EARLY DINOSAUR ADAPTATIONS TO COLD EXPLAINS THEIR TRIASSIC HIGH-LATITUDE BIAS AND GLOBAL EXPANSION THROUGH THE END-TRIASSIC MASS EXTINCTION

From their outset, Triassic dinosaurs were mid- to high-paleolatitude animals, now known from above the arctic circle (1), when continental drift is taken into account (2,3). Herbivorous dinosaurs were entirely restricted to these higher latitudes, while small carnivorous dinosaurs became progressively more abundant and larger in the low-paleolatitudes simultaneously (4). Primitively present, filamentous insulating integument (inferred even for the ‘prosauropods’) facilitated survival in high-latitudes during the freezing winters that characterized at least the paleo-arctic even during times of very high pCO₂ (1). Pseudosuchians, which were, and are, uninsulated, were absent to extremely rare in the highest paleolatitudinal assemblages [e.g., (5)], but dominant in the lower latitudes (6). The adaptations to cold, most notably insulation, ‘preadapted’ dinosaurs to survive the intense volcanic eruptions of the Central Atlantic Magmatic Province. Herbivorous dinosaurs, both small and large, including the oldest definitive ornithischians, plausibly migrated into low-latitudes from the higher latitudes during the earliest of the eruptive pulses. Larger carnivorous theropods migrated in from higher latitudes or rapidly evolved in situ, as well. All large non-insulated land animals became extinct during this time (1). Afterwards, dinosaurs continued to occupy high-latitudes with ‘prosauropods’ being known from near the South Pole, while pseudosuchians remain unknown from the same region. Dinosaurs were, and are, fundamentally cold-adapted animals, accounting for their survival though multiple episodes of volcanic and impact winters of the Mesozoic.

1 Olsen et al (2022) Science Advances 8(26):eabo6342: 2 van Hinsbergen et al (2014-2022) paleolatitude.org: 3 Kent et al (2021) PNAS 118:e2020778118: 4 Whiteside et al (2015) PNAS 112:7909: 5 Tolchard et al (2019) J Afr Earth Sci 103610: 6 Olsen et al (2002) Science 296:1305