Anacleto Formation

Anacleto Formation
Stratigraphic range: Upper Cretaceous
Type Geological formation
Unit of Neuquén Group
Underlies Allen Formation
Overlies Bajo de la Carpa Formation
Location
Country  Argentina

The Anacleto Formation is a geologic formation with outcroppings in the Argentine Patagonian provinces of Mendoza, Río Negro, and Neuquén. It is the youngest formation within the Neuquén Group and belongs to the Río Colorado Subgroup. Formerly that subgroup was treated as a formation, and the Anacleto Formation was known as the Anacleto Member.[1]

The type locality of this formation lies 40 kilometers west of the city of Neuquén. At its base, the Anacleto Formation conformably overlies the Bajo de la Carpa Formation, also of the Río Colorado Subgroup, and it is in turn unconformably overlain by the Allen Formation of the younger Malargüe Group.[2]

The Anacleto Formation varies between 60 and 90 meters thick, and consists mainly of claystones and mudstones, purple and dark red in color, of fluvial origin. Geodes are often found scattered throughout this formation.[3]

Age

Era: Mesozoic
Period: Late Cretaceous
Faunal stage: early Campanian
Absolute Age: ~83 to ~78 mya

Fauna

Antarctosaurus wichmannianus with a human for size comparison
Aucasaurus garridoi

Nests of dinosaur eggs, many with preserved embryos inside, have been discovered in large quantities at the famous Auca Mahuevo locality, and have been attributed to titanosaurs.[4]

Known from bones found in the Anacleto Formation are:

The oldest known unequivocal bird footprints from South America were also discovered in the Anacleto Formation. The small footprints were tentatively assigned to the ichnogenus Aquatilavipes and might have been produced by Patagopteryx (whose fossils were only found in the Bajo de la Carpa Formation however) or some unknown wader-like bird; they lack a hind toe. Ignotornis refers to similar footprints made by larger birds with a small hind toe; they might have been left by Neuquenornis, but this is also only known from the Bajo de la Carpa Formation. Footprints of these two ichnogenera have also been found elsewhere, but it must be understood that assignment to the same ichnogenus does not imply a close relatedness of the organisms that produced these traces, only a similar morphology.[6]

Even smaller and somewhat unusual footprints assigned to Barrosopus are only known from the Anacleto Formation. They were almost certainly made by some tiny theropod, but whether this was a bird is not quite clear: the innermost front toes of the animal leaving these tracks attached in a position higher than the others. In that, and in their dimensions, they are a very close match for the odd-footed enantiornithine bird Yungavolucris brevipedalis, but this is only known from the Maastrichtian Lecho Formation which is some 10 million years younger.[7]

See also

Footnotes

  1. ↑ Sánchez et al. (2006)
  2. ↑ Fossa Mancini et al. (1938), Leanza et al. (2004)
  3. ↑ Leanza et al. (2004), Sánchez et al. (2006)
  4. ↑ Salgado et al. (2005), Sánchez et al. (2006)
  5. ↑ Agustín G. Martinelli, Joseph J.W. Sertich, Alberto C. Garrido and Ángel M. Praderio (2012). "A new peirosaurid from the Upper Cretaceous of Argentina: Implications for specimens referred to Peirosaurus torminni Price (Crocodyliformes: Peirosauridae)". Cretaceous Research. in press. doi:10.1016/j.cretres.2012.03.017.
  6. ↑ Coria et al. (2002), Lockley et al. (2006)
  7. ↑ Chiappe (1993), Coria et al. (2002), Lockley et al. (2006)

References

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