what is the phylogenetic relationship of sharks with the vertebrate subphylum?
97580
Easy. Sharks belong within the subphylum Vertebrata.
530101
Most sharks are ovoviviporous with the eggs being fertilized by a male but developing internally. There would be numerous eggs all in a clump, whereas a single ostrich egg would be larger than one individual shark egg, not a clump of sharks eggs.
534770
It is a lobe-finned fish; the evolutionary relationships of the coelacanths to the other two living groups of lobe-finned fish (Sarcopterygii), the lungfish (Dipnoi), and the land vertebrates (Tetrapoda) remain debated until today. Since its discovery, many comparative morphologists and paleontologists considered the coelacanth to be the closest living relative of the land vertebrates, although the lungfish were historically thought, and continued to be thought by some researchers, to hold that claim. More recently, however, several analyses began to challenge the sistergroup relationship between the coelacanth and the tetrapods, first on morphological and paleontological grounds and later based on molecular phylogenetic analyses.
280517
the 7 living classes of vertebrate are distuingished mostly on the basis of their skeletal system\n\na) agnatha - consist of jawless fish that don't have scales ex. lampreys and hagfish\nb) chondrichthyes - consisting of hard rubber like cartilages ex. sharks and rays\nc) osteichthyes - bony fish ex. tuna, bass, salmon\nd) amphibia - lives under water and part land ex. frogs, toads, salamander\ne) reptilia - have lungs to breathe on land and skin does not need to be wet ex. turtles, lizards, alligators\nf) aves - include all birds\ng) mammalia - large animals ex. dogs, cats, humans
1172565
These steps will separate most modern animal phyla.\n\nDeveloping:\nFrom a single cell to a multi-cellular body\nFrom radial to bilateral body symmetry\nFrom spiral to radial plane of cleavage in egg division\nFrom a blastopore that forms a mouth to a blastopore that forms the anus\nFrom an incomplete digestive track to complete\nFrom no coelom, to a pseudocoel, to a true coelom\nFrom a true coelom with 2 layers to one with 3 layers\nFrom a ventral nervous system to one that is dorsal\nComplicated organ systems: excretory, circulatory, respiratory\nFrom a non-segmented body to segmentation
1042893
The ones that actually adhere to the sharks are remoras. They're fishes belonging to order Perciformes, family Echeneidae, and they have a dorsal sucking disk with which they attach to sharks , but also to other bony fishes, turtles or marine mammals. These fish clean their "host" and feed on their leftovers.\nThis is what a remora looks like:\nhttp://www.amonline.net.au/fishes/fishfacts/images/enaucsh2.jpg\n\nThe other, more typical-looking fish with dark and light vertical stripes, are pilotfish. These also belong to order Perciformes, but to a different family, the Carangidae. Their scientific name is Naucrates ductor. They were called "pilotfish" because of the belief that they "guided" sharks. Actually, they're semi-obligate commensals of sharks, rays, other bony fishes and turtles, which means that they depend very much on them to feed on their leftovers.\nThis is what a pilotfish looks like:\nhttp://www.horta.uac.pt/imagdop/Servicos/Naucrates_ductor/035_s410_31.jpg
25919
Mammals such as your cat and us evolved from early amniotes called Therapsids, as the Professor stated. Therapsids were sometimes called "Mammal-like reptiles" but in fact, all the "modern reptiles" (lizards, snakes, crocs, turtles) evolved from another "branch" of early amniotes. The things that all amniotes have in common either 1) were inherited from a common ancestor or 2) evolved independently and achieved similar aspect. Most of the times you can tell when this is the case because such features look superficially similar, but not so much under closer examination. For example, vertical pupils are characteristic of many nocturnal animals that are very dissimilar, such as cats, alligators, or some frogs; these were acquired independently and these animals regulate their eyes somewhat differently. However, all vertebrates have one pair of eyes; this is an inherited shared trait.
448301
I saw that picture. She had the babies inside her. I can't remember if it was an ichthyosaur or a mesosaur
343898
The most recent common ancestor of mammals and the bird/reptile clade was probably a terrestrial creature.  The most recent common ancestor of all live mammals was also terrestrial.  The animals along that direct line of descent were also all probably terrestrial.\n\nCastorocauda was a semi-aquatic animal that evolved along a side branch of that line.  Semi-aquatic mammals have evolved many times among modern mammals.  Examples are beaver, otter, platypus, star-nosed mole, hippo, muskrat, water vole, yapok, desman, nutria, and others.  These can all be traced to terrestrial ancestors.\n\nModern marine mammmals can also all be traced to terrestrial ancestors.  \n\nThe closest living relatives to whales and dolphins are the hippos.  They evolved from a terrestrial even-toed ungulate.\n\nThe closest living relatives to the manatees and dugongs are the elephants and hyraxes.  They evolved from a terrestrial afrotherian.\n\nThe closest living relative to the seals, sea lions, and walrus are raccoons, weasels, skunks, badgers, red pandas, and their relatives.  They evolved from a terrestrial caniform carnivoran.
504128
Sharks do have backbones, as all vertebrates. Sharks do not have true bone, but their cartilaginous skeleton can be heavily calcified so that their vertebrae have the apperance of "bone" because they look like hard white cylindric spools. You might have seen their vertebrae made into necklaces and such by artisans. \nThis is what a shark trunk vertebra looks like:\nhttp://www.marinebiodiversity.ca/shark/english/porbeagle_vertebra__copy.jpg\nAnd without the neural and haemal arches they look like this: \nhttp://homepage.mac.com/mollet/Cm/BaskingSharkImages/basking%20shark%20vertebra%204.jpg\n\nAnd these are fragments of backbones:\nhttp://www.indonetwork.info/member/77806_backbone2.jpg\n\n(Notice the white color because the cartilage is calcified.)\n\nAlmost all the cartilaginous fish have backbones made of vertebrae (i.e. both sharks and skates/rays); the exception are the chimaeras or ratfish which do not have vertebrae, but retain a notochord (the primitive condition).
20204
"Members of most [shark] species bear live young, but a few of the smaller sharks lay eggs containing much yolk and enclosed in horny shells."  See link below for full encyclopedia entry.
919165
Homology is evidence of common ancestry.  Homology is the divergence of a structure in a commom ancestor in its descendants.  The classic example of homology is the vertebrate forelimb.  The forelimb (arm) of a human has the same bones and underlying structure as that of most other mammals such as the whale, cat, dog, horse, cow, mouse, bat, and deer (etc.).  Also homology provides a large amount of evidence that supports evolution.
277528
A mammal? Nah. An organism? Yep. All living things are organisms, it's just some are a tad more complex than others. If a shark was a mammal, then it would have to have shark boobies, right? Whoa - there's a scary picture... a shark with boobies. Kinda reminds me of my ex-wife....
628268
Very good answers by Calimecita (sorry though, the corect spelling is oxyrinchus; as you point out correctly it's named after the sharp nose, not the ancient city; it's a rather common mistake) and Haysoos.  Nonetheless, here a few other characteristics and a few thoughts about some of the characteristics mentioned.  The problem with cladistic analyses (i.e., reconstructing their phylogeny, or "family tree" if you like) of elasmobranchs (sharks, skates, and rays) is that they are often based on rather poor characteristics.  Even the great Leonard Compagno used characters such as body length, which is a rather variable, and therefore unreliable characteristic.  Now, the autapomorphies (characteristics of a particular taxon, or taxonomic group) listed by Calimecita are overall rather strong and reliable characteristics.  There are always two dorsal fins, with the second one being very much smaller than the first one.  So are the presence of the anal fin and the absence of the nictitating membranes (fancy word for eyelids in sharks), but the size and postion of the mouth is not quite as good a characteristic.  The most reliable apomorphies are actually embryonic characteristics, since they seem to have the least variability.  Here, the way embryos receive nutrients during gestation is actually a very helpful trait.  (Mind you, this is nothing you can see when you see either species in the wild...)\n\nBoth Carcharodon carcharias and Isurus oxyrinchus are oophagous, which means that throughout large parts of the gestation period the mother will continue to ovulate and shuttle eggs down the isthmus of her uterus into each of the uterine horns.  There the already developing embryos eat the eggs.  At one point the embryo's stomach is so far extended it looks as if the animal has swallowed a football.\nIn one lamniform species embryophagy has been demonstrated.  In the sand tiger shark (Carcharias taurus), the first embryo to hatch in each uterine horne will eat its siblings before entering the oophagous phase, in which it will eat the eggs ovulated by its mother.  \n\nFurthermore, embryos of both species have functional teeth at one point in their development (meaning teeth are erect and hard).  However, unlike in C. taurus, which eats its siblings early on, C. carcharias and I. oxyrinchus form functional teeth later in development.  In a study I did some thirteen years ago (damn, time flies...) on two sister species from the same family (lamnidae), Lamna ditropis and Lamna nasus, I found that mid-term embryos actually develop two fang-like teeth, one on either side of the lower jaw, while term embryos had a full set of functional teeth.  Back then, I called them eulabetic (lat. hold fast) teeth, since we assumed that their function was to aid the embryo in holding on to the egg capsules it consumed in utero.  It would be interesting to see whether C. Caracharias and I. oxyrinchus likewise have eulabetic teeth as mid-term embryos, but it is not easy getting embryos of either.  And since we didn't observe any in the embryos we had (which were about the same developmental phase as the L. ditropis we looked at), I think that eulabetic teeth are actually one of the autapomorphies of the genus Lamna.\n\nWell, as I said, just a bit of an addition to the excellent answer of Calimecita.  A friend once asked me how to tell makos and great whites apart.  I told him that the overall headshape is slightly different, to which he said that he can't see the difference on pics or film...  I mentioned the eyes and coloration, but neither were clear enough for him.  Finally I mentioned,, that the dentition is rather specifi for both species.  Makos have elongated slightly curved teeth in the lower jaw, while great whites don't.  His response: "Listen, if I see the teeth it's too !@#$$% close!"  Good point.\n\nThanks for the fun question! Always good to get an elasmobranch question in here.
862177
.  Animals which have a simple evolutionary history are usually soft bodied, and soft bodies animal do not leave good fossils.  It is easy to find analogs for evolutionary steps toward certain animals, the whale for example,  but finding an clear-cut sequence of fossils is difficult.\n.  But, looking at analogs, consider the weasel, the otter, the seal, the manatee and the whale.  The difference between any two steps in this sequence is fairly small, but the difference from one end to the other seems quite large.\n.  There are enough fossils whose ages may be determined that, studied as a group, studied as a group, they demonstrate an increase in complexity of organisms over time and indicate familial relationships.  Bony headed fishes, known only from fossils, were the ancestors of fish like the coelacanth.  Fishes like the collegian were ancestral to both modern fishes and the fish which pulled themselves up from the water on strong, bony fins.\n.  The horse has some obvious ancestors, but the the fossil record of those ancestor becomes weaker as you go back in time.  The fossil record  between shrew like mammals and those creatures which had some horse like characteristics has big gaps in it..
163746
It is the comparative similarity in embryos of vertabrae orgaisms.  An example is if you look at several vertabrae organisms (example: human, chicken, turtle embryos) they will look similar.  This suggests that they have a recent common ancestor since they have similar developmental/early anatomical traits.
480663
How can there be a new phylogeny? I thought that the phylum for humans is chordata. If our phylogeny is different than that of chordata, then we would be composed of differently right? Maybe I'm not understanding the question very well...