Oryzias, Jordan & Snyder, 1906

Benton, MJ, Donoghue, PCJ, Vinther, J, Asher, RJ, Friedman, M & Near, TJ, 2015, Constraints on the timescale of animal evolutionary history, Palaeontologia Electronica (Florence, Italy) 15 (1), pp. 1-107 : 42-43

ORYZIAS – CICHLIDAE (36)

Node Calibrated. Divergence between Atherinomorpha and Cichlidae . This delimits one of the two major unnamed crown clades within Ovalentaria, but not crown Ovalentaria itself (Wainwright et al., 2012).

Fossil Taxon and Specimen. Ramphexocetus volans from the ‘Calcari nummulitici’ of Bolca, Italy (holotype MGUP 8866 , Museo di Geologia e Paleontologia, University of Padua, Padua, Italy) .

Phylogenetic Justification. Ramphexocetus has not been included in a formal cladistic analysis. However, it presents a series of characters that are interpreted as synapomorphies of successively more restrictive clades within Atherinomorpha. Ramphexocetus can be placed within Beloniformes on the basis of its caudal fin (Rosen and Parenti, 1981), which has an expanded ventral lobe that contains more principal fin-rays than the dorsal lobe (Bannikov et al., 1985). The position of this genus can be further restricted to Exocetoidei, based on the presence of a greatly enlongated dentary (Rosen and Parenti, 1981). This feature is apparent at some point of the life history of most beloniforms, and is retained in adults as a ‘halfbeak’ condition comparable to that of Ramphexocetus in species traditionally assigned to Hemiramphidae , which appears to be paraphyletic ( Lovejoy et al., 2004). Among exocetoids, enlarged pectoral and pelvic fins of the kind found in Ramphexocetus are characteristic of Exocetidae (flying fishes).

Minimum Age. 49.11 Ma

Soft Maximum Age. 130.8 Ma

Age Justification. The age of the fish-bearing horizons of the ‘Calcari nummulitici’ at Bolca can be tightly constrained on the basis of biostratigraphy. Medizza (1975) assigned these deposits to the Discoaster sublodensis Zone (NP 14) on the basis of calcareous nannoplankton, while the larger foraminifera reported by Papazzoni and Trevisani (2006) place the unit within SBZ 11. NP 14 and SBZ 11 overlap narrowly in the late Ypresian, and the age of the fish beds at Bolca can be approximately correlated with the base of NP 14, which is dated as 49.11 Ma (Anthonissen and Ogg, 2012). We accept this date as a fossil-based minimum for the last common ancestor of Atherinomorpha and Cichlidae .

Given that the anatomy of Ramphexocetus suggests that this genus occupies a relatively nested position within crown Atherinomorpha, is it probable that the minimum age for the Atherinomorpha – Cichlidae divergence given here is a substantial underestimate. We therefore suggest the use of a generous soft maximum bound. Percomorphs, and acanthomorphs more generally, are unknown from a series of fish faunas of mid-late Early Cretaceous age that represent a range of depositional settings from fully marine to lacustrine: the Gault Clay of England (Albian; Gale and Owen, 2010; Forey and Longbottom, 2010; Nolf, 2010), Helgoland in Germany (Aptian; Taverne, 1981b), the Crato Formation of Brazil (Martill, 1993; early interpretations of Araripichthys as a lampridiform have been decisively rejected by Patterson, 1993a and Maisey and Moody, 2001), and the Coquiero Seco Formation of Brazil (Gallo and Cohelo, 2008). The oldest of these deposits, the Coquiero Seco Formation of Brazil, yields the oldest putative representative of Eurypterygii, (the clade containing Aulopiformes, Myctophiformes, and Acanthomorpha), and provides the basis for our estimated maximum age divergence between Tetraodontiformes and Ovalentaria. The Barremian is dated to approximately 130.8-126.3 Ma (Ogg et al., 2012b); we derive our soft maximum from the oldest limit.

Discussion. The fish beds at Bolca yield a diversity of atherinomophs in addition to Ramphexocetus, but we have selected this genus as our calibration because its placement within the clade is the most clearly and robustly supported by available character evidence. Ramphexocetus is joined by the hemiramphid ‘ Hemiramphus ’ edwardsi, putative atherinids assigned to Atherinia but in need of revision, and a series of genera of uncertain affinities and placed in extinct families: Rhamphognathus ( Rhamphognathidae ), Mesogaster and Lettellagnathus ( Mesogasteridae ) (Blot, 1980; Bannikov, 2008).

Several atherinomorphs of Late Cretaceous to Paleocene age are mentioned in the literature, but none has been described in sufficient detail to meaningfully assess phylogenetic placement. Isolated scales from the Thanetian Maiz Gordo Formation of Argentina have been identified as belonging to indeterminate poeciliids, but have not been described or illustrated (Cione, 1986), and the reliability of identifications drawn from such remains must be questioned. Gayet (1991) figured material from the Maastrichtian-Danian el Molino Formation of Bolivia that she compared with Cyprinodontiformes. This interpretation is doubtful, however, as the caudal-fin skeleton of these fishes does not appear to match the condition found in living members of the group. Gayet (1991) also reports isolated pharyngeal teeth from the Cenomanian Miraflores Formation of Boliva that broadly resemble those of cyprinodontiforms, but we have no confidence in this phenetic identification.