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Re: New Antarctic findings of Upper Cretaceous and lower Eocene loons



Not having seen the paper yet I cannot say much about this. However, Chatterjee 
seems convinced that at least some Polarornis material = Vegavis, which would 
make it anseriform instead of gaviiform.



Regards,

Eike




--------------------------------------------
David Černý <david.cerny1@gmail.com> schrieb am So, 8.11.2015:

 Betreff: Re: New Antarctic findings of Upper Cretaceous and lower Eocene loons
 An: dinosaur@usc.edu
 Datum: Sonntag, 8. November, 2015 10:14 Uhr
 
 If confirmed, the
 conclusions of this paper would have pretty
 far-reaching implications for the early
 evolution of modern birds. For
 starters,
 phylogenomic dating analyses suggest that loons diverged
 from their extant sister group in the Paleocene
 (Jarvis et al. 2014;
 Prum et al. 2015), so
 this would be one of the few cases in the bird
 tree of life where molecular data underestimate
 (rather than
 overestimate) the age of a node
 relative to the fossil record.
 
 It would also mean that the earliest phase of
 neoavian
 diversification, which corresponds
 to a "bush" of extremely short
 branches in molecular trees and which even
 whole-genome analyses might
 be unable to
 resolve into a neat sequence of bifurcations, happened
 prior to the K--Pg boundary. Recently, some
 authors on both sides of
 the
 "rocks-vs.-clocks" debate (e.g., Ksepka &
 Phillips 2015; Prum et
 al. 2015; Suh et al.
 2015) apparently came to agree that this region
 of bird phylogeny represents an explosive
 radiation into ecological
 niches emptied by
 the K--Pg extinction. If Acosta Hospitaleche and
 Gelfo are right in assigning the Maastrichtian
 fossils to Gaviiformes,
 this explanation
 obviously doesn't work, which makes me wonder if they
 could have misidentified the material. They
 seem to have good enough
 evidence that the
 fossils belong to neornithines, although they do
 mention that the morphology of the hypotarsus
 is unclear in what they
 interpret as an
 indeterminate Cretaceous loon. However, their
 phylogenetic analysis is based on Livezey and
 Zusi's (2007) data
 matrix that includes
 very few fossils and routinely fails to recover
 well-supported clades, as should be obvious
 from the fact that they
 get 100% bootstrap
 support for a loon-grebe group. Could the fossils
 perhaps belong to some other, earlier-diverged
 neornithine lineage?
 
 
 *Refs:*
 
 Jarvis
 ED, Mirarab S, Aberer AJ, Li B, Houde P, Li C, Ho SYW,
 Faircloth BC, Nabholz B, Howard JT, Suh A,
 Weber CC, Fonseca RRd, Li
 J, Zhang F, Li H,
 Zhou L, Narula N, Liu L, Ganapathy G, Boussau B,
 Bayzid MdS, Zavidovych V, Subramanian S,
 Gabaldón T, Capella-Gutiérrez
 S,
 Huerta-Cepas J, Rekepalli B, Munch K, Schierup M, Lindow B,
 Warren
 WC, Ray D, Green RE, Bruford M, Zhan
 X, Dixon A, Li S, Li N, Huang Y,
 Derryberry
 EP, Bertelsen MF, Sheldon FH, Brumfield RT, Mello CV,
 Lovell PV, Wirthlin M, Schneider MPC,
 Prosdocimi F, Samaniego JA,
 Velazquez AMV,
 Alfaro-Núñez A, Campos PF, Petersen B, Sicheritz-Ponten
 T, Pas A, Bailey T, Scofield P, Bunce M,
 Lambert DM, Zhou Q, Perelman
 R, Driskell AC,
 Shapiro B, Xiong Z, Zeng Y, Liu S, Li Z, Liu B, Wu K,
 Xiao J, Yinqi X, Zheng Q, Zhang Y, Yang H, Wang
 J, Smeds L, Rheindt
 FE, Braun M, Fjeldså J,
 Orlando L, Barker K, Jønsson KA, Johnson W,
 Koepfli KP, O'Brien S, Haussler D, Ryder
 OA, Rahbek C, Willerslev E,
 Graves GR, Glenn
 TC, McCormack J, Burt D, Ellegren H, Alström P,
 Edwards SW, Stamatakis A, Mindell DP, Cracraft
 J, Braun EL, Warnow T,
 Jun W, Gilbert MTP,
 Zhang G 2014 Whole genome analyses resolve the
 early branches in the tree of life of modern
 birds. Science 346(6215):
 1320–31
 
 Ksepka DT, Phillips MJ 2015
 Avian diversification patterns across the
 K-Pg boundary: Influence of calibrations,
 datasets, and model
 misspecification. Ann Mo
 Botan Gard 100(4): 300–28
 
 Livezey BC, Zusi RL 2007 Higher-order phylogeny
 of modern birds
 (Theropoda, Aves:
 Neornithes) based on comparative anatomy: II. –
 Analysis and discussion. Zool J Linn Soc
 149(1): 1–95
 
 Prum RO,
 Berv JS, Dornburg A, Field DJ, Townsend JP, Moriarty
 Lemmon
 E, Lemmon AR 2015 A comprehensive
 phylogeny of birds (Aves) using
 targeted
 next-generation DNA sequencing. Nature 526(7574):
 569–73
 
 Suh A, Smeds L,
 Ellegren H 2015 The dynamics of incomplete lineage
 sorting across the ancient adaptive radiation
 of neoavian birds. PLoS
 Biol 13(8):
 e1002224
 
 -- 
 David Černý