Azpelicueta et al.—Kooiichthys jono (Teleostei, Siluriformes) Discussion
Phylogeny.—Catfishes are known since the Upper Cretaceous but especially during the Cenozoic when they became wide- spread mostly in freshwater. Only two extinct catfish families are recognized: Hypsidoridae in the Eocene of North America (Grande, 1987) and Bachmanniidae in the Eocene of South America (Azpelicueta and Cione, 2011). Another putative extinct family from South America, Andinichthyidae, based on three genera of the Upper Cretaceous and Paleocene of Bolivia is not supported by enough evidence (Arratia and Gayet, 1995). Grande (1987) proposed the first cladistic relationships of catfishes. In his hypothesis, Diplomystidae was the sister group of all remaining catfishes (Siluroidei). Other subsequent morphological analyses agree in considering that family as the most basal catfish group (for a synthesis of the literature see Rodiles-Hernández et al., 2009 and Azpelicueta and Cione, 2011). Sullivan et al. (2006), in a molecular analysis, proposed a radically different phylogeny where Loricarioidei was the sister group of Diplomystidae + the other catfishes. Recently, we suggested that the family Bachmanniidae was the sister group of Diplomystidae and both the sister group of all other Siluriforms based on a phylogenetic morphological analysis (Azpelicueta and Cione, 2011). Grande (1987) and Arratia (1992) diagnosed Siluroidei by the following characters: 17 or fewer principal caudal rays (vs. 18 in Diplomystes and other teleosts such as most characiformes); an extension of lamellar bone below the ventral surface of fifth centrum; fifth centrumjoined closely to complex centrumby two ventral ridges of superficial ossification; dorsal and ventral hypohyal of different sizes; maxilla with two rudimentary processes bearing small facets for articulation with autopalatine. According to these characters, the newgenus Kooiichthys is not a Siluroidei. In this paper, we reanalyze siluriform relationships considering the data matrix used by Rodiles-Hernández et al. (2005) and our modifications (due to the fragmentary preserva- tion of the fossil, we only observed 30% of the characters inclu- ded in their matrix). The analysis under equal weights produce 1312 equally most parsimonious trees of 737 steps (CI = 42.9; RI = 73.3), whereas the analyses under implied weighting with concavity values (K) from 3 to 100 produced different most parsimonious tree topologies ranging from 754 (CI = 41.9; RI = 72.2) to 737 steps (CI = 42.9; RI = 73.3) All these trees are congruent in a basal polytomy in the Siluriformes composed of the Diplomystidae, Bachmanniidae, Kooiichthys, and the Siluroidei (Fig. 11). This polytomy is not resolved because the lack of information about synapomorphies relating some pair of these taxa, rather than for conflict of information. The new genus Kooiichthys is supported by four exclusive autapomorphies; sand clock-shaped autopalatine, posterior limb of autopalatine widening strongly, postarticular arm of autopalatine longer than prearticular arm, and a metapterygoid longer than broad. We suggest that, although the morphology of the new
species Kooiichthys jono is very different from the other fossil and recent taxa, it is not worthwhile to erect a new family based on it until finding more complete material.
Comparison of K. jono with Diplomystidae and Bachmanniidae.— Kooiichthys jono n. gen. n. sp. shares a synapomorphy (double anterior autopalatine head) and other characters with these two taxa
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such as the anteriorly narrow mesethmoid, mesethmoid-frontal suture convex and not interdigitated, anterior and posterior fonta- nelles very large, lateral ethmoid almost completely covered by frontal, lateral ethmoid deep with an extended suture with orbito- sphenoid, orbitosphenoid deep, toothed maxilla, maxilla bone head with autopalatine condyles paired; vomerine tooth plate, “palatal” accesory tooth plates, autopalatine with a double articulation for maxilla and a large articulation with lateral ethmoid, anterior and posterior ceratohyals with straight suture, first vertebra unfused and short, fifth vertebra not joined to Weberian complex centrum, suture between coracoids without interdigitations. Kooiichthys jono shares with Diplomystidae the rhomboidal shape of vomer but this state is unknown in Bachmanniidae. This character was considered to be a synapomorphy of Diplomystidae (Arratia, 1987, 1992). Kooiichthys jono differs fromDiplomystidae and Bachmanniidae in having very large size, robust mesethmoid with large cornua, very wide posteriorly mesethmoid, large anterior metapterygoid process on which contact the autopalatine, a much longer maxilla, shorter Weberian complex, and pectoral spine serrae smaller. Kooiichthys jono differs from Diplomystidae in having ornamented skull roof, absence of spatulate teeth, and pectoral spine with posterior sulcus. Kooiichthys jono differs from Bachmanniidae in having much smaller and slender teeth, a quadrate without an anteroventral process, and a different shaped parurohyal.
Comparison of Kooiichthys with the other marine catfishes.— There are two marine or amphibiotic catfish families: Plotosidae and Ariidae. Both are Siluroidei. Besides, Kooiichthys jono n. gen. n. sp. clearly differs from ariids because they present the external posterior branch of lateral ethmoid columnar, lateral ethmoid and frontal bones connected mesially and laterally delimiting a fontanel, and otic capsule enlarged (Marceniuk et al., 2012). Kooiichthys jono clearly differs from plotosids because the absence of a specialized buccal and pharyngeal dentition among other cranial characters.
Comments on some characters of Kooiichthys.—The most striking feature of Kooiichthys n. gen. is the very strong autopalatine, with anterior and posterior portions depressed, expanded and equally wide. The middle portion of the bone is narrow and the posterior end gently convex. The postarticular portion is longer than the anterior one. The posterior end contacts the long anterior metapterygoid process. The metap- terygoid is notably longer than broad, an uncommon shape in siluriforms. Bachmanniidae, Diplomystidae, and Hypsidoridae have a depressed, anteriorly broad autopalatine with two anterior condyles for maxilla. Kooiichthys has an anterior notch also present in Bachmannia and in most species of Diplomystes (Arratia, 1987) but absent in Hypsidoris (Grande, 1987). Kooiichthys has a toothed maxilla, a primitive catfish character only known otherwise in Diplomystidae, Hypsidoridae, and Bachmanniidae but the shape differs in them. Kooiichthys has the longestmaxilla with the higher number of tooth rows. Themaxilla of Diplomystidae is longer than that of Hypsidoridae which is longer than that of Bachmanniidae. A maxilla with one anterior process bearing two articulations for autopalatine and completely separating premaxilla and autopalatine is present in adult diplomystids. Arratia (1992) considered that condition unique in Diplomystidae. We found the same character in Kooiichthys.
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