AMNIOTES
EUREPTILES
Eureptilia is an extremely large taxonomic grouping that includes a variety of Permo-Carboniferous reptiles formerly classified as anapsids as well as the entirety of Diapsida, which includes lepidosauromorphs (lizards, snakes, amphisbaenians, tuatara) and archosauromorphs (dinosaurs, crocodiles, birds). Many of the more derived diapsids could grow to quite large sizes (dinosaurs, for example), but most Paleozoic eureptiles were small and of a comparable size to modern lizards. One diverse group, the captorhinids, is abundant at the Richards Spur locality and is arguably the most abundant amniote fossil known from the early Permian. Many members of this group feature multiple tooth rows (see figures below), a relatively unusual feature among tetrapods. Captorhinids are one of the earliest radiations of eureptiles, beginning in the Carboniferous, and although many were relatively small in size, some lineages got progressively larger later in the Permian.
Eureptilia is an extremely large taxonomic grouping that includes a variety of Permo-Carboniferous reptiles formerly classified as anapsids as well as the entirety of Diapsida, which includes lepidosauromorphs (lizards, snakes, amphisbaenians, tuatara) and archosauromorphs (dinosaurs, crocodiles, birds). Many of the more derived diapsids could grow to quite large sizes (dinosaurs, for example), but most Paleozoic eureptiles were small and of a comparable size to modern lizards. One diverse group, the captorhinids, is abundant at the Richards Spur locality and is arguably the most abundant amniote fossil known from the early Permian. Many members of this group feature multiple tooth rows (see figures below), a relatively unusual feature among tetrapods. Captorhinids are one of the earliest radiations of eureptiles, beginning in the Carboniferous, and although many were relatively small in size, some lineages got progressively larger later in the Permian.
Recent eureptile publications
- deBraga, M., Bevitt, J.J., and Reisz, R.R. 2019. A new captorhinid from the Permian cave system near Richards Spur, Oklahoma, and the taxic diversity of Captorhinus at this locality. Frontiers in Earth Science 7: 112. doi: 10.3389/feart.2019.00112
- Modesto, S.P., Scott, D. and Reisz, R.R. 2018. A new small captorhinid reptile from the lower Permian of Oklahoma and resource partitioning among small captorhinids in the Richards Spur Fauna. Papers in Palaeontology 4(2): 293-307. DOI: 10.1002/spp2.1109
- Haridy, Y., LeBlanc, A.R.H. and Reisz, R.R. 2017. The Permian reptile Opisthodontosaurus carrolli: a model for acrodont tooth replacement and dental ontogeny. Journal of Anatomy, 232(3): 371-382. DOI: 10.1111/joa.12754
- Modesto, S.P., Flear, V.J., Dilney, M.M. and Reisz, R.R. 2016. A large moradisaurine tooth plate from the Lower Permian of Texas and its biostratigraphic implications. Journal of Vertebrate Paleontology, 36(6): e1221832. DOI: 10.1080/02724634.2016.1221832
- Modesto, S.P., Scott, D. and Reisz, R.R. 2018. A new small captorhinid reptile from the lower Permian of Oklahoma and resource partitioning among small captorhinids in the Richards Spur Fauna. Papers in Palaeontology 4(2): 293-307. DOI: 10.1002/spp2.1109
- Reisz, R., Haridy, Y. and Müller, J. 2016. Euconcordia nom. nov., a replacement name for the captorhinid eureptile Concordia Müller and Reisz, 2005 (non Kingsley, 1880), with new data on its dentition. Vertebrate Anatomy Morphology Palaeontology, 3: 1-6. DOI: 10.18435/B53W22
PARAREPTILES
Parareptiles are the "other reptiles," so to speak. Although they have frequently been proposed to be the sister group to turtles (a historically confusing group to place phylogenetically because of their specialized anatomy), this is no longer a widely held hypothesis, and parareptiles likely did not produce any living descendants. Parareptiles are most abundant in the Permian but do make it across the Permo-Triassic boundary into the Triassic. The majority of them were small and superficially quite similar to lizards, but they are not closely related regardless of the relationship between parareptiles and turtles. There were a few notable deviations from the typical parareptilian anatomy as well. The mesosaurs are a group of medium-sized freshwater reptiles with thin, needle-like teeth - the genus Mesosaurus is found in both South Africa and South America, which was one of the early lines of evidence in support of the theory of continental drift because of the implausibility of a freshwater animal traversing such a great distance through the ocean. The pareiasaurs are large, robust herbivores with bony armor plates in their skin that have sometimes been suggested to be the precursors to the turtle shell; however, different types of dermal plates (osteoderms) occur in a variety of tetrapods (crocodiles and dinosaurs, to name some examples), and their presence may be analogous rather than homologous. Parareptiles are known from around the world, but they are especially diverse at the Richards Spur site, with eight species presently known, many of which have been named only in the last decade.
Parareptiles are the "other reptiles," so to speak. Although they have frequently been proposed to be the sister group to turtles (a historically confusing group to place phylogenetically because of their specialized anatomy), this is no longer a widely held hypothesis, and parareptiles likely did not produce any living descendants. Parareptiles are most abundant in the Permian but do make it across the Permo-Triassic boundary into the Triassic. The majority of them were small and superficially quite similar to lizards, but they are not closely related regardless of the relationship between parareptiles and turtles. There were a few notable deviations from the typical parareptilian anatomy as well. The mesosaurs are a group of medium-sized freshwater reptiles with thin, needle-like teeth - the genus Mesosaurus is found in both South Africa and South America, which was one of the early lines of evidence in support of the theory of continental drift because of the implausibility of a freshwater animal traversing such a great distance through the ocean. The pareiasaurs are large, robust herbivores with bony armor plates in their skin that have sometimes been suggested to be the precursors to the turtle shell; however, different types of dermal plates (osteoderms) occur in a variety of tetrapods (crocodiles and dinosaurs, to name some examples), and their presence may be analogous rather than homologous. Parareptiles are known from around the world, but they are especially diverse at the Richards Spur site, with eight species presently known, many of which have been named only in the last decade.
Recent parareptile publications
- MacDougall, M.J., Winge, A., Ponstein, J., Jansen, M., Reisz, R.R., Fröbisch, J. 2019. New information on the early Permian lanthanosuchoid Feeserpeton oklahomensis based on computed tomography. PeerJ 7: e7753. DOI: 10.7717/peerj.7753
- Haridy, Y., MacDougall, M.J. and Reisz, R.R. 2017. The lower jaw of the Early Permian parareptile Delorhynchus, first evidence of multiple denticulate coronoids in a reptile. Zoological Journal of the Linnean Society, 0:00-00 (advance article). DOI: 10.1093/zoolinnean/zlx085
- MacDougall, M.J., Scott, D., Modesto, S.P., Williams, S.A. and Reisz, R.R. 2017. New material of the reptile Colobomycter pholeter (Parareptilia: Lanthanosuchoidea) and the diversity of reptiles during the early Permian (Cisuralian). Zoological Journal of the Linnean Society, 180(3): 661-671. DOI: 10.1093/zoolinnean/zlw012
- Haridy, Y., MacDougall, M.J., Scott, D. and Reisz, R.R. 2016. Ontogenetic change in the temporal region of the Early Permian parareptile Delorhynchus cifellii and the implications for closure of the temporal fenestra in amniotes. PloS one, 11(12): e0166819. DOI: 10.1371/journal.pone.0166819
- MacDougall, M.J., Modesto, S.P. and Reisz, R.R. 2016. A new reptile from the Richards Spur Locality, Oklahoma, USA, and patterns of Early Permian parareptile diversification. Journal of Vertebrate Paleontology, 36(5): e1179641. DOI: 10.1080/02724634.2016.1179641
NON-THERAPSID SYNAPSIDS
Non-therapsid synapsids (encompassing caseids and pelycosaur-grade synapsids) are the more basal group of synapsids and include perhaps the best-known Permian tetrapod, the sail-backed Dimetrodon. Like their descendants, the therapsids and eventually the mammals, they display the "synapsid condition": a single opening, equivalent to a human's temple, in the side of the skull. Although they are more closely related to mammals than they are to other prehistoric beasts like the dinosaurs, early synapsids were far more reptilian in form. Many were carnivores, such as the large Dimetrodon and smaller, more lightly built forms like Aerosaurus, which were probably monitor-lizard-like predators. Another large genus, Ophiacodon, is sometimes considered to have been a semi-aquatic fish eater, though its high slender snout (which would be difficult to swing through the water) cannot easily be reconciled with this interpretation. Others, such as the sail-backed Edaphosaurus and the peculiar Cotylorhynchus (an animal whose tiny head seems mismatched with its huge, stocky body) represent some of the earliest known herbivores. Both Dimetrodon and Edaphosaurus are famous for the enormous spines growing upward from their vertebrae, which may approach a metre in length and which support a large sail. No one knows the exact function of this "sail", although a role in visual signalling during mating season and/or temperature regulation (by providing a large surface for heat loss or gain) seems likely. Because the Richards Spur assemblage features smaller animals, we do not have large synapsids such as Dimetrodon or Edaphosaurus, but there are remains of smaller carnivorous forms called varanopids that could have been the apex predators of the ecosystem.
Non-therapsid synapsids (encompassing caseids and pelycosaur-grade synapsids) are the more basal group of synapsids and include perhaps the best-known Permian tetrapod, the sail-backed Dimetrodon. Like their descendants, the therapsids and eventually the mammals, they display the "synapsid condition": a single opening, equivalent to a human's temple, in the side of the skull. Although they are more closely related to mammals than they are to other prehistoric beasts like the dinosaurs, early synapsids were far more reptilian in form. Many were carnivores, such as the large Dimetrodon and smaller, more lightly built forms like Aerosaurus, which were probably monitor-lizard-like predators. Another large genus, Ophiacodon, is sometimes considered to have been a semi-aquatic fish eater, though its high slender snout (which would be difficult to swing through the water) cannot easily be reconciled with this interpretation. Others, such as the sail-backed Edaphosaurus and the peculiar Cotylorhynchus (an animal whose tiny head seems mismatched with its huge, stocky body) represent some of the earliest known herbivores. Both Dimetrodon and Edaphosaurus are famous for the enormous spines growing upward from their vertebrae, which may approach a metre in length and which support a large sail. No one knows the exact function of this "sail", although a role in visual signalling during mating season and/or temperature regulation (by providing a large surface for heat loss or gain) seems likely. Because the Richards Spur assemblage features smaller animals, we do not have large synapsids such as Dimetrodon or Edaphosaurus, but there are remains of smaller carnivorous forms called varanopids that could have been the apex predators of the ecosystem.
Recent non-therapsid synapsid publications
- Maho, S., Gee, B.M., and Reisz, R.R. 2019. A new varanopid synapsid from the early Permian of Oklahoma and the evolutionary stasis in this clade. Royal Society Open Science 6:191297. DOI: 10.1098/rsos.191297
- Brink, K.S., MacDougall, M.J., and Reisz, R.R. 2019. Dimetrodon (Synapsida: Sphenacodontidae) from the cave system at Richards Spur, OK, USA, and a comparison of Early Permian–aged vertebrate paleoassemblages. The Science of Nature 106:2 DOI: 10.1007/s00114-018-1598-1
- Reisz, R.R. 2019. A small caseid synapsid, Arisierpeton simplex gen. et sp. nov., from the early Permian of Oklahoma, with a discussion of synapsid diversity at the classic Richards Spur locality. PeerJ 7: e6615. doi: 10.7717/peerj.6615
- LeBlanc, A.R.H., Brink, K.S., Whitney, M.R., Abdala, F., and Reisz, R.R. 2018. Dental ontogeny in extinct synapsids reveals a complex evolutionary history of the mammalian tooth attachment system. Proceedings of the Royal Society B, Biological Sciences 285(1890): 20181792. DOI: 10.1098/rspb.2018.1792
Therapsids
Therapsids are the more derived group of synapsids that originate from the pelycosaur-grade synapsids and that eventually replaced them as the dominant synapsids during the Middle Permian. Although still reptilian like their ancestors, many of the features associated with the evolution of mammals appear in therapsids, such as a more upright posture, a hard secondary palate separating the mouth cavity from the air passages (allowing mammals to breathe while eating), a lower jaw composed mostly of the dentary bone, and a dentition composed of multiple, different tooth types. Some therapsids were large, active predators, such as the biarmosuchians and the theriodonts, while others like the anomodonts were herbivorous. Some of these animals were very peculiar-looking; the dinocephalians, an early group of therapsids from the Middle Permian, often feature thickened skulls with knobs and other bony protrusions. The dicynodonts, a group within the anomodonts, fed using beaks similar to those of living turtles and birds; many dicynodonts were entirely toothless, and others had only large canine tusks that may have been used in fighting or digging rather than in feeding. The group that eventually gave rise to modern mammals is the cynodonts, which roughly means "dog-tooth" and which refers to the especially prominent canine teeth. Therapsids declined into the Mesozoic, but some non-mammalian therapsids persisted all the way into the Cretaceous, well after the origin of crown mammals. Because the non-therapsid synapsids were the most abundant during the early Permian, we do not have any therapsids from Richards Spur, but Robert has dabbled in therapsids from other localities in the past.
Therapsids are the more derived group of synapsids that originate from the pelycosaur-grade synapsids and that eventually replaced them as the dominant synapsids during the Middle Permian. Although still reptilian like their ancestors, many of the features associated with the evolution of mammals appear in therapsids, such as a more upright posture, a hard secondary palate separating the mouth cavity from the air passages (allowing mammals to breathe while eating), a lower jaw composed mostly of the dentary bone, and a dentition composed of multiple, different tooth types. Some therapsids were large, active predators, such as the biarmosuchians and the theriodonts, while others like the anomodonts were herbivorous. Some of these animals were very peculiar-looking; the dinocephalians, an early group of therapsids from the Middle Permian, often feature thickened skulls with knobs and other bony protrusions. The dicynodonts, a group within the anomodonts, fed using beaks similar to those of living turtles and birds; many dicynodonts were entirely toothless, and others had only large canine tusks that may have been used in fighting or digging rather than in feeding. The group that eventually gave rise to modern mammals is the cynodonts, which roughly means "dog-tooth" and which refers to the especially prominent canine teeth. Therapsids declined into the Mesozoic, but some non-mammalian therapsids persisted all the way into the Cretaceous, well after the origin of crown mammals. Because the non-therapsid synapsids were the most abundant during the early Permian, we do not have any therapsids from Richards Spur, but Robert has dabbled in therapsids from other localities in the past.
Recent therapsid publications
- Fröbisch, J. and Reisz, R.R. 2011. The postcranial anatomy of Suminia getmanovi (Synapsida: Anomodontia), the earliest known arboreal tetrapod. Zoological Journal of the Linnean Society, 162(3): 661-698. DOI: 10.1111/j.1096-3642.2010.00685.x