Osteology and relationships of Thaiichthys nov. gen.: a Ginglymodi from the Late Jurassic – Early Cretaceous of Thailand

Abstract

The osteology of Thaiichthys buddhabutrensis, nov. gen., from the Late Jurassic -Early Cretaceous of Thailand is described on the basis of a collection of well-preserved specimens. The mode of preservation of the material allows describing the external anatomy, as well as some elements of the internal anatomy (braincase, elements of the vertebral column). Most of the cranial and postcranial skeleton shows a rather conservative anatomy for 'semionotiformes', but the jaw apparatus displays specializations. Variations observed in the ossification pattern of the skull roof and of the cheek, in the morphology of the median dorsal scales and in fin rays' count indicate that caution should be applied when these characters are used in diagnoses and in phylogenetic analyses. A phylogenetic analysis including a set of gars, of 'semionotiformes', of Macrosemiiformes and of Halecomorphi shows the following features: (1) the monophyly of Holostei; (2) sister-pair relationships between Tlayuamichin ⁄ Semiolepis, Isanichthys ⁄ 'Lepidotes' latifrons and Araripelepidotes ⁄ Pliodetes; (3) the latter pair, together with Thaiichthys and possibly 'Lepidotes' mantelli, are resolved as stem Lepisosteiformes; and (4) the 'semionotiformes' (a group gathering species of Semionotus and Lepidotes) do not form a clade.

A Late Cretaceous marine long snout “pejelagarto” fish (Lepisosteidae, Lepisosteini) from Múzquiz, Coahuila, northeastern Mexico

“…The short snout and most basal members of this order as it was defined by L opez-Arbarello (2012) and Cavin et al (2013), also are the oldest taxa; Lepidotes includes only Early Jurassic species; Scheenstia, Isanichthys, and Thaiichthys are Late Jurassic-Early Cretaceous (Neocomian); and Pliodetes and Ararilepidotes are only known from the Early Cretaceous (Albian). In contrast, the long snout, crown, and younger lepisosteiforms are known since the Early Creataceous (Table 1); Obaichthys decoratus Wenz & Brito, 1992; O. africanus Grande, 2010; Dentilepisosteus leavis (Wenz & Brito, 1992); and Atractosteus (Oniichthys) falipoui (Cavin & Brito, 2001) are Early Cretaceous-early Late Cretaceous (from Aptian to Late Cenomanian); the age of Lepisosteus indicus (Woodward, 1890) is Late Cretaceous (Maastrichthian) or Early Paleogene (Paleocene).…”

A new species of the ginglymodian fish Isanichthys (Actinopterygii, Holostei) from the Late Jurassic Phu Kradung Formation, northeastern Thailand

“…Importantly, a clade called Semionotiformes is resolved: it comprises the Semionotidae, the Callipurbeckiidae, and the Macrosemiidae. The set of characters used in López-Arbarello's analysis differs from the set of characters used in analyses of Cavin (2010), Cavin et al (2013) and in the present study. We discuss and compare our results with those of López-Arbarello (2012).…”

“…3, 4). A small dermal component of the sphenotic process is also visible in specimens of other ginglymodians (see Cavin et al 2013 for a review). In gars the sphenotic is visible laterally and separated from the dermosphenotic (Grande 2010).…”

“…Lepisosteiformes and Macrosemiiformes are well characterized by osteological characters, but the "Semionotiformes" are still poorly defined (Cavin 2010;Cavin et al 2013). In these studies, the "Semionotiformes" are positioned as stem taxa to the Lepisosteiformes, but show poorly resolved intrarelationships.…”

A Berriasian actinopterygian fauna from Cherves-de-Cognac, France: Biodiversity and palaeoenvironmental implications

“…Differences between the Cherves material and S. mantelli are also observed, such as the suture between both frontals, which is straight in S. mantelli and apparently sinusoidal in the Cherves-de-Cognac taxon. But examination of this feature in a large population of the ginglymodian, Thaiichthys buddhabutrensis from the Lower Cretaceous of Thailand, indicates that the pattern of the suture between paired bones on the skull roof may vary within a species (Cavin et al, 2012).…”