Tumor Found in 255 Million Year old Gorgonopsid Tooth Fossil

When paleontologists at the University of Washington cut into the fossilized jaw of a distant mammal relative, they got more than they bargained for -- more teeth, to be specific.

As they report in a letter published Dec. 8 in the Journal of the American Medical Association Oncology, the team discovered evidence that the extinct species harbored a benign tumor made up of miniature, tooth-like structures. Known as a compound odontoma, this type of tumor is common to mammals today. But this animal lived 255 million years ago, before mammals even existed.

"We think this is by far the oldest known instance of a compound odontoma," said senior author Christian Sidor, a UW professor of biology and curator of vertebrate paleontology at the Burke Museum of Natural History and Culture. "It would indicate that this is an ancient type of tumor."

Before this discovery, the earliest known evidence of odontomas came from Ice Age-era fossils.

"Until now, the earliest known occurrence of this tumor was about one million years ago, in fossil mammals," said Judy Skog, program director in the National Science Foundation's Division of Earth Sciences, which funded the research. "These researchers have found an example in the ancestors of mammals that lived 255 million years ago. The discovery suggests that the suspected cause of an odontoma isn't tied solely to traits in modern species, as had been thought."

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Synapsids Developed the Diaphragm for Breathing Very Early

A caseian point for the evolution of a diaphragm homologue among the earliest synapsids

Authors:

Lambertz et al

Abstract:

The origin of the diaphragm remains a poorly understood yet crucial step in the evolution of terrestrial vertebrates, as this unique structure serves as the main respiratory motor for mammals. Here, we analyze the paleobiology and the respiratory apparatus of one of the oldest lineages of mammal-like reptiles: the Caseidae. Combining quantitative bone histology and functional morphological and physiological modeling approaches, we deduce a scenario in which an auxiliary ventilatory structure was present in these early synapsids. Crucial to this hypothesis are indications that at least the phylogenetically advanced caseids might not have been primarily terrestrial but rather were bound to a predominantly aquatic life. Such a lifestyle would have resulted in severe constraints on their ventilatory system, which consequently would have had to cope with diving-related problems. Our modeling of breathing parameters revealed that these caseids were capable of only limited costal breathing and, if aquatic, must have employed some auxiliary ventilatory mechanism to quickly meet their oxygen demand upon surfacing. Given caseids’ phylogenetic position at the base of Synapsida and under this aquatic scenario, it would be most parsimonious to assume that a homologue of the mammalian diaphragm had already evolved about 50 Ma earlier than previously assumed.

pop sci write up.

The Complicated Teeth of Sphenacodonts

Pre Mammalian Permian Therapsids Were Hairy: Evidence From Upper Permian Coprolites

Microbiota and food residues including possible evidence of pre-mammalian hair in Upper Permian coprolites from Russia

Authors:

Bajdek et al

Abstract:

Coprolites (fossil faeces) provide direct evidence on the diet of its producer and unique insights on ancient food webs and ecosystems. We describe the contents of seven coprolites, collected from the Late Permian Vyazniki site of the European part of Russia. Two coprolite morphotypes (A, B) contain remains of putative bacteria, cyanobacteria, fungi, protists, invertebrate eggs, arthropod elements, undigested bone and tooth fragments, fish scales and elongated hair-like structures with hollow interiors. Content, size and shape of the coprolites together with the associated body fossil record suggest that the most probable scat-producers were carnivorous tetrapods; the bone-rich morphotype A reveals short food retention time and a fast metabolism and is therefore assigned to therapsid carnivores whereas morphotype B with rarer and degraded bones are assigned to archosauromorphs or other non-therapsid carnivores. The general coprolite matrix contains abundant micron-sized spheres and thin-walled vesicles which are interpreted as oxide and phosphatic pseudomorphs after microbial cells. From analyses of the undigested bones, we infer that they represent remains of actinopterygian fish, a therapsid and unrecognizable parts of amphibians and/or reptiles. Additionally, hair-like structures found in one coprolite specimen occur as diagenetically altered (oxide-replaced) structures and moulds (or partly as pseudomorphs) in a microcrystalline carbonate-fluoride-bearing calcium phosphate. This suggests that the latest Permian therapsids probably were equipped with hair-like integument or hairsuit. If true, this is by far the oldest evidence of this mammalian character in the stem group of mammals.

Canada to America: DIE, DIMETRODON! DIE!

Re-evaluation of the historic Canadian fossil Bathygnathus borealis from the Early Permian of Prince Edward Island

Authors:

Brink et al

Abstract:

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.

Actually, its an attempt to 'save' the name.  I was being a turkey.  They recommend keeping the name 'Dimetrodon' because under the rules of naming fossils, the earliest name has priority.  The Canadian specimen was named earlier than the ones Cope named.  Therefore, by the rules the genus Dimetrodon ought to become Bathygnathus.  Dimetrodon is one of those iconic names though and why they are trying to save it.  However, that didn't work for Brontosaurus (sorta) and Seismosaurus, so its unlikely to do so here.

Appears Dimetrodon Relative Ophiacodon was Warm Blooded

Most people know that ‘warm-bloodedness’ is a characteristic of mammals. This trait actually encompasses a suite of physiological processes that help to maintain a relatively high, constant body temperature using heat generated internally. A new study by Christen Don Shelton of the University of Cape Town, South Africa and his colleague, Martin Sander at the University of Bonn, Germany, presented at this year’s Society of Vertebrate Paleontology meeting, shows that this character may have shown up in the ancestors of modern mammals far earlier than was previously thought.

One associated effect of being ‘warm-blooded’ is a relatively fast growth-rate. Mammals (and birds, who are also ‘warm-blooded’) tend to grow much faster than ‘cold-blooded’ vertebrates, like fish and reptiles. This fast growth rate is in turn associated with a particular type of bone growth pattern, called fibrolamellar bone (FLB). Both mammals and birds have FLB, and Shelton and his colleague investigated its presence in an early fossil relative of mammals, Ophiacodon.

Ophiacodon is distantly related to the large sail-back reptile, Dimetrodon, that people may be familiar with, and lived in North America around 280-300 million years ago. Although it didn’t look particularly mammal-like (you could be forgiven for calling it a ‘lizard’), it has many characters that link it with mammals. The highly vascularized tissue had previously been observed in Ophiacodon, but its presence had been written off to ecological factors, like its aquatic lifestyle, rather than to its fundamental physiology. Shelton looked at a number of bones of Ophiacodon of individuals of different ages, and found that the more likely explanation is that Ophiacodon was at least partly ‘warm-blooded’

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Synapsids and Diapsids Developed Their Tympanic Membranes (ear drums) Independently

Developmental genetic bases behind the independent origin of the tympanic membrane in mammals and diapsids

Authors:

Kitazawa et al

Abstract:

The amniote middle ear is a classical example of the evolutionary novelty. Although paleontological evidence supports the view that mammals and diapsids (modern reptiles and birds) independently acquired the middle ear after divergence from their common ancestor, the developmental bases of these transformations remain unknown. Here we show that lower-to-upper jaw transformation induced by inactivation of the Endothelin1-Dlx5/6 cascade involving Goosecoid results in loss of the tympanic membrane in mouse, but causes duplication of the tympanic membrane in chicken. Detailed anatomical analysis indicates that the relative positions of the primary jaw joint and first pharyngeal pouch led to the coupling of tympanic membrane formation with the lower jaw in mammals, but with the upper jaw in diapsids. We propose that differences in connection and release by various pharyngeal skeletal elements resulted in structural diversity, leading to the acquisition of the tympanic membrane in two distinct manners during amniote evolution.

Eriphostoma microdon: new Specimens of the Oldest Permian Gorgonopsid Found

New information on the morphology and stratigraphic range of the mid-Permian gorgonopsian Eriphostoma microdon Broom, 1911

Authors:

Kammerer et al

Abstract:

New specimens of the oldest gorgonopsian taxon Eriphostoma microdon from the Pristerognathus Assemblage Zone (AZ) of South Africa significantly improve our understanding of the anatomy of this taxon. The new specimens consist of nearly complete skulls and lower jaws and allow for a more complete diagnosis of Eriphostoma than was possible based on the poorly preserved holotype. In addition to the characteristic palatal dentition and delta-shaped palatine bosses previously recognized for Eriphostoma, this taxon can be diagnosed by the presence of three close-packed upper postcanines occupying an indented margin of the maxilla, a large, tetragonal-to-rounded preparietal bone, and large, paired interorbital depressions expanding outwards in front of the pineal boss. The revised diagnosis permits Eoarctops vanderbyli, Galesuchus gracilis, and Scylacognathus parvus to be synonymized with Eriphostoma microdon, as previously suspected. Among gorgonopsians, Eriphostoma is most similar to Aelurosaurus and Gorgonops, although these similarities are likely plesiomorphic for Gorgonopsia. Eriphostoma ranges from the Tapinocephalus AZ (where it is the only valid gorgonopsian known from the Karoo Basin) through the Pristerognathus AZ (where it co-occurs with Gorgonops).

Changes in Permian Pecylosaur Composition of Permian Terrestrial European Ecologies

Patterns of changes in Theromorph taxa of Permian terrestrial communities of Eastern Europe

Author:

Ivakhnenko

Abstract:

The evolution of Late Permian tetrapod communities which include Theromorpha is examined in the territory of Eastern Europe. It is noteworthy that changes in the taxonomic composition of analogous ecobiomorph groups are connected with certain biotic or abiotic factors. The analysis of these factors allows the recognition of presumable causes of the crises in communities, which are determined to a greater or lesser extent by taxonomic changes. It is shown that the crisis in the middle of the Permian was caused primarily by abiotic (tectonic) reasons, while the crisis at the end of the Permian was complex, determined by a combination of biotic, local tectonic, and global factors.

Evolution of Prehensile Digits in Non-Anomodont Synapsids

Range of Movement in Ray I of Manus and Pes and the Prehensility of the Autopodia in the Early Permian to Late Cretaceous Non-Anomodont Synapsida

Authors:

Kümmell et al

Abstract:

The mobility of ray I was analysed in seventy-eight Early Permian to Late Cretaceous specimens of non-mammalian Synapsida and one extant mammal. In all non-mammaliamorph Synapsida investigated, ray I formed a digital arcade. The first phalanx was maximally extendable to the zero position in the metapodiophalangeal joint I. Metapodiale I was the functional equivalent to a basal phalanx of digits II–V. In contrast, there was no digital arcade in ray I in Mesozoic Mammaliamorpha. Phalanx 1 I was dorsally extendable and metapodiale I was functionally part of the metapodium. During the propulsion phase, autopodial rotation occurred in the majority of Synapsida with abducted limb posture. Regarding ray I, the reduction of autopodial rotation can be estimated, e.g., from the decrease of lateral rotation and medial abduction of the first phalanx in the metapodiophalangeal joint I. Autopodial rotation was high in Titanophoneus and reduced in derived Cynodontia. In Mammaliamorpha the mobility of the first ray suggests autopodial rolling in an approximately anterior direction. Most non-mammaliamorph Therapsida and probably some Mesozoic Mammaliamorpha had prehensile autopodia with an opposable ray I. In forms with a pronounced relief of the respective joints, ray I could be opposed to 90° against ray III. A strong transverse arch in the row of distalia supported the opposition movement of ray I and resulted in a convergence of the claws of digits II–V just by flexing those digits. A tight articular coherence in the digital joints of digits II–V during strong flexion supported a firm grip capacity. Usually the grip capacity was more pronounced in the manus than in the pes. Prehensile autopodia of carnivorous Therapsida may have been utilized to hold prey while biting, thus helping to avoid fractures of the laterally compressed fangs.

Evidence of Parallel Evolution in Synapsids From Caseid Casea broilii

New Postcranial Material of the Early Caseid Casea broilii Williston, 1910 (Synapsida: Caseidae) with a Review of the Evolution of the Sacrum in Paleozoic Non-Mammalian Synapsids

Authors:

LeBlanc et al

Abstract:

Here we use the description of a new specimen of the small caseid synapsid Casea broilii that preserves the sacral, pelvic and hind limb regions in great detail and in three dimensions, as a unique opportunity to reevaluate the early stages in the evolution of the sacrum in the lineage that led to mammals. We place this new material in the context of sacral evolution in early caseid synapsids and conclude that the transition from two to three sacral vertebrae occurred in small-bodied species, suggesting that it was not an adaptation to heavy weight bearing. Furthermore, we compare descriptions of sacral anatomy among known early synapsids, including caseids, ophiacodontids, edaphosaurids, varanopids, and sphenacodontians and review sacral evolution in early synapsids. Based on the descriptions of new species of caseids, edaphosaurids, and varanopids over the past several decades, it is clear that a sacrum consisting of three vertebrae evolved independently at least four times in synapsids during the Late Carboniferous and Early Permian. Furthermore, similarities in the morphologies of the sacral vertebrae and ribs of these early synapsids lead us to conclude that an anterior caudal vertebra had been incorporated into the sacral series convergently in these groups. Given the repeated acquisition of a three-vertebra sacrum in early synapsids and no apparent link to body size, we argue that this sacral anatomy was related to more efficient terrestrial locomotion than to increased weight bearing.

Pennsylvanian Carboniferous Synapsid Ianthodon schultzei Revisited

New information on the cranial and postcranial anatomy of the early synapsid Ianthodon schultzei (Sphenacomorpha: Sphenacodontia), and its evolutionary significance

Authors:

Spindler et al

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.

Caseid Tracks in Lower Permian Oklahoma?

Dimetropus osageorum n. isp. from the Early Permian of Oklahoma (USA): A Trace and its Trackmaker

Authors:

Sacchi et al

Abstract:

A new ichnospecies is named as Dimetropus osageorum n. isp. within the ichnogenus Dimetropus Romer and Price, 1940. The new ichnotaxon comes from the Lower Permian Midco Member of the Wellington Formation, cropping out near Perry, Noble Co. (Oklahoma, USA), and differs from congeneric ichnospecies in the apparent heteropody and in the proportionally shorter digits. The characters of the new ichnotaxon, together with comparative analysis of footprints and of known skeletal remains, suggest referral of the trackmaker to the Caseidae, although edaphosaurid affinities cannot be excluded. Tracks referred to Dimetropus exhibit wide variation, and their respective trackmakers may be ascribed to an accordingly wide range of different zoological taxa among non-therapsid Synapsida and not only to Sphenacodontidae as has been generally believed. At the same time, the process of attributing ichnotaxa, on the basis of well preserved tracks and by comparison with known skeletal remains, is validated.

Synapsid Sphenacodontian Tooth Evolution/Revolution

First record of plicidentine in Synapsida and patterns of tooth root shape change in Early Permian sphenacodontians

Authors:

Brink et al

Abstract:

Recent histological studies have revealed a diversity of dental features in Permo-Carboniferous tetrapods. Here, we report on the occurrence of plicidentine (infolded dentine around the base of the tooth root) in Sphenacodontia, the first such documentation in Synapsida, the clade that includes mammals. Five taxa were examined histologically, Ianthodon schultzei, Sphenacodon ferocior, Dimetrodon limbatus, Dimetrodon grandis, and Secodontosaurus obtusidens. The tooth roots of Ianthodon possess multiple folds, which is generally viewed as the primitive condition for amniotes. Sphenacodon and D. limbatus have distinctive “four-leaf clover”-shaped roots in cross section, whereas Secodontosaurus has an elongate square shape with only subtle folding. The most derived and largest taxon examined in this study, D. grandis, has rounded roots in cross section and therefore no plicidentine. This pattern of a loss of plicidentine in sphenacodontids supports previous functional hypotheses of plicidentine, where teeth with shallow roots require folds to increase the area of attachment to the tooth-bearing element, whereas teeth with long roots do not. This pattern may also reflect differences in diet between co-occurring sphenacodontids as well as changes in feeding niche through time, specifically in the apex predator Dimetrodon.

Being Nocturnal Predates Mammals: Synapsids Were Nocturnal During the Late Carboniferous

Nocturnality in synapsids predates the origin of mammals by over 100 million years

Authors:

Angielczyk et al

Abstract:

Nocturnality is widespread among extant mammals and often considered the ancestral behavioural pattern for all mammals. However, mammals are nested within a larger clade, Synapsida, and non-mammalian synapsids comprise a rich phylogenetic, morphological and ecological diversity. Even though non-mammalian synapsids potentially could elucidate the early evolution of diel activity patterns and enrich the understanding of synapsid palaeobiology, data on their diel activity are currently unavailable. Using scleral ring and orbit dimensions, we demonstrate that nocturnal activity was not an innovation unique to mammals but a character that appeared much earlier in synapsid history, possibly several times independently. The 24 Carboniferous to Jurassic non-mammalian synapsid species in our sample featured eye morphologies consistent with all major diel activity patterns, with examples of nocturnality as old as the Late Carboniferous (ca 300 Ma). Carnivores such as Sphenacodon ferox and Dimetrodon milleri, but also the herbivorous cynodont Tritylodon longaevus were likely nocturnal, whereas most of the anomodont herbivores are reconstructed as diurnal. Recognizing the complexity of diel activity patterns in non-mammalian synapsids is an important step towards a more nuanced picture of the evolutionary history of behaviour in the synapsid clade.

Alierasaurus ronchii: a new Giant Caseid Synapsid From Cisuralian Permian Sardinia

Alierasaurus ronchii, gen. et sp. nov., a caseid from the Permian of Sardinia, Italy

Authors:

Romano et al

Abstract:

A giant caseid, Alierasaurus ronchii, gen. et sp. nov., is herein described, based on a partial postcranial skeleton collected from the Permian Cala del Vino Formation (Alghero, Nurra, northwest Sardinia). Despite the highly conservative morphology of ribs and vertebral material, typical of caseids, the very well-preserved foot elements show highly autapomorphic features, warranting assignment of the specimen to a new genus. In particular, the fourth metatarsal is not short and massive, as in other large caseids, and shows a distinct axial region. Finally, the claw-shaped ungual phalanges are autapomorphic in being proportionately very short, with a strong double ventral flexor tubercle positioned very close to the proximal phalangeal rim, and a distal end that is not spatulate, but rather subtriangular in transverse section. Principal component and reduced major axis slope analyses, performed on 10 caseid specimens, suggest that the observed changes in overall shape of metatarsal IV were mainly linked to the enormous body size reached by the Sardinian specimen.

Mammalian Faunal Transition in Berriasian/Barremanian Cretaceous North America

Earliest Cretaceous mammals from the western United States

Authors:

Cifelli et al

Abstract:

Mammalian diversity in North America shifted significantly during the Early Cretaceous, from archaic groups dominant in the well-sampled faunas of the Late Jurassic to advanced forms (including early members of modern clades) by the Albian–Cenomanian. However, the dynamics of this transition are poorly understood, since faunas of earliest Cretaceous age are unknown. Here we describe the first fossil mammals from exposures of the Lakota Formation in the Black Hills of South Dakota, a unit correlated with the upper Berriasian–lower Barremian and positioned stratigraphically between the underlying Morrison Formation and Aptian–Albian units exposed elsewhere in North America. The mammalian fauna from the Lakota Formation is transitional with regard to the North American fossil record, representing a broad spectrum of both Jurassic and Cretaceous lineages: present are “plagiaulacidan” multituberculates allied with Late Jurassic Allodontoidea and Early Cretaceous Plagiaulacoidea; the geologically youngest dryolestoid(s) and “triconodontine” triconodontids (characteristic Late Jurassic taxa from the Morrison Formation); the oldest spalacotheriid “symmetrodont”; the first record of an amphitheriid-like stem zatherian from North America (abundant in the Middle Jurassic–earliest Cretaceous of Europe); and the oldest North American tribosphenic mammal (abundant and diverse on the continent by the end of the Early Cretaceous). Taxa making their first North American appearance in the Lakota Formation (Plagiaulacoidea, including a genus also known from the Purbeck of Britain; Spalacotheriidae, stem Zatheria, Tribosphenida) are also known from the Early Cretaceous of Western Europe, suggesting the possibility that they represent immigrants.

Pelycosaur Pantelosaurus Bonebed From Permian Germany

From about 1.2 meters long , internationally unique fossil record of Pantelosaurus ( Haptodus ) Saxonicus ( Saxon Pelycosaurier the Permian period ) were obtained on May 6, 2014, a special drill two fossil bone samples to investigate this in more detail . The scientists hope the basis of the bone thin sections of the samples in the microscope to detect cell pattern in order to meet , among others, statements regarding the growth of animals.

The Saxon - Pelycosaurier finds come from the Doehlen pool near Freital and were discovered in the early 20th century when mining as Beifund . Frederik Spindler, a paleontologist at the University of Freiberg , Dr. Johannes Richter , Head of Unit for geoarchives , geoinformation , Collections State Agency for Environment , Agriculture and Geology, and Christians Shelton of the University of Bonn withdrawals , the samples in Freiberg.

The tests run as part of a three-year DFG research project on "Revision of the early Sphenacodontier " . The joint project is running since May 2012 under the direction of Prof. Jörg W. Schneider (TU Freiberg ) and Professor Martin Sander of the Steinmann Institute in Bonn . In the summer of 2013, the researchers have made similar investigations on alleged pups this dinosaur .

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Eocasea martini: a new Carnivorous Caseid Synapsid From Pennsylvanian Carboniferous Kansas

The Oldest Caseid Synapsid from the Late Pennsylvanian of Kansas, and the Evolution of Herbivory in Terrestrial Vertebrates

Authors:

Reisz et al

Abstract:

The origin and early evolution of amniotes (fully terrestrial vertebrates) led to major changes in the structure and hierarchy of terrestrial ecosystems. The first appearance of herbivores played a pivotal role in this transformation. After an early bifurcation into Reptilia and Synapsida (including mammals) 315 Ma, synapsids dominated Paleozoic terrestrial vertebrate communities, with the herbivorous caseids representing the largest vertebrates on land. Eocasea martini gen. et sp. nov., a small carnivorous caseid from the Late Carboniferous, extends significantly the fossil record of Caseidae, and permits the first clade-based study of the origin and initial evolution of herbivory in terrestrial tetrapods. Our results demonstrate for the first time that large caseid herbivores evolved from small, non-herbivorous caseids. This pattern is mirrored by three other clades, documenting multiple, independent, but temporally staggered origins of herbivory and increase in body size among early terrestrial tetrapods, leading to patterns consistent with modern terrestrial ecosystem.

Pelycosaurian-grade Synapsids Have a Very Incomplete Fossil Record

Current and historical perspectives on the completeness of the fossil record of pelycosaurian-grade synapsids

Authors:

Brocklehurst et al

Abstract:

Understanding of the early evolution of tetrapods may have been influenced by the effects of geological and anthropogenic sampling biases, as suggested by previous studies. Here we make a thorough assessment of how these and other biases affect the record of pelycosaurian-grade synapsids, a group of tetrapods that dominated the terrestrial realm during the late Carboniferous and early Permian. Modified versions of the character and skeletal completeness metrics are used to assess the completeness of the known specimens, while a recently published supertree of basal synapsids is tested for congruence between the stratigraphic and phylogenetic hypotheses. A historical analysis is also applied to the record in order to show how the biases in the study of this group over the past centuries may have influenced the current record. The results show that the completeness of basal synapsid specimens shows very little variation throughout the Early Permian. A peak in skeletal and character completeness metric values in the Middle Permian (Wordian) is attributed to exceptional preservation of the Mezen fauna. A significant negative correlation is found between the skeletal completeness metric and a taxic diversity curve of pelycosaurs, implying a tendency to name many species based on poor material. The lack of correlation between the character completeness metric and diversity is attributed to the history of discovery in the group: the majority of pelycosaur species were named between the 1930s and 1960s, when character based assignments were secondary to size, location and stratigraphy. A strong correspondence between the phylogeny and stratigraphy implies a reliable phylogenetic hypothesis, but the low relative completeness index score suggests that a great deal of the fossil record is missing. While the relative completeness index has improved over the past century, the rate of improvement has slowed in the last two decades, and the slowing rate of discovery of new species suggests that the limit of what the fossil record of pelycosaurs has to offer is being approached. A consistent shape of diversity curves over the past century implies that the same biases which affected the record in the past are still affecting it now. This study highlights the need for sampling correction methods to be employed in studies of early synapsids.