Caseidae are an Extinction family of basal that lived from the Late Carboniferous to Middle Permian between about 300 and 265 million years ago. Fossils of these animals come from the south-central part of the United States (Texas, Oklahoma, and Kansas), from various parts of Europe (European Russia, France, Germany, Sardinia, and Poland), and possibly from South Africa if the genus Eunotosaurus is indeed a caseid as some authors proposed in 2021. Caseids show great Taxonomy and morphological diversity. The most basal taxa were small Insectivore and Omnivore forms that lived mainly in the Upper Carboniferous and Lower Permian, such as Eocasea, Callibrachion, and Martensius. This type of caseid persists until the Guadalupian with Phreatophasma and may be Eunotosaurus. During the early Permian, the clade is mainly represented by many species that adopted a Herbivore diet. Some have evolved into gigantic forms that can reach in length, such as Cotylorhynchus and Alierasaurus, making them the largest Permian synapsids. Caseids are considered important components of early terrestrial in vertebrate history because the numerous herbivorous species in this family are among the first terrestrial to occupy the role of primary consumer. The caseids experienced a significant evolutionary radiation at the end of the early Permian, becoming, with the captorhinid eureptiles, the dominant herbivores of terrestrial ecosystems in place of the Edaphosauridae and Diadectidae.
In 2016 and 2022, paleontologists proposed a semiaquatic lifestyle for the most derived genera like Cotylorhynchus and Lalieudorhynchus, but this hypothesis is disputed by other researchers.
With a fossil record spanning from the Late Carboniferous to the Middle Permian, caseids are one of the basal synapsids groups (formerly known as "pelycosaur") having the largest Stratigraphy range. They also represent one of only two basal synapsid groups (along with the Varanopidae) to survive in therapsid-dominated terrestrial communities. Thus, the last known caseids come from the Stratum of the Guadalupian (Upper Roadian-Wordian) of France and European Russia, where they cohabited notably with . These last caseids still show a certain morphological diversity with medium to large herbivores ( Ennatosaurus and Lalieudorhynchus), as well as small predatory or omnivorous forms such as Phreatophasma and possibly Eunotosaurus. Caseids are so far unknown in Upper Permian strata and probably disappeared at the end of the Middle Permian. They were replaced by (with similar dentition) and .
Description
Caseids measured from less than to in length.
They had a small head wider than high and with a forward-inclined snout, a very short neck, a long tail, robust forelimbs, and a body of variable proportions depending on their diet. Small insectivorous species like
Eocasea had an unexpanded trunk.
Others with an omnivorous diet like
Martensius had a barely enlarged rib cage, a more elongated skull, smaller
, and a snout less inclined forward than in herbivorous caseids.
The latter were characterized by their disproportionately small
skull compared to the size of the body. The postcranial skeleton indeed shows a spectacular increase in the volume of the
rib cage, which becomes very wide and barrel-shaped, probably to accommodate a particularly developed intestine, necessary for the digestion of high-fiber rich plants. In these forms, the skull has very large external nostrils and a very short facial region with a strong forward inclination of the end of the snout which clearly overhangs the dental row. The temporal fenestrae are also relatively large (especially in
Ennatosaurus), the supratemporals are large in size, and, on the
Occipital bone surface, the paroccipital processes are massively developed, establishing strong supporting contacts with the
Squamosal bone.
The dorsal surface of the skull is covered with numerous small pits. These suggest the presence of large
Reptile scale on the head of these animals.
Numerous
Lip Foramen running parallel to the ventral edge of the
premaxilla and
maxilla, as well as along the dorsal edge of the dentary, suggest the presence of scaly "lips" which must have concealed the dentition when the jaws were closed.
The
Tooth, simply conical and pointed in insectivorous species, adopt in herbivorous species a leafy or spatulate morphology and are provided with more or less numerous cuspules. Numerous small teeth also adorned several bones of the palate. Herbivorous species do not show a simple evolutionary trend towards increasing tooth complexity.
Thus, the teeth of the basal taxa
Casea and
Arisierpeton have three cuspules
just like in the more derived forms
Cotylorhynchus and
Caseopsis.
and
Euromycter, which occupy an intermediate
Phylogenetics position, have teeth bearing 5 to 7 cuspules and 5 to 8 cuspules respectively.
, one of the most derived caseids, has teeth with 5 cuspules.
In
Angelosaurus the teeth have a bulbous morphology with very short and wide crowns. Their sturdiness and the significant wear they show indicate that
Angelosaurus must have fed on tougher plants than those on which most other herbivorous caseids fed.
Herbivorous caseids also show very different dietary adaptations from those seen in another group of basal synapsids, the
Edaphosauridae. The latter had, in addition to the marginal dentition, a dental battery made up of numerous teeth located both on the
palate and on the inner surface of the lower jaws. In herbivorous caseids, the palatal teeth are smaller, and the inner surface of the lower jaws bears no teeth. Instead of a dental battery, they had a massive
tongue (as indicated by the presence of a highly developed
hyoid apparatus found in
Ennatosaurus and
Euromycter) perhaps rough, with which they had to compress food against the palatal teeth.
The forelimbs of caseids are often more robust than the hindlimbs. It has indeed been observed that the bones of the forelimbs gained in robustness from the beginning of the evolution of the group, before the appearance of large species, while the hindlimbs remained slenderer. These characteristics suggest that the initial strengthening of the forelimbs was probably related to a particular function such as digging, and that this trait was later Exaptation by more derived and larger caseids to support their weights of up to several hundred kilograms.
Footprints
Many vertebrate tracks have been proposed as belonging to Caseidae. In the early 2000s, large footprints known as
Brontopus from the Permian Lodève basin in southern
France were considered to belong either to a caseid or
therapsid.
In 2019, Lorenzo Marchetti and colleagues, however, determined that dinocephalians were most likely the trackmakers of the ichnogenus
Brontopus.
In 2012, Rafael Costa da Silva and colleagues proposed that the ichnogenus
Chelichnus, widely distributed in Permian desert facies (fossil
) of
Europe,
North America and
South America, could represent caseids footprints.
In 2019, Marchetti and colleagues, however, reinterpreted
Chelichnus as a
nomen dubium and a
taphotaxon, this type of track showing false anatomical features generated by locomotion on sandy inclined paleosurface.
In 2014, Eva Sacchi and colleagues described the ichnotaxon
Dimetropus from about a hundred isolated footprints and several trackways from the early Permian Wellington Formation in
Oklahoma. The morphological study of these footprints and their comparison with tetrapod skeletons revealed that they probably belong to a large caseid comparable in size to
Cotylorhynchus (the latter from more recent strata).
According to Sacchi and colleagues, some footprints from the Lodève Basin (unspecified geological formation) are similar to those from the Wellington Formation and these authors designate them as
Dimetropus cf.
osageorum.
The study by Sacchi et al. also demonstrates that the ichnogenus
Dimetropus exhibits great morphological variation and that its producers can be assigned to different zoological groups among non-therapsid synapsids and not just
Sphenacodontidae as once thought.
In 2021, Rafel Matamales-Andreu and colleagues assigned footprints found in the Lower Permian (
Artinskian-
Kungurian) Port des Canonge Formation in
Mallorca to a caseid. These footprints resemble those of
D. osageorum but they also have differences. These footprints are left in open nomenclature as cf.
Dimetropus sp.. They are, however, smaller than those of
D. osageorum and would have been produced by a caseid of modest size with proportions comparable to
Ennatosaurus.
Paleobiology
Diets
During their evolutionary history, caseids shifted from faunivorous to herbivorous diet, a pattern that also occurred independently in other Carboniferous and Permian tetrapod groups such as
and
Edaphosauridae. Earliest and most basal caseids, such as the late Carboniferous
Eocasea and the early Permian
Callibrachion had an unexpanded rib cage and dentition composed of very small conical teeth suggesting an insectivorous diet. Another basal caseid,
Martensius, has a slightly enlarged barrel-shaped trunk and dentition in which teeth indicative of an
Insectivore diet in juveniles have been
Ontogeny replaced in adults by teeth suggesting an
Omnivore diet. In
Martensius, the adult was still able to feed on insects, but it also possesses a draft of the herbivorous diet specializations present in later caseids, such as a relatively short, slightly forward-inclined snout, and a dentition that is almost
Heterodont in the upper jaws and completely homodont in lower jaws. The sequence of dental trait acquisition in
Martensius suggests that intestinal vegetation processing preceded
Mouth processing in the evolution of caseid herbivory. A juvenile insectivorous diet would have provided the opportunity for successful introduction into the intestine of microorganisms capable of
Endosymbiont cellulolysis, particularly if the prey ingested were herbivorous insects which harbor such microorganisms in their viscera. Subsequently, the caseids adopted a strictly herbivorous diet and evolved into gigantic forms. These herbivorous caseids had spatulate teeth equipped with more or less numerous cuspules and a very enlarged and barrel-shaped rib cage which must have housed highly developed intestines necessary for the digestion of plants with low nutritional value. This adaptation would partly explain the diversification and expansion of the group at the end of the Lower Permian and during the Middle Permian, because it allowed them to exploit a fiber-rich plant resource that had by then become abundant and widespread. Nevertheless, small probably faunivorous caseids like
Phreatophasma seem to have persisted until the Middle Permian.
Semiaquatic vs terrestrial lifestyle
Caseids are generally considered primarily terrestrial animals. Everett C. Olson in particular considered that the degree of ossification of the skeleton, the relatively short feet and hands, the massive claws, the limbs with very powerful extensor muscles, and the solid sacrum, strongly suggested a terrestrial lifestyle. Olson did not rule out that the caseids spent some time in water, but he considered locomotion on land to be an important aspect of their lifestyle.
It has been suggested that the very powerful forelimbs, with strong and very tendinous extensor muscles, as well as very massive claws, could be used to dig up roots or tubers.
However, the very short
neck implied a low amplitude of vertical movements of the head which precluded the large species from feeding at ground level.
Another hypothesis suggests that the caseids could have used their powerful forelimbs to fold large plants towards them, which they would have torn off with their powerful claws.
Other hypotheses suggest that some caseids such as
Cotylorhynchus used their limbs with powerful claws to defend themselves against predators, or during intraspecific activities linked in particular to
reproduction. According to Olson, an interesting thing about this, is that almost all known specimens of the species
Cotylorhynchus have one to ten ribs broken and healed during life.
Finally, for some authors, the large derived caseids would have been
semiaquatic animals that used their hands with large claws like
, which could also be used to manipulate the plants on which they fed.
In 2016, Markus Lambertz and colleagues questioned the terrestrial lifestyle of large caseids like Cotylorhynchus. These authors showed that the bone microstructure of the humerus, femur and ribs of adult and immature specimens of Cotylorhynchus resembled that of aquatic animals more than that of terrestrial animals, the bones having a very spongy structure, an extremely thin cortex, and having no distinct Medullary cavity. This low bone density would have been a handicap for animals weighing several hundred kilos with a strictly terrestrial lifestyle. Lambertz et al. also argued that the joints between the vertebrae and the dorsal ribs allowed only small ranges of motion of the rib cage, thus limiting costal ventilation. To overcome this, they proposed that a proto-diaphragm was present to facilitate breathing, especially in aquatic environment. These authors also consider that the arid Paleoclimatology to which the caseid deposits correspond are not incompatible with an aquatic lifestyle of these animals. These paleoenvironments in fact included a significant number of water bodies (rivers, lakes and lagoons). The arid conditions could have been the reason why the animals would sometimes congregate and eventually die. In addition, arid environments have a low density of plants, which would require even more locomotor effort to find food. Thus, for Lambertz et al., large caseids like Cotylorhynchus must have been mainly aquatic animals that only came on dry land for the purposes of reproduction or thermoregulation.
This hypothesis is however disputed by Kenneth Angielczyk and Christian Kammerer as well as by Robert Reisz and colleagues based on Paleontology and Taphonomy data combined with the absence in these large caseids of morphological adaptations to an aquatic lifestyle. According to Angielczyk and Kammerer, the low bone density of caseids identified by Lambertz et al. does not resemble that of semiaquatic animals, which tend to have a more strongly ossified skeleton to provide passive buoyancy control and increased stability against current and wave action. Cotylorhynchus bone microstructure is more similar to what is seen in animals living in the Pelagic zone, such as and , which emphasize high maneuverability, rapid acceleration and hydrodynamic control of buoyancy. However, the caseid morphology was totally incompatible with a Pelagic zone lifestyle. Thus, due to these unusual data, Angielczyk and Kammerer consider that the available evidence is still insufficient to question the more widely assumed terrestrial lifestyle of caseids.
In 2022, Werneburg and colleagues proposed a somewhat different semiaquatic lifestyle, in which large caseids like Lalieudorhynchus (whose bone texture is even more osteoporotic than in Cotylorhynchus) would be ecological equivalents of modern Hippopotamus, passing part of their time in the water (being underwater walkers rather than swimming animals) but coming on dry land for food.
Evolution
Caseids first appear in the fossil record at the end of the Carboniferous and are already present in both
North America and
Europe with small predatory forms like
Eocasea and
Datheosaurus.
These faunivorous caseids also exist at the beginning of the lower Permian, such as
Callibrachion,
and may have existed until the base of the middle Permian with
Phreatophasma.
During the Permian, the representatives of the clade mainly evolved towards herbivory. These herbivorous caseids experienced an important evolutionary radiation during the second half of the lower Permian by becoming, with the moradisaurine
Captorhinidae Eureptilia, the main herbivores of terrestrial
instead of
Edaphosauridae and
Diadectidae. The decline of edaphosaurids and the propagation of caseids coincides with an aridification of the environment that occurred from the
Artinskian and which would have favored the caseid expansion.
and
Taphonomy data indicate that the majority of edaphosaurids favored humid habitats (their remains are found mainly in lacustrine and marshy deposits) while herbivorous caseids generally lived in drier
where ponds and streams water were ephemeral.
The last caseids date from the Middle Permian and are mainly known in Europe with
Phreatophasma and
Ennatosaurus from the
Roadian-
Wordian of Russia,
from the Roadian-(Wordian?) of Sardinia,
and
Lalieudorhynchus from the late Wordian-early
Capitanian of southern France.
In North America,
Angelosaurus and
Cotylorhynchus from the Chickasha Formation in Oklahoma probably date to the early Roadian, while the caseids from the San Angelo Formation in Texas are slightly older and may straddle the
Kungurian-Roadian boundary but it is not yet clear whether they date from the latest Kungurian or from the earliest Roadian.
Paleobiogeography
Caseid
have been found in the southern and central
United States (
Texas,
Oklahoma,
Kansas),
France,
Germany,
Poland,
Sardinia, and
European Russia. This geographical distribution corresponds to the paleoequatorial belt of
Pangaea during the Carboniferous and the Permian, with the exception of the Russian localities which were located at the level of the 30th parallel north where a more temperate climate prevailed. The absence in Russia of terrestrial vertebrate localities prior to the
Kungurian does not allow us to know the precise moment of the arrival of caseids in this region of the world.
According to Werneburg and colleagues, the presence of caseids at this
Latitude suggests their possible existence in the temperate regions of
Gondwana.
A possible Gondwanan occurrence was proposed as early as the 1990s by Michael S.Y. Lee and in 2021 by Asher J. Lichtig and Spencer G. Lucas, who reinterpreted the middle Permian taxon
Eunotosaurus from
South Africa as a small burrowing caseid.
Between these two dates, other researchers classified
Eunotosaurus as a
Parareptilia or a
pantestudines.
If the first three authors are correct,
Eunotosaurus would be the first caseid found in the Southern Hemisphere and the last known representative of the family with a latest
Capitanian age for the most recent specimens.
Elsewhere in Gondwana, the presence of the
ichnotaxon Dimetropus in the Permian of
Morocco suggests the future discovery of basal synapsids (including caseids) in the Permian basins of
North Africa, which were also part of the paleoequatorial belt and constituted one of the main migratory routes between the Northern and Southern Hemispheres.
Phylogeny
The family Caseidae was erected by Samuel Wendell Williston in 1911.
In 1940,
Alfred Romer and L.W. Price placed Caseidae and
Edaphosauridae in the same suborder, which they named Edaphosauria.
This group is now abandoned, the edaphosaurids being closer to the
Sphenacodontia (with which they form the
clade Eupelycosauria) than to the caseids.
The latter are grouped with the
Eothyrididae in the clade
Caseasauria, which represent the most basal
.
The first Phylogenetics analysis of caseids was published in 2008 by Hillary C. Maddin and colleagues. In this analysis, the genus Oromycter occupies the most basal position within the clade. Ennatosaurus is the sister group of a clade containing Cotylorhynchus and Angelosaurus. This analysis reveals for the first time the paraphyly of the genus Casea, the species "Casea" rutena representing a distinct genus which will be named in 2011 Euromycter.
Below is the first cladogram of caseids published by Maddin et al. in 2008.
Another phylogenetic analysis carried out in 2012 by Benson includes the genus Trichasaurus which occupies an intermediate position between Casea and "Casea" rutena. Ennatosaurus is identified as the sister group of a clade including Angelosaurus and the three species of Cotylorhynchus. Within the latter genus, Cotylorhynchus romeri is the sister group of the two species C. hancocki and C. bransoni.
Below is the cladogram of Caseasauria published by Benson in 2012.
In 2015, Marco Romano and Umberto Nicosia published the first cladistic study including almost all Caseidae (with the exception of Alierasaurus from Sardinia, then considered too fragmentary). This study again resolves the genus Casea as paraphyletic, with the species "Casea" nicholsi representing a distinct unnamed genus. In their most parsimonious analysis, Ruthenosaurus is closely related to Cotylorhynchus hancocki. Ennatosaurus occupies a higher position than in previous analyses, and is identified as more closely related to Angelosaurus. However, the close relationship between A. dolani and Ennatosaurus may be biased by the extreme incompleteness of the material from the North American species.
Below is the cladogram of caseids published by Romano and Nicosia in 2015.
A phylogenetic analysis published in 2016 by Neil Brocklehurst and colleagues includes for the first time the genera Callibrachion and Datheosaurus which are identified as basal caseids occupying an intermediate position between Eocasea and Oromycter.
Below is the phylogenetic analysis published by Neil Brocklehurst and colleagues in 2016.
In 2017 Romano and colleagues published the first phylogenetic analysis including the genus Alierasaurus. The latter is recovered as the sister taxon of the genus Cotylorhynchus.
Below is the phylogenetic analysis published by Romano and colleagues in 2017.
In describing the species Martensius in 2020, Berman and colleagues published two in which Martensius is identified as one of the most basal caseids, and is positioned just above the Late Carboniferous Eocasea. In the first cladogram, the position of the remaining caseids is poorly resolved. In the second cladogram, Casea is positioned above Martensius bromackerensis, and is followed by a polytomy between Oromycter, Trichasaurus, and a clade of remaining caseid. Within these remaining taxa, a sequence of branching taxa begins with Casea nicholsi, followed by Euromycter, then Ennatosaurus, then Angelosaurus, then an apical clade of the three Cotylorhynchus species plus Alierasaurus. In this final clade, Cotylorhynchus hancocki and C. bransoni are sister taxa and the clade forms a polytomy with C. romeri and Alierasaurus ronchii.
Below are the two caseid cladograms published by Berman and colleagues in 2020.
In 2022, Werneburg and colleagues described the genus Lalieudorhynchus and published a phylogenetic analysis which concluded that the genera Angelosaurus and Cotylorhynchus are Paraphyly and are represented only by their type species. In this analysis, Cotylorhynchus romeri is positioned just above the genus Angelosaurus, and forms a polytomy with a clade containing Ruthenosaurus and Caseopsis and another clade containing Alierasaurus, the two other species of Cotylorhynchus and Lalieudorhynchus. Within this latter clade, Alierasaurus is the sister group of "Cotylorhynchus" bransoni and a more derived clade including Lalieudorhynchus and "Cotylorhynchus" hancocki.
Below is the cladogram published by Werneburg and colleagues in 2022.
Notes
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