Influenza A virus subtype H5N1 report that examined the shape of hundreds of fossilized shark teeth suggests that modern shark biodiversity was triggered yesteryear the end-Cretaceous volume extinction event, almost 66 meg years ago.
Late Maastrichtian marine assemblage [Credit: Julius Csotonyi] |
Much similar several other vertebrate groups during the Cretaceous (142-66 meg years ago), shark multifariousness looked really dissimilar from today. Ground sharks (Carcharhiniformes) are the most various shark grouping living today, amongst over 200 dissimilar species. However, spell dinosaurs dominated terrestrial environments during the Cretaceous, Mackerel sharks (Lamniformes) were the dominant shark forms of the sea.
"Our report institute that the shift from lamniform- to carcharhiniform-dominated assemblages may good bring been the number of the end-Cretaceous volume extinction," said projection leader in addition to Uppsala doctoral pupil Mohamad Bazzi.
Sharks are ane of the major groups that survived the Cretaceous-Palaeogene volume extinction and, today, carcharhiniforms are typified yesteryear forms such every bit the Tiger, Hammerhead, in addition to Blacktip Reef sharks in addition to lamniforms yesteryear the Great White in addition to Mako sharks.
"Unlike other vertebrates, the cartilaginous skeletons of sharks produce non easily fossilize in addition to then our cognition of these fishes is largely express to the thousands of isolated teeth they shed throughout their lives," says Mr. Bazzi. "Fortunately, shark teeth tin tell us a lot almost their biology, including information almost diet, which tin shed lite on the mechanisms behind their extinction in addition to survival."
The squad used "cutting-edge" analytical techniques to explore the variation of molar shape inwards carcharhiniforms in addition to lamniforms in addition to measured multifariousness yesteryear calculating the arrive at of morphological variation, also called disparity.
"Going into this study, nosotros knew that sharks underwent of import losses inwards species richness across the extinction." said Dr. Nicolás Campione at the University of New England, who co-devised the project. "But to our surprise, nosotros institute virtually no alter inwards disparity across this major transition. This suggests to us that species richness in addition to disparity may bring been decoupled across this interval."
Despite this seemingly stable pattern, the report institute that extinction in addition to survival patterns were substantially to a greater extent than complex. Morphologically, at that topographic point were differential responses to extinction betwixt lamniform in addition to carcharhiniform sharks, amongst prove for a selective extinction of lamniforms in addition to a subsequent proliferation of carcharhiniforms (the largest lodge of living sharks today) inwards the immediate aftermath of the extinction.
"Carcharhiniforms are the most mutual shark grouping today in addition to it would seem that the initial steps towards this authority started merely about 66 meg years ago," said Mr. Bazzi, who remarks that farther enquiry is notwithstanding needed to empathise the multifariousness patterns of other shark groups, along amongst the human relationship betwixt diet in addition to molar morphology.
Although the mechanisms that triggered such a shift inwards sharks tin live hard to interpret. The squad hypothesises that changes inwards nutrient availability may bring played an of import role. The end-Cretaceous extinction saw to major losses inwards marine reptiles in addition to cephalopods (e.g. squids) in addition to the post-extinction basis saw the ascent of bony fishes. In addition, it is probable that the loss of apex predators (such every bit lamniforms in addition to marine reptiles) benefited mid-trophic sharks, a purpose fulfilled yesteryear many carcharhiniforms.
"By studying their teeth, nosotros are able to larn a glimpse at the lives of extinct sharks," said Dr. Campione, "and yesteryear agreement the mechanisms that bring shaped their development inwards the past, possibly nosotros tin render some insights into how to mitigate farther losses inwards electrical flow ecosystems."
Approximately 50% of the shark species inwards the IUCN are considered to live either endangered, threatened, or near-threatened.
The report is published inwards Current Biology.
Source: Uppsala University [August 02, 2018]
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