Non-amniotes
Temnospondyls
Temnospondyls are an order of extinct anamniotes that are one of the earliest groups of tetrapods. They were a tremendously successful group, ranging from small, salamander-sized terrestrial forms to giant 6-meter aquatic predators. Before the evolution of other tetrapod groups, they were often apex predators in many of the environments in which they occurred. Some of them even returned to the ocean! Temnospondyls are characterized by giant openings on the roof of their mouth called interpterygoid vacuities (among other defining features) that may have played a role in stress distribution while feeding, respiration, or muscle storage. Many of them have tiny teeth numbering in the hundreds on the bony surfaces inside of their mouth, as well as enlarged teeth often called 'fangs' or 'tusks,' although they are really just big teeth. Temnospondyls declined sharply after the Triassic period (likely correlated with the rise of crocodilians and at the same time but independent of the rise of the dinosaurs) and petered out in the Cretaceous, but they may still exist today, as they have also been linked to the evolutionary origins of the three modern amphibian orders: Anura (frogs and toads), Urodela (salamanders and newts), and Apoda (caecilians). The most widely accepted hypothesis at present (aptly named the Temnospondyl Hypothesis) suggests that all three originated from within the temnospondyls (though not necessarily all from the same lineage). Our lab focuses mainly on a group of Permo-Carboniferous terrestrial amphibians called the dissorophoids, a subset of which (the amphibamids) are thought to be the closest known ancestors of modern amphibians. These amphibians are common at Richards Spur and show lots of adaptations for a fully terrestrial lifestyle, relatively uncommon among amphibians of the time, as well as a bunch of weird features like bony armor and enlarged nostrils.
Temnospondyls are an order of extinct anamniotes that are one of the earliest groups of tetrapods. They were a tremendously successful group, ranging from small, salamander-sized terrestrial forms to giant 6-meter aquatic predators. Before the evolution of other tetrapod groups, they were often apex predators in many of the environments in which they occurred. Some of them even returned to the ocean! Temnospondyls are characterized by giant openings on the roof of their mouth called interpterygoid vacuities (among other defining features) that may have played a role in stress distribution while feeding, respiration, or muscle storage. Many of them have tiny teeth numbering in the hundreds on the bony surfaces inside of their mouth, as well as enlarged teeth often called 'fangs' or 'tusks,' although they are really just big teeth. Temnospondyls declined sharply after the Triassic period (likely correlated with the rise of crocodilians and at the same time but independent of the rise of the dinosaurs) and petered out in the Cretaceous, but they may still exist today, as they have also been linked to the evolutionary origins of the three modern amphibian orders: Anura (frogs and toads), Urodela (salamanders and newts), and Apoda (caecilians). The most widely accepted hypothesis at present (aptly named the Temnospondyl Hypothesis) suggests that all three originated from within the temnospondyls (though not necessarily all from the same lineage). Our lab focuses mainly on a group of Permo-Carboniferous terrestrial amphibians called the dissorophoids, a subset of which (the amphibamids) are thought to be the closest known ancestors of modern amphibians. These amphibians are common at Richards Spur and show lots of adaptations for a fully terrestrial lifestyle, relatively uncommon among amphibians of the time, as well as a bunch of weird features like bony armor and enlarged nostrils.
Recent temnospondyl publications
- Atkins, J.B., Reisz, R.R., and Maddin, H.C. 2019. Braincase simplification and the origin of lissamphibians. PloS one 14(3): e0213694. doi: 10.1371/journal.pone.0213694
- Gee, B.M., Bevitt, J.J., and Reisz, R.R. 2019. A juvenile specimen of the trematopid Acheloma from Richards Spur, Oklahoma and challenges of trematopid ontogeny. Frontiers in Earth Science 7: 37. doi: 10.3389/feart.2019.00038
- Gee, B.M., Bevitt, J.J., and Reisz, R.R. 2019. Dissorophid diversity at the early Permian cave system near Richards Spur, Oklahoma, USA. Palaeontologia Electronica 22.2.46. doi: 10.26879/976
- Gee, B.M., Scott, D., and Reisz, R.R. 2018. Reappraisal of the Permian dissorophid Fayella chickashaensis. Canadian Journal of Earth Sciences 55(10): 1103-1114. DOI: 10.1139/cjes-2018-0053
- Gee, B.M. 2018. Reappraisal of the early Permian dissorophid Alegeinosaurus from Texas, USA. Paläontologische Zeitschrift 00: 00-00 (early view). DOI: 10.1007/s12542-018-0421-9
- Gee, B.M. and Reisz, R.R. 2018. Cranial and postcranial anatomy of Cacops morrisi, a eucacopine dissorophid from the early Permian. Journal of Vertebrate Paleontology 38(2): e1433186. DOI: 10.1080/02724634.2018.1433186
- Gee, B.M. and Reisz, R.R. 2018. Postcrania of large dissorophids from Richards Spur, Oklahoma. Fossil Record 21: 79-91. DOI: 10.5194/fr-21-79-2018
- Gee, B.M., Haridy, Y. and Reisz, R.R. 2017. Histological characterization of denticulate palatal plates in an Early Permian dissorophoid. PeerJ, 5: e3727. DOI: 10.7717/peerj.3727
Lepospondyls
In comparison to temnospondyls, lepospondyls are a very confusing (and probably artificial) group. Although they have traditionally been regarded as amphibians, with some groups even being proposed as ancestral to the modern caecilians (burrowing, limbless amphibians), there have been numerous shifts regarding their proposed evolutionary affinities, as they have also been tied to reptiles. Quite possibly, some are anamniotes (though not closely related to temnospondyls), and others are amniotes. Because lepospondyls are grouped only by their vertebral morphology, which is not very reliable and entirely responsible for the current state of confusion regarding their taxonomy, they show an even wider range of anatomical variation than temnospondyls. They range from Diplocaulus, a fairly well-known aquatic form with a flat, boomerang-shaped head, to the limbless aistopods, which had over 200 vertebrae in their backbone (humans have 33 for reference). As with the temnospondyls, another hypothesis regarding amphibian origins suggests that all modern amphibians came from lepospondyls (aptly named the Lepospondyl Hypothesis), but there is not as much support for this hypothesis, particularly given that some of the previous purported caecilian ancestors may be amniotes. Intermittently, our lab works on 'microsaurs,' a group of relatively small lepospondyls that run the gamet from aquatic gill-bearing forms (microbrachomorphs) to fully-terrestrial burrowing forms (recumbirostrans). Curiously, some of these forms are very similar to reptiles of the same time period...
In comparison to temnospondyls, lepospondyls are a very confusing (and probably artificial) group. Although they have traditionally been regarded as amphibians, with some groups even being proposed as ancestral to the modern caecilians (burrowing, limbless amphibians), there have been numerous shifts regarding their proposed evolutionary affinities, as they have also been tied to reptiles. Quite possibly, some are anamniotes (though not closely related to temnospondyls), and others are amniotes. Because lepospondyls are grouped only by their vertebral morphology, which is not very reliable and entirely responsible for the current state of confusion regarding their taxonomy, they show an even wider range of anatomical variation than temnospondyls. They range from Diplocaulus, a fairly well-known aquatic form with a flat, boomerang-shaped head, to the limbless aistopods, which had over 200 vertebrae in their backbone (humans have 33 for reference). As with the temnospondyls, another hypothesis regarding amphibian origins suggests that all modern amphibians came from lepospondyls (aptly named the Lepospondyl Hypothesis), but there is not as much support for this hypothesis, particularly given that some of the previous purported caecilian ancestors may be amniotes. Intermittently, our lab works on 'microsaurs,' a group of relatively small lepospondyls that run the gamet from aquatic gill-bearing forms (microbrachomorphs) to fully-terrestrial burrowing forms (recumbirostrans). Curiously, some of these forms are very similar to reptiles of the same time period...
Recent lepospondyl publications
- Gee, B.M., Bevitt, J.J., Garbe, U., and Reisz, R.R. 2019. New material of the ‘microsaur’ Llistrofus from the cave deposits of Richards Spur, Oklahoma and the paleoecology of the Hapsidopareiidae. PeerJ 7:e6327 DOI: 10.7717/peerj.6327
Reptiliomorphs
Reptiliomorphs are reptile-like anamniotes - essentially, they are intermediate between early tetrapods that were closer to amphibians such as temnospondyls and reptiles such as eureptiles. Although some reptiliomorph lineage certainly gave rise to reptiles, many reptiliomorphs actually continued to diversify well after this split and lived alongside both amphibians and reptiles by the early Permian; the non-amniote reptiliomorphs eventually go extinct in the Triassic. As a result of their intermediate evolutionary position, many of these forms resemble something of a mixture of an amphibian and a reptile, with some being aquatic and others being terrestrial. Two clades of reptiliomorphs are found at Richards Spur, albeit from extremely fragmentary material, the seymouriamorphs (represented by their namesake, Seymouria) and the diadectomorphs. It seems that at least some seymouriamorphs went through an aquatic larval stage in which they had gills and then metamorphosed into terrestrial adults in a similar fashion to frogs. Seymouria is arguably the best-known of the group, being known from complete skeletons, including a famous pair preserved in parallel to each other that are called the "Tambach Lovers" for the mostly speculative suggestion that they died while mating. Diadectomorphs were large reptiliomorphs, some of which were herbivorous (diadectids) and some of which were carnivorous (limnoscelids). The record of both groups is much better at other early Permian localities, such as in Texas and Germany, which may indicate that they were not very common at Richards Spur, being generally larger than most of the animals that we find at the site.
Reptiliomorphs are reptile-like anamniotes - essentially, they are intermediate between early tetrapods that were closer to amphibians such as temnospondyls and reptiles such as eureptiles. Although some reptiliomorph lineage certainly gave rise to reptiles, many reptiliomorphs actually continued to diversify well after this split and lived alongside both amphibians and reptiles by the early Permian; the non-amniote reptiliomorphs eventually go extinct in the Triassic. As a result of their intermediate evolutionary position, many of these forms resemble something of a mixture of an amphibian and a reptile, with some being aquatic and others being terrestrial. Two clades of reptiliomorphs are found at Richards Spur, albeit from extremely fragmentary material, the seymouriamorphs (represented by their namesake, Seymouria) and the diadectomorphs. It seems that at least some seymouriamorphs went through an aquatic larval stage in which they had gills and then metamorphosed into terrestrial adults in a similar fashion to frogs. Seymouria is arguably the best-known of the group, being known from complete skeletons, including a famous pair preserved in parallel to each other that are called the "Tambach Lovers" for the mostly speculative suggestion that they died while mating. Diadectomorphs were large reptiliomorphs, some of which were herbivorous (diadectids) and some of which were carnivorous (limnoscelids). The record of both groups is much better at other early Permian localities, such as in Texas and Germany, which may indicate that they were not very common at Richards Spur, being generally larger than most of the animals that we find at the site.
Richards Spur reptiliomorph publications
- Reisz, R.R. and Sutherland, T.E., 2001. A diadectid (Tetrapoda: Diadectomorpha) from the Lower Permian fissure fills of the Dolese Quarry, near Richards Spur, Oklahoma. Annals of Carnegie Museum, 70(2): 133-142. [Link]
- Sullivan, C. and Reisz, R.R., 1999. First record of Seymouria (Vertebrata: Seymouriamorpha) from Early Permian fissure fills at Richards Spur, Oklahoma. Canadian Journal of Earth Sciences, 36(8): 1257-1266. DOI: 10.1139/e99-035