First of all, here are some temnospondyls. This composite image was compiled by repositioning the reconstructions provided by DeFauw (1989): looks neat, doesn't it?
So, I recently returned from the 69th Society of Vertebrate Paleontology meeting, this year held in Bristol, UK: in other words, OUTSIDE OF NORTH AMERICA for the first time ever. It was combined with another meeting I normally attend, SVPCA (Symposium on Vertebrate Palaeontology and Comparative Anatomy), but I think that people sometimes forgot about this. The meeting was enormous and the sheer quantity of talks and posters, and people to meet and catch up with, was overwhelming. By necessity, sessions ran in parallel and - because I generally attended Mesozoic-, archosaur- and squamate-themed sessions - I missed everything on non-amniotes and synapsids. Together with Mike P. Taylor and Matt Wedel, I presented the poster 'Extant animals provide new insights on head and neck posture in sauropods' (oh, you mean you can get 'old insights' too?). It went down a storm and people seemed to like it [below: me with the poster. I don't have a good pic showing all three SV-POWsketeers posing with the poster, unfortunately]. More on it later, either here or at SV-POW! (which is soon approaching its second birthday by the way). Anyway, I'd like to discuss SVP stuff but I can't, so here's something completely different.
One of the people I met for the first time at the meeting was the legendary David MarjanoviÄ. One thing led to another, and here we are, back with the temnospondyls. I wrote this text in 2007 and was planning to complete the entire series before Tet Zoo-ing it. In the end, I've decided to publish and be damned, and to post the bits that look 'complete enough'. Have made a few attempts to incorporate two additional years of references, but please do tell me if I've missed anything and I'll then update the text. For the background and intro stuff you'll need to see Temnospondyls the early years (part I) and Temnospondyls the early years (part II), both of which were recently tinkered with and added to Palaeos [here and here], with my permission) .
Euskelians vs limnarchians
'Higher' temnospondyls (by which I mean those temnospondyls other than the edopoids and so on discussed in my previous articles) fall into two major clades, and in a large analysis of temnospondyl affinities published in 2000 Adam Yates and A. Anne Warren formerly named these Euskelia and Limnarchia. Euskelia means something like 'well limbed' and refers to the fact that members of this group typically possess well ossified limb bones that sport prominent crests and processes for muscle attachment (Euskelia was phylogenetically defined (Yates & Warren 2000, p. 85) as the stem-based clade that includes all those taxa closer to Eryops than to Parotosuchus*) [in adjacent image, the well ossified Eryops forelimb on the right represents Euskelia, while the poorly ossified Mastodonsaurus forelimb on the left represents Limnarchia. Image from Schoch (1999)]. Limnarchia means 'marsh ruler': the name refers both to the longevity of this clade (it is unique in making it into the Jurassic and Cretaceous) and the aquatic adaptations present in many of its members. Limnarchia was phylogenetically defined as the stem-based clade that includes all taxa closer to Parotosuchus than to Eryops (Yates & Warren 2000, p. 87). More recent phylogenies (see supertrees in Ruta et al. 2003, 2007), while supporting the division of 'higher' temnospondyls into Euskelia and Limnarchia, have found some of the clades thought by Yates & Warren (2000) to belong to Limnarchia (notably Dvinosauria) to fall outside of the Euskelia-Limnarchia clade [image below shows Ruta et al.'s (2007) temnospondyl supertree. You can't see all the names of course, but just look how many clades there are in this major radiation].
* A capitosaurian stereospondyl. Stereospondyli is a large and diverse mostly Mesozoic limnarchian temnospondyl clade.
Euskelians can be united on the basis of their broad postparietal bones, by the presence of a distinct articular surface for the radius on the humerus, and by many other characters: as a rough generalization, they were terrestrial animals with robust limbs. As always there were exceptions, and some members of the clade were aquatic. Yates & Warren (2000) found Euskelia to consist of two clades: Dissorophoidea and Eryopoidea. In this article we're going to look at just a few of the dissorophoids: the remaining dissorophoids, and the eryopoids, will be looked at later. There really are that many temnospondyls: it's shocking (I thought about writing 'schochking' but that seemed really lame. It's an in-joke).
Dissorophoids: body armour and 'flat porcupines'
Dissorophoids are most often represented in the literature by Cacops from the Permian of Texas. It was about 40 cm long and had a row of armour plates that grew in a line along the length of its back [reconstructions of Cacops are shown here: the one above is by John Sibbick, the one below is by Samuel Williston]. Cacops belongs to the Dissorophidae, a dissorophoid clade known from North America and Russia and with a range extending from the Upper Carboniferous to the Upper Permian. Their diagnostic median armour (sometimes presumed to afford protection from predators, or to provide support for trunk musculature), combined with their stout, well ossified limbs, absence of lateral-line canals and other features, indicates that that they were terrestrial. Their otic notch is sometimes enclosed by bone on all sides and almost certainly housed a tympanum - an ear drum - that was used in terrestrial hearing.
In Cacops and similar forms the median armour plates were fused to the tops of the neural spines, and in some dissorophids the spines became elongate, the distinctive sculpturing at their tips apparently representing the original armour scute. Hyper-elongate spines, presumed to have formed a sail-like structure superficially similar to that of the synapsid Dimetrodon, were present in Platyhystrix and Astreptorhachis. Though it has been argued that these taxa should be separated from the dissorophids and awarded their own 'family', the Platyhystricidae, this is not useful given that there are intermediate forms with mid-length neural spines, such as Aspidosaurus. What these animals did with their long neural spines is not known. Contrary to what it says in some popular books there is no indication that the spines were associated with the high degree of vascularisation needed for a thermoregulatory role, and Vaughn (1971) thought that they probably initially evolved to provide mechanical support during terrestrial locomotion [adjacent Platyhystrix reconstruction by Arthur Weasley].
Closely related to dissorophids were the amphibamids (here taken to include the micropholids, following Schoch & Rubidge 2005). Characterized by particularly short, undifferentiated ribs, strongly reduced palatal bones and other characters, amphibamids were less than 40 cm long and had proportionally large, robust limbs and short tails. Restorations of amphibamid species were produced by Daly (1994) in her description of the new Carboniferous taxon Eoscopus lockardi: her drawings (two of which are shown here: they depict Eoscopus lockardi with Amphibamus lyelli below) make the animals look something like big-headed, scaly-skinned, short-tailed salamanders, though different species differ in how long their legs appear.
Within some amphibamid species there is a large amount of variation in skull shape, with small individuals being far shorter-snouted than large individuals. Lateral-line canals were absent and in the large basal amphibamid Micropholis from Lower Triassic South Africa, the limb proportions are suggestive of competent terrestrial abilities [skull of Micropholis shown here, from Boy (1985)]. Some amphibamids (Amphibamus and Doleserpeton) were tiny, and exhibited a suite of peculiar features: very thin skull bones, proportionally huge orbits and huge palatal vacuities, and skull bones in which the external sculpture is poorly developed. These forms also possess pedicellate teeth: this is the tooth type characteristic of living amphibians (the tooth crown sits on a flexible base composed of uncalcified fibrous tissue). Micropholis lacked pedicellate teeth and the other mentioned characters (Schoch & Rubidge 2005).
The closely related trematopids (previously referred to by some as trematopsids) were more conservative, and were mostly restricted to the Late Carboniferous and Early Permian of the USA (a German member of the group was reported in 1998 and a Czech one more recently). Strongly adapted for terrestrial life, one of their most distinctive features is a relatively enormous, bizarrely elongate external nostril, the function of which remains unknown: Bolt (1974) suggested that it may have housed a salt gland [skull of the trematopid Phonerpeton from the Lower Permian of Texas shown here, from Dilkes (1990)]. Trematopid vertebrae were well ossified and the trunk region was covered by small, non-overlapping bony scutes in some species at least (like Anconastes vesperus from Late Carboniferous New Mexico). Trematopid skulls are also distinctive in that the otic notch is long and slit-like. In Acheloma, the notch is so small that the tympanum within the notch (assuming, that is, that it was present) would apparently have been too small to function effectively in the transmission of airborne sounds (Dilkes & Reisz 1987). Schoch & Rubidge (2005) found trematopids to be more basal within Dissorophoidea than were dissorophids and amphibamids.
Return to the water: neotenic micromelerpetontids (or not)
While - as noted earlier - euskelians were generally terrestrial animals, a few dissorophoid groups were secondarily aquatic. Long known informally as branchiosaurs, these rather small, salamander-like forms were sometimes regarded as the larvae of large-bodied temnospondyls. Indeed some 'branchiosaurs' have turned out to be the larvae of certain limnarchians, but the others represent two distinct, apparently neotenic dissorophoid clades: Branchiosauridae and Micromelerpetontidae.
Micromelerpetontids are known from the Upper Carboniferous and Lower Permian of Europe and only three genera are known: Limnogyrinus, Micromelerpeton [shown above, from here] and Branchierpeton. All are long-bodied with short limbs. Larval micromelerpetontids were tiny animals (less than 10 cm long) with poorly ossified skeletons and large external gills, but even in adults, lateral line canals and short external gills persisted, so they too were predominantly aquatic (Witzmann & Pfretzschner 2003). 'Large' micromelerpetontids (with skulls nearly 50 mm long) exhibiting features typical of a terrestrial lifestyle have been reported from Germany, and the question remains as to whether these represent primitive members of the group, or advanced forms that have switched from an aquatic lifestyle back to terrestriality, or simply the adults of the smaller aquatic forms.
If we ignore these large, terrestrial forms for the time being, the broad, short micromelerpetontid snout suggests that they were aquatic suction feeders, and they probably preyed on invertebrates, small fish and perhaps other small temnospondyls. Unlike living amphibians, we must remember that these animals possessed a scaly skin, so the adults would presumably have relied less on cutaneous respiration than do living aquatic amphibians. How micromelerpetontids are related to other dissorophoids has provide controversial: they have been regarded as the closest relatives of branchiosaurids or amphibamids, as an aquatic side-branch of the terrestrial dissorophids, and most recently as the most basal of all dissorophoids (Schoch & Rubidge 2005).
And - with branchiosaurids, eryopoids, dvinosaurs and all those tens of limnarchian clades still to go, I must leave. I know you want more, sorry.
For previous articles on temnospondyls and other non-amniote tetrapods please see...
- Temnospondyls the early years (part I)
- Crassigyrinus, or... How I'd love a giant killer Carboniferous tadpole for a pet
- Temnospondyls the early years (part II)
- Lysorophians and aïstopods
Refs - -
Bolt, J. R. 1974. Osteology, function, and evolution of the trematopsid (Amphibia: Labyrinthodontia) nasal region. Fieldiana Geology 33, 11-30.
Boy, J. A. 1985. Ãber Micropholis, den letzten Ãberlebenden der Dissorophoidea (Amphibia, Temnospondyli; Unter-Trias). Neues Jahrbuch fur Geologie und Paläontologie, Monatshefte 1985, 29-45.
Daly, E. 1994. The Amphibamidae (Amphibia: Temnospondyli), with a description of a new genus from the Upper Pennsylvanian of Kansas. The University of Kansas Museum of Natural History, Miscellaneous Publications 85, 1-59.
DeFauw, S. L. 1989. Temnospondyl amphibians: a new perspective on the last phases in the evolution of the Labyrinthodontia. Michigan Academician 21, 7-32.
Dilkes, D. W. 1990. A new trematopsid amphibian (Temnospondyli: Dissorophoidea) from the Lower Permian of Texas. Journal of Vertebrate Paleontology 10, 222-243.
- . & Reisz, R. R. 1987. Trematops milleri Williston, 1909 identified as a junior synonym of Acheloma cumminsi Cope, 1882, with a revision of the genus. American Museum Novitates 2902, 1-12.
Ruta, M., Jeffery, J. & Coates, M. I. 2003. A supertree of early tetrapods. Proceedings of the Royal Society of London B 270, 2507-2516.
- ., Pisani, D., Lloyd, G. T. & Benton, M. J. 2007. A supertree of Temnospondyli: cladogenetic patterns in the most species-rich group of early tetrapods. Proceedings of the Royal Society of London B 274, 3087-3095.
Schoch, R. R. 1999. Comparative osteology of Mastodonsaurus giganteus (Jaeger, 1828) from the Middle Triassic (Lettenkeuper: Longobardian) of Germany (Baden-Württemberg, Bayern, Thüringen). Stuttgarter Beiträge zur Naturkunde Serie B (Geologie und Paläontologie) 278, 1-175.
- . & Rubidge, B. S. 2005. The amphibamid Micropholis from the Lystrosaurus Assemblage Zone of South Africa. Journal of Vertebrate Paleontology 25, 502-522.
Vaughn, P. P. 1971. A Platyhystrix-like amphibian with fused vertebrae, from the Upper Pennsylvanian of Ohio. Journal of Paleontology 45, 464-469.
Witzmann, F. & Pfretzschner, H.-U. 2003. Larval ontogeny of Micromelerpeton credneri (Temnospondyli, Dissorophoidea). Journal of Vertebrate Paleontology 23, 750-768.
Yates, A. M. & A. A. Warren. 2000. The phylogeny of the "higher" temnospondyls (Vertebrata: Choanata) and its implications for the monophyly and origins of the Stereospondyli. Zoological Journal of the Linnean Society 128: 77-121.
- Log in to post comments
More like this
Daly's amphibamids remind me of some of the quadrupedal herps that wander through some of Escher's figures.
Bummer, no picture of this semi-mythological being. I want to know if he has pointed ears, like Spock.
Heh, for once I get the Tet Zoo in-joke. I think.
...or like the ancestors of Kermit the Frog.
'Would you like to buy a wovel?'
...and I would need to buy a spellchecker.
<happy happy joy joy>
I need to look up Schoch (1999). Distal carpal 4 is ossified and the others are not? That would mess majorly with everything we thought we knew about limb evo-devo.
They don't support anything, they're supertrees (as the titles helpfully mention). They show the consensus of recent results, but they aren't results of a phylogenetic analysis themselves; they are of no interest outside history of science (or when you urgently need a comprehensive phylogenetic hypothesis, would need to make your own data matrix, and can't afford to do that).
Erm, no â it's supposed to be a crocodile-like exoskeleton, providing support for the backbone, much like in chroniosuchians. As armour it belongs on Failblog, what with hardly covering anything.
Did you run a spellchecker over the lateral-line canals�
Possible. In other words, I can't imagine another function for this huge oval structure. However, being legendary, I'd like to see a bit more information about stapes size and anatomy before I commit to that interpretation. Sigurdsen (2009) has an illustration of how tiny, tiny, tiny the stapedes of a goliath frog are.
And a Czech one, good old Mordax, in an SVP meeting abstract in 2007. Should get published soon, I suppose.
Well, a rather small "otic" notch is plesiomorphic, and Trematopidae and Dissorophidae + Amphibamidae ?including Branchiosauridae appear to be sister-groups, so an autapomorphic enlargement (and perhaps gain of a tympanum) look like the most parsimonious interpretation to me⦠have I overlooked something?
Or just simply adults (real adults this time), as an SVP meeting abstract from 2007, with a title that starts with "Finally grown up", argues.
Metamorphosed adults of the branchiosaurid Apateon gracilis were reported in 1991 and (in more ontogenetic detail and in English) in 2006; Apateon caducus, however, really was neotenic according to that same 2006 paper.
Pointed ears would fit, but I have to disappoint. And while my hair is smooth, it's not black. And I'm not even capable of lifting just one eyebrow <sniff>
The z is just for fun (some kind of 16th-century affectation or something). Ignore it. :-)
Thanks for those comments. At the time of writing (doubtless it will change in 20 minutes or so), the article is getting top billing in that 'Now on ScienceBlogs' line at the top! Anyway, I'll go make a few corrections/updates now, thanks David and others. Dartian: I do have photos of David and have put one on Facebook. I didn't see pointed ears. Nor does he look like his Spec version :(
On the carpals of Mastodonsaurus, Schoch (1999) says that they're often missing due to small size, and he doesn't say that distal carpal 4 was definitely absent.
And I agree about the Escheresqueness of Daly's amphibamids :)
Or not. Just started reading the Schoch & Fröbisch paper in the Systematic Biology issue of June 2009 (Syst. Biol. always takes its time to arrive over here). In those trees where the relationships are resolved, Dissorophidae and Trematopidae are sister-groups with respect to Amphibamidaeâ¦
Unfortunately, though, I'm still uncannily similar to it.
Schoch (1999: 130) doesn't mention any carpals except intermedium and ulnare, but says there's an articulated (if fragmentary) specimen. Eryops is not mentioned in the text at all. Confusing.
Good call on the Escher. They also make me think of Dia de Los Muertes.
@David MarjanoviÄ: "They don't support anything, they're supertrees (as the titles helpfully mention). They show the consensus of recent results, but they aren't results of a phylogenetic analysis themselves; they are of no interest outside history of science (or when you urgently need a comprehensive phylogenetic hypothesis, would need to make your own data matrix, and can't afford to do that)."
Holy Words!
damn it, darren, this is so much fun to read it's almost pr0nographic! it boggles the mind you don't get paid to do this.
What is that taxon with the very long snout? I am super interested...
Incidentally, got a bigger version of the first pic? Would make a nice wallpaper.
It says "Trematosauridae" next to it, and trematosaurids are indeed long-snouted marine temnospondyls, but this one almost overdoes it, IIRC.
I like that dissorophids are figured looking just the way dinosaurs were imagined a century and a half ago.
<facepalm> That's what's always so familiar about Cacops! It looks like Owen's Megalosaurus!!!
:-o
Except for the sprawling limbs, it's really remarkably similar.
I was thinking of the Waterhouse Hawkins Iguanodon, myself, but I see the precervical resemblance to M..
How can those of us who would sooner gouge our eyes out with the jagged shard of our own ulna than sign up on Facebook get to see the photo of the legendary David MarjanoviÄ?
Very interesting stuff.
Is there any indication that there could be some kind of neotenic populations of Micromelerpetontids, in a similar way as some extant caudata populations (as in Mesotriton alpestris)?
RE: neoteny/paedomorphosis in micromelerpetontids:
I don't know if this is the case for micromelerpetontids, but at least one species of branchiosaurid seems to show this sort of facultative lifestyle, which Dave already mentioned a few posts up. Of course, this depends on the existence of micromelerpetontids and branchiosaurids as "real" groups; recent analyses are placing both as derived amphibamids way up on the batrachomorph stem (see the Frobisch & Schoch paper previously cited). So it would seem that there is some confusion about how exactly the miniaturized and neotenic dissorophoids all fit together. There are certainly some confounding factors (that is, convergent neoteny, see Wiens et al. 2005) that could be hindering recovery of a "true" phylogeny. So the problem is sort of difficult to resolve at some level, because our understanding of the evolutionary processes driving perceived neoteny in the clade depend on the phylogeny, and our phylogeny is itself pretty bunged up by ontogenetic processes within the clade.
On that, at least, Dave and I will agree.
RE: Platyhystrix, Astreptorhachis, and Aspidosaurus.
Dissorophid armor is not all created equal. In the more derived dissorophoids (Cacops, Alegeinosaurus, Dissorophus, Broiliellus, etc) there are two layers of dorsal ossifications, with a lower osteoderm ossifying to the neural spines of the thoracic vertebrae and the upper osteoderms forming the typical "carapace." In Platyhystrix, Astreptorhachis, and Aspidosaurus, the external armor fuses directly to the neural spine. So, it's not *just* the general appearance of the armor which differentiates the sailbacks from the rest, there are some more robust differences.
Also, contra Dave, armor of Dissorophus is pretty wide and covers a great deal of the dorsal region of the animal. There are also additional lateral ossicles on other dissorophids suggesting that the dorsal armor was probably a little more comprehensive than just the single median row. There are certainly a plethora of alternate explanations for this (Dave cited biomechanical properties of the thoracic skeleton, and there are other possibilities as well) but I'm not sure there is enough data to completely reject a defensive utility of those structures based on the current published literature at this time.
Excellent post - fascinating creatures.
Are you sure you met the MarjanoviÄ - surely it is a mythical being? If you didn't manage to bag a specimen then surely the least we can ask for is a photo to prove it exists (I was going to say a DNA sample, but decided that sounded wrong on so many levels). Having had the odd verbal duel (friendly, obviously), I would have liked to know what he looks like.
As for your previous post about Bristol zoo - its one of my favourite zoos - I guess the fact that we used to go there a couple of times every year when I was a kid, and more recently occasionally take my nephews, means it has lots of fond memories for me. It no longer has elephants etc, but it has sloths, fruit bats and aye ayes which I think more than makes up for it.
That includes myself, just for the record.
Yeah, and there are other such cases. For example, some of the similarities between lysorophian lepospondyls and lissamphibians smell of paedomorphosis â if, that is, we assume that lysorophians and lissamphibians had similar ontogenies! If we don't, we're reduced to helpless guesses, even though there are some tetrapod-wide indicators of paedomorphosis in lysorophians (persistent suture between centrum and neural arches⦠persistent suture between left and right neural arches, for crying out loud).
Oops, true. Exhibit A: Dissorophus multicinctus which resembles armadillos in more than the name. Thanks for reminding me, I was thinking too much of just Cacops (illustrated above).
Hey Darren, I enjoyed your article. One question: did terrestrial temnospondyls (or any at all) have lizard-like "lips"?
Quoting Dave:
Right. Lysorophians are almost certainly paedomorphic. The persistence of the suture between the centrum and neural arch is one of many paedomorphic features; there are a lot of portions of the dermal skull that are simply incompletely ossified or which never ossify (circumorbital bones, portions of the dermal palate, etc), and retention of a well-developed branchial skeleton into adulthood all point to paedomorphosis as a major driving factor in the origin of the lysorophians. There are, of course, multiple paths towards miniaturization in amphibians, but not all lysorophians are miniature (see: Molgophis and 'Brachydectes' elongatus), nor are all modern paedomorphic amphibians 'miniature.' Ultimately, Dave and I disagree on the importance of these characteristics in context of lissamphibian origins, but paedomorphosis as a major driver in diversification of paleozoic tetrapods is itself interesting considering that paedomorphosis is a major source of variation in modern amphibians as well.
It should be noted that Dissorophis itself is by far the most spectacular. It's armor rivals that of Peltobatrachus, and is deserving of Bakker's neologism "Armadillo toad".
It should be noted that Dissorophis itself is by far the most spectacular. It's armor rivals that of Peltobatrachus, and is deserving of Bakker's neologism "Armadillo toad".
What makes Daly's amphibamids (and the six-legged roll-ups in Escher's 'House of Stairs') look particularly odd is that the fore and hindlimbs are drawn almost the same, with the knees bending parallel to the elbows. Isn't that just wrong?
Checking Escher images, the cute little guys in 'Reptiles' remind me more of Mekosuchus... whose nasal bones I found recently. Probably not so stumpy in real life.
And I spent just long enough on Facebook to find that picture of David. Darren, can you confirm that he was actually shooting laser beams from his eyes?
Careful there. All this is true if we assume a lissamphibian- or temnospondyl-like ontogeny for lysorophians (or at least their non-paedomorphic ancestors). Well, assuming a lissamphibian-like one begs the question, and the temnospondyls are rather far away on the tree. Unfortunately, the only known lepospondyl skull ossification sequence (a very partial one -- three stages) is that of the highly derived aïstopod Phlegethontia, and that one is just plain weird, being neither similar to those of lissamphibians or temnospondyls, nor ever leading through a stage similar to what lysorophians look like, so it doesn't help.
Sure, there are a few characteristics of lysorophians that make sense if we assume 1) paedomorphosis and 2) a lissamphibian-like ontogeny, such as the extremely broad cultriform process of the parasphenoid (exaggerated all the way to completely obliterating the interpterygoid vacuities) or the arrangement of the vomerine teeth, which look just like in larval/neotenic salamanders (...just salamanders... not frogs or caecilians). Assumption number 1 is supported by a couple of vertebrate-wide indicators of morphological immaturity, most drastically by the suture between left and right neural arches. But where exactly do we take assumption number 2 from? We have to beware of circular logic here.
In short, we don't know exactly which character states of lysorophians are due to their undisputed paedomorphosis and which are not.
I don't think we do.
Of course it is. But at least she didn't forget the scales like just about everyone else does.
BTW, I want that picture. :-)
RE: Dave:
Well, sort of. We also have developmental sequences for non-tetrapods (e.g. Eusthenopteron, Dipterus, numerous basal actinopterygians, and various modern taxa, and while there are certainly non-homologies between a lot of the specific bones, the general regions of the skull and their order of ossification seems somewhat conserved, as does the order of ossification of tissue type derivatives (i.e. splanchnocranium vs. neurocranium vs. dermatocranium). So while the temnospondyl and lissamphibian data may not be directly applicable to lepospondyls, I think largely that there are some hard and fast rules concerning the distribution of ossification in space and time in the vertebrate skull. I'm really not convinced at this moment that lepospondyls have flat-out changed patterns of neural crest cell migration early on in tetrapod evolution and thus have acquired a completely unique sequence of chondrification and ossification. I am convinceable, but I'd need to see some significant developmental work backing that up.
Phlegethontia has (Anderson 2002). I'm not saying any other lepospondyl is like that, but Ph. is majorly weird.
Anyway, I just found an example where lysorophians show evidence of deviating from temnospondyl (and apparently lissamphibian, and to some degree even amniote) ontogeny: rib length relative to vertebra length. Relative rib length increases in temnospondyl ontogeny (known from branchiosaurids, micromelerpetontids, Archegosaurus, and Sclerocephalus), fitting the idea that paedomorphosis is responsible for the extremely short (or, in most crown-group frogs and except for the sacral pair, altogether absent) ribs of lissamphibians; lysorophians have very long ribs instead (as does Batropetes, BTW). Peramorphosis for the ribs and paedomorphosis for the rest of the body? Even though elongate lissamphibians have tiny ribs? Sounds unlikely to me.
Now, ribs⦠Jennifer Olori is working on lepospondyl postcranial ossification sequences (a few are known, mostly Microbrachis and Hyloplesion, apart from Phlegethontia), so we can expect to learn something on that soon. For cranial ossification sequences we'll have to wait for more discoveries; Phlegethontia means that all phylogenetic bracketing gives ambiguous results.
David, do you support more, with nowadays data, the lepospondyl origin of lissamphibia?
At the moment, yes, though the distance to the temnospondyl hypothesis (in terms of additional steps needed on at least some data matrices) is not very large.
Also, within the lepospondyl hypothesis, the "nectrideans"-including-aïstopods could be closer to Lissamphibia than the lysorophians are.
RE: Dave:
I suppose that the early complete ossification of the vertebrae is weird, but the rest of the organism is relatively sensible in ossification sequences. There are also potentially some distinct (functional) reasons for such early ossifications. I'm also somewhat skeptical of the idea that we're seeing as complete an ossification sequence as we think. Basically, there's a lot we don't know about aistopods that needs to be resolved.
Well, I think this is one of those cases where we have reason to believe that some aspects of lysorophian anatomy have been modified by paedomorphosis, but not all aspects. I'm not really sure why this should be all that surprising, although I do think this should raise questions as to the exact morphology of the thoracic musculature in lepospondyls in general.
So I've heard. Once again concerning Phlegethontia, though, I don't think it is as completely weird as you're making it out to be. I am curious to see what the basal microbrachomorphs are going to turn up vis a vis development, though.
Jugal before premaxilla? Sensible? Zonked out, I tell you.
I don't have the 2002 or the 2003 paper here, but the 2007 book chapter illustrates the three known stages of skull ossification again (in lateral view, which is most likely all that is known):
Smallest: complete caudal half of braincase except crests, frontal, maxilla, surangular, angular.
Intermediate: the above + lacrimal, dentary, rostrodorsal and rostroventral corners of "postfrontal" (likely separate postfrontal and postorbital), jugal, all of ?quadratojugal/squamosal except dorsal process; complete, unbroken ventral margin of orbit and cheek region.
Largest: the above + all the rest: premaxilla, complete and single "postfrontal", dorsal process of ?quadratojugal/squamosal, sagittal and nuchal crests of braincase.
Pretty much all that's normal here is the early appearance of the frontal, don't you think?
Nobody has said it's complete. I, for one, keep whining about how it's only 3 stages :-)
Understatement :-)
In principle, paedomorphosis and peramorphosis for different characters of the same animal is not surprising, but I'd expect that to apply to things like dermal vs endochondral skeleton or limb ratios; I just can't think of a reason why the ribs of all things should be peramorphic in an otherwise paedomorphic animal, especially when that never happens in, one would think, comparable lissamphibians.
Good point.
BTW, I wouldn't use the term "microbrachomorphs". Even the original paper, Carroll & Gaskill (1978), expresses skepticism about the monophyly of that grouping; and while ("microsaur" phylogeny being extremely volatile in general) Hyloplesion, Microbrachis and Odonterpeton do tend to end up somewhere close to each other (like forming a paraphyletic series), the brachystelechids are usually far off (sometimes forming part of Anderson's Recumbirostra, sometimes not).
Hello darren: could you please tell me what the name of the crown-group tetrapods is? Thank you!
What that name is depends on who you listen to. If you listen to Michel Laurin, it's Tetrapoda (and temnospondyls, anthracosaurs, even seymouriamorphs are not tetrapods). If you listen to most other people, the crown-group currently lacks a name.
Given the current degree of uncertainty about where the Lissamphibia fit on the tree, would it be too much to ask all reputable paleontologists to REFRAIN from naming the crown group of tetrapods for a while? If a name got into currency and there was then a major change of opinon about the contents of the crown group, I think the literature could become very confusing: imagine reading a paper, looking at the date, and asking yourself "What do you suppose the author of this thought was IN xxxx?"
A few years of writing "Crown Tetrapoda" or "Lissamphibia+Amniota" with no one-word name until the situation is clarified would surely be preferable!
Thank you for your answers, i appreciate them
I'd have another question: is is true dat anurans and caudates are temnospondyls and gymnophions are lepospondyls? Sorry for being possibly wrong
This is one of the three hypotheses -- and if you had read the previous comments, you'd already know that.
While we're at it, is it official, down on paper, registered with the Phylocode people, that "Lissamphibia" is the last common ancestor of frogs, salamanders and Gymnophiona with all of its descendents? Because, if it is, and if a phylogenetic hypothesis according to which they aren't closely related is substantiated, the paleontological community will have to issue an embarrassed press release:
"About those Carboniferous and Permian types that we all called "Amphibians" for most of the 20th C, and that we professionals spent the last couple of decades trying to tell you weren't really Amphibians-- well, they are now Amphibians again."
Indeed: it is a reconstruction of Aphaneramma, a lonchorhynchine trematosaurid from the Early Triassic of Svalbard (probably made from the figures of the monographs of Säve-Söderbergh, 1935 or 36). At the time of DeFauw (1989), it was the only trematosaurid for which postcranial material was known - until the description of new material of Wantzosaurus by Steyer (2002) and Trematolestes by Schoch (2006).
Some trematosaurids were found in marine beds (where they co-occur with ammonoids), but not all: some of them were found in lacustrine (Cosgriffius from Arizona), fluvial (Trematosaurus) or fluvio-estuarine deposits (Trematolestes from Germany).
Yeah, but did you even see Cosgriffius, or Platyoposaurus ? (OK, the latter is not a trematosaurid, but an archegosaurid, but it's pretty amazing too, isn't it ?)
Platyoposaurus is made of awesome!
To my shame, I hadn't noticed that the triangle-headed Cosgriffius is a trematosaurid. I'm not very familiar with stereospondyls -- most phylogenetic work on limbed vertebrates in general ignores them completely.
Something similar will be, with the important difference that the definition will contain external specifiers: if (for example) Eryops or Homo fall inside the smallest clade that contains frogs, salamanders & caecilians, that clade must not be called Lissamphibia, and the name self-destructs.
The PhyloCode will only be implemented upon publication of the companion volume. Could take another year or two.
By the way, I have stuff on trematosaurs just about done. Just need to get through eryopoids, dvinosaurids,tupilakosaurids, trimerorhacids, eobrachyopids, archegosauroids, lapillopsids and capitosaurs first.
PhyloCode volume is indeed nearly there, but we're not sure how nearly there, especially given that new submissions are still being produced. Had a long chat about it with Jacques at SVP and have ended up taking on the Theropoda contribution. Email me if you work on theropods and want to be involved.
Names that self-destruct... Fascinating idea: I must get serious and learn how PhyloCode is supposed to work in detail!
Certainly that would help with the "confusing literature" problem I imagined: in the case supposed (in comment #37), a reader finding "Lissamphibia" in an article would at least have a "heads up" that they were dealing with an article written before...
(Thanks, DM: I hadn't been aware of the relevant feature of PhyloCode. I plead amateur status.)
http://www.ohiou.edu/phylocode
Can be read in one evening.
There's also a Wikipedia article on phylogenetic nomenclature, but even though I created it, I can't recommend it right now, because some ignoramus added irrelevant mentions of "cladistics" and even "cladism" to it, and I have yet to check what else is now wrong or misleading.
Impressively detailed list... Did you manage to attend Anne Warren's SVP talk about tupilakosaurids and brachyopids (not eo-)?
Darren:
All the birds too?
I hope this phylocodery won't eat up precious time that could be spent writing blog posts instead...
Well, I (and a group of colleagues) are only worried about the definition of Theropoda itself, not the definitions of the many constituent clades. Good call though :)
As for 'eating up precious time that could be spent writing blog posts', it's funny to hear you say this. I'm under huge pressure for lots of reasons (and from lots of people) to blog LESS and concentrate on paper-writing MORE. Blog-writing gets me paying work (because publishers and so on see my stuff), but it doesn't help with academic kudos.
I realised only after pressing the 'Post' button that I should have been more clear. With 'precious time' I meant the time that's left over for you from taking care of your family, writing technical papers, and various other things such as finding the time to eat and to sleep. I've never presumed anything else than that all those have priority over blogging.
And, you see, for a moment there I was envisaging a scenario where you're pouring through mountains of ornithological literature for the single purpose of being able to create phylogenetic definitions for every muttonbird and buttonquail and whatnot bird taxon...
D'oh! 'poring through'.
'Me fail English? That's unpossible!' -Ralph Wiggum
Ruta et al.'s (2007) temnospondyl supertree is just begging to be put onto a T-shirt.. but it would have to be one with a fine weave.
Has anyone suggested yet that sailbacks could have had a sonic use.. as sounding boards, acting as directional emitters, or receivers, for the vibrations of their mating calls, say? Did extinct foms do so? Are there osteological correlates of the vocal sacs (elastic throat pouches) in extant amphibians, that could bear on this?
If some species had hearing that was not acute then tactile detection of booming sound pulses might be useful.. and a big area of sensitive skin held taut between rigid spines, it seems to me, might be a handy organ for that.
David Marjanovic--
Thank you for the references (comment #45)! Have only skimmed so far, but will return to study in detail.
---Note 2.1.2 (in Articles) should be printed in bold Italics, all capitalized!
---4.3(a) might be an embarrassment: I suspect Mike Taylor may be right about the future relative importance of electronic and paper publication.
AFAIK not, and that's a good idea! Considerably less likely than the usual one (use as a visual signal), but sails as receivers ought to work.
Nowadays it's not news anymore. The mid-late 1980s, when some people wrote "every node must be named", are over.
The idea is that you should not need a special apparatus (beyond glasses...) to read any valid publication. It's entirely possible that this will become an embarrassment.
Note 2.1.2 (from the PhyloCode page):
and David:
That's all fine and well, but are there also some universal rules about what nodes/clades must be named? If there aren't, how is 'taxonomic freedom' to be avoided?
Allen:
Article 4.3(a):
As I interpret it, the key word word in that passage is 'solely'. In other words, that while electronic publication is allowed and even encouraged, the publications should also exist as physical copies. Which is perfectly sensible and indeed farsighted.
He may be. But that remains to be seen.
No, why?
What do you mean -- how to stop people from immortalizing themselves by naming boatloads of clades and creating frightful messes in the future? Peer review is required for valid publication, for example. Also, there are recommendations against "wholesale conversions" of series of preexisting names, especially by people who haven't worked on the clades in question.
David:
Yes, that's what I mean. Who can objectively decide which clades 'need' to be named and which don't? Peer reviewers? They are themselves fallible, subjective human beings. You've said before here on Tet Zoo that splitting and lumping will be 'impossible' under phylogenetic nomenclature; maybe I'm missing something but I don't see how that is possible unless there are some hard and fast rules about what can be named and what can't (e.g., a rule that says that a species pair is too small a clade to be named).
To take a real-world example of a frightful nomenclatural mess: What would be the appropriate number of named clades within the great ape clade Hominoidea (i.e., the LCA of Hylobates and Homo plus all their descendants)? Who on earth can objectively decide that? There are nearly as many opinions as there are experts working on the systematics of extinct and extant hominoids and there certainly is no shortage of already proposed clade names. Is, say, Hominini a superfluous or a necessary clade name? What about Gorillini? Is there a clade called Australopithecini, or, if there isn't, do we need one? What about Hominina? What's the PhyloCode companion volume's stance on the issue of hominoid nomenclature?
This sort of thing has been discussed in the literature on phylogenetic nomenclature; if I remember correctly there's coverage of it in Padian et al. (1999) and Joyce et al. (2004). Because workers only tend to use those clade names that 'matter' (i.e., for the stable nodes that get supported in most analyses), the many others that get named fall by the wayside, and it doesn't matter that they were ever named. If your analysis doesn't find an Australopithecini or Hominina, do those names matter? On the other hand, if your analysis does support those clades, is it a bad thing if the names are already there? Even better if they have a published definition.
Having said all that - most workers seem to be behaving with restraint these days. We went through a phase in the 1980s where every single node was getting named (see Sereno (1986) on ornithischians and Gaffney & Meylan (1988) on turtles). That seems to have died out (so far as I know).
Refs - -
Gaffney, E. S. & Meylan, P. A. 1988. A phylogeny of turtles. In Benton, M. J. (ed) The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds. Clarendon Press (Oxford), pp. 157-219.
Joyce, W. G., Parham, J. F. & Gauthier, J. A. 2004. Developing a protocol for the conversion of rank-based taxon names to phylogenetically defined clade names, as exemplified by turtles. Journal of Paleontology 78, 989-1013.
Padian, K., Hutchinson, J. R. & Holtz, T. R. 1999. Phylogenetic definitions and nomenclature of the major taxonomic categories of the carnivorous Dinosauria (Theropoda). Journal of Vertebrate Paleontology 19, 69-80.
Sereno, P. 1986. Phylogeny of the bird-hipped dinosaurs (Order Ornithischia). National Geographic Research 2, 234-256.
Gower & Wilkinson (1996) also included a discussion of why naming (just about) every node is irresponsible and to be avoided...
Gower, D. J. & Wilkinson, M. 1996. Is there any consensus on basal archosaur phylogeny? Proceedings of the Royal Society of London/ B 263, 1399-1406.
Splitting & lumping refer to taking a name and applying it to a different clade than before even though our knowledge of the phylogeny has not changed. That is indeed impossible in PN. Once, for example, Hominoidea has been defined as the MRCA of Homo and Hylobates plus all its descendants, you can't shift the name to, say, the MRCA of Homo and Pongo plus all its descendants, because you can't change the definition.
Cruel abuse of temnospondyl in cheesy German talent show:
http://www.welt.de/fernsehen/article4284636/Sommermaedchen-Das-Fernsehe…
Err... 'Cruel'?
I disagree. Having five fingers per hand, this thing is not a temnospondyl (unless Caerorhachis is one). Apart from its size, it could be a very young Eucritta⦠or a seymouriamorph maybeâ¦
However, dragging anything into Pro7 is most certainly cruel. <vehement nodding>
> Err... 'Cruel'?
Getting dragged out of your pond and into Pro7 by a bunch of amniotes (even if they are moderatly attractive by amniote standards)? Most definitely cruel... :D
> Having five fingers per hand, this thing is not a
> temnospondyl
So all those recostructions of five-fingered temnospondyls in the literature (Bakker's *Cacops* in TDH, waving its five-fingered hand in a semaphore-like movement, to name but one example) and on the internet are wrong :-O?
http://en.wikipedia.org/wiki/Trematopsidae
http://en.wikipedia.org/wiki/Acheloma
http://en.wikipedia.org/wiki/File:Eryops_megacephalus_skeleton_front.JPG
To finally correct myself...
It's Mordex laticeps. And it still hasn't been published.
Yes.
OK, the early-20th-century reconstructions of the hand of Eryops actually show a prepollex; that would make five "fingers" total. But the disarticulated material needs to be completely redescribed, and AFAIK nobody's doing that.
All actually known and not too disarticulated temnospondyl hands show four fingers, just like how the feet show five toes.