Denticeps clupeoides as key species for understanding the evolution of Clupeiformes and Otomorpha (Teleostei)

The Clupeocephala are a large group among the Teleostei which include all recent teleosts except the Elopomorpha and Osteoglossomorpha which are the basal Teleostei. Clupeocephala were defined by Patterson and Rosen (1977) containing the subcohorts Clupeomorpha (e.g. engraulids, clupeoids) and the formerly big group of the “Euteleostei” (e.g. catfishes, salmonids, galaxiids, atherinids, percoids) which at this time included also the Ostariophysi (e.g. Rosen 1973, Fink and Weitzman 1982). The phylogeny within the basal Clupeocephala has changed very often over the time and has first been supported by morphological characters. The inclusion of the Ostariophysi into the Euteleostei was questioned by Fink and Fink (1981). Later on, the Ostariophysi together with the Clupeiformes built the subcohort Otomorpha (= Ostarioclupeomorpha, Arratia (1997) or Otocephala, Johnson and Patterson (1996)) and together with the Euteleostei they form the Clupeocephala. The relationship between the sister groups Otomorpha and Euteleostei was supported by morphological (e.g. Lauder and Liem 1983, Arratia 2010) and molecular findings (e.g. Broughton 2010, Near et al. 2012, Betancur- R et al. 2013, 2017). However, it is morphologically and molecularly controversial in which of the two sister groups the order Alepocephaliformes should be located (see chapters 1.1.1 and 1.1.3). Patterson and Rosen (1977) defined five synapomorphic characters for the Clupeocephala. Two of these (‘retroarticular excluded from joint surface of quadrate’ and ‘articular and granular bones fused’) were first mentioned by Nelson (1973). These characters were discussed and modified by Taverne (1989), Arratia and Schultze (1991) and Arratia (1997, 1999, 2010). After a critical analysis of twelve possible synapomorphic characters by Arratia (2010) the following synapomorphies are valid until today: (1) Autopalatine bone ossifies early in ontogeny (Arratia and Schultze 1991, Arratia 1999) (2) Hyoidean artery pierces ventral hypohyal (Arratia 1999) (3) Tooth plate of cartilaginous fourth pharyngobranchial element forms by growth of only one tooth plate (first Patterson and Rosen 1977, modified by Lauder and Liem 1983 and Arratia 2010).