Vertebrata-Craniata Look for this name in NCBI Wikipedia Animal Diversity Web
http://palaeo-electronica.org/content/fc-1 Benton et al. 2015
node minimum age |
The holotype of Arandaspis prionotolepis was recovered from the Stairway Sandstone Formation of Mt Watt, Amadeus Basin, Northern Territory, Australia (Ritchie and Gilbert-Tomlinson, 1977). The age of the formation is constrained by the occurrence of the conodont Lenodus sp. cf. L. variabilis in the middle part of the Stairway Sandstone which Davies et al. (2011) interpret as evidence for an early Darriwilian age. This is based on the assumption that Lenodus sp. cf. L. variabilis falls within the taxonomic range of Lenodus variabilis and L. antivariabilis which have a stratigraphic range limited to the upper Baltoniodus norrlandicus Zone to the Eoplacognathus variabilis and Yangtzeplacognathus crassus zones (Löfgren and Zhang, 2003). The most secure geochronological date appropriate to constrain the minimum age of the holotype of Arandaspis prionotolepis is the Darriwillian-Sandbian boundary, which is dated at 458.4 Ma ± 0.9 Myr, thus 457.5 Ma.
node maximum age |
The soft maximum constraint encompasses the possibility that putative Cambrian vertebrates, such as Haikouichthys, Myllokunmingia (Shu et al., 1999), Zhongjianichthys (Shu, 2003), are stem-cyclostomes. Thus, our soft maximum is based on the maximum age interpretation of the Lantian Biota (Yuan et al., 2011). This, together with the Doushantuo Biota (Yuan et al., 2002), provide a series of Lagerstätten preserving the biota in Orsten- and Burgess Shale-like modes of fossilization. None of these Lagerstätten, least of all the Lantian, preserves anything that could credibly be interpreted as even a total group eumetazoan and on this basis we define out soft maximum constraint at 635.5 Ma ± 0.6 Myr (Condon et al., 2005) and, thus, 636.1 Ma.
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Arandaspis prionotolepis is unequivocally a member of the gnathostome total group, based on a number of phylogenetic analyses (Janvier, 1996a, 1996b; Donoghue et al., 2000; Donoghue and Smith, 2001). It exhibits a number of unequivocal characters exclusive to total-group gnathostomes, most obviously including a mineralized dermal skeleton.
Janvier, P. 1996. The dawn of the vertebrates: characters versus common ascent in the rise of current vertebrate phylogenies. Palaeontology, 39:259-287.
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