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Rahonavis
Temporal range: Late Cretaceous (Maastrichtian) 72.1–66 Ma
Reconstructed skeleton, Royal Ontario Museum
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: Paraves
Clade: incertae sedis
Genus: †Rahonavis
Forster et al., 1998b
Type species
†Rahonavis ostromi
(Forster et al., 1998a) Forster et al., 1998b
Synonyms
  • Rahona Forster et al. 1998 non Griveaud 1975
  • Rahona ostromi Forster et al. 1998a

Rahonavis is a genus of bird-like theropod from the Late Cretaceous (Maastrichtian, from about 70 to 66 mya) of what is now northwestern Madagascar. It is known from a partial skeleton (UA 8656) found by Catherine Forster and colleagues in Maevarano Formation rocks at a quarry near Berivotra, Mahajanga Province.[1] Rahonavis was a small predator, at about 70 centimetres (2.3 ft) long and 0.45-2.27 kg (1-5 lbs),[2] with the typical dromaesaurid-like raised sickle claw on the second toe. It was the first coelurosaur discovered in Africa, with Nqwebasaurus being the second.[3]

The name Rahonavis means, approximately, "cloud menace bird", from Malagasy rahona (RA-hoo-na, "cloud" or "menace") + Latin avis "bird". The specific name, R. ostromi, was coined in honor of John Ostrom.[citation needed]

Discovery and species

[edit]
Skeletal diagram showing remains of the holotype specimen

The fossilized remains of Rahonavis were first recovered from the Maevarano Formation in Madagascar in 1995 by a joint expedition of SUNY and the University of Antananarivo, near the village of Berivotra. Most geological formations in this area are covered in dense grass, making identification of fossils difficult. However, when a portion of hillside was exposed by fire, the remains of a giant titanosaur were revealed. It was during the excavation of this find that paleontologists discovered the bones of Rahonavis among the bones of the much larger dinosaur. Rahonavis is known from this single specimen, consisting of the hind limbs, trunk, portions of the tail (all of which were found articulated), as well as portions of the wing and shoulder bones. Rahonavis was one-fifth larger than the closely related Archaeopteryx, about the size of a modern raven.[4]

The discoverers of Rahonavis initially named it Rahona but changed the name after discovering that the name Rahona was already assigned to a genus of lymantriid moths.[5][6]

The lack of well-documented relatives of this species notwithstanding, a single thoracic vertebra (NMC 50852) most similar to those of R. ostromi was found in the Albian to Cenomanian Kem Kem Beds in Morocco. Lacking the pleurocoels found in Rahonavis and having a larger neural canal, it appears to belong to a different genus. Although former character can vary in species of the same genus, in individual vertebrae of the same animal, and ontogenetically, the distance in space and time suggests that whatever this specimen may be, it does not belong into Rahonavis.[7]

A dentary has been found in association with the holotype, though it is seldom described.[8]

Classification

[edit]
Size compared to a human hand

Rahonavis has historically been the subject of some uncertainty as to its proper taxonomic position – whether it is a member of the clade Avialae (birds) or a closely related dromaeosaurid. The presence of quill knobs on its ulna (forearm bone) led initially to its inclusion as an avialan; however, the rest of the skeleton is rather typically dromaeosaurid in its attributes. Given the extremely close affinities between basal birds and their dromaeosaurid cousins, along with the possibility that flight may have developed and been lost multiple times among these groups, it has been difficult to place Rahonavis firmly among or outside the birds.

Rahonavis could be a close relative to Archaeopteryx, as originally suggested by the describers, and thus a member of the clade Avialae, but while the pelvis shows adaptations to flight similar in function to those of Archaeopteryx, some fringe researchers have claimed that these may have been independently derived.[9]

Beginning in the early 2000s, a consensus emerged among most theropod researchers that Rahonavis was more closely related to deinonychosaurs than to avialans, and specifically was a member of the South American dromaeosaurid clade Unenlagiinae. A 2005 analysis by Makovicky and colleagues found Rahonavis to be closely related to the unenlagiines Unenlagia and Buitreraptor.[10] Norell and colleagues (2006) also found Rahonavis to lie within the Unenlagiinae, as the sister taxon to Unenlagia itself.[11] A 2007 study by Turner and colleagues again found it to be an unenlagiine dromaeosaurid, closely related to Unenlagia.[12]

This consensus has been challenged, however, by a few studies published since 2009 that have found many traditional "dromaeosaurids", including the unenlagiines, closer to Avialae than to dromaeosaurines. A large analysis published by Agnolín and Novas (2013) recovered Rahonavis as closer to Avialae than to Dromaeosauridae.[13] A cladistic analysis by Cau (2018) recovered Rahonavis as a probable relative of the long-tailed Early Cretaceous avialans Jeholornis and Jixiangornis.[14] The analysis of Hartman et al. (2019) "strongly rejected" the supposed avialan position of Rahonavis, finding its placement in Unenlagiinae better supported as it takes 10 less steps. This placement suggests Rahonavis is one among multiple different paravian lineages that evolved flight independently.[15] In 2020, Rahonavis and the South American Overoraptor were found to be sister taxa in a clade sister to the Avialae with a dataset based on that of the 2013 study.[16] As of 2020, it is undecided among paleontologists whether the paravian Rahonavis is an unenlagiine, a dromaeosaurid, or an avialan.[8]

Paleobiology

[edit]
Hypothetical life restoration

Although numerous artists' reconstructions of Rahonavis show it in flight, it is not clear that it could fly; there has even been some doubt that the forearm material, which includes the quill knobs, belongs with the rest of the skeleton. Some researchers have suggested that Rahonavis represents a chimera consisting of the forelimb of a bird conflated with the skeleton of a dromaeosaurid, and consider Rahona as described a nomen dubium.[9] The nearby discovery of the primitive bird Vorona berivotrensis at least shows that the possibility of a mix-up cannot be fully excluded. However, many other scientists, including the original describers of Rahonavis, maintain that its remains belong to a single animal, citing the close proximity of the wing bones to the rest of the skeleton. All the bones attributed to Rahonavis were buried in an area "smaller than a letter-sized page", according to co-describer Luis M. Chiappe in his 2007 book Glorified Dinosaurs. Additionally, Chiappe argued that suggestions of a chimera by paleornithologist Larry Martin were based on Martin's misinterpretation of the wing and shoulder bones as being more advanced than they really are.[4]

A speculative restoration of two Rahonavis (hypothetically-depicted male & female) on a charred branch.

Chiappe maintained that Rahonavis could probably fly, noting that its ulna was large and robust compared to Archaeopteryx, and that this fact, coupled with the prominent quill knobs, suggest that Rahonavis had larger and more powerful wings than that earlier bird. Additionally, Rahonavis shoulder bones show evidence of ligament attachments allowing the independent mobility needed for flapping flight. Chiappe concluded that Rahonavis was capable of flight, though it would have been more "clumsy in the air than modern birds."[4] Agnolín and Novas (2013) noted that, like Microraptor, a bat-like flightstroke using the deltoideus complexes seems to have been likely in R. ostromi.[13]

See also

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References

[edit]

Further reading

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Rahonavis

View on Grokipedia
from Grokipedia
Rahonavis ostromi is a small paravian theropod from the () of northwestern , known primarily from a single partial skeleton that includes elements of the , forelimbs, , and hind limbs. Approximately 70 centimeters in length and weighing between 0.5 and 1 , it displays a combination of bird-like traits—such as ulnar papillae suggesting feathered wings—and dromaeosaurid characteristics, including a robust second pedal digit with a sickle-shaped adapted for predation. Originally described as Rahona ostromi in 1998 and renamed Rahonavis later that year due to a preoccupied name, the was discovered in 1995 within the Maevarano Formation, a semi-arid coastal deposit to about 70 million years ago. The specimen (UA 8656) preserves key anatomical features that highlight its transitional morphology between non-avian theropods and early birds, such as a reversed hallux for perching, pneumatic vertebrae, and a long, slender pubis with a distal foot. Detailed osteological studies using CT scans have revealed internal structures like pneumatic foramina in the vertebrae and fused sacral elements, supporting its agile, possibly arboreal lifestyle. Evidence of on the unguals further indicates that R. ostromi was likely covered in feathers, potentially enabling gliding or limited flight capabilities. Additional referred specimens, including a partial dentary (FMNH PA 740), humeri (FMNH PA 746, UA 9604), and an (FMNH PR 2821), have been identified, providing further insights into its . Phylogenetically, Rahonavis ostromi occupies a controversial position within , with analyses placing it either as a basal avialan near or within the dromaeosaurid subfamily , reflecting ongoing debates about character evolution in maniraptoran theropods. Its discovery provides critical evidence for the theropod ancestry of birds, particularly in the southern , and underscores the diversity of paravians in the . These specimens make it a significant, though still rare, in understanding avian origins.

Discovery and naming

Discovery

The holotype specimen of Rahonavis ostromi (UA 8656) was discovered in 1995 during a joint expedition conducted by and the Université d'Antananarivo. The partial skeleton was unearthed at quarry site MAD 93-18 in the Berivotra Study Area, within the Basin of northwestern . Excavation efforts recovered the specimen from fluvial sediments in Level 4 of the Anembalemba Member, representing a channel lag deposit. The preserved elements include one cervicodorsal , six dorsal vertebrae, a comprising six fused sacral vertebrae, 13 caudal vertebrae with 12 chevrons; both ilia, both pubes, and both ; both femora, both tibiae, both fibulae; the right astragalus and calcaneum; the right (metatarsals I–V), an incomplete left metatarsal IV, and left pedal phalanges I-1 to I-2, II-1 to II-3, III-1 to III-4, IV-1 to IV-5, with unguals II–IV, plus right pedal phalanx II-2; the left ; the right ; and the right . Referred material includes distal humeri (FMNH PA 746, UA 9604) and a dentary (FMNH PA 740). The bones were partially articulated upon discovery, indicating minimal post-mortem disturbance. Following recovery, the specimen was prepared using mechanical methods and consolidated with epoxy resin by a team including preparator V. Heisey, with additional work conducted in both Madagascar and the United States. It is currently housed in the collections of the Université d'Antananarivo, under catalog number UA 8656. The Maevarano Formation, from which the holotype derives, dates to the Maastrichtian stage of the Late Cretaceous, approximately 70–66 million years ago. This unit consists of fluvial and lacustrine deposits that have yielded a diverse vertebrate assemblage, including the abelisaurid theropod Majungasaurus crenatissimus, the noasaurid Masiakasaurus knopfleri, crocodyliforms such as Mahajangasuchus insignis, turtles, and the enantiornithine bird Vorona berivotrensis.

Etymology and species

Rahonavis was originally named Rahona ostromi in 1998 by Catherine A. Forster, , Luis M. Chiappe, and David W. Krause, based on a partial (UA 8656) recovered from the Upper Maevarano Formation in northwestern . The genus name Rahona derives from the Malagasy word rahona (pronounced RAH-hoo-nah), meaning "menace" or "cloud," with the intended interpretation "menace from the clouds" to reflect the taxon's presumed aerial predatory capabilities and bird-like morphology. The specific epithet ostromi honors John H. Ostrom, the paleontologist whose work on theropod-bird relationships, particularly through studies of , significantly advanced the understanding of avian evolution. Shortly after publication, the original genus name Rahona was found to be preoccupied by a genus of lymantriid moths (Rahona Griveaud, 1975), prompting the same authoring team to emend it to Rahonavis in a formal correction. The replacement name Rahonavis incorporates the Malagasy root rahona with the Latin avis ("bird"), yielding an approximate meaning of "cloud menace bird" or "menace bird from the clouds." Only a single , R. ostromi, is currently recognized within the , represented primarily by the and associated elements from the same quarry locality indicating at least two individuals. No additional species have been proposed, despite the Maevarano Formation yielding other paravian taxa such as Vorona berivotrensis.

Description

Skeletal elements

The specimen of Rahonavis ostromi (UA 8656) represents an incomplete, partially articulated postcranial skeleton of an adult individual, preserving elements primarily from the trunk, pectoral , forelimbs, pelvic , hindlimbs, and caudal series, but lacking the and most . The bones were discovered in close association within approximately 500 cm², with some disarticulated elements (such as the left ) found up to 1 m away, and exhibit pristine preservation without significant distortion. A detailed osteological redescription in provided revised measurements and clarified articulation details for the preserved elements. Trunk elements include a partial formed by six fused sacral vertebrae measuring 41.9 mm in length, along with several dorsal vertebrae featuring hyposphene-hypantra articulations and large vertebral canals occupying 42–62% of centrum height. are present but fragmentary, with cervicodorsal parapophyses indicating unfused conditions, and possible fragments occur as isolated elements without clear articulation. The pectoral girdle preserves a right measuring 82.2 mm in length, with a facet and process. bones include a right with a prominent deltopectoral crest, subequal right (126.9 mm long) and (132.3 mm long, 150% of length) that articulate closely, the ulna bearing six knobs, and partial manual digits with recurved claws. A boomerang-shaped and fused sternal plates are also preserved, contributing to the ventral thoracic structure. Pelvic elements consist of partial left and right ilia (66.7–67.7 mm long, with the preacetabular comprising 55% of total length and a dorsoventrally compressed postacetabular ) and (27.3 mm long, short and platelike). The caudal series includes 13 preserved vertebrae, with centra elongating from 6.3 mm at to 25.8 mm at Cd13, procoelous from Cd6 to Cd12, and a transition point at Cd9; elongated chevrons (12 preserved, ranging 4.3–23.3 mm in length and up to 11.6 mm high) extend posteriorly, indicating a likely comprising 22–23 vertebrae total. Hindlimb bones feature a robust right (87.6 mm long) with a straight, subcircular shaft and no distinct separating the head from the trochanteric crest, a (118.1 mm long, approximately 35% longer than the ) that is cylindrical and straight, and a slender (15% of tibial proximally, tapering to a narrow spine). The metatarsus is arctometatarsal, with unfused but closely appressed elements—metatarsal II (44.1–44.7 mm), the dominant metatarsal III (47.8–48.1 mm), and metatarsal IV (45.3–47.7 mm), where metatarsal I is 19% the length of II. Pedal unguals are falcate and enlarged, particularly the sickle-shaped of digit II (twice the length of II-2), with a reversed hallux. These proportions suggest a small-bodied paravian.

Size and morphology

Rahonavis ostromi was a small-bodied paravian theropod exhibiting a gracile build, with an estimated total length of approximately 70 cm based on the original description and proportional reconstructions. The morphology featured long, slender hindlimbs relative to the trunk, with the tibia (118.1 mm) exceeding the femur by 35%, suggesting adaptations for agility and cursorial movement. Forelimbs were reduced in overall robustness but possessed elongated arms, as evidenced by the ulna (132.3 mm) surpassing the femur length by 51%, indicative of potential aerodynamic functions. The pelvis was narrow and elongate, with the ilium measuring 67.1 mm (about 76.5% of femur length) and featuring a long preacetabular process, contributing to a lightweight, streamlined body plan. In proportions, Rahonavis closely resembled , particularly in the relative lengths of the , , and , as well as the stiff, plate-like chevrons supporting the , but differed in possessing a dromaeosaurid-like enlarged on the second pedal digit. Early size estimates from the original description placed the animal at about 70 cm in length, based on limited preserved elements, while subsequent analyses in refined these figures by incorporating comparisons to complete paravian skeletons and accounting for missing portions such as additional caudal vertebrae.

Classification

Phylogenetic analyses

Modern cladistic analyses position Rahonavis ostromi within , the clade encompassing , , and avialans, though its precise placement remains debated, with many analyses favoring its inclusion in the subfamily of . This placement reflects its shared derived traits with other paravians, including an elongated snout, modifications to the pelvic girdle such as a vertically oriented pubis, and adaptations in the pes like a reduced metatarsal III. Key supporting characters include quill knobs on the indicative of pennaceous feathers, markedly elongated forelimbs relative to body size, and a distinctly curved pedal ungual II resembling the sickle claw of . A detailed osteological reassessment by Forster et al. in 2020 reinforced Rahonavis as a member of Unenlagiinae, nesting it as sister taxon to the South American Overoraptor chimentoi within this Gondwanan clade, based on expanded character matrices emphasizing axial and appendicular morphology. Similarly, Cau et al.'s 2020 analysis of paravian body plan evolution, incorporating Halszkaraptor escuilliei, recovered Rahonavis within Unenlagiinae through a dataset of 1807 characters across 185 taxa, highlighting homoplasies in cranial and postcranial features. In these frameworks, Rahonavis is nested alongside Austroraptor cabeki, Unenlagia comahuensis, and Buitreraptor debilis, forming a monophyletic Gondwanan subclade characterized by cursorial adaptations and aerial capabilities. However, some subsequent analyses have placed it within Avialae or as Paraves incertae sedis, underscoring ongoing debates. Immunohistochemical evidence from preserved soft tissues further bolsters Rahonavis's paravian affinities. Analysis of feather-like structures revealed immunoreactivity consistent with , a protein unique to sauropsids and prevalent in avian , supporting its close relation to feathered maniraptorans without resolving finer subfamily distinctions. Initially interpreted as a basal bird akin to Archaeopteryx, subsequent sampling has shifted consensus toward a non-avialan paravian position.

Debates and revisions

Upon its initial description in 1998, Rahonavis ostromi was classified within Avialae as a basal bird and the sister taxon to Archaeopteryx lithographica, primarily due to avian-like features such as quill knobs on the ulna indicative of flight feathers and a reversed hallux for perching. Subsequent studies between 2002 and 2007 shifted its placement to Dromaeosauridae, specifically within the subfamily Unenlagiinae, based on shared derived traits in the pedal phalanges (such as a reduced penultimate phalanx) and pelvic morphology (including a rectangular ischium). This reassignment was supported by Novas et al. (2005), who identified additional synapomorphies linking Rahonavis to South American unenlagiines like Unenlagia and Buitreraptor. A hypothesis proposed in 2001 suggested that the holotype specimen (UA 8656) might represent a taxonomic chimera, with forelimb elements potentially belonging to a bird and hindlimb elements to a non-avialan dromaeosaurid, due to discrepancies in proportional scaling and taphonomic positioning. This idea was refuted by a detailed 2020 osteological restudy, which confirmed the elements derive from a single individual through analysis of shared preservation patterns, size consistency, and articulated associations in the quarry. Taxonomic uncertainty persists due to limited material and variable results in phylogenetic analyses, with some recovering Rahonavis outside stable resolution within . Its exclusively Gondwanan distribution, alongside other unenlagiines from and , continues to favor an affinity within , though the limited material hampers definitive placement. Recent analyses as of 2021 maintain a prevailing position within amid ongoing debate.

Paleobiology

Locomotion capabilities

Rahonavis possessed gracile hindlimbs adapted for agile, bipedal locomotion, with a (118.1 mm) significantly longer than the (87.6 mm), facilitating efficient stride length and speed on terrestrial substrates. The foot morphology, with a robust second pedal digit, further supported maneuverability and stability during rapid movements, akin to other paravians. The enlarged, sickle-shaped ungual on pedal digit II, measuring approximately 22 mm, likely served for prey capture or substrate grasping during climbing, reflecting predatory or semi-arboreal behaviors common in dromaeosaurids. The forelimbs of Rahonavis were elongated relative to the hindlimbs, with an (132.3 mm) exceeding tibia length, indicating specialized functions beyond basic terrestrial support. Robust manual phalanges and strong claws suggest capabilities for predatory grasping or arboreal , allowing the animal to secure prey or navigate vertical surfaces. A well-developed provided structural support for pectoral girdle muscles, potentially aiding in forelimb elevation and balance during locomotion or proto-aerial activities. Evidence for aerial locomotion includes ulnar quill knobs, which anchored 8–9 pennaceous secondary , implying the presence of feathered wings suitable for aerodynamic functions. However, the animal's small estimated body mass (around 1 kg) and robust bone morphology indicate limited aerial prowess, likely restricted to clumsy or short-distance rather than powered flight. No skeletal features, such as an ossified sternum or keeled sternum, support sustained flapping capabilities. Biomechanical comparisons to highlight similarities in quadrupedal climbing, where elongated forelimbs and feathered wings could assist in ascending inclines or trees using a combination of grasping and flapping. Recent models estimate for Rahonavis at approximately 2.0–2.5 g/cm², approaching but not fully meeting thresholds for efficient powered flight, suggesting marginal aerial performance at best.

Integument and feathers

Direct evidence for feathered integument in Rahonavis ostromi comes from the specimen (UA 8656), which preserves distinct ulnar papillae—small tubercles on the dorsal surface of the interpreted as quill knobs for anchoring large pennaceous feathers on the wings. These structures are analogous to those in modern birds, where they secure secondary , and in other paravians such as microraptorines like Microraptor zhaoianus, which exhibit similar attachments for vaned wing feathers. Given its position within , Rahonavis is inferred to have possessed a fully feathered body covering, including pennaceous feathers on the limbs and possibly filamentous protofeathers or pycnofibers on the trunk, consistent with the integumentary profile of close relatives like Anchiornis huxleyi and . No direct impressions of feathers or skin are preserved in the known fossils, limiting observations to skeletal indicators and phylogenetic bracketing. Molecular analysis of demineralized bone matrix from the Rahonavis has revealed immunological reactivity consistent with fragments, a protein unique to archosaurs and characteristic of avian-like integumentary structures such as feathers and scales. This finding supports the presence of keratin-based soft tissues in Rahonavis, aligning it biochemically with feathered paravians. Such feathers likely served functions including thermal insulation, visual display, and aerodynamic support, potentially aiding in gliding behaviors inferred from skeletal morphology. However, no details on feather coloration, microstructure, or filament distribution are preserved due to the absence of soft tissue impressions. The Maevarano Formation, where Rahonavis fossils occur, exhibits taphonomic conditions that can preserve vascular soft tissues in archosaurs, though biases toward bone over integument limit direct evidence; recent analyses confirm potential for such preservation in this arid, fluvial depositional environment.
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