Paleo-nursery

Cambrian fossil deposit near Kunming, China, contains a trove of larval and juvenile organisms.

Bluish-reddish worm spiraled on sandy background.

Maotianshania cylindrica, a priapulid worm.

Xianfeng Yang, Yunnan Key Laboratory for Palaeobiology, Yunnan University

Bluish-reddish worm spiraled on sandy background.

Maotianshania cylindrica, a priapulid worm.

Xianfeng Yang, Yunnan Key Laboratory for Palaeobiology, Yunnan University

Ancient soft-bodied organisms are rarely preserved in the fossil record. Even more unusual is the preservation of younger life stages, particularly for invertebrates whose juve­niles are fairly small, grow up quickly, and represent only a fraction of the total population. However, an exceptionally well-pre­served fossil deposit in southwest China near Kun­ming is yielding hordes of soft-bodied creatures and juveniles in its mudstone layers. A research team led by paleontologist Xianfeng Yang of Yunnan University has uncovered thousands of marine invertebrate fossils—many of them ju­veniles—that were buried in a Cambrian-era sea approximately 518 million years ago. 

Among the 118 species found in the de­posit—including seventeen new to science— most are the ancestors of today’s arthro­pods, sponges, algae, and marine worms. There were also a few hard-bodied animals including the ancestors of jawless fishes. So far, two fossil-rich layers have yielded 2,846 specimens, with more than 90 per­cent of them com­ing from the lower layer known as the Haiyan Lagerstätte. This layer is also where researchers unearthed the ma­jority of soft-bodied creatures and juveniles, turning up stunningly pre­served features such as compound eyes, tentacles, and diges­tive tracts. 

The surprising concentration of so many eggs, lar­vae, juveniles, and subadults in one place has led researchers to suggest that it was a “paleo-nursery,” where prehistoric marine life could take refuge from predators and reproduce or molt in its relatively protected waters. The team surmises that a paleo-nursery could have been quickly buried in sediment by a massive storm or earthquake event. How­ever, the presence of several fossil-contain­ing layers in this outcrop led the research team to consider another possibility—that this area of prehistoric sea was subjected to rapid environmental changes, perhaps in oxygen or salinity, creating boom-and-bust cycles. In that scenario, marine life would periodically flood in and reproduce when environmental conditions were favorable, but get wiped out when catastrophic natu­ral events changed conditions. 

The discovery of this fossil deposit in­vites further research, such as studying the development and evolution of Cambrian marine life in new detail, according to Pennsylvania State University paleontolo­gist and co-author Julien Kimmig. The Cambrian marks the emergence of many animal taxa. “Understanding not only what animals were present, but how they grew from larval to adult stages and what mor­phological traits they might share will give us a better understanding of the relation­ships of modern and ancient animals,” said Kimmig. (Nature Ecology and Evolution

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