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A new bird from the Upper Cretaceous Two Medicine Formation of Montana

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David J. Varricchio 5

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Abstract: A partial humerus, ulna, and radius compose the type specimen of a new bird, Piksi barbarulna, new genus and species, from the Late Cretaceous (Campanian) Two Medicine Formation of western Montana. This ornithothoracine taxon differs from all other birds in having an enlarged dorsal epicondyle and a reduced ventral condyle on the humerus with corresponding modifications on the articular surface of the ulna. Among modern birds, Piksi is most similar to galliforms, but the paucity of unambiguous characters and its unusual morphology defy placement within any extant “order” and strongly questions any neornithine affinities. Instead, Piksi appears to have a fairly basal position within Ornithothoraces. Several morphologic features of Piksi occur in phylogenetically diverse but morphologically similar birds, such as galliforms, tinamous, and some columbiforms. The new bird comes from an inland, relatively dry paleo-environment. Atypical for a Cretaceous avian record dominated by waterfowl, Piksi appears to represents a heavy-bodied ground bird. Searching of inland depositional environments may yield new and ecologically distinct avian varieties. Résumé : Une partie d’un humérus, d’un cubitus et d’un radius forment le spécimen type d’un nouvel oiseau, Piksi barbarulna, nouveau genre et nouvelle espèce, de la Formation de Two Medicine (Crétacé tardif - Campanien), de l’ouest du Montana. Ce taxon ornithothoracine diffère de tous les autres oiseaux car il a un épicondyle dorsal élargi et un condyle ventral réduit sur l’humérus ainsi que les modifications correspondantes sur la surface articulaire du cubitus. Parmi les oiseaux modernes, Piksi ressemble le plus aux Galliformes, mais la rareté de caractères non ambigus et sa morphologie inhabituelle empêchent de le placer dans un « ordre » existant quelconque et posent de sérieuses questions quant aux affinités néornithines. Au lieu, Piksi semble occuper une position assez à la base des Ornithothoraces. Plusieurs caractéristiques morphologiques de Piksi se retrouvent dans des oiseaux phylogénétiquement différents mais morphologiquement semblables, tels que les galliformes, les tinamous et quelques columbiformes. Le nouvel oiseau provient d’un paléo-environnement intérieur relativement sec. Ce qui est non typique pour les gisements fossilifères aviaires du Crétacé dominés par de la sauvagine, Piksi semble représenter un oiseau terrestre à forte corpulence. La recherche dans les environnements de déposition à l’intérieur des terres pourra donner des variétés aviaires nouvelles et écologiquement distinctes. [Traduit par la Rédaction]

Introduction

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Despite many recent discoveries of fossil birds, the Cretaceous record of extant avian orders remains poor (Chiappe 1995a; Feduccia 1995; Cooper and Penny 1997; Padian and Chiappe 1998). To date, only four modern orders apparently occur in Cretaceous beds (Brodkorb 1963; Olson and Parris 1987; Chatterjee 1989; Tokaryk and James 1989; Olson 1992; Noriega and Tambussi 1995). All represent either waterfowl or shorebirds: Gaviiformes (loons), Anseriformes (e.g., ducks, screamers), Charadriiformes (e.g., gulls, sandpipers, auks), and Procellariiformes (e.g., petrels, albatrosses). One possible terrestrial lineage, Psittaciformes (parrots), may also occur in the Cretaceous (Stidham 1998; but see Dyke and Mayr 1999). Nevertheless, molecular data (Hedges et al. 1996; Cooper and Penny 1997) and possibly fossil gap analysis

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Received 22 January 2001. Accepted 11 July 2001. Published on the NRC Research Press Web site at http://cjes.nrc.ca on January 7, 2002. Paper handled by Associate Editor H.-D. Sues.

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D.J. Varricchio. Carthage College, Kenosha, WI 53140-1994, U.S.A. (e-mail: djv@carthage.edu). Can. J. Earth Sci. 39: 19–26 (2002)

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(Marshall 1999) indicate that many more lineages should have first occurrences in the Cretaceous. Instead these missing orders do not appear until the Paleocene or Eocene (Cooper and Penny 1997). Due to the limited morphologic and taxonomic diversity of Cretaceous forms, Feduccia (1995) proposed an explosive radiation of modern groups after a Cretaceous–Tertiary extinction of more primitive forms, such as enantiornithines and ichthyornithiforms. A new taxon, Museum of the Rockies (MOR) 1113, described here consists of a partial wing from the Campanian Two Medicine Formation of western Montana. This fossiliferous Formation consists of nonmarine sediments deposited between the Cordilleran mountain belt and the shore of the Cretaceous Interior Seaway (Rogers 1997). The Two Medicine differs from contemporary formations of the western North America in having a higher proportion of floodplain mudstones and more event horizons, such as nests and bonebeds (Rogers 1993). A number of dinosaur taxa, Maiasaura peeblesorum, an undescribed Gryposaur, Orodromeus makelai, Styracosaurus ovatus, Achelosaurus horneri, and Einiosaurus procurvicornis, appear restricted to the Formation (Weishampel and Horner 1990; Sues and Norman 1990; Dodson and Currie 1990; Sampson 1995). Currently, the avifauna consists of an enantiornithine, Avisaurus

DOI: 10.1139/E01-057

© 2002 NRC Canada

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gloriae (Varricchio and Chiappe 1995) and MOR 1113. Although fragmentary, MOR 1113 is significant in that it comes from an inland paleo-environment and exhibits a morphology distinct from any known Cretaceous or Paleogene avian group.

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Systematic paleontology Aves Ornithothoraces incertae sedis Piksi barbarulna, gen. et sp. nov. Etymology “Piksi,” a Blackfoot word, acknowledges the Blackfeet Nation, where the new specimen occurred. “Piksi” means “big bird” and “chicken” (Uhlenbeck and Van Gulik 1930) and represents the interpretation of the Two Medicine form as a heavy-bodied, ground bird with similarities to the Galliformes. “Barbarulna” combines the Latin words barbarus and ulna to mean “strange-elbow” and refers to the autapomorphic aspects of the new species. Holotype MOR 1113, right humerus, ulna, and radius. Collected in 1991 by Gloria Siebrecht for the Museum of the Rockies, Montana State University, Bozeman, Montana.

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Horizon and locality Two Medicine Formation, Cretaceous, Campanian, MOR locality TM-088, Bob’s Vacation Site, Glacier County, Montana, U.S.A. Locality TM-088 has an extent of 25 m2 (Nassar 1991) and comes from the middle of the Formation. It dates to roughly 75–76 million years ago, based on its position relative to dated ash beds (Rogers et al. 1993). Stratigraphic and sedimentologic information places this locality at near maximum regression of the Interior Seaway and at least 350 km inland from the paleo coastline (Cobban et al. 1994). The assemblage, preserved within a silty claystone, contains very few elements larger than 10 cm in greatest length. Most are less than 3 cm. Bones range from well preserved through well abraded and include articulated to isolated elements. The assemblage contains a dromaeosaurid skeleton; an in situ Troodon egg clutch; abundant Orodromeus elements from hatchlings through adults; abundant small theropod teeth; a few tyrannosaurid and hadrosaurid teeth; lizard elements, several associated to articulated frogs; marsupial and multituberculate teeth; miscellaneous isolated bones; and terrestrial planispiral gastropods. The absence of any strictly aquatic animals suggests only very ephemeral water. The site appears to represent a small floodplain depression, possibly a vernal pool. Diagnosis Medium-sized bird; large dorsal epicondyle on the humerus subequal to the dorsal condyle; flexor process (processus flexorius of Baumel and Witmer 1993) of the humerus with a proximodistally angled wall; large dorsal cotyla on the ulna, twice as broad as the ventral cotyla; dorsal cotyla on the ulna with an elongate outline; and ulna shaft lacking quill knobs (papillae remigalis ventralis).

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Two of these features clearly represent autapomorphies of Piksi barbarulna: the large dorsal epicondyle of the humerus and the large dorsal cotyla of the ulna. Three additional features may be autapomorphies but also occur in several unrelated groups. Ichthyornis and Musophagiformes show a similar angled wall of the flexor process; Podicipediformes have an elongate dorsal cotyla; and Tinamiformes, Phoenicopteriformes, and taxa outside of Ornithurae all lack quill knobs. The absence of quill knobs in MOR 1113 may be due to poor preservation or represent a primitive feature. Description MOR 1113 consists of the distal portion of the right humerus; a fragmentary right ulna with both ends and most of the shaft; and the proximal half of the right radius (Figs. 1, 2). Crushing has distorted both the humerus and ulna. Table 1 lists measurements for these elements. Based on measurements of the humerus, Piksi barbarulna represents a bird roughly the size of a red-necked pheasant, Phasianus colchicus (Crowe and Short 1992). The preserved humerus (Figs. 1, 2) includes the shaft distal from the proximal margin of the brachial fossa through a complete distal end. The humerus has three main surfaces in cross section: an irregular anterior surface with three subequal condyles (the dorsal epicondyle, dorsal condyle, and the ventral condyle, and a smaller terminal ventral epicondyle); a posterior concave surface bearing a depression (the olecranon fossa and humerotricipital sulcus), set between a posterior dorsal ridge of the humerus shaft and the ventral ridge of the flexor process; and a convex dorsal face with a faintly irregular surface and a small (~2 mm diameter) circular depression near the distal margin. On the anterior face, the brachial fossa appears well formed and distinct but lacks any surface modification suggestive of muscle scarring. The fossa terminates at the dorsal and ventral condyles. The dorsal epicondyle is exceptionally broad in anterior view and nearly matches the dorsal condyle in breadth. It projects anteriorly as a low ridge with a broad connection with the dorsal condyle. Its smooth surface and size suggest it contributed significantly to the ulna articulation. A small subcircular muscle scar with a raised dorsal edge sits proximal to the dorsal epicondyle. This likely corresponds to the processus surpacondylaris dorsalis. Anteriorly, the dorsal condyle has a typical neornithine look, being a narrow rounded tongue-like projection inclined towards the ventral condyle. In distal view the dorsal condyle and epicondyle coalesce and form a distal platform, a broad roughly triangular and relatively flat articulating surface (Figs. 1C, 2B). The posterior corner of the triangle continues as a ridge running down the posterodorsal margin of the humeral shaft. Crushing of the shaft has accentuated this ridge. The flat articulating surface occupies roughly 60% of the distal breadth of the humerus. Consequently, the ventral condyle is dorsoventrally narrow (3.5 mm wide). Its rounded articulating surface extends from the posterior to several millimeters up the anterior side of the humerus. This condyle projects 2 mm beyond the flat articulating surface of the dorsal condyle and epicondyle. A much smaller ventral epicondyle bears a small (1.5 mm wide) anterior-facing articular surface. © 2002 NRC Canada

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Fig. 1. MOR 1113: humerus, ulna, and radius of Piksi barbarulna. (A, B, C) Right distal humerus in posterior, anterior and distal views. In C, anterior is down and note distal platform (dp) formed by coalescing of dorsal condyle and epicondyle. (D, E) Right proximal ulna in proximal and dorsal views. Ulna shaft is largely reconstructed. (F, G) Right proximal radius in proximal and dorsal views. ap, articulating pit; b, brachial fossa; dc, dorsal condyle; dct, dorsal cotyla; de, dorsal epicondyle; dp, distal platform; ds, dorsal supracondyle; f, flexor process; o, olecranon; of, olecranon fossa; rt, radial tubercle; vc, ventral condyle; vct, ventral cotyla; and ve, ventral epicondyle. Scale bar = 20 mm.

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On the posterior face of the humerus, the flexor process projects almost as far distally as the ventral condyle. Its roughened surface bears a slight ridge that angles dorsally and forms the concave wall of a small pocket immediately posterior to the ventral condyle. This pocket represents the olecranon fossa. The ulna (Figs. 1D, 1E) consists of four unconnectable fragments with a minimum total length of 97 mm. If complete, the ulna probably measured slightly longer than 100 mm. Unfortunately, lithostatic crushing has distorted the proximal third of the diaphysis. A large portion (~40%) of the diaphysis lacks bone, being represented merely by the calcite and sediment that once filled the marrow cavity. Recent (i.e., post-fossilization) weathering accounts for the loss. The small olecranon barely extends beyond the proximal cotylas. With the ulna articulated with the humerus and fully extended, the olecranon abuts the bony wall formed by the ventral ridge of the flexor process. A low intercotyla crista separates the ventral cotyla from the much larger dorsal one. The ventral cotyla occupies only 27% (3.1 of 11.4 mm) of

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the proximal end’s breadth. It is roughly circular and slightly concave. In contrast, the dorsal cotyla has an elongate articulating surface divided in two. A more ventral half lies perpendicular to the axis of the ulna shaft, while the exterior (dorsal) half sits angled anteriorly (Fig. 1D). These two portions of the dorsal cotyla do articulate with the subequal dorsal condyle and epicondyle, respectively. Except for a slight rise just distal to the olecranon, the proximal end appears devoid of significant muscle scars and tubercles. Crushing damage may obscure some. The bowed shaft has a subcircular cross-section. A flatter anterior face runs down the proximal 40% of the bone. No feather papillae occur, but the poor preservation of the diaphyseal portions may obscure their presence. The simple and poorly preserved distal end of the ulna exhibits few features. It bears a semi lunate dorsal condyle, a large ventral condyle, a deep intercondyle sulcus, but only a weakly developed to absent carpal tubercle. The radius (Figs. 1F, 1G) consists of a well-preserved proximal fragment, including an uncrushed articular end and Š 2002 NRC Canada

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Fig. 2. MOR 1113: Piksi barbarulna, right distal humerus in anterior (A) and distal (B) views. Note anterior is up in B. See Figs. 1A–1C for identification of structures. Scale bar = 5 mm.

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Table 1. Measurements (in mm) of Piksi barbarulna. 75

Preserved length of humerus Dorsal-ventral width of distal end of humerus Anterior-posterior width of distal end of humerus Width of ventral condyle Width of dorsal condyle Width of dorsal epicondyle Minimum preserved length of ulna (all four pieces) Estimated total length of ulna Total length of biggest intact portion (proximal end) Dorsal-ventral width of proximal end of ulna Anterior-posterior width of proximal end of ulna Dorsal-ventral width of ventral cotyla Anterior-posterior width of ventral cotyla Dorsal-ventral width of dorsal cotyla Anterior-posterior width of dorsal cotyla Dorsal-ventral width of ventral half of dorsal cotyla Dorsal-ventral width of dorsal half of dorsal cotyla Dorsal-ventral width of distal end of ulna Anterior-posterior width of distal end of ulna Greatest length of radius proximal fragment Length of second radius fragment Greatest breadth of proximal end of radius Width perpendicular to above

20 14.3 8.8 3.5 4.4 3.6 96 100+ 54.4 11.4 5.1 3.1 2.5 ~7.8 3.4 4.5 4.1 8.2 6.8 42.1 11 6.9 4.1

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ulna’s in a comparable position are 4.7 mm and 5.1 mm. The diaphysis bears a flattened face beginning about 30 mm distal to the proximal end. A tiny foramen sits at 26.5 mm down.

Phylogenetic analysis

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much of the diaphysis (total length = 42 mm). A second diaphyseal fragment measures ~11 mm. When viewed proximally, the articular surface has an oval outline. A shallow circular pit occupies most of the broader end. A raised knob with a rough texture and small pit, the radial tubercle (tubercalis bicipitale radialis), sits about 5 mm distal to the articular end. The diaphysis is significantly narrower than that of the ulna. At 41 mm down its length, minimum and maximum diameters measure 2.5 mm and 3.5 mm; the

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A cladistic analysis was used to assess the position of Piksi barbarulna within Aves and its potential inclusion within Neornithes. This used 26 characters of the humerus, ulna, and radius (Table 2). Some characters were derived from the literature (See Table 2 for references.) and others compiled here for the first time. The 35 taxa consisted of nine fossil forms and representatives of 20 extant lineages, 18 orders, plus ratites and Turnicidae (Table 3). Fossil taxa include the Cretaceous Enantiornithes, Icthyornis (Marsh 1880), and Torotix clemensi (Brodkorb 1963) and the Paleogene Telmatornis priscus (Olson and Parris 1987), Presbyornis (Olson and Feduccia 1980),Telmabates antiquus (Howard 1955), the lithornithiform Lithornis (Houde 1988), the coliiform Sandcoleus copiosus (Houde and Olson 1992), and the galliform Palaeortyx gallica (Mourer-Chauviré 1992). A total of 61 extant species were originally scored. Seven modern orders were excluded. These either had no available specimens (Trogoniformes) or appeared so dissimilar to Piksi to make them uninformative for the analysis (Sphenisciformes, penguins; Caprimulgiformes, nightjars; Apodiformes, swifts, hummingbirds; Coraciiformes, hornbills, rollers; Piciformes, woodpeckers; and Passeriformes, perching birds). For ten lineages, at least three familially distinct species were originally scored, with the final analysis using the most representative single taxon. Since some researchers place the Cracidae (curassows) in an order separate from the galliforms (Sibley and Ahlquist 1990), both cracid and non-cracid © 2002 NRC Canada

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Table 2. List of characters used in the cladistic analysis. 75

(1)

Circular muscle scar on the dorsal side of the distal humerus: absent (0), present (1).

(2)

Well-developed brachial fossa: absent (0), present (1) (Chiappe and Calvo 1994). Distal condyles located on the anterior aspect of the humerus: absent (0), present (1) (Chiappe and Calvo 1994). Small dorsal supracondyle on humerus: absent (0), present (1). Large dorsal epicondyle, subequal to dorsal condyle: absent (0), present (1). Broad connection between dorsal condyle and epicondyle: absent (0), present (1). Dorsal condyle with tongue-like shape in anterior view: absent (0), present (1). Dorsal condyle angled at 20°–30° away from long axis of humerus: absent (0), present (1). Dorsal condyle broader than ventral condyle: absent (0), present (1). Dorsal condyle and epicondyle form “distal platform”: absent (0), present (1). Ventral condyle longer proximodistally than ventrodorsally broad: absent (0), present (1). At least 45% of the ventral condyle located distal to the dorsal condyle: absent (0), present (1). Ventral epicondyle a small, flat anterior facing facet: absent (0), present (1). Ventral epicondyle not projecting distally beyond ventral condyle: absent (0), present (1). Well-developed olecranon fossa: absent (0), present (1) (Chiappe 1991). Strong flexor process on humerus: absent (0), present (1). Dorsal wall of flexor process angles proximodorsally: absent (0), present (1). No groove between olecranon and cotylas of ulna: absent (0), present (1) (Chiappe and Calvo 1994). Ventral cotyla of ulna disc-shaped: absent (0), present (1). Ventral cotyla much smaller than dorsal cotyla (1/2 the width): absent (0), present (1). Elongate dorsal cotyla: absent (0), present (1). Ulna shaft without quill knobs: absent (0), present (1) (Elzanowski1995). Distal end of ulna with semi-lunate condyle: absent (0), present (1) (Chiappe 1991). Radius with proximal subcircular articulating pit: absent (0), present (1). Radius shaft much narrower (< 0.7) than ulna shaft: absent (0), present (1) (Chiappe and Calvo 1994). Radius shaft without axial groove: absent (0), present (1) (Chiappe 1991).

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(4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26)

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galliforms were incorporated. Two orders, Columbiformes and Cuculiformes, had two very distinct representatives and so both examples were included in the analysis. The analysis utilized heuristic searches of the data matrix to generate a phylogenetic hypothesis. Note, this analysis does not represent an attempt to resolve phylogenetic relationships among ingroup taxa. Instead, it focused on the placement of Piksi only and in this manner is similar to that of Frankfurt and Chiappe (1999).

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The heuristic search generated a strict consensus tree with 35 steps, a Consistency Index of 0.74, and a Retention Index of 0.90. This tree placed most taxa on a large polytomy with one branch consisting of a clade formed by the Oligocene galliform Palaeortyx, the tinamiform, the columbiform Goura, the two extant galliforms and Piksi (Fig. 3). Three ambiguous characters of the humerus unite these taxa: a broad connection between the dorsal condyle and epicondyle, the dorsal and epicondyle form a distal platform, and at least 45% of the ventral condyle extends distally beyond the dorsal condyle. On this branch, Goura sits as the closest sister taxon to a polytomy formed by the modern galliforms and the Two Medicine taxon. A ventral condyle that is longer proximodistally than dorsoventrally broad ambiguously defines this node. Finally, the two extant galliforms and Piksi unambiguously share a dorsal condyle of the humerus that is dorsoventrally broader than the ventral condyle.

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Discussion Piksi possesses (1) a radial shaft diameter / ulna shaft diameter less than 0.7 (Chiappe 1995a), (2) a well developed olecranon fossa (Chiappe 1991), (3) distal condyles located on the anterior aspect of the humerus (Chiappe 1995b), and (4) a semi-lunate distal articular surface on the ulna and clearly sits within the Ornithothoraces (sensu Chiappe and Calvo 1994) in a more derived position than Iberomesornis. Placement within the Ornithothoraces though is not immediately obvious. For example, although the Two Medicine form does posses a well-developed dorsal cotyla on the ulna, it lacks other enantiornithine synapomorphies, including: a transversely oriented dorsal condyle of the humerus, a poorly developed ventral condyle, an axial groove on the radius shaft, and a groove separating the ulna’s dorsal cotyla from the olecranon (Walker 1981; Chiappe and Calvo 1994; Sanz et al. 1995). Piksi does exhibit one synapomorphy of the Ornithurae, a brachial depression on the humerus (Chiappe and Calvo 1994), but appears to lack quill knobs on the ulna shaft (Elzanowski 1995). Since at least two extant groups, Tinamiformes and Phoenicopteriformes (flamingos) also lack quill knobs, their absence in Piksi can not alone remove it from the Ornithurae. Patagopteryx (Alvarenga and Bonaparte 1992, Figs 10, 11; Chiappe 1995b), hesperornithiforms, and icthyornithiforms (Marsh 1880) also appear quite different from this Two Medicine form. The cladistic analysis (Fig. 3) failed to distinguish neornithine birds from more primitive outgroups (Enantiornithes, Ichthyornis) with the available characters. Thus no feature of MOR 1113 definitively places Piksi within Neornithes. Nevertheless, the analysis did place Piksi in a strictly neornithine group consisting of three galliforms (including the Oligocene Palaeortyx), the tinamous Cryptoreilus, and the large crowned-pigeon Goura. Given this phylogenetic mix, it is not surprising that only ambiguous features unite these taxa. The cladistic analysis indicated an apparently unambiguous feature, a dorsal condyle dorsoventrally broader than the ventral, linking Piksi with the two extant galliforms. Although occurring in both cracids and phasianids, this feature is absent in the two other living families of galliforms, the Megapodiidae and Numididae. Furthermore, this feature occurs in the Early Cretaceous Confuciusornis © 2002 NRC Canada

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Table 3. Data matrix of morphological characters used in the phylogenetic analyses. 75

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Characters 1 through 26

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Troodon formosus Deinonychus antirrhopus Enantiornithes — Neuquenornis volans ratites — Struthio camelus Tinamiform — Cryptureilus soui Procellariiform — Diomedea irrorata Gaviiform — Gavia arctica Podicipediform — Podiceps cristatus Pelecaniform — Sula basana Ciconiiform — Scopus umbretta Phoenicopteriform — Phoenicopterus sp. Falconiform — Buteo jamaicensis Anseriform — Aythya affinis Galliform-1 — Ortalis motmot Galliform-2 — Dendragapus obscurus Turnicid — Turnix varia Gruiform — Aramus guarauna Charadriiform — Himantopus mexicanus Pteroclidiform — Pterocles quadricinctus Columbiform-1 — Columba palumba Columbiform-2 — Goura cristata Psittaciform — Nestor notabilis Musophagiform — Tauraco hartlaubi Cuculiform 1 — Coccyzus erythro Cuculiform 2 — Opisthocomus hoazin Strigiform — Tyto alba Lithornithiform — Lithornis sp. Telmatornis priscus Presbyornis sp. Telmabates antiquus Torotix clemensi Icthyornis Coliiform — Sandcoleus copiosus Galliform — Palaeortyx gallica Piksi barbaruna

sanctus, which has a fairly basal position within Aves (Chiappe et al. 1999). Given the paucity of ornithurine characters in Piksi barbarulna, this possibly plesiomorphic feature may better reflect the primitive nature of this taxon. Three factors complicate the definitive placement of Piksi barbarulna. First, the specimen consists of only fragmentary wing elements. Further, these bones come from the elbow region, an area critical to wing function. With strong functional constraints, avian elbow morphology may not represent an ideal character source for phylogenetic study. Results of the cladistic analysis do appear influenced by wing use. In the search-generated consensus tree, ratites fall outside of all other birds and closest to non-avian, nonflying theropods. Further, Piksi groups most closely with galliforms, the columbiform Goura, and the tinamiform. These extant forms all represent heavy-bodied, ground-feeding birds. All have short, rounded wings and make only short strong flights (Goodwin 1983; Terres 1995; Feduccia 1996). Finally, the Piksi specimen, although very incomplete, still exhibits several apomorphies. These include two non-ambiguous and three ambiguous ones (see Diagnosis). None occurs in

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10110 ?0010 00110 10110 11110 11100 11100 11110 11110 11110 11100 11110 11110 11110 11110 01110 11110 11100 11110 11110 11110 11110 01110 11100 11110 11110 ?0110 ?1110 ?1110 ?1110 11110 11110 ?1100 ?1110 11111

10001 00010 ?1000 00010 00000 01101 01000 10010 11101 01111 01100 00111 01100 00000 01001 00111 01100 00011 01101 00011 01101 00011 01101 01011 11100 00111 11111 11111 11111 11111 01100 01111 01101 00111 01101 00011 11101 00111 01100 00011 01101 11111 01101 00011 01101 00101 01100 00101 01100 00111 01101 00111 01100 00111 01001 00111 01101 00111 0110? 0111? 01101 00111 01100 00111 01100 00011 11101 01111 11111 11111

00100 01000 1 00100 01000 1 100?? ?11?1 0 00110 01111 1 10110 01111 1 10110 00111 1 10110 00111 1 10110 10111 1 10110 00111 1 10110 00111 1 10110 01111 1 10110 00111 1 10110 00111 1 10110 00111 1 10110 00111 1 10110 00111 1 10110 00111 1 10110 00111 1 10110 00111 1 10110 00111 1 10110 00111 1 10110 00111 1 11110 00111 1 10110 00111 1 10110 00111 1 10110 00111 1 10110 00111 1 10110 0???? ? 10??? ????? ? ??110 00111 1 10??? ????? ? 11110 00111 1 00110 01111 1 10110 0?1?? ? 11111 11111 1

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any of the galliforms examined. Most unusual is the enlarged dorsal epicondyle of the humerus and the corresponding expansion and elongation of the dorsal cotyla of the ulna. Although some groups, galliforms, anseriforms, tinamiforms, and pteroclidiforms (sand grouse), show an increased role of the epicondyle in the articular surface, no modern or fossil forms examined display anything close to the expansion present in Piksi. Despite some shared features discussed above, the articulating ends of the humerus and ulna in Piksi appear radically different from extant galliforms; fossil galliforms like Archaealectrornis sibleyi (Crowe and Short 1992), Paraortyx brancoi, Pirortyx major, and Palaeortyx intermedia (Mourer-Chauviré 1992); and any of the examined taxa. Uniquely in Piksi, the ventral condyle plays a less significant role in the articular surface with the dorsal condyle and epicondyle forming roughly 60% of the width of the articular surface. These differences suggest that Piksi represents a lineage distinct from any extant “order” and that the similarities with galliform species are simply functional convergences. The lack of quill knobs and definitive neornithine characters plus the © 2002 NRC Canada

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Fig. 3. Strict consensus tree resulting from heuristic search using phylogenetic analysis using parsimony (PAUP; Swofford 1993). Matrix consists of 35 taxa of extant and extinct birds (Table 3) and 26 characters of the humerus, ulna, and radius (Table 2). Extinct taxa marked with +. The non-avian maniraptoran dinosaurs Troodon and Deinonychus were assigned as outgroups. Character distribution is as follows (ambiguous traits marked with *): Node 1, ventral cotyla of ulna disc-shaped, distal end of ulna with semi-lunate condyle, radius with proximal subcircular articulating pit, and radius shaft much narrower (< 0.7) than ulna shaft; Node 2, *well-developed brachial fossa, *dorsal condyle angled at 20°–30° away from long axis of humerus, *well-developed olecranon fossa, *no groove between olecranon and cotylas of ulna; Node 3, *broad connection between dorsal condyle and epicondyle, *dorsal condyle, and epicondyle form “distal platform,” *at least 45% of the ventral condyle located distal to the dorsal condyle; Node 4, *ventral condyle longer proximodistally than ventrodorsally broad; Node 5, dorsal condyle broader than ventral condyle.

crowned-pigeon Goura, and tinamous with the pheasant-sized Piksi barbarulna. The shared wing features suggests that Piksi also represents a heavy-bodied, ground-feeding bird. Its locality, an inland, relatively dry, floodplain environment supports this interpretation. Piksi clearly represents a morphology distinct from many of the Late Cretaceous ornithurine lineages, Gaviiformes, Anseriformes, Charadriiformes, Procellariiformes, Hesperornithiformes, and Icthyornithiformes, which primarily represent waterfowl and shorebirds. The low diversity of Cretaceous birds likely results from the delicate nature of bird skeletons and the bias towards species preferring wetter depositional settings (Padian and Chiappe 1998). Piksi suggests that exploration of more inland settings may indeed yield new and ecologically distinct varieties. Although modern bird “orders” are predicted to exist in the Cretaceous, their recognition may remain difficult both due to the fragmentary nature of avian specimens and the autapomorphic nature of the taxa.

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Acknowledgments Many thanks go to both the Museum of the Rockies and the Department of Earth Sciences at Montana State University (MSU) for supporting this work; Jack Horner; Jim Schmitt; Gloria Siebrecht; the families of Vernon and Lewis Carroll; the Blackfoot Nation; Elaine Nissen and Frankie Jackson for illustrations; the ornithology collections at the American Museum of Natural History in New York, the Field Museum in Chicago, and the zooarchaeology collections at MSU; Scott Ogerri for surviving the Mosquito Wars of 1993; Luis Chiappe, Peter Houde, Sylvia Hope, Cathy Forster, Gareth Dyke and Tom Stidham for general fossil bird advice; and as usual Greg Erickson. Bruce Selyem (MOR) provided the photographs. Comments of both referees helped greatly. This work was supported, in part, by a Collection Study Grant from the Ornithology Department at the American Museum of Natural History.

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Varricchio, 2002  

Received 22 January 2001. Accepted 11 July 2001. Published on the NRC Research Press Web site at http://cjes.nrc.ca on January 7, 2002. Can....

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