500 Million Years of Fish Evolution

500 Million Years of Fish Evolution Compared to dinosaurs, mammoths and saber-toothed cats, fish evolution may not seem all that interesting - until you realize that if it werent for prehistoric fish, dinosaurs, mammoths, and saber-toothed cats would never have existed. The first vertebrates on the planet, fish provided the basic body plan subsequently elaborated on by hundreds of millions of years of evolution: in other words, your great-great-great (multiply by a billion) grandmother was a small, meek fish of the Devonian period. (See a gallery of prehistoric fish pictures and profiles, a list of 10 recently extinct fish, and a slideshow of 10 Prehistoric Fish Everyone Should Know.) The Earliest Vertebrates: Pikaia and Pals Although most paleontologists wouldnt recognize them as true fish, the first fish-like creatures to leave an impression on the fossil record appeared during the middle Cambrian period, about 530 million years ago. The most famous of these, Pikaia, looked more like a worm than a fish, but it had four features crucial to later fish (and vertebrate) evolution: a head distinct from its tail, bilateral symmetry (the left side of its body looked like the right side), V-shaped muscles, and most importantly, a nerve cord running down the length of its body. Because this cord wasnt protected by a tube of bone or cartilage, Pikaia was technically a chordate rather than a vertebrate, but it still lay at the root of the vertebrate family tree. Two other Cambrian proto-fish were a bit more robust than Pikaia. Haikouichthys is considered by some expertsat least those not overly concerned by its lack of a calcified backbone - to be the earliest jawless fish, and this inch-long creature had rudimentary fins running along the top and bottom of its body. The similar Myllokunmingia was slightly less elongated than either Pikaia or Haikouichthys, and it also had pouched gills and (possibly) a skull made of cartilage. (Other fish-like creatures may have predated these three genera by tens of millions of years; unfortunately, they havent left any fossil remains.) The Evolution of Jawless Fish During the Ordovician and Silurian periods - from 490 to 410 million years ago - the worlds oceans, lakes, and rivers were dominated by jawless fish, so named because they lacked lower jaws (and thus the ability to consume large prey). You can recognize most of these prehistoric fish by the -aspis (the Greek word for shield) in the second parts of their names, which hints at the second main characteristic of these early vertebrates: their heads were covered by tough plates of bony armor. The most notable jawless fish of the Ordovician period were Astraspis and Arandaspis, six-inch-long, big-headed, finless fish that resembled giant tadpoles. Both of these species made their living by bottom-feeding in shallow waters, wriggling slowly above the surface and sucking up tiny animals and the waste of other marine creatures. Their Silurian descendants shared the same body plan, with the important addition of forked tail fins, which gave them more maneuverability. If the -aspis fish were the most advanced vertebrates of their time, why were their heads covered in bulky, un-hydrodynamic armor? The answer is that, hundreds of millions of years ago, vertebrates were far from the dominant life forms in the earths oceans, and these early fish needed a means of defense against giant sea scorpions and other large arthropods. The Big Split: Lobe-Finned Fish, Ray-Finned Fish, and Placoderms By the start of the Devonian periodabout 420 million years agothe evolution of prehistoric fish veered off in two (or three, depending on how you count them) directions. One development, which wound up going nowhere, was the appearance of the jawed fishes known as placoderms (plated skin), the earliest identified example of which is Entelognathus. These were essentially larger, more varied -aspis fish with true jaws, and the most famous genus by far was the 30-foot-long Dunkleosteus, one of the biggest fish that ever lived. Perhaps because they were so slow and awkward, placoderms vanished by the end of the Devonian period, outclassed by two other newly evolved families of jawed fish: the chondrichthians (fish with cartilaginous skeletons) and osteichthyans (fish with bony skeletons). The chondrichthians included prehistoric sharks, which went on to tear their own bloody path through evolutionary history. The osteichthyans, meanwhile, split into two further groups: the actinopterygians (ray-finned fish) and sarcopterygians (lobe-finned fish). Ray-finned fish, lobe-finned fish, who cares? Well, you do: the lobe-finned fishes of the Devonian period, such as Panderichthys and Eusthenopteron, had a characteristic fin structure that enabled them to evolve into the first tetrapods - the proverbial fish out of water ancestral to all land-living vertebrates, including humans. The ray-finned fish stayed in the water, but went on to become the most successful vertebrates of all: today, there are tens of thousand of species of ray-finned fish, making them the most diverse and numerous vertebrates on the planet (among the earliest ray-finned fish were Saurichthys and Cheirolepis). The Giant Fish of the Mesozoic Era No history of fish would be complete without mentioning the giant dino-fish of the Triassic, Jurassic and Cretaceous periods (though these fish werent as numerous as their oversized dinosaur cousins). The most famous of these giants were the Jurassic Leedsichthys, which some reconstructions put at a whopping 70 feet long, and the Cretaceous Xiphactinus, which was only about 20 feet long but at least had a more robust diet (other fish, compared to Leedsichthys diet of plankton and krill). A new addition is Bonnerichthys, yet another large, Cretaceous fish with a tiny, protozoan diet. Bear in mind, though, that for every dino-fish like Leedsichthys there are a dozen smaller prehistoric fish of equal interest to paleontologists. The list is nearly endless, but examples include Dipterus (an ancient lungfish), Enchodus (also known as the saber-toothed herring), the prehistoric rabbitfish Ischyodus, and the small but prolific Knightia, which has yielded so many fossils that you can buy your own for less than a hundred bucks.

What is the ACT A Complete Explanation of the Test

What is the ACT A Complete Explanation of the Test SAT / ACT Prep Online Guides and Tips If you’ve found this article, you’ve probably vaguely heard of the ACT (and if you hadn’t before, well, you have now!). Maybe you have some idea that it has something to do with college, but you’re still pretty confused about what exactly it is. I’m here to help! The ACT, like the SAT, is a standardized test used for college admissions. If you’re planning to apply to college in the US you’ll almost certainly have to take one of these tests (and you may need to even if you’re planning on going to school elsewhere). This post will take you through everything need to know about the ACT- from why students take it to what it covers to when you should plan to take it yourself. Why Do People Take the ACT? The ACT is a standardized test designed to show colleges how prepared you are for higher education by measuring your reading comprehension, knowledge of writing conventions, and computational skills and then comparing youwith the rest of the high schoolers who take it. It essentially serves as a nation-wide college admission test (though it's far from the only factor schools consider). Most four-year schools require applicants to submit either ACT or SAT scores (they don't distinguish between the two), which can then make up as much as 50% of the admission decision. A strong standardized test score is a key part of your application. There are also a lot of students who are required to take the ACT by their high school. A number ofstates use the ACT as a state-wide assessment test, so every junior at a public school takes the ACT. Which Schools Accept the ACT? There's a common misconception that some colleges only accept SAT scores and won't take ACT scores. This is not the case: all four-year colleges and universities in the US accept ACT scores, and the schoolsdon't distinguish between the two tests. You can takewhichever you prefer. However, there are a few schools, including George Washington University, Hampshire College, and California State University, that either don't require ACT or SAT scores or have flexible policies on standardized tests. If you're an international student looking to attend a U.S. school, you will need to take either the ACT or the SAT. If you're an American student planning to apply to international schools, you will probably still need to take one of these standardized tests, but it will depend on the school you're applying to and which country it's in. Two-year colleges and trade schools generally don't require applicants to take the ACT but will sometimes accept it in lieu of a placement test. MIT, one of the many colleges that requires an ACT score. What Does the ACT Cover? The ACT consists of four sections- English, Math, Reading, and Science- plus an optional writing test.With the exception of the writing section, the test is entirely multiple choice: the math questionshavefive answer choices and the others all have four. The chart quantifiesthe basic structure of the test (the sections are in the same order they appear on the test).For more details on what's actually on the ACT, you can follow the links to full breakdowns of each section. Section Questions Time English 75 questions 45 min Math 60 questions 60 min Reading 40 questions 35 min Science 40 questions 35 min Writing 1 prompt 40 min How Is the ACT Scored? ACT scores can feel arbitrary, so let's break down where that mysterious number between 1 and 36 actually comes from. For each section of the ACT, you'll get a raw score, which is the number of questions you get right. That is then converted into a scaled score between 1 and 36. The composite score is simply the average of your four section scores (the writing is left out because it's optional). In the US, the average score hovers around a 21, although there's some variance from year to year. Though it's easy to fixate on trying to get as high a score as possible, most student don't need a 36. Instead, you should determine what a good score is for the schools (and scholarships) you're planning to apply to. When Should You Take the ACT? When you take the ACT will depend on what kind of score you're looking for, when your application deadlines are, and whether you live in one of the states that require it. Generally speaking, however, the ideal time to take the ACT for the first time is thewinter of your junior year- when you’ve covered most of the material in school but still have time to take it again ifyou want to. We're just getting started! Time to make a plan. Everything You Need to Plan for the ACT Having read this post, you hopefully feel a bit more clear about what the ACT is. But the tricky part is still to come: preparing for the test. I've compiled a list of the key questions you should ask yourself as you begin to plan for college applications. Should I take the ACT or SAT? This question concerns a lot of students, but it's not as important as it seems, since most students don't see that much of a difference between their scores on the two tests. The New SATis especially similar to the ACT. If you'renot sure which test to take, you can use our fool-proof method to determine which test is better for you or try our quiz fordeciding between the new SAT vs. the ACT. Also keep in mind that if you'll be taking the ACT in school anyways, it will be simplerto stick with that test, since you may have some prep lessons in class and it will save you money on registration. What ACT score do I need to get into college? Your score goal will depend on which schools you want to apply to. Use this form to calculate your ideal ACT score. What's the best way for me to prepare for the ACT? As you prepare for the ACT, you'll need to decide whether you want to hire a tutor or study on your own. You may also want to consider an online program like PrepScholar! If you decide to study on your own, make sure you get the best book for your needs. Whatdo I need to know to prepare for the ACT? There are three key pieces to preparing for the ACT: understanding how the test works, reviewing the material, and practicing. To get a sense of how to think effectively about the ACT, download our guide to the 5 strategies that you must use. For specifics on content and question types, try our complete guides to each section of the test: English, math, reading, and science. You can find the best ACT practice tests here and an in depth guide on how to use them here. Disappointed with your ACT scores? Want to improve your ACT score by 4+ points? Download our free guide to the top 5 strategies you need in your prep to improve your ACT score dramatically.