where are these fossils preserved?
Museo de La Plata, Argentina
Vegavis
The holotype specimen of "Vegavis" is held by the Museo de La Plata, Argentina. 
how many years ago was the thescelosaurus in existence? More than 66 million years ago which period was that? Late Cretaceous period describe this creature's physical characteristics. Its size has been estimated in the 2.5–4.0 m range for length, a weight of 200–300 kilograms and it may have been sexually dimorphic, with one sex larger than the other in which region were their fossils discovered? Niobrara County, Wyoming, USA who discovered them? John Bell Hatcher and William H. Utterback were these fossils recovered and preserved somewhere in an institution? Smithsonian Institution's National Museum of Natural History were there any body organs of this creature recovered? Remnants of a four-chambered heart and an aorta but these conclusions have been disputed can you name a few other species from that period you mentioned earlier? Hadrosaurs, ankylosaurs and ceratopsians can you name a few birds which existed during that period? Vegavis, Yungavolucris and Avisaurus can you name a few mammals during that period? Cimolodont, multituberculates, metatherians and eutherians what plants were found during that period? Magnolias, sassafras, roses, redwoods and willows with reference to the first bird mentioned during that period, were their fossils recovered? Yes. On Vega Island, Antarctica
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Vegavis [SEP] Description
The discovery of the type species, Vegavis iaai, demonstrates that the major groups of bird alive today had already diversified in the Cretaceous. This supports the longstanding phylogenetic inferences of paleornithologists. It has been hailed as the first definitive physical proof that representatives of some of the groups of modern birds lived in the Mesozoic. The holotype specimen of "Vegavis" is held by the Museo de La Plata, Argentina. The specimen, cataloged as MLP 93-I-3-1, was found in the López de Bertodano Formation at Cape Lamb on Vega Island, Antarctica, in 1993, but was only described as a new species in 2005 because it consists of the very delicate remains of one bird embedded in a concretion, which had to be meticulously prepared for study.