610), together with the NEXUS files required for performing maximum parsimony and Bayesian inference analyses, .tre files containing the MPTs from each TNT analysis, and the 50% majority rule consensus tree from each MrBayes analysis (accessible as .zip folders in "Documents" section of the same MorphoBank project). Sues and Schoch (2023) recently described Rutiotomodon tytthos, a new trilophosaurid from the Middle Triassic of Germany, and recognized Coelodontognathus ricovi from the Lower Triassic deposits of Russia as the oldest known trilophosaurid. Information from Sues and Schoch (2023) was incorporated in the description and discussion; however, incorporation of Rutiotomodon tytthos and Coelodontognathus ricovi into our modified phylogenetic dataset will be the subject of future work.…”

“…Sues and Schoch (2023) recently described Rutiotomodon tytthos, a new trilophosaurid from the Middle Triassic of Germany, and recognized Coelodontognathus ricovi from the Lower Triassic deposits of Russia as the oldest known trilophosaurid. Information from Sues and Schoch (2023) was incorporated in the description and discussion; however, incorporation of Rutiotomodon tytthos and Coelodontognathus ricovi into our modified phylogenetic dataset will be the subject of future work. Anatomical Abbreviations-c.b., cancellous bone; ci, cingulum; cu, cusp; d, dentary; de, dentine; en, enamel; for, foramina; p.c., pulp cavity; sw, swollen base.…”

“…in UCMP 37804, teeth 9-15 in Variodens (based on the reconstruction of Robinson 1957-equivalent to teeth 5-11 in NHMUK PV R36850, which is missing the anterior dentary teeth), teeth 6-11 of Tricuspisaurus (NHMUK PV R6106-equivalent to teeth 1-6 in fig. 2F of Chambi-Trowell et al, 2021), the available crowns in the maxilla of Rutiotomodon tytthos (SMNS 97028), all except the last erupting crown of Coelodontognathus ricovi (PIN 4137/127, and referred tooth PIN 4137/128) (Sues & Schoch, 2023), and the mediolaterally widened crowns in specimens of Trilophosaurus are considered premolariform ( 3-5) (see below for missing tooth positions and the Discussion for a justification of correlates). Note that the distal crowns of Teraterpeton hrynewichorum (Sues, 2003) bear some similarities with the molariforms of Anisodontosaurus and Variodens (i.e., enlarged swollen base, prominent central cusp), but in the absence of more precise data we refrain from establishing direct homologies among the crowns of these taxa.…”