So C et al. (2024), Fossil amphibian offers insights into the inter...

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Proc Biol Sci 2024 Oct 30;2912033:20241041. doi: 10.1098/rspb.2024.1041.

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Fossil amphibian offers insights into the interplay between monsoons and amphibian evolution in palaeoequatorial Late Triassic systems.

So C , Kufner AM , Pardo JD , Edwards CL , Price BR , Bevitt JJ , LeClair-Diaz A , St Clair L , Mann J , Teran R , Lovelace DM .

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The severe greenhouse climate and seasonality of the early to mid-Late Triassic are thought to have limited terrestrial diversity at lower latitudes, but direct adaptations to these harsh conditions remain limited in vertebrates at the palaeoequator. Here, we present Ninumbeehan dookoodukah gen. et sp. nov., an early amphibian with specialized adaptations for seasonal estivation from the upper Jelm Formation of the Late Triassic of Wyoming, USA. Ninumbeehan are found in an association of vertebrate estivation burrows across a locally dense horizon, offering insights into the evolution and ecology of vertebrates amid the challenging conditions of low-latitude Late Triassic ecosystems. Estivation chambers were excavated within point bar deposits of an ephemeral river system, recording the cyclical signature of Triassic megamonsoons and documenting a vertebrate response to annual climate extremes across tens to hundreds of seasons. Phylogenetic analysis recovers Ninumbeehan within a group of temnospondyls characterized by fossorial adaptation, underscoring the widespread adoption of burrowing and estivation in total group Lissamphibia. Ninumbeehan hints at the pivotal role seasonal dynamics played in shaping amphibian evolution.

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	Figure 1. (a) Representative stratigraphic profile of the upper Chugwater Group in the Dubois Area modified after [19]. (b) Paleogeographic map showing Carnian precipitation (green area= ca 1-7 mm d−1) modified after [9]. (c) Modern geography of North America with grey square denoting position of (d). (d) demonstrates the stratigraphic areal distribution of continental Triassic units of the Rocky Mountain West, USA. Abbreviations: Carb, carbonate; Congl, conglomerate CSS, coarse-grained sandstone; DA, Dubois Area; EB, Eagle Basin; FM, Formation; FSS, fine-grained sandstone; LS, limestone; Mdst, mudstone; MSS, medium-grained sandstone; OC, Otis Chalk; Slt, siltstone; SS, sandstone.
	Figure 2. Burrow localities, size distribution, and morphotypes of the Serendipity beds (yellow lines), upper Jelm Formation, near Dubois, WY, and collection localities: (a) (1) Serendipity, (2) DoJo, and (3) Independence. (b) Plot of representative burrows (n = 88) from the three localities (data in the table 1) demonstrating size distribution and general morphology of burrows (1, UWGM 7191; 2, 7188; 3, 7193; 4, 7194; 5, 7196; 6, 7189; 7, 7192; 8, 7195; 9, 7190). (c) Neutron tomography rendering of UWGM 2204 (morphosource.org; ID:000609370) containing a skeleton and rhizoliths within burrow, purple = rhizolith network from top 2 cm of burrow (left), volume rendering (right). (d) Micro-computed tomography rendering of UWGM 7438 with a partially articulated skeleton (left), highlighted skeleton (middle), burrow cast volume rendering (right).
	Figure 3. Reconstruction of cranium and lower jaw of Ninumbeehan dookoodukah based on UWGM 7264 and UWGM 2164, respectively. Holotype cranium (UWGM 7264) in (a) dorsal, (b) ventral, and (c) left lateral views. Paratype mandible (UWGM 2164) in (d) labial, and (e) lingual views. Abbreviations: a, articular; ang, angular; apf, anterior palatal fenestra; c, choana; c1, coronoid 1 (=’precoronoid’); c2, coronoid 2 (=’intercoronoid’); c3, coronoid 3 (=’coronoid’); cp, cultriform process of the parasphenoid; d, dentary; ect, ectopterygoid; ex, exoccipital; f, frontal; ipv, interpterygoid vacuity; j, jugal; Mkf, Meckelian fenestra; m, maxilla; n, nasal; en, external naris; o, orbit; p, parietal; pa, prearticular; pal, palatine; pas, parasphenoid; pf, parietal foramen; pm, premaxilla; po, postorbital; pof, postfrontal; pp, postparietal; pt, pterygoid; q, quadrate; qj, quadratojugal; sp, splenial; psp, postsplenial; sq, squamosal; st, supratemporal; stf, subtemporal fenestra; sur, surangular; t, tabular; v, vomer. All scale bars equal to 1 cm.
	Figure 4. Phylogenetic distribution of known cases of burrowing and burrow morphology among temnospondyls, including modern amphibians. (a) Simplified phylogeny of temnospondyls. (b) Cranial reconstructions of fossil temnospondyl taxa in lateral (left) and dorsal (centre) view with schematic drawings of associated burrow morphology (right). (c) Cranial reconstructions of extant amphibians in lateral (left) and dorsal (right) view with schematics of burrow morphology (below). Asterisks denote burrows that were found in proximity to temnospondyl body fossils. The dagger denotes the secondary occupancy of a burrow.
	Figure 5. Life reconstruction of Ninumbeehan dookoodukah in a palaeoenvironment reconstruction depicting its life and burrowing across seasons. (a) Ninumbeehan is resting on the edge of a river with a low water table as the wet season ends. (b) A small community of Ninumbeehan are in their estivation burrows at the apex of the arid season. (c) The onset of the humid season brings rain, triggering a mass emergence of Ninumbeehan from their estivation burrows. Some individuals expire before the incoming rains, leaving them to be preserved as fossils. Copyright: Gabriel N. Ugueto.