Megan Zhou
No author given, but is based on materials provided by the University of Michigan.
Published: January 7, 2014
Summary:
310 million years ago, Bandringa sharks had migrated downstream from freshwater swamps to a tropical coastline. This left behind fossil evidence of one of the earliest known shark nurseries. Paleontologists from the University of Michigan concluded that all known species of Bandringa are long-snouted, bottom-feeding predators that lived in an ancient river delta system. This fossil discovery is the earliest known example of shark migration to spawn, and this behavior is still present in species known today. Along with being the earliest example of a shark nursery with egg cases and small sharks preserved in the same sediments, these Bandringa fossils also are the only known example of a freshwater to saltwater shark migration. Today, no shark alive breeds in the open ocean and spends the rest of their lives in freshwater. These Bandringa sharks are most likely one of the earliest close relatives of modern sharks. Bandringa was discovered originally in 1969, and was always thought that the genus contained two species, one that lived in freshwater areas and another that lived in the shallow ocean. With these new fossils and reevaluating 24 different ones, the paleontologists Sallan and Coates concluded that the Bandringa were a single species that lived, at different times of their lives, in both fresh and salt waters. This reclassification as a single species creates a more complete picture of the extinct shark’s anatomy and helps the discovery of some previously unreported features such as downward jaws, spines, and sensory organs. This is the first fossil evidence for a shark nursery is the earliest evidence for segregation of the juveniles and adults.
Connection:
This article relates to our study on evolution, specifically classification and the fossil record. We have learned how fossils are made, and it had initially led the scientists to believe that they were two species. The freshwater sites having these shark fossils tended to preserve the bones and cartilage, while the marine sites was able to preserve the soft tissue. This also lead to the misclassification of the species as two. This also relates to our study on Darwin and how he has mistakenly classified the finches as different species of birds due to the evidence that he had at the time. Similarly, the paleontologists did not make the connection that the Bandringa sharks were one species before they had the fossil evidence from this nursery. These shark fossils shown in the fossil record also displays our study about the age of these fossils. Because these are 310 million year old fossils, they would have been layered upon layered with other fossils on top of them, due to relative dating.
Why do you think modern-day sharks cannot breed in the ocean and spend the rest of their lives in freshwater, if their possible ancestors were able to do so?
ReplyDeleteDo you know which modern sharks that the Badringa sharks are close relatives to?
ReplyDeleteI do not know of which modern sharks that the Badringa sharks are close relatives to, but there are tiger sharks in Hawaii that do migrate. But no modern shark migrates like these extinct sharks did, breeding in the ocean and coming back to freshwater. However, a fossil impression left by a juvenile Bandringa shark does resemble the modern-day sawfish and paddlefish. These fishes have the extremely long spoonbill "snouts", that look very similar to the fossils of the Bandringa sharks.
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