Start by taking a look at the classification that you'll be heldresponsible for on the midterm. This is in your Illustrated Notesand I want to spend just a few minutes summarizing the kind ofinformation that is included in this sort of classification whichis called a Hierarchical Classification. You can see it lookslike an outline with various sections indented within other sections. And one of the major pieces of information that is included inhere is how similar and therefore how closely related differentgroups of animals are.
So for example if we look at the 2 subclasses that you saw indemonstration of living taxa yesterday, that includes the sharksand rays and the ratfish/rabbitfish, chimeras whatever you callit (Subclass Elasmobranchii and Subclass Holocephali). These2 subclasses, they are placed within the Class Chondrichthyesreflecting their similarity and that they both have a cartilaginougskeleton and presumably some common ancestors. So those 2groups are more closely related to each other than either oneof them would be to any other group of animals. And similarlythe advanced ray fined, bony fish are grouped into SubclassActinopterygii in part of the basis of the presence ofthe kind of fins that they have but also on the basis of othercharacteristics.
We have this related this in similarity. Usually some set offeatures will be used to define these higher levels in the classification. And that's another terminology that I want to be sure we're clearabout. The lowest, if you take a look at this classification,the lowest level in the classification for the sharks is the SubclassElasmobranchii. Higher levels in the classification ofthe sharks would then be Class Chondrichthyes, SuperclassGnathostomata, Subphylum Vertebrata and soforth. Those are higher levels in the classification and thereare of course much lower levels in the classification than areshown here. Going all the way to subspecies. But for the purposesof this course, we're trying to establish kind of an outline ofthe characteristics in the classification of these groups.
Now when we look at groupings like the sequence, we look at thesequence in which these classes are listed starting with ClassPlacodermi, Class Chondrichthyes, ClassAcanthodia, and Class Osteichthyes. Therestill is a tendency to group them according to somebody's assumptionsabout degree of similarity so the fact that Acanthodia is herenear Osteichthyes is based upon the assumption that the Acanthodiaare closer to the ancestry of the Osteichthyes. Placodermi arecloser to the ancestry of the Chondrichthyes and that's why theyare listed there.
There is also a tendency, which is not uniform, but there isa tendency to list more primitive groups higher in the classificationso you'll see up here we have the Jawless Vertebrates in SuperclassAgnatha even within the Class Agnatha the Ostracoderms,the early groups are placed here above the living forms and sothere is that tendency, but that tendency is not uniformly adheredto. You'll remember that I told you that the Class Acanthodiais the oldest group of vertebrates with jaws. AndPlacodermi is the second oldest group and you'll noticethat Placodermi is listed above Acanthodia. So that's what Imean when I say that the tendency to list older groups first isnot uniformly adhered to. So the actual ancestor descendent relationshipsof the animals are not clearly communicated by this kindof classification. We are trying to indicate some degrees ofsimilarity but it is definitely not true that the CartilaginousFish gave rise to the Bony Fish. That's not true. So that wouldbe an erroneous interpretation. The actual ancestor descent relationshipswe have to get from some other source and that's not communicatedin this kind of classification.
Now let's talk about the kinds of questions you're going to begetting on the midterm a week from today on the information thatI'm giving you in lecture today and Dr. Baskin (sp) will be completingin lecture on Friday. The questions are going to look somethinglike: (blank) is a Subclass including vertebrateswith separate external gill slits and a heterocercal tail. Thatwould be an example of a kind of question that you might be asked. So that tells you in order to answer these questions you needto know 2 things, you need to know the characteristics of theorganisms otherwise you're not going to have any idea who I'mtalking about. And the second thing you're going to need to knowis that you're going to know that classification in other words,the answer to this question is the sharks but you're notgoing to get any points if you put down sharks. You're goingto have to put down Elasmobranchii.
Now you must know all of the characteristics of the taxa thatI tell you. You cannot say well my God there's 15 things he toldme about sharks, I can't learn all 15, I'm going to learn 5. So you have to learn all the characteristics. And then the nextthing is you have to know the higher levels of the classification. Because this question might say (blank) isa class including vertebrates withseparate external gill slits andheterocercal tail. Same characteristics but I'mspecifying a different level in the classification. What wouldbe the answer if the question were that way? Class Chondrichthyes. Or it might say (blank) is a Superclassincluding vertebrates with separateexternal gill slits and heterocercaltail in which case the answer would be Gnathostomataor Subphylum. So you need to learn the entire classification. I think the best way to study the characteristics is by havinga set of characteristics and the answer is the scientific nameof the taxa rather than the other way around. In other words,learn the way you're going to be tested. Like: if I have thesecharacteristics, what animal is that?
In summary, study all the characters, associate them with thelowest levels in the classification, know the entire classificationand if you choose to be ready to write it out on the exam, writeout a very abbreviated version, don't try to write the whole thingout. I can't tell you how many exams I've seen where the studentshad written out essentially regurgitated that what you see rightthere to the last letter and then answered 1/3 of the essay question. That's not good tactics. The fill in the blank questions aregoing to be a worth a total of 28 points. Fourteen of them at2 points a piece. The essay is going to be worth 30 points. So don't spend half the period getting 28 points and totally blowthe other 30.
So let's go on to a little bit about these animals. I've alreadytold you about the Jawless Vertebrates and the Fossil Groups,the Order Osteostraci, I've told you about Placodermi,I've told you about Acanthodia. I mentioned Rhipidistia,those are the fossil ancestors of the amphibians and the restof the terrestrial vertebrates. There's a picture of oneof those animals on the page about the Evolution of Jaws.
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Well among the living jawless vertebrates the first one is theOrder Petromyzontiformes. And this material iscovered in your illustrated notes once again. The amount of materialthat I'll be giving you should fit within the space on those notesso that you end up with an illustrated set of notes. I'll be tellingyou the Number of Species but I do not require you to rememberthose numbers down to the nearest 1, I would not have a questionbased upon your ability to remember that this taxon has 30 andthat one has 32 for example. I recommend you just remember thetaxa that are huge, there are some and in each of the groups ofvertebrates we'll be studying there's usually 1 that is kind ofa mega-taxon. Many times there's a taxa that only has a singlespecies and that's interesting given that we're not breaking hisclassification down very far. And then sort of, is it generallyunder a 100 or is it somewhere between a 100 and 1,000. Thosekind of general ranges of sizes would be sufficient.
There are 30 living species of Lampreys. And they have a worldwidedistribution except they are not found in the tropics. They are found in both fresh water and marine habitats. The largest adult lampreys get to be about 1 meter inlength and you saw one of approximately that size in lab yesterday. The Natural History of these animals falls into 2 basically differentlifestyles. There are 2 basically different types of lampreys.
1) The one that you saw in lab is an example of a specieswhich when they metamorphose from the Ammocetes larva into anadult form, become ecto-parasites - they use their sucker diskto attach themselves to the side of a body of another fish asthis one is doing here in the picture. It has a kind of a raspingtongue that burrows a little hole in the side of the fish andit kind of sucks the blood and body fluids out of the animal ultimatelyweakening it to the point that the host dies.
2) The other type of adult lamprey has a much more pleasantlifestyle as an adult. After it metamorphoses into an adult,it develops functional gonads, that's part of metamorphosis inthese animals, it doesn't feed at all and it's called the brook-lamprey(remember in the Ammocetes larva which is 1 of the 2 animals thatyou've looked at in lab yesterday, it has a velum which is a littledevice that pumps the water through and they are filter feeders,an Ammocetes larva will grow up to a length of around 20 centimetersand then it'll metamorphose, depending on which species it is,it'll go for this ecto-parasitic adult lifestyle or it'll becomethe other species what are called "brook-lampreys")and the brook-lamprey uses it's sucker disk to attach ontorocks in the flowing streams where it has been living as an Ammoceteslarva. And they don't feed, after they metamorphose they don'tlive for very long, they metabolize their body tissues, they don'tfeed, and they just live for sex. That's the only function ofthe adult brook-lamprey is reproduction, so they look for mates,the female lay eggs, and the males fertilize them. And that littlepicture down at the bottom of the page is x-rated lamprey sex. The female holds onto the rock and the male holds onto her, shesheds her eggs (she may lay anywhere from 100 to 1,000 eggs) andthen the male sheds his sperm. So they have external fertilization. Then the eggs settle into the sand and after awhile in about2 weeks they'll hatch into an Ammocetes larva which will havethe lifestyle of a filter-feeder living burrowed in the sand. After around 3 to 7 years (it varies with the species), thenand growing up to the size of around 10 to 20 centimeters, thenthey will metamorphose into one of these 2 types of adult species.
Question: Can one of the brook-lamprey Ammocetes become oneof the ecto-parasites? No, it's species specific. Some specieswhen they metamorphose into an adult are going to be brook-lampreysand they are going to spend their life sucking on rocks and theother species will become the marine lampreys and they're goingto be ones to become the ecto-parasites. So different specieshave different life histories. They all have an ammocetes larvalstage but then what they do when they metamorphose is different. There are 30 species, some species do one and other species dothe another.
Now the name of this group, Petromyzontiformes translates as StoneSucker. And that comes from the life history of the brook-lamprey. Petro means rocks. Anadromous means they go up-stream to breed,Catadromous means they go down-stream, or out to sea, to breed.
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Order Myxiniformes. The other group of living jawless vertebrates are the Hagfish also known as the "slime-hags". They are worm-like animals. There are a total of 15 species. They have a world-wide distribution and they are foundonly in the marine environment (that is in oceans - saltwaters. Fresh water means streams and lakes). Usually they arefound living on the continental shelf which is the extension ofthe continent that goes out a couple 100 miles from shore in mostcases and gets several 100 meters deep. And they live on thecontinental shelf near the mouths of major rivers. Because theseanimals are scavengers, they are going to live on the decayingbodies of organisms, strictly fish, that die in the river andgot carried downstream by the river and then sort of settled downonto the bottom of the ocean where hagfish can find them and eaton them.
There's no correlation between marine environment and fresh waterenvironment in terms of what's more primitive and more advanced. In terms of the evolution of the bony fish, it looks like mostbony fish originated in Devonian fresh water environments andthen invaded the oceans. But that happened after the Devoniansometime so it's an event that occurred hundreds of millions ofyears ago.
Anatomy of the Hagfish: These animals have no paired appendages,they are long, sort of worm-like, kind of pinkish and purplishin color, the largest ones are less than a meter in length asyou saw in lab there. Eyes are degenerate, covered with continuouslayer of skin. They have what we would call vestigial eyes. A vestigial organ is one which is a degenerate remnant ofa formerly completely functional organ. So the eyes of the hagfish,their ancestors somewhere hundreds of millions of years ago hadpresumably relatively good vertebrate eyes but as part of theiradaptation to this burrowing systems, their eyes became vestigialand covered over with continuous layers of skin. They have separateexternal gill slits along the side of the body. You probablysaw those on the hagfish in lab.
Reproduction of the Hagfish: These animals have externalfertilization producing an egg that has a clear shell. And theyexhibit an unusual life history in terms of their participationin reproduction - they exhibit what we call "seriallyhermaphroditic". Which means that an individual hagfishhas the genetic information in the embryonic primordia that canallow it to develop either a male or female gonad. It eitherdevelops testis or it can develop an ovary. If it produces testis,then it functions like a male, produces sperm when it mates, thenext year if there are too many males around and not enough females,the animal would rather switch than fight and the next year itwill have it's ovaries be functional and produce eggs that arefertilized by some other male. So that's what we mean by serialhermaphroditism. A hermaphrodite is an animal that can functionas either male or female and there are some lower worm invertebratetypes of animals that can actually do both simultaneously. Theseanimals cannot do both simultaneously but they can do one in oneyear and perform as the opposite sex the next year.
There's no larval stage in hagfish. They exhibit direct development,that is they come out looking basically like an adult. The 2types of living jawless vertebrates are probably not very closelyrelated to one another. They have very different lifestyles andthere are a whole series of anatomical characteristics of hagfishthat are different. They have only a single semicircular canalwhereas most vertebrates have 2 or 3. Their body fluids havea higher salt concentration than sea water and that's not foundin any other group of vertebrates. No group of vertebrates hasa total body fluid salt concentration that's even half of seawater, these guys have a salt concentration that's higher thansea water.
They are called slime-hags because of the fact that when a fishermancatches one of these things, if he puts it in a bucket of seawater, the water can produce such a giant amount of mucous inthat bucket and it has the consistency of a bucket of jello ina matter of couple of hours. The animal produces just huge amountsof this slimy mucous, really an attractive group of animals.
Question: What do they feed on? They feed on dead bodies,anything that comes along, they are scavengers.
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The rest of the animals that I'll be talking about are in theSuperclass Gnathostomata the vertebrates with jaws and the firstclass of living Gnathostomes that I'll talk about is the ClassChondrichthyes. The fish with cartilaginous skeletons.2 subclasses, I've already mentioned, the first one is the SubclassElasmobranchii and these are the sharks, skates, and rays.
There are 575 species in this subclass. They have a world-widedistribution and all but one species are marine. Thereis one species of freshwater shark but all the rest of the sharksare found only in oceans.
Anatomy of the shark: The sharks are sort of the prototypeof the subclass, the majority of the species. They have a heterocercaltail (that is a tail that is very strongly asymmetrical with theaxis of the vertebral column extending up into the dorsal lobe). They have separate external gill slits, you can see those alongsideof the body behind the eye and in front of the pectoral fin. They have a spiracle, characteristic that we don't see in anyother living fish but is find in many fossil fish. Paired appendageswith the pectoral fins all the way up here near the front andthe pelvic fins back by the anus in the primitive position.
Skates and rays are dorso-ventrally flattened, largely bottomdwelling animals. Of course they can get up and swim a distanceif they want to but most of them will spend a significant partof their existence sitting on the bottom.
No members of the Subclass Elasmobranchii have a swim bladder. And it appears that their cartilaginous skeleton is an adaptationto minimize the density of their body. Historically zoologistsinterpreted the cartilaginous skeleton of these animals as beinga primitive feature. And that's because when you study the embryologicaldevelopment of bone, in most cases bone is preformed as a cartilageand then it becomes replaced with bony material and so the assumptionwas that if cartilage is an early embryological feature and boneis a more advanced embryological feature than the cartilage skeletonsof this class of animals is a primitive feature but subsequentwork indicates that that's probably not the case and it makesmore sense to think of the cartilaginous skeleton as being a wayof decreasing the density of their body. Bone with a mineralmatrix that you've looked at in lab is much more dense than cartilage. And so an animal with a skeleton of bone is going to be denserthan water and have a great tendency to sink to the bottom whereasan animal with a skeleton of cartilage will still be denser thanwater but not as much denser than water and it won't have to swimquite as hard to keep from sinking. So presumably the reason thatthey evolved a cartilaginous skeleton was that they never evolveda swim bladder so they have a separate evolutionary history, theyare not descended from some Devonian fish with swim bladders orlungs.
Many sharks, as another adaptation to decrease their density,their bodies have huge livers and the liver is filled with anoil that is quite a bit less than water. So they have a liverthat functions almost like a neutral buoyancy device.
Sharks range in size. The smallest sharks are around 25centimeters in length and the largest one is 20 meters in lengthand weighs 10 tons. It's a huge filter feeding shark. Most sharksare carnivores, that is they eat meat, specifically when we saythat we mean eating vertebrate food. But there are some exceptionsto that and the largest of all of them is that exception.
Also Skates and rays will frequently feed on mollusks, variouskinds of invertebrate animals. The manta ray which you may haveseen, is one of these really huge, 6 or 8 foot wingspan, and theyessentially fly through the water. They also are big filter feedersfeeding on the zooplankton that's suspended in the ocean.
Sharks have very sensitive organs that can detect electrical fieldsthat are called the Ampullae of Lorenzini. The Ampullae of Lorenzini are little gelatinous pits on the surfaceof the head of the animal and they can detect very weak electricalfields. Shark using the Ampullae of Lorenzini can detect a fishthat's buried in the sand by sensing the electrical field producedby the beating of the fish's heart or by the electrical fieldthat's produced by the muscles that may be ventilating the fish'sgills. Even though it may be very several centimeters below thesurface of the sand, and there's no scent coming out, they alsohave a very good sense of smell but it has been shown that theycan detect animals purely on the basis of an electrical field.
Reproduction in Sharks: Covers the full range of embryonicdevelopment. Of course they have internal fertilization as I'vealready mentioned and that internal fertilization is achievedby means of a clasper. The male has finger-like extensions onhis pelvic fins that convey the sperm - his cloaca to the female'scloaca. So this is the intermittent organ that sharks have. Butfollowing fertilization, some species of sharks are oviparous,some are ovoviviparous, and some are viviparous so there are somelivebearing sharks and some egg-bearing sharks and some that havethat evolutionary intermediate condition. They exhibit directdevelopment so a baby shark looks basically like an adult shark,it does not undergo any kind of major metamorphosis. And thereis no parental care, even among the live-bearing sharks, oncethe babies are born, they are on their own.
In some of the viviparous species, they have a well developedplacenta which is developed from the yolk sac and their directnutrient transfer between the maternal blood stream and the bloodstreamof the developing embryo in the form of via this placenta. Inother species of sharks the nutrient transfer occurs by meansof uterine milk. The picture on the bottom of the page here showsyou the ventral view shows the claspers on the male shark. Andthat includes the skates and rays as well.
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The other group of cartilaginous fish is a much smaller group,this is the Subclass Holocephali. You saw one ofthese in lab. There are only 25 species, they have a number ofdifferent kinds of strange names, the Chimaera, ratfish, rabbitfish. The group as a whole has a world-wide distribution andthey are found only in marine waters spending most of theirlives in fairly deep marine waters greater than 80 meters deep. So that's 240 feet, that's well below where human skin-diversspend very much time and so these animals are not really verywell known.
Anatomy of the Ratfish: All of them are less than ameter in length and so from a human prospective these arerare animals. They are rarely seen because they spend most oftheir life in deep marine waters. They do come in to breed atnight in shallow waters so their egg cases are found in sandyareas in shallow waters but of course it's hard to go skin-divingand see a lot at night and they are not very well known. Theydo have a cartilaginous skeleton as you would imagine they wouldhave to have to be placed in the Class Chondrichthyes. But insteadof having separate external gill slits, they have an operculum- in this case the operculum is just made up of a layer ofskin so we call it a fleshy operculum. That's to distinguishit from the bony operculum that we'll see in the bony fish.
Feeding of Ratfish: And these animals feed on a varietyof different kinds of invertebrates: shrimp, mollusks, sea urchins. Their are said to be durophagus - phagus refers to eatingand durophagus refers to the fact that they eat things that arehard. So instead of having a bunch of separate teeth, somethingsimilar to what we have or what sharks have, the teeth in theseanimals are fused into great big plates that they can use to crushthe sea urchins and mollusks and other things like that, thatthey eat.
Reproduction of Ratfish: They also have internal fertilization. They have 2 pair of claspers. We saw those in lab as well, thoseare located in the same general area as the pelvic fins. Theyalso have this funny little hook like structure, called a cephalicclasper on their forehead which nobody is really sure what it'sfunction is. And they are oviparous laying fairly large eggs- 10 centimeters in diameter eggs that are covered with a clearprotein shell. They also exhibit direct development so the babyHolocephalians, when they hatch out look basically like theiradults.
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The rest of the fish are placed in the Class Osteichthyes,that is the bony fish. And the skeleton composed of bone is 1of the features that unites the members of this class. Thereare also details of the structure of the skulls of their headsor the bones in their skulls but the main thing that we can identifyis that they have a bony skeleton and that the class is dividedinto 2 major subdivisions:
Subclass Sarcopterygii SubclassActinopterygii
The main thing I want to point out is the -terygii refersto fins, in this case Sarco refers to fleshy and Actino refersto needle. So the actinopterygians have fins that are supportedby needle-like fin rays. But this is the body of the animal,the fin of a sarcopterygian might look something like this - itwould have perhaps several series of bony elements outside ofthe body wall, muscles around them, maybe some smaller bony elementsand then the distal portion (the more distant portion of the fin)is supported by needle-like fin rays. But the base of the finis like a little arm, if you look in the illustrated notes atthe fins of this animal here, you can see what I mean by that.Or if you look at the fins of the lungfish you can also see afleshy based fin.
Whereas the Subclass Actinopterygii, if this is the body of the animal, the fin rays, the needle-like supporting structures forthe fin go all the way down to the body wall, now within the bodywall there is going to be some kind of skeletal supporting elementwithin there but the base of the fin does not have this fleshyarm-like appearance to it. So that's the difference between the2 subclasses, Sarcopterygii and Actinopterygii.
The Subclass Sarcopterygii is divided into 2 superorders. And the first one that I'll talk about is the SuperorderDipnoi. I already mentioned these animals, Dipnoi meansdouble breathing, these are the lungfish, they have both gillsand lungs simultaneously. Basically fairly normal fishy gillsbut they also have a lung which is an outgrowth from their digestivetract. A structure that evolved completely independently fromgills. In other words, if a lung had evolved from gills thatan animal couldn't have both of them. But gills and lungs areseparately derived features and these animals do have both.
Now there are only 6 living species of lungfish. And eventhough they are in evolutionary and blind alley if you will havingonly given rise to 6 living species, they are still very interestingbecause they tell us something about what the other groups ofDevonian fish with lungs were like - that gave rise to the terrestrialvertebrates. The Dipnoi have an unusual distribution, they arefound in Africa, Australia and South America in fresh waterhabitats only. Now that distribution is one of a number ofexamples of similar distributions on what I'll refer to as theSouthern Continents (Africa, South American and Australia) whichwere a real problem to the zoologists who were interested in studyingthe distributions of animals because it was pretty difficult tounderstand how an animal that could only live in fresh water,no fossil lungfish have ever been found in marine habitats, howcould an animal that only lives in fresh water have obviouslyclosely related species on 3 Southern Continents that are allseparated from one another by thousands of miles of open ocean.Of course the geologists solved that problem for the zoologistsabout 25 years ago when the occurrence of continental drift wasestablished. And at the time during the Devonian that these animaloriginally evolved and lived in fresh water all the continentsof the earth were united in a single giant super continent thatwe call Pangea. So it makes it a little bit easier to explainthis distribution on Southern Continents if they were all foundin fresh water streams in Pangea and then the continents wentdrifting off at their own leisurely rates to their present locationssimply carrying these fresh water species with them.
First fossils of the Dipnoi: Are found in the EarlyDevonian.
Anatomy of Dipnoi: And the 6 living species are somewhatdifferent in their appearance. This Australian one is shown foryou here. A couple of interesting things about their biology. They all feed on invertebrates and they all have durophagus dentition,that is teeth that are fused into plates that are used for crushingtheir food.
The African species exhibits what's called aestivation. In these animals, they dig burrows into the mudin the bottom of their ponds. If the pond dries up,the animal will just go down into it's burrow and secretea mucous cocoon around it's body and essentially gointo a state of physiological suspended animation andthey can stay, when the pond is completely dried up and the mudon the bottom of the pond is baked hard by the African sun, theseguys will be a couple of feet down beneath the surface in moistsoil surrounded by their mucous cocoon and they can staythere for up to 4 years in this state of aestivation untilthe rains come back and fill up the pond and then you just addwater and you have instant fish. Only the African speciesexhibit aestivation. After 4 years, they sort of run outof gas and they have a very low metabolic rate and they are accumulatingmetabolic waste products in their tissues and eventually theywould effectively just starve or else just die in their own toxinsif the rains didn't come in 4 years or less.
Reproduction of Dipnoi: They all have externalfertilization. And they are oviparous. Both the African andthe South American forms big burrows in which they place theireggs and the males will defend the eggs from other predators;but there's no parental care after the eggs hatch, the babiesare on their own.
So those are the lungfish, an interesting group. Primarily becauseof what they tell us about what the rest of the Sarcopterygianswere like.
This is an overview where we're going to go in this lecture. We're dealing with the group Class Osteichthyesor bony fishes. And this group consists of really 2 separatenatural groups of organisms. One of which we refer to as SubclassSarcopterygii or fleshy-finned fishes, a term which you arenot using here, may be sort of similar to the group you're talkingabout Superorder Crossopterygii. And don't worry aboutcopying this down, you'll get all this information later. TheSARCOPTERYGIAN group, actually includes you and me in manypeople's classification. Means fleshy-finned fish, this is afin (arm) right here and it's sort of fleshy and that group saysa number of things including lungfish, coelacanth, and crossopterygianswhich are mentioned on your sheet. And of course these are therelatives of the amphibians which are indicated here in this partof the diagram (he's using a diagram on the board that isn't includedin any of our illustrated notes Hoyt gave us).
The other major branch of the "Osteichthyes" or bonyfishes is the Subclass Actinopterygii or ray-finned fishes. You had some representatives in lab and this group Actinopterygiiconsists of 3 major groups. The rather primitive group calledthe Infraclass Chondrostei - we know that that means thatthey are the closest relatives of all the rest of them and theyare considered relatively primitive, relative to the rest of them.
And then there's a major group here, the Series Holostei andthe last group the Series Teleostei and the Teleostei areby far the largest group of vertebrates (about 30,000 species).
This gives you a little idea of where we're going in this lecture. We're going to cover these groups. Us being mammals we spenda lot more time in this course on mammals.
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History of Discovery of the Coelacanth: The SuperorderCrossopteryaii consists of 2 groups. The first of thesewe're going to talk about listed here is the Order Actinistiaor Coelacanth (pronounced sea-la-canth). And that group ismainly a fossil group, the coelacanth as illustrated hereis the only one living species. There are a number offossil things. There's only a single living one. A number ofyears ago (in the early '30's before WWII) there appeared offthe coast of South Africa (sp) a very strange looking fish. ButJ.L.B. Smith who was the ichthyologist of the Museum of SouthAfrica at the time recognized that this was a rare species, theonly known living member of this large group of fossil fishescalled the Actinistia and he set up a search for another specimen. It wasn't until after WWII they were able to get them. Thesethings were found first off the coast of Madagascar which isa marine environment, deep water. The local natives knewwhat it was, it was actually better known in the Comoro Islandswhich is not far away. There are many specimens which have nowbeen found. The interesting part about this story is that thisspecimen, once discovered was really quite a find, the only livingmember of this large fossil group which is related to the Tetrapodsand that's you and I. It was immediate fame and fortune for anyonethat can describe these things in any detail so what happenedis that the French who happened to have control of this area atthe time, immediately said "no specimens leave the country,we've got them all, we are going to describe this thing and nobodyelse can look at until we've done so". It took them about20 years to do it and they finally did describe it.
Reproduction of the Coelacanth: It has internal fertilizationthat is it gives birth to live and kicking young. It's unknownhow they do this but the males have no clasper but they are viviparous- they give birth to live young. Nobody knew about this untilone day a physiologist came by the museum (American Museum ofNatural History in New York [1972]) and wanted to look at thekidney of the coelacanth, so we opened up this huge vat of alcoholin which this large coelacanth specimen was found and he cut thething open, it had actually been cut open for some other studiesbut he was poking around in the area where the kidney is foundand that same area is where the oviduct is found, and felt theselumps in the oviduct of this large specimen, which was a female. And they cut open the oviducts and there were some baby coelacanths.
Feeding of the Coelacanth: And I should say also thatthey are predators utilizing a special rostral organ to detectthe electric field produced by the prey. They are very sensitiveto the electric field that is produced by the prey item in thewater and they feed in that way.
Anatomy of the Coelacanth: They get up to about 2 metersin length and about 80 kilograms. They are adapted for visionin low light, and they have a structure that's helps them do thatcalled the tapetum lucidium, which is a structure in theback of the eye that reflects light back through the eye throughthe retina.
These animals were known as fossils from the cretaceous (sp) andis compared here to another group I'm going to tell you aboutshortly. See they have the fleshy-fin, the base of each of thefin has a fleshy lobe, a number of other characteristics, thegill, cover are all basically fishy. And he looks like a prettynormal fish unless you know what you're looking for which thetaxidermist who originally saw this thing did and that is howthese things were found. We can compare these also to some ofthe other fossil groups, this is strictly fossil thing here Osteolepisand the point of this is to show you that they all have prettymuch the similar appearance but the fleshy lobe is compared tothis fossil Actinopterygian, this is pretty primitive,here's our Sarcopterygian - fleshy lobes to the fins. Here's the Coelacanth his name happens to be Latimeria named after Latimer who was the person who called us to the attentionof J.L.B. Smith and realized
This is also is a point to show about the skeleton of this thing. And if we look at the internal skeleton we see that the fin raysall come out from a central base here of bony elements and thatintroduces us to the other group which is not listed on your sheetup there that Dr. Hoyt asked me to tell you about and that's theOrder Rhipidistia. So far we were talking about the Order Actinistia- the coelacanth. Now we're going to introduce another orderwhich is the rhipidistia. So add this to your important stuffto know.
Order Rhipidistia
Genus - Eusthenopteron
Let me give you some points about this and why we bother. Firstof all, a word about these things, this is a totally fossil group,no living representatives are known and just for your informationif you're ever reading the zoology book and you see that littlesign stuck in front, that little cross, in front of the name ofa group, that means that's it's only known for fossils.
And this group Eusthenopteron belongs to the Order Rhipidistiaand remember we're still in the Superorder Crossopterygii areconsidered to be the closest relatives of the amphibians whichmeans all the 4-legged beasts. It's known only as a fossil. And there's a point to make here, and notice the representationhere of the bones of the base of the fin. There are set up asa series of bones articulated with each other like so. This fish,the eusthenopteron guy, has bones in the base of it's pectoralfin which can be identified as the same bones humerus, radius,and ulna as 4-legged beasts have in their limbs and the same withthe the hind limbs but especially the fore limbs. I'm not goingto go into the details of it but I wanted you to see that thebasic architecture here somewhat similar to our coelacanth butin this one we have the central core of bony elements which onecan imagine would be able to begin to support the organism againstthe force of gravity in perhaps a terrestrial __type environmentalthough it's quite clear from looking at the relationships ofall these organisms together that what was going on in the earlyevolution of tetropods is that they were walking around underwater virtually. They were using tetrapod locomotion in an aquaticenvironment and only then adapting that to perhaps getting outof the water to get to another piece of water and that's the evolutionaryscenario for the origin of paired appendages. And this is thebeast which is the closest relative _of the common ancestor whoactually did that. And by way of comparison we are next goingto talk about the lungfish.
Superorder Dipnoi (lungfish) again:
Notice the central core of bony elements also in similar arrangement,not exactly, this is the one that we can get the radius, humerus,and ulna and which are the bones of our upper limb. But here'sthe skeleton of a lungfish and you can see the comparison.
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Subclass Actinopterygii (Ray-finned fish) and the first of the3 major groups is the Infraclass Chondrostei. Chondro refersto cartilage because these guys have almost entirely cartilaginousinternal skeletons. They have bone, however, on the outside inthe form of dermal bone in the skin, in some cases very heavydermal bone in the case of the sturgeon.
There are about 36 living species and their distribution is largelythe Northern Hemisphere and Africa.
PALEONISCOID (Extinct now) - Notice the heavy bony scales, thevery long jaw, heavy bones around the eye and the skull, givesit sort of a paleozoic leer in a way as many have said. Noticethere are no fleshy lobes associated with the fins, right thisis a ray-finned fish, not a sarcopterygian. Notice also the upperlobe of the tail appears larger and if you actually had the specimenbefore you and look at the skeleton you would see that the axisof the body goes into the upper lobe. And that means that thetail is heterocercal.
Now let's talk about the living species of which there are 36. The first of these is the STURGEON - there are 23 species. Theyget anywhere from 1 to 6 meters in length and they are largelybenthic (sp) animals that live entirely in the Northern Hemispherein both North America and Eurasia. They live largely in freshwater but can also get into brackish (sp) water, especially inthe area of the Mediterranean and the Baltic so they are anadromis(sp) they swim upstream to breed. And they have a axis of thebody going into the upper lobe which of course is that heterocercalcondition. Large bony plates on the side of the body that youno doubt saw in lab. They have a sucterial mouth underneath along rostrum here, these are the guys that are responsible forcaviar (sp) - fish eggs. And caviar you know comes from Russiaso you might know there must be Russia and that's exactly wherethe largest ones are found. Although we do have some nice onesin the Mississippi River in our country. Notice also the primitiveplacement of the fins, pectorals low down, pelvics far _back. That condition we can see in all these animals.
PADDLEFISH - There are only 2 species of this thing. And thisfigure doesn't give them justice, this large extension on therostrum here is actually a big flat paddle, in fact it looks somethinglike this.
They have little tiny eyes. The paddle is about half our greaterthan the actual length of the rest of the body of the animal. It lives in the Mississippi River. It has a very strange modeof feeding, it's a filter feeder, it sort of drops it's jaws anduses it's mouth as a big trammel (sp) net to get fish and planktonand that's how it makes a living. The interesting point aboutthis thing,it gets about 2 meters long, is that in the YangtzeRiver there's another species. Instead of having a big flat snoutit's got a sword like snout like this.
And it lives in the Yang Sea River. They are both strictly freshwater and they are each other's closest living relatives separatedby thousands of miles of ocean. The paddlefishes are interesting,they have the upper part of Mississippi they are good eating fish. They have almost an entirely cartilaginous skeleton, they havevery weak scales, only their fin rays are bony so every now andthen somebody pulls one in and report them as a new species ofshark.
The last group of Chondrostei that we're going to deal with arethe AFRICAN REED FISHES - There are 11 living species. Thesethings get a little more than a meter in length. They occur inAfrica. And they are also known in the aquarium trade as reedfishes. They are rather strange beasts.
They are all very active predators.
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Series Holostei - Infraclass Neopterygii
Series Holostei
Series Teleostei
So what we have is a classification that consists of the InfraclassChondrostei and the Infraclass Neopterygii and the Neopterygiihas in it the Holostei and the Teleostei. And we're now talkingabout the Holostei. You've got to learn all these terms.
First of all we have only 8 living species of these things. Theylive in North America, all of them live in North America. Andthere is however an excellent fossil record, these used to bethe dominant Actinopterygian fishes of the world being havinglots of species known as fossils from both marine and fresh waterhabitats. But they've been largely replaced ecologically and otherwise by the Teleostei which we're going to talk about next.
A few things about these guys. They are mainly, the living onesare all fresh water. Fossils goes back to the upper Permian times- where they were the dominant fresh water fishes. They basicallyhave 4 characteristics:
1) They are able to rotate the maxilla, the maxilla is the boneof the jaw which you see shown in this figure and the premax isthe little bone right in front of it which is barely visible. And when these guys lower their lower jaw like so shown in thisfigure, the maxilla can rotate down and forward. This is ourfriend Ami_a, this is the gar that you've seen in lab. So thisis one of the
major advancements, the beginning of the loosening up of thesejaw bones and the rotating forward of the maxilla as the jaw opens. That's very important in feeding.2) Then there's the abbreviatedheterocercal tail. Which means the shortened version of the heterocercaltail. The axis of the body goes into the upper lobe here butnot nearly as far. 3) Then there's the reduction of the bodyarmor and the simplification of the scales except the Gar. Whatthis means is that these animals now instead of having the reallyheavy bony scales that we showed you in many of the Chondrostei,we now have much thinner bony scales. This is particularly shownin the Amia also known as the Bowfin. Many of the fossils havethis condition. It turns out the Gar still have pretty heavyscales. So this is an all or nothing kind of situation, youhave to understand that ever species is busy trying to make aliving on it's own, not trying to be characteristic of it's groupand the Gar still has their heavy scales. 4)The pelvic finsbegin to move forward relative to the pectorals. Not as far forwardas the Teleostei but further forward than in the previous groupChondrostei.
The living forms are all specialized for their own meanings andare not necessarily representative of the fossils of the moreprimitive ones that occurred earlier. But ever species for thatmatter is busy making it's own living and cannot sit around simplybeing primitive so that we can study them in the labs.
Natural History: The living forms are carnivores where the extinctform showed a great deal more diversity. Another interestingpoint about them is that the only living representatives herethe gar and bowfin both live in North America and they both livebasically in the same area. And that area is the big area, betweenthe Atlantic Ocean and the Plain of the Appalachian Mountains. The old mountains are a stable and have been eroded away. Allthe way from New York up to Canada and down to South Florida. Fresh water habitat.
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Infraclass Neopterygii - Series Teleostei. The classificationwe're giving you down here gives you the idea of the relationshipsof these things.
Here we have the Infraclass Chondrostei and here Holostei andTeleostei form the Infraclass Neopterygii. These 2 are more closelyrelated __to each other than either one is to the Chondrosteins.
Now the Teleostei are by far the largest group of vertebratesnow matter how you cut it. At least 30,000 living species andwe're still discovering new ones all the time. Anywhere from2 to 3 hundred families. This is the majority of all vertebrates. More than all the vertebrates put together. They have a world-widedistribution in both marine and fresh water. From the deepestoceans that you can get any kind of sampling here down to youfill find these fishes up into the highest Andes further you cango without any difficult and Himalayians and places like thatsmall mountain streams, you can still find teleostei fishes.
Fossils known from the Jurassic time.
We see in these things a number __of features that are worth pointingout. The caudal fin now is no longer any remnant, in early developmentyou can see the remnant of the the heterocercal nature of thefin. And at the early development, the ends of the notochordturns upward. It is not evident in the adult and this conditionis referred to as Homocercal. You can see that essentially thebackbone ends and the lobes are equal. Now in some fish, the upperlobe is larger, some fish the lower lobe is larger, some fishthe lobes ends in a point, you name it that's the variety we findin Teleostei. Everything you think about in fish is these guys. Trout, catfish, etc.
Anatomy: Another feature of these things is that they have awell controlled swim bladder - what this means is that there is__a bubble of gas, a bladder full of gas inside the animal. Andthis affords them something really quite phenomenal and that isneutral buoyancy and they can control this very well. They havehover in mid-water without having to swim real hard to stay there. All they have ctenoid scales which means a flat plate of bone,and little projections on one edge of it. The scales look roundlike this with rings which can be used to age the fish. Theselittle projections on the back edge like so.
That's considered a more advanced condition. Notice also thepositions of the fin which is in the more advanced ones that'snow shown in this figure, we'll see it when we get to the perch. The pectoral fin is up high on the side of the body and the pelvicfin is right below it practically up to the throat, immediatelybelow it. This affords them extreme advantages in locomotion. You are much better off if you have your pelvic fin right upnear your center of gravity than if you have your pelvic fin wayback here where it's wagging around as you flip your body forwardand back side to side as you do your swimming.
Reproduction: In terms of this, there is tremendous diversity. The primitive condition is oviparous which means laying eggs. And in other cases there is internal fertilization - giving birthto live young like sharks and coelacanths do. So there's enormousdiversity, everything in between. Sometimes there's internalfertilization and the egg hatches inside that's called ovoviviparous. Sharks have the same degree of diversity.
We have 3 minutes so I want to give you an idea of the 3 majorthings that count for the success of these animals in my view.One of them is the development of protrusible jaws. In amia andother holosteins, there is the loosening up of the jaw bones sothat the maxilla swings forward. In a teleostei fish like this,there's the snout from there to there has a protrusible jaw, hasa mechanism which is allows it to protrude it's jaws, the lengthof the head more or less like so. At least in some cases, insome cases more. I'm not saying all of them do this but manyof them do and the most advanced ones have that capability. Inaddition to that when the lower jaw is dropped and the gill areais flared out what they produce is a huge suction. Open the mouth,protrude the jaws toward the prey, and expand the oral pharyngealcavity, which means what you have is a vacuum cleaner with a protrusiblenozzle namely the jaws. It's a tremendously efficient feedingmechanism given the fact especially that they are neutrally buoyantand that brings us to the second of the 3 things that makes theseguys so successful. If you are neutrally buoyant at the sametime, swim bladder where you can carefully control the amountof gas in the swim bladder so that at any depth you can be neutrallybuoyant . Not all teleostei are all neutrally buoyant._à And the third last thing, is their locomotion mechanism. Onceyou are neutrally buoyant and can maneuver around and that bringsus to this fin position. When your fin is right next to yourcenter of gravity, when you stick your fin out to stop or turn,the line of force goes right through the center of gravity sotheir is no torc. This is not so in a shark. The fins are positionedlow so the animal must deal with torc. It is an advantage tohave your pelvic fins forward and your pectoral fin higher onthe body, extremely expandable oral pharyngeal cavity with protrusiblejaw (vacuum cleaner with a protrusible nozzle) and neutral buoyancy. With all this we find that Teleostei do especially well in habitatswhere the substrate hetero (not clear), there's all kind of cracksand crevices, go to a coral reef in the tropics and you just findall sorts of fishes, every species is specialized for their ownthing involving that coral reef which is a huge city almost.