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From top to bottom (A) a skull of an Anapsid, (B) a Synapsid (stem-mammal) skull, and (C) a Diapsid skull. [a]

Temporal fenestrae are openings in the temporal region of the skull of some amniotes, behind the orbit (eye socket). These openings have historically been used to track the evolution and affinities of reptiles. Temporal fenestrae are commonly (although not universally) seen in the fossilized skulls of dinosaurs and other sauropsids (the total group of reptiles, including birds).[1] The major reptile group Diapsida, for example, is defined by the presence of two temporal fenestrae on each side of the skull. The infratemporal fenestra, also called the lateral temporal fenestra or lower temporal fenestra, is the lower of the two and is exposed primarily in lateral (side) view.

Temporal fenestrae in relation to the other skull openings in the dinosaur Massospondylus, a type of diapsid.

The supratemporal fenestra, also called the upper temporal fenestra, is positioned above the other fenestra and is exposed primarily in dorsal (top) view. In some reptiles, particularly dinosaurs, the parts of the skull roof lying between the supratemporal fenestrae are thinned out by excavations from the adjacent fenestrae. These extended margins of thinned bone are called supratemporal fossae.

Synapsids, including mammals, have one temporal fenestra, which is ventrally bordered by a zygomatic arch composed of the jugal and squamosal bones. This single temporal fenestra is homologous to the infratemporal fenestra, as displayed most clearly by early synapsids.[2] In later synapsids, the cynodonts, the orbit fused with the fenestral opening after the latter had started expanding within the therapsids. Most mammals have this merged configuration. Later, primates re-evolved an orbit separated from the temporal fossa. This separation was achieved by the evolution of a postorbital bar, with haplorhines (dry-nosed primates) later evolving a postorbital septum.[3]

Physiological speculation associates temporal fenestrae with a rise in metabolic rates and an increase in jaw musculature. The earlier amniotes of the Carboniferous did not have temporal fenestrae, but two more advanced lines did: the synapsids (stem-mammals and mammals) and the diapsids (most reptiles and later birds).

Fenestration types

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There are four types of amniote skull, classified by the number and location of their temporal fenestrae. Though historically important for understanding amniote evolution, some of these configurations have little relevance to modern phylogenetic taxonomy. The four types are:

  • Anapsida – No openings. The plesiomorphic ("primitive") condition exemplified by amphibians as well as some early reptiles like captorhinids and parareptiles. Turtles have an anapsid skull, but this was likely acquired secondarily from a diapsid ancestor.
  • Synapsida – One low opening (beneath the postorbital and squamosal bones). A monophyletic group including mammals and their ancestors.
  • Euryapsida – One high opening (above the postorbital and squamosal bones). Euryapsids are a polyphyletic group, as reptiles with euryapsid skulls lack a shared common ancestor. Euryapsids evolved from a diapsid configuration, losing their lower temporal fenestra. Examples of euryapsid reptiles include ichthyosaurs, plesiosaurs, placodonts, and Trilophosaurus.
  • Diapsida – Two openings. A monophyletic group including all modern reptiles and birds. Turtles, though not diapsids in a purely anatomical sense, qualify as members of the clade Diapsida due to their likely diapsid ancestry. Some diapsids, particularly modern lizards, have an infratemporal fenestra which is open from below due to a lack of contact between the jugal and quadratojugal bones.

Notes

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References

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Temporal fenestra

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A temporal fenestra (plural: ) is a cranial opening in the temporal region of the , situated between the and occiput, that accommodates the adductor musculature and bony arcades while reducing overall weight. These fenestrae first appeared in early amniotes as adaptations for enhanced feeding mechanics, evolving from a solid (anapsid-like) condition through biomechanical stresses associated with biting and head movements. In amniotes, the configuration of temporal fenestrae serves as a key taxonomic feature, distinguishing major clades based on the number and position of openings. Anapsid skulls lack temporal fenestrae, featuring a fully enclosed temporal , as seen in early reptiles and secondarily in due to specialized neck retraction. Synapsid skulls, ancestral to mammals, possess a single lower (infratemporal) below the postorbital and squamosal bones, facilitating jaw muscle expansion for powerful bites. Diapsid skulls, typical of reptiles including , snakes, crocodilians, birds, and dinosaurs, exhibit two fenestrae—an upper (supratemporal) and a lower (infratemporal)—bounded by temporal arches that optimize stress distribution during mastication. The and diversity of temporal fenestrae reflect functional adaptations to diverse feeding strategies across Amniota and extinct tetrapods, with variations in temporal morphology also observed in lissamphibians and other groups, though phylogenetic interpretations have shifted with new . Biomechanically, these openings enhance muscle leverage and skull lightness without compromising structural integrity, influencing macroevolutionary patterns in diversity.

Anatomy

Definition

A temporal fenestra is an opening, or "window," in the temporal region of the , positioned posterior to the and lateral to the braincase, surrounded by bones and partly by that enclose the jaw musculature. These fenestrae form through the opening of sutures between skull bones or the embryological failure to close such sutures, resulting in spaces that typically approach a for efficient muscle attachment. The term "temporal fenestra" originates from the Latin tempus, referring to the temple or side of the head, and fenestra, meaning window, reflecting the anatomical position and aperture-like structure of these features. The bony margins of temporal fenestrae are formed by several cranial elements, including the postorbital, parietal, squamosal, jugal, and quadratojugal bones, which create arcades that define the openings. While the size and number of these fenestrae vary across taxa, they are characteristic of amniotes and distinct from other cranial openings, such as the located anterior to the and unrelated to adductor musculature. These structures primarily facilitate the expansion and attachment of jaw-closing muscles.

Location and boundaries

The temporal fenestrae are positioned on the lateral aspect of the vertebrate , situated posterior to the and superior to the articulation. This placement positions them within the temporal region, facilitating spatial integration with surrounding cranial elements while maintaining structural integrity of the roof. In reptiles, which exhibit two temporal fenestrae per side, the upper temporal fenestra is bounded anteriorly by the postorbital bone, posteriorly by the squamosal bone, and dorsally by the , with its ventral margin formed by the contact between the postorbital and squamosal. The lower temporal fenestra, in contrast, is delimited dorsally by the postorbital and squamosal bones, ventrally by the jugal and quadratojugal bones, anteriorly by the jugal, and posteriorly by the quadratojugal. These boundaries create a that defines the openings while supporting adjacent dermal bones. In synapsids, including mammals, a single temporal fenestra persists, typically bounded anteriorly by the postorbital and jugal bones, posteriorly by the squamosal, dorsally by the parietal or frontal bones, and ventrally by the composed of the jugal and squamosal. Variations in boundary bones occur across lineages, particularly through fusion and reduction. In mammals, evolutionary modifications include the incorporation of the quadrate into the as the and the loss of the quadratojugal, resulting in a simplified ventral boundary dominated by the jugal-squamosal , while the dorsal margin may involve expanded frontal or parietal contributions. These changes reflect adaptations in architecture without altering the fundamental lateral positioning. The temporal fenestrae maintain proximity to the , from which they are partially separated by the in synapsids, ensuring compartmentalization of cranial spaces.

Types of fenestration

Anapsid condition

The condition is characterized by the complete absence of temporal fenestrae, resulting in a solid temporal roof composed entirely of dermal bones that provides a continuous bony behind the . This configuration represents the plesiomorphic state for amniotes, where the temporal region lacks any openings, ensuring full coverage and structural integrity. Structurally, the closed temporal region in anapsids features the fusion or close apposition of key dermal bones, including the postorbital, squamosal, and supratemporal, which together form an unperforated barrier over the lateral and posterior aspects of the skull. Additional contributions from bones such as the parietal, jugal, and quadratojugal reinforce this solid framework, creating a scutal-like structure that resists external pressures and protects underlying tissues. In contrast to diapsid skulls with dual temporal openings, this arrangement eliminates any fenestration, prioritizing rigidity over flexibility. The implications of this closed temporal architecture include restricted internal space for the expansion of adductor muscles, which originate from the undersurface of the dermatocranial bones and insert onto the without additional room for bulging. This limitation is closely associated with an akinetic skull, where reduced enhances overall stability but constrains dynamic movements of the upper relative to the braincase. Representative taxa exhibiting the anapsid condition include early reptiles such as captorhinids (e.g., Captorhinus aguti), which retain this primitive solid-roofed skull as a basal feature. Turtles (Testudines), including modern forms like Chelonoidis nigra and stem-group representatives such as Proganochelys, display an anapsid skull through secondary closure of temporal fenestrae, despite their underlying diapsid ancestry. This evolutionary reversal in turtles supports specialized functions like head retraction into the shell.

Synapsid condition

The synapsid condition is characterized by a single infratemporal , also known as the lower temporal , located on each side of the , with no corresponding supratemporal or upper opening present. This configuration distinguishes synapsids from other lineages and represents a key synapomorphy for the , originating in the Late Carboniferous period. Structurally, the infratemporal in synapsids is bounded anteriorly by the jugal and postorbital bones and posteriorly by the squamosal bone, forming a distinct opening posterior to the that accommodates musculature. In early synapsids, this is relatively modest in size, but it often enlarges significantly in more derived forms such as therapsids, allowing for expanded attachment sites of the adductor muscles. Evolutionarily, the underwent notable modifications within synapsids, particularly in mammal-like reptiles where it expanded to support larger muscles, enhancing bite force and feeding efficiency. In mammals, the structure further evolves such that the infratemporal becomes recessed and integrated into the lateral temporal wall of the braincase, bordered laterally by the robust formed by the fusion of the jugal and squamosal bones. Key examples illustrate this condition across synapsid diversity; in early synapsids like Dimetrodon, a Permian pelycosaur, the fenestra is a prominent single opening behind the orbit, serving as a foundational trait linking it to mammalian ancestry. In modern mammals, the recessed fenestra persists as the space posterior to the orbits and lateral to the braincase, facilitating the passage and attachment of temporalis muscles while maintaining structural integrity via the zygomatic arch.

Diapsid condition

The diapsid condition is characterized by the presence of two temporal fenestrae on each side of the : the supratemporal fenestra, located dorsally, and the infratemporal fenestra, positioned ventrally. These openings distinguish diapsids from other skull configurations and are a defining synapomorphy of the clade Diapsida, which includes most extant reptiles and birds. The supratemporal is bordered anteriorly by the postorbital bone, posteriorly by the squamosal, and dorsally by the parietal, with the postfrontal often contributing to its anterior margin in many taxa. The infratemporal lies below it, bounded anteriorly by the jugal and postorbital, posteriorly by the squamosal, and ventrally by the quadratojugal in forms where this bone is present. These are separated by two temporal bars: a dorsal bar formed by the postorbital and squamosal, and a ventral bar comprising the jugal and quadratojugal. Variations occur across diapsid subgroups, including the occasional presence of an anterior to the , which is distinct from the temporal openings and primarily found in archosauromorphs. In (lizards and snakes), the lower temporal bar is often reduced or lost, enhancing , while in snakes, the fenestrae may fuse or diminish further due to extreme skull modifications. Crocodilians retain the full configuration with prominent, well-defined fenestrae, and birds (archosaurs) typically lose the upper temporal bar, resulting in merged openings. The (Sphenodon) exemplifies the primitive state with intact dual fenestrae.

Evolutionary history

Origin in early amniotes

Early amniotes, emerging during the period around 356–310 million years ago (as of 2025 fossil evidence), possessed a primitive condition characterized by solid temporal regions without any fenestrae, resembling the morphology inherited from their reptiliomorph ancestors. This scutal (fully ossified) temporal roof provided structural integrity, likely adapted from earlier designs that resisted hydrostatic pressures in aquatic environments before the full terrestrial transition. Stem-amniotes such as Westlothiana lizziae, dating to approximately 346 million years ago from the Early of , exemplify this condition with a compact, unperforated roof, marking the basal state prior to crown-group diversification. As amniotes radiated into the Permian period (299–252 million years ago), the primitive solid temporal region persisted in many basal lineages, including early eureptiles like the captorhinids, which retained an anapsid-like for robust cranial support during feeding. Initial innovations in temporal architecture began to appear in stem-diapsid forms around 310 million years ago, with the first evidence of lower temporal openings emerging as subtle excavations that hinted at future fenestration patterns. These early modifications are interpreted as adaptations to accommodate expanding adductor muscles, facilitating more efficient biting mechanics in terrestrial habitats while beginning to reduce weight. Fossil evidence from transitional taxa illuminates this origin, particularly Eunotosaurus africanus from the Middle Permian of (approximately 260 million years ago), which displays an incipient upper temporal fenestra revealed through μCT scanning. This fenestra, potentially homologous to those in later diapsids, represents an early stage in skull lightweighting, allowing for a lighter cranium without compromising structural strength for muscle attachment. Similarly, basal diapsids like Petrolacosaurus kansensis from the Late of (around 300 million years ago) show the onset of a bifenestral condition, with both upper and lower openings that underscore the gradual from the solid primitive state toward more specialized configurations in crown amniotes.

Divergence in synapsids and diapsids

The divergence of temporal fenestra patterns occurred in the Late Carboniferous period, approximately 318 million years ago, when early amniotes split into the synapsid and sauropsid (later including diapsids) lineages. Synapsids retained or developed a single infratemporal fenestra, while diapsids acquired the characteristic dual fenestrae (supratemporal and infratemporal), marking a key phylogenetic split that influenced subsequent evolution in each group. In the synapsid lineage, the single temporal fenestra underwent progressive enlargement, beginning with basal forms like pelycosaurs in the Early Permian, where it accommodated adductor muscles for enhanced . This trend intensified in therapsids during the Middle to Late Permian, with the fenestra broadening mediolaterally and the postorbital-squamosal bar strengthening, facilitating more efficient mechanics and supporting the development of specialized such as canines. By the Triassic-Jurassic boundary, around 205 Ma, this configuration had evolved into the mammalian condition, characterized by an even larger that allowed for the expansive mass essential to mammalian mastication, as seen in early mammaliaforms like . The trajectory stabilized the bifenestrate condition in major subclades, including lepidosauromorphs (ancestors of and snakes) and archosauromorphs (ancestors of crocodilians, dinosaurs, and birds), where the two permitted greater muscle attachment areas and lightness without compromising structural integrity. However, secondary losses occurred in derived groups; for instance, , now recognized as diapsids originating in the that secondarily lost their temporal early in their evolution, resulting in an anapsid-like for enhanced protection and aquatic adaptations. In birds, an subgroup, the upper temporal fenestra was reduced during the , leading to a merger of the two openings into a single large fenestra by the , which supported the lightweight crania necessary for flight. Key evolutionary events further shaped these patterns, notably the end-Permian mass extinction around 252 Ma, which decimated synapsid diversity but allowed surviving therapsids with enlarged to dominate post-extinction terrestrial ecosystems, while lineages, though less documented in the Permian fossil record, began their radiation toward modern forms. Additionally, the euryapsid condition—featuring a single supratemporal —emerged as a derived modification within , particularly in marine reptiles like ichthyosaurs, where the lower closed secondarily to streamline the skull for aquatic predation, as evidenced by to fossils. Recent 2025 discoveries, including trackways dated to 356 Ma from , have pushed back the estimated origin of amniotes by at least 35–40 million years, providing new insights into the early of temporal fenestration patterns.

Functional role

Jaw muscle attachment

The temporal fenestrae primarily function as attachment sites for the adductor muscles, providing space for their expansion and allowing larger muscle cross-sections without necessitating thicker skull bones, which reduces overall cranial weight while enhancing mechanical efficiency. This arrangement supports the origin and insertion of key muscle groups, such as the temporalis and pterygoideus, facilitating powerful jaw closure essential for feeding. In diapsids, the upper temporal fenestra (supratemporal fenestra) primarily accommodates the superficial portions of the temporalis muscle (m. adductor mandibulae externus superficialis), which originates from the parietal and squamosal bones bordering the fenestra, while the lower temporal fenestra (infratemporal fenestra) houses deeper adductors, including parts of the pterygoideus group (e.g., m. pterygoideus dorsalis and ventralis), attaching to the quadrate and pterygoid. In contrast, synapsids feature a single temporal fenestra that serves as the origin site for both the temporalis and masseter muscles, with the temporalis attaching to the squamosal and the masseter to the zygomatic arch extending from the fenestra, enabling integrated adduction. This specialized anatomy confers a biomechanical advantage by increasing muscle volume and leverage, thereby amplifying bite force; for instance, enlarged allow greater of the adductors, correlating with enhanced force generation during mastication. Comparatively, fenestra size often scales with muscle volume demands, as seen in forms with larger openings supporting robust adductors for high-force biting, though exact proportions vary by dietary adaptations without altering the core attachment function. In advanced synapsids like mammals, the recession of the temporal fenestra into the cranium further protects these muscles during occlusion.

Implications for skull mechanics

In some diapsids, such as squamates, the configuration of temporal fenestrae—particularly the absence of the lower temporal bar—facilitates streptostyly, a form of suspension mobility where the can rotate relative to the , thereby reducing joint forces and overall stress during biting activities. This kinetic mechanism allows for greater jaw protrusion and gape, minimizing torsional loads on the cranium by distributing forces more dynamically across the temporal region. However, many diapsids, including crocodilians, birds, and rhynchocephalians like Sphenodon, exhibit monimostyly with a fixed quadrate and limited . In contrast, the synapsid condition with a single infratemporal generally results in a more rigid kinetic setup that prioritizes force transmission over flexibility. Temporal fenestrae contribute to efficient stress distribution by lightening the 's overall mass while the surrounding bony arches, such as the , act as reinforcing struts that resist torsion and compressive strains during feeding. In diapsids like Sphenodon, finite element analyses reveal uniform von Mises strain distribution (typically 400–2500 microstrain) across the fenestrated , with the lower temporal bar serving as a compressive brace to prevent localized peaks under unilateral bite loads. Similarly, in such as Salvator merianae, the postorbital bar associated with the upper temporal fenestra reduces tensile and compressive strains by over 50% in key regions like the , enhancing structural integrity without excessive bone mass. Feeding mechanics are closely tied to fenestration patterns, where the single temporal fenestra in synapsids supports enlarged jaw adductor muscles for generating high bite forces suited to slow, powerful crushing or shearing actions, as seen in early mammal-like reptiles. Dual fenestrae in diapsids, however, enable a lighter, more versatile architecture that accommodates faster cycles and rotational velocities for prey capture, with bite forces scaling posteriorly (e.g., up to 216 N in Sphenodon) while maintaining low energy expenditure. This configuration correlates with predatory adaptations, allowing diapsids to handle diverse diets through improved compared to the force-focused synapsid design. Variations in fenestra size and secondary closures impact skull mechanics, particularly gape angle and rigidity; larger fenestrae in diapsids increase maximum gape for engulfing prey, but reductions or closures, as in , revert the system to a more akinetic state with enhanced resistance to bending stresses for durophagous feeding. In such cases, the loss of fenestrae leads to higher bite forces (e.g., through reinforced adductor chambers) but at the cost of reduced kinetic flexibility and increased cranial mass. Pathological enlargements or asymmetries in fenestrae, though rare in fossils, could compromise torsional stability, potentially limiting feeding efficiency in affected individuals.

Examples across taxa

In mammals

In mammals, the single temporal fenestra inherited from synapsid ancestors is deeply inset into the lateral surface of the , forming the expansive that serves as the primary space for the . This fossa is bounded superiorly by the temporal lines on the cranium and inferiorly by the , creating a confluent opening that merges with the in most species. Adaptations in the temporal fenestra vary across mammalian lineages to support diverse feeding strategies. In herbivorous mammals such as cows, the is notably enlarged to house expanded masseter and temporalis muscles, enabling sustained grinding of fibrous vegetation. In contrast, monotremes like the exhibit a reduced temporal fenestra, with a more fused and compact structure that aligns with their specialized electroreceptive bill and limited mobility. Diversity in the temporal region reflects evolutionary divergences within mammals. Marsupials retain a more reptile-like configuration, with the and temporal fenestra often confluent and the contributing to the , providing greater exposure for musculature. Placentals, however, show advanced fusion in the temporal region, including loss of the postorbital bar and integration of elements like the ectotympanic, resulting in a more enclosed and braincase-dominant . Fossil transitions illustrate the progression from cynodont ancestors to modern mammals. In early mammaliaforms like Morganucodon, a Late Triassic cynodont, the temporal fenestra is significantly enlarged relative to earlier synapsids, occupying much of the cheek region and supporting enhanced jaw adductor muscles for precise occlusion. This configuration persists and diversifies in modern orders, such as Carnivora, where the temporal fossa remains prominent to facilitate powerful predatory bites.

In reptiles and birds

In reptiles, the condition is characterized by two temporal fenestrae per side: an upper (supratemporal) fenestra and a lower (infratemporal) fenestra, which accommodate the expansion of adductor muscles during feeding. In such as the (Iguana iguana), both fenestrae are well-developed, providing attachment sites for the in the upper opening and the pterygoideus muscle in the lower, enabling efficient closure for diverse diets ranging from to . These openings enhance muscle leverage without requiring excessive thickening, supporting varied predatory and herbivorous behaviors in over 7,000 species. Snakes exhibit modifications to this diapsid pattern, with the upper temporal arcade often reduced to facilitate , allowing independent movement of bones for prey engulfment. This reduction, seen across approximately 4,000 snake species, minimizes bony constraints while preserving space for hypertrophied jaw muscles, adapting the for large prey whole. Crocodilians, in contrast, retain the full configuration with prominent upper and lower fenestrae, which support powerful adductor muscles essential for their ambush predation strategy and high bite forces exceeding 16,000 N in species like the (Crocodylus porosus). Turtles represent a notable variation, having secondarily closed both temporal fenestrae through of the temporal region, resulting in an anapsid-like that strengthens the cranium against stresses from their rigid feeding mechanisms and protective shell integration. Birds, as derived archosaurs within the clade, display further modifications where the upper temporal fenestra is reduced or lost due to the loss of the upper temporal bar, merging it with the lower fenestra into a single, enlarged infratemporal opening. This configuration lightens the , correlating with the of beak-based feeding and flight adaptations, as the prominent lower fenestra accommodates reduced but efficient muscles for seed-cracking or extraction in diverse avian diets. Across more than 10,000 , this modified fenestration supports ecological roles from aerial predation to ground foraging, reflecting the diapsid heritage streamlined for avian lightweight crania. The living diversity of reptiles and birds encompasses over 20,000 species, the vast majority of which retain temporal fenestrae in some form as diapsids, underscoring the evolutionary success of this skull architecture in terrestrial and aerial environments.

In extinct groups

In early synapsids, such as the pelycosaurs, a single lateral temporal fenestra was a defining feature, providing space for jaw adductor musculature and appearing in fossils from the Early Permian around 290 million years ago. Exemplified by Dimetrodon, this fenestra occupied the temporal region behind the orbit, bordered by the postorbital, squamosal, and jugal bones, and supported enhanced biting efficiency in these carnivorous forms. The structure marked an evolutionary innovation in basal synapsids, distinguishing them from anapsid reptiles and facilitating the diversification of mammal-like lineages during the late Paleozoic. Among extinct diapsids, the Lower Prolacerta broomi exemplifies the classic dual fenestrae condition, with a distinct upper temporal fenestra (supratemporal) and lower temporal fenestra (infratemporal) separated by robust postorbital-squamosal and jugal-quadratojugal arches. This configuration, preserved in South African fossils approximately 245 million years old, underscores the early establishment of skull architecture in lepidosauromorphs, allowing for expanded jaw muscle attachments and lighter crania. In later diapsids like dinosaurs, such as Tyrannosaurus rex, the temporal fenestrae retained the diapsid pattern but featured reinforced bony arches to withstand immense bite forces, with the upper (dorsotemporal) fenestra integrating pneumatic features for strain distribution during feeding. These adaptations highlight evolutionary experiments in , evident in theropod fossils where fenestrae contributed to cranial flexibility and weight reduction. Unique fenestration patterns also characterized other extinct groups, including traditional euryapsids like s, which exhibited a single upper temporal fenestra due to the loss of the lower one, a derived condition now recognized as stemming from ancestors. skulls, such as those from the , displayed this supratemporal opening bounded by a broad upper arch, supporting aquatic predation while reducing . Pareiasaurs, Permian parareptiles, showed incipient temporal openings in some taxa, as in Tiarajudens eccentricus, where a moderately sized temporal fenestra paralleled the in length and hinted at transitional anapsid-to- morphologies around 260 million years ago. The Permian-Triassic mass extinction profoundly impacted diversity, yet temporal fenestration proved advantageous for surviving lineages, particularly diapsids, which radiated rapidly in the to repopulate terrestrial and aquatic niches. Fossils from South African and Brazilian sites indicate that groups with dual fenestrae, like early archosauromorphs, benefited from enhanced mechanics that supported varied diets amid post-extinction ecological upheaval, contributing to ecosystem recovery by the . This fenestration-enabled adaptability contrasted with the decline of fenestra-lacking parareptiles, underscoring its role in the dominance of diapsid reptiles.

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  50. https://elischolar.library.yale.edu/cgi/viewcontent.cgi?article=1115&context=peabody_museum_natural_history_postilla
  51. https://pubs.usgs.gov/pp/0503c/report.pdf
  52. https://ajsonline.org/article/61239.pdf
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  54. https://www.geol.umd.edu/~jmerck/geol431/lectures/18euryapsida.html
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  56. https://pmc.ncbi.nlm.nih.gov/articles/PMC8141288/
  57. https://www.researchgate.net/publication/233715731_A_new_parareptile_with_temporal_fenestration_from_the_Middle_Permian_of_South_Africa
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