4/11/2023 0 Comments Kt boundaryAmmonoids produce planktonic larvae (plankton fared poorly at the K–Pg boundary), whereas those nautiloids that survived produced fewer, larger eggs. With their similar physiologies, nautiloids may have avoided extinction by employing an alternative reproductive strategy. While similar in appearance, ammonites belong to a different order of cephalopoda to the modern nautilus and were more closely related to squid, octopus and cuttlefish. In reality, nautiluses have evolved little over the last 500 million years and were considerably more varied in size and shape in the Ordovician period (some species topped 2.5 m). You could be forgiven for assuming that the chambered nautilus (below), found in tropical Pacific waters at depths of around 300 m, are directly descended from the extinct-but once abundant-ammonites (above). It wiped out pretty much every animal on land larger than a rat, and also put paid to much that lived in the sea as well.įor instance, the ammonites-a group of cephalopod molluscs resembling the chambered nautilus still found in the tropical Pacific-completely disappeared despite dominating the oceans for more than 200 million years. Rivers bore the debris back to the seafloor in the process of relentless levelling that nature undertakes, gradually building up a geological record in the sediment that accumulated close to the coast.īut then occurred an event that changed life here and everywhere else on Earth. Dinosaurs probably roamed the land and erosion was steadily nibbling away at the hills. Sixty-five million years ago, these formations were sludge on the seafloor off the coast of a very different New Zealand. Geologists come from all over the globe to see the rocks in Mead Stream. Murray pointed us in the direction of the south branch of Mead Stream and wished us luck. We’d travelled with Hamish Murray (one of the family who owns 40,000 ha Bluff Station at Kekerengu, midway between Blenheim and Kaikoura) for some 30 km along a farm road in his ute, climbing over a low saddle near the eastern end of the Seaward Kaikouras and winding west towards the lower ramparts of the Inland Kaikouras. After all, we were well off the beaten track. When I’d spoken with Chris Hollis, a geologist from GNS Science, on the phone a few days earlier, I could hear doubt in his voice that we’d be able to find the spot. Judging from the rock formations, we were certainly in the right area, but finding the exact spot-a layer of rock just centimetres wide laid down 65 million years ago-could prove tricky. I peered at the sheaf of papers in my hand, looking for congruence between the detail that appeared in the grainy pictures and the rocks beside us. All that is left of that cataclysmic change is a scar of clay-like rock exposed in a few dozen locations around the world. Most ecosystems suffered massive destruction, and it took a million years or more for life to return to a semblance of order, though it was never the same as it had been. Half of all organisms were rendered extinct, including the dinosaurs. Sixty-five million years ago, life on Earth faced an apocalypse. Joy Lines, my fossicking companion, and I were on a journey back to the end of an epoch. But down where we were, there was no hint of sun. The formation continued for hundreds of metres up the steep cliffs above us, up into patches of sunlight. Parallel layers of whitish rock containing darker interior bands plunged down to meet the stream ahead of us. We sloshed up the meandering stream bed, examining the rocky walls as we went. There was snow on the mountains nearby, and in the dark gorge the winter water was icy.
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