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Osteichthyes 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 Guiyu oneiros was recovered from the Kuanti Formation, just below the first stratigraphic occurrence of the conodont index fossil Ozarkodina crispa, at a locality near Xiaoxiang Reservoir, Qujing, Yunnan, China (Wang, 2001; Zhu et al., 2009). However, since it is not possible to discriminate whether the first occurrence of O. crispa here coincides, postdates or antedates its first occurrence in the type Ludlow of the Welsh Borderlands (it is not demonstrated that the occurrence of G. oneiros occurs within the preceding Ozarkodina snajdri biozone), the most appropriate age interpretation should be based on the geochronological age of the top of the O. crispa biozone which immediately precedes the Ludlow-Pridoli boundary in both the type Ludlow in the Welsh Borderlands of England, and at the GSSP section for the Ludlow-Pridoli in the Daleje Valley, Prague, Czech Republic where it is dated as 423 Ma ± 2.3 Myr (Melchin et al., 2012). This yields a minimum age estimate of 421.7 Ma.
node maximum age |
Estimation of a soft maximum for the osteichthyan crown is complicated by the highly fragmentary nature of most gnathostome remains older than Guiyu (reviewed by Qu et al., 2010), coupled with ongoing revision to interpretations of the relationships of extinct gnathostome assemblages to living groups (Brazeau, 2009; Davis et al., 2012; Zhu et al., 2013; Dupret et al., 2014; Brazeau and Friedman, 2014). Scales aligned with chondrichthyans, the living sister group of osteichthyans, have been reported from the Middle Ordovician (Dariwillian; Sansom et al., 2012), but these taxonomic interpretations are admittedly tentative and supported by few characters. Similarly meagre remains from the Late Ordovician of Siberia are identified as the oldest acanthodians (Karatajuté-Talimaa and Predtechenskyj, 1995; figure 5), a problematic group of jawed vertebrates that have recently been interpreted as stem chondrichthyans, stem osteichthyans, stem gnathostomes, or some combination of the three (Brazeau, 2009; Davis et al., 2012; Zhu et al., 2013; Brazeau and Friedman, 2014; Dupret et al., 2014). It is widely agreed that placoderms are a grade of stem gnathostomes (Friedman, 2007a; Brazeau, 2009; Davis et al., 2012; Zhu et al., 2013; Dupret et al., 2014; Brazeau and Friedman, 2014), more distantly related to osteichthyans than either chondrichthyans or acanthodians. However, the first record of placoderms postdates the earliest remains interpreted as possible chondrichthyans or acanthodians (Karatajuté-Talimaa and Predtechenskyj, 1995; Sansom et al., 2012). The first placoderms are known from the early Silurian (late Llandovery) of China (Wang, 1991). Unlike the oldest examples of chondrichthyans or acanthodians, the earliest placoderms can be clearly aligned with taxa known on the basis of more complete remains from younger strata, and are attributed to yunnanolepiform antiarchs. Rocks of early Silurian age also yield a diversity of jawless fishes (Janvier and Blieck, 1993; Karatajuté-Talimaa and Predtechenskyj, 1995), but no remains clearly attributable to crownward portions of the osteichthyan stem despite the presence of suitable depositional settings. We therefore propose the base of the Llandovery, dated at 443.4 Ma ± 1.5 Myr (Melchin et al., 2012, p. 550), as a soft maximum bound for the divergence of crown Osteichthyes.
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Several clear features, including the presence of rhombic scales with peg-and-socket articulations, indicate that Guiyu is an osteichthyan. More specifically, Guiyu presents several synapomorphies of lobe-finned fishes, with resolved phylogenetic solutions placing this genus on the sarcopterygian stem within the osteichthyan crown (Zhu et al., 2009; Friedman and Brazeau, 2010; Davis et al., 2012).sarcopterygian stem within the osteichthyan crown (Zhu et al., 2009; Friedman and Brazeau, 2010; Davis et al., 2012).
Zhu, M., Zhao, W., Jia, L., Lu, J., Qiao, T., and Qu, Q. 2009. The oldest articulated osteichthyan reveals mosaic gnathostome characters. Nature, 458:469-474.
Friedman, M. and Brazeau, M.D. 2010. A reappraisal of the origin and basal radiation of the Osteichthyes. Journal of Vertebrate Paleontology, 30:35–56.
Davis, S.P., Finarelli, J.A., and Coates, M.I. 2012. Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes. Nature, 486:247–250.
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