Cranial morphology of the avian alvarezsauridae: evidence

from a new relative of Mononykus

Luis M. Chiappe1, Mark A. Norell2, and James M. Clark3

1Department of Ornithology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, U.S.A.2Department of Vertebrate Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, U.S.A.

3Department of Biological Sciences, George Washington University, Washington, D. C. 20052, U.S.A.

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Joint American Museum of Natural History and Mongolian Academy of Sciences Expeditions have recovered over

20 alvarezsaurid (Theropoda: Aves) specimens in the Late Cretaceous of Mongolia’s Gobi Desert1. Here we

describe a new taxon closely related to Mononykus2,3. This material includes two exquisitely preserved skulls—the

first known for Alvarezsauridae—which provide additional support for the group’s avian relationships4,5, first

postulated on primarily postcranial evidence2,3. This evidence includes the presence of avian characters such as

the absence of a contact between the jugal and postorbital, and between the quadratojugal and squamosal, a

movable joint between quadratojugal and quadrate, separate squamosal and braincase articulations of the

quadrate, confluence between the caudal tympanic recess and columellar recess, a triradiate palatine, an

unusually large foramen magnum, and the loss of a coronoid bone. The configuration of the temporal region of

the skull and its articulation with the rostrum strongly suggest the capability for prokinetic movement, and support

the idea that prokinesis preceded other types of avian intracranial kinesis.

Aves (Avialae sensu Gauthier, 1986) Linnaeus, 1758

Metornithes Perle et al., 1993

Alvarezsauridae Bonaparte, 1991

Mononykinae, new taxon (Fig. 4)

Shuvuuia deserti, new genus and species.

Holotype—MGI 100/975 (Mongolian Geological Institute, Ulaanbaatar).

Referred specimens—MGI N 100/99, MGI 100/977, MGI 100/1001. Previously these specimens, including the holotype,

were referred to Mononykus4.

Etymology—Shuvuuia from the Mongolian "shuvuu" meaning bird and deserti in reference to the semi-arid depositional

environment of the Djadokhta Formation1.

Locality and Horizon—Ukhaa Tolgod (MGI 100/975, MGI 100/977, MGI 100/1001) and Tugrugeen Shireh (MGI 100/99),

South Gobi Aimak, Mongolia. Tentatively Djadokhta Formation (Late Cretaceous/Campanian?)1,6.

Diagnosis—A mononykine (Fig. 4) distinguished from Mononykus olecranus by its less

compressed cervical centra with large pneumatic foramina, humeral deltopectoral crest continuous with its head, pubis of

subcircular section, femoral and tibiotarsal shafts bowed latero-medially, and medial margin of astragalus' ascending

process less excavated. Shuvuuia deserti shows a lesser degree of co-ossification of the proximal tarsals to the tibia and

among metacarpals in specimens of comparable size to the holotype of Mononykus olecranus, suggesting a lower rate of

bone co-ossification. The new species differs from Parvicursor remotus by the absence of a ventral keel in the rostralmost

synsacral vertebra and by the lesser co-ossification between proximal tarsals and the tibia. Shuvuuia deserti differs from

all alvarezsaurids by the presence of a sharp ridge on the medial margin of the distal tibiotarsus, a character interpreted

as an autapomorphy. The skull of Shuvuuia deserti displays a number of characters interpreted as autapomorphies,

including the articulation between quadrate and postorbital, elongate basipterygoid processes, numerous teeth, hypertrofied

prefrontal/ectethmoid (see below for problematic interpretation of this bone). These characters, however, may prove to

diagnose a more inclusive taxon following the discovery of additional alvarezsaurid cranial material.

Description. The delicate skull is elongate with large orbits and terminal tear-shaped nares (Figs. 1-3). The maxilla forms

most of the snout’s lateral surface as in other early birds10. The caudal half forms a slender bar ventrally bordering the

antorbital fossa. The dentigerous margin of the premaxilla is not preserved but the maxilla bears numerous tiny, unserrated

teeth, identical to Mononykus2. Teeth are absent behind the rostral third of the antorbital fossa. On the dentary the teeth

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lay in a continuous groove.

The lacrimal has an expanded rostral process and a tiny caudal extension resembling the L-shaped lacrimal of

Archaeopteryx and other non-avian theropods11. The orbit is walled rostrally by a problematic large ossification, widely

exposed on the skull roof. It could be interpreted as a large prefrontal, but both elements meet ventral to the frontals—a

condition unknown in dinosaurs12. In this respect, this element resembles more an avian ectethmoid; yet no ectethmoid

is known to be exposed dorsally13.

The postorbital fails to reach the rod-like jugal so the orbit and infratemporal fossa are continuous; a condition

known only for metornithine birds among archosaurs14,15—although this condition may be present in Archaeopteryx4. The

jugal and quadratojugal are fused into a jugal bar which forms a tiny fork on its caudal end. Shuvuuia also contrasts with

non-avian archosaurs, in which the quadratojugal bears a tall dorsal process sutured to the quadrate14,15. In Archaeopteryx16

and an enantiornithine hatchling17 this process is significantly shorter and not sutured to the quadrate. The triradiate

squamosal is not incorporated into the braincase of Shuvuuia, Archaeopteryx, and other early avians, which retain a

complete, diapsid supratemporal fenestra16,17.

Like in other birds, the paroccipital processes are short and not perforated by the caudal tympanic recess, which

opens inside the collumelar recess4. The foramen magnum is proportionally larger than in any non-avian dinosaur12 and

the caudally directed occipital condyle is very small. The basipterygoid processes are unusually long and almost vertically

oriented.

The quadrate is tall and slender, resembling Archaeopteryx and the enantiornithine Gobipteryx in that it is nearly

one-fourth the length of the skull16. This bone also resembles Archaeopteryx in the strong rostro-caudal compression of

its latero-distal corner16. Proximally, the quadrate has two well-differentiated heads. The lateral articulates with a

squamosal-postorbital facet, while the medial is dorso-caudally directed toward the braincase. The palatine is long and

slender, lacking the jugal process and tetraradiate aspect of non-avian theropods16.

Discussion. The skull of Shuuvuia offers further evidence for the avian affinities of this group and emphasizes the highly

specialized nature of this bizarre lineage; just as in the postcranium, Shuuvuia displays a number of unusual cranial

characters, and characters restricted to Aves among dinosaurs12. The configuration of the jugal and suspensorium of

Shuvuuia (Fig. 1) suggests capacity for intracranial kinesis 15,18-20(e.g. the elevation and depression of the rostrum). Without

ventral squamosal and dorsal quadratojugal processes, the streptostylic quadrate was free to swing antero-posteriorly15,18-20.

The lack of a connection between the jugal and postorbital freed the jugal to act as a strut between quadrate and rostrum.

Forces directed longitudinally from the quadrate would rotate the rostrum around a transverse axis at a flexion area just

anterior to the orbit. A thinning of the jugal (bending zone) just caudal to its lacrimal contact and the loose connection

between the frontals and the preorbital bones (nasals and prefrontals/ectethmoids) indicate that the snout may have moved

as a unit like in prokinetic birds15,18-20 (Fig. 1C). The absence of a continuous naso-orbital septum agrees with this

interpretation. Prokinesis is usually regarded as the primitive type of kinesis derived from either akinetic or mesokinetic

archosaurian skulls15,18-20 and has been reported in a number of early birds21-23. The design of the skull of Shuvuuia suggests

that some motion, most likely prokinetic, was possible, thus supporting this interpretation.

Methodology. A cladistic analysis based on 90 characters (six multistate) places the Alvarezsauridae as the sister-taxon

to all avians except for Archaeopteryx (Fig. 4; see Supplementary Information for character list, data matrix, and node

diagnoses). Cranial characters in Shuvuuia shared only with birds among dinosaurs include the absence of a postorbital-

jugal contact, the movable joint (not sutured) between quadratojugal and quadrate, the separate articulation of the quadrate

with the braincase, and the disproportionately large foramen magnum relative to the occipital condyle. The skull of

Shuvuuia also shares with Archaeopteryx and other avians characters that are absent in velociraptorine theropods—the

outgroup selected for the present cladistic analysis. These include the absence of squamosal-quadratojugal contact, a

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triradiate palatine, a caudal tympanic recess confluent with the columellar recess, the absence of a coronoid in the

mandible, and unserrated tooth crowns.

Certain workers have claimed that alvarezsaurids are either specialized ornithomimosaurs24,25 or a different group

of non-maniraptoran theropods26, although in neither case a cladistic analysis has been published. Our phylogenetic

studies, as well as independent cladistic analyses, indicate that the few similarities between alvarezsaurids and non-

maniraptoran coelurosaurs are convergent4,5,7,8,27. For example, the ornithomimosaur Pelecanimimus bears numerous, tiny

teeth with unserrated crowns restricted to the anterior part of the maxilla28 and ornithomimosaurs (as well as

oviraptorosaurs and therizinosaurids among non-avian maniraptorans) lack a coronoid bone29. Furthermore, if the preorbital

ossification of Shuvuuia is identified as a prefrontal, it is larger than that of most maniraptoran dinosaurs and more

comparable in size to that of ornithomimosaurs30. However, placing alvarezsaurids outside Maniraptora would require

homoplasy in an extensive number of maniraptoran, avian, and metornithine synapomorphies4,5,7,8,27.

References

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8. Novas, F. E. Anatomy of Patagonykus puertai (Theropoda, Maniraptora, Alvarezsauridae) from the Late Cretaceous

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13. Cracraft, J. The lacrimal-ectethmoid bone complex in birds: a single character analysis. Am. Midl. Nat. 80, 316-359

(1968).

14. Romer, A. S. Osteology of the Reptiles (Univ. Chicago Press, Chicago, 1956).

15. Zusi, R. L. in The Skull (eds Hanken, J & Hall, B. K.) vol. 2, 391-437 (Univ. Chicago Press, Chicago, 1993).

16. Elzanowski, A. & Wellnhofer, P. (1996). Cranial morphology of Archaeopteryx: evidence from the seventh skeleton.

J. Vert. Paleont. 16, 81-94 (1996).

17. Sanz, J. L. et al. A nestling bird from the Early Cretaceous of Spain: implications for avian skull and neck evolution.

Science 276, 1543-1546 (1997).

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18. Zusi, R. L. A functional and evolutionary analysis of rhynchokinesis in birds. Smith. Contr. Zool. 395, 1-40 (1985).

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of birds. Quart. Rev. Biol. 35, 206-220 (1960).

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21. Bühler, P. On the morphology of the skull of Archaeopteryx. in The beginnings of Birds (eds Hecht, M. K., Ostrom, J.

H., Viohl, G. & Wellnhofer, P.) 135-140 (Proceedings of the International Archaeopteryx Conference, Eichstätt,

1985).

22. Hou, L., Martin, L. D., Zhou, Z. & Feduccia, A. Early adaptive radiation of birds: evidence from fossils from northeastern

China. Science 274, 1164-1167 (1996).

23. Bühler, P., Martin, L. D. & Witmer, L. M. Cranial kinesis in the Late Cretaceous birds Hesperornis and Parahesperornis.

Auk 105, 111-122 (1988).

24. Martin, L.D. & Rinaldi, C. How to Tell a Bird from a Dinosaur. Maps Digest, 17, 190-196 (1994)

25. Feduccia, A. The origin and evolution of birds (Yale Univ. Press, New Haven, 1996).

26. Sereno, P. The origin and evolution of dinosaurs. Annu. Rev. Earth Planet. Sci. 25, 435-489 (1997).

27. Forster, C. A., Chiappe, L. M., Krause, D. W. & Sampson, S. D. The first Cretaceous bird from Madagascar. Nature

382, 532-534 (1996).

28. Pérez-Moreno, B. P. et al. A unique multitoothed ornithomimosaur from the Lower Cretaceous of Spain. Nature 370,

363-367 (1994).

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Therizinosauridae) from Mongolia. Am. Mus. Nov. 3115, 1-39 (1994).

30. Osmólska, H., Roniewicz, E. & Barsbold, R. A new dinosaur, Gallimimus bullatus n. gen. n. sp. (Ornithomimidae) from

the Upper Cretaceous of Mongolia. Palaeont. Pol. 27, 103-143 (1972).

Acknowledgements. We thank A. Davidson and M. Ellison for the preparation and illustration of the specimens,

respectively. A. Milner, L. Witmer, G. Zweers, and J. Vanden Berge provided useful reviews and discussions. The Chapman

and Frick Memorial Funds of the AMNH, and the National Science Foundation (DEB-9407999) provided support for this

research.

Figure captions

Figure 1. A, B, Skull and jaw of Shuvuuia deserti (MGI 100/1001) in right lateral (A) and left lateral (B; only postorbital

region and with left jaw removed) views. C, Reconstruction of the skull of Shuvuuia deserti displaying its kinematic capacity

for elevating the snout independent from the braincase. Placement of flexion areas or bending zones at the base of the

snout, both dorsally and ventrally, suggest that the snout moved as a single unit, like in all prokinetic birds. Note that

Shuvuuia’s prokinetic movement differs from the modern type of prokinesis in that the dorsal bending zone lies between

the frontals and the nasal-preorbital bones, and not between the frontals and the nasal-premaxillaries. Abbreviations: art,

articular; atf, antorbital fossa; d, dentary; fr, frontal; jbr, jugal bar; lcr, lacrimal; mdf, mandibular fossa; mx, maxilla; po,

postorbital; q, quadrate; sq, squamosal.

Figure 2. Skull and right jaw of Shuvuuia deserti (MGI 100/1001) in dorsal (A), ventral (B), and caudal (C) views.

Abbreviations: bpt, basipterygoid process; bsr, basisphenoidal recess; fm, foramen magnum; hyo, hyoid; occ, occipital

condyle; p, parietal; poo, preorbital ossification (prefrontal/ectethmoid; see text); pop, paroccipital process; pt, pterygoid;

stf, supratemporal fenestra; others as in Fig. 1.

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Figure 3. Skull and jaws of Shuvuuia deserti (MGI 100/977) in dorsal (A) and ventral (B) views. Abbreviations: art, articular;

mxf, maxillary fenestra; n, nasal; pal, palatine; pmx, premaxilla; psr, parasphenoidal rostrum; san, surangular; slr, sclerotic

ring; others as in Fig. 2.

Figure 4. A, Some morphological differences between Shuvuuia deserti (left row) and Mononykus olecranus (right row)

(figures not in scale). 1, Shuvuuia has a cranio-dorsally expanded deltopectoral crest that is continuous with the humeral

head while Mononykus exhibits a pillar-like deltopectoral crest (see arrow). 2, Shuvuuia possesses a sharp ridge (larger

arrow) on the medial margin of the distal end of the tibia which is absent in Mononykus and lacks the deep medial notch

(smaller arrow) at the base of the ascending process of Mononykus. 3-4, The centra of Shuvuuia’s cervico-dorsal (3) and

anterior dorsals (4) are much less compressed than those in Mononykus. For autapomorphic characters and further

differences see Diagnosis in text. B, Phylogenetic position of the Alvarezsauridae and interrelationships among its

component taxa. Consensus cladogram derived from three most parsimonious trees with different topologies for the

mononykine taxa under the implicit enumeration command (finds all shortest trees) of computer program “Hennig 86”

(length: 115 steps, CI: 0.83, RI: 0.82 for both the consensus and the fundamental cladograms). Mononykinae is

phylogenetically defined as the common ancestor of Mononykus, Shuvuuia, and Parvicursor plus all its descendants.

Supplementary Information to be made available on Nature’s Web site

Cladistic Analysis. List of characters and data matrix informative for resolving the phylogenetic relationships of the taxa

included in Figure 4 (multistate characters treated as non-additive). Scoring for Enantiornithes is based on a combination

of the anatomical information provided by the indisputable enantiornithines Neuquenornis volans (Chiappe & Calvo, 1994),

Cathayornis yandica (Zhou et al., 1992; Martin & Zhou, 1997), Eoalulavis hoyasi (Sanz et al., 1996), Concornis lacustris

(Sanz et al., 1995), Gobipteryx minuta (Elzanowski, 1977, 1981; including undescribed material), the El Brete

enantiornithines (Chiappe, 1993, 1996), and a hatchling specimen from the Early Cretaceous of Catalonia (Sanz et al.,

1997). The scoring for Ornithurae is based on the anatomy of the basal ornithurines Hesperornis regalis (Marsh, 1880),

Ichthyornis dispar (Marsh, 1880), Ichthyornis victor (Marsh, 1880), and Ambiortus dementjevi (Kurochkin, 1985). For the

interrelationships within Enantiornithes see Chiappe (1993) and Sanz et al. (1995); basal ornithurine relationships are

discussed in Cracraft (1986).

1. Rostral portion of premaxillae unfused (0) or fused (1) in adults.

2. Frontal process of premaxilla short (0), relatively long to very long, at least approaching the rostral border of the

antorbital fossa (1).

3. Cup-shaped caudal maxillary sinus: absent (0), present (1).

4. Caudal margin of naris farther rostral than (0) or, nearly reaching or overlapping (1) the, rostral border of the antorbital

fossa.

5. Triradiate palatine (jugal process absent): absent (0), present (1).

6. Postorbital-jugal contact: present (0), absent (1).

7. Quadratojugal sutured to the quadrate (0), or joined by a ligament (1).

8. Quadratojugal-squamosal contact: present (0), absent (1).

9. Quadrate articulating only with the squamosal (0), or with both prootic and squamosal (1).

10. Caudal tympanic recess opens on the rostral margin of the paraoccipital process (0), or into the columellar recess (1).

11. Coronoid bone: present (0), absent (1).

12. Teeth in adults: with serrated crown (0) or unserrated crowns (1).

13. One or more pneumatic foramina piercing the centra of mid-anterior cervicals beyond the level of the parapophysis-

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diapophysis: present (0), absent (1).

14. Anterior cervical vertebrae heterocoelous: absent (0), present (1).

15. Carotid processes in intermediate cervicals: absent (0), present (1).

16. Prominent ventral processes on cervico-dorsal vertebrae: absent (0), present (1).

17. Cervico-dorsal vertebrae with parapophyses located at the same level as the prezygapophyses: absent (0), present

(1).

18. Wide vertebral foramen in thoracic vertebrae, vertebral foramen/articular cranial facies ratio (vertical diameter) larger

than 0.40: absent (0), present (1).

19. Hyposphene-hypantrum accessory intervertebral articulations in dorsal vertebrae: present (0), absent (1).

20. Synsacrum formed by 7 or fewer (0), or 8 or more vertebrae (1).

21. Cranial articular surface of synsacrum strongly concave: absent (0), present (1).

22. Caudal portion of the synsacrum forming a prominent ventral keel: absent (0), present (1).

23. Caudal articular surface of synsacrum convex: absent (0), present (1).

24. Prezygapophyses of distal caudal vertebrae: elongate (0), short or absent (1).

25. Caudal vertebrae: amphicoelous (0), or procoelous (1).

26. First caudal centrum strongly compressed ventrally: absent (0), present (1).

27. Elongated (much longer than wider) proximal haemal arches: absent (0), present (1).

28. Pygostyle: absent (0), present (1).

29. Caudal vertebral count larger than 35 (0) or fewer than 25-26 (1).

30. Coracoid and scapula articulate through a broad, sutured articulation (0), or through more localize, less extensive

facets (1).

31. Scapula articulated at the shoulder (proximal) end of coracoid (0), or well below it (1).

32. Coracoid and scapula placed in the same plane (0), or forming a sharp angle (1) at the level of the glenoid cavity.

33. Coracoid shape: elongated with subrectangular profile (0), short (1), strut-like (2).

34. Bicipital tubercle (= acrocoracoidal process): present (0), absent (1).

35. Supracoracoid nerve foramen of coracoid centrally located (0), or displaced (often as an incision or even without

passing through) toward the medial margin of coracoid (1).

36. Scapular caudal end blunt and usually expanded (0), or tapered to sharp point (1).

37. Prominent acromion in the scapula: absent (0), present (1).

38. Boomerang-shaped furcula, with interclavicular angle approximately 90/ (0), or U-shaped furcula, with an

interclavicular angle less than 70/ (1).

39. Sternum subquadrangular to transversally rectangular (0) or longitudinally rectangular (1).

40. Ossified sternal keel: absent (0), present (1).

41. Proximal and distal humeral ends twisted (0), or expanded nearly in the same plane (1).

42. Ventral tubercle of humerus projected ventrally (0), proximally (1), or caudally, separated from the humeral head by

a deep capital incision (2).

43. Humerus with distinct transverse ligamental groove: absent (0), present (1).

44. Humeral pneumatic fossa: absent (0), present (1).

45. Humeral distal condyles mainly located on distal (0), or cranial (1) aspect.

46. Humerus with two (0), or a single distal condyle (1).

47. Well-developed olecranal fossa on the caudal face of the distal end of humerus: absent (0), present (1).

48. Ulna shorter than (0), or subequal in length to, or longer than, humerus (1).

49. Diameter of ulnar shaft: radial shaft/ulnar shaft ratio larger (0), or smaller (1) than 0.70.

50. Olecranon process on ulna: relatively small (0), hypertrophied, nearly one-third (1) or one-half (2) the length of the

ulna.

8

51. Distal end of ulna subrectangular and transversely compressed (0), or subtriangular in shape (1).

52. Semilunate ridge on ulnar dorsal condyle: absent (0), present (1).

53. Ulnare (scapholunar) of round to sub-rectangular shape (0) or U-shaped to heart-shaped (1).

54. Distal carpals and proximal portion of metacarpals unfused (0), or fused forming a carpometacarpus (1).

55. Extensor process on carpometacarpus: absent or rudimentary (0), present (1).

56. Alular metacarpal (I)/major metacarpal (II) length ratio smaller than or equivalent to 0.30: absent (0), present (1).

57. Alular metacarpal massive, depressed, and quadrangular-shaped: absent (0), present (1).

58. Alular digit (I) long, exceeding the distal end of the major metacarpal (0), or short, not surpassing this metacarpal (1).

59. Alular digit (I) large, robust, and dorsoventrally compressed: absent (0), present (1).

60. Prominent ventral projection of the latero-proximal margin of the proximal phalanx of alular digit (digit I): absent (0),

present (1).

61. Alular ungual phalanx with two, ventro-proximal foramina: absent (0), present (1).

62. Pelvic elements unfused (0), or fused or partially fused (1).

63. Pubis subvertically oriented (0), or well-retroverted (1).

64. Prominent antitrochanter: absent (0), caudally directed (1), or dorso-caudally directed (2).

65. Iliac fossa for M. cuppedicus (=M. iliofemoralis internus): present (0), absent or rudimentary (1).

66. Iliac brevis fossa: present (0), absent (1).

67. Pubic pedicel ventrally or caudoventrally (0), or cranioventrally projected (1).

68. Supracetabular crest on ilium absent or rudimentary (0), extending throughout the acetabulum (1), or extending only

over the rostral half of the acetabulum (2).

69. Ischiadic terminal processes in contact (0), or lacking contact (1).

70. Ischium less than two-thirds (0), or two-thirds or more of pubis length (1).

71. Obturator process of ischium: prominent (0), or reduced or absent (1).

72. Pubic apex in contact (0), or lacking contact (1).

73. Pubis shaft laterally compressed throughout its length: absent (0), present (1).

74. Pubic foot: present (0), absent (1).

75. Pubic apron more than one-third the length of the pubis (0), shorter or absent (1).

76. Laterally compressed and kidney-shaped proximal end of pubis: absent (0), present (1).

77. Femur with distinct fossa for capital ligament: absent (0), present (1).

78. Femoral anterior trochanter nearly confluent with the greater trochanter (0), or fused to it forming the trochanteric crest

(1).

79. Femoral posterior trochanter: present (0), absent (1).

80. Conical and strongly distally projected lateral condyle of femur: absent (0), present (1).

81. Femoral popliteal fossa distally bounded by a complete transverse ridge: absent (0), present (1).

82. Tibiofibular crest on the lateral condyle of femur: absent (0), present (1).

83. Tibia, calcaneum, and astragalus unfused or poorly coosified (sutures still visible) (0), or complete calcaneo-

astragalar-tibial fusion (1).

84. Medial border of tibiotarsus at nearly the level of lateral border (0) or strongly projected proximally (1).

85. Proximal end of fibula prominently excavated by a medial fossa (0), or nearly flat (1).

86. Fibula with tubercle for M. iliofibularis anterolaterally (0), laterally or caudolaterally or caudally (1) directed.

87. Fibula reaching the proximal tarsals (0), or greatly reduced distally, without reaching these elements (1).

88. Distal tarsals free (0), or completely fused to the metatarsals (1).

89. Metatarsal V: present (0), absent (1).

90. Proximal end of metatarsal III in the same plane as metatarsals II and IV (0), reduced, not reaching the tarsals

(arctometatarsalian condition) (1), or plantarily displaced with respect to metatarsals II and IV (2).

9

Data Matrix

Taxa\character 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

Velociraptorinae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Archaeopteryx 0 1 0 1 1 ? 1 1 ? 1 1 1 0 0 ? 0 0 ? ? 0 0 ? 0 1 0 ? 0 0 1 0 0 0 0 0 0 0 1 0 ? ? 0 0 0 0 0

Mononykus ? ? ? ? ? ? ? ? ? 1 ? 1 1 0 1 1 1 1 1 ? 1 1 1 ? 1 1 ? ? ? 0 0 0 1 1 0 0 0 ? 1 1 1 1 0 0 1

Shuvuuia 0 0 ? 0 1 1 1 1 1 1 1 1 0 0 1 1 1 1 1 0 1 1 1 1 1 1 1 0 1 0 0 0 1 1 0 0 0 ? 1 1 1 1 0 0 1

Parvicursor ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 1 ? 0 ? ? ? 1 1 ? 0 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

Alvarezsaurus ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0 ? ? 0 0 0 ? 1 1 1 1 ? ? 0 0 0 ? ? 0 ? 0 ? ? ? ? ? ? ? ?

Patagonykus ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 1 ? 1 1 1 ? 1 1 ? ? ? 0 0 ? 1 1 0 ? ? ? ? ? ? 1 0 0 1

Enantiornithes 1 1 1 1 1 1 1 1 ? ? 1 1 1 1 1 1 0 1 1 1 1 0 0 1 0 0 0 1 1 1 1 1 2 0 1 1 1 1 1 1 0 2 1 1 1

Ornithurae 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 1 0 0 0 1 0 0 0 1 1 1 1 1 2 0 1 1 1 1 1 1 1 2 1 1 1

Taxa\character 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

Velociraptorinae 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Archaeopteryx 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 ? 0 0 ? 0 1 0 0 0 0 0 ? 0 0 0 ? 0 0 0 ? ? 0 0 0 0

Mononykus 1 0 0 0 2 1 0 ? 1 0 0 1 0 1 1 1 1 ? 1 1 ? 1 2 ? ? ? ? ? ? ? 1 0 1 1 1 0 0 0 1 1 ? 1 ? ? 1

Shuvuuia 1 0 0 0 2 1 0 ? 1 0 0 1 0 1 1 1 ? 1 1 1 0 1 2 1 1 1 1 1 1 1 1 ? ? 1 ? 0 ? 0 1 1 1 1 0 0 1

Parvicursor ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 1 ? 1 ? ? ? ? 1 1 1 1 1 ? 1 ? ? 1 1 1 ? 0 0 1 1 1 1 0 ? 1

Alvarezsaurus ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 0 ? ? ? 1 0 1 1 ? ? ? ? ? ? ? ? ? ? 0 ? ? ? 0 ? ? ? 0 ? ? 0

Patagonykus 1 0 ? 0 1 1 0 ? 1 0 ? 1 0 1 1 ? 0 0 1 1 ? 1 1 ? ? ? 1 1 0 1 0 ? 0 0 1 0 0 0 0 ? ? 0 ? ? 0

Enantiornithes 0 1 1 1 0 1 1 1 1 1 1 0 1 0 0 0 1 1 2 0 1 0 0 0 1 0 0 0 0 1 0 1 1 0 0 1 1 1 0 1 ? 1 1 1 0

Ornithurae 0 1 1 1 0 1 1 1 1 1 1 0 1 0 0 ? 1 1 2 1 1 0 0 1 1 1 1 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 1 2

Synapomorphies diagnosing different nodes of Figure 4 (asterisked characters have equivocal optimization; a “-“

preceding the character number indicates a reversal):

Node 1 (Aves): 2*, 4*, 5, 6*, 7, 8, 9*, 10, 11, 12, 15*, 18*, 19*, 24, 29, 37-40*, 56*, 69*, 71, 85*, 86*

Node 2 (Metornithes): 2-4*, 6*, 9*, 13*, 15*, 16, 18*, 19*, 33a*, 33b*, 37-41*, 42a*, 42b*, 45, 51, 53*, 54, 56*, 62*, 63*,

64a*, 64b*, 65*, 69*, 70, 72*, 73*, 75, 78*, 85*, 86*

Node 3 (Alvarezsauridae): 2-4*, 13*, 23*, 25, 26, 27, 33a,*, 33b*, 34*, -37*, 38*, 41*, 42a*, 42b*, 46*, 50a*, 50b*, 53*,

56*, 57*, 59*, 60*, 62*, 63*, 64a*, 64b*, 65*, 67, 68a

69*, 72*, 73*, 78*, 80*

Node 4 (Patagonykus + Mononykinae): 2-4*, 13*, 17*, 21, 22, 23*, 33a*, 34*, 38*, 41*, 42a*, 46*, 50a*, 50b*, 53*, 56*,

57*, 59-63*, 64a*, 69*, 72*, 73*, 78*, 80*

Node 5 (Mononykinae): 2-4*, 13*, 17*, 38*, 41*, 50b*, 53*, -56*, 61-63*, 68b, 69*, 74*, 76, 78*, 79, 84, 87, 90

Ornithurae + Enantiornithes: 1, 2-4*, 13*, 14, 20, 28, 30, 31, 32, 33b*, 35, 36, 37*, 38*, 41*, 42b*, 43, 44, 47, 48, 49,

52, 53*, 55, 56*, 58, 62*, 63*, 64b*, 65*, 66, 69*, 72*, 73*, 77, 78*, 81, 82, 83, 87, 88, 89

10

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