New Material of Paleocene-Eocene Pellornis (Aves: Gruiformes) Clarifies the Pattern and Timing of the Extant Gruiform Radiation

Abstract

Pellornis mikkelseni is an early gruiform from the latest Paleocene-earliest Eocene Fur Formation of Denmark. At approximately 54 million years old, it is among the earliest clear records of the Gruiformes. The holotype specimen, and only material thus far recognised, was originally considered to comprise a partial postcranial skeleton. However, additional mechanical preparation of the nodule containing the holotype revealed that the skeleton is nearly complete and includes a well-preserved skull. In addition to extracting new information from the holotype, we identify and describe two additional specimens of P. mikkelseni which reveal further morphological details of the skeleton. Together, these specimens show that P. mikkelseni possessed a schizorhinal skull and shared many features with the well-known Paleogene Messelornithidae (“Messel rails”). To reassess the phylogenetic position of P. mikkelseni, we modified an existing morphological dataset by adding 20 characters, four extant gruiform taxa, six extinct gruiform taxa, and novel scorings based on the holotype and referred specimens. Phylogenetic analyses recover a clade containing P. mikkelseni, Messelornis, Songzia and crown Ralloidea, supporting P. mikkelseni as a crown gruiform. The phylogenetic position of P. mikkelseni illustrates that some recent divergence time analyses have underestimated the age of crown Gruiformes. Our results suggest a Paleocene origin for this important clade, bolstering evidence for a rapid early radiation of Neoaves following the end-Cretaceous mass extinction.

Comprehensive taxon sampling and vetted fossils help clarify the time tree of shorebirds (Aves, Charadriiformes)

“…The post-Eocene dates suggested for the Alcidae/Stercorariidae divergence (or even more inclusive clades) by recent studies therefore exemplify the "zombie lineage" problem described by Springer et al (2017), in which molecular divergence times turn out to be younger than the known fossil record allows. The same underestimation of divergence times was recently reported for the Gruiformes by Musser et al (2019), and may be relatively widespread as a result of efforts to correct for the implausibly old divergences yielded by earlier studies by means of overly stringent calibration choice. Conversely, the criteria employed here that allowed calibration 8 to be used could be criticized as too lax given the fragmentary nature of the material and the long temporal gap separating it from the next oldest pan-alcid occurrence.…”

A Phylogenomic Supertree of Birds

“…Fossil Specimen: Pellornis mikkelseni MGUH 29278 Phylogenetic Justification: Pellornis has been recovered as a member of Messelornithidae, a clade that has been supported by synapomorphies as sister taxon to Rallidae+Heliornithidae [166] or Rallidae to the exclusion of Heliornithidae [167]. Recent work [168] supports the former position for Pellornis and Messelornithidae, and that is used here. Minimum Age Constraint: 53.9 Ma Maximum Age Constraint: 66.5 Ma Age Justification: The fossil is from the Fur Formation of Denmark.…”

Phylogenomic Reconstruction Sheds Light on New Relationships and Timescale of Rails (Aves: Rallidae) Evolution

“…The divergence times obtained using a Bayesian relaxed-clock model and a non-Bayesian model were mostly similar when Belgirallus was used as a crown Rallidae representative. As illustrated in our node dating analyses, the root and origin of Rallidae were estimated to be 33 (32)(33)(34)(35)(36) Mya using a Bayesian approach or 34 (32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44) Mya with a non-Bayesian method. However, the credibility intervals (uncertainty) for the origin of Rallidae estimated in RelTime were rather wide compared with the 95% highest posterior density (HPD) intervals in BEAST2.…”

“…We applied the method of Claramunt and Cracraft [23], in which prior calibration densities were modeled based on available fossil records. We placed an exponential prior on the crown ages of Gruiformes (offset: 52, mean: 8.5) and a lognormal prior on the age of the Rallidae (offset: 32.6, mean: 1.1, standard deviation: 1.8) based on densities inferred by Stervander et al [15], which were themselves based on thoroughly examined fossil data [43,44].…”