The Traditional View: Reptile-like Amphibians
Diadectomorphs are widely considered to be reptile-like amphibians that lived during the Late Carboniferous and Early Permian. However, no diadectomorph tadpoles are known and these taxa lack a long list of amphibian characters (see below). These often big (2-3 m long), bulky (wider than tall torsos) taxa include herbivores and carnivores, all were slow-moving and cold-blooded.
The Heretical View
The larger study found diadectomorphs to nest within the Reptilia and within the Lepidosauromorpha branch. So tadpoles will never be found. Additions to the diadectomorphs include Solenodonsaurus, Lanthanosuchus, chroniosuchids, Tetraceratops and Procolophon, which nests as a sister to Diadectes. Pareiasaurs, like Anthodon and turtles are also basal diadectomorphs. All were derived from earlier precursor sisters to Oedaleops, Romeria primus and Concordia. Successors within this monophyletic clade branching off Lanthanosuchus and Nyctiphruretus include lizards, snakes, pterosaurs and their kin.
There are no other “amphibians” that even vaguely resemble this group of bulky Early Permian reptiles — especially those close to basal reptiles like Cephalerpeton, Casineria and Westlothiana. Calling diadectomorphs “reptile-like amphibians” was a mismatch from the beginning.
The Procolophon Missed Connection
The resemblance between the recognized reptile Procolophon and Diadectes was completely overlooked. The resemblance between pareiasaurs and diadectids was also overlooked. None of these taxa have labyrinthodont teeth. None have palatal fangs. None have an intermedium (a bone in the temple of pre-reptile amphibians).
The Otic Notch
Diadectomorphs did have a classic amphibian trait: an otic notch, which is a concave embayment at the back of the skull, roofed over by an overhang of skull roof. Presumably it framed a large eardrum or tympanum. Trouble is, these well-established reptiles also had an otic notch: Concordia, Oedaleops, Procolophon, Odontochelys, Proganochelys, Lanthanosuchus and Macroleter and Sauropareion. They’re all sisters to the diadectidomorphs.
The Age of Bulk – The Early Permian in Pangaea
It’s odd to consider that reptiles as fragile and aerial as pterosaurs and kuehneosaurs could have evolved from bulky diadectids and flattened lanthanosuchids, but the family tree indicates exactly such a lineage. Diadectes and Limnoscelis were formerly considered dead-ends. Now they are key taxa. So, what was happening in the Early Permian to encourage such bulking up?
The continents were locked together into a supercontinent known as Pangaea, with the east coast of North America blended into western Europe and north Africa. The Appalachian and Atlas mountains were virtually continuous and equatorial. From Texas to Germany the climate was tropical. This is the zone that produced most of the known basal diadectomorphs in vast coal forests. Large carnivores, like Dimetrodon, were on the rise. Dimetrodon warmed up faster and was able to become more active earlier aided by its large dorsal-sail solar collector. The bulk of a large Diadectes or Anthodon stored heat better due to a smaller surface-to-volume ratio. Retaining a portion of yesterday’s heat within a bulky body is considered inertial homeothermy. Larger plant eaters are better able to defend themselves due to their bulk and the risk the predator takes trying to attack larger prey.
It’s too bad that traditional paradigms continue to hamper working palaeontologists when a large gamut study is available that more parsimoniously nests several misplaced and enigmatic taxa and clades. Hopefully this blog will jog others to create trees with a similar large gamut of taxa to test and refine the present one.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.
Berman, DS et al. 2004. A new diadectid (Diadectomorpha), Orobates pabsti, from the Early Permian of Central Germany. Bulletin of Carnegie Museum of Natural History 35 :1-36. doi: 10.2992/0145-9058(2004)35[1:ANDDOP]2.0.CO;2
Berman DS, Sumida SS, and Lombard RE 1992. Reinterpretation of the temporal and occipital regions in Diadectes and the relationship of diadectomorphs. Journal of Paleontology 66:481-499.
Berman DS, Sumida SS and Martens T 1998. Diadectes (Diadectomorpha: Diadectidae) from the Early Permian of central Germany, with description of a new species. Annals of Carnegie Museum 67:53-93.
Berman DS Reisz RR and Scott D 2010. Redescription of the skull of Limmoscelis paludis Williston (Diadectomorpha: Limnoscelidae) from the Pennsylvanian of Canon del Cobre, northern New Mexico: In: Carboniferous-Permian Transition in Canon del Cobre, Northern New Mexico, edited by Lucas, S. G., Schneider, J. W., and Spielmann, New Mexico Museum of Natural History & Science, Bulletin 49, p. 185-210.
Cope ED 1878a. Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas. Proceedings of the American Philosophical Society 17:505-530.
Cope ED 1878b. A new Diadectes. The American Naturalist 12:565.
Kissel R 2010. Morphology, Phylogeny, and Evolution of Diadectidae (Cotylosauria: Diadectomorpha). Thesis (Graduate Department of Ecology & Evolutionary Biology University of Toronto).
Moss JL 1972. The Morphology and phylogenetic relationship of the Lower Permian tetrapodTseajaia campi Vaughn (Amphibia: Seymouriamorpha): University of California Publications in Geological Sciences 98:1-72.
Romer AS 1946. The primitive reptile Limnoscelis restudied American Journal of Science, Vol. 244:149-188
Vaughn PP 1964. Vertebrates from the Organ Rock Shale of the Cutler Group, Permian of Monument Valley and Vicinity, Utah and Arizona: Journal of Paleontology 38:567-583.
Williston SW 1911. A new family of reptiles from the Permian of New Mexico: American Journal of Science, Series 4, 31:378-398.