New late Eocene and Oligocene remains of the flightless, penguin-like plotopterids (Aves, Plotopteridae) from western Washington State, U.S.A.

ABSTRACT

We describe new plotopterids (Aves, Plotopteridae) from late Eocene and Oligocene strata in western Washington State, U.S.A. The specimens belong to four new species of these flightless, wing-propelled seabirds, three of which are named and assigned to two new supraspecific taxa, Olympidytes, gen. nov., and Klallamornis, gen. nov. We confirm previous observations on a high diversity of plotopterids in the Paleogene of North America, but because the fossils are from different formations, it remains elusive how many of the six currently recognized species from western Washington actually coexisted. Tonsala, the only previously described plotopterid taxon from the Olympic Peninsula, is likely to occupy a more basal phylogenetic position than the other plotopterids of this geographic area. Olympidytes and Klallamornis may be successive sister taxa of Copepteryx and Hokkaidornis from the late Oligocene of Japan, but a determination of the exact affinities of the new taxa requires the discovery of further fossils. Notably, the geochronologically youngest plotopterid, the early Miocene Plotopterum, differs from earlier taxa in plesiomorphic features and is here considered to be among the phylogenetically most basal plotopterids. The late Eocene basal Phocavis likewise temporally overlaps with more derived plotopterid taxa. The coexistence of basal and more derived plotopterids in the late Eocene may indicate a rapid evolution of plotopterids towards the late Eocene. The factors that allowed the persistence of basal taxa into the Miocene remain, however, elusive, and so are those that triggered the evolution of wing-propelled diving in these highly specialized birds.

Citation for this article: Mayr, G., and J. L. Goedert. 2016. New late Eocene and Oligocene remains of the flightless, penguin-like plotopterids (Aves, Plotopteridae) from western Washington State, U.S.A.. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1163573.

http://zoobank.org/urn:lsid:zoobank.org:pub:2B9124B1-0076-498C-A95D-F99B8F53500F

ACKNOWLEDGMENTS

We are indebted to B. Thiel, who collected the holotype of Olympidytes thieli and donated the specimen to SMF. We are further grateful to O. Vogel for the expert preparation of the fossils and to S. Tränkner for taking the photographs. The holotype specimen of Klallamornis abyssa was collected during field work by J. and G. Goedert, supported by the National Geographic Society (grant 4439-90), supervised by L. Barnes (LACM), and administered by the LACM and its foundation. We thank M. Berglund (deceased), R. ‘Fritz’ Clark (deceased, formerly LACM), and D. Starr for donating specimens used in this study. For access to fossil specimens, we thank S. McLeod and Vanessa Rhue (both LACM). B. Crowley prepared the coracoid referred to Klallamornis abyssa; C. Sidor, M. Rivin, and R. Eng (UWBM) provided photos and data for plotopterid material in the Burke Museum. Finally, we thank T. Ando and S. Kawabe for providing photographs of a Plotopterum femur from Japan. Comments from P. Scofield, an anonymous reviewer, and the editor, T. Worthy, improved the manuscript.

NOTE ADDED AT PROOF

Following submission of our revised manuscript, a new plotopterid from the late Oligocene of Canada, Stemec suntokum, was described by Kaiser et al. (2015). This species is only known from a coracoid, which closely resembles that of Plotopterum joaquinensis. Like the coracoid of Plotopterum, the coracoid of S. suntokum differs markedly from those of Tonsala and Klallamornis in presumably plesiomorphic features, the significance of which needs to be evaluated in future studies. Furthermore, Kaiser et al. (2015) list revised stratigraphic dates for Copepteryx hexeris and Plotopterum joaquinensis, which they consider to be of early and of late Oligocene age, respectively.