Welcome back, err, me! And, while I could have started with 'here are the things I saw on holiday', I became concerned that my list of bats and raptors might seem a bit mundane in comparison to what certain of my friends have encountered (wait until you see what Carel got to see). Anyway, to business. Tet Zoo regulars will know that I've had a thing about anurans (frogs and toads) recently (go here, here or here); the reasons for this will become clear soon enough. And to make things easier in the articles that will follow, I thought it might be a good idea to produce a short article on anuran phylogeny and diversity. That didn't work, and it soon became a series of long articles. I will try to avoid all the family-level groups, otherwise things will certainly not be so short. Anurans have to be among the most incredible, charismatic and jaw-droppingly ridiculous of all tetrapods. Why? Well...
Consider how bizarre their skeletons are: anurans have (at most) nine presacral vertebrae, and some have as few as five; ribs are either highly reduced or absent; the radius and ulna are fused (forming the radioulna); the bones of the pectoral girdle are highly reduced and complimented by an assortment of new weird bits; the pelvis consists of a rod-like central unit (the urostyle) surrounded by two super-long, shaft-like ilia; and in their (generally) elongate hindlimbs, the tibia and fibula are fused (forming the tibiofibula) while the ankle bones are elongated to form a long 'extra' limb segment. This is one of the most modified skeletal plans in the whole of Tetrapoda: it is, we think, highly specialised for jumping, and the inheritance and retention of this bauplan means that anurans are, as a group, astoundingly uniform.
The diversity seen in anuran reproductive biology beggars belief. It's true that the majority of anurans reproduce and develop in the manner that's most familiar to us: pair mates and lays eggs in water, tadpoles emerge from eggs, tadpoles grow into little frogs, frogs leave water. But about 20 anuran lineages have evolved direct development where a free-swimming tadpole phase is skipped and a terrestrial egg develops into a terrestrial froglet. Others make bubble nests (these might be on the water surface, or in terrestrial vegetation), others carry their eggs wound round their hindlimbs, or carry their tadpoles, or their froglets, on their backs, others retain the developing babies in a pouch, submerged in specially grown skin on the back, in a vocal sac, or in the stomach (yes, stomach: adjacent image shows gastric-brooding frog Rheobatrachus silus in the act of 'giving birth'. Discovered in 1973, it is apparently now extinct). Some exhibit parental care of eggs, tadpoles and/or froglets: some feed their babies on unfertilized eggs, and in some species males and females are pair-bonded and provide extended biparental care (Caldwell 1997). Individuals in some aquatic-spawning species practise clutch piracy: males actually grab freshly-laid egg masses and fertilize them (Vieites et al. 2004).
Amplexus - the behaviour in which a male grabs hold of a female in order to fertilize her eggs when they are expelled - is often assisted by special spiny nuptial pads on the hands, arms or chest; some round-bodied species use a secreted glue to remain in contact; in some of the South American harlequin toads (Atelopus), couples may remain in amplexus for several months. Internal fertilization has evolved in the North American tailed frogs (hey, that ain't no tail baby), in some African bufonids (Nectophrynoides and perhaps Mertensophryne) and in some Caribbean leptodactylids (some Eleutherodactylus species). Most male anurans use vocal displays to attract females, but some indulge in combat, and the males of some anuran species exhibit curved spines on the hands or arms; members of many clades have evolved enlarged tooth-like structures in the lower jaws (these are called odontoids: with the exception of Gastrotheca, no anuran has a mandibular dentition) (Emerson & Ward 1998, Fabrezi & Emerson 2003). In contrast to the majority of anurans, the males of these spiny or fanged species are larger than the females.
Tadpoles aren't all the same. Some [like the Xenopus tadpoles shown in the adjacent image] are filter-feeders with paired barbels at the corners of the mouth (or even multiple barbel-like structures [properly called barbellae], as in the burrowing toad Rhinophrynus); most possess keratinized beaks surrounded by rows of black, comb-like labial teeth and fleshy papillae. Species that inhabit fast-flowing water adhere to rocks with sucker-like discs on their mouths or bellies, and some cling to vertical waterfalls using these organs. Some tadpoles complete metamorphosis in a couple of weeks; others take years, and grow to a size that rivals that of their parents. And there's so much more stuff to say about anurans... their ears, their vocal displays, their repeated evolution of skin toxicity, their repeated crossings of marine barriers, their excursions into arboreal and fossorial lifestyles, their sometimes projectile tongues, and so on and on. I'm telling you, there's no end to the frickin' awesomeness of frogs and toads.
While there have been occasional suggestions that some basal anurans (Ascaphus and Leiopelma) might have arisen separately from the other anuran groups, it is clear from their extremely characteristic anatomy that anurans are monophyletic. A few fossil 'proto-anurans' are known, the most basal of which are the Early Triassic taxa Triadobatrachus massinoti from Madagascar and Czatkobatrachus polonicus from Poland. These animals share a list of derived characters with extant anurans, including a short body, strongly reduced tail and elongate hindlimbs, but lack many others, including the radioulna, tibiofibula, reduced compliment of dorsal vertebrae and urostyle. The name Anura is currently used for the node-based clade that includes all extant anuran species, whereas the stem-based clade that includes Anura and all taxa closer to anurans than to other lissamphibians is termed Salientia (Ford & Cannatella 1993, Evans & Borsuk-Białynicka 1998, Cannatella & Hillis 2004). The aim of the article here (and the following two or so) is to quickly review anuran diversity: I've tried to avoid getting into the highly complex historical stuff. Good historical reviews of anuran classification are provided by Ford & Cannatella (1993), Pugener et al. (2003), Cannatella & Hillis (2004) and Frost et al. (2006). Particularly good non-technical reviews of anuran diversity include those provided by Arak (1986), Mattison (1987) and Zweifel (2000). The standard work on the anuran fossil record is Sanchiz (1998).
Generally regarded as the most basal of anurans (although wait for the next article) are the North American tailed frogs (Ascaphus: adjacent pic shows A. truei) and the New Zealand frogs (Leiopelma). Whether the members of these groups should be classified together (in a group usually termed Ascaphidae, although Leiopelmatidae Mivart, 1869 has priority and Amphicoela was used in some of the older literature), or as entirely distinct, has proved controversial. Leiopelma shares derived characters with other aurans that aren't present in Ascaphus (including long bony processes on the sternum and the route of the facial nerve), and Ford & Cannatella (1993) coined Leiopelmatanura for a clade that included Leiopelma and other anurans but not Ascaphus. Recent molecular evidence and a reassessment of the morphological data has led some authors to unite the two again (Gao & Wang 2001, Roelants & Bossuyt 2005, Frost et al. 2006). Despite their basal position within anuran phylogeny, both Ascaphus and Leiopelma are specialised and unusual, with such unique features as a male intromittent organ (in Ascaphus).
Also universally regarded as basal within anuran phylogeny are the fire-bellied toads, midwife toads, painted frogs and jungle toads or barbourulas, sometimes called the disk-tongued frogs for the obvious reason. Distributed across Eurasia and parts of northern Africa, these smallish (SVL 30-70 mm) anurans include both predominantly aquatic species (like the fire-bellied Bombina species, famous for exposing their vividly coloured undersides in a distinctive anti-predator display) as well as terrestrial forms (like the midwife toads Alytes, a group of European species that may mate away from water: the males then carry the strings of eggs wrapped around their hindlimbs, eventually depositing the tadpoles in water. See adjacent image).
Traditionally united as the Discoglossidae, synapomorphies uniting these species had never been identified until recently, and consequently it has been widely suspected that discoglossids are not monophyletic. Ford & Cannatella (1993) argued that fire-bellied toads and barbourulas should be classified in a distinct group, Bombinatoridae, and that discoglossids were more closely related to all 'higher' anurans, forming with them the clade Discoglossanura. However, monophyly of discoglossids (sensu stricto) and bombinatorids has been strongly supported by other studies (Haas 2003, Roelants & Bossuyt 2005, Frost et al. 2006) and Gao & Wang (2001) argued that characters of the vomers, clavicles, facial foramina and the elongate coracoid provided support for the monophyly of the traditional Discoglossidae. Some workers prefer the name Alytidae for discoglossids.
So that's part I done, part II to follow next of course...
Refs - -
Arak, A. 1986. Frogs. In Halliday, T. & Adler, A. (eds) Animals of the World: Reptiles and Amphibians. The Leisure Circle (Wembley, UK), pp. 36-51.
Caldwell, J. P. 1997. Pair bonding in spotted poison frogs. Nature 385, 211.
Cannatella, D. C. & Hillis, D. M. 2004. Amphibians: leading a life of slime. In Cracraft, J. and Donoghue, M. (eds), Assembling the Tree of Life. Oxford University Press (Oxford), pp. 430-450.
Emerson, S. B. & Ward, R. 1998. Male secondary sexual characteristics, sexual selection, and molecular divergence in fanged ranid frogs of southeast Asia. Zoological Journal of the Linnean Society 122, 537-553.
Evans, S. E. & Borsuk-Białynicka, M. 1998. A stem-group frog from the Early Triassic of Poland. Acta Palaeontologica Polonica 43, 573-580.
Fabrezi, M. & Emerson, S. B. 2003. Parallelism and convergence in anuran fangs. Journal of Zoology 260, 41-51.
Ford, L. S. & Cannatella, D. C. 1993. The major clades of frogs. Herpetological Monographs 7, 94-117.
Frost, D. R., Grant, T., Faivovich, J., Bain, R. H., Haas, A., Haddad, C. F. B., De Sá, R. O., Channing, A., Wilkinson, M., Donnellan, S. C., Raxworthy, C. J., Campbell, J. A., Blotto, B. L., Moler, P., Drewes, R. C., Nussbaum, R. A., Lynch, J. D., Green, D. M. & Wheeler, W. C. 2006. The amphibian tree of life. Bulletin of the American Museum of Natural History 297, 1-370.
Gao, K.-Q. & Wang, Y. 2001. Mesozoic anurans from Liaoning Province, China, and phylogenetic relationships of archaeobatrachian anuran clades. Journal of Vertebrate Paleontology 21, 460-476.
Haas, A. 2003. Phylogeny of frogs as inferred from primarily larval characters (Amphibia: Anura). Cladistics 19, 23-90.
Mattison, C. 1987. Frogs & Toads of the World. Blandford, London.
Pugener, L. A., Maglia, A. M. & Trueb, L. 2003. Revisiting the contribution of larval characters to an analysis of phylogenetic relationships of basal anurans. Zoological Journal of the Linnean Society 139, 129-155.
Roelants, K. & Bossuyt, F. 2005. Archaeobatrachian paraphyly and pangaean diversification of crown-group frogs. Systematic Biology 54, 111-126.
Sanchiz, B. 1998. Salientia. Handbuch der Paläoherpetologie, Teil 4. Verlag Dr. Friedrick Pfeil, München.
Vieites, D. R., Nieto-Román, S., Barluenga, M., Palanca, A., Vences, M. & Meyer, A. 2004. Post-mating clutch piracy in an amphibian. Nature 431, 305-308.
Zweifel, R. G. 2000. Frogs and toads. In Cogger, H. G., Gould, E., Forshaw, J., McKay, G. & Zweifel, R. G. (consultant eds) Encyclopedia of Animals: Mammals, Birds, Reptiles, Amphibians. Fog City Press (San Francisco), pp. 516-545.
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And they're so cute, so lickable !
And then there's the oddities of chromosomes and sex determination in Leiopelma - four different species, at least three distinct modes of sex determination, sometimes different modes within the one species!
Just wanted to say thanks for another great post... your blog is my favorite here by far and I love the fact that you mainly stick to science. To often the blogs here are more about politics than the nitty-gritty science..
Whenever the subject of biological weirdness in frogs comes up, I'm reminded of an old National Geographic special about Lake Etosha in Namibia. The lake, which dries up every year and then refills every rainy season, is home to a population of African giant bullfrogs. Bullfrog tadpoles must grow to adult size within the time that the lake is full, so they need a lot of food, fast. Many of them get it by turning cannibal. "In fact," said the narration, "many bullfrogs reach adulthood without eating anything but their own kind."
In connection with anuran evolution, I also recall something I read somewhere about the basal frog genera you mention, Ascaphus and Leiopelma. It said that these frogs retain the muscles for moving a tail, even though the tail itself is absent. Leiopelma is also unusual in that it has no tadpole stage, while Ascaphus has become so adapted to its cold-water streams that it can no longer live in warmer water.
Priceless image file names again!
And in spite of all this, the cleithrum is STILL THERE! AAARGH! Everywhere else among crown-group tetrapods it went out of fashion in the Permian (except in Proganochelys and Kayentachelys).
GAH! I'll read that immediately!
In Ascaphus, these muscles are used to move the, er, male intromittent organ that is so well visible in the photo.
Wonderful animals, incredible diversity constrained by the common plan.
I had a pet Ceratophrys ornata for some time - so much character, so little activity! The colour scheme was wild, like some kid had tried to paint camouflage and got it rather wrong! Unfortunately it died of constipation (sort of) - I made the mistake of keeping it on gravel rather than moss because that was easier for me to clean, unfortunately when it swallowed a piece of gravel too big to 'pass' it clogged its intestines up, and just try finding a vet who will operate on small frog! I tried to clean and keep the skeleton, but the pieces are so fragile it was not succesful.
By the way, I agree with 'person', its good that you avoid going political or theological. Stick to the natural history and science.
I don't see any mention of frogs being able to change their sex. Did Jurassic Park get it wrong again?
What about the kind who have massive tadpoles and wee adults?
(I cant name them, Im sorry)
Grafe and Linsenmair (1989) documented facultative female to male sex change in Hyperolius viridiflavus. This publication almost certainly inspired the deus ex anura scene in Jurassic Park.
Well Darren, I have it on *ahem* good authority that '280 million year old frogs' show no differences with those alive today. Tail? What tail?
You're probably thinking of the South American pseudids, or paradox frogs (they're regarded by some workers as members of Hylidae and not as a distinct 'family'). In the best known of the 10 or so species, Pseudis paradoxa, the tadpole reaches 250 mm, yet the metamorphosed adult is 70 mm long.
You know that's not a salientian fossil? It's (I think) the Jurassic proto-salamander Karaurus. Good job as always, those clever creationists. Even if it was a '280 million-year-old'* proto-frog, there are, as you know of course, important differences between such basal forms and modern anurans.
* The oldest known salientians (Triadobatrachus and Czatkobatrachus) are more like 245 million years old (280 would put the fossil in the early Permian!).
If Jurassic Park was inspired by Grafe and Linsenmair (1989), they inexplicably changed East African frogs to West African frogs. This could be the least publicized trivial error in JP, unless of course the same phenomenon is now known to also occur in the West African populations.
Certainly interesting critters.
In the earlier posts you mention "amphibian crisis". Certainly many anurans are endangered. But this numbers can be inflated by low data. Now, Red List uses strict (or, rather, nonsensically automatic) criteria, among others,
- known from one locality or endemic to small area. Now, anurans are particularily little studied and many are known only from type locality. I wonder how many frogs were classified as threatened only because of small range?
The "280-million-year-old frog fossil" must be a parody. Every moron can see the tail and the short hindlimbs. It is not even necessary to know what a frog skeleton actually looks like.
(Yes, it is Karaurus, which is from the Kimmeridgian in the Late Jurassic not 280, but between 150 and 155 Ma old.)
Why not err on the side of caution? Isn't it better when additional research changes the status of a species from "threatened" to "least concern" than from "least concern" to "extinct"?
BTW, Darren, thanks a lot for the response by Frost et al. to Wiens' critique. I'm reading it right now.
That 280 Ma old frog" is, unfortunately, not a parody. The picture is from Harun Yahya's Atlas of Creation, which looks like a bad parody but isn't. That book was sent to universities, libraries etc. all around the world.
Parallel Convergence, Generally speaking:
Anurans: Throat sac buoyancy, vocal mate selection, no tail
Salamanders: no, no, long tail
Hominoids: Laryn. air sac buoyancy, vocal mate selection, no tail
Monkeys: no, no, mid to long tail
Aves: Resp. air sac buoyancy, vocal mate selection, short tail
Reptiles: no, no, long tail
Walruses: Pharyn. air sac buoyancy, vocal mate selection, short tail
Mustelids: no, no (scent), long tail
Pterodons: soft tissue air sac, vocal mate sel., reduced tail later
Dinos: no, no, long tail
Sadly, no. That's a tongue-well-out-of-cheek figure from Atlas of Creation vol. 1 by "Harun Yahya". Labeling a Jurassic urodele as a '280-million-year-old frog' turns out to be a relatively accurate claim as far as that book goes.
I have painstakingly documented some of the more hilarious figures from the Atlas but the Oktar brigade's litigiousness has kept me from blogging about it so far. Hooray for self-censorship!
I knew that frogs 'n' toads were awesome as adults, but I had no idea that their tadpole stages were so diverse! Keratin beaks? Go figure! Something I've always wondered about early tetrapods: Do you think that landlubbers like Ichthyostega and its ilk had larval stages? I ask this because amphibians and amniotes are likely sister groups (unless amniotes evolved directly from amphibians), and amniotes "hatch" into miniature adults, more or less. I also wonder what kind of genetic modifications allowed that sort of growth spurt in the embryo...
Ah, Harun Yahya, that caricature of himself.
DDeden, stop it with "buoyancy". Frogs and salamanders -- remember that newts are salamanders, too -- have no interest in extra buoyancy, and walruses have a vested interest in negative buoyancy.
Also, apparently all saurischians had air sacs, and probably all dinosaurs did. Furthermore, there is so far no evidence for noisemaking in pterosaurs, even though it's certainly not impossible.
Ichthyostega was not a landlubber. For example, it retained internal gills and was incapable of putting its feet on the ground right side down.
However, it certainly had a larval stage, even though there was no drastic metamorphosis, but only a gradual change. This is well documented in several temnospondyl species (with varying drastic-nesses of metamorphosis). External gills are also known from the neotenic lepospondyl Microbrachis. Bony "fish" also have larval stages (and no sharp metamorphosis).
So, we amniotes have moved the larval stage into the egg and no longer bother growing external gills and the tail fin.
The tadpole is an extreme development: a very early stage is lengthened and built upon with additions like the beak and the cover over the actually external gills (and the growing forelimbs).
Amphibians and amniotes are indeed almost* sister-groups -- but Ichthyostega was not an amphibian! And probably the temnospondyls weren't amphibians either, but that is an ongoing controversy.
* Solenodonsaurus and the diadectomorphs -- a total of maybe 10 species -- are even closer to Amniota. Unless the temnospondyls are amphibians; then that number rises dramatically.
DM: stop it with "buoyancy". Frogs and salamanders -- remember that newts are salamanders, too -- have no interest in extra buoyancy, and walruses have a vested interest in negative buoyancy.
DD: Frogs hop, float and vocalize because they separated buoyancy from respiration (as did apes), unlike salamanders. Walruses float asleep, dive awake.
DM: Also, apparently all saurischians had air sacs, and probably all dinosaurs did. Furthermore, there is so far no evidence for noisemaking in pterosaurs, even though it's certainly not impossible.
DD: All dinos had soft tissue air sacs in the throat region? Well, there were a lot of shallow seas, and I haven't heard that they had subcutaneous fat layers for thermosulation/buoyancy so it's possible. But I'm not talking about the sinuses in bones, just inflatable throat sacs.
Pterosaurs must have reduced their weight (as birds did). Water surface floaters require air or fat, flyers can't have much fat. Pterosaurs presumably had good vision and auditory senses, poor olfaction and gustatory senses, mating vocalizations would be expected, especially among arborealists.
[The following is from my blog]
Teeth & Armor Speculations
Introversion of external hair (armor) to internal "teeth"
Baleen whales (blue, humpback, right whales) developed their baleen (whalebone stringy teeth) on the upper jaw, because their fish & mollusc eating ancestors had had walrus-like mustache whiskers which gradually migrated from the upper lip into the upper gums (over a period of a million years), changing from nerve-rich sensory bristles to long net-like filters, straining krill and small fish while allowing water to escape the mouth. (This is one of my hypotheses, haven't seeen any confirmation from others.)
Extroversion of internal teeth to external scales (armor):
Lamphrey (and hagfish?) types lack jaws, but have replaceable teeth which are used to grasp. Is it possible that fish scales derived from multiple teeth replacing (like in sharks, but non-jawed) in a previously non-scaled lamphrey-like ancestor? Various fish scales do resemble teeth in some way, although many have become ultra-smooth for high-speed hydrodynamics. Do fish embryos develop their scales in a cephalo-caudal direction starting at the head? Do primitive scaled fish have more dental-like scales?
Is this a new idea, or has anyone heard of it before? (This is another hypothesis)
On that 'Harun Yahya' (actually Adnan Oktar) Atlas of Creation book, did anyone see the excellent Science quote concerning Kevin Padian's view...
LOL.
How come someone (no-one knows who) is able to put so much money and effort into a project like this? Where are all the rich, generous benefactors who are prepared to pour money into the production and distribution of books about real science? If they're reading this, I'm available :) [as are I-don't-know-how-many of my friends and colleagues].
Frogs don't always float; for floating you only need lungs, as you have surely often demonstrated yourself.
Why in the throat region? But cervical air sacs, along and inside the neck vertebrae, were present at least in most saurischians (birds are saurischians and still have them, except for those that are most heavily adapted to diving). And air sacs are always soft tissue.
Inflatable throat sacs don't leave evidence on bones. But, hey, frigatebirds have them...
...where no dinosaur except for birds has ever lived.
The bats still haven't done it.
Whether there were any arborealists is still not clear. But anyway, you can't use what is expected as evidence for another argument.
Likely. But it doesn't need to have been gradual. Just switch on hair growth on the palate, and there you are.
Possible, but heavily discussed, and I haven't followed the last few decades of the discussion. Note that the opposite direction -- scales on the mouth growing into teeth -- is also possible.
Wouldn't surprise me, because most embryonic development starts at the head. But here, too, there is no need for a gradual change; just switch on tooth growth all over the body instead of just in one narrowly confined region.
Sharks certainly do.
----------
Because cre_ti_nism in general, and Mr. Oktar in particular, is apparently a huge business in Turkey.
One rumour has it that all of the thousands of photos taken by other people were used without permission or license...a nice way to cut costs!
DM: Frogs don't always float; for floating you only need lungs, as you have surely often demonstrated yourself.
DD: Frogs can breathe (how much %?) through their skin, I can't. Throat air sacs keep the nose above water during nasal exhale, minimizing energy costs at rest. Humans with subcutaneous fat backfloat at rest without keeping their lungs air filled, the external nose at the highest point of the body, like sea otters.
DD: All dinos had soft tissue air sacs in the throat region?
DM: Why in the throat region?
DD: Throat sacs caused tail reduction in Hominoids and anurans, floating with nose uppermost.
DM: But cervical air sacs, along and inside the neck vertebrae,
DD: With cervical air sacs, would the nose be kept above water surface or not? If so, tail would be lost eventually, as in Hominoids and anurans. If not, then these air sacs were not for vertical flotation, but for some other purpose.
DM: were present at least in most saurischians (birds are saurischians and still have them, except for those that are most heavily adapted to diving). And air sacs are always soft tissue.
DD: Very pneumaticised animals with throat air sacs like birds do not indicate vertical flotation. Very non-pneumaticised animals with throat air sacs like frogs and Hominoids do indicate vertical flotation.
DM: Inflatable throat sacs don't leave evidence on bones. But, hey, frigatebirds have them...
DD: Both Lucy and Selam (A Afarensis) had laryngeal air sacs as do other hominoids (except vestiges in small gibbons and humans), indicated by the hyoid bones.
DD: Well, there were a lot of shallow seas
DM: ...where no dinosaur except for birds has ever lived.
DD: I don't know, lack data.
DD: Pterosaurs must have reduced their weight (as birds did).
DM: The bats still haven't done it.
DD: Flying foxes weigh the same as similar sized arboreals and terrestrials?
DD: mating vocalizations would be expected, especially among arborealists.
DM: Whether there were any arborealists is still not clear. But anyway, you can't use what is expected as evidence for another argument.
DD: True.
DD: Introversion of external hair (armor) to internal "teeth"
DM: Likely. But it doesn't need to have been gradual. Just switch on hair growth on the palate, and there you are.
DD: Example? Hair grows in the nose, but AFAIK not in the oral cavity, and never had before in ancestors. Baleen is evolutionarily recent, the baleen whale ancestors already had had wide separation between the mouth and blowhole, so it is unlikely that nasal hairs would form on the oral area of the palate IMO due to a genetic switch. Humans have everted lips, baleen whales have inverted lips.
DD: Extroversion of internal teeth to external scales (armor):
DM: Possible, but heavily discussed, and I haven't followed the last few decades of the discussion. Note that the opposite direction -- scales on the mouth growing into teeth -- is also possible.
DD: Possible but less likely, since teeth move from interior to exterior in sharks.
DD: Do fish embryos develop their scales in a cephalo-caudal direction starting at the head?
DM: Wouldn't surprise me, because most embryonic development starts at the head. But here, too, there is no need for a gradual change; just switch on tooth growth all over the body instead of just in one narrowly confined region.
DD: A switch requires a past successful selection for it in ancestors (genetic recipe). Gradual migration or expansion of denticles does not.
DD: Do primitive scaled fish have more dental-like scales?
DM: Sharks certainly do.
DD: yes.
"...How come someone (no-one knows who) is able to put so much money and effort into a project like this? Where are all the rich, generous benefactors who are prepared to pour money into the production and distribution of books about real science?..."
Being from the same country as the knob-headed Harun Yayha, I know that that book was printed through a very simple trade: Yahya's gang gave the printing press a villa to print x many copies. These guys have a sort of organization that's a cross between J. Edgar Hoover and Rasputin, they actively blackmail, engage in petty mafia-style affairs and even rip money off off people by collecting "Muslim Aid" style donations that, somehow, never-ever get to the needy.
Ancient amphibian imprints.
Look ma, no scales, scutes, feathers, hairs or denticles!
Most primitive fishes have heavy bony armour, bone appears to have evolved as a largely external structure initially, and only later been used to support the internal skeleton. While the very earliest chordates are not armoured, Anaspids, the line closest to the lampreys certainly were.
Frogs can, but not enough for all their needs. BTW, about 1 % of your breathing is done through the skin, too.
Bears, various cats, various bats... tail reduction is common among mammals.
The nose would be kept above the water surface anyway, and the air sacs were clearly for other purposes. At least the vast majority of birds has retained the cervical air sacs.
But frogs don't float vertically. They swim horizontally. Even when calling.
Reference, please.
Then start learning... anything about dinosaurs! Please. You need data first so you can build speculations on them.
Wouldn't surprise me. They clearly weigh more than a bird of the same size.
That's called stabilizing selection: mutations happen, but their carriers don't survive. Take that away and behold the diversity of homeotic mutations.
Tooth replacement isn't the same as the origin of teeth, and the tooth replacement mechanism of modern sharks is an innovation.
I don't understand what you mean. Any change in the phenotype requires selection to become established in a population (unless drift suffices).
Temnospondyl imprints.
Anurans: Throat sac buoyancy, vocal mate selection, no tail
Salamanders: no, no, long tail
Hominoids: Laryn. air sac buoyancy, vocal mate selection, no tail
Monkeys: no, no, mid to long tail
=======
DD: Throat sacs caused tail reduction and loss in Hominoids and anurans, floating with nose uppermost.
Both Lucy and Selam (A Afarensis) had laryngeal air sacs as do other hominoids (except vestiges in small gibbons and humans), indicated by the hyoid bones.
DM: Reference, please.
DD: will get the apith ones. You agree about the apes having them, right?
DD: Pterosaurs must have reduced their weight (as birds did).
DM: The bats still haven't done it.
DD: Flying foxes weigh the same as similar sized arboreal and terrestrial mammal relatives?
DD: Pterosaurs weighed the same as similar sized arboreal and terrestrial reptile relatives?
The hyoid of DIK-1-1 is only the second example in the hominin fossil record12, and this element was previously unknown for any species earlier than Neanderthals. Its similarities with Pan and Gorilla hyoids suggest that the bulla-shaped body is the primitive condition for African apes and humans, rather than the more shallow, bar-like body shown by modern humans and Pongo. The bulla-shaped body almost certainly reflects the presence of laryngeal air sacs characteristic of African apes24.
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from here.
I've put a link to this post and its successors up at Linnaeus' Legacy.
[from Darren: thanks Chris!]
{theropod} dinosaurs most closely resemble diving birds like penguins in the uncinate processes in breathing, I wonder if frogs (compared to salamanders) and humans (compared to typical monkeys) have any parallel to that.
No, almost all birds have uncinate processes. And so do crocodiles and the entirely terrestrial tuataras.
Nope. All lissamphibians have very short ribs (usually about as long as a vertebra), except for most frogs -- which have no ribs at all whatsoever. But then, they don't use their ribs or lack thereof for breathing movements. We have no trace of anything similar to uncinates.
Sorry I haven't replied to your earlier comment yet. Maybe in the weekend.
The nasal uncinate process in humans (part of the ethmoid bone) apparently isn't related to the mentioned uncinate process (see my link), but is related to respiration.
I meant parallel in the functional sense rather than in the morphological sense. Just for example, breath holding in different animals might use different bones, muscles, tissues but with the same functional parallel of apnea.