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<a rel = "lightbox" href = "https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/2019/halfabillion.jpg" title = "Gnathostomulide Rastrognathia macrostoma, these microscopic animals have a jaw apparatus similar to Amiskwia, which scientists in this study are now proposing, are among the closest living relatives of live arrowworms. Amiskwia It turns out to be the fossil link between these groups of animals. Credit: Martin Vinther S & # 248; rensen / SNM Denmark ">
Gnathostomulide Rastrognathia macrostoma, these microscopic animals have a jaw apparatus similar to Amiskwia, which scientists in this study are now proposing, are among the closest living relatives of live arrowworms. Amiskwia It turns out to be the fossil link between these groups of animals. Credit: Martin Vinther Sørensen / SNM Denmark
Amiskwia was originally described by the famous paleontologist Charles Doolittle Walcott (1850-1927) in 1911, who likened it to modern arrow worms (chaetognaths) – a group of worms living in the area. ocean are ferocious predators, with many thorns on their heads. to grab a little prey.
Such organisms are found around the world at sites such as the famous Burgess Shale in the Canadian Rockies, where their soft bodies are preserved.
The strange anatomy presented by these animals led the American paleontologist Stephen Jay Gould (1941-2002) to assume that these organisms represented extinct body planes that are no longer visible today and that, if we remount the Cambrian clocks, more from 500 million years ago, and let 's try the tape of life again, so maybe the living animals today would be very different.
More than 50 years after Doolittle Walcott presented his theory on AmiskwiaScientists studied his affinities and rejected his interpretation because they found no evidence of canonical striking spines.
Instead, they suggested that it could be a ribbon worm, or its own distinct lineage, remotely connected to anything that looks like it today. .
Jakob Vinther, School of Earth Sciences and Biological Sciences, University of Bristol, and Luke Parry, currently at Yale University, studied specimens from Amiskwia, kept at the Smithsonian Institution, they found something that had been missed before.
Dr. Vinther said: "I coated the specimen with ammonium chloride smoke to bring out the relief of the fossil, and then I could see that there was in head a pair of sturdy elements. "
<a href = "https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/hires/2019/1-halfabillion.jpg" title = "The fossil, Amiskwia sagittiformis Burgess shale (508 million years old), preserving bilateral elements of the jawbone inside his head. These jaw elements resemble those of rotifers and gnathostomulids, while the body resembles arrowworms. Credit: Luke Alexander Parry / University of Bristol – Yale University ">
The fossil, Amiskwia sagittiformis Burgess shale (508 million years old), preserving bilateral elements of the jawbone inside his head. These jaw elements resemble those of rotifers and gnathostomulids, while the body resembles arrowworms. Credit: Luke Alexander Parry / University of Bristol – Yale University
In interpreting these structures as a set of jaws, their resemblance led him to think of a group of animals called gnathiferans, which includes rotifers, gnathostomulids and micrognathozoans. These animals are microscopic worms, with a distinctive internal jaw apparatus.
Scientists have understood that Amiskwia suddenly had a gnathiferous jaw, but an arrow worm body.
Dr. Vinther said: "The weird combination of anatomy seemed totally foreign to 2012.
"Some people have suggested that there might be a relationship between arrowworms and genitals, based on shared possession of a jawbone, both made up of a substance called chitin.
"However, there was little other evidence suggesting a relationship, such as evidence of phylogenetic analyzes of DNA."
Luke Parry added, "It was a total heresy to propose that the Gnathifera and Arrowworms be linked at the time, so we delayed the publication of our intriguing results for fear of criticism from our peers.
"However, new DNA studies have revealed that arrowworms were increasingly closely associated with Gnathifera in the Tree of Life.
<a rel = "lightbox" href = "https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/2019/2-halfabillion.jpg" title = "The head of the arrow worm, Parasagitta elegans. This group of animals is the closest living relative of Amiskwia. Credit: Rafael Martin Ledo / Counselor for Education # 243; Cantabr no. for ">
The head of the arrow worm, Parasagitta elegans. This group of animals is the closest living relative of Amiskwia. Credit: Rafael Martin Ledo / Council of Education of Cantabria
"In particular, some researchers have found that arrowworms shared a duplication of the important genes of Hox with a gnathifer, rotifers, and we suddenly did not feel deadlocked."
Now the authors have published their findings in the journal Current biology. The study follows a new phylogenetic study that finds solid support for arrowworms forming an evolutionary group with gnathiferans.
Luke Parry said, "We are delighted to see that these researchers have discovered a relationship between arrowworms and rotifers.
"Our phylogenetic analysis, based on anatomical features, also suggests a relationship between these two groups of animals."
The researchers find that Amiskwia is a line of arrow-worm stems that possesses the jaw-like apparatus seen in the Gnathiferian worms.
This jaw has evolved to become the formidable spines of live arrowworms, which are now an important link in the marine food chain. Small crustacean larvae have developed long protective spines to protect themselves from ingestion by arrow worms.
Explore further:
Bizarre hard-fisted creatures finally placed on the tree of life
More information:
"Bilateral jaw elements in Amiskwia sagittiformis make it possible to bridge the morphological gap between gnathifers and chaetognathes" L. Parry and J. Vinther, Current biology, 2019.
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