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Monotremata Look for this name in NCBI Wikipedia Animal Diversity Web
http://palaeo-electronica.org/content/fc-5 Phillips, 2015
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Obdurodon dicksoni occurs in Faunal Zones B and C of the Riversleigh local faunas (northwestern Queensland). The holotype is known from the early Middle Miocene Faunal Zone C (Ringtail Site). However, slightly older Ob. dicksoni molars and a partial dentary are known from Faunal Zone B sites (Nevilleâ€™s Garden and Dirkâ€™s Towers). Early Miocene dates have consistently been attributed to Faunal Zone B sites by biocorrelation (e.g., Black, 1997; Travouillon et al., 2006). More recently Black et al. (2012) noted that U/Pb radiometric dating of speleothems now confirms this timing. However, until the new dates are published I consider the top of the Early Miocene to provide a minimum for Riversleigh Faunal Zone B and hence, for the crown Monotremata divergence.
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Potential crown monotremes are traceable at least back to the Paleocene (~61 Ma) Monotrematum sudamericanum from Argentina, which is known from several ornithorhynchid-like molars (Pascual et al., 1992) and distal femora (Forasiepi and Martinelli, 2003). Earlier (Maastrichtian) well-sampled South American faunas lack any monotremes. However, sparse Australasian fossil records provide no solid evidence for mammal faunas lacking crown monotremes until the Albian Lightning Ridge (Flannery et al., 1995) and Dinosaur Cove (Rich and Vickers-Rich, 2003) faunas. I use the base of the Albian as a soft maximum for Monotremata.
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All formal and informal cladistic analyses of monotremes favour grouping Obdurodon with the modern Ornithorhynchus to the exclusion of tachyglossids (e.g., Musser, 1999; Luo et al., 2007; Rowe et al., 2008). Moreover, Phillips et al. (2009) found high statistical support for an Obdurodon - Ornithorhynchus sister-grouping, for which unambiguous synapomorphies include rostral elements (nasal, maxilla, septomaxilla) forming a board â€˜billâ€™, a robust posterolateral maxillary process and several endocranial characters (see Macrini et al., 2006). The sister relationship between living ornithorhynchids and tachyglossids is uncontroversial in molecular and morphological studies (e.g., van Rheede et al., 2006; Luo et al., 2007; Phillips et al., 2009).
Musser, A.M. 1999. Diversity and relationships of living and extinct monotremes. Australian Mammalogy, 21:8-9.
Luo, Z-X., Chen, P., Li, G., and Chen, M. 2007. A new eutriconodont mammal and evolutionary development in early mammals. Nature, 446:288-293.
Rowe, T., Rich, T.H., Vickers-Rich, P., Springer, M., and Woodburne, M.O. 2008. The oldest platypus and its bearing on divergence timing of the platypus and echidna clades. Proceedings of the National Academy of Sciences USA, 105:1238-1242.
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