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Pisanosaurus
Temporal range: Late Triassic
~229 Ma
↓
Reconstruction of the skull, white bones are known, light grey bones were known from heavily eroded impressions
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: †Ornithischia (?)
Genus: †Pisanosaurus
Casamiquela, 1967
Species:
†P. mertii
Binomial name
†Pisanosaurus mertii
Casamiquela, 1967

Pisanosaurus (/pɪˌsænəˈsɔːrəs/ piss-AN-ə-SOR-əs) is an extinct genus of early dinosauriform, likely an ornithischian or silesaurid, from the Late Triassic of Argentina. It was a small, lightly built, ground-dwelling herbivore, that could grow up to an estimated 1 m (3.3 ft) long. Only one species, the type, Pisanosaurus mertii, is known, based on a single partial skeleton discovered in the Ischigualasto Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina. This part of the formation has been dated to the late Carnian, approximately 229 million years ago.[1]

Discovery and naming

[edit]
Reconstructed skeleton reflecting the traditional interpretation of Pisanosaurus as an ornithischian dinosaur, Royal Ontario Museum

Pisanosaurus is known from a single fragmented skeleton discovered in 1962 by Galileo Juan Scaglia at the Hoyada del Cerro Las Lajas locality[1] (also known as Agua de Las Catas)[2] in the Ischigualasto Formation of La Rioja Province, Argentina.[3]

The genus is based on a specimen given the designation PVL 2577, which consists of a partial skull including a fragmentary right maxilla with teeth, and incomplete right mandibular ramus (lower jaw), six incomplete cervical vertebrae, seven incomplete dorsal vertebrae, molds of five sacral vertebrae, a rib and several rib fragments, a fragmentary right scapula, a coracoid, molds of a fragmentary ilium, ischium and pubic bone, an impression of three metacarpals, the complete femora, the right tibia, the right fibula, with an articulated astragalus and calcaneum, a tarsal element with a metatarsal, metatarsals III and IV, three phalanges from the third toe and five phalanges (including the ungual) from the fourth toe, and an indeterminate long bone fragment.[4]

The genus name Pisanosaurus means "Pisano's lizard" and combines "Pisano" in honor of Argentine paleontologist Juan Arnaldo Pisano of La Plata Museum, with a Latin "saurus" from the Greek (σαύρα) meaning "lizard".[5][6] Pisanosaurus was described and named by Argentine paleontologist Rodolfo Casamiquela in 1967. The type and only valid species known today is Pisanosaurus mertii. The specific name honors the late Araucanian naturalist Carlos Merti.

Description

[edit]

Based on the known fossil elements from a partial skeleton, Pisanosaurus was a small, lightly built dinosauriform, reaching 1–1.3 m (3.3–4.3 ft) in length and 2 kg (4.4 lb) in body mass.[7][8] These estimates vary due to the incompleteness of the holotype specimen PVL 2577. The orientation of the pubis is uncertain, with some skeletal reconstructions having it projecting down and forward (the propubic condition) similar to that of the majority of saurischian dinosaurs.[9]

According to a redescription by José Bonaparte in 1976, Pisanosaurus has some distinctive characteristics. The acetabulum (hip socket) is open. The peduncles of the ilium are short, resulting in a low and axially elongated acetabulum. The upper region of the ischium is wide, larger than that of the pubic bone. The metacarpals of the hand are apparently elongated, measuring about fifteen millimeters.[2]

Classification

[edit]
Ornithischia
Cladogram of basal Ornithischia after Butler et al. (2008), showing the position of Pisanosaurus as the earliest example of an ornithischian.[3]

Pisanosaurus is the type genus of the Pisanosauridae, a family erected by Casamiquela in the same paper which named Pisanosaurus.[4] The family Pisanosauridae has fallen into disuse; a 1976 study considered the group synonymous with the already named Heterodontosauridae,[2] though this is not followed by more recent studies.

The exact classification of Pisanosaurus has been the topic of debate by scientists for over 40 years; until 2017, the consensus was that Pisanosaurus is the oldest known ornithischian, part of a diverse group of dinosaurs which lived during nearly the entire span of the Mesozoic Era. More recently, some authors have begun to consider it a non-dinosaurian silesaurid,[10][11] though this hypothesis has not reached a consensus either.[1]

Ornithischian hypothesis

[edit]
Restoration reflecting the traditional interpretation of Pisanosaurus as an ornithischian dinosaur

Pisanosaurus has traditionally been classified as very basal within Ornithischia; the postcrania seem to lack any good ornithischian synapomorphy and it was even suggested by Paul Sereno in 1991 that the fossil is a chimera.[12] However, recent studies suggest that the fossils belong to a single specimen.[3][13]

Over the years, Pisanosaurus has been classified as a heterodontosaurid, a fabrosaurid, a hypsilophodont and has also been considered the earliest known ornithischian. A 2008 study placed Pisanosaurus outside of (and more basal than) Heterodontosauridae. In this study, Pisanosaurus is the earliest and most primitive ornithischian.[3] This assignment is also supported by Norman et al. (2004), Langer et al. (2009) and the controversial Ornithoscelida hypothesis of Baron, Norman & Barrett (2017).[14][15][16] Other primitive ornithischians include Eocursor, Trimucrodon, and possibly Fabrosaurus.

The hypothesis of ornithischian affinities for Pisanosaurus has not fallen out of favor despite competition from alternative hypothesis. Silesaurid-like traits, for example, may be dinosaurian plesiomorphies (ancestral conditions) rather than unique characteristics of silesaurids.[1]

Silesaurid hypothesis

[edit]
Restoration of Pisanosaurus as a silesaurid

A phylogenetic analysis informally conducted by Agnolin (2015) recovered Pisanosaurus as a possible non-dinosaurian member of Dinosauriformes related to the silesaurids.[17] In 2017, two studies independently came to the conclusion that Pisanosaurus was a silesaurid: one was an expansive redescription by Agnolin and Rozadilla,[18] and the other was a re-analyzed Ornithoscelida matrix by Baron, Norman, & Barrett.[11] Pisanosaurus was also found as a silesaurid in a 2018 paper which combined the descriptive work of Agnolin and Rozadilla (2017) with the phylogenetic matrix of Baron, Norman, & Barrett (2017).[19]

The placement of Pisanosaurus is reliant on the placement of silesaurids as a whole, a situation which has invited much debate. While Silesauridae is often considered a monophyletic sister group of dinosaurs, some studies consider it a paraphyletic grade ancestral to ornithischian dinosaurs in particular. One such study is Müller & Garcia (2020).[20] Although they regarded Pisanosaurus as the basal-most ornithischian, taxa often considered members of Silesauridae form a step-wise arrangement up to Pisanosaurus. It acts a transitional form positioned on a rung between the "silesaurid" grade (Asilisaurus, Sacisaurus, Silesaurus, etc.) and traditional ornithischians (Eocursor, Scutellosaurus, Heterodontosaurus, etc.). This phylogenetic position may explain why some authors consider Pisanosaurus a silesaur and others consider it an ornithischian, as following Müller & Garcia, Pisanosaurus has traits of both groups.[20][21]

Paleoecology

[edit]

The fossils of Pisanosaurus were discovered in the "Agua de las Catas" locality at the Ischigualasto Formation in La Rioja, Argentina. Originally dated to the Middle Triassic,[2] this formation is now believed to belong to the Late Triassic Carnian stage, deposited approximately 228 to 216.5 million years ago.[3] This specimen was collected by José Fernando Bonaparte, Rafael Herbst and the preparators Martín Vince and Scaglia in 1962, and is housed in the collection of the Laboratorio de Paleontologia de Vertebrados, Instituto "Miguel Lillo", in San Miguel de Tucumán, Argentina.

The Ischigualasto Formation was a volcanically active floodplain covered by forests, with a warm and humid climate,[22] though subject to seasonal variations including strong rainfalls.[23] Vegetation consisted of ferns, horsetails, and giant conifers, which formed highland forests along the banks of rivers.[24] Herrerasaurus remains appear to have been the most common among the carnivores of the Ischigualasto Formation.[25] Sereno (1993) noted that Pisanosaurus was found in "close association" with therapsids, rauisuchians, archosaurs, Saurosuchus and the dinosaurs Herrerasaurus and Eoraptor, all of whom lived in its paleoenvironment. Bonaparte (1976) postulated that Pisanosaurus played a role in a fauna dominated by therapsids. The large carnivore Herrerasaurus may have fed upon Pisanosaurus. Herbivores were represented by rhynchosaurs such as Hyperodapedon (a beaked reptile); aetosaurs (spiny armored reptiles); kannemeyeriid dicynodonts (stocky, front-heavy beaked quadrupedal animals) such as Ischigualastia; and traversodontids (somewhat similar in overall form to dicynodonts, but lacking beaks) such as Exaeretodon. These non-dinosaurian herbivores were much more abundant than early dinosaurs.[26]

References

[edit]
[edit]
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Pisanosaurus

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from Grokipedia
Pisanosaurus mertii is an extinct genus of small basal dinosauriform that lived during the Carnian stage of the Late Triassic epoch in what is now northwestern Argentina. Known solely from a single partial skeleton discovered in the middle section of the Ischigualasto Formation, it represents one of the earliest known members of Dinosauriformes and is characterized by its small size, with hindlimb bones such as the tibia measuring approximately 161 mm in length. The preserved elements include parts of the right maxilla with 11 teeth, the right mandible with 15 teeth featuring leaf-shaped crowns indicative of a herbivorous diet, seven dorsal vertebrae, three caudal vertebrae, and elements of the right hind limb including the tibia, fibula, and metatarsals. Originally described in 1967 by Argentine paleontologist Rodolfo Casamiquela as a primitive ornithischian dinosaur within the suborder Ornithopoda and the newly erected family Pisanosauridae, P. mertii was based on the holotype specimen PVL 2577, unearthed in 1962 near Agua de las Cañas in La Rioja Province. The formation's age is estimated at around 231–225 million years ago, placing it among the oldest potential ornithischian records, though the Ischigualasto Formation is renowned for yielding early dinosaurs like Eoraptor and Herrerasaurus. Key diagnostic features include a deep adductor fossa on the mandible, an elongated postdentary portion of the jaw, and a palisade-like arrangement of teeth fused to the jaw bones without prominent canines. The classification of Pisanosaurus mertii remains controversial, reflecting broader uncertainties in early dinosaur phylogeny. While initial interpretations positioned it as a basal ornithischian potentially linking pseudosuchians to later and forms, a 2017 phylogenetic reassessment by Novas and colleagues argued that shared traits such as reduced tooth denticles, fused teeth to the jaw, and a fibular on the tibia align it more closely with , a group of non-dinosaurian dinosauriforms. However, more recent analyses, including a 2024 study on early Asian ornithischians, recover P. mertii as the earliest-diverging ornithischian dinosaur, supporting its inclusion within Dinosauria based on updated character matrices and additional specimens. This debate underscores Pisanosaurus's importance in understanding the origins and initial diversification of ornithischians during the .

Discovery and naming

Discovery history

The holotype specimen of Pisanosaurus mertii (PVL 2577), consisting of a partial skeleton, was discovered in 1962 during an expedition to the in Province, northwestern . The fossils were unearthed by paleontologist Galileo Juan Scaglia, along with team members including José F. Bonaparte, Rafael Herbst, and preparator Martín Vince, at the locality known as Hoyada del Cerro Las Lajas (also referred to as Agua de las Catas near km 461 on National Route 40). This site lies within the lower to middle section of the formation, specifically the upper layers of the Hyperodapedon Assemblage Zone, dated to approximately 229–228 million years ago based on U-Pb geochronology from intercalated tuffs. Following its recovery, the specimen was prepared and initially studied under the auspices of the Instituto Miguel Lillo in Tucumán, , where it was transported for safekeeping and analysis. Rodolfo Casamiquela provided the first formal description and publication of PVL 2577 in 1967, interpreting it as a primitive ornithischian and establishing the new and within the family Pisanosauridae. Early assessments by the discovering team, including Bonaparte, viewed the fossil as representative of an early true , marking it as one of the oldest known ornithischians from the Period. The specimen remains housed at the Instituto Miguel Lillo in , serving as the sole basis for the .

Etymology and validity

The genus name Pisanosaurus derives from "Pisano," honoring the Argentine paleontologist Juan Pisano of the , combined with the Greek word sauros, meaning "" or "," yielding "Pisano's ." The species mertii commemorates the Araucanian naturalist and Carlos Merti, who contributed to early explorations of the . The type specimen, designated PVL 2577 and housed at the Instituto Miguel Lillo in Tucumán, , consists of a partial preserving a fragmentary right with 11 teeth and a probable 12th root, an incomplete right with 15 teeth, a small left fragment, portions of three caudal vertebrae, nine incomplete dorsal vertebrae, one with two fragments, a complete right and articulated with the astragalus and calcaneum, a second distal tarsal fused to a metatarsal, two metatarsals with incomplete digits, and an indeterminate fragment. No additional referred specimens have been assigned to the , rendering Pisanosaurus mertii monotypic based on this alone. The taxonomic validity of Pisanosaurus has been debated since its description due to the fragmentary and poorly preserved nature of the holotype, which some researchers suggested might represent a taxonomic chimera composed of elements from multiple individuals or taxa. However, a redescription by Bonaparte in 1976 affirmed its integrity as a distinct , emphasizing diagnostic features such as the palisade-like with precise occlusion, the elongated postdentary portion of the relative to the dentary, and the descended mandibular articular condyle. Subsequent analyses, including a comprehensive phylogenetic reassessment in 2017, upheld the genus as a valid nomen despite reinterpreting its affinities, citing these same cranial and dental traits as sufficient for taxonomic distinction. By 2020, ongoing revisions continued to recognize Pisanosaurus mertii as a monotypic without synonymy or invalidation, supported by its unique combination of primitive ornithischian-like features in the limited material.

Description

Size and general morphology

Pisanosaurus mertii was a diminutive dinosauriform, with an estimated total body length of 1–1.3 meters (3.3–4.3 feet) and a body mass of approximately 2 kilograms. These estimates derive from the incomplete skeleton (PVL 2577), which includes elements such as a measuring 160.7 mm in length, indicating a small overall scale comparable to other early dinosauriforms. The general build of P. mertii was lightly constructed and slender, characteristic of a ground-dwelling adapted for in its . Its frame featured elongated hindlimbs relative to the forelimbs, with a reduced (158.7 mm long) and a functionally three-toed, foot, supporting efficient terrestrial movement. The open of the further underscores its dinosauriform affinities, facilitating a more upright posture than in more basal archosaurs. Locomotion in P. mertii is inferred to have been primarily bipedal, with a horizontal orientation and extended hindlimbs enabling rapid bursts of speed suitable for navigating a forested environment. Limb proportions suggest possible facultative quadrupedality, allowing occasional use of the forelimbs for stability or , consistent with interpretations placing it among basal dinosauriforms like silesaurids. This agile, versatile gait would have aided in evading predators while browsing low vegetation.

Skeletal features

The preserved cranial material of Pisanosaurus mertii includes a fragmentary featuring a right with 11 teeth and a dentary with 15 teeth. The teeth are low-crowned and leaf-shaped with denticles, consistent with a herbivorous diet. The postcranial includes seven articulated dorsal vertebrae, fragmentary vertebrae of uncertain position (possibly cervical or caudal), three anterior caudal vertebrae, and a partial . Additional elements comprise a right , right , incomplete right ilium, right pubis, proximal portions of right , distal ends of the femora, right , right , right astragalus, right calcaneum, and some pedal phalanges. The features a short ilium with elongated peduncles, along with the pubis and that form a closed . The includes a straight with distal end preserved (estimated length approximately 90 mm), a , and metatarsals, features that suggest bipedal locomotion. Partial elements, including a right and , are preserved, with possible impressions of metacarpals. Key diagnostic traits include asymmetrical enamel on the teeth and a perforated .

Classification

Ornithischian hypothesis

Pisanosaurus mertii was originally classified as a primitive , specifically within the suborder , upon its description in 1967 from fragmentary remains collected in the of . This initial assignment positioned it as one of the earliest known members of , reflecting the group's diversification during the . Subsequent analyses reinforced this view; for instance, Norman et al. (2004) supported its placement as a basal based on shared dental and pelvic features with later , emphasizing its role in understanding early herbivorous adaptations. Key anatomical evidence for the ornithischian hypothesis includes the and morphology. The are leaf-shaped with marginal denticles, indicative of a herbivorous diet typical of ornithischians, and arranged in a manner suggesting an inset tooth row. The lower exhibits a structure interpreted as a predentary-like element at the anterior tip, a diagnostic ornithischian feature that facilitates beak-like cropping of vegetation. Additionally, the pelvic girdle shows an ornithischian-style hip socket, with a configuration allowing for the retroverted pubis seen in derived ornithischians, supporting bipedal locomotion and stability. In phylogenetic analyses, Pisanosaurus has been recovered as basal to Genasauria, the clade encompassing more derived ornithischians like thyreophorans and ornithopods. For example, Butler et al. (2008) positioned it near in their comprehensive study of ornithischian relationships, using 221 characters across 46 taxa to highlight its primitive status within the group. A phylogenetic analysis incorporating early Asian ornithischian specimens recovered Pisanosaurus as the earliest-diverging ornithischian dinosaur. This placement underscores the hypothesis's strength in aligning Pisanosaurus with the early radiation of ornithischians, providing a temporal anchor for the clade's origin amid the diversification of dinosaurian lineages.

Silesaurid hypothesis

The silesaurid hypothesis proposes that Pisanosaurus mertii represents a non-dinosaurian dinosauromorph closely allied with , rather than a basal ornithischian . This classification was more explicitly advanced through detailed redescription and phylogenetic analyses in subsequent works. Agnolín and Rozadilla (2017) provided a comprehensive reassessment of the specimen (PVL 2577), arguing for its placement within due to a suite of shared derived traits. Independently, Baron et al. (2017) incorporated Pisanosaurus into a revised dinosaur phylogeny, recovering it as a silesaurid and using this to support redefining to exclude silesaurids as stem-group forms. Key evidence supporting silesaurid affinities includes several postcranial and dental features that align Pisanosaurus more closely with silesaurids like Silesaurus opolensis and Asilisaurus congensus than with ornithischians. Dental morphology features asymmetrical enamel thickness and reduced denticles on leaf-shaped crowns, traits shared with silesaurids and indicative of similar herbivorous adaptations, while lacking the thicker, symmetrical enamel of definitive ornithischians. Additionally, the shows no clear ornithischian synapomorphies, such as an opisthopubic ilium or expanded preacetabular process; instead, it retains plesiomorphic dinosauromorph conditions like fused teeth to the jaw bones and shared sacral ribs across vertebrae, further supporting exclusion from Dinosauria. Phylogenetic analyses under the silesaurid hypothesis consistently nest Pisanosaurus within as a derived member, often positioned near or other silesaurids based on character matrices emphasizing postcranial data. Agnolín and Rozadilla (2017) recovered it in a clade with these genera using a modified from prior dinosauromorph studies, while Baron et al. (2017) placed it among silesaurids in their ornithoscelidan framework, treating as the sister group to a restricted Dinosauria comprising and . This positioning implies silesaurids as stem-dinosaurs, extending the group's known diversity into the stage of the . The implications of classifying Pisanosaurus as a silesaurid challenge the timeline of early dinosaur radiation by removing the oldest purported ornithischian record, suggesting Ornithischia originated no earlier than the Early Jurassic. This hypothesis underscores the paraphyletic nature of Triassic dinosauromorphs and highlights how incomplete preservation of Pisanosaurus—lacking key cranial elements—has fueled debate, potentially delaying recognition of dinosaur diversification until after the Norian-Rhaetian boundary.

Transitional form hypothesis

A recent phylogenetic analysis by Müller and Garcia (2020) proposed an alternative hypothesis positioning Pisanosaurus mertii as a stem-ornithischian, with traditional silesaurids forming a paraphyletic assemblage of stem taxa leading to core ornithischians. This study incorporated expanded character datasets and 36 taxa, recovering Pisanosaurus as the sister taxon to more derived ornithischians like Heterodontosaurus tucki, while suggesting an evolutionary origin for Ornithischia in the Middle to early Late Triassic. Supporting evidence includes a mosaic of traits in Pisanosaurus, such as silesaurid-like forelimbs and possible ankylothecodont , combined with ornithischian features like leaf-shaped teeth indicative of herbivory and a showing early predentary affinities. These characteristics imply a gradual evolutionary transition rather than a clear between silesaurids and ornithischians, with Pisanosaurus bridging the gap through secondary adoption of omnivorous or herbivorous adaptations from faunivorous ancestors. However, the hypothesis faces uncertainties due to the limited and fragmentary material of Pisanosaurus, which comprises only about 40% of the and exhibits high levels of in phylogenetic matrices, resulting in low branch support and bootstrap values. The authors emphasize that additional discoveries from the are essential to resolve its exact position and test the of . As of , the transitional form hypothesis remains debated among paleontologists, but it has gained traction in recent phylogenetic studies that increasingly view silesaurids as stem-ornithischians, challenging stricter dichotomies and highlighting Pisanosaurus as a key in early dinosaur evolution.

Geological setting

The , situated in northwestern within the Ischigualasto-Villa Unión Basin, represents a key Upper Triassic unit from the Upper Carnian stage of the period. This formation, which unconformably overlies the Los Rastros Formation and is overlain by the Los Colorados Formation, spans a thickness of up to 1,059 meters and consists predominantly of red-bed sediments deposited in a continental rift setting along the western margin of . Radiometric dating using U-Pb zircon from interlayered constrains the age of the to approximately 231–225 million years ago (Ma), with the base dated at 230.23 +1.88/−0.86 Ma and the top at 221.36 +0.44/−1.31 Ma. More precisely, levels associated with the Hyperodapedon Assemblage Zone, where Pisanosaurus mertii occurs, yield ages around 229 Ma, such as 229.25 ± 0.10 Ma from the Toba-2 at 107 meters above the base. These dates, derived from CA-TIMS analysis of volcanic zircons, indicate deposition over roughly 5–6 million years in a tectonically active basin influenced by Andean arc . Stratigraphically, the formation is divided into lower, middle, and upper sections, featuring a sequence of fluvial and volcanic deposits. The lower section (0–310 m above base) includes meandering fluvial channels with sandstones and conglomerates, siltstones and mudstones, and tuffaceous layers, transitioning upward to more pedogenically altered overbank deposits in the middle section. Pisanosaurus mertii was recovered from upper levels within this lower section, corresponding to the Cancha de Bochas Member and the Assemblage Zone at approximately 110–260 meters above the base. Volcanic input increases in the upper third, with prominent welded tuffs and ignimbrites reflecting proximity to eruptive centers. Fossils in the , including those of Pisanosaurus, are primarily preserved in sediments, which account for about 88% of the 385 documented occurrences across the unit. These fine-grained mudstones and siltstones facilitated rapid burial, minimizing and scavenging, as evidenced by the presence of articulated skeletons and low time-averaging in autochthonous assemblages. The dynamic , characterized by frequent overbank flooding and falls, promoted this taphonomic mode, particularly in the fossil-rich Cancha de Bochas Member.

Paleoenvironment and fauna

The , where Pisanosaurus mertii was discovered, represents a semi-arid paleoenvironment characterized by broad floodplains traversed by meandering, low-sinuosity rivers and influenced by periodic rainfall events. Sedimentary deposits include conglomeratic sandstones, siltstones, and mudstones, with paleosols indicating seasonal aridity and the development of calcic horizons in the lower sections where Pisanosaurus occurs. Volcanic activity contributed pyroclastic material, such as tuffs and bentonites, particularly in upper levels, but the lower strata feature a relatively stable fluvial system with crevasse splays and overbank fines preserving fossils. was dominated by gymnosperms, including like Agathoxylon (affiliated with ) and corystosperms, alongside herbaceous elements such as equisetaleans and ferns, forming low-statured woodlands and riparian zones adapted to seasonal water availability. As a small-bodied , Pisanosaurus likely occupied a niche low-lying , such as ferns and young shoots in settings, inferred from its featuring leaf-shaped teeth suited for grinding plant matter. This dietary adaptation positioned it among early herbivores exploiting post-Permian recovery niches in a landscape with limited large competitors. The fauna associated with Pisanosaurus in the lower includes carnivorous early dinosaurs like ischigualastensis and murphi, as well as the omnivorous lunensis, suggesting a diverse predator that may have preyed on small herbivores. Synapsids were prominent, with herbivorous rhynchosaurs such as sanjuanensis and traversodont cynodonts like Exaeretodon argentinus filling larger grazing roles, while archosauriforms including Proterochampsa barrionuevoi and temnospondyl amphibians occupied aquatic and semi-aquatic habitats. No direct small-herbivore competitors are noted among contemporaneous taxa, indicating Pisanosaurus exploited an underfilled ecological space. Ecologically, Pisanosaurus represents a basal form in the early diversification of herbivorous archosaurs, contributing to the initial radiation of small-bodied tetrapods in floodplains following the Permian-Triassic extinction. Its presence in the underscores the role of such taxa in stabilizing food webs amid fluctuating climatic conditions.

References

  1. https://naturalhistory.si.edu/sites/default/files/media/translated_publications/Casamiquela_67.pdf
  2. https://www.tandfonline.com/doi/full/10.1080/14772019.2017.1352623
  3. https://www.cell.com/iscience/fulltext/S2589-0042(24)02868-2
  4. https://www.nature.com/articles/s41598-020-67854-1
  5. https://www.tandfonline.com/doi/abs/10.1080/14772019.2017.1352623
  6. https://www.researchgate.net/publication/318909984_Phylogenetic_reassessment_of_Pisanosaurus_mertii_Casamiquela_1967_a_basal_dinosauriform_from_the_Late_Triassic_of_Argentina
  7. https://www.jstor.org/stable/1303575
  8. https://royalsocietypublishing.org/doi/10.1098/rsbl.2020.0417
  9. https://bpb-eu-w2.wpmucdn.com/blogs.bristol.ac.uk/dist/5/537/files/2019/07/2012Complete.pdf
  10. https://pmc.ncbi.nlm.nih.gov/articles/PMC3491919/
  11. https://doi.org/10.1016/j.isci.2024.111641
  12. https://www.tandfonline.com/doi/abs/10.1017/S1477201907002271
  13. https://doi.org/10.1098/rsbl.2020.0417
  14. https://www.tandfonline.com/doi/abs/10.1080/02724634.2013.809285
  15. https://www.cambridge.org/core/journals/paleontological-society-special-publications/article/paleoenvironment-and-taphonomy-of-the-dinosaurbearing-ischigualasto-formation-upper-triassic-argentina/C32EEE47DAD5820763A298AF6910C5FF
  16. https://pubs.geoscienceworld.org/sepm/palaios/article/23/12/778/145949/Late-Triassic-Environmental-Evolution-in
  17. https://www.cambridge.org/core/journals/journal-of-paleontology/article/araucariaceous-fossil-woods-from-the-upper-triassic-ischigualasto-formation-san-juan-province-argentina-paleofloristic-and-paleoclimatic-implications/90D282BC758667BC3C1F72DE4C75B4F6
  18. https://d3qi0qp55mx5f5.cloudfront.net/paulsereno/i/docs/13-JVP-Martinez_et_al-Vert._Succ.pdf
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