The life of “Pineapple Bun”
Fish Fossils of Hong Kong
A recent media report brought encouraging news. A fish fossil discovered by HKU researchers years ago in a rock specimen on the north shore of Sai Kung has been identified as Paralycoptera Wui, an allied species of Lycoptera, by Prof. CHANG Mee-mann from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (CAS).
Paralycoptera fossil (Photo: Prof. CHANG Mee-mann)
What is Lycoptera ?
Lycoptera was a small prehistoric fish that flourished in the age of the dinosaurs (approximately 125 million years ago). It lived in freshwater lakes, and the adult measured about 10 cm in length. It had a wide mouth with numerous sharp conical teeth and fed on small organisms in water. The species has long been extinct. The only allied species extant today are the well-known Arapaima and Arowana, which are both Osteoglossidae (bonytongues). Distinctive features include a bony tongue equipped with small teeth which are very different from those of modern fish. From the distribution of fossils, it can be determined that its range was limited to Asia. Most of the fossils were found in northern China. The discovery in Hong Kong is the first record in the south. The Lai Chi Chong coast, where the fossil was found, has been identified by geological studies as a crater lake or a lake close to a crater. This small fish was quickly buried in volcanic materials, and silt subsequently washed into the lake. After long ages of geological processes, it became part of the rock that formed, and the anoxic, germ-free environment kept it from rotting. It was preserved in its original form and was accidentally discovered by geologists more than 10 years ago. Today, it has finally been brought to light, and the public has the opportunity to learn more about this species.
What other fish fossils have been discovered in Hong Kong?
Apart from the newly discovered Paralycoptera, several rare fish fossils were found around Plover Cove Reservoir a few decades ago. By coincidence, we rediscovered these precious fossils. They are incomplete, mostly scales.
Bothriolepis fossil replica
Coelacanth fossil replica
Hongkongichthys youngi fossil replica
Moythomasia sp. fossil replica
Bothriolepis was a primitive fish widely distributed across the world during the Devonian Period (approximately 360 to 420 million years ago). This fossil discovery confirms that Hong Kong’s geological history goes back 400 million years. Bothriolepis was a small, prehistoric fish generally found in rivers or estuaries. Its distinctive features include a cartilaginous skeleton and bony carapace made up of small plates encasing the head and thorax. These pitted plates with curved grooves give the species its name. It had a pair of fin-like structures, called appendages, also covered by armoured plates. Some believe they facilitated balancing; others say they were tools for digging up food in the sand.
According to fossil records, this fish species occurred more than 300 million years ago. It was thought to have been extinct for 65 million years, but a living specimen (known as Latimeria) was caught by deep sea fishermen in the Indian Ocean near Southern Africa a few decades ago. It is now confirmed as an extant species, and a famous living fossil. The coelacanth has well-developed muscles at the base of its pectoral fins, pelvic fins, anal fins and the 2nd dorsal fin. The body is covered by three layers of large calcareous scales. The coelacanth is unique in that it has no sternum. It is ovoviviparous. The juvenile can survive on its own at birth.
Hongkongichthys youngi was a lobe-finned fishes. This Devonian freshwater species had fleshy fins with bones and strong muscles inside to support its body weight as it crawled across the marshes. It could breathe air directly with its gills. The bones in its skull and spine, its teeth and the skeletal arrangement of its fleshy fins were similar in structure to primitive amphibians. It is believed to be the ancestor of amphibians.
Moythomasia sp. is an extinct Devonian species. This small freshwater fish with large eyes was adapted to murky water habitats. It was covered with primitive bony rhombic scales.
Where can they be seen?
To give the public a closer look at these fishes, we have produced a set of replica models and animations. To see them at close range, visit the palaeoecology corner in the Woodside Biodiversity Education Centre in Hong Kong.
Woodside Biodiversity Education Centre Website: http://www.afcd.gov.hk/english/country/cou_lea/cou_lea_ven/woodside.html
Woodside Biodiversity Education Centre