Upper Cretaceous Vertebrate Fauna at Dzharakuduk, Kyzylkum Desert, Uzbekistan: Biostratigraphy, Biogeography, and Phylogeny

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9804771ArchibaldMain objectives of this proposed work are: 1) to continue extensive collecting at Dzharakuduk (Late Cretaceous, Turonian? - Campanian), Kyzylkum Desert, Uzbekistan, 2) to place these important collection in a global biostratigraphic, paleoecologic, and biogeographic context, 3) and to continue the description and phylogenetic analyses of extensive collections already recovered.Field studies at Dzharakuduk, central Kyzylkum Desert, Uzbekistan were begun in the late 1970's by the late Russian paleontologist Lev A. Nessov and students, continued by the Nessov and the PI in 1994, and by a crew of 11 persons including the PI and co-Pi in 1997. These studies, and the publications that are beginning to result from them, demonstrate that this area is the taxonomically richest (over 130+ species have been reported) and arguably one of the most important Late Cretaceous vertebrate faunas in all of Eurasia. The slightly younger sites (Late Cretaceous, Campanian) in the world-famous Gobi Desert produce more complete material, but the more fragmentary material from Dzharakuduk is often exquisite, preserving considerable anatomical detail or even whole cranial and limb elements that are almost unknown from Late Cretaceous sites in North America. The extensive surface collecting that had been conducted in the past at Dzharakuduk was also done in 1997, but key producing intervals were flagged and intensively dry screened in the last three days of the field season. Almost as many specimens of vertebrates (e.g., mammals) were recovered in two and one-half days of screening and sorting (10 mammals recovered) compared all of the previous three weeks of surface colecting (15 mammals recovered). Thus, extensive dry screening at certain Dzharakuduk sites will be of key importance during the next three field seasons.The Dzharakuduk escarpment includes about 200 meters of sediment. Nessov argued that the vertebrate-bearing sites at Dzharakuduk were a combination of fluvial and brackish-water environments, underlain and overlain by marine rocks. The underlying rocks were argued to be Turonian in age, while those above in the escarpment were thought to be uppermost Cretaceous and Paleogene. The discover during our reconnaissance in 1994 of an ammonite (later identified as Santonian in age) at the top of the escarpment demonstrated that no Paleogene sediments were exposed there. During our more extended work in 1997 it was shown that the Dzharakuduk sites are all fluvial in origin and are bracketed by a series of peneplanation events of long, but undetermined age. The underlying sediments are definitely marginal marine, but establishing an age remains elusive. The overlying sediments range from marginal marine to fully marine, and have yielded a very rich fauna of marine invertebrates (80+ species) near the top of the exposure. A slightly lower invertebrate fauna also yielded thousands of shark teeth (12-15 species). Both faunas require detailed study, but are suggestive of an age as old as Santonian to as young as early Campanian. This very preliminary analysis suggesests the earlier assessment of a Coniacian age for the continental vertebrate sites at Dzharakuduk may be correct, or a slightly younger Santonian age is possible. Samples of sediments yielding various microfossils were made, but we await funding for preparation and study of these as well as the macroinvertebrates. The fluvial sites representing low coastal plains at Dzharakuduk are very paleoecologically similar to Late Cretaceous sites in North America, but are very unlike those in the Gobi, which are much more upland, dry, and aeolian dominated. The abundance of fishes including sharks, amphibians, and aquatic turtles at both Dzharakuduk and in the Late Cretaceous of North America stronly suggest this paleoecological similarity, but more thorough comparisons will only be possible if funds are secred to permit complete sorting, curation, and faunal analyses.In addition to faunal analysis and paleoecological interpretations of the vertebrates and invertebrates , a very important component of this proposed work is phylogenetic analysis of selected taxa. A variety of shorter papers and larger, mostly synoptic catalogies have appeared (mostly) in Russian by Nessov and his students on various aspects of the vertebrate fauna, but larger, more detailed studies have begun on various vertebrate taxa. The first monographic treatment of vertebrates from Dzharakuduk including a phylogenetic analysis was recently published by Nessov, the PI, and Kielan-Jaworowska (1997). This a monographic study of the alpha-level taxonomy of "zhelestids" as well as a phylogenetic analysis of these placental mammals showing their relationships to their sister taxon Ungulata (a variety of extict taxa plus the extant ungulates, sub-ungulates, and whales), which do not appear until near the K/T boundary some 20 million years after the Dzharakuduk "zhelestids". Based on these "zhelestids" from Dzharakuduk the PI was able to name and describe a new superordinal taxon of mammals, the Ungulatomorpha. The proposed grant will permit the recovery and study of other vertebrates from Dzharakuduk that will surely be of equal interest for phylogenetic studies.