Fish with secondary sexual characteristics found from the Middle Triassic of China
|Female specimen of Venusichthys comptus before (a) and after coated with |
ammonium chloride [Credit: XU Guanghui]
The Luoping Lagerstatte fossil beds are composed of thinly laminated micritic limestone alternating with silty limestone, indicating a semi-enclosed intraplatform depositional environment. This new species has a blunt snout, an elongate and fusiform body, and an almost homocercal caudal fin with a forked profile. All 30 specimens represent a small-sized primitive neopterygian with a standard length ranging from 25 to 38 mm.
|Male specimens of Venusichthys comptus before (a) and after coated with ammonium|
chloride (b), scale bars equal 3 mm [Credit: XU Guanghui]
"The superb preservation of skeletal details demonstrates a differentiation of phenotypic traits between presumed males and females", said lead author XU Guanghui of the IVPP, "Among 30 cataloged specimens, one-third of the individuals bear pointed tubercles on cranial bones, scales and fins, and a hook-like contact organ anterior to the anal fin and are interpreted as being males".
|Secondary sexual characteristics on cranial bones, in dorsal fin with arrows indicating|
pointed tubercles along its leading ray, and anal fin with arrow indicating hook-like
contact organ anterior to anal fin [Credit: XU Guanghui]
The living sexually dimorphic ray-finned fishes, including several families of cypriniform fishes and a few gonorynchiform and salmonoid fishes, bear breeding tubercles and contact organs on the head, scales and fins of the male that come in direct contact with the female during prespawning behavior or during the spawning, or that come into contact with other males during fights and defense of territories. Therefore, the secondary sexual characteristics of Venusichthys are similar in shape and distribution, to the breeding tubercles and contact organs of living sexually dimorphic ray-finned fishes, and consequently, they may have had similar functions.
Source: Chinese Academy of Sciences [February 18, 2016]