Deduction of conodont’s feeding habit: evidence from late Cambrian to early Ordovician conodont fossils, North, China
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Abstract:
As a pharyngeal feeding organ of conodont animals, the conodonts have their unique biological characteristics. Based on the abundant conodont fossils data from late Cambrian?earliest Ordovician in the Yaowang Mountain section in Qingzhou, Shandong Province, North China, this article discusses the physiological wear of the conodonts when exercising their feeding functions such as filter-feeding. Three types of wear of the Carboniferous conodonts: breakage (part of conodont is broken by external force and removed from the main body), spalling (exfoliation of outer growth layer and exposure of inner growth layer), and polishing (surface ornamentation of conodont becoming shallow or disappearing because of abrasion) can be compared with the conodonts in this study. A new wear method: grinding (similar to the polishing process, but after surface ornamentation disappeared, abrasion keeps happening and makes the surface rough) and a phenomenon of repair after wear are proposed. The mineral composition of conodonts is mainly fluorapatite, and its Mohs’ scale of hardness is 5. Those minerals that can cause spalling and grinding of co-nodonts should be harder than fluorapatite. The common minerals with hardness higher than 5 in Mohs’ scale of hardness are feldspar and quartz, which are the main sand components. Conodont animals may swallow sand from the seafloor, find out the food, transport it into the digestive tract with the conodont apparatus, and then spit out the large or small sand. This method of feeding can be called the “sand grain rummaging type”. Conodont animals with this feeding mode need to live close to the sand of the seafloor. Apart from breakage, spalling, and grinding, there is another mode of wear: polishing. The particles that can cause polishing should be smaller and softer than fluorapatite crystals. The common mineral in the sea with a hardness lower than 5 is calcite (Mohs’ scale of hardness is 3). Therefore, it can be inferred that the food of conodont animals also includes zooplankton with calcite or aragonite shells. When taking small zooplankton into the mouth, a large amount of calcite shells wears out the tip of the conodont and polish its surface. Conodont animals with this mode of feeding are called the “plankton filter-preying type”.
