Youngolepis
| Youngolepis | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Lochkovian to Pragium (Lower Devonian) | ||||||||||||
| 419.2 to 407.6 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Youngolepis | ||||||||||||
| Chang & Yu , 1981 |
Youngolepis is an extinct genus of fish from the class of the meat fin (Sarcopterygii) that occurred in the Lower Devonian. Fossils of the genus have been found in southern China's Yunnan Province. The genus was named in honor of the Chinese paleontologist Young Chungchien by Zhang Miman (Mee-mann Chang) and XB Yu in 1981.
features
Youngolepis is a small predatory fish and was less than 30 cm long. The genus is best known for its skull fossils. The skull bones are heavy and thick, the body covered with thick, rhombic cosmoid scales. The snout and outer nostrils point downwards, as in Diabolepis . The posterior nostrils lie at the posterior end of the small premaxillary. The rostrum and lower jaw are covered with numerous tubes. The eyes were small. Rows of small bones surround the most important paired skull bones, a feature that is also found in lung fish (Dipnoi). The frontal is long, the parietal is short. The neurocranium is not completely divided into two sections, as in the coelacanth . On the head side there is a bone plate, which consists of those skull elements that correspond to the Squamosum , Quadratojugale and Praeoperculare , and whose pattern is reminiscent of the cheekbones of the osteolepiformes . The sutures are always visible between the premaxillary and the head shield formed from the frontal and ethmoid . As with the lungfish, the Jugale is larger than the Lacrimale. The parasphenoid is large and long.
The scales are covered with a thick, smooth cosmin layer and have small pores (25–60 µm). The pores on the lower jaw are larger (75–100 µm). The pores of the scales are lined with an enameloid layer, a substance similar to tooth enamel , a feature that Youngolepis shares with the Porolepiformes . Westoll lines, more or less concentric lines in the cosmoid scales of the lung fish, which are interpreted as growth rings, are missing.
Systematics
Youngolepis is assigned to the Dipnomorpha , the sister group of the Tetrapodomorpha (tetrapods including their fish-like trunk group representatives), to which today's lung fish also belong. Youngolepis is the sister taxon of a clade from Diabolepis and the lungfish.
literature
- M.-M. Chang, XB Yu: A new crossopterygian, Youngolepis praecursor, gen. Et. sp. nov., from the lower Devonian of E. Yunnan, China , Sci. Sin., Vol. 24, 1981, pp. 89-97
- M.-M. Chang: Rhipidistians, Dipnoans and Tetrapods , in: Hans-Peter Schultze, Linda Trueb (Eds.), Origins of the higher groups of tetrapods, Controversy and Consensus, Cornell University Press, 1991
- John A. Long: The Rise of Fishes . The Johns Hopkins University Press, 1995, ISBN 0-8018-4992-6 .
Web links
- Palaeos: Youngolepis