Lepidotes

Abstract: The East African Rift separates the northwestern and southeastern Ethiopian high plateaus, which are capped by massive Cenozoic volcanics overlying thick deposits of marine and nonmarine Mesozoic sediments During geological mapping projects of the 1920s-1930s, a few Mesozoic vertebrate fossils were found on the southeastern plateau in contrast, beginning in 1976, and then from 1993 to the present, paleontological field work in the Abay (Blue Nile) River gorge along the eastern edge of the northwestern plateau resulted in the discovery of fossil chondrichthyans (Priohybodus, Hybodus, Rhinobatos), osteichthyans (Lepidotes, cf Pycnodus), dipnoans (Asiatoceratodus), chelonians (Pelomedusidae, Plesiochelyidae, Pleurosternidae), crocodylians (Goniopholis), dinosaurs, (cf Acrocanthosaurus Hypsilophodontidae), pollen and other microfossils documenting a coastal biota in part, if not entirely, of latest Jurassic (Tithonian) age These fossils include new biogeographic records for Africa and document biostratigraphic range extensions The Ethiopian Mesozoic fauna adds to the growing evidence of limited interchange of vertebrates between Africa and Western Europe during the transition from the Jurassic into the Cretaceous

Abstract: A new semionotiform fish, Isanichthys palustris gen. et sp. nov., is described from the Late Jurassic – Early Cretaceous Phu Kradung Formation, north-east Thailand. I. palustris is known from a single, nearly complete specimen found alongside abundant Lepidotes specimens at the Phu Nam Jun locality. I. palustris shows a mixture of semionotid-like characters, such as the pattern of cheek ossifications, and lepisosteid-like characters, such as the body shape and a dorsal fin opposed by an anal fin. I. palustris possesses only some of the characters currently used to define the Semionotidae. Cladistic analyses including various semionotid and gar taxa, together with Amia calva and Leptolepis coryphaenoides, suggest that the Semionotiformes (Lepisosteidae and ‘Semionotidae’) form a monophyletic clade, but the ‘Semionotidae’ taxa form an unresolved polytomy. The relationships between Semionotiformes, Halecomorphi and Teleostei are unresolved. When restricted to the best-known taxa, however, the analysis shows the monophyly of the Semionotidae sensu stricto (Semionotus + Lepidotes) and a sister-group relationship between halecomorphs and teleosts. These last two results are regarded as the preferred hypothesis for further studies. I. palustris is the only known example of a predaceous, probably piscivorous, ‘semionotid’. It illustrates the great diversity and ecological adaptation of the semionotiforms during the Late Jurassic – Early Cretaceous. We question the phylogenetic relationships of ‘ancient fishes’ founded on molecular-based trees because we suspect that the use of very few Recent taxa as representatives of previously diverse lineages is an inevitable, but important, bias in the construction of such trees.

Abstract: The mid-Cretaceous vertebrate assemblage from south-eastern Morocco is one of the most diversified continental vertebrate assemblages of this time worldwide. The bony fish component (coelacanths, lungfishes and ray-finned fishes) is represented by relatively complete specimens and, mostly, by fragmentary elements scattered along 250 kilometres of outcrops. Here we revisit the bony fish assemblage by studying both isolated remains collected during several fieldtrips and more complete material kept in public collections. The assemblage comprises several lungfish taxa, with the first mention of the occurrence of Arganodus tiguidiensis, and possibly two mawsoniid coelacanths. A large bichir cf. Bawitius, is recorded and corresponds to cranial elements initially referred to ‘Stromerichthys’ from coeval deposits in Egypt. The ginglymodians were diversified with a large ‘Lepidotes’ plus two obaichthyids and a gar. We confirm here that this gar belongs to a genus distinctive from Recent gars, contrary to what was suggested recently. Teleosteans comprise a poorly known ichthyodectiform, a notopterid, a probable osteoglossomorph and a large tselfatiiform, whose cranial anatomy is detailed. The body size and trophic level for each taxon are estimated on the basis of comparison with extant closely related taxa. We plotted the average body size versus average trophic level for the Kem Kem assemblage, together with extant marine and freshwater assemblages. The Kem Kem assemblage is characterized by taxa of proportionally large body size, and by a higher average trophic level than the trophic level of the extant compared freshwater ecosystems, but lower than for the extant marine ecosystems. These results should be regarded with caution because they rest on a reconstructed assemblage known mostly by fragmentary remains. They reinforce, however, the ecological oddities already noticed for this mid-Cretaceous vertebrate ecosystem in North Africa.

Abstract: Lepidotes gloriae, sp. nov. (Actinopterygii: Semionotiformes) from the Late Jurassic of Western Cuba is described. The skeletal anatomy of this fish shows two features previously unknown in Lepidotes Agassiz, 1832: 1) presence of two pairs of ectopterygoids and 2) presence of dermometapterygoids. Skeletal elements whose structure is little known or even unknown in other species of Lepidotes have been studied in detail in L. gloriae: 1) branchial tooth plates, 2) endoskeletal shoulder girdle, 3) posttemporal, 4) clavicle, 5) pelvic girdle, and 6) caudal fin skeleton. The sensory canal system on the head of L. gloriae is unique among other species of Lepidotes in having the median part of the supratemporal commissure enclosed within the parietals, in having a medio-anteriorly directed branch of the infraorbital canal behind the orbit reaching from the dermopterotic into the frontal, and in having the ventral part of the median pit line of the skull roof replaced by a short canal traversing the derm...