Hiodontidae, Valenciennes, 1847

Hilton, Eric J. & Lavoué, Sébastien, 2018, A review of the systematic biology of fossil and living bony-tongue fishes, Osteoglossomorpha (Actinopterygii: Teleostei), Neotropical Ichthyology 16 (3), pp. 1-35 : 4

Hiodontidae .

Hiodontidae ( Fig. 3 ), which is regarded as the living sister group of all other extant Osteoglossomorpha ( Taverne, 1979; Li, Wilson, 1996a; Hilton, 2003; Zhang, 2006; Wilson Murray, 2008), with one or two genera ( Hiodon and † Eohiodon ); the fossil taxa † Yanbiania and † Jiaohichthys from the Early Cretaceous of China and † Plesiolycoptera from the Mid Cretaceous of China are stem group Hiodontiformes. Hiodon comprises two extant species ( H. alosoides and H. tergisus ), both found exclusively in the freshwater rivers and lakes throughout much of North America east of the Rocky Mountains. These fishes have a generalized, laterally compressed body, with large eyes, a forked caudal fin, and a silvery body with cycloid scales ( Hilton et al., 2014). The parasphenoid and basihyal toothplate are armed with large, caniniform teeth that serve the so-called “parasphenoid-tongue bite apparatus” ( Hilton, 2001). The osteology of Hiodon has been described by Taverne (1977) and Hilton (2002), with specific aspects of its skeleton described by others (e.g., caudal skeleton, Schultze, Arratia, 1988) due in part to its overall plesiomorphic morphology, which has led to its use as a representative basal teleost in broad based systematic analyses (see discussion and references by Hilton, 2002).

The three species of † Eohiodon from the Early Eocene of western North America have been regarded as close relatives of the extant genus Hiodon ( Li et al., 1997a; Hilton, Grande, 2008; Fig. 3b ). Indeed, because of the absence of any synapomorphies distinguishing the species of † Eohiodon from those of Hiodon , Hilton, Grande (2008) regarded it as a synonym of Hiodon . The two extant species of Hiodon possess a post-pelvic bone, and this is considered a synapomorphy of the extant taxa ( Hilton, 2003), although the condition in most fossil taxa, including † H. consteniorum and the species of † Eohiodon , is unknown ( Hilton, 2003). Murray et al. (2010: fig. 10) illustrated a fragmentary bone that they interpreted as a postpelvic bone in † Schuleichthys brachypteryx, a species from the Early Cretaceous of China that was left as incertae sedis at the base of Osteoglossomorpha. These authors suggested that the presence of a postpelvic bone in † Schuleichthys was a character of a broader group and therefore resurrected the genus † Eohiodon (see also Murray et al., 2018). However, we find the published photograph documenting the postpelvic bone in † Schuleichthys to be unconvincing, and maintain that until this element is clearly seen in taxa outside of the extant taxa, it should be considered to be a synapomorphy of these two extant taxa. Regardless, there has yet to be any synapomorphies identified that group the taxa previously included in the genus † Eohiodon (i.e., all diagnostic characters cited for the genus, such as low vertebral and fin ray counts, are plesiomorphic, being similar to stem group Hiodontiformes and † Lycopteridae ). We therefore support the interpretation that those taxa previously included in † Eohiodon should be regarded as stem group Hiodon ( Hilton, Grande, 2008).

Figures

Fig. 3. Hiodontidae. a. Hiodon alosoides (VIMS 12099). b. †Hiodon falcatus, Eocene, Wyoming, USA (UMA F10651). Scale bars = 2 cm.