Xu Chu

Costal aspiration breathing was an evolutionary innovation that was fundamental to the conquest of the terrestrial realm by amniotes (mammals, reptiles, birds and their common ancestor)^1,2,3,4,5. Extant amniotes use an integrated thoracic skeleton for costal-muscle-generated inhalation and exhalation, differing substantially from their anamniote relatives, which possess more passive cutaneous and buccal pumping forms of ventilation. This difference extends into the Palaeozoic era, but the evolutionary transformation between these modes of breathing is undocumented and largely unclear^6,7,8,9,10 in the absence of soft tissue fossils. Here we present the mummified early Permian reptile Captorhinus, which includes a covering of three-dimensional skin, native protein remnants and a complete shoulder girdle and ribcage with preserved cartilages. These are the oldest-known preserved cartilages and protein remnants in a terrestrial vertebrate. High-resolution neutron computed tomography and histology data reveal previously undescribed structures, including the cartilaginous sternum, sternal ribs, rib extensions and epicoracoids. Our skeletal reconstruction of this ancient reptile reveals the precise relationships between the ribcage and the shoulder girdle, and their pivotal role in the evolution of terrestrial breathing and locomotor regimes^11,12. This finding substantially changes expectations of soft tissue preservation in deep time to reveal the potential ancestral amniote breathing mechanism and its impact on terrestrial vertebrate evolution.

In response to westward subduction of the Paleo-Pacific, the North China Craton experienced the uplift of an eastern coastal plateau followed by subsidence in the Early Cretaceous, which potentially drove a shift in climatic patterns. Here we use the oxygen isotope ratios of garnets from magmatic-hydrothermal ore systems to infer the origins and signatures of mineralization fluids during this tectonic transition. The garnet oxygen isotope values range from approximately –11.4 to +13.5‰, with extremely depleted oxygen isotope ratios exclusively found in the northern margin, indicating extensive involvement of meteoric and lacustrine fluid in the back-arc hinterland. This geological record aligns with climate modeling exhibiting that the coastal plateau amplified northeastward transport of moisture from tropical Tethyan Ocean. The long-distance transport strongly depleted ¹⁸O and ²H (D). As the cratonic lithosphere thinned and the plateau subsided, the Pacific influences began to dominate the climatic pattern of East Asia.

Contact metamorphism of carbonate rocks in response to fluid infiltration releases carbon dioxide (CO ₂ ), potentially affecting Earth's carbon budget over geological timescales. This process was notably active in the Cretaceous when the closure of the Neo‐Tethys Ocean led to extensive arc magmatism in southern Tibet, coincident with a greenhouse climate interval. These arc plutons intersected carbonate sequences and formed widespread calcsilicate rocks. The mineral assemblages of these rocks record both the progression and duration of the CO ₂ release. In this study, we focus on a representative aureole in southern Tibet that was metamorphosed by a ∼64 Ma granitoid pluton of the Gangdese Batholith. The aureole presents lithologic zonation, with the inner garnet‐wollastonite zone indicating equilibrium with a water‐rich fluid at ∼525°C. Large garnet porphyroblasts feature cross‐cutting veins of secondary garnets that illustrate several stages of interface‐coupled dissolution‐reprecipitation processes facilitated by fluid infiltration. Diffusion modeling for Mg concentration profiles across vein‐host garnet yields a brief high‐temperature stage (25–150 kyr)—a duration still significantly overestimated considering factors that may accelerate diffusion in garnet, such as lattice parameters and hydration. Such short timescale aligns with conduction modeling of a cooling pluton, which, combined with the bulk‐rock mass balance analysis, indicates a local carbon flux comparable to fluxes at other modern tectonic settings. The metamorphic decarbonation, potentially episodic, in the continental arc may have been an important endogenic carbon source in the late Cretaceous.

Models concerning the diffusion of divalent cations (Ca²⁺, Mg²⁺, Fe²⁺, and Mn²⁺) in garnet have been subject to extensive research and application over several decades, yet discrepancies among available models persist. Particularly the diffusion rate of Mn²⁺, which is the fastest in garnet, varies by more than two orders of magnitude for garnets in eclogite. In this study, we use an eclogitic breccia sample from the Western Tianshan (ultra-) high-pressure metamorphic belt for calibration. The thermobarometry indicates that the sample experienced exhumation from ~2.45 GPa, ~480°C to 1.85 GPa, ~515°C. Previous geochronological constraints estimate the exhumation duration to be a couple of million years to up to 15–20 Myr, with an average slab exhumation rate of ~3.5 mm/year. Although the estimates entail significant uncertainties, this range is still smaller than the discrepancy of Mn diffusion rate predicted among diffusion models. Thus, this natural sample provides valuable insights for calibrating the available diffusion models. Our analysis of garnet compositional profiles demonstrates that the diffusion rates (D_i) at the pressure and temperature of interest are D_Ca:D_Fe:D_Mg:D_Mn = 0.2:0.4:1:2.4. By integrating garnet profiles, pressure–temperature–time information, and existing experimental data, we refine each diffusion model for Mn²⁺, thereby reducing the uncertainties associated with down-temperature extrapolation. Application of the newly calibrated models indicates that the oscillatory zoning of Mn²⁺ at the garnet rim is best described by a brief thermal excursion (~0.4 Myr, >20°C) at ~1.9 GPa. This minor thermal pulse punctuating the general exhumation path could be indicative of shear heating between nappes or momentary involvement in the mantle wedge, suggesting stacking or partial reactivation of the thrusts during exhumation.