Prominent Lateral Ridges Research Articles

A new Eocene citharinoid fish (Ostariophysi: Characiformes) from Tanzania

ABSTRACT A single specimen of the anterior portion of a small fish was collected from the Eocene Mahenge site of Tanzania in 1996. The specimen, preserved as part and counterpart natural mold, is identified as belonging to a characiform fish, although the presence of a Weberian apparatus has not been confirmed beyond doubt. Features of the bones, such as the prominent lateral ridge on the anterodorsal corner of the opercle, the fused postcleithra 2+3, and the lack of a dentary symphyseal hinge, indicate that the fish is related to the Citharinidae and Distichodontidae. The fossil cannot be included in any known genus, and is described here as a new genus and species, Eocitharinus macrognathus. The fossil record of characiforms includes few articulated skeletons, of which only one had been reported previously from Africa, described in the family Characidae (=Alestidae).

Reconstruction of the enigmatic Late Cambrian Climactichnites

Climactichnites Logan, 1860, is known only from its large trail up to 20 cm in width, a trace superficially resembling a rope ladder. Prominent lateral ridges are parallel throughout the length of the trail; they may be smooth and hemispherical in cross-section or crenulated, much like a pie crust. Between these ridges is a series of raised dune-like bars and furrows dug into the substrate. The bars and furrows show considerable individual variation between trails and also variation along a trail. Ovoid impressions are known which occur at the start of trails. The posterior of these impressions is well rounded; the anterior is triangular, and for a short distance from the impression, the trail is developed on only one side. One exceptionally preserved impression shows curved, closely spaced, fine lines parallel to the posterior.The trails are found only in sandstone, and where they are present, they are abundant. Slightly equivocable evidence indicates a Dresbachian (early Late Cambrian) age for the occurrences in New York, Missouri, and Wisconsin; trails in Ontario and Quebec are less certainly dated. Desiccation cracks and air escape hole suggest that the trail was fully exposed to the atmosphere.From this data, a large number of sketches were made to reconstruct an animal able to make such a trail. Each attempt produced new speculation on the morphology. In the final rendition, the animal is bilaterally symmetrical, broad and low. The integument is tough, and the sole bears a subcentral mouth anteriorward. Lateral flaps scraped and compressed damp sand to make the parallel ridges. The anterior was strongly musculated and thin. This anterior flap grasped the sediment, alternating on either side of the animal to pull the form forward when the lateral flaps were relaxed. Curved rows of cilia on the posterior moved loose sand into dunes between the furrows formed by the anterior flaps.This reconstruction is like that of no other animal known in the Vendian or the Phanerozoic.