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Journal articles on the topic 'Sphenacodontidae'

Author: Grafiati

Published: 4 June 2025

Last updated: 23 June 2025

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1

SPINDLER, Frederik. "Re-evaluation of an early sphenacodontian synapsid from the Lower Permian of England." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 111, no. 1 (2019): 27–37. http://dx.doi.org/10.1017/s175569101900015x.

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ABSTRACTThe holotypic isolated maxilla of the early sphenacodontian Haptodus grandis from the Cisuralian of England is revisited. A unique character combination includes haptodontine-grade traits like less specialised teeth and a high number of precanines, but at the same time a shortened lacrimal that is separated from the naris, which is strongly diagnostic of Sphenacodontoidea. As the specimen cannot be assigned to any known taxon, the new taxon Hypselohaptodus grandis gen. nov. is proposed. Comparison with other sphenacodontians reveals a mosaic distribution of maxillary features, most significantly regarding the precanine region. Preliminary character histories preclude Hypselohaptodus from Sphenacodontidae, but suggest a haptodontine-grade or basal therapsid position. The latter hypothesis is substantiated by an ecological model of episodic wet phases in an overall trend of aridification throughout the Permian, to explain the rareness of non-sphenacodontid sphenacodontians in the fossil record. Also from the early Permian of England, an isolated dentary has previously been assigned to Ophiacodon, but can be shown to be either a sphenacodontian, possibly affiliated with Hypselohaptodus, or a robust, Stereorhachis-like ophiacodontid. The absence of Ophiacodon in the intramontaneous Permian basis of Europe is explained by a narrow environmental tolerance range requiring limnic connection with lowland basins.

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2

Reisz, Robert R., and David S. Berman. "Scoliomus puercensis Williston and Case, 1913, identified as a junior synonym of Sphenacodon ferox Marsh (Reptilia, Pelycosauria)." Canadian Journal of Earth Sciences 22, no. 8 (1985): 1236–39. http://dx.doi.org/10.1139/e85-126.

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The pelycosaurian reptile Scoliomus puercensis Williston and Case, 1913, based on several postcranial elements from the Permo-Pennsylvanian redbeds of the Cutler Formation of north-central New Mexico, proves on comparative study to be a junior synonym of Sphenacodon ferox of the family Sphenacodontidae. As Romer and Price noted, features originally cited as unique to the holotype are attributable to imperfect restoration. Although correctly recognizing S. puercensis as belonging to the suborder Sphenacodontia, they mistakenly assigned it to the family Varanopseidae, mainly on the basis of its small size.

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3

Shelton, Christen D., P. Martin Sander, Koen Stein, and Herman Winkelhorst. "Long bone histology indicates sympatric species of Dimetrodon (Lower Permian, Sphenacodontidae)." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 103, no. 3-4 (2012): 217–36. http://dx.doi.org/10.1017/s175569101300025x.

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ABSTRACTThe Briar Creek Bonebed (Artinskian, Nocona Formation) in Archer County is one of the richest sources of Dimetrodon bones in the Lower Permian of Texas, USA. Based on size, a small (D. natalis), an intermediate (D. booneorum), and a large species (D. limbatus) have been described from this locality. It has been proposed that these traditionally recognised species represent an ontogenetic series of only one species. However, the ontogenetic series hypothesis is inconsistent with the late ontogenetic state of the small bones, as suggested by their osteology and degree of ossification. Histological analysis of newly excavated material from the Briar Creek Bonebed has resolved some of the discretion between these two competing hypothesis, confirming the coexistence of a small (D. natalis) with at least one larger Dimetrodon species. An external fundamental system is present in the largest sampled long bones identified as D. natalis. The histology of D. natalis postcrania is described as incipient fibro lamellar bone. This tissue is a combination of parallel-fibred and woven-fibred bone that is highly vascularised by incipient primary osteons. The species status of D. booneorum and D. limbatus remain unresolved.

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4

Brink, K. S. "Case 3695DimetrodonCope, 1878 (Synapsida, sphenacodontidae): proposed conservation by reversal of precedence withBathygnathusLeidy, 1853." Bulletin of Zoological Nomenclature 72, no. 4 (2015): 297–99. http://dx.doi.org/10.21805/bzn.v72i4.a17.

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5

Berman, David S., Amy C. Henrici, Stuart S. Sumida, and Thomas Martens. "New materials of Dimetrodon teutonis (Synapsida: Sphenacodontidae) from the Lower Permian of Germany." Annals of the Carnegie Museum 73, no. 2 (2004): 108–16. http://dx.doi.org/10.5962/p.316083.

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6

Berman, David S., Amy C. Henrici, Stuart S. Sumida, and Thomas Martens. "New materials of Dimetrodon teutonis (Synapsida: Sphenacodontidae) from the Lower Permian of Germany." Annals of the Carnegie Museum 73 (June 11, 2004): 108–16. https://doi.org/10.5281/zenodo.13667618.

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7

Fröbisch, Jörg, Rainer R. Schoch, Johannes Müller, Thomas Schindler, and Dieter Schweiss. "A new basal sphenacodontid synapsid from the Late Carboniferous of the Saar-Nahe Basin, Germany." Acta Palaeontologica Polonica 56, no. 1 (2010): 113–20. https://doi.org/10.4202/app.2010.0039.

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Fröbisch, Jörg, Schoch, Rainer R., Müller, Johannes, Schindler, Thomas, Schweiss, Dieter (2011): A new basal sphenacodontid synapsid from the Late Carboniferous of the Saar-Nahe Basin, Germany. Acta Palaeontologica Polonica 56 (1): 113-120, DOI: 10.4202/app.2010.0039, URL: http://dx.doi.org/10.4202/app.2010.0039

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8

Falconnet, Jocelyn. "The sphenacodontid synapsid Neosaurus cynodus, and related material, from the Permo-Carboniferous of France." Acta Palaeontologica Polonica 60, no. 1 (2013): 169–82. https://doi.org/10.4202/app.2012.0105.

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Falconnet, Jocelyn (2015): The sphenacodontid synapsid Neosaurus cynodus, and related material, from the Permo-Carboniferous of France. Acta Palaeontologica Polonica 60 (1): 169-182, DOI: 10.4202/app.2012.0105, URL: http://dx.doi.org/10.4202/app.2012.0105

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9

Berman, David S., Robert R. Reisz, Thomas Martens, and Amy C. Henrici. "A new species of Dimetrodon (Synapsida: Sphenacodontidae) from the Lower Permian of Germany records first occurrence of genus outside of North America." Canadian Journal of Earth Sciences 38, no. 5 (2001): 803–12. http://dx.doi.org/10.1139/e00-106.

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A new species of the sphenacodontid synapsid Dimetrodon, D. teutonis, is described on the basis of a single, adult specimen consisting of a large portion of the presacral vertebral column. The holotype was collected from the Lower Permian Tambach Formation, lowermost formational unit of the Upper Rotliegend, of the Bromacker quarry locality in the midregion of the Thuringian Forest near Gotha, central Germany. This is the first record of the genus outside of North America and, therefore, provides not only additional biological evidence of a continuous Euramerican landmass during the Early Permian, but also the absence of any major physical or biological barrier to faunal interchange of terrestrial vertebrates. An estimated weight of 14 kg for D. teutonis is half that of the smallest, previously recognized species, D. natalis. Sphenacodontid phylogeny indicates that the diminutive size of D. teutonis represents an autapomorphy and is in general accord with the absence of large-sized, basal synapsid predators at this truly terrestrial upland locality. It is speculated that the diminutive size of D. teutonis was probably an adaptation to a truly terrestrial, relatively uplands existence like that represented by the Bromacker locality. Here it subsisted on small vertebrates (and possibly large invertebrates) of the Bromacker assemblage, in which the dominant members in both size and abundance were herbivorous diadectids, and it was unlikely to encounter large predators.

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10

REISZ, ROBERT R., DAVID S. BERMAN, and DIANE SCOTT. "The cranial anatomy and relationships of Secodontosaurus, an unusual mammal-like reptile (Synapsida: Sphenacodontidae) from the early Permian of Texas." Zoological Journal of the Linnean Society 104, no. 2 (1992): 127–84. http://dx.doi.org/10.1111/j.1096-3642.1992.tb00920.x.

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11

Brink, Kirstin S., Hillary C. Maddin, David C. Evans, and Robert R. Reisz. "Re-evaluation of the historic Canadian fossil Bathygnathus borealis from the Early Permian of Prince Edward Island." Canadian Journal of Earth Sciences 52, no. 12 (2015): 1109–20. http://dx.doi.org/10.1139/cjes-2015-0100.

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The holotype and only known specimen of Bathygnathus borealis is a partial snout with maxillary dentition of a presumed sphenacodontid from the Lower Permian (Artinskian 283–290 Ma) redbeds of Prince Edward Island, Canada. Due to its incomplete nature, assessment of the taxon’s systematic position within a cladistic analysis had never been performed. However, recent recognition of the phylogenetic utility of tooth characters in sphenacodontids now allows for a modern phylogenetic evaluation of B. borealis. Results show that B. borealis is the sister taxon of Dimetrodon grandis, which is supported by dental characters: crowns with mesial and distal denticles and roots elongate, lacking plicidentine. An autapomorphy of B. borealis is the large facial exposure of the septomaxilla. As Bathygnathus has priority over Dimetrodon in the scientific literature, we suggest a reversal of precedence is required to preserve the familiar name Dimetrodon and to maintain universality, thus recognizing the new species Dimetrodon borealis.

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12

Didier, Gilles, and Michel Laurin. "Distributions of extinction times from fossil ages and tree topologies: the example of mid-Permian synapsid extinctions." PeerJ 9 (December 9, 2021): e12577. http://dx.doi.org/10.7717/peerj.12577.

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Given a phylogenetic tree that includes only extinct, or a mix of extinct and extant taxa, where at least some fossil data are available, we present a method to compute the distribution of the extinction time of a given set of taxa under the Fossilized-Birth-Death model. Our approach differs from the previous ones in that it takes into account (i) the possibility that the taxa or the clade considered may diversify before going extinct and (ii) the whole phylogenetic tree to estimate extinction times, whilst previous methods do not consider the diversification process and deal with each branch independently. Because of this, our method can estimate extinction times of lineages represented by a single fossil, provided that they belong to a clade that includes other fossil occurrences. We assess and compare our new approach with a standard previous one using simulated data. Results show that our method provides more accurate confidence intervals. This new approach is applied to the study of the extinction time of three Permo-Carboniferous synapsid taxa (Ophiacodontidae, Edaphosauridae, and Sphenacodontidae) that are thought to have disappeared toward the end of the Cisuralian (early Permian), or possibly shortly thereafter. The timing of extinctions of these three taxa and of their component lineages supports the idea that the biological crisis in the late Kungurian/early Roadian consisted of a progressive decline in biodiversity throughout the Kungurian.

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13

Lucas, Spencer G. "Comment (Case 3695) — Support for the proposed conservation of Dimetrodon Cope, 1878 by reversal of precedence with Bathygnathus Leidy, 1853 (Synapsida: Sphenacodontidae)." Bulletin of Zoological Nomenclature 74, no. 1 (2017): 46. http://dx.doi.org/10.21805/bzn.v74.a013.

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14

Spindler, F., D. Scott, and R. R. Reisz. "New information on the cranial and postcranial anatomy of the early synapsid <i>Ianthodon schultzei</i> (Sphenacomorpha: Sphenacodontia), and its evolutionary significance." Fossil Record 18, no. 1 (2014): 17–30. http://dx.doi.org/10.5194/fr-18-17-2015.

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Abstract. Newly identified material belonging to the holotype specimen of Ianthodon schultzei substantially increases our knowledge of this poorly known basal sphenacodont synapsid from the fossil site in Garnett, Kansas (Missourian, Late Pennsylvanian). The original description, based on a partial dermal skull roof, is augmented with information on the palate and braincase, together with data on the mandible and a few postcranial elements. The known skeletal morphology resembles that of Haptodus garnettensis, another synapsid taxon known from this locality, but with fewer marginal, distinctly recurved teeth and smaller teeth on the transverse flange of the pterygoid. Although recognizing that the holotype and only known specimen represents a juvenile individual, Ianthodon appears to reflect a more basal sphenacodontian condition than H. garnettensis. A restricted phylogenetic analysis based on previous work and newly scored characters for Ianthodon, Cutleria and Pantelosaurus supports this hypothesis. The Garnett locality appears to preserve an assemblage of synapsids (Haptodus, Ianthasaurus, Ianthodon) that are close to the base of the large clade that includes Edaphosauridae and Sphenacodontia, suggesting that an initial diversification of this clade occurred well within the Carboniferous Period.

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Reisz, Robert R., and Michel Laurin. "A reevaluation of the enigmatic Permian synapsid Watongia and of its stratigraphic significance." Canadian Journal of Earth Sciences 41, no. 4 (2004): 377–86. http://dx.doi.org/10.1139/e04-016.

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The enigmatic synapsid Watongia, initially described on the basis of fragmentary remains from the Chickasha Formation of Oklahoma as an early therapsid (a gorgonopsian), is redescribed and is shown to represent the largest known varanopid synapsid. Its assignment to the Varanodontinae (Varanopidae: Synapsida) is supported by several diagnostic features, including a strongly recurved marginal dentition with both posterior and anterior, unserrated, cutting edges, quadratojugal with two discrete superficial rami, a large lateral tuberosity on the postorbital, short, deep excavations on the neural arches, and a broad, short radiale. The presence in Watongia of a posterolateral process of the frontal precludes therapsid or sphenacodontid affinities. The previously described preparietal that provided the strongest evidence of therapsid affinities for Watongia is shown to be based on misinterpreted skull fragments that were incorrectly assembled. The presence of a varanopid in the Chickasha Formation is consistent with a Guadalupian age (Middle Permian), and in the absence of large sphenacodontids and therapsids, Watongia was probably the top predator of its terrestrial vertebrate community.

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16

Kammerer, Christian F. "Comment (Case 3695) — Additional remarks in support of the proposed conservation of Dimetrodon Cope, 1878 by reversal of precedence with Bathygnathus Leidy, 1853 (Synapsida, Sphenacodontidae)." Bulletin of Zoological Nomenclature 74, no. 1 (2017): 132. http://dx.doi.org/10.21805/bzn.v74.a035.

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17

Spindler, Frederik. "A faunivorous early sphenacodontian synapsid with a diastema." Palaeontologia Electronica 23, no. 1 (2019): 1–9. https://doi.org/10.26879/1023.

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18

Spindler, Frederik. "The skull of Tetraceratops insignis (Synapsida, Sphenacodontia)." Palaeovertebrata 43, no. 1 (2020): e1. http://dx.doi.org/10.18563/pv.43.1.e1.

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19

Spindler, F., D. Scott, and R. R. Reisz. "New information on the cranial and postcranial anatomy of the early synapsid Ianthodon schultzei (Sphenacomorpha: Sphenacodontia), and its evolutionary significance." Fossil Record 18, no. 1 (2014): 17–30. https://doi.org/10.5194/fr-18-17-2015.

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Spindler, F., Scott, D., Reisz, R. R. (2015): New information on the cranial and postcranial anatomy of the early synapsid Ianthodon schultzei (Sphenacomorpha: Sphenacodontia), and its evolutionary significance. Fossil Record 18 (1): 17-30, DOI: 10.5194/fr-18-17-2015, URL: http://dx.doi.org/10.5194/fr-18-17-2015

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20

Reisz, Robert R., Diane Scott, and Jack van Bendegem. "Atlas–axis complex of Secodontosaurus, a sphenacodontid mammal-like reptile (Eupelycosauria: Synapsida) from the Lower Permian of Texas." Canadian Journal of Earth Sciences 29, no. 3 (1992): 596–600. http://dx.doi.org/10.1139/e92-051.

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The description of the atlas–axis complex of Secodontosaurus (an Early Permian synapsid) indicates that sphenacodontids share with primitive therapsids the derived feature of a tall atlantal pleurocentrum that extends to the ventral edge of the vertebral column. Although similar, the postcranial skeletons of Dimetrodon and Secodontosaurus can be differentiated by the distinct shape and size of the latter's axial neural spine and posterior zygapophysis.

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21

Brocklehurst, Neil, and Kirstin S. Brink. "Selection towards larger body size in both herbivorous and carnivorous synapsids during the Carboniferous." FACETS 2, no. 1 (2017): 68–84. http://dx.doi.org/10.1139/facets-2016-0046.

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Body size is one of the most important characteristics of an organism, impacting a great variety of ecological characteristics. The influence of diet on body size has received considerable attention, with previous studies suggesting a greater tendency towards increased body size in herbivores than macro-carnivores. The earliest known herbivorous and macro-carnivorous synapsids provide an ideal case study for examining body size evolution in different dietary regimes. Sphenacomorpha contains two lineages: Edaphosauridae (some of the most abundant terrestrial herbivores in the late Carboniferous and early Permian), and Sphenacodontia (the largest and most abundant carnivores of that time). Phylogenetic comparative analyses are used to compare trait evolution in sphenacomorphs, including a Bayesian method for identifying branches along which phenotypic selection occurred. Two branches show rapid increases in body size in the late Carboniferous. The first occurred in Edaphosauridae, along the branch leading to the herbivorous members. The later shift towards larger size occurred in Sphenacodontia, producing a clade of large carnivores. It is possible that the rapid appearance of large herbivorous synapsids in the Carboniferous provided the selective pressure for carnivores to increase their size. Following these two shifts, rates of evolution in edaphosaurids slowed significantly, but the carnivorous sphenacodontians showed further increases.

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22

Fröbisch, Jörg, Rainer R. Schoch, Johannes Müller, Thomas Schindler, and Dieter Schweiss. "A New Basal Sphenacodontid Synapsid from the Late Carboniferous of the Saar-Nahe Basin, Germany." Acta Palaeontologica Polonica 56, no. 1 (2011): 113–20. http://dx.doi.org/10.4202/app.2010.0039.

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23

Hook, Robert W., and Nicholas Hotton. "A new sphenacodontid pelycosaur (Synapsida) from the Wichita Group, Lower Permian of north-central Texas." Journal of Vertebrate Paleontology 11, no. 1 (1991): 37–44. http://dx.doi.org/10.1080/02724634.1991.10011374.

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24

Huttenlocker, Adam K., Elizabeth Rega, and Stuart S. Sumida. "Comparative anatomy and osteohistology of hyperelongate neural spines in the sphenacodontids Sphenacodon and Dimetrodon (Amniota: Synapsida)." Journal of Morphology 271, no. 12 (2010): 1407–21. http://dx.doi.org/10.1002/jmor.10876.

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25

EVANS, DAVID C., HILLARY C. MADDIN, and ROBERT R. REISZ. "A RE-EVALUATION OF SPHENACODONTID SYNAPSID MATERIAL FROM THE LOWER PERMIAN FISSURE FILLS NEAR RICHARDS SPUR, OKLAHOMA." Palaeontology 52, no. 1 (2009): 219–27. http://dx.doi.org/10.1111/j.1475-4983.2008.00837.x.

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26

Kissel, Richard A., and Thomas M. Lehman. "Upper Pennsylvanian tetrapods from the Ada Formation of Seminole County, Oklahoma." Journal of Paleontology 76, no. 3 (2002): 529–45. http://dx.doi.org/10.1017/s0022336000037355.

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A recently discovered tetrapod-bearing locality (OMNH V1005) in the Upper Pennsylvanian Ada Formation of Oklahoma has produced the remains of six taxa: the pelycosaurian-grade synapsid Ophiacodon cf. mirus, an indeterminate sphenacodontian pelycosaur, the temnospondyl Eryops? sp., the rare diadectid Diasparactus zenos, and two unidentified taxa known only from jaw fragments. The skeletal material comprises an allochthonous assemblage transported by low-velocity currents prior to burial. Except for four articulated Ophiacodon vertebral segments, all fossil material recovered in situ was disarticulated. The bones were not exposed to prolonged periods of weathering prior to burial. OMNH V1005 records the first occurrence of Eryops, Diasparactus, and Ophiacodon from the Pennsylvanian of Oklahoma. The presence of Diasparactus zenos indicates that this species was not endemic to New Mexico, as formerly believed. An associated dentary provides the first well-preserved cheek teeth of Diasparactus zenos. Compared to other North American diadectid genera, these teeth resemble more closely those of Diadectes than those of Desmatodon. The occurrence of Ophiacodon mirus, which was previously known from Lower Permian strata of New Mexico, extends both the stratigraphic and geographic range of this species. The Ada assemblage resembles those found in Permo-Carboniferous deltaic deposits in the southwestern United States.

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Blob, Richard W. "Evolution of hindlimb posture in nonmammalian therapsids: biomechanical tests of paleontological hypotheses." Paleobiology 27, no. 1 (2001): 14–38. http://dx.doi.org/10.1666/0094-8373(2001)027<0014:eohpin>2.0.co;2.

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Analyses of limb joint morphology in nonmammalian therapsid “mammal-like reptiles” have suggested that among many lineages, individual animals were capable of shifting between sprawling and upright hindlimb postures, much like modern crocodilians. The ability to use multiple limb postures thus might have been ancestral to the generally more upright posture that evolved during the transition from “mammal-like reptiles” to mammals. Here I derive a biomechanical model to test this hypothesis through calculations of expected posture-related changes in femoral stress for therapsid taxa using different limb postures. The model incorporates morphological data from fossil specimens and experimental data from force platform experiments on iguanas and alligators.Experimental data suggest that the evolutionary transition from sprawling to nonsprawling posture was accompanied by a change in the predominant loading regime of the limb bones, from torsion to bending. Changes in the cross-sectional morphology of the hindlimb bones between sphenacodontid “pelycosaurs” and gorgonopsid therapsids are consistent with the hypothesis that bending loads increased in importance early in therapsid evolution; thus, bending stresses are an appropriate model for the maximal loads experienced by the limb bones of theriodont therapsids. Results from the model used to estimate stresses in these taxa do not refute the use of both sprawling and more upright stance among basal theriodont therapsids. Thus, the hypothesis that the use of multiple postures was ancestral to the more upright posture typical of most mammals is biomechanically plausible. Model calculations also indicate that the axial rotation of the femur typical in sprawling locomotion can reduce peak bending stresses. Therefore, as experimental data from alligators and iguanas suggest, the evolution of nonsprawling limb posture and kinematics in therapsids might have been accompanied by increased limb bone bending stress.

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Huttenlocker, Adam K., Suresh A. Singh, Amy C. Henrici, and Stuart S. Sumida. "A Carboniferous synapsid with caniniform teeth and a reappraisal of mandibular size-shape heterodonty in the origin of mammals." Royal Society Open Science 8, no. 12 (2021). http://dx.doi.org/10.1098/rsos.211237.

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Heterodonty is a hallmark of early mammal evolution that originated among the non-mammalian therapsids by the Middle Permian. Nonetheless, the early evolution of heterodonty in basal synapsids is poorly understood, especially in the mandibular dentition. Here, we describe a new synapsid, Shashajaia bermani gen. et sp. nov., based on a well-preserved dentary and jaw fragments from the Carboniferous–Permian Halgaito Formation of southern Utah. Shashajaia shares with some sphenacodontids enlarged (canine-like) anterior dentary teeth, a dorsoventrally deep symphysis and low-crowned, subthecodont postcanines having festooned plicidentine. A phylogenetic analysis of 20 taxa and 154 characters places Shashajaia near the evolutionary divergence of Sphenacodontidae and Therapsida (Sphenacodontoidea). To investigate the ecomorphological context of Palaeozoic sphenacodontoid dentitions, we performed a principal component analysis based on two-dimensional geometric morphometrics of the mandibular dentition in 65 synapsids. Results emphasize the increasing terrestrialization of predator–prey interactions as a driver of synapsid heterodonty; enhanced raptorial biting (puncture/gripping) aided prey capture, but this behaviour was probably an evolutionary antecedent to more complex processing (shearing/tearing) of larger herbivore prey by the late Early to Middle Permian. The record of Shashajaia supports the notion that the predatory feeding ecology of sphenacodontoids emerged in palaeotropical western Pangea by late Carboniferous times.

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"Opinion 2446 (Case 3695) – Dimetrodon Cope, 1878 (Synapsida, Sphenacodontidae): name conserved." Bulletin of Zoological Nomenclature 76, no. 1 (2019): 200. http://dx.doi.org/10.21805/bzn.v76.a063.

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30

Brink, Kirstin S., Mark J. MacDougall, and Robert R. Reisz. "Dimetrodon (Synapsida: Sphenacodontidae) from the cave system at Richards Spur, OK, USA, and a comparison of Early Permian–aged vertebrate paleoassemblages." Science of Nature 106, no. 1-2 (2019). http://dx.doi.org/10.1007/s00114-018-1598-1.

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31

Didier, Gilles, and Michel Laurin. "Testing extinction events and temporal shifts in diversification and fossilization rates through the skyline Fossilized Birth‐Death (FBD) model: The example of some mid‐Permian synapsid extinctions." Cladistics, April 23, 2024. http://dx.doi.org/10.1111/cla.12577.

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AbstractIn the last decade, the Fossilized Birth–Death (FBD) process has yielded interesting clues about the evolution of biodiversity through time. To facilitate such studies, we extend our method to compute the probability density of phylogenetic trees of extant and extinct taxa in which the only temporal information is provided by the fossil ages (i.e. without the divergence times) in order to deal with the piecewise constant FBD process, known as the “skyline FBD”, which allows rates to change between pre‐defined time intervals, as well as modelling extinction events at the bounds of these intervals. We develop approaches based on this method to assess hypotheses about the diversification process and to answer questions such as “Does a mass extinction occur at this time?” or “Is there a change in the fossilization rate between two given periods?”. Our software can also yield Bayesian and maximum‐likelihood estimates of the parameters of the skyline FBD model under various constraints. These approaches are applied to a simulated dataset in order to test their ability to answer the questions above. Finally, we study an updated dataset of Permo‐Carboniferous synapsids to get additional insights into the dynamics of biodiversity change in three clades (Ophiacodontidae, Edaphosauridae and Sphenacodontidae) in the Pennsylvanian (Late Carboniferous) and Cisuralian (Early Permian), and to assess support for end‐Sakmarian (or Artinskian) and end‐Cisuralian mass extinction events discussed in previous studies.

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32

MAHO, Tea, Robert HOLMES, and Robert R. REISZ. "Visual methods for documenting the preservation of large-sized synapsids at Richards Spur." Comptes Rendus Palevol 23, no. 7 (2024). http://dx.doi.org/10.5852/cr-palevol2024v23a7.

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Large isolated skeletal elements, including those of sphenacodontid and ophiacodontid synapsids from the upland cave systems of the Richards Spur locality, Oklahoma, are described. Multiple forms of visual representation, including coquille and stipple drawings, are used to document and examine the isolated elements. A fragmentary anterior portion of a dentary has the sphenacodontid four-leaf clover plicidentine attachment within the tooth roots, but the teeth are all of uniform size, and the symphyseal area is relatively slender and does not curve upward, suggesting that the specimen may not belong to any known member of the clade. A larger humerus with only the distal end preserved and a complete astragalus have distinct characteristics which are attributable to the sphenacodontid Dimetrodon Cope, 1878. A second, smaller humerus was identified to belong to Ophiacodon Marsh, 1878, cf. O. navajovicus and represents the first record of an ophiacodontid at Richards Spur. Finally, two large sphenacodontid interclavicles were discovered, with one having unusual growths representing a pathological condition. Typically, large amniotes are quite rare in this early Permian upland ecosystem, but the discovery of the new material shows that large synapsids are present at Richards Spur.

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Spindler, Frederik. "A faunivorous early sphenacodontian synapsid with a diastema." Palaeontologia Electronica, 2019. http://dx.doi.org/10.26879/1023.

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Falconnet, Jocelyn. "The sphenacodontid synapsid Neosaurus cynodus, and related material, from the Permo-Carboniferous of France." Acta Palaeontologica Polonica, 2013. http://dx.doi.org/10.4202/app.2012.0105.

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Knaus, Philipp L., Anneke H. van Heteren, Jacqueline K. Lungmus, and P. Martin Sander. "High Blood Flow Into the Femur Indicates Elevated Aerobic Capacity in Synapsids Since the Synapsida-Sauropsida Split." Frontiers in Ecology and Evolution 9 (December 24, 2021). http://dx.doi.org/10.3389/fevo.2021.751238.

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Varanids are the only non-avian sauropsids that are known to approach the warm-blooded mammals in stamina. Furthermore, a much higher maximum metabolic rate (MMR) gives endotherms (including birds) higher stamina than crocodiles, turtles, and non-varanid lepidosaurs. This has led researchers to hypothesize that mammalian endothermy evolved as a second step after the acquisition of elevated MMR in non-mammalian therapsids from a plesiomorphic state of low metabolic rates. In recent amniotes, MMR correlates with the index of blood flow into the femur (Qi), which is calculated from femoral length and the cross-sectional area of the nutrient foramen. Thus, Qi may serve as an indicator of MMR range in extinct animals. Using the Qi proxy and phylogenetic eigenvector maps, here we show that elevated MMRs evolved near the base of Synapsida. Non-mammalian synapsids, including caseids, edaphosaurids, sphenacodontids, dicynodonts, gorgonopsids, and non-mammalian cynodonts, show Qi values in the range of recent endotherms and varanids, suggesting that raised MMRs either evolved in synapsids shortly after the Synapsida-Sauropsida split in the Mississippian or that the low MMR of lepidosaurs and turtles is apomorphic, as has been postulated for crocodiles.

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Laurin, Michel, and Gilles Didier. "The rise and fall of Varanopidae† (Amniota, Synapsida)." Frontiers in Earth Science 13 (March 20, 2025). https://doi.org/10.3389/feart.2025.1544451.

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Study of past biological crises is now a timely topic because we may be in the midst of an anthropogenic mass extinction event. A skyline Fossilized Birth-Death (FBD) analysis of a dataset of 21 varanopid taxa, ranging in geological age from the mid-Pennsylvanian to the late Guadalupian, was undertaken to assess the impact of putative mass extinction events on the Varanopidae. Our results suggest that this clade diversified in the Pennsylvanian but dwindled in diversity in the Cisuralian. This is reminiscent of the evolution of biodiversity displayed by ophiacodontids, edaphosaurids and sphenacodontids (abbreviated “the OES grade” from here on) in the same time interval. These patterns are possibly linked to a warming and aridification trend (perhaps local and linked to movements of plates in Pangea) that spanned most of the Early Permian. However, contrary to these last three clades (OES), varanopids survived until near the end of the Capitanian; this differential fate may be linked to differences in habitat use (mainly lowland for the OES grade; often more upland for varanopids). Models that include a mass extinction event that eliminated all varanopids in the late Capitanian, when a mass extinction event has been recognized by previous studies, have the most support from the data. This suggests that the last varanopids were among the many victims of the Capitanian crisis. Our analyses also support the existence of a previously unrecognized moderate extinction event in the Asselian.

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