New Papers in AMNovitates

["Jaime A. Headden" <qilongia@yahoo.com>]

Some new papers from AMNovitates of interest.

  Dashzeveg D., L. Dingus, D. B. Loope, C. C. Swisher, III, Dulam
   T., & M. R. Sweeney. 2005. New stratigraphic subdivision,
   depositional environment, and age estimate for the Upper
   Cretaceous Djadokhta Formation, southern Ulan Nur Basin,
   Mongolia. _American Museum Novitates_ 3498:1-31.

Abstract:
  "Studies of key and newly discovered sections of the Upper
   Cretaceous Djadokhta Formation along the southern margin of the
   Ulan Nur Basin allow a new subdivision based on lithology. The
   formation and its members were mapped at both Bayn Dzak, an
   area that includes the Flaming Cliffs, and Tugrugyin Shireh, an
   area about 50 km to the northwest of Bayn Dzak. Stratigraphic
   sections at both localities were remeasured. The considerably
   enlarged formation comprises a lower Bayn Dzak Member,
   dominated by moderate reddish orange sands with subordinate
   mudstone units, and an upper Tugrugyin Member, composed of pale
   orange to light gray sands. Investigations of key sections at
   Tsonzh and Alag Teer demonstrate the presence of transitional
   mudstone lenses between these members within the Djadokhta
   Formation. Two distinct, sandy, sedimentologic facies are
   recognized in both members. Cross-bedded intervals,
   occasionally exhibiting wind-ripple cross lamination, document
   the presence of a Cretaceous dunefield in the Ulan Nur Basin.
   Structureless intervals are interpreted to represent wet sandy
   fluvial deposits and debris flows that moved down the dune
   faces. In the Bayn Dzak Member, lenses of brownish mudstone are
   interpreted to represent interdune deposition in shallow ponds
   by fluvial action. Fluvial action is also represented in the
   Bayn Dzak Member by beds of caliche, which contain conglomerate
   at the base but fine upward into limestone.
  "The vertebrate fauna from the Djadokhta Formation is
   summarized. Although the Bayn Dzak fauna lived somewhat earlier
   than that from Tugrugyin Shireh based on the superposition of
   the members, it is not clear how much earlier. The fauna from
   the Djadokhta Formation has previously been assigned ages from
   Cenomanian to earliest Maastrichtian. New magnetostratigraphic
   data document a sequence of normal and reversed magnetozones
   through the Bayn Dzak Member up into the basal Tugrugyin
   Member. The presence of reversed magnetozones establishes that
   the sediments containing the faunas were probably deposited
   after C34n. The quick stratigraphic succession of normal and
   reversed magnetozones suggests, but does not clearly establish,
   that the sediments may have been deposited during the rapid
   sequence of polarity changes in the late part of the Campanian
   between about 75 to 71 Ma."

  Clarke, J. A., M. A. Norell, & Dashzeveg D. 2005. New avian
   remains from the Eocene of Mongolia and the phylogenetic
   position of the Eogruidae (Aves, Gruoidea). _American Museum
   Novitates_ 3494:1-17.

Abstract:
  "A well-preserved nearly complete avian tarsometatarsus was
   collected by the 2002 expedition of the Mongolian Academy of
   Sciences from upper Eocene deposits exposed at the locality of
   Alag Tsav in the Eastern Gobi desert (Dornogov Aimag) of
   Mongolia. The new specimen is identified as part of a proposed
   Eogruidae clade, although it is unclear whether it is
   appropriately the holotype of a new species within this clade
   or referable to a previously named species. The clade Eogruidae
   has, as its current contents, species named as part of the
   traditional families Eogruidae + Ergilornithidae, which include
   several taxa of completely didactylous and apparently
   flightless birds. Referral of the new fossil to the clade
   Eogruidae is on the basis of derived reduction/loss of the
   metatarsal II trochlea.
  "A series of phylogenetic analyses was used to investigate the
   systematic position of Eogruidae (including the new fossil, IGM
   100/1447), which have been proposed to be a dominant part of
   Eocene to Miocene Asian faunas. First, the Mayr and Clarke
   (2003) dataset for crown clade Aves was used to investigate
   placement of Eogruidae within Aves, using a more completely
   known eogruid, *Eogrus aeola*, as an exemplar taxon. *Eogrus
   aeola* was identical to the new tarsometatarsus for all scored
   characters. A strict consensus cladogram of three most
   parsimonious trees from 1000 replicate heuristic searches
   placed *Eogrus aeola* in an unresolved polytomy with Psophiidae
   and Gruidae (Trumpeters and Cranes).
  "Given the results of this analysis, Eogruidae (including IGM
   100/1447) was analyzed in the suborder Grues dataset of Livezey
   (1998). Eogruidae was placed as the sister taxon to an Aramidae
   + Gruidae clade in the strict consensus cladogram of the eight
   most parsimonious trees resulting from a branch and bound
   search. Because monophyly of the traditional order Gruiformes
   has been repeatedly questioned, and the outgroups used in the
   original Grues dataset were identified through analyses
   assuming monophyly, the impact of removing these assumptions
   was investigated. Placement was robust to both changing
   outgroup assumptions and to swapping in the more incompletely
   known IGM 100/1447 as an exemplar for Eogruidae."

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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