The Late Cretaceous Arctic (roughly 100–66 million years ago) hosted vibrant, high-latitude ecosystems unlike today’s tundra, supporting dinosaurs, birds, mammals, fish, and diverse vegetation despite extreme seasonality.

During the Late Cretaceous, northern Alaska (including the Prince Creek Formation, ~73 million years old, Campanian-Maastrichtian) sat at paleolatitudes of ~80–85°N. Earth was in a greenhouse state with higher sea levels and no permanent polar ice caps, but high latitudes still experienced:

• Polar nights: Up to ~4 months (around 120 days) of continuous winter darkness.
• Temperatures: Mean annual ~5–6°C (41–43°F), with warm-month means ~10–14.5°C and cold-month means near or slightly below freezing (~–2°C). Snowfall and freezing conditions occurred, but no year-round ground ice.
• Precipitation: Relatively high and humid, supporting lush vegetation on a low-gradient coastal/alluvial plain with rivers, floodplains, lakes, ponds, swamps, and tidal influences.

This created a polar forest/woodland environment—deciduous and coniferous trees, angiosperms (flowering plants), ferns, mosses, herbs, and shrubs—more akin to a cool-temperate or riparian forest than modern Arctic barrenness.

The Prince Creek Formation (and related sites) yields the northernmost known Mesozoic terrestrial vertebrate assemblage, often called the Paanaqtat Province, with many endemic species.

Dinosaurs (many juveniles and bonebeds indicate year-round residency and breeding):

• Hadrosaurs (e.g., Edmontosaurus relatives) — preferred wetter lowland/deltaic habitats.
• Ceratopsians (e.g., Pachyrhinosaurus perotorum) — more upland/coastal plain.
• Tyrannosaurs (e.g., Nanuqsaurus).
• Smaller theropods (troodontids, dromaeosaurids).
• Others: Thescelosaurids, etc.

Evidence suggests physiological adaptations (possibly endothermy or homeothermy) and behaviors like overwintering or torpor allowed survival through dark, cold winters.

Birds (Avialans): Diverse assemblage including hesperornithines (diving birds), ichthyornithines, and early crown birds. Abundant perinatal (baby) fossils provide the oldest direct evidence of polar bird nesting/breeding, dating back ~73 million years—birds have used high-latitude breeding strategies for nearly half their evolutionary history.

Mammals: Small-bodied, including the recently described multituberculates (Camurodon borealis, Qayaqgruk peregrinus, Kaniqsiqcosmodon polaris). These rodent-like animals showed dietary niche partitioning (herbivorous to omnivorous) in a resource-variable environment. Other groups: metatherians (marsupial-like).

Fish and Others: Teleosts (including early salmonids and esocids adapted to high latitudes), paddlefish, rare sharks. Aquatic ecosystems mixed freshwater and estuarine influences.

Three new species of small, rodent-like mammals (multituberculates) from ~73 million-year-old fossils in Alaska’s Prince Creek Formation shed light on how life thrived in the ancient Arctic’s extreme conditions.

A new paper published May 2026 in Proceedings of the National Academy of Sciences (PNAS) by Sarah L. Shelley and colleagues analyzes fossils from Alaska’s Prince Creek Formation (~73 million years old, Campanian-Maastrichtian). It describes three new multituberculate species and uses phylogenetic/biogeographic analyses to show that high-latitude ecosystems actively shaped mammal evolution.

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Newly discovered species in ancient Arctic reveal how animals might have survived extremes

The Arctic served as both a corridor for intercontinental dispersal and a cradle for mammalian evolutionary innovation during the Late Cretaceous, well before the K-Pg mass extinction ~66 million years ago.

This 2026 PNAS paper by Sarah L. Shelley and colleagues (including Jaelyn J. Eberle, Gregory M. Erickson, and Patrick S. Druckenmiller) fundamentally reframes high-latitude regions not as evolutionary “backwaters” or marginal habitats, but as dynamic arenas for biotic interchange (dispersal corridors) and in situ innovation (cradles of diversification). It draws on the northernmost Mesozoic mammal fossils from the ~73 Ma (Campanian-Maastrichtian) Prince Creek Formation, Alaska (paleolatitude ~80–85°N).

Multituberculates were a highly successful, long-lived (Jurassic to Oligocene) clade of small, rodent-like mammals known for complex, multi-cusped teeth adapted for varied diets. The Prince Creek specimens are isolated teeth (examined via morphology and micro-CT), revealing:

Camurodon borealis (“northern curved-tooth”): Northernmost record of Cimolomyidae. Tooth morphology indicates primarily herbivorous habits.

Qayaqgruk peregrinus (“the little wandering hero”): Allied with Asian (Mongolian) Djadochtatherioidea. Omnivorous (insects + plants). Name honors Inuit legendary hero; “peregrinus” nods to its wandering/dispersal.

Kaniqsiqcosmodon polaris (“polar frost ornamented tooth”): Oldest known Microcosmodontidae. Omnivorous but likely plant-dominant. Suggests high-latitude origin for a lineage that later diversified in North America post-K-Pg.

Pronounced dental variation among these co-occurring species points to ecological niche partitioning — critical in a highly seasonal polar environment with limited resources, months of polar night, freezing temperatures, snowfall, and a cool mean annual temperature (~6°C/42°F) supporting polar forests rather than modern tundra.

This adaptability likely contributed to multituberculates’ resilience, including survival of the K-Pg extinction (unlike non-avian dinosaurs).

The authors integrated comparative dental morphology with phylogenetic analyses (using existing matrices, TNT/MrBayes etc.) and biogeographic modeling:

Dispersal (Corridor Role): Q. peregrinus provides the earliest direct evidence (~91.82 Ma) of multituberculate movement from Asia to North America via a terrestrial Beringian corridor. This predates many other documented exchanges and shows the Arctic was a viable highway for mammals during the Cretaceous, not just the Pleistocene.

Diversification & Endemism (Cradle Role): K. polaris implies a high-latitude origin for Microcosmodontidae, a derived North American group that radiated in the Paleocene. C. borealis extends the range of Cimolomyidae northward. The Arctic thus fostered both immigrant success and local evolutionary novelty.

These findings build on prior Prince Creek work (dinosaurs, birds, other mammals like metatherians and eutherians) and challenge “out-of-the-tropics” models that downplay high latitudes in deep-time innovation.

The Prince Creek Formation records a vibrant, dinosaur-bearing polar ecosystem with evidence of overwintering strategies in vertebrates (e.g., nesting at high latitudes). For small mammals:

• Seasonal extremes selected for dietary flexibility (herbivory to omnivory).
• Connectivity via Beringia allowed gene flow and range expansion.
• Pre-adaptation hypothesis: Traits honed in polar seasonality (e.g., resource opportunism) may have aided some lineages through the K-Pg crisis and into the Paleogene recovery.

Broader Implications and Caveats

Challenges traditional views: Polar regions were active contributors to mammalian dynamics, not just sinks or filters.

Relevance to modern change: Highlights mammalian resilience to climatic extremes and the role of connectivity in diversification — pertinent amid current Arctic warming and habitat shifts.

Data quality: Relies on teeth (common for microfossils); future jaw/skull finds could refine phylogenies. Sample size is small but significant given the rarity of high-latitude Mesozoic mammals.

Timing: Dispersal estimate (~91.82 Ma) comes from calibrated phylogenetic/biogeographic models; uncertainties in fossil ages and rates exist but are standard in the field.

In summary, this work elevates the Cretaceous Arctic from a peripheral curiosity to a key evolutionary theater. It underscores how extreme, connected environments can drive dispersal, niche differentiation, and origination — patterns that helped shape mammalian history across the K-Pg boundary. The full open-access paper (with extensive supplements, 3D models, code, and matrices) is available on PNAS for those wanting primary details.

Published: Proceedings of the National Academy of Sciences Peer-Reviewed

DOI: 10.1073/pnas.2601794123

Authors: Sarah L. Shelley, Jaelyn J. Eberle, Gregory M. Erickson and Patrick S. Druckenmiller

Abstract

High-latitude terrestrial ecosystems are commonly viewed as marginal environments to deep-time evolutionary innovation, yet their role in shaping biotic dispersal, diversification, and survivorship remains poorly understood.

The Upper Cretaceous Prince Creek Formation of northern Alaska (paleolatitude ~80–85°N) yields the most northerly known Mesozoic mammals and provides a rare opportunity to examine the ecological and biogeographic roles of polar terrestrial ecosystems.

Here, we describe three multituberculate species, Camurodon borealis, Qayaqgruk peregrinus, and Kaniqsiqcosmodon polaris, and integrate comparative morphology with phylogenetic and biogeographic analyses to evaluate patterns and timing of dispersal and diversification across a high-latitude Asian–American terrestrial corridor. 

Qayaqgruk peregrinus is recovered within the Mongolian Djadochtatherioidea, representing the earliest direct evidence for multituberculate dispersal from Asia into North America. 

Kaniqsiqcosmodon polaris constitutes the oldest known member of the Microcosmodontidae, suggesting a high-latitude origin for a derived North American lineage that later diversified during the Paleocene following the Cretaceous–Paleogene mass extinction. 

Camurodon borealis represents the northernmost occurrence of the Cimolomyidae.

Pronounced variation in dental morphology among the Prince Creek multituberculates indicates ecological differentiation and niche partitioning within an extreme, highly seasonal polar environment.

Our findings indicate that Late Cretaceous Arctic ecosystems supported both sustained intercontinental exchanges as early as 91.82 Ma and endemism.

Our results challenge interpretations of polar regions as evolutionary peripheries and instead identify them as important contributors to mammalian evolutionary dynamics prior to the Cretaceous–Paleogene mass extinction.