Perspicaris – Middle Cambrian (508 Ma)Today is a special day for a couple of reasons! 1) I get

Perspicaris – Middle Cambrian (508 Ma)Today is a special day for a couple of reasons! 1) I get totalk about the Burgess Shale again, and, 2) Today’s animal is MSPTD’s veryfirst requested animal! So, before I get into the writeup, I want to thank@futureimagineer843 for requesting this animal! This writeup was a lot of funand I hadn’t actually heard of this one before xe mentioned it. Also, if youever want me to talk about a specific animal, requests are something I amabsolutely open to.Our third trip to the Burgess Shale, the famous Cambrianfossil bed from British Columbia, examines a lesser-known and lesser-understoodanimal named Perspicaris. Using Perspicaris, we can really put intoperspective how much of a treasure trove the Burgess Shale really is. This is oneof the more rare animals from the Burgess Shale, and it’s known from only 202specimens. For comparison, we have around 50specimens of Tyrannosaurus rex, ananimal found in significantly younger rocks and one of the better-knowntheropod dinosaurs. It might sound ridiculous to call it rare, but those 202fossils of Perspicaris make up only 0.38% of the Greater Phyllopod Bed,where most of the Burgess Shale fossils have been found.We don’t know much about Perspicaris.It’s a really weird animal. It’s really similar to a common Burgess Shaleanimal called Canadaspis (known from4,525 specimens and making up about 9% of the organisms found), and we canextrapolate a bit about its appearance and how it might have acted from lookingat it.Perspicaris is atiny arthropod. It was less than an inch in length (2-3cm), and bears more thana passing resemblance to shrimp and other modern crustaceans. We’re unsure ofwhether or not it was an early crustacean, a basal Euarthropod (the moderngroups of arthropods), or from a family outside of that group that left no descendants.It’s definitely some kind of arthropod, but getting more specific is prettyhard. That’s the problem with the Cambrian fauna, and one of the reasons it’sso fascinating. This is when just about everymodern phylum evolved, so when can we say they split for sure? It’s also hard to say what the hell it was doing with thatbody plan. It had big eyes on the end of stalks and limbs that could have aidedswimming. But, it didn’t have any claws or enlarged biramous limbs (limbs thatbranch into two different segments that are usually adapted to some special purpose),so if it was swimming, how did it eat? We know Canadaspis was a bottom-feeder, but don’t have any evidence forthat in Canadaspis. This brings up the question: How do we know all these thingsabout prehistoric animals? We use a lot of methods to figure out all this.Since the Cambrian Explosion, most animals fill different roles in a given modernecosystem. A lot of those ecosystems have parallels between each other. Let’suse the Great Barrier Reef and an African savannah as an example. I’ll simplifyit, because food webs can be really complex and can make it hard to get what I’mgetting at. At the base of both ecosystems are vegetation. In the Reef,it’s algae and kelp. In the savannah, it’s grass. Then you have the herbivoreswho eat those things. So, dugongs/krill, and gazelles/wildebeests. Then youhave the carnivores, which eat other animals, like tiger sharks and lions. Alot of animals have a parallel animal in other ecosystems, and we can applythat same logic to prehistoric ecosystems, too. We can figure out roughly whereanimals fall in prehistoric food webs based on the features they share withmodern animals. Canadaspis has a lotin common with modern benthic (bottom-feeding) animals, so we can say prettyconfidently that it was a bottom-feeder. But what do you do when you have ananimal like Perspicaris, which has amix of traits but nothing pointing definitively in any direction? You speculate.Throw stuff at your peers and see what sticks. Perspicaris looks abit like tadpole shrimp. They have plenty of differences, but in broad strokesthey look alike. Now, tadpole shrimp are bottom-feeders, too, but doesn’t haveeyestalks like Perspicaris. Ourfriend here shares that with internet celebrity called the mantis shrimp, whichactively hunts larger prey. But it doesn’t have claws like the mantis shrimp,so…You see the problem. That’s why paleontologists debate alot. A lot of media likes to sensationalize these disagreements like they’rerap beefs or something, but no they’re usually just discussions about stuffwhere people don’t agree. You know, like, how science works.  Also, the media tends to latch onto the more outlandishstuff. There are plenty of folks around who still correct people by sayingstuff like, “Actually, they found out that T.rex was a scavenger,” even though it was a theory that people only reallylooked at because Jack Horner liked it, and Jack Horner is, putting it lightly,a big fucking deal. That being said, there’s a truckload of evidence againstthat, and most scientists brush it off because Tyrannosaurus was built like a predator. Maybe I’ll talk about thatsomeday.So, what’s the deal with Perspicaris?In short: ¯\_(ツ)_/¯. It’s a weird littlearthropod with a really vague body shape, and it’s really hard to figure it outbecause it doesn’t really look much like anything around now. And the thing itdoes look like has specializations it lacks. They’re little mysteries in afield full of little mysteries.P.S. I have to talk about this whenever the Burgess Shale comes up, but Perspicaris has really pretty fossils. -- source link

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