what traits makes biologists think that  sponges are the most ancestral of all living animals?
611595
Three major factors:\n\n1: Lack of symmetry. Sponges simply grow, plant like, to suit their environment. They have neither radial nor bilateral symmetry.\n\n2)Lack of tissues and organs. Sponges have some specialised cell types, but those cells are scattered more or less at random over the body. The cells aren't arranged into co-operative organ and tissue systems as they are in higher animals.\n\n3)The similarity of the choanocytes to choanoflagellates. There is no clear dividing line between the primary functional cells of sponges and the single-celled choanoflagellates.
102781
Kingdom Animalia\nPhylum Porifera\nFamily Agelasidae\nOrder: Agelasida \nGenus: Agelas\nSpecies: Agelas clathrodes
790810
Every fossil, every observation in biology points to evolution. There is nothing that goes against it or points to a different way to scientifically explain modern diversity. There is not one fossil or one piece of DNA that does NOT point to evolution.\nCreation relies on a lot of belief and the ability to dismiss all the known evidence, since ancient Greece to the present time, in the case for evolution.\nEvolution, on the other hand, keeps presenting solid evidence, regardless of those who believe otherwise. \n\nHere is a theoretical example of natural selection and adaptation.\n\nSay you have an island, about twenty miles from any other island, where there is a species of bird, say finches. In any population of birds, there is going to be a variety of beak sizes and wing sizes, (like nose and ear size, and height variation in humans), suddenly there was a drought, lasting several years, and the main food source of the finches, say, sesame seed, was destroyed, and all they had to eat was wheat, which is harder to break and eat than sesame. \nWhat characteristics would give one bird an advantage over another? Those with smaller beaks would have more difficulty cracking the wheat and feeding it to any baby birds, therefore they would have less live young. Those with largeer, stronger beaks would crack and eat more wheat and have more live young. Chances are, that their offspring would have, on average, larger, stronger beaks than those of small beaked finches. The stronger your beak, the more you eat, the more children you have. \nSo what other characteristics? Those with stronger, larger wings could try to find other food, but if they can't make to the other island, they die, those that make it to the other island, and if it has food, will have, on average, larger wings than those that didn't make it. They wil have more children, who, on average, will have larger wings.\nThese are simplified examples, it is more complex than this, but the basics are there.\n\nAnother, real life example is the Peppered moth.\nHere is the Wikipedia link\nhttp://en.wikipedia.org/wiki/Peppered_moth_evolution\n\nThis is evolution at work.\nRead more about evolution, but do it with an open mind. It wiil be of no use looking at evidence if you have already decided to reject it. Remember, you are doing science, at that is what scientist do. The more you read, the more you will understand. Try "Origin of Species " by Charles Darwin as a start, or try Google for a summary.\n\nGood luck to you.
234955
The very oldest species on Earth are the cyanobacteria, which seem to have been around virtually unchanged for nearly 4 billion years. This is based on fossils of that age that have been compared under high-powered microscopes to existing species of these bacteria. Other bacteria that are about as old are the archaea, which thrive in acidic, high- temperature, or high-radiation environments. \n\nAnother remnant of ancient organisms includes the stromatolites, mounds of algae and bacteria that today grow in the Bahamas, Shark's Bay Australia, and a few other limited environments. They have been around, also largely unchanged, for over 3 billion years and at one time were the Earth's dominant form of life. \n\nOn the animal side of things, the brachiopod Lingulaa is probably the oldest, having existed nearly unchanged for over 500 million years, and the horseshoe crab (limulus) has been on the planet for several hundred million years, too. Since the average "lifespan" of a species is only a few million years, having such ancient species around is very impressive. \n\nA good book about the earliest life is "Cradle of Life" by J. William Schopf. He is one of the premier scientists doing this sort of research. At a more advanced level, he has edited two scientific books, "Earth's Earliest Biosphere" and "The Proterozoic Biosphere", which should be in your university's geology or science library.
792821
Yes. See the links below. I highly encourage everyone who doubts evolution to spend a little time browsing the "tree of life  web" site www.tolweb.org. Look both at the tree diagrams, showing how life has evolved into different species, but also look at the titles of the papers that are referenced on each page. For example, from the Primates page, there are papers with these titles:\n\n"Toward a phylogenetic classification of primates based on DNA evidence complemented by fossil evidence. "\n"A molecular view of primate phylogeny and important systematic and evolutionary questions. "\n"Molecular timing of primate divergences as estimated by two nonprimate calibration points."\n"The oldest known anthropoid postcranial fossils and the early evolution of higher primates."\n"Molecular evidence on primate phylogeny from DNA sequences. "\n\nThere is a huge body of scientific literature that doesn't just say "we think we evolved from apes". It explains in great detail the evolution of all life, and shows where humans fit in the families of hominids, primates, and mammals. There is a great deal of evidence, not just from fossil evidence, but from DNA evidence. The DNA evidence is now far more powerful than the fossil evidence.
600482
kingdom animalia consits of some phylums. they are\nporifera (sponge)\ncoelentrata (jellyfish)\nplatyhelmintes \nnemathelmintes \nanellida (earthworms, leech)\nmollusca (SHELLS, OYSTERS AND SQUIDS)\narthropoda (crabs, insect, centipide)\nechinodermata (spine skinned animal)\nchordata (animals that have bones)
937960
That all living organisms (known to date) come from one ancestor (somewhat of a pre-cell)
371165
we talked about this in my biology class and we came up with birds. We found out that they are related to prehistoric times to the Teridactyl. They have similar body stuctures except much larger. Stubby legs and wings with bones is another similarity. They also build nests and lay eggs. \n\nBacteria is an excellent organism to support the theory of evolution. Bacteria are "cells" that have their chromosomes scattered all throughout it making it very unorganized. However over time a nucleus was formed and all of the chromosomes were kept here and other cell structures were formed along with cilia on the cell membrane for propulsion. This evolving into the first single celled organism.
349428
One of the features taken as evidence that two organisms share a common ancestor is the possession of a number of unique traits that are found in those organisms, and are not found in other groups of organisms.\n\nThe following is a (partial) list of the characters shared by all chordates (the phylum to which vertebrates belong)\n\n- Possession of a notochord (which is a dorsal axial rod of vacuolated muscular cells surrounded by a connective tissue which forms in the blastocyst from the roof of the archenteron).  The notochord functions as a skeleton and resists deformation when muscles contract.\n\n- Pharyngeal gill slits (originally for filter feeding, also for respiration)\n\n- Dorsal hollow nerve cord derived by invagination of ectoderm along the dorsal midline, sometimes with anterior expansion (brain)\n\n- Postanal tail (major locomotory organ in most chordates)\n\n- Subpharyngeal gland, which is secretory tissue in the endoderm of the pharynx floor (endostyle in protochordates, thyroid gland in 'higher' chordates)\n\n- Ventral heart\n\n- Segmented body with segmented axial muscles, axial skeleton, gill arches, nerves, aortic arches\n\n- Ectodermal ciliated canal (endocrine function, pituitary in 'higher' chordates)\n\nIn addition, there are several features unique to the the vertebrates:\n\n- Neural crest cells (arising from neural groove, become melanocytes, sensory neurons etc.)\n\n- Endoskeleton of bone and/or cartilage\n\n- 3 part brain\n\n- Muscular pharyngeal pump\n\n- Jointed internal skeleton (unique in Animal Kingdom)\n\n- Unsegmented gonads\n\n- Usually with a skeletal cylinder protecting the dorsal hollow nerve cord (i.e. vertebrae)\n\n- Pharynx is chiefly respiratory\n\n- Gas bladder for buoyancy control and respiration (in most)\n\n- Paired jaws (in most)\n\n- Paired appendages (in most)\n\n- Cranium protecting the brain (poorly developed in some)\n\nAll of these features are shared between all the vertebrates, from nasty lamprey and disgusting hagfish to cute kitty cats and arrogant humans to giant blue whales and extinct ankylosaurs.\n\nThe possession of all of these features suggests that these organisms share a common ancestor from which they inherited all these traits.
19920
Sponges grow in the ocean. That just kills me. I wonder how much deeper the\nocean would be if that didn't happen. -- Steven Wright
422928
I would have to say porpoises/dolphins...\nAccording to this article, they are smarter than chimps and possibly as intelligent as man...\nhttp://www.amusingfacts.com/facts/Detail/smart-porpoise.html\n\nAlso see:\nhttp://en.wikipedia.org/wiki/Dolphin_brain\nhttp://www.daviddarling.info/encyclopedia/D/dolphins.html\nhttp://www.wdcs.org/dan/publishing.nsf/allnews/239F297BE9A133F380256FC700323B80\nhttp://whales7.tripod.com/policies/levasseur/levass2f.html
169702
-they were excellent mothers\n-the most ferocious lived in the cretacious period in the ocean.\n-a t-rex bite was so powerful, scientists have found teeth marks on fossils.\n-when brontosaurus flicked its tail, the sound was so crisp, it broke the sound barrier.
788917
Have a look at the limbs of a lizard.  Not too unlike ours - has all the same sections in the same places.  Some even have five "fingers".  \n\nWhen mammals came along they took the format much further - creating ungulates with two toes, horses with one, dogs with four and a dew claw.  \n\nEven whales have the skeletal bones of hands in their pectoral fins.  \n\nLemurs are supposedly more primitive than monkeys and apes, but go see them at a zoo.  I was lucky enough to hand feed one, and it has hands remarkably like a tiny human.  It was unreal.  \n\nThe format has changed constantly, built on a vertibrate format developed initially by fish.
530192
Well, on this Earth, primates are the ancestors of the only known sentient species.  I don't know that these means that humans are the 'best' species, even if we are (arguably) the most intelligent.\n\nIf the human evolutionary path is any indication, there may be some prerequisites for the development of sentience.  A large brain is the most obvious one, but things such as free and mobile appendages suitable for tool use may also be required.  As far as bats go, they are limited in the size that their brains can grow to and still be able to maintain flight.  Their forelimbs are also not readily available for manipulatory organs.  \n\nSo a sentient bat species would probably be unlikely.  The ecological niche of intelligent species would probably go to a different species that already displays some of these adaptations to some extent.\n\nMice are a remote possibility for potential sophonts.  They can achieve a semi-bipedal stance and use their forepaws for some remarkable manipulations.  Their current small size is their chief impediment.  Increasing body and brain size to an extent to make them candidates for sentience would also slow them down, remove their stealthiness and ability to fit into tight spaces, and many of the other adaptations that allow them to survive in a world full of predators.\n\nOther than the great apes, I think one of the major candidates for potential for sentience is the racoons.  They are already pretty smart, near the top of the food chain, versatile, adaptable, omnivorous, and curious, and have very well developed forepaws with perhaps the highest level of manual dexterity of any mammal outside the primates.  \n\nI seem to recall a novel by Stephen R. Boyett called 'The Architect of Sleep' in which a man goes to a parallel universe where racoons evolved sentience instead of the primates.  It seemed to be an aquel (a book that fails to spawn the expected series of sequels), but if I remember correctly it was quite intriguing.\n\nAnother intriguing species with curiosity, adaptability, intelligence and manipulative abilities that I think would make an interesting candidate for the development of sentience are some of the large cephalopods (like the giant Pacific octopus, Humboldt's squid or even the giant squid!!)  - imagine the society they might create.
995191
They're critters that permanently attach themselves to something and live out their lives there, like many sea creatures- usually they are motile as larvae and then settle on an object as an adult. Very few are sessile their entire lifespan but many many spend their adulthood that way.\n\nExamples- barnacles, sponges, corals\n\nWhen applied to plants (I assumed you meant animals, but just in case... ) it refers to leaves or stems that grow directly from the stem without a stalk.
304666
The very oldest species on Earth are the cyanobacteria, which seem to have \nbeen around virtually unchanged for nearly 4 billion years. This is based \non fossils of that age that have been compared under high-powered \nmicroscopes to existing species of these bacteria. Other bacteria that \nare about as old are the archaea, which thrive in acidic, high- \ntemperature, or high-radiation environments. \n\nAnother ancient organisms are the stromatolites, mounds of algae and \nbacteria that today grow in the Bahamas, Shark's Bay Australia, and a few \nother limited environments. They have been around, also largely \nunchanged, for over 3 billion years and at one time were the Earth's \ndominant form of life. \n\nOn the animal side of things, the brachiopod Lingula is probably the \noldest, having existed nearly unchanged for over 500 million years, and \nthe horseshoe crab (limulus) has been on the planet for several hundred \nmillion years, too. Since the average "lifespan" of a species is only a \nfew million years, having such ancient species around is very impressive. \n\nA good book about the earliest life is "Cradle of Life" by J. William \nSchopf. He is one of the premier scientists doing this sort of research. \nAt a more advanced level, he has edited two scientific books, "Earth's \nEarliest Biosphere" and "The Proterozoic Biosphere", which should be in If you are a "separator" (I’m not sure if that is the correct word), instead of a “grouper” there are a LOT of things you could see as very young species. For instance, marine iguanas (are they called green iguanas?) are very different depending on what island they live on. Some people see those as separate species so there are some that are still in the process of adapting to changes that are seen to be becoming a new species. Also, a lot of migrating birds can reproduce with different species to form new species that are not barren like mules or anything like that, they can become their own species I guess. But I think a grouper would say they are all the same species if they can interbreed and have offspring that can reproduce. Like, all green iguanas are one species.
83020
Actually, sponges are mostly colonial. They belong to Pylum Porifera and are almost exclusively marine.  Many smaller individuals group together and partner to form the structures you see and function as a unit. There are species which are solitary. Solitary sponges and colonies range in diameter from about 1/2 in. to 5 ft (1–150 cm) and vary greatly in shape. Some are branched, some more or less globular, and some are thin encrustations on rocks and pilings.\nPoriferans  are one of the simplest multi-cellular animals. 98% of this phylum consists of marine species. They have a cellular level of organization, without any organs or tissues. Sponges consist of several different cell types, each specialized for a different purpose and all working independently of one another. Canals run throughout the body of the sponge, cycling through water for feeding, gamete dispersal, waste disposal, and gas exchange. Colonial sponges often have many small ostia (inflow; sing. ostium) and share one large osculum (outflow; pl. oscula). Structure is present in the form of calcium carbonate or silica spicules embedded in a gelatinous mesohyl layer. Also embedded in the mesohyl are unspecialized cells called archaeocytes. Archaeocytes perform various functions, including: intracellular digestion, gamete production, and waste elimination. Sponges also have the amazing ability to self-recognize and reform if broken apart; archaeocytes are thought to function in this as well. Flagellated cells, called choanocytes or collar cells, create water flow as well as capture small food particles and incoming sperm. Sponges are divided into three classes, distinguished by differences in structure: Demospongiae (like your common bath sponge), Calcarea, and Hexactinallida. They are also divided into functional groups based on form complexity.\n\nSo the answer is really BOTH.