Bruce Museum

Polar ecosystems are structured and enriched by birds, which nest there seasonally and serve as keystone ecosystem members. Despite the ecological importance of polar birds, the origins of high-latitude nesting strategies remain obscured by a sparse fossil record. We report an extreme-latitude Arctic avialan assemblage from the Prince Creek Formation of Alaska—the northernmost Late Cretaceous terrestrial ecosystem. Numerous three-dimensionally preserved fossils constitute one of the most taxonomically rich Late Cretaceous avialan assemblages, including members of Hesperornithes, Ichthyornithes, and near-crown or crown birds (Neornithes), recording a previously undocumented interval in avialan evolution. Abundant perinatal fossils represent the oldest evidence of birds nesting at polar latitudes, which demonstrates that birds began using seasonal polar environments for breeding during the Cretaceous, long before their modern descendants.

ABSTRACT Albatrosses are among the most intensely studied groups of living birds, yet their fossil record remains sparse. Despite modern albatrosses being more abundant and widespread in the Southern Hemisphere, the vast majority of fossil albatrosses identified to date come from Northern Hemisphere localities. Here, we describe Plotornis archaeonautes sp. nov., a new albatross species from the earliest Miocene that represents the earliest record of Procellariiformes in New Zealand and the earliest uncontroversial record of the clade Pan-Diomedeidae from the Southern Hemisphere. Phylogenetic analyses support the placement of Plotornis outside of the clade uniting all extant albatrosses. The new fossil reveals that stem lineage albatrosses were widespread by the onset of the Neogene. Although the humerus of Plotornis archaeonautes exhibits a short processus supracondylaris dorsalis, this early species may have possessed at least one of the unique ossifications associated with the patagial bracing system present in modern albatrosses.

1) Measurements from modern and fossil penguin skulls (Thomas_et_al_Supplemental Data Table S1.xlsx). 2) R code and data for comparing mean annual sea surface temperature at penguin breeding colonies, as well as the morphological characters used for phylogenetic analysis (Thomas_et_al_Supplementary Data.docx)..

Our understanding of the earliest stages of crown bird evolution is hindered by an exceedingly sparseavian fossil record from the Mesozoic era. The most ancient phylogenetic divergences among crown birds are known to have occurred in the Cretaceous period1-3, but stem-lineage representatives of the deepest subclades of crown birds-Palaeognathae (ostriches and kin), Galloanserae (landfowl and waterfowl) and Neoaves (all other extant birds)-are unknown from the Mesozoic era. As a result, key questions related to the ecology4,5, biogeography3,6,7 and divergence times1,8-10 of ancestral crown birds remain unanswered. Here we report a new Mesozoic fossil that occupies a position close to the last common ancestor of Galloanserae and fills a key phylogenetic gap in the early evolutionary history of crown birds10,11. Asteriornis maastrichtensis, gen. et sp. nov., from the Maastrichtian age of Belgium (66.8-66.7 million years ago), is represented by a nearly complete, three-dimensionally preserved skull and associated postcranial elements. The fossil represents one of the only well-supported crown birds from the Mesozoic era12, and is the first Mesozoic crown bird with well-represented cranial remains. Asteriornis maastrichtensis exhibits a previously undocumented combination of galliform (landfowl)-like and anseriform (waterfowl)-like features, and its presence alongside a previously reported Ichthyornis-like taxon from the same locality13 provides direct evidence of the co-occurrence of crown birds and avialan stem birds. Its occurrence in the Northern Hemisphere challenges biogeographical hypotheses of a Gondwanan origin of crown birds3, and its relatively small size and possible littoral ecology may corroborate proposed ecological filters4,5,9 that influenced the persistence of crown birds through the end-Cretaceous mass extinction.

Avian diversification has been influenced by global climate change, plate tectonic movements, and mass extinction events. However, the impact of these factors on the diversification of the hyperdiverse perching birds (passerines) is unclear because family level relationships are unresolved and the timing of splitting events among lineages is uncertain. We analyzed DNA data from 4,060 nuclear loci and 137 passerine families using concatenation and coalescent approaches to infer a comprehensive phylogenetic hypothesis that clarifies relationships among all passerine families. Then, we calibrated this phylogeny using 13 fossils to examine the effects of different events in Earth history on the timing and rate of passerine diversification. Our analyses reconcile passerine diversification with the fossil and geological records; suggest that passerines originated on the Australian landmass ∼47 Ma; and show that subsequent dispersal and diversification of passerines was affected by a number of climatological and geological events, such as Oligocene glaciation and inundation of the New Zealand landmass. Although passerine diversification rates fluctuated throughout the Cenozoic, we find no link between the rate of passerine diversification and Cenozoic global temperature, and our analyses show that the increases in passerine diversification rate we observe are disconnected from the colonization of new continents. Taken together, these results suggest more complex mechanisms than temperature change or ecological opportunity have controlled macroscale patterns of passerine speciation.

The rapidly expanding interest in, and availability of, digital tomography data to visualize casts of the vertebrate endocranial cavity housing the brain (endocasts) presents new opportunities and challenges to the field of comparative neuroanatomy. The opportunities are many, ranging from the relatively rapid acquisition of data to the unprecedented ability to integrate critically important fossil taxa. The challenges consist of navigating the logistical barriers that often separate a researcher from high-quality data and minimizing the amount of non-biological variation expressed in endocasts - variation that may confound meaningful and synthetic results. Our purpose here is to outline preferred approaches for acquiring digital tomographic data, converting those data to an endocast, and making those endocasts as meaningful as possible when considered in a comparative context. This review is intended to benefit those just getting started in the field but also serves to initiate further discussion between active endocast researchers regarding the best practices for advancing the discipline. Congruent with the theme of this volume, we draw our examples from birds and the highly encephalized non-avian dinosaurs that comprise closely related outgroups along their phylogenetic stem lineage.

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