An ancient marine reptile found in China — Hupehsuchus nanchangensis — may have been a filter feeder similar to a modern bowhead or right whale, according to an analysis of the skulls from two newly discovered specimens. The findings, published in BMC Ecology and Evolution, represent an example of convergent evolution (where similar features evolve independently in different species) and provide insights into the feeding behaviour of these ancient reptiles.
Filter feeding involves an animal moving through the water and extracting small organisms, such as krill or plankton, for food via sieve-type mechanisms. Filter feeding fish such as basking sharks use their gills to retain food from water, while filter feeding whales sift material through baleen plates. To date, there has been very little evidence suggesting that ancient marine reptiles from the Mesozic Era (252 to 66 million years ago) were filter feeders due to a lack of the appropriate features in fossil records.
Now, Long Cheng and colleagues present evidence suggesting that Hupehsuchus nanchangensis, a marine reptile dating to the early Triassic Period between 249 and 247 million years ago, may have in fact been a filter feeder akin to some modern baleen whales. The authors examined two new specimens of H. nanchangensis which were discovered in the Jialingjiang Formation (Lower Triassic) in Hubei Province. One specimen is well-preserved from head to clavicle (collarbone), while the other is a nearly complete skeleton. The authors compared the shape and dimensions of the latter skull to 130 skulls from different aquatic animals, including 15 species of baleen whale, 52 species of toothed whale, 23 seal species, 14 crocodilians, 25 bird species, and the platypus.
H. nanchangensis’s skull possessed an unusual, toothless snout with two long bones in the upper skull framing a narrow space. It also had a narrow mandible (lower jaw) that was loosely connected to the rest of the skull and would have allowed it to expand its mouth cavity to accommodate large gulps of water. While no evidence of baleen was found in the specimens, the authors do note a series of grooves around the edge of the palate (roof of the mouth), which may have indicated the presence of soft tissues that could have played a similar role in filter feeding.
H. nanchangensis was likely a slow swimmer due to its rigid body, which suggests it might have fed in a style similar to that of a bowhead or right whale, which swim with their mouth open near the surface of the ocean in order to strain food from the water. High levels of competition for food at this point in the Triassic may have caused H. nanchangensis to develop this specialised feeding method, add the authors.
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Notes to editor:
1. Research article:
“First filter feeding in the Early Triassic: cranial morphological convergence between Hupehsuchus and baleen whales”
BMC Ecology and Evolution 2023
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