19 The Campanian Crucible: A synthesis of vertebrate paleobiogeography and ecosystem dynamics in Laramidia

Laramidia’s Campanian deposits reveal vertebrate diversification, geographic isolation, and provincialism, and its fossil record informs paleoecology and biogeography. This session synthesizes research on evolution, endemism, WIS dynamics, and underexplored geochronology across this Late Cretaceous landscape.

Tuesday, 19 May 2026
8:00 AM - 12:00 PM
Alvarado C

Campanian Mammals from Arctic Laramidia: Evidence for Endemism and Intercontinental Dispersal in northern Alaska

Paper number: 19-10
Program: Technical Sessions
Time: 11:00 AM – 11:20 AM

Authors

Abstract

During the Late Cretaceous, the paleo-Arctic region of Laramidia was inhabited by a diverse vertebrate fauna that included non-avian dinosaurs, birds, fishes, and mammals. Campanian strata of the Prince Creek Formation (PCF) in northern Alaska (~80 - 85° N paleolatitude) are best known for their endemic dinosaurian fauna, whereas fossil mammals are relatively rare and only recently described. The majority of mammalian fossils recovered from the PCF are teeth and jaw fragments of the tiny, endemic metatherian Unnuakomys belonging to the North American family Pediomyidae. Two species - U. hutchisoni and an undescribed taxon with a slightly larger dentition - imply that a single lineage of pediomyid colonized the Arctic and evolved in geographic isolation. Additionally, we recognize three new species of multituberculates, two of which represent the northernmost members of the North American families Cimolomyidae and Microcosmodontidae. The third species falls within the Djadochtatherioidea, a clade previously restricted to the Late Cretaceous of Mongolia, and represents the earliest direct evidence of an Asia-to-Laramidia dispersal of multituberculates. The first eutherian to be described from the PCF, the endemic leptictidan Sikuomys mikros is the sister taxon to mid-latitude North American Gypsonictops, although is noticeably smaller than its lower latitude relatives. From a paleoecological standpoint, the pattern in which the smallest species of a lineage occurs at the highest latitudes and coldest environments suggests S. mikros did not hibernate, but was active year-round, similar to living shrews and voles. At least two more eutherian species are represented in the PCF, one of which falls within the Late Cretaceous Asian Zalambdalestidae based on both parsimony and Bayesian analyses. By virtue of its geography, northern Laramidia preserves novel data for understanding the Arctic as a faunal crossroad between Asia and North America as well as a crucible of vertebrate evolution.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410518

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