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Maniraptora

Maniraptora is a diverse clade of coelurosaurian theropod dinosaurs defined as all species more closely related to modern birds than to ornithomimids, encompassing birds (Aves) and their closest non-avian relatives.^[1] Originating in the Jurassic around 165–150 million years ago, possibly as early as the Middle Jurassic based on recent European discoveries,^[2] this group represents the most diverse clade of dinosaurs, spanning the Jurassic to the present day (surviving as birds) across all continents.^[3]^[1] Key synapomorphies of Maniraptora include a semilunate carpal bone in the wrist that allows for folding akin to modern birds, a fused clavicle forming a furcula (wishbone), a fused sternum, a downward-pointing pubis, a shortened and stiffened tail, elongated forelimbs with an enlarged manus, and the presence of pennaceous feathers.^[1]^[3] These adaptations reflect a stepwise accumulation of avian-like traits, particularly accelerating in this clade, with shifts toward knee-driven locomotion, sideways-oriented shoulder joints, and dietary diversification from carnivory to herbivory and omnivory.^[4]^[3] Few maniraptorans retain the basal theropod's fully carnivorous condition, highlighting their evolutionary experimentation.^[3] The major subgroups of Maniraptora include Therizinosauria (herbivorous forms with massive claws, such as Therizinosaurus), Alvarezsauria (small insectivores with specialized, reduced forelimbs like Mononykus), Oviraptorosauria (omnivorous, toothless dinosaurs such as Oviraptor and the giant Gigantoraptor), and Eumaniraptora, which further divides into Deinonychosauria (encompassing sickle-clawed dromaeosaurids like Velociraptor and long-snouted troodontids) and Avialae (the clade including modern birds and their direct ancestors).^[1]^[3] This phylogeny underscores Maniraptora's central role in avian evolution, with forelimb modifications facilitating flight and pelvic musculature changes supporting enhanced cursoriality and bipedal efficiency on the line to birds.^[1]^[4] Despite a patchy fossil record, maniraptorans exhibit convergent evolution in traits like flight capability and insular adaptations, making them pivotal for understanding theropod diversity and the origins of flight.^[1]^[3]

Definition and Etymology

Naming and Discovery History

The clade Maniraptora was initially proposed by Jacques Gauthier in 1986 as a monophyletic group within Theropoda, encompassing dinosaurs more closely related to birds than to ornithomimids, based on shared derived features such as a semilunate carpal bone enabling folding of the hand. This proposal marked a key application of cladistic methods to theropod phylogeny, emphasizing evolutionary relationships over traditional grade-based groupings.^[5] Key early discoveries laid the groundwork for recognizing maniraptoran diversity. Velociraptor mongoliensis was described by Henry Fairfield Osborn in 1924 from fossils collected during the American Museum of Natural History's Central Asiatic Expeditions to the Gobi Desert in the early 1920s, revealing a swift, sickle-clawed predator that hinted at agile theropod behaviors. Decades later, John H. Ostrom's 1969 description of Deinonychus antirrhopus from the Cloverly Formation in Montana demonstrated bird-like traits in a non-avian theropod, including enlarged forelimbs and a cursorial posture, thereby revitalizing the dinosaur-bird linkage first suggested by Thomas Huxley in the 1860s.^[6] The name "Maniraptora" was coined by Jacques Gauthier in 1986, derived from Latin manus (hand) and raptor (thief or plunderer), referring to the clade's characteristic enlarged forelimbs adapted for grasping and equipped with sickle-shaped claws. Following the 1980s shift to cladistics, the concept evolved to incorporate a broader array of coelurosaurs; modern phylogenies include oviraptorosaurs, initially misplaced but confirmed as maniraptorans through analyses of cranial and postcranial synapomorphies like edentulous jaws and pygostyle precursors.^[7] Scansoriopterygids, known from Jurassic Chinese fossils, were similarly integrated based on shared maniraptoran hand morphology and arboreal adaptations.^[8] Post-2020 refinements have strengthened these ties through new fossils, such as the alvarezsaurid Jaculinykus yaruui from Mongolia's Baruungoyot Formation, whose avian-like sleeping posture and specialized manus confirm alvarezsaurid placement within Maniraptora via updated phylogenetic matrices.^[9] Similarly, the therizinosaurid Paralitherizinosaurus japonicus from Japan's Osoushinai Formation reveals derived claw functions aligned with maniraptoran herbivory trends, extending the clade's known paleobiogeography and temporal range.^[10] Recent 2024 analyses using machine learning on UK Middle Jurassic microvertebrate faunas have confirmed additional early maniraptoran records, supporting an initial radiation in the Middle Jurassic.^[11]

Phylogenetic Definition and Diagnosis

Maniraptora is a stem-based clade within Theropoda, formally defined as all taxa sharing a more recent common ancestor with Aves than with Ornithomimus velox. This definition, proposed by Gauthier in 1986, anchors the group to the avian lineage while excluding more basal coelurosaurs, thereby encompassing a diverse array of bird-like dinosaurs from the Late Jurassic to the present.^[12] The clade is diagnosed by a suite of synapomorphies that highlight adaptations for enhanced forelimb mobility and predatory efficiency. Key features include relatively elongate forelimbs (compared to more basal theropods), with three-fingered hands featuring elongated manual phalanges; a semi-lunate carpal bone that permits pronounced wrist flexion; a reduced olecranon process on the ulna; and fused cranial trochanters on the femur. In more derived subgroups, the pubis is rotated posteriorly, contributing to a retroverted pelvic configuration. These traits collectively distinguish Maniraptora from basal theropods and facilitate behaviors such as grasping and, in some cases, aerial capabilities.^[12] Unlike the broader Coelurosauria, which includes tyrannosauroids and compsognathids with more generalized theropod morphologies, Maniraptora emphasizes advanced avian-like traits, such as refined manual dexterity and pedal specialization, reflecting a specialized evolutionary trajectory toward flight and arboreal or cursorial lifestyles.^[12]^[13]

Anatomy

Skeletal Features

Maniraptora exhibit distinctive forelimb morphology characterized by an elongated humerus and radius, which contribute to enhanced reach and flexibility. The manus is three-fingered with subequal digits I-III, where digit III is robust and not reduced as in more basal theropods. A key feature is the semi-lunate carpal, a composite bone formed by the fusion of distal carpals 1 and 2, enabling a pulley-like mechanism for wrist flexion and folding.^[14] This carpal, along with a wedge-shaped radiale allowing up to 60° abduction in some taxa like Deinonychus, facilitates asymmetric wrist mobility essential for maniraptoran limb function.^[15] Hindlimb adaptations in several maniraptoran subgroups, such as paravians and alvarezsauroids, include the arctometatarsal foot, where metatarsal III is pinched proximally between metatarsals II and IV, reducing its width while maintaining length for efficient weight distribution during locomotion. This condition is evident in paravians, such as dromaeosaurids, where the foot supports agile movement. Additionally, pedal digit II bears a hypertrophied, falciform ungual phalanx forming a sickle claw, which is retractable and held off the ground in taxa like Deinonychus, distinguishing it from the subequal digits in birds.^[16] The pelvic girdle and vertebral column show specialized traits, including a backward-rotated pubis in Paraves (e.g., troodontids and dromaeosaurids) and Oviraptorosauria, converging on an opisthopubic condition that alters muscle origins and enhances pelvic mobility. Extensive pneumatization invades the vertebrae and ribs, lightening the axial skeleton; for instance, cervical and dorsal vertebrae in therizinosaur Nothronychus exhibit complex pneumatic foramina linked to air sac diverticula.^[17]^[18] Cranial features include a kinetic skull with flexible jaw joints, where the quadrate and laterosquamosal articulations permit streptostylic motion, as seen in oviraptorosaurs and basal avialans. Large orbits in troodontids indicate expanded visual capabilities, supported by fenestrated sclerotic rings in fossils like cf. Archaeopteryx.^[19]^[20] Variations across subgroups highlight skeletal diversity. Therizinosauria display robust, herbivore-adapted limbs with massively enlarged manual unguals (up to 70 cm in Therizinosaurus) and a widened pelvis for gut support, contrasting the slender builds of other maniraptorans. Alvarezsauridae feature highly specialized tubular forelimbs that are highly reduced relative to the hindlimbs, with a hypertrophied digit I bearing a large claw and reduced digits II-III, adapted for forceful prying.^[21]

Integument and Feathers

The integument of basal maniraptorans, such as Sinosauropteryx, consisted of simple, hair-like filamentous protofeathers that formed a fringe along the midline of the body and tail, likely serving functions in insulation or display. These structures were unbranched and measured up to 40 mm in length, covering much of the animal's body except the head and limbs. In more derived members of Pennaraptora, such as Caudipteryx and Microraptor, feathers evolved into complex pennaceous forms featuring a central rachis and symmetrical vanes, enabling greater structural integrity. Asymmetrical flight feathers, with expanded vanes on one side, appeared in avialans like Archaeopteryx, marking a key adaptation for aerodynamic roles.^[22] Feather distribution in paravians was extensive, often covering the entire body including the wings, tail, and legs, as evidenced by impressions and quill knobs on ulnae and tibiae in taxa like Velociraptor and Zhenyuanlong. Diversity in feather morphology included pennaceous primaries and secondaries for lift, alongside downy underfeathers for insulation. Color patterns, inferred from melanosome structures, ranged from reddish-brown stripes in Sinosauropteryx to iridescent black-and-white in Anchiornis, suggesting roles in camouflage or signaling.^[23] The evolutionary progression of feathers in Maniraptora transitioned from simple filaments for thermoregulation and display in non-volant forms to vaned structures supporting gliding or powered flight in later lineages.^[24] Fossil evidence from juveniles and embryos, such as those of oviraptorosaurs like Similicaudipteryx, reveals ontogenetic development from protofeathers to fully pennaceous feathers by late juvenile stages, indicating feathers were integral from early growth. While most maniraptorans trended toward comprehensive feathering, exceptions included scaled regions on the feet of some dromaeosaurids, such as Velociraptor, where quill knobs are absent on pedal phalanges, suggesting a mosaic integument with scales persisting for pedal function.^[25]

Classification

Major Constituent Groups

Maniraptora is characterized by a diverse array of subgroups that showcase adaptations ranging from herbivory to specialized predation and arboreal lifestyles. The primary constituent groups include Therizinosauria, Alvarezsauria, Oviraptorosauria, and Paraves, with smaller clades such as Scansoriopterygidae representing additional morphological experimentation within the clade. These groups collectively highlight the evolutionary flexibility of maniraptorans, particularly in forelimb structure and dietary strategies. Therizinosauria represents a lineage of herbivorous theropods distinguished by their robust, sloth-like builds, elongated necks, and enormous manual claws adapted for foraging or defense. These dinosaurs evolved pot-bellied torsos to accommodate expanded digestive systems for processing plant material, diverging markedly from the carnivorous ancestry of other coelurosaurs. Exemplars like Therizinosaurus from the Late Cretaceous of Asia illustrate the group's extreme claw development, with hand unguals exceeding 1 meter in length.^[26] Alvarezsauria comprises small-bodied, insectivorous maniraptorans with highly specialized forelimbs featuring a single massive claw on a robust arm, likely used for digging or probing termite mounds. Their short, powerful humerus and reduced outer digits suggest a pincer-like function for extracting prey from soil or wood. Mononykus, a Late Cretaceous representative from Mongolia, exemplifies this adaptation, with its body length around 1 meter and a lifestyle inferred from the anatomical modifications for myrmecophagy.^[27] Oviraptorosauria includes crested theropods known for their toothless beaks, short tails, and evidence of egg-brooding behavior, indicating omnivorous or carnivorous diets supplemented by scavenging or small vertebrate predation. Their distinctive pneumatic skulls and elaborate cranial crests likely served display or thermoregulatory functions. Genera such as Oviraptor and Citipati from the Late Cretaceous of Asia demonstrate brooding postures over nests, underscoring parental care in this group.^[28] Paraves encompasses the most bird-like maniraptorans, subdivided into Dromaeosauridae, Troodontidae, and Avialae. Dromaeosaurids were agile, sickle-clawed predators with stiffened tails for balance during pursuit hunting, as seen in Deinonychus from the Early Cretaceous of North America. Troodontids featured enlarged brains relative to body size, suggesting enhanced sensory capabilities and possibly omnivorous habits, exemplified by Troodon from the Late Cretaceous. Avialae includes modern birds and their immediate fossil relatives, such as Archaeopteryx, marking the transition to powered flight with feathered wings. Minor groups like Scansoriopterygidae highlight arboreal specializations within Maniraptora, with elongated third fingers and evidence of patagial membranes for gliding between trees. Yi qi from the Middle Jurassic of China represents this clade, featuring a unique wing structure supported by a styliform element rather than primary feathers.^[29] Overall, Maniraptora exhibits substantial diversity, with over 100 described genera spanning body lengths from approximately 0.5 meters in small alvarezsaurids and scansoriopterygids to 6 meters in large oviraptorosaurs and dromaeosaurids. This range underscores the clade's adaptive radiation across terrestrial and aerial niches.

Phylogenetic Relationships

Maniraptora represents a derived subclade within Coelurosauria, encompassing theropod dinosaurs more closely related to birds than to other coelurosaurs such as tyrannosaurids or ornithomimosaurs. The clade is characterized by specialized adaptations for grasping and potentially powered locomotion, with its basal structure featuring Alvarezsauria and Therizinosauria as early-branching members. Phylogenetic analyses consistently recover Alvarezsauria as the sister group to all other maniraptorans, followed by Therizinosauria, with the two together forming the sister taxon to the more derived Pennaraptora. This positioning is supported by shared derived traits, including an elongated manual digit III and modifications to the pelvic girdle for enhanced mobility. The core topology of Maniraptora places Pennaraptora as the clade uniting Oviraptorosauria and Paraves, the latter further dividing into Dromaeosauridae (including eudromaeosaurs and microraptorines), Troodontidae, and Avialae. A comprehensive cladogram from Cau (2020), incorporating over 50 taxa and 300+ morphological characters, reinforces this framework, highlighting synapomorphies such as the furcula (a fused clavicle acting as a spring-like structure for forelimb movement) and a semi-lunate carpal bone enabling swiveling wrists. These features underscore the evolutionary progression toward avian-like locomotion within the clade. Within Paraves, Avialae emerges as the bird-containing crown group, defined phylogenetically as all maniraptorans more closely related to modern birds (Aves) than to oviraptorosaurs, troodontids, or dromaeosaurids. The phylogenetic position of Scansoriopterygidae remains debated, with various analyses placing it as basal paravians or within Avialae. Recent phylogenetic updates have refined internal relationships, with 2023 analyses using machine learning on dental morphology confirming the presence of maniraptorans in Middle Jurassic assemblages, implying early divergences within the clade around 170–160 million years ago. Molecular clock estimates, calibrated against fossil constraints, suggest the initial split between Alvarezsauria and other maniraptorans occurred in the Early Jurassic (circa 190 Ma), with Pennaraptora diversifying by the Middle Jurassic. These timelines align with fossil evidence from Laurasian deposits, providing a temporal scaffold for the clade's radiation.

Alternative Classifications

Jacques Gauthier originally defined Maniraptora in 1986 as a clade encompassing all saurischian dinosaurs more closely related to birds than to Ornithomimus velox, thereby including a wide range of "bird-like" theropods such as dromaeosaurids, troodontids, oviraptorids, and early avialans.^[12] This broad inclusion highlighted shared derived features like a semilunate carpal and reversed hallux, positioning Maniraptora as a key group in theropod evolution toward avian lineages.^[12] During the 1990s, several studies questioned the monophyly of Deinonychosauria, the clade uniting dromaeosaurids and troodontids, based on discrepancies in cranial and pedal anatomy that suggested convergent evolution of certain traits.^[30] For instance, reexamination of Dromaeosaurus albertensis revealed features like a reduced antorbital fenestra and specialized foot morphology that did not align neatly with troodontid conditions, prompting debates on whether Deinonychosauria represented a natural group or a grade.^[30] Ongoing controversies surround the phylogenetic affinity of Troodontidae to Avialae, with multiple analyses recovering Troodon and related taxa as closer to birds than to dromaeosaurids due to shared encephalization and jaw mechanics adapted for precision biting.^[31] The placement of Therizinosauria is accepted within Maniraptora, though its exact position relative to other groups varies in cladistic studies.^[32] Alternative hypotheses include grade-based classification systems, such as those proposed by Kevin Padian, which treat Maniraptora as a paraphyletic assemblage of successively bird-like theropods rather than a strict clade, emphasizing evolutionary grades over node-based definitions to better reflect transitional morphologies toward flight.^[33] More recent critiques, including those from 2018, have challenged the over-reliance on wrist bone configurations like the semilunate carpal for defining Paraves, arguing that developmental plasticity and homoplasy in carpals may inflate support for certain avian affinities.^[34] New fossil discoveries post-2020, such as additional troodontid specimens from the Upper Cretaceous of Inner Mongolia, have helped resolve some debates on body size evolution but have reopened questions about alvarezsaurid placement within Maniraptora, as their specialized forelimbs show potential convergences with paravians that complicate basal relationships.^[35] These finds underscore alvarezsaurids' enigmatic position, with analyses variably nesting them as basal maniraptorans or closer to oviraptorosaurs based on tuberosities and humeral morphology. Persistent uncertainties in maniraptoran phylogeny stem from low bootstrap support in several clades, often below 50% for interrelationships among paravians and therizinosaurians, reflecting character conflicts and incomplete sampling.^[37] Furthermore, the scarcity of Jurassic maniraptoran fossils from Asia highlights the need for more discoveries from formations like the Daohugou Beds to clarify early divergences and test the consensus topology against alternative interpretations.^[2]

Evolutionary History

Temporal Range and Origins

Maniraptora originated from early coelurosaurs during the Middle Jurassic, approximately 170 million years ago, as indicated by analyses of body mass evolution rates across theropod lineages.^[38] The earliest potential records of maniraptorans come from the Tiaojishan Formation in China, dated to around 165 million years ago in the Middle to Late Jurassic, with specimens like Anchiornis representing basal paravians.^[39] Definitive evidence appears in the Late Jurassic, about 150 million years ago, marked by Archaeopteryx from the Solnhofen Limestone in Germany, which exemplifies the early diversification of avialans within Maniraptora.^[5] A major diversification peak occurred in the Early Cretaceous, particularly around 125 million years ago in the Yixian Formation of Liaoning, China, where feathered paravians such as troodontids and dromaeosaurids exhibit advanced integumentary structures and aerial adaptations.^[40] This Asian radiation coincided with the exploitation of small-bodied niches, enabling maniraptorans to occupy ecological roles distinct from larger theropods, and was potentially influenced by the rise of angiosperms, which altered vegetation and prey availability during the mid-Cretaceous.^[41] By the Late Cretaceous, maniraptorans achieved a global distribution, with records spanning Laurasia and Gondwana, including alvarezsaurids and oviraptorosaurs in Asia and North America, as well as dromaeosaurids in Antarctica and South America.^[42]^[43] Non-avian maniraptorans were largely eliminated at the Cretaceous-Paleogene (K-Pg) boundary approximately 66 million years ago, due to the Chicxulub impact and associated environmental catastrophes, while the avialan lineage survived, giving rise to modern birds. Biogeographically, Maniraptora was predominantly Laurasian in origin and distribution, with early coelurosaur ancestors likely evolving in northern Pangaea before dispersing southward; notable Gondwanan occurrences include unenlagiine dromaeosaurids like Unenlagia from Late Cretaceous deposits in Patagonia, Argentina. This southern record underscores a broader Late Cretaceous expansion beyond Laurasia.^[2]

Key Fossil Discoveries

The discovery of Archaeopteryx lithographica in 1861 from the Solnhofen Limestone of Bavaria, Germany, marked the first fossil evidence linking dinosaurs to birds, with its feathered wings and skeletal features preserved in fine-grained limestone.^[44] This specimen, described by Christian Erich Hermann von Meyer, revealed a mosaic of reptilian and avian traits, including teeth and a long bony tail alongside flight-capable feathers.^[44] Subsequent finds in the same Lagerstätte, totaling over a dozen specimens by the early 21st century, further illuminated early maniraptoran morphology through exceptional soft-tissue preservation.^[44] In 1969, John H. Ostrom described Deinonychus antirrhopus from multiple partial skeletons unearthed in the Cloverly Formation of Montana, USA, providing the first detailed insight into dromaeosaurid anatomy with its iconic sickle-shaped claw and agile build.^[6] These Early Cretaceous fossils, dating to approximately 115 million years ago, showcased articulated limbs and vertebrae that highlighted maniraptoran cursorial adaptations.^[6] The late 1990s and early 2000s saw transformative discoveries from the Yixian Formation in Liaoning Province, China, part of the Jehol Biota, where lagerstätten conditions preserved feathers and soft tissues in unprecedented detail. Sinosauropteryx prima, announced in 1996, was the first non-avian dinosaur with preserved filamentous protofeathers, found in Barremian sediments around 125 million years old. This basal coelurosaur, followed by the four-winged dromaeosaurid Microraptor zhaoianus in 2000, demonstrated aerodynamic structures like pennaceous feathers on limbs, revolutionizing views on powered flight origins. The Tiaojishan Formation, a Middle-Late Jurassic lagerstätte in northeastern China dated to about 160 million years ago, yielded gliding maniraptorans like Epidexipteryx hui in 2008, featuring ribbon-like tail feathers and membranous wings preserved in volcanic ash deposits. These finds filled critical gaps in early maniraptoran evolution, showing diverse integumentary structures predating the Cretaceous radiation. Recent post-2020 discoveries continue to expand maniraptoran diversity. In 2021, an exquisitely preserved oviraptorosaur embryo, nicknamed "Baby Yingliang," was reported from Ganzhou City in Fujian Province, China, within a Late Cretaceous egg showing curled posture and skin impressions indicative of feathering.^[45] This 66-72 million-year-old specimen, analyzed via CT scanning, revealed embryonic skeletal details linking non-avian theropods to avian development.^[45] In 2023, isotopic analyses of troodontid teeth from multiple North American sites, including Mongolian comparisons, provided evidence of omnivorous diets through elevated carbon and nitrogen signatures in enamel, addressing dietary gaps in this clade.^[46] Concurrently, a new small-bodied maniraptoran, Migmanychion laiyangensis, was described from the Lower Cretaceous Longjiang Formation in Inner Mongolia, China, based on limb bones revealing basal paravian traits.^[47] A 2024 discovery of Diuqin lechiguanae, an unenlagiine paravian from the Late Cretaceous Bajo de la Carpa Formation in Patagonia, Argentina, extended the Gondwanan distribution of advanced maniraptorans, with its partial skeleton preserving pneumatic vertebrae and elongated snout.^[48] This find parallels emerging South American records pushing southern hemisphere ranges.^[48] Exceptional preservation in sites like Solnhofen has been complemented by modern techniques, such as CT scans on museum specimens of Archaeopteryx and Anchiornis, uncovering hidden braincase and feather vane structures without destructive sampling.^[49] New Jurassic taxa, including scansoriopterygids from Tiaojishan, have addressed basal maniraptoran gaps by revealing quill knobs and furcula in 150-160 million-year-old deposits. As of 2025, ongoing applications of advanced imaging and phylogenetic analyses continue to refine our understanding of maniraptoran evolution.

Paleobiology

Diet and Feeding

The ancestral diet of Maniraptora is inferred to have been primarily carnivorous to omnivorous, based on the presence of ziphodont teeth—laterally compressed, serrated structures adapted for slicing flesh—and grasping hands suited for capturing prey. Coprolite evidence from maniraptoran relatives, containing bone fragments and fish scales, further supports this predatory habit, indicating consumption of vertebrate and possibly aquatic prey. Within Maniraptora, dietary specializations diverged markedly among subgroups. Dromaeosaurids were hypercarnivores, relying on serrated, blade-like teeth for shearing meat and enlarged sickle-shaped claws on their feet and hands for restraining struggling prey during cursorial hunts in open terrains.^[50] In contrast, therizinosaurs exhibited a derived herbivorous diet, characterized by edentulous or leaf-shaped teeth in the rostrum for cropping vegetation, along with gastroliths in the digestive tract for grinding plant matter; this shift to herbivory occurred around 100 million years ago in the Early Cretaceous, facilitated by an enlarged gut for microbial fermentation of fibrous material.^[51]^[52] Alvarezsaurids adopted a myrmecophagous (ant- and termite-eating) lifestyle, with their short, tubular snouts, reduced dentition, and powerful forelimbs enabling them to probe and excavate insect colonies from soil or wood.^[21] Feeding strategies varied with ecology and morphology across maniraptorans. Cursorial predation dominated in dromaeosaurids, who pursued prey on the ground using speed and precise strikes. Arboreal foraging likely prevailed in scansoriopterygids, small climbers with elongated fingers and reversed hallux for gripping branches while gleaning insects or fruits from trees. Fossil nest associations indicate oviraptorosaurs brooded their own eggs, with jaw morphology adapted for crushing hard objects, consistent with an omnivorous diet that may have included seeds, fruits, or shellfish.^[28] Stable isotope analysis of bone collagen in some paravians reveals piscivory, with elevated nitrogen-15 levels indicating a diet rich in aquatic fish, potentially supplementing terrestrial hunting in coastal or riverine habitats. Dental microwear studies on troodontids exhibit pitting and scratches consistent with durophagy, implying occasional consumption of hard-shelled invertebrates or seeds alongside softer prey. These variations highlight the trophic flexibility of Maniraptora, enabling adaptive radiations into diverse niches.^[53]

Reproduction and Growth

Maniraptorans laid elongated eggs belonging to the elongatoolithid morphotype, characterized by asymmetrical, subspherical to elongate shapes that were often arranged in pairs within clutches, reflecting the presence of two functional ovaries unlike the single left ovary in modern birds.^[54] These paired arrangements in oviraptorosaur clutches, such as those of Citipati, suggest bilateral ovulation, allowing for larger reproductive output compared to the unilateral system in Aves.^[55] Eggshell formation in maniraptorans like troodontids involved a slower calcification process than in extant birds, with growth lines in Troodon eggshells indicating a reptile-like rate extended over weeks rather than days, potentially enabling thicker shells for protection. A 2025 study confirmed the biogenic origin of secondary eggshell units in non-avian dinosaur eggshells, including those attributed to maniraptorans, indicating complex mineralization processes similar to modern birds.^[56]^[57] Fossil evidence from nesting sites reveals brooding behaviors in maniraptorans, with adults adopting postures over clutches to incubate eggs using body heat. In oviraptorosaurs, specimens of Citipati osmolskae from the Late Cretaceous Djadokhta Formation preserve adults in canonical brooding positions atop nests containing up to 20 eggs, some with preserved embryos at advanced developmental stages.^[58] Similarly, troodontid nests of Troodon formosus show radial egg arrangements in shallow depressions, with multiple nests clustered in localities suggesting possible colonial nesting to dilute predation risk.^[57] Hatchlings likely emerged with an egg tooth for pipping, as inferred from embryonic theropod fossils exhibiting caruncle-like structures analogous to those in birds.^[59] Growth in maniraptorans featured rapid juvenile phases akin to modern birds and mammals, with bone histology revealing dense vascularization and woven-fibered bone indicative of high metabolic rates during early ontogeny.^[60] However, non-avian maniraptorans exhibited indeterminate growth, continuing to add external layers to long bones throughout adulthood without a distinct cessation, as seen in oviraptorosaur and dromaeosaurid femora.^[61] Microstructural analysis of cortical bone often shows lines of arrested growth (LAGs), reflecting seasonal pauses in deposition linked to environmental fluctuations, such as arid cycles in Gobi Desert formations.^[62] Sexual dimorphism in maniraptorans may have manifested in display structures, with oviraptorosaurs potentially exhibiting larger cranial crests or elongated tail feathers in males for courtship, as suggested by size variations in Oviraptor and Conchoraptor specimens.^[63] Parental care is inferred from brooding fossils, where adults guarded nests against predators, with bone histology in Citipati and Troodon indicating energetic costs consistent with biparental or male-biased investment similar to some modern ratites.^[64] The avian-style reproductive traits in Maniraptora, including hard-shelled eggs and brooding, originated around 150 million years ago in the Late Jurassic, coinciding with the divergence of paravians from earlier theropods.^[65] High reproductive output, with clutches of 15–30 eggs in oviraptorosaurs, likely compensated for elevated juvenile predation rates in Mesozoic ecosystems, enhancing lineage persistence despite high mortality.^[66] Feathered embryos in oviraptorid eggs further link these traits to the evolution of integumentary insulation for incubation.^[67]

Behavior and Ecology

Maniraptorans exhibited a range of locomotor strategies adapted to their diverse habitats, with many ground-dwelling forms relying on bipedal cursoriality for efficient running and predation.^[4] This is evidenced by robust pelvic musculature in dromaeosaurids and troodontids, which supported high-speed pursuits and agile maneuvers on terrestrial terrains.^[4] In arboreal or semi-arboreal lineages, such as the paravian Microraptor, four-winged configurations enabled gliding between trees, with a biplane arrangement of fore- and hindwing feathers allowing undulatory flight paths covering over 40 meters at speeds of 12–15 m/s.^[68] Powered flight emerged within Avialae, the bird-containing clade of Maniraptora, through modifications to flapping mechanics that transitioned from gliding precursors to sustained aerial locomotion.^[69] Biomechanical analyses of dromaeosaurid leaps suggest these dinosaurs used powerful hindlimb extensions and incipient wing flapping to launch attacks, enhancing predatory efficiency.^[70] Indicators of elevated intelligence in Maniraptora are particularly prominent in Troodontidae, where large brain-to-body ratios yield encephalization quotients comparable to those of modern birds, implying advanced sensory processing and problem-solving capabilities.^[71] This elevated encephalization supported potential complex foraging strategies, such as nocturnal hunting or manipulation of prey, though direct evidence for tool use remains speculative and unverified in the fossil record.^[71] Social behaviors in Maniraptora likely included gregariousness, as inferred from monospecific bonebeds and parallel trackways suggesting group movement among dromaeosaurids like Deinonychus.^[72] While early interpretations proposed cooperative pack hunting based on multiple Deinonychus specimens associated with larger Tenontosaurus prey, reevaluations indicate these aggregations may reflect scavenging or opportunistic grouping rather than coordinated predation.^[72] Display structures, such as crests in oviraptorosaurs and elongated tail feathers in paravians, probably served mating functions, with substrate scraping behaviors documented in theropod track sites pointing to courtship rituals.^[73] Vocalization in non-avian maniraptorans was likely produced via laryngeal mechanisms similar to those in other reptiles, with the syrinx evolving later within Aves. Ecologically, Maniraptora occupied varied niches across Mesozoic ecosystems, with dromaeosaurids and troodontids acting as apex or mesocarnivore predators that influenced prey populations and competed with early mammals for small vertebrate resources.^[74] Feathered herbivorous forms, such as therizinosaurians, may have contributed to seed dispersal through frugivory, filling roles akin to modern avian pollinators in forested environments.^[74] Juvenile maniraptorans often partitioned into smaller prey niches, reducing overlap with adults and enhancing clade diversity.^[75] Recent studies bolster inferences of sociality and movement patterns in paravians, including 2020 trackway analyses from the Cenomanian Candeleros Formation revealing parallel theropod paths indicative of gregarious travel among large-bodied forms.^[76] Isotopic analyses of tooth enamel in Late Cretaceous paravians suggest limited migration, with stable carbon and oxygen ratios indicating residency in localized habitats rather than long-distance seasonal movements.^[77]

References

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Maniraptoran dinosaurs
The clade Maniraptora (which is defined as containing all dinosaurs closer to birds than to ornithomimids ) is the group of theropod dinosaurs that many ...
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Maniraptorans are the most diverse clade of dinosaurs. None retain a basal theropod form: indeed, very few retain the ancestral carnivorous condition.
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Maniraptoran pelvic musculature highlights evolutionary patterns in ...
Mar 4, 2021 · Previous studies document a stepwise accumulation of avian-like features in theropod dinosaurs that accelerates in the clade Maniraptora.
[4]
Review The Origin and Diversification of Birds - ScienceDirect.com
Oct 5, 2015 · ... Jacques Gauthier and colleagues used the revolutionary new technique of cladistics to place birds within the family tree of dinosaurs [14].
[5]
[PDF] Osteology oi Deinonychus antirrhopus, an Unusual Theropod from ...
19, Article 2. (1967). Publications Committee: A. Lee McAlester, Chairman. N. Philip Ashmole. John H. Ostrom. Keith S. Thomson.
[6]
[PDF] Avialan status for Oviraptorosauria - Acta Palaeontologica Polonica
Oviraptorosauria is a clade of Cretaceous theropod dinosaurs of uncertain affinities within Maniraptoriformes. All pre− vious phylogenetic analyses placed ...
[7]
A new Jurassic scansoriopterygid and the loss of membranous ...
May 8, 2019 · One of the most surprising of these is that of the scansoriopterygid (Theropoda, Maniraptora) Yi qi, which has membranous wings-a flight ...
[8]
https://pubmed.ncbi.nlm.nih.gov/31068719/
[9]
https://doi.org/10.1371/journal.pone.0293801
[10]
Saurischian Monophyly and the Origin of Birds
GAUTHIER: SAURISCHIAN MONOPHYLY up "a very interesting field of inquiry" that inspired him to devote "all my disposable leisure during the winter of 1867-8 ...
[11]
[PDF] A NEW PHYLOGENY OF THE CARNIVOROUS DINOSAURS
ABSTRACT: The last several years have seen the discovery of many new theropod dinosaur taxa. Data obtained from these and from fragmentary forms not ...
[12]
Homologies and homeotic transformation of the theropod ... - Nature
Aug 13, 2014 · The 'semilunate' structure is formed by a large medial distal carpal and a small distal carpal 4 in the younger individual and by a single ...
[13]
[PDF] folding in maniraptoran theropod dinosaurs The asymmetry of the ...
In the present paper we review the features of the avian carpus that facilitate a large range of abduction, and investigate the distribution of similar features.
[14]
Didactyl Tracks of Paravian Theropods (Maniraptora) from the ...
A comparison with other didactyl tracks gives new insights into the foot morphology of advanced maniraptoran theropods and contributes to knowledge of their ...
[15]
Evolutionary changes in pubic orientation in dinosaurs are more ...
Mar 31, 2018 · Among dinosaurs, the pubis has convergently retroverted four times in Maniraptora (Theropoda) and once in Ornithischia.
[16]
Vertebral pneumaticity of the North American therizinosaur ...
Oct 12, 2020 · Maniraptoran theropods are frequently characterized as possessing cervical internal pneumatization, but invasion of the caudal vertebrae is ...
[17]
Cretaceous bird with dinosaur skull sheds light on avian cranial ...
Jun 23, 2021 · The transformation of the bird skull from an ancestral akinetic, heavy, and toothed dinosaurian morphology to a highly derived, lightweight, ...
[18]
Edentulism, beaks, and biomechanical innovations in the evolution ...
Dec 2, 2013 · Results of finite-element analyses provide evidence that keratinous beaks play an important role in enhancing cranial stability by mitigation ...Restored Skull Model · Rhamphotheca-Bearing Models · Neck Muscles
[19]
Morphological and functional diversity in therizinosaur claws ... - NIH
While some therizinosaur taxa used their claws in a generalist fashion, other taxa were functionally adapted to use the claws as grasping hooks during foraging.
[20]
Restudy of shoulder motion in the theropod dinosaur Mononykus ...
Dec 5, 2023 · The inference that alvarezsaurids were myrmecophagous is therefore supported by their forelimb morphology. The use of the specialized hands ...
[21]
A monodactyl nonavian dinosaur and the complex evolution ... - PNAS
Although the transition from nonavian dinosaurs to birds is now understood in far more detail (33), current evidence confirms that asymmetric feathers of modern ...Missing: sources | Show results with:sources
[22]
A bony-crested Jurassic dinosaur with evidence of iridescent ...
Jan 15, 2018 · The tibial feathers have barbs with an angle of about 25 degrees to the rachis, forming nearly symmetrical vanes on either side of the rachis.
[23]
A new feather type in a nonavian theropod and the early evolution of ...
We report a feather type in two specimens of the basal therizinosaur Beipiaosaurus, in which each individual feather is represented by a single broad filament.Missing: sources | Show results with:sources
[24]
Exceptional preservation and foot structure reveal ecological ...
Dec 20, 2022 · Two scale types are visible on the pes: scutellate scales (~0.23–1.07 mm diameter) covering most of the dorsal surface of the pes, and scutate ...
[25]
A taxonomic and phylogenetic re-evaluation of Therizinosauria ...
Therizinosaurians comprise a poorly understood clade of coelurosaurian dinosaurs that are largely marginalized as evolutionary misfits in palaeoecological ...
[26]
A new alvarezsaurian theropod from the Upper Jurassic Shishugou ...
Aug 13, 2019 · Alvarezsaurian dinosaurs, a group of bizarre theropods with greatly shortened and modified forelimbs, are known mostly from the Cretaceous ...
[27]
Cranial functional specialisation for strength precedes ... - Nature
Apr 10, 2024 · Oviraptorosauria, a clade of maniraptoran theropod dinosaurs from the Cretaceous of Laurasia, is currently represented by approximately ...
[28]
A bizarre Jurassic maniraptoran theropod with preserved evidence ...
Apr 29, 2015 · A recently discovered fossil belonging to the Scansoriopterygidae, a group of bizarre dinosaurs closely related to birds, represents a new ...Missing: Scansoriopterygidae | Show results with:Scansoriopterygidae
[29]
New information on the anatomy and relationships of ...
ABSTRACT. Dromaeosaurus albertensis was one of the first small theropods described that was based on reasonably good cranial material.
[30]
The phylogenetic affinities and morphological peculiarities of the ...
Dec 6, 2021 · The most parsimonious topology reconstructed by our analyses places Troodontidae closer to Avialae than Dromaeosauridae, which comprises ...
[31]
(PDF) A taxonomic and phylogenetic re-evaluation of ...
Aug 6, 2025 · The phylogenetic analysis presented is the most comprehensive yet conducted for Therizinosauria, and provides a foundation for scrutinizing previous ...
[32]
The Origin of Birds and the Evolution of Flight | Request PDF
Aug 9, 2025 · GAUTHIER (1986) described 84 synapomorphies (shared derived characters) of Saurischian dinosaurs (which also include theropods and birds) and ...
[33]
Paravian Phylogeny and the Dinosaur-Bird Transition: An Overview
In this phylogenetic scheme, Paraves includes the clades Avialae (including Scansoriopterygidae) and Archaeopterygidae + Deinonychosauria. Godefroit et al. ( ...
[34]
New troodontid theropod specimen from Inner Mongolia, China ...
Jul 23, 2021 · A new troodontid (LH PV39) recovered from the Upper Cretaceous Wulansuhai Formation, Inner Mongolia, China, is described, highlighting the dorsoventrally ...
[35]
(PDF) Alvarezsaurid relationships reconsidered - ResearchGate
The phylogenetic position of Alvarezsauridae was discussed heatedly in the past, but the current consensus is that they are basal maniraptorans Novas & Pol 2002 ...Missing: debate | Show results with:debate
[36]
Re-evaluation of the Haarlem Archaeopteryx and the radiation of ...
Dec 2, 2017 · Our results indicate an explosive radiation of maniraptoran coelurosaurs probably in isolation in eastern Asia in the late Middle Jurassic.
[37]
Machine learning confirms new records of maniraptoran theropods ...
Apr 13, 2023 · Maniraptora is a diverse and speciose clade of theropod dinosaurs that includes some of the most familiar small-bodied predators of the ...
[38]
Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years ...
May 6, 2014 · Inference of high early rates in Maniraptora would be more likely, due either to concentration of short branch durations at the base of the ...
[39]
Re-evaluation of the Haarlem Archaeopteryx and the radiation of ...
Dec 2, 2017 · Given the probably Oxfordian age of the anchiornithids from the Tiaojishan Formation [6], basically all maniraptoran clades must have been ...
[40]
The early evolution of feathers: fossil evidence from Cretaceous ...
A new Chinese specimen indicates that 'protofeathers' in the Early Cretaceous theropod dinosaur Sinosauropteryx are degraded collagen fibres. Proc. R. Soc ...
[41]
Dinosaur biodiversity declined well before the asteroid impact ...
Jun 29, 2021 · The latest thorough analyses of fossil data found no evidence for a decline of non-avian dinosaurs before their extinction, and little evidence ...
[42]
A new alvarezsaurid dinosaur (Theropoda, Alvarezsauria) from the ...
Nov 15, 2023 · Alvarezsauria is a group of bizarre maniraptoran theropods whose latest-branching members possess remarkably avian homoplasies such as a ...
[43]
New evidence on the colour and nature of the isolated ...
Jan 24, 2012 · In 1861, Archaeopteryx lithographica was unearthed from the 150-million-year-old Solnhofen Lagerstätte. The mosaic of reptilian traits (for ...
[44]
New biogeochemical insights into Mesozoic terrestrial paleoecology ...
Nov 15, 2023 · Troodontids, which have been variably hypothesized as either faunivorous, omnivorous, or herbivorous due to their distinct and unusual dentition ...
[45]
A new theropod dinosaur from the Lower Cretaceous Longjiang ...
Although this new taxon is confidently referred to Maniraptora, this result is based uniquely on derived features of the hand: only additional material could ...
[46]
Diuqin lechiguanae gen. et sp. nov., a new unenlagiine (Theropoda
Jun 14, 2024 · New theropod dinosaur from the Upper Cretaceous of Patagonia sheds light on the paravian radiation in Gondwana. Sci Nat-Heidelberg. 2020;107:24.
[47]
Exceptional dinosaur fossils reveal early origin of avian-style digestion
Sep 21, 2018 · Xu, X. et al. A new feathered maniraptoran dinosaur fossil that fills a morphological gap in avian origin. Chinese Science Bulletin 54, 430–435 ...
[48]
A microraptorine (Dinosauria–Dromaeosauridae) from the Late ...
Mar 31, 2009 · Preparation of the fossil revealed that it represents a new genus of the clade Dromaeosauridae, a group of birdlike, carnivorous theropods (30).Missing: diet | Show results with:diet<|separator|>
[49]
A new North American therizinosaurid and the role of herbivory in ...
Here, Therizinosauria is recovered as the sister taxon to the five other major maniraptoran clades (i.e. as the basalmost maniraptoran clade) (figure 2 ...<|control11|><|separator|>
[50]
A new transitional therizinosaurian theropod from the Early ... - Nature
Mar 22, 2019 · The highly modified pelvic girdle and appendage of therizinosaurians are among the most bizarre structures known in any theropod dinosaur, and ...<|separator|>
[51]
Dental microwear reveals mammal-like chewing in the ... - PeerJ
Jul 6, 2016 · Dental microwear reveals mammal-like chewing in the neoceratopsian dinosaur Leptoceratops gracilis. Research Article · Evolutionary Studies.
[52]
Incubation behaviours of oviraptorosaur dinosaurs in relation to ...
May 16, 2018 · Our study demonstrates that characteristics of oviraptorosaur eggs and clutches provide new insight into incubation methods for a large ...2. Material And Methods · Figure 1 · 3. ResultsMissing: ovaries slow calcification 2023
[53]
A Second Specimen of Citipati Osmolskae Associated With a Nest of ...
Apr 26, 2018 · Here we report on a second nesting oviraptorid specimen (IGM 100/1004) sitting in a brooding position atop a nest of eggs from Ukhaa Tolgod, Omnogov, Mongolia.
[54]
(PDF) Nest and egg clutches of the dinosaur Troodon formosus and ...
Aug 9, 2025 · An unusual trace containing eggs of the 50 kg-plus theropod dinosaur, Troodon formosus, represents one of the best preserved dinosaur nests.
[55]
An oviraptorid preserved atop an embryo-bearing egg clutch sheds ...
May 15, 2021 · Here we report the first non-avialan dinosaur fossil known to preserve an adult skeleton atop an egg clutch that contains embryonic remains.
[56]
A New Picture of Dinosaur Nesting Ecology | American Scientist
Dinosaur nests evolved from an ancestral state of soft-shelled eggs buried underground to hard, sometimes colorful eggs incubated in partially open nests.Missing: Maniraptora | Show results with:Maniraptora
[57]
Osteohistological analyses reveal diverse strategies of theropod ...
We find that in skeletally mature gigantic theropods, weight-bearing bones consistently preserve extensive growth records, whereas non-weight-bearing bones are ...Missing: Maniraptora indeterminate pauses
[58]
[PDF] Evolution of Bone Histological Characters in Amniotes, and the ...
Histological studies have established relationships between the microstructural features of bone, the growth rates of primary cortical bone, and whole-body ...
[59]
Seasonal bone growth and physiology in endotherms shed light on ...
Aug 9, 2025 · Growth is arrested during the unfavourable season concurrently with decreases in body temperature, metabolic rate and bone-growth-mediating ...Missing: Maniraptora pauses<|separator|>
[60]
Does mutual sexual selection explain the evolution of head crests in ...
Among maniraptorans, oviraptorosaurs are well known for their casque-like crests and appear unique among non-avialian maniraptorans in this respect: non- ...
[61]
Avian paternal care had dinosaur origin - PubMed
Dec 19, 2008 · To assess parental care in Cretaceous troodontid and oviraptorid dinosaurs, we examined clutch volume and the bone histology of brooding adults.
[62]
The evolution of nest site use and nest architecture in modern birds ...
Jul 10, 2023 · Troodon (Paraves) provides a crucial evolutionary link between their earlier crocodilian sister taxa in the Archosauria and their later avian ...
[63]
Eggshell Porosity Provides Insight on Evolution of Nesting in ...
Nov 25, 2015 · Two general nest types are recognized among living archosaurs: 1) covered nests, in which eggs are incubated while fully covered by nesting ...
[64]
Elongatoolithid eggs containing oviraptorid (Theropoda ...
Mar 25, 2016 · The new specimens represent the first known oviraptorid embryos associated with pathological eggshells. The absence of structural and ...
[65]
Biplane wing planform and flight performance of the feathered ...
Microraptor gui, a four-winged dromaeosaur from the Early Cretaceous of China, provides strong evidence for an arboreal-gliding origin of avian flight.Hindlimb Posture And... · Fig. 2 · Flight Performance
[66]
'Dinosaur-bird' macroevolution, locomotor modules and the origins ...
Aug 17, 2021 · In particular, the fossil record of several maniraptoran groups clearly shows that aerial locomotion was developed before an 'avialization' ( ...
[67]
[PDF] an evaluation of flapping-based locomotory hypotheses in bird ...
Jul 7, 2016 · Here we examine the effectiveness of three hypothesized pathways for the evolution of the flight stroke, the forelimb motion that powers aerial ...
[68]
Revisiting Russell's troodontid: autecology, physiology, and ...
Jun 18, 2021 · Indeed, the estimated encephalization quotient (EQ) for Russell's “Stenonychosaurus inequalis” ranges from 0.24 to 0.34 (Russell and Séguin 1982) ...
[69]
(PDF) A Reevaluation of Cooperative Pack Hunting and ...
Aug 3, 2025 · In this paper we assess the hypothesis of mammal-like cooperative pack hunting in D. antirrhopus and other nonavian theropods by examining the behaviors of ...<|separator|>
[70]
Theropod courtship: large scale physical evidence of display arenas ...
Jan 7, 2016 · Here we present extensive and geographically widespread physical evidence of substrate scraping behavior by large theropods considered as ...
[71]
New perspectives on the origins of the unique vocal tract of birds - NIH
Mar 28, 2019 · If the syrinx followed an evolutionary path similar to the origins of flight, then the syrinx could have first evolved in nonavian dinosaurs ( ...
[72]
Niche Partitioning in Theropod Dinosaurs: Diet and Habitat ... - Nature
Dec 14, 2018 · Niche partitioning is an ecological phenomenon wherein multiple competing organisms coexist in the same environment by maximizing their ...
[73]
The influence of juvenile dinosaurs on community structure and ...
Feb 26, 2021 · We demonstrate that juvenile megatheropods likely filled the mesocarnivore niche, resulting in reduced overall taxonomic diversity.
[74]
Gregarious behaviour among non-avian theropods inferred from ...
Jan 15, 2020 · Here, we report five parallel theropod trackways of large track size (average length of 28 cm) in the Cretaceous (Cenomanian) Candeleros ...
[75]
New application of strontium isotopes reveals evidence of limited ...
Mar 4, 2020 · Dinosaur migration patterns are very difficult to determine, often relying solely on the geographical distribution of fossils.