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AW: New Papers High Voltage




> Lockley, M., Chin, K., Houck, K., Matsukawa, M., and
> Kukihara, R. 2009. New
> interpretations of Ignotornis, the first-reported Mesozoic
> avian footprints:
> implications for the paleoecology and behavior of an
> enigmatic Cretaceous
> bird. Cretaceous Research. doi:
> 10.1016/j.cretres.2009.04.001.
> 
> ABSTRACT: The type material of Ignotornis mcconnelli, the
> first reported
> Mesozoic bird track, consists of a large, monospecific
> sample of ~70
> footprints comprising at least 15 recognizable trackways.
> However, the exact
> type horizon and locality, discovered in 1930 in the
> Cretaceous Dakota Group
> near Golden, Colorado, was not indicated in the original
> 1931 description by
> Maurice Mehl, and only the single holotype trackway was
> illustrated. In
> 1988, the known sample was doubled by the discovery of ~70
> additional tracks
> representing at least seven trackways, but again the exact
> type horizon and
> locality remained uncertain. In 2007, we discovered what we
> infer to be the
> original type locality, and identified approximately 150
> additional
> footprints comprising at least 17 additional trackways.
> During the study we
> also located three more specimens, in other collections,
> comprising at least
> 60 tracks and 10 trackways. Thus, the type (holotype,
> paratype, and
> topotype) sample now consists of ~360 footprints comprising
> about 50
> trackways, of which 41 have been measured. Although most
> footprints from the
> 1930, 1988, and 2007 finds all appear to originate from the
> same âtypeâ'
> horizon associated with a volcanic ash, a few tracks were
> found in 2007 at
> two additional levels.
> Â ÂÂÂThe relatively long, reversed
> hallux and the incipient semi-palmate
> webbing in the hypex between digits III and IV make
> Ignotornis distinct from
> any other Cretaceous bird tracks known from North America.
> These features,
> used to infer the extant forms with which Ignotornis is
> most convergent, are
> reminiscent of small herons, and unlike the typical tracks
> of most
> Cretaceous shorebird-like species which resemble those of
> plovers and
> sandpipers. Clearly defined parallel and sub parallel
> trackways indicate
> gregarious behavior, while some trackways indicate unusual
> âshufflingâ and
> âstop-startâ progression, probably related to some type
> of âfoot-stirringâ
> foraging activity. The concentration of abundant Ignotornis
> tracks at a
> single locality within the ichnologically-famous
> âDinosaur Freewayâ
> (represented by more than 60 dinosaur and crocodile
> dominated track
> assemblages) suggests that the Ignotornis track maker was a
> ârare-birdâ in
> the region during the Cretaceous.

Hm, interesting. IIRC there has never been any attempt to ascertain whether the 
different midfoot anatomy of Enantiornithes and Ornithurae/ornithuromorphs (and 
heterodontosaurs) would yield consistent differences in the ichnological record.

Has there been any _Ichthyornis_ record where presence or absence of webbing 
could be discerned? 


Regards,

Eike