Diverse assemblage of Middle Triassic continental tetrapods from the Newark Supergroup of Nova Scotia (Canada)

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

“…Teeth of Trilophosaurus have three (in T. buettneri , T. dornorum , and T. jacobsi ) or two (in T. phasmalophos ) large, labiolingually aligned cusps, which are linked by transverse occlusal ridges [ 10 , 27 , 31 ]. Tricuspisaurus thomasi , Variodens inopinatus , and an indeterminate Middle Triassic trilophosaurid from Nova Scotia each have teeth with three labiolingually positioned cusps [ 20 , 33 ]. By contrast, Teraterpeton hrynewichorum has more bulbous maxillary and dentary teeth with two mesiodistally aligned cusps [ 32 ].…”

“…However, recent time-calibrated phylogenies of Archosauromorpha have predicted a much longer temporal range of this clade, extending back into the Permian [ 6 , 22 , 42 ]. The isolated tooth crown from the Economy Member of the Wolfville Formation in Nova Scotia, Canada provided the first evidence of a Middle Triassic trilophosaurid [ 33 ]. It forms a flattened platform bearing three labiolingually arranged cusps (character-state 83(1)), the central one of which is the smallest.…”

“…Its skull differs considerably from those of Trilophosaurus buettneri and T. jacobsi, particularly in the elongation of the snout (and external narial fenestra) and the structure of the teeth. In addition, an isolated tricuspid tooth crown from the Middle Triassic Economy Member of the Wolfville Formation was identified as an indeterminate trilophosaurid [33].…”

New specimen and redescription of Anisodontosaurus greeri (Moenkopi Formation: Middle Triassic) and the spatiotemporal origins of Trilophosauridae

“…It is worth noting that many of these lineages are small-bodied (Kaye & Padian, 1994; Heckert, 2004), and the very few known microvertebrate assemblages of the Moenkopi Formation are poorly sampled compared with those of the Upper Triassic (Benz, 1980; Morales, 1987; Schoch et al, 2010). On the other hand, there are also elements of continuity: trilophosaurids, tanystropheids, rhynchosaurs, and poposauroids are documented archosauromorph lineages from the Moenkopi Formation (Formoso et al, 2019; Haque et al, 2021; Morales, 1987; Nesbitt, 2005a, 2005b, 2005c, 2005d; Nesbitt et al, 2006; Schoch et al, 2010; Welles, 1947), and these groups are also known and have similar ecological modes (based on similar dentition, body size, and inferred locomotion) in the overlying Dockum Group and Chinle Formation or other contemporaneous or older formations in North America (i.e., Popo Agie Formation: Gauthier et al, 2011; Lees, 1907; Lucas et al, 2002; Mehl, 1915; Tarailo & Fastovsky, 2012; Wolfville Formation: Sues & Olsen, 2015; Sues et al, 2020; 2021). This mismatch in taxonomic and ecological diversity could have multiple explanations.…”

“…This lack of information on early archosauromorph evolution is particularly apparent in the low latitudes of Pangea where later assemblages from the Upper Triassic represent some of the most diverse archosauromorph assemblages known (e.g., those from the Chinle Formation and Dockum Group assemblages; e.g., Heckert, 2004;Kaye & Padian, 1994;Long & Murry, 1995;Martz et al, 2012;Stocker, 2013;Stocker et al, 2016Stocker et al, , 2019. Underlying those Upper Triassic assemblages, the vertebrate assemblages of the Lower to Middle Triassic Moenkopi Formation lack many of the diverse archosauromorph lineages known from those later units (Haque et al, 2021;Morales, 1987;Nesbitt, 2005aNesbitt, , 2005bNesbitt, , 2005cNesbitt, , 2005dNesbitt et al, 2006), even though some elements of continuity across major clades (i.e., tanystropheids, poposauroids, rhynchosaurs, footprint taxa, and serrated archosauriform teeth) exist with other North America Carnian assemblages (e.g., Sues & Olsen, 2015;Sues et al, 2020). This mismatch in assemblage composition suggests that the early archosauromorph lineages present in the Late Triassic in the low latitudes: (1) were genuinely not present in the Moenkopi Formation and appeared via cladogenesis and/or immigration from other parts of Pangea after the deposition of the Moenkopi Formation and prior to the deposition of the Chinle Formation and Dockum Group; or (2) were present in the Moenkopi Formation, but were rare or unrecognized in the Moenkopi paleocommunity, or not recovered due to taphonomic or collection biases; or (3) or a combination of both of these factors.…”