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, 108 (37), 15253-7

Mass Extinction of Birds at the Cretaceous-Paleogene (K-Pg) Boundary

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Mass Extinction of Birds at the Cretaceous-Paleogene (K-Pg) Boundary

Nicholas R Longrich et al. Proc Natl Acad Sci U S A.

Abstract

The effect of the Cretaceous-Paleogene (K-Pg) (formerly Cretaceous-Tertiary, K-T) mass extinction on avian evolution is debated, primarily because of the poor fossil record of Late Cretaceous birds. In particular, it remains unclear whether archaic birds became extinct gradually over the course of the Cretaceous or whether they remained diverse up to the end of the Cretaceous and perished in the K-Pg mass extinction. Here, we describe a diverse avifauna from the latest Maastrichtian of western North America, which provides definitive evidence for the persistence of a range of archaic birds to within 300,000 y of the K-Pg boundary. A total of 17 species are identified, including 7 species of archaic bird, representing Enantiornithes, Ichthyornithes, Hesperornithes, and an Apsaravis-like bird. None of these groups are known to survive into the Paleogene, and their persistence into the latest Maastrichtian therefore provides strong evidence for a mass extinction of archaic birds coinciding with the Chicxulub asteroid impact. Most of the birds described here represent advanced ornithurines, showing that a major radiation of Ornithurae preceded the end of the Cretaceous, but none can be definitively referred to the Neornithes. This avifauna is the most diverse known from the Late Cretaceous, and although size disparity is lower than in modern birds, the assemblage includes both smaller forms and some of the largest volant birds known from the Mesozoic, emphasizing the degree to which avian diversification had proceeded by the end of the age of dinosaurs.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Coracoids of stem avians from the late Maastrichtian of western North America. Left coracoids (right coracoids reversed) in lateral, dorsal, and medial views. (Scale bars, 10 mm.) (A) cf Avisaurus archibaldi YPM 57235. (B) Enantiornithine A NMC 9528. (C) Enantiornithine B YPM 57823. (D) Palintropus retusus YPM 2076. (E) Ornithurine D UCMP 187207. YPM, Yale Peabody Museum; NMC, Canadian Museum of Nature; UCMP, University of California Museum of Paleontology.
Fig. 2.
Fig. 2.
Tarsometatarsi of Hesperornithes from the late Maastrichtian of western North America. Left tarsometatarsi in medial, dorsal, plantar, and lateral view. (A) Hesperornithiform A RSM P2315.1. (B) Hesperornithiform B RSM P2604.1. I, facet for metatarsal I; II, metatarsal II; III, metatarsal III; IV, metatarsal IV; dvf, distal vascular foramen; fl, dorsal flange of metatarsal IV; RSM, Royal Saskatchewan Museum. (Scale bar, 1 cm.)
Fig. 3.
Fig. 3.
Coracoids of derived Ornithurae from the late Maastrichtian of western North America. Left coracoids and right coracoids reversed for comparison. (A) Ornithurine A UCMP 53963. (B) Ornithurine B UCMP 129143. (C) Ornithurine C SDSM 64281. (D) “Cimolopteryx” maxima UCMP 53973. (E) Ornithurine E AMNH 13011. (F) Ceramornis major UCMP 53959. (G) “Cimolopteryx” minima UCMP 53976. (H) “Cimolopteryx” petra AMNH 21911. (I) Cimolopteryx rara YPM 1805. (J) Ornithurine F UCMP 53957. acf, acrocoracoid fossa; lf, lateral fossa, str, strut; UCMP, University of California Museum of Paleontology; SDSM, South Dakota School of Mines; AMNH, American Museum of Natural History; YPM, Yale Peabody Museum. (Scale bar, 1 cm.)
Fig. 4.
Fig. 4.
Phylogeny showing relationships and stratigraphic distribution of late Maastrichtian birds (bold) and other avians. Note that the extension of neornithine branches into the mid Late Cretaceous is the result of an unresolved polytomy; the earliest fossil evidence of Neornithes is Maastrichtian (9). See SI Appendix for full results and details of the analysis.
Fig. 5.
Fig. 5.
Size range in late Maastrichtian birds. A, Hesperornithiform A; B, Hesperornithiform B; C, cf Avisaurus archibaldi; D, Ornithurine C; E, Ornithurine F; F, Cimolopteryx maxima; G, Enantiornithine A; H, Ceramornis major; I, Ornithurine D; J, Ornithurine B; K, Enantiornithine B; L, Palintropus retusus; M, Ornithurine A; N, Cimolopteryx rara; O, Cimolopteryx petra; P, Ornithurine E; Q, Cimolopteryx minima.

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