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 Marjanović. 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. Über Micropholis, den letzten Überlebenden 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.