current position:Home>The gripper appendages found in trilobites in the Middle Cambrian revealed their mating behavior

The gripper appendages found in trilobites in the Middle Cambrian revealed their mating behavior

2022-05-07 11:54:40Chinese industry information station

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stay 5 month 6 Published in Japan 《 Geology 》 In a new study in the Journal , A doctoral student in the Department of organic and evolutionary biology at Harvard University Sarah R. Losso and Javier Ortega-Hernández The professor revealed fossils from the Middle Cambrian Olenoides serratus Mating behavior of trilobites .

Trilobites are a group of 5.2-2.5 Arthropods 100 million years ago , It may be close to the branching point of the two main arthropod groups , Chelidopods ( The horseshoe crab 、 Spiders and scorpions ) And polypods ( Centipede 、 Crabs and insects ). They dominate the Paleozoic fossil record , Found on all continents , And more than 2 10000 described species . They are named for their trefoil appearance of a durable exoskeleton rich in calcite , This kind of exoskeleton is easy to preserve , And produced a good fossil record . The morphology of trilobites has been widely studied , But little is known about trilobite reproduction . Rare examples include unfertilized eggs found under the head of what may be a female specimen , And the fertilized eggs deposited in the sediments during the Cambrian period . Researchers hypothesized , Large groups of trilobite fossils together may represent large-scale molting and mating events , Similar to those observed in living marine species , Like Atlantic Limulus Limulus polyphemus. However , The reproductive behavior of trilobites , Including mating and fertilization , In fact, it is still unknown .

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Losso On right Olenoides A comprehensive re description of the form of , He studied the Royal Museum of Ontario 、 Each of the invertebrate paleontology collections of the geological survey of Canada and the Smithsonian Institution Olenoides serratus The specimens were imaged .O. serratus Known from the North beauty Several locations , But all specimens with appendages were collected from the Burgess Shale in British Columbia, Canada . Unlike exoskeletons , Appendage ( Antenna 、 Legs and gills ) Not often saved , Because they are not reinforced with calcite . The preservation of appendages requires unique conditions at the time of burial , These conditions exist in Burgess Shale and other rare sites with special fossil preservation . While examining a well preserved fossil from the Burgess Shale in the Royal Museum of Ontario ,Losso Specially modified gripper appendages similar to adult male horseshoe crab were found in the middle of the body , This suggests a similar mating strategy .

Losso Examined what is known so far 65 A specimen preserved with appendages .23 The legs of two specimens were preserved in the correct parts of the body , An appendage similar to a gripper was found there ; However , Because of its complete exoskeleton , Even if there is a gripper attachment, it will not be seen , Because its size is reduced . Four specimens provide the first 10 And the 11 A clear view of the appendages , But there's only one O. serratus The specimen shows that its appendage is modified into a holding device . The other three specimens have visible appendages , Has a more traditional leg like appearance .

Although with a gripper O. serratus The specimen lacks half the exoskeleton , But it's good for researchers .Losso say :“ This specimen is really unique , It's well preserved , Enough to show the special details of the appendage transformed into a gripper , But it was broken again , So we can actually see these reduced limbs , Otherwise they will be covered by the dorsal exoskeleton . Here's the irony , If this specimen is better preserved , With a complete dorsal exoskeleton , We wouldn't have as much information about his limbs as we do now .”

Losso Several measurements were made on each part of the reduced appendage , And compare them with the appendages in the same specimen body and the differences in the same position Olenoides Compare known appendages in . This shows that , The smaller appendages have a unique shape , Only in this specimen do we know . then ,Losso The special appendages of other living arthropods were studied for comparison , And understand what these appendages can do .

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There are thousands of trilobite species , They have a 2 Billions of years . But without a close living relative , It's hard to know reproductive behavior . Although Tachypleus Limulus has no close relationship with trilobites , But it is often used as a modern analog , Because they look like trilobites on the surface , Make it a useful comparison . The horseshoe crab , image Limulus equally , It's a marine arthropod , Famous for large-scale spawning off the coast of Delaware and Cape Cod .

Gripper is a special hook like appendage often found in male arthropods . During mating , The male grasps the female with a gripper . Different groups depend on the exact mating pattern of the group , The appendages evolved in different parts of the body . Gillopods and horseshoe crabs have evolved grippers , But depending on the female exoskeleton , Their functions are also different .

Losso say :“ We know it can't be for chewing , Because these appendages are not near the head or mouth , They are in the middle of the body . This shows the sexual dimorphism of trilobites , But in this case , It's only expressed on the appendages . This tells us more about the reproduction of trilobites and how they mate , This was hard to understand before , And it's very speculative based on modern analogy .”

“ There are few cases where fossils directly inform reproductive ecology and behavior , Especially in such ancient fossils . under these circumstances , Because there is a very special structure adapted to this function , So it is possible to make this special argument , More specifically, trilobites ,”Ortega-Hernández say .“ This is indeed the first time it is possible to show that these limbs have been so severely modified for this function . And it provides strong evidence , It shows that there were Limulus, Or Limulus like behavior , It exists entirely through integration . therefore , It really helps us understand how these animals lived millions of years ago .”

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