comment on this calibration

Threskiornithidae

Lineage (NCBI): This node has no ancestors.
 node name
Threskiornithidae     Look for this name in NCBI   Wikipedia   Animal Diversity Web
 
  recommended citations
http://palaeo-electronica.org/content/fc-7 Smith and Ksepka, 2015
 
  node minimum age
0 Ma
The calibrating specimen was collected from the lower Eocene Fur Formation of northwest Denmark (Lindow and Dyke, 2006; Mayr and Bertelli, 2011). Nearly 180 layers of volcanic ash are interbedded within the Fur Formation (Egger and Brückl, 2006; Lindow and Dyke, 2006). The upper set of more closely spaced, black basaltic ash layers are numbered ranging from +1 to +140 in ascending stratigraphic order, whereas the lower set of more widely spaced, light colored layers are numbered from -1 to -39 in descending order (Bøggild, 1918; Egger and Brückl, 2006). Two 39Ar/40Ar radioisotopic dates have been reported from these ash layers, including a date of 54.04 +/- 0.14 Ma from layer +19 and a date of 54.52 +/- 0.05 Ma from layer -17 (Chambers et al., 2003). More recently, a reanalysis of the 39Ar/40Ar radioisotopic dates from layer -17 produced an age of 55.12 +/- 0.12 Ma (Storey et al., 2007), and adjusting this estimate based on the recalibration of the Fish Canton Tuff (~28.201 Ma) sanidine reference standard (Kuiper et al., 2008) for 39Ar/40Ar radioisotopic dates yields a corrected age of 55.48 +/- 0.12 (Westerhold et al., 2009). Within the time period bounding layer -17 and +19, approximately 0.5 m of volcanic ash and 19.5 m of diatomite were deposited (Bøggild, 1918; Egger and Brückl, 2006). However, the precise horizon from which these MGUH 20288 was collected has not been reported, so whether these dates provide a minimum age, maximum age, or together bound the age of the fossils cannot be determined. With these considerations in mind, youngest possible age for MGUH 20288, inclusive of error is 53.9 Ma.
 
  node maximum age
53.9 Ma
None specified.
 
 primary fossil used to date this node 
 
MGUH 20288
Rhynchaeites sp., Wittich, 1898
Location relative to the calibrated node: Stem

[show fossil details]
     Locality: Fur Formation
     Geological age: Eocene, Paleogene, Cenozoic


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  phylogenetic justification
The referral of MGUH 20288 to Rhynchaeites sp. is based on the following combination of characters, distributed throughout the postcranial skeleton (potential autapomorphies of Rhynchaeites indicated with an asterisk): sternum with a wide trabecula mediana bounded by a single pair of caudal incisions (of similar depth to Rhynchaeites messelensis); a metatarsal I with a shorter and wider articular process for the tarsometatarsus than in extant Threskiornithidae; *a proximomedially projecting medial portion of the proximal tarsometatarsus (a distinct, but somewhat similar character is present in Gavia, Podiceps, and some procellariiforms; see Smith, 2010, character 411); the fossa for metatarsal I is located close to the medial surface of the shaft of the tarsometatarsus (a fossa in a fully medial position is present in Plotopteridae; see Smith, 2010:Character 435); *the presence of a short tendinal ossification on the plantar surface of the tarsometatarsus; and near-identical proportions of the hindlimb and pedal segments (which are also distinct from extant Threskiornithidae), with the exception that MGUH 20288 is slightly larger than some Rhynchaeites messelensis specimens (Mayr and Bertelli, 2011, table 1). Phylogenetic placement of Rhynchaeites messelensis (Figure 1.2) as a member of total group Threskiornithidae is based on three apomorphic characters discussed by Peters (1983) and Mayr (2002a): an elongate recurved bill; a schizorhinal bill with a dorsoventrally broad basal segment of the ventral bar, and a notarium consisting of at least three fused thoracic vertebrae (Livezey and Zusi, 2006, character 892). Within waterbirds, a notarium is present in Podicipedidae, Phoenicopteridae, Threskiornithidae, and Pelecanidae (Livezey and Zusi, 2006; though in Pelecanidae, only two vertebrae anterior to the synsacrum are included, leading these authors to suggest that this taxon does not have a notarium sensu stricto). Additional potential apomorphies (optimization as apomorphies dependent upon topology of extant waterbird lineages relative to Threskiornithidae) uniting Rhynchaeites messelensis and Threskiornithidae include: 1) a dorsoventrally deep sternal keel (Livezey and Zusi, 2006, character 1199; see also Smith, 2010, character 133); 2) a postacetabular blade of the ilium that is as long as or extends further caudally than the caudal end of the ischium (Livezey and Zusi, 2006, character 1914; Smith, 2010, character 320); 3) a fibula that is at least 3/4 the length of the tibiotarsus, but still does not reach its distal end (Livezey and Zusi, 2006, character 2191; convergently present in Podiceps within waterbirds); 4) a medially located sulcus extensorius on the distal tibiotarsus (Livezey and Zusi, 2006, character 2178); and 5) the relative distal extents of the trochleae metatarsals are II < III > IV, and II > IV (Livezey and Zusi, 2006, character 2361; Smith, 2010, character 445). Of these traits, characters 1, 3, 4, and 5 are present in the calibrating specimen Rhynchaeites sp. MGUH 20288.
 
  phylogenetic reference(s)
Mayr, G. and Bertelli, S. 2011. A record of Rhynchaeites (Aves, Threskiornithidae) from the early Eocene Fur Formation of Denmark, and the affinities of the alleged parrot Mopsitta. Palaeobiodiversity and Palaeoenvironments, 91:229–236.
 
 tree image (click image for full size) 
tree image
Figure 3 from Smith and Ksepka (2015).
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