Tetrapod Zoology

i-2af017c2772b63886b8fff89d7d971cd-Waving_golden_frog_wikipedia_Jan-2010.jpg

South America has a diverse and well-studied toad fauna. The continent’s toads include some decidedly untoad-like taxa, such as the brightly coloured stubfoot toads or harlequin frogs. These remarkable little animals are superficially similar to the better known poison-dart frogs. What makes South America’s toads particularly interesting is that several of them occupy a basal position within bufonid phylogeny: in the phylogeny generated by Frost et al. (2006), Melanophryniscus, an Atelopus + Osornophryne clade, and Dendrophryniscus are all at the base of Bufonidae, while in Pramuk et al.’s (2008) phylogeny, Melanophryniscus, Atelopus, Nannophryne, Rhaebo and Dendrophryniscus are all at the base of Bufonidae. The paraphyly of these South American toads relative to all the others suggests that toads originated on the continent [waving Panamanian golden frog A. zetecki shown here; photo by Brian Gratwicke, from wikipedia].

Melanophryniscus, the South American redbelly toads, are an interesting little group, often mentioned in herpetology books because of their habit of contorting themselves such that their brightly coloured hands and feet and ventral surfaces are exposed when they’re threatened by predators. Other anurans with brightly coloured, toxic ventral surfaces (like fire-bellied toads) do this too: the distinctive, concave-backed posture they exhibit is termed ‘Unkenreflex’. Of the 24 currently recognised redbelly toad species, ten have been named since 2000. Some walk, others hop.

Stubfoot toads or harlequin toads

i-3626eeeaf68c55dcbd3ec2fa6684e554-Atelopus_spurrelli_Mauricio-Rivera-Correa_Jan-2010.jpg

One of the largest toad genera is the entirely South American Atelopus (86 species are known as of December 2009), the members of which are called harlequin or stubfoot toads, or clown frogs. The ‘stubfoot’ name comes from the fact that many of these toads really do have stumpy looking feet (though the hands are often long and slim). Some species are further unusual in possessing only four toes: a character seen elsewhere among Anura in some brachycephalids and in the African four-digit toads (Didynamipus). What’s more, some species exhibit intraspecific variation in digit number: in A. exiguus from Ecuador, five toes are normal, but some individuals have only four (Coloma et al. 2000) [image below shows intraspecific variation in pedal digital count in A. exiguus; from Coloma et al. (2000). The tiny element on the medial side is the prehallux]. Rather than hopping around, harlequin toads exhibit a distinctive ambling walk [photo of Condoto stubfoot A. spurrelli by Mauricio Rivera Correa, from wikipedia].

i-51c49a1ca0a78c5e962b0163ceb8163d-Atelopus-exiguus_pedal-digit-variation_Coloma-et-al-2000.jpg

In contrast to Bufo (sensu stricto) and other, more familiar, toad groups, the head is longer than it is broad in harlequin toads, and the snout is usually rather pointed, with the upper jaw overhanging the lower one. The tympanum and various other ear structures are absent in many species. Some – most notably the Panamanian golden frog A. zeteki [shown at top of article] – cannot communicate with sounds and use semaphore. For more on this see the Tet Zoo toad article on reproductive biology.

i-3b84583e833e37979338ebdfdb70a7d7-Savage-1972-variation-in-Atelopus-varius-Jan-2010.jpg

The best known Atelopus species are beautiful little animals. Among the better known species, the Harlequin frog, Veragoa stubfoot or Clown frog A. varius is wonderfully mottled with red and yellow-orange on a black background, while the Panamanian golden frog is (as the name suggests) golden yellow, for example [extent of variation inferred for A. varius by Savage (1972) shown above]. This colouring is aposematic: harlequin toads are highly toxic, with the skin secretions of a single Panamanian golden frog being potent enough to kill 1200 mice (Savage 2002). However, they’re not all brightly coloured: A. lynchi from Ecuador and Colombia (named in 1981) is brown and patternless, and other species might be too (these other species look brown in preservative, and might not have been so dull in life) [a dull individual of A. flavescens shown below (members of the species are normally more colourful: see comments); photo by Hugo Claessen, from wikipedia].

i-4be7dcb7c3d9c47d9e9da0e0074ef2f3-Atelopus_flavescens_Hugo-Claessen_Jan-2010.jpg

Many harlequin toads frequent montane streams. Their tadpoles are of the specialised, stream-dwelling sort and possess large abdominal suckers. Highly restricted ranges are typical within the group, and it’s been suggested that speciation within this group, particularly in the northern Andes, was driven by Pleistocene glaciation and orogenesis (Lötters & De La Riva 1998). Notably, the more widespread members of the group – like the Condoto stubfoot A. spurrelli and Veragoa stubfoot – are lowland species… though suggestions that these widespread ‘species’ might actually be species complexes consisting of more than one taxon complicate this otherwise tidy picture. As is the case with other speciose toad genera (most notably Bufo sensu lato), there’s a tradition of breaking down this large group into many smaller ‘species groups’, some of which do indeed seem to correspond to clades.

Plump toads, not all of which are plump

Osornophryne Ruiz-Carranza & Hernández-Camacho, 1976, sometimes called the plump toads, is apparently the sister-taxon to Atelopus. In fact the only plump toad species known prior to 1976 was originally included within Atelopus (another six species have since been named). Together with Frostius and some other South American taxa, plump toads are sometimes regarded as belonging to a toad group known as the atelopids or atelopines. A close relationship between Osornophryne and Atelopus appears intuitively unlikely, as the plump toads are – as their name suggests – pretty different in appearance from harlequin toads.

i-ef3192a9567bac80148514aad63c4186-Osornophyrne-Jan-2010-resized.jpg

Not only are plump toads, well, plump (though, ha ha, some species are not: adjacent image shows ‘plump’ O. bufoniformis vs gracile O. guacamayo; from Gluesenkamp (1995)), they’re usually said to have a reduced phalangeal formula (though read on) and extensively webbed hands and feet. The webbing has been suggested to be an adaptation ‘for locomotion on rocky and mossy crevices’ (Gluesenkamp 1995, p. 275), and, despite the webbing and reduced phalangeal formula, the digits are long and flexible in some species (specifically the strongly arboreal O. guacamayo). Having said that plump toads have a reduced phalangeal formula, the members of the genus are variable with regard to this feature, both intragenerically and (as in Atelopus) intraspecifically (Coloma et al. 2000).

Plump toads lack parotoid glands and auditory structures (tympanum, tympanic annulus and stapes), and the skin on their heads is firmly fused to the underlying bones. They’re also unusual in having only six or even five presacral vertebrae. The typical number for toads is eight: six presacrals are also present in the South American bush toads (Oreophrynella), but it isn’t yet clear whether this character is convergent or evidence of an affinity. Fusion of the atlas and axis is another unusual feature seen in plump toads, as is inguinal amplexus. While most plump toads are terrestrial, individuals of some species have been discovered at the bottom of stream beds, while others have been discovered in arboreal habitats.

Implications for origins?

Here ends our brief look at some of the most ‘stem-ward’ of living toads: we’ll look at more of them later. Besides indicating a South American origin for crown-toads, what might the taxa discussed here tell us about the earliest members of the crown-toad clade? Aposematic colours are seen in some of these taxa, as are specialisations towards life in cool, rocky environments like upland streams and gorges. However, other basal toad clades (like Rhaebo) aren’t like this, so (as far as I can tell) there’s no obvious indication that such things as aposematism or upland habitat choice were widespread among basal crown-toads.

And – unfortunately – the fossil record doesn’t tell us much either way, as fossil representatives of the lineages leading to redbelly toads, stubfoot toads and plump toads are currently unrecognised. This is despite the fact that these animals must have originated during or before the Paleocene.

More soon!

For previous articles in the Tet Zoo toads series see…

For previous articles on hyloid anurans see…

Refs – -

Coloma, L.A., Lötters, S. & Salas, A. W. 2000. Taxonomy of the Atelopus ignescens complex (Anura: Bufonidae): designation of a neotype of Atelopus ignescens and recognition of Atelopus exiguus. Herpetologica 56, 303-324.

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.

Gluesenkamp, A. G. 1995. A new species of Osornophryne (Anura: Bufonidae) from Volcán Sumaco, Ecuador with notes on other members of the genus. Herpetologica 51, 268-279.

Lötters, S. & De La Riva, I. 1998. Redescription of Atelopus tricolor from southeastern Peru and adjacent Bolivia, with comments on related forms. Journal of Herpetology 32, 481-488.

Pramuk, J. B., Robertson, J. B., Sites, J. W. & Noonan, B. P. 2008. Around the world in 10 million years: biogeography of the nearly cosmopolitan true toads (Anura: Bufonidae). Global Ecology and Biogeography 17, 72-83.

Savage, J. M. 1972. The harlequin frogs, genus Atelopus, of Costa Rica and western Panama. Herpetologica 28, 77-94.

- . 2002. The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago and London.

Comments

  1. #1 Dallas Krentzel
    January 4, 2010

    How do they come up with an estimate like: “the skin secretions of a single Panamanian golden frog [are] potent enough to kill 1200 mice (Savage 2002)”? I checked the Savage paper and searched for the word ‘mice’ and ’1200′ but couldn’t find anything about it. As someone who has worked in a pharmacology department, I’m not sure what is supposed to be meant by that statement, but I’m interested. Does that mean that if all of the venom was extracted from the toad there would be enough to ration out venom to 1200 mice at the LD50 dosage?

  2. #2 John Scanlon FCD
    January 4, 2010

    The yellow-green skin secretions of Osornophryne guacomayo are being investigated as a potentially tasty and nutritious condiment suitable for nachos or chips… (No, I just made that up)

    Happy 2010 to all!

  3. #3 Michael P. Taylor
    January 5, 2010

    So what happened to Amphocoelias part 2?

  4. #4 David Marjanović
    January 5, 2010

    I’m learning a lot here.

    So what happened to Amphocoelias part 2?

    Never mind the temnospondyls… :-)

  5. #5 tdh
    January 5, 2010

    In linguistics, colonies tend to be more conservative than their origins. For example, American English (especially Boston-Brahmin) is supposed closer in pronunciation to Revolution-era British English than is modern British English. It must be difficult to find intraspecific variation in the fossil record, but that ought to be a more reliable indicator of origins, absent older fossils.

  6. #6 Alan
    January 5, 2010

    If toads originated in South America, when and how did they disperse around the world? Given their worldwide distribution, if they only left when the Central American landbridge rose above sea level, they seem to have dispersed far and wide very quickly. Or is this apparent centre of origin an artifact of mass extinctions in Africa or other southern continents?

  7. #7 David Marjanović
    January 5, 2010

    For example, American English (especially Boston-Brahmin) is supposed closer in pronunciation to Revolution-era British English than is modern British English.

    In some respects, certainly. In others, the opposite is the case – B[a]ston-Brahmin has merged a lot of vowels into its otherwise ancient [a], and like most modern English Englishes it drops r except in front of vowels.

  8. #8 Andreas Johansson
    January 5, 2010

    So what happened to Amphocoelias part 2?

    It got eaten by a Tyrannophryne regina.

  9. #9 Bob Michaels
    January 5, 2010

    Frogs and toads don`t usually generate much excitement for me.They are all members of Anura. However,this class of vertebrates is most numerous with new species constantly being disovered. Would you say that tropical Frogs are more plentiful then Toads, as far as the number of species?

  10. #10 David Marjanović
    January 6, 2010

    Would you say that tropical Frogs are more plentiful then Toads, as far as the number of species?

    Define “frog” and “toad” first. The animals with common names that include these words don’t form separate clades, it’s completely chaotic.

  11. #11 Bob Michaels
    January 6, 2010

    David, I always felt that Toads are more land oriented, whereas Frogs were found in or about ponds & streams.
    Toads have stubbier bodies and shorter hind legs used for walking instead of hopping. Skin is wartier. I was told as a kid if you handle toads you would get warts.
    When i lived on Staten Island NY some 31 yrs ago my lawn had many Toads appear at dusk. Frogs on the other hand i observed at High Rock nature park croaking away in the pond. That`s my basic distinction. What`s yours?

  12. #12 Andreas Johansson
    January 6, 2010

    Tangential, but this should interest every tetrapod zoology fan:

    http://www.nature.com/news/2010/012345/full/news.2010.1.html

    Briefly, what appears to be tetrapod trackways are reported from strata some 18 Myr older than the oldest body fossils known.

  13. #13 Darren Naish
    January 6, 2010

    Thanks, Andreas. Here’s what I just posted on Ed Yong’s Not Exactly Rocket Science blog…

    Finally, mainstream support for Henderson’s hypothesis that Acanthostega and Ichthyostega were the secondarily aquatic descendants of earlier, more terrestrial tetrapods…

    Henderson, D. M. 1999. Late Devonian amphibians as secondarily aquatic tetrapods. In Hoch, E. & Brantsen, A. K. (eds) Secondary Adaptation to Life in Water. University of Copenhagen, p. 18.

    I’m not being entirely serious :)

  14. #14 David Marjanović
    January 6, 2010

    I always felt that Toads are more land oriented, whereas Frogs were found in or about ponds & streams.

    Toads have stubbier bodies and shorter hind legs used for walking instead of hopping. Skin is wartier.

    This kind of distinction will make you end up with artificial groups, as opposed to groups which each descend from a single common ancestor, and it’s difficult or impossible to figure out where to draw the line.

    What`s yours?

    I don’t make one. At best I might be caught using the term “true toads” for Bufonidae and “Real True Frogs” for Ranidae, but that means that some species with “frog” in their English names are in fact true toads (such as the Panamanian golden “frog” at the top of this page), some land-living species are true frogs (like the European grass frog or whatever Rana temporaria is called in English), and the vast majority of… uh… tailless limbed amphibians (tree”frogs”, poison-dart “frogs”, spadefoot “toads”, clawed “toads”, fire-bellied “toads”, and so on and so forth) are neither frogs nor toads.

    However, I use “frogs” as the cover term for all tailless limbed amphibians (Salientia) all the time. That means toads are frogs, too.

    Confused yet? :-)

    BTW, ` is the grave accent (àèìòù). You’re looking for the apostrophe: ‘.

    I’m not being entirely serious :)

    It’s hard to imagine internal gills and a complete tail fin, among other things, in a secondarily aquatic animal.

  15. #15 David Marjanović
    January 6, 2010

    …But… anyway… under your distinction frogs are much more diverse than toads, even though most live in the trees rather than in water, and even though a few of them (mentioned in the post) are in fact “true toads” (bufonids). Too cool how the species of Atelopus are variably called “harlequin toads”, “stubfoot toads”, “harlequin frogs” and “clown frogs”… :-)

  16. #16 Bob Michaels
    January 6, 2010

    Definition of Toads versus Frogs from the ” Encyclopedia of Animals A complete Visual Guide”
    Univ of Cal Press ISBN 0-520-24406-0
    Toads family ( Bufonidae) have short legs for hopping, dry warty skin and are terrestrial. Frogs( Family Ranidae) have long, slender legs for leaping great distances, moist skin, and are aquatic. The use of the term “Toad” depends on the region of the world you are in. in Africa, the smooth and moist- skinned aquatic Cape clawed frog ( Xenopus gilli) is called a clawed Toad.”

  17. #17 John Scanlon FCD
    January 6, 2010

    Bob M, does that encyclopaedia say that all anurans are either ranids or bufonids? That’s like thinking every person in the world lives in the UK or the US, or that all electromagnetic radiation is either yellow or green. Get over it, there are more interesting things in reality.

  18. #18 DD
    January 7, 2010

    “…Acanthostega and Ichthyostega were the secondarily aquatic descendants of earlier, more terrestrial tetrapods…” DN

    Yes, with early Tiktaalik-type as grandaddy of both ray fin fish and tetrapods. Pentadactyle condition is always primitive.

    “It’s hard to imagine internal gills and a complete tail fin, among other things, in a secondarily aquatic animal.” DM

    I don’t understand that. Fish with gas sac lungs /permeable skin can seal their internal gills and during seasonal drought of inland shallow seas can burrow/estivate/sleep allowing ossification of cartilage as part of respiration while inactive, unlike always mobile non-bony sharks.

    “..aquatic Cape clawed frog..” BM

    Cape clawed frog, Cape clawless otter… an odd match.

  19. #19 Dr. Nick
    January 7, 2010
    For example, American English (especially Boston-Brahmin) is supposed closer in pronunciation to Revolution-era British English than is modern British English.

    In some respects, certainly. In others, the opposite is the case – B[a]ston-Brahmin has merged a lot of vowels into its otherwise ancient [a], and like most modern English Englishes it drops r except in front of vowels.

    Actually, “Boston Brahmin” and certain other New England dialects are unusual in North America in not merging the “broad a” of “father” with the “short o” of “bother”. This, together with non-rhoticity (r-dropping) and the shift of /æ/ to /a/ (“broad a”) before voiceless fricatives and in certain other environments, contributes to the perception of this dialect as “British English”-like and therefore archaic.

  20. #20 Dartian
    January 7, 2010

    DD:

    Cape clawed frog, Cape clawless otter… an odd match.

    Or so they may seem to an English speaker. In Afrikaans, for example, these two species’ names are kaapse platanna and groototter, respectively…

  21. #21 David Marjanović
    January 7, 2010

    Definition of Toads versus Frogs from the ” Encyclopedia of Animals A complete Visual Guide”

    See, Xenopus is neither a bufonid nor a ranid. It’s a pipid.

    Yes, with early Tiktaalik-type as grandaddy of both ray fin fish and tetrapods.

    <headdesk>

    No, Tiktaalik is more closely related to the tetrapods than most other sarcopterygians are – including the coelacanths, the lungfishes and porolepiforms, Eusthenopteron, Panderichthys, and lots more.

    Pentadactyle condition is always primitive.

    You’re making that up.

    Fish with gas sac lungs /permeable skin can seal their internal gills and during seasonal drought of inland shallow seas can burrow/estivate/sleep

    You do know that most lungfishes lack gills…?

    allowing ossification of cartilage as part of respiration

    ??? ??? ???
    ??? ??? ???
    ??? ??? ???

    always mobile non-bony sharks

    Have you never seen a reef shark sleep on TV? Only a small clade of big pursuit hunters like the great white shark have to stay mobile to breathe. They are the exception among sharks, not the rule.

  22. #22 Sven DiMilo
    January 7, 2010

    allowing ossification of cartilage as part of respiration while inactive

    ??? ??? ???

  23. #23 David Marjanović
    January 8, 2010

    have to stay mobile to breathe

    Argh! Moving, not simply mobile.

  24. #24 DD
    January 8, 2010

    That’s interesting about the plump toads having webbing ‘for locomotion on rocky and mossy crevices’.

    on primitive 5 digits: echinoforms have 5 arms
    land snails have 4 tentacles & 1 radula = 5
    squid have 8 arms and 2 long thumbs = 10
    hexapods have 3 legs + 2 wings x 2 = 10
    crabs have 8 digits/legs and 2 claws = 10
    bilateral biaxial pentadactyle tetrapods have
    2 sets of 5 digits x 2 = 20
    The tree of life is rooted in pentameric symmetry AFAICT.

    Acanthostega is claimed to have interdigital webbing, but triangular toe prints show scaley skin not supple webs, so large forms would be expected to derive duplicated digits for broader/better support/traction in mud/water/sand.
    A. may have had an internal gill chamber:
    http://www.jstor.org/pss/4096912

    “One of the earliest Carboniferous tetrapods known is Casineria. No small tetrapods are known from the Devonian, but during Romer’s Gap tetrapods evolved into a number of small terrestrial forms like Casineria, and the pentadactyl limb first appeared. Evolution of small size might have been one of the possible responses to low atmospheric oxgyen, by exploiting the advantages of a favorable surface to volume ratio for an animal that retained some dependence on cutaneous gas exchange.” wiki: casineria

  25. #25 Cameron
    January 8, 2010

    DD (#24):

    The tree of life is rooted in pentameric symmetry AFAICT

    I don’t think you mean a compound intermediate between a monomer a polymer with 5 subunits – I assume you mean pentamerous? You need examples from outside of Animalia to conclude that the tree of life as a whole is “rooted” in this trait. The only clade which has this sort of symmetry, Echinodermata, undergoes a body-axis shift and torsion to acquire a pentamerous body plan from a typical bilateral one. Echinoderms are also not perfectly symmetrical, clearly visible externally in the madreporite of sea stars, and can have a number of arms greater than, and even not divisible by, 5.

    on primitive 5 digits

    In crown-group tetrapods, yes. However, digits aren’t exactly symmetrically arranged.

    land snails have 4 tentacles & 1 radula = 5

    It would make much more sense of the structures were homologous.

    squid have 8 arms and 2 long thumbs = 10

    Thumbs? Cephalopods as a whole, possibly even nautili (long story), may have had 10 appendages as a plesiomorphy.

    crabs have 8 digits/legs and 2 claws = 10

    Why only count the pereopods in decapods? Look up “Decapod anatomy” in Wikipedia, not a whole lot of 5′s coming up there.

    hexapods have 3 legs + 2 wings x 2 = 10

    “Hexapod” is not synonymous with “Insect”.

  26. #26 David Marjanović
    January 9, 2010

    on primitive 5 digits: echinoforms have 5 arms

    These aren’t digits. Not even anywhere near. Even on the Hox gene expression level they’re not comparable.

    land snails have 4 tentacles & 1 radula = 5

    How many legs does a dog have if you call the tail a leg? Four. Calling the tail a leg doesn’t make it a leg.
    – ascribed to Abraham Lincoln

    squid have 8 arms and 2 long thumbs = 10

    Each of them consisting of a pair of primordia that fuse in the embryo.

    Really basal molluscs lack all that stuff, of course.

    hexapods have 3 legs + 2 wings x 2 = 10

    Early Carboniferous ones had 3, not 2, pairs of wings.

    And why do you count the walking legs but not the jaws, antennae, and so on? These are arthropods you’re talking about.

    crabs have 8 digits/legs and 2 claws = 10

    Same again. Also, isopods (wood lice) walk on 7 leg pairs.

    The tree of life is rooted in pentameric symmetry AFAICT.

    First of all, all your examples are triploblastic animals. “Life” my ass.

    Secondly, as demonstrated above, what you’re doing isn’t science, it’s numerology – you’re trying to find the number 5 somewhere, anywhere, with no regard for homology even in basic gene expression.

    Acanthostega is claimed to have interdigital webbing, but triangular toe prints show

    No footprints are known to have been made by Acanthostega.

    A. may have had an internal gill chamber

    It clearly did.

    a number of small terrestrial forms like Casineria

    We don’t know if it was terrestrial or amphibious.

    Echinoderms are also not perfectly symmetrical, clearly visible externally in the madreporite of sea stars, and can have a number of arms greater than, and even not divisible by, 5.

    There are sea stars with 14 arms.

    The only clade which has this sort of symmetry, Echinodermata, undergoes a body-axis shift and torsion to acquire a pentamerous body plan from a typical bilateral one.

    In ontogeny, that is.

  27. #27 Christopher Taylor
    January 9, 2010

    Early Carboniferous [insects] had 3, not 2, pairs of wings.

    Couldn’t let this one past, sorry. The first pair of “wings” in supposedly six-winged insects were expanded pronota (lateral extensions of the prothorax). They weren’t wings as they were fixed in place, not articulated like wings.

  28. #28 David Marjanović
    January 10, 2010

    But homologous to wings. And to the gill part of a biramous limb.

  29. #29 Cameron
    January 10, 2010

    In ontogeny, that is.

    Which appears to recapitulate their phylogeny

    Smith AB. 2008. Deuterostomes in a twist: the origins of a radical new body plan. Evolution & Development 10(4), 493-503.

  30. #30 Christopher Taylor
    January 10, 2010

    But homologous to wings. And to the gill part of a biramous limb.

    Maybe homologous to wings (in the sense of serially homologous, and serial homology is pretty significant for arthropods), but it all depends on the still highly vexed question of how insect wings originated. Definitely not homologous to leg exites, though. Pronota are extensions of the tergite (the dorsal body plate), not of the legs.

  31. #31 David Marjanović
    January 11, 2010

    in the sense of serially homologous

    Oops, yes, of course.

    Definitely not homologous to leg exites, though. Pronota are extensions of the tergite (the dorsal body plate), not of the legs.

    Gene expression sez they’re homologous nonetheless, surprising as that is.

  32. #32 Christopher Taylor
    January 11, 2010

    Gene expression sez they’re homologous nonetheless, surprising as that is.

    I’ll grant you that one. However, I’ve come to wonder whether the gene expression patterns represent co-option rather than true homology, in the same way that some of the same genes are involved in eye and leg development in chordates and arthropods, despite the almost certain absence of both in the common ancestor of the two.

    Dammit, I think I’m going to have to do a proper post at my own site about insect wing origins.

  33. #33 David Marjanović
    January 11, 2010

    The genes involved in limb development in vertebrates and arthropods are involved in all body outgrowths (in vertebrates at least): limbs, hair, scales, feathers, teeth, taste buds… Looks like the last common ancestor had some kind of body outgrowth, even if that just means the “corners” of a flatworm.

    The eyes probably are homologous at the most basic level. (A very basic one, considering the rhabdomeric photo receptors in the eyes of arthropods and certain nerve cells in the retina – but not the actual photoreceptor cells – in vertebrates.)

  34. #34 DDeden
    February 7, 2010

    Due to quake (6.5, 5.9) & storm translocations, I’m busy, so briefly: penta-mer-ic/ous/al aka pentadactyle aka 5 digit symmetry is basal to all life which undergoes spheroidal stages (egg/seed/spore etc.) including viruses & bacteria AFAICT. 14 legged sea stars are derived just as centipedes are derived from initial pentaforms. Snail tentacles & radula are feeding-assistive appendages, the radula derived from the primal GI trapdoor/sphincter, as did the thumb-mandible-tongue complex. Gene expression interpretation (Hox genes) is still in its infancy. Not sure, but insect wings may be equivalent to interdigital webbing between digits rather than to actual legs, explaining why adult (basal winged) insects/crustaceans don’t have external soft skin tissue, unlike mollusks and early insect larvae (parallel to naked-skin webbed toads vs never-fully-naked webbed birds). DD “echinoforms have 5 arms/digits” DM “These aren’t digits.” Yes, they are, change your perspective 90 degrees, they surround the GI ‘tube’ in the common fashion, but lack the derived trap-door thumb, relying instead on internal GI hydraulic musculature, thereby freeing the digits for locomotion and prying of bivalve mollusks. Cameron: “The only clade which has this sort of symmetry, Echinodermata, undergoes a body-axis shift and torsion to acquire a pentamerous body plan from a typical bilateral one.” If it can’t feed, it is a free-swimming but not free-living embryo. Pentamer = feeding capability, the 5 digits as feeding/breathing appendages.

  35. #35 David Marjanović
    February 7, 2010

    Gene expression interpretation (Hox genes) is still in its infancy.

    No.

    Your knowledge about the current knowledge of development genetics is in its infancy.

    That’s called the Dunning-Kruger effect: you don’t know, and you don’t even know that you don’t know, so you merrily make arguments from ignorance without noticing — and without noticing that not everyone knows as little as you.

    Not sure, but insect wings may be equivalent to interdigital webbing between digits rather than to actual legs,

    Completely and utterly wrong.

    explaining why adult (basal winged) insects/crustaceans don’t have external soft skin tissue, unlike mollusks and early insect larvae (parallel to naked-skin webbed toads vs never-fully-naked webbed birds).

    Do you know what a cuticle is?

    All arthropods have one, at all stages of life from before hatching.

    You have never seen an insect’s skin. It is never exposed to the environment.

    DM “These aren’t digits.” Yes, they are

    No, they’re not, and this isn’t a matter of perspective! It’s a matter of homology!!!

    <headdesk>

    I have enough. Go to your nearest university library, crack open 5 books on animal anatomy and on development biology, spend a couple of days reading them, and then come back.

  36. #36 Cameron
    February 7, 2010

    Pentamer = feeding capability, the 5 digits as feeding/breathing appendages.

    In the immortal words of Liz Lemon: “what the what?”

  37. #37 Nathan Myers
    February 9, 2010

    I think I’m going to have to do a proper post at my own site about insect wing origins.

    Please, please do.

  38. #38 Dartian
    February 9, 2010

    Nathan:

    Please, please do.

    He did.

  39. #39 DDeden
    February 14, 2010

    DD: “allowing ossification of cartilage as part of respiration”
    DM & Sven: ??? ??? ???
    DD: see links at my blog: http://the-arc-ddeden.blogspot.com/2010/02/interim.html

    It is all connected, non-bony sharks don’t sleep like bony fish metabolically and do not excrete calcium carbonates (byproduct of bone formation) which has resulted in moderated pH of seawater. Not coincidentally, human freedivers can fill their naso-sinus and middle ear cavities with this balanced pH seawater in order to avoid gas equalization of their pneumatic sinuses repeatedly while deep cyclical forage-diving.
    DM: “No.”
    DD: Far more yes than no, but it is evolving, thankfully.

  40. #40 David Marjanović
    February 14, 2010

    From the press release you quote:

    This calcium carbonate is being produced by bony fish, a group that includes 90% of marine fish species but not sharks or rays. These fish continuously drink seawater to avoid dehydration. This exposes them to an excess of ingested calcium, which they precipitate into calcium carbonate crystals in the gut. The fish then simply excrete these unwanted chalky solids, sometimes called ‘gut rocks’, in a process that is separate from digestion and production of faeces.

    This is copied & pasted from your blog.

    It’s not a byproduct of bone formation (how actually could it be?), it’s a byproduct of the teleost method of osmoregulation. Water seeps out through the skin of those animals, so they need to drink. Drinking gives them a higher intake of salt and calcium than needed. They excrete the excess salt through the gills and the excess calcium through the gut.

    Chondrichthyans and coelacanths don’t lose water. Their body fluids have the same osmotic pressure as seawater, so they don’t lose water and don’t need to drink. Instead of salt, their body fluids contain urea.

    You don’t even mention a connection to cartilage (or the absence of dermal bone) in your blog post, and I can’t imagine where any might come from.

    Finally, bone isn’t calcium carbonate, it’s mostly calcium phosphate. I’m not sure if you know this.

    Not coincidentally, human freedivers can fill their naso-sinus and middle ear cavities with this balanced pH seawater in order to avoid gas equalization of their pneumatic sinuses repeatedly while deep cyclical forage-diving.

    What does respiration have to do with any of this?

  41. #41 DDeden
    February 14, 2010

    When I said ‘bone formation’, I include bone maintenance as mineral storage depot, as in vertebrates, not just the initial fetal bone growth. No CaCO3 isn’t bone (~CaPO4x), it accretes in mollusc shells; while sponges accumulate silica/carbonate skeletons, in teleosts CaCO3 is excreted and CaPO4 is accreted primarily during static sleep, a gravitational differential is required (astronauts in microgravity lose bone) so teleosts have buoyant air sacs.

    “Respiratory surfaces such as the alveoli of the lung, and gills in aquatic animals also serve in osmoregulation and excretion. Respiratory surfaces are the chief avenues for the excretion of carbon dioxide and metabolic water, as well as other gaseous wastes, in animals”
    http://www.cartage.org.lb/en/themes/sciences/zoology/animalphysiology/osmoregulation/osmoregulation.htm

    An animal awake/mobile has efficient respiration, but a static/sleeping animal accumulates H+ ions due to low O2 high CO2 resulting in acidosis at the alveolar/gill fringes; CaCO3 and CaPO4 are buffering agents in sleep respiration AFAICT, resulting in bone and gut rocks rather than cartiligous skeletons. Why are there no cartiligous terrestrial fauna? Because they can’t breathe while sleeping IMO.

  42. #42 David Marjanović
    February 15, 2010

    a gravitational differential is required (astronauts in microgravity lose bone) so teleosts have buoyant air sacs.

    <sigh>

    No, what’s required is force. Bone has a mechanical function, and when that function isn’t needed, the bone is destroyed because it’s not necessary to maintain it. In humans, one of those functions is to keep the body from collapsing; that can’t happen without gravity, so lack of gravity results in bone reduction.

    The swim bladder, on the other hand, functions so as to give the fish the same overall density as the water it is in, regardless of the depth. The very “purpose” is to make the fish immune to gravity! Bone is nonetheless maintained not just as a mineral reservoir but also to make sure that the muscles end up moving the body instead of just bending it.

    Same thing: mechanical function: resistance to pressure. Gravity has nothing to do with it, except in those cases where it generates pressure.

    “Respiratory surfaces such as the alveoli of the lung, and gills in aquatic animals also serve in osmoregulation and excretion. Respiratory surfaces are the chief avenues for the excretion of carbon dioxide and metabolic water, as well as other gaseous wastes, in animals”

    Yes, and?

    An animal awake/mobile has efficient respiration, but a static/sleeping animal accumulates H+ ions due to low O2 high CO2 resulting in acidosis at the alveolar/gill fringes

    If it breathes too little, which I wager it doesn’t. See also below.

    CaCO3 and CaPO4 are buffering agents in sleep respiration AFAICT

    Then why aren’t they in the blood? The blood is what’s extremely sensitive to changes in pH (too acidic, and it turns to cottage cheese). Why is the CaCO3 excreted instead and the CaPO4 locked away?

    There are indeed mono- and dihydrogen phosphate ions in the blood. They function as a buffer against pH changes. I bet sharks have that, too.

    Why are there no cartil[agin]ous terrestrial fauna? Because they can’t breathe while sleeping IMO.

    This is fractally wrong: no matter how closely you look at it, it’s still wrong.

    First of all, only a few species of ocean-cruising sharks cannot breathe when they don’t move. All other cartilaginous vertebrates actively ventilate the gills. Have you never seen a reef shark sleep on TV? It lies on the ground and moves the skin around its gill slits, inhaling through the spiracle and exhaling through the (other) gill slits.

    The ocean-cruisers were already moving all the time anyway, so they don’t need to actively ventilate their gills and have got away with losing this ability.

    So, breathing isn’t the reason why there are no terrestrial chondrichthyans. Instead, terrestrial vertebrates need a robust limb skeleton and a robust vertebral column that can withstand the pressure generated by gravity. That requires serious amounts of bone. Calcified cartilage – often found in chondrichthyans – probably isn’t enough, and if it were, the tetrapods got to land first anyway, so the question is moot… :-)

  43. #43 DDeden
    February 15, 2010

    Youtube: Bouncing toad vs spider, woodpecker vs snake
    http://www.dormivigilia.com/?p=1147

    DM: “That requires serious amounts of bone.”
    Which requires more ‘serious’ bone, a seacow or sauropod? Why?

  44. #44 DDeden
    February 16, 2010

    Shark teeth contain CaPO4, shark eye pupils dilate unlike teleosts, spiracle-breathing resting reef sharks visually track divers’ movements (through nictating membranes) so not deep sleeping, AFAIK no sharks engage in deep sleep. Serotonin (among other functions) in brain is involved in sleep/mood, serotonin in gut is involved in bone degrading via blood platelets at bone receptor sites, not sure how that fits with pH but deep sleep requires energy-efficient respiration and acidosis in blood triggers SCN via chemoreceptors to breathe, any positive ions in the blood might interfere with that so mineral depots (marine shark teeth, terrestrial bone) may be required.

  45. #45 David Marjanović
    February 16, 2010

    serotonin in gut is involved in bone degrading via blood platelets

    What? How does that hormone get into the gut, how does it act on either blood platelets or bone when it’s in the gut, and what do blood platelets have to do with bone? They’re not osteoclasts. Did you mean macrophages?

    not sure how that fits with pH

    It doesn’t. You’re trying to see a pattern where there is none.

    deep sleep requires energy-efficient respiration

    Which sharks have when at rest, with the exception of a handful of ocean-cruising species! How often do I need to repeat this! The Great White is an oddity among sharks, it’s not the normal state of affairs!!!

    any positive ions in the blood might interfere with that so mineral depots (marine shark teeth, terrestrial bone) may be required

    As I already said: there’s phosphate in the blood anyway.

    Which requires more ‘serious’ bone, a seacow or sauropod? Why?

    The former, because it has large lungs that can’t be collapsed and nonetheless needs to have the same density as water. This doesn’t apply to anything but tetrapods (not even lungfish, AFAIK — their lungs are smaller).

    Whales have osteoporotic bone, very spongy, and are capable of suffocating under their own weight on land. They can collapse their lungs, so they don’t need extra ballast.

    Eusthenopteron had a very, very thin bone cortex and a huge spongiosa (Laurin et al. 2007). Like a whale with a film of solid bone on.

  46. #46 Owlmirror
    February 16, 2010

    You’re trying to see a pattern where there is none.

    Biological apophenia?

  47. #47 DDeden
    February 16, 2010

    DM: What? DD: http://www.sciencenews.org/view/feature/id/43994/title/Serotonin_What_the_gut_feeds_the_bones

    DM: So, breathing isn’t the reason why there are no terrestrial chondrichthyans. Instead, terrestrial vertebrates need a robust limb skeleton and a robust vertebral column that can withstand the pressure generated by gravity. That requires serious amounts of bone.

    DM: The former (seacow), because it has large lungs that can’t be collapsed and nonetheless needs to have the same density as water.

    DD: So breathing isn’t significant, but non-collapsable lungs are significant. What is the difference? Fish have air sacs, bone and deep sleep; seacows and turtles have lungs, bone and deep sleep, sharks have none of these. Do pollywogs have deep sleep, or do only adult (bony) frogs sleep and “hibernate” during drought/winter?

  48. #48 DDeden
    March 21, 2010

    For ease of comprehension, see my comments here:

    http://www.lucasbrouwers.nl/blog/2010/03/on-the-origin-of-animals/

  49. #49 David Marjanović
    March 22, 2010

    http://www.sciencenews.org/view/feature/id/43994/title/Serotonin_What_the_gut_feeds_the_bones

    Thanks, that’s interesting, and was news to me.

    But why did you mention it in the context of sleep? Serotonin doesn’t even pass through the blood-brain barrier.

    So breathing isn’t significant, but non-collapsable lungs are significant.

    No, lungs have nothing to do with sleep! Animals that breathe through lungs, dive, and can’t collapse their lungs need pachyostosis/osteosclerosis to stay down!

    Fish have air sacs

    Deep-sea ones don’t.

    sharks have none of these

    For the at least third time, all sharks except two or three freaks – pelagic cruising specialists like the great white – have deep sleep! They lie on the bottom to sleep! Have you never even seen that on TV!

    <sigh>

    Do pollywogs have deep sleep

    Probably, but I don’t know.

    http://www.lucasbrouwers.nl/blog/2010/03/on-the-origin-of-animals/

    At least leave the poor viruses out of it. Their shape is determined by things like electrostatic attraction… the coat of a virus is basically a crystal.

  50. #50 DD
    April 27, 2010

    Melatonin (sleep control) is derived from serotonin in the skull, bone is derived from serotonin in the gut. Deep sleep/REM/dreams somehow relate to bone formation via respiration, IMO.

  51. #51 David Marjanović
    April 28, 2010

    Deep sleep/REM/dreams somehow relate to bone formation via respiration, IMO.

    Why, when they have nothing in common except the same substance being produced in two totally different places in the body? Again, serotonin can’t pass the blood-brain barrier.

  52. #52 Peter Mudde
    August 27, 2010

    On Atelopus-toads..
    I am sorry to emntion that Atelopus toads are among those which suffer the most from the worldwide Chytrid infections killing off Anura.. A lot of those 86 species haven’t been seen since the 1990′s.. In Costa Rica Alelopus varius was a rather comon species -I have been walking along a small creek near Monteverde where you could se a male every five meters or so – but since 1990 there are only rumours of it being found.
    In teh Guyanan lowlands species seem to be quite safe. But I have to disagree about Atelopus flavescens. They can be a bright golden yellow with a beautiful salmon red belly. The one on the picture happens to be a bit dull, being brown instead of orange or yellow on its back.