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An ornithurine bird coracoid from the Late Cretaceous of Alberta, Canada

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The Cretaceous birds of Alberta are poorly known, as skeletal elements are rare and typically consist of fragmentary postcranial remains. A partial avian coracoid from the upper Campanian Dinosaur Park Formation of Alberta, Canada can be referred to the Ornithurae, and is referred to here as Ornithurine G (cf. Cimolopteryx). Its structure is similar to previously described ornithurine coracoids from Alberta and other localities in North America, particularly those belonging to the genus Cimolopteryx. A comparison of these elements indicates that the new coracoid is distinct; however, its preservation prevents complete diagnosis. As other Cimolopteryx are Maastrichtian in age, Ornithurine G (cf. Cimolopteryx) also represents the earliest occurrence of a Cimolopteryx-like anatomy. A pneumatized coracoid is a diagnostic trait of Neornithes, often associated with the presence of a pneumatic foramen. Ornithurine G (cf. Cimolopteryx) does not preserve this feature. CT and micro-CT scans of both pneumatic and apneumatic coracoids of modern birds show similar internal structures to Ornithurine G (cf. Cimolopteryx), indicating that pneumaticity of the coracoid cannot be determined in the absence of an external pneumatic foramen. A comparison between members of Cimolopterygidae, including Cimolopteryx and Lamarqueavis, raises questions about the assignment of Lamarqueavis to the Cimolopterygidae, and the validity of this family as a whole.
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1An ornithurine bird coracoid from the Late Cretaceous of Alberta, Canada
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3Sydney R. Mohr*,1, John H. Acorn2, Gregory F. Funston1, Philip J. Currie1
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51Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E9
6corresponding author*: smohr@ualberta.ca
7funston@ualberta.ca
8pjcurrie@ualberta.ca
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10 2Department of Renewable Resources, University of Alberta, Edmonton, AB, T6G 2H1
11 jacorn@ualberta.ca
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23 Abstract: The Cretaceous birds of Alberta are poorly known, as skeletal elements are rare
24 and typically consist of fragmentary postcranial remains. A partial avian coracoid from the upper
25 Campanian Dinosaur Park Formation of Alberta, Canada can be referred to the Ornithurae, and is
26 referred to here as Ornithurine G (cf. Cimolopteryx). Its structure is similar to previously
27 described ornithurine coracoids from Alberta and other localities in North America, particularly
28 those belonging to the genus Cimolopteryx. A comparison of these elements indicates that the
29 new coracoid is distinct; however, its preservation prevents complete diagnosis. As other
30 Cimolopteryx are Maastrichtian in age, Ornithurine G (cf. Cimolopteryx) also represents the
31 earliest occurrence of a Cimolopteryx-like anatomy. A pneumatized coracoid is a diagnostic trait
32 of Neornithes, identified by the presence of a pneumatic foramen. Ornithurine G (cf.
33 Cimolopteryx) does not preserve this feature. CT and micro-CT scans of both pneumatic and
34 apneumatic coracoids of modern birds show similar internal structures to Ornithurine G (cf.
35 Cimolopteryx), indicating that pneumaticity of the coracoid cannot be determined in the absence
36 of an external pneumatic foramen. A comparison between members of Cimolopterygidae,
37 including Cimolopteryx and Lamarqueavis, raises questions about the assignment of
38 Lamarqueavis to the Cimolopterygidae, and the validity of this family as a whole.
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46 Introduction
47 Cretaceous bird material in Alberta is rare and consists of fragmentary and isolated
48 postcranial elements, most of which are not specifically diagnosable (Currie 1995). As a result,
49 relatively little is understood about the Late Cretaceous avifauna of the province. Despite
50 expectations to the contrary, definitive examples of neornithine and enantiornithine birds from
51 this period remain unknown in Alberta (Longrich 2006, 2009). Current fossil evidence suggests
52 that non-neornithine ornithurine birds were the predominant and most diverse group present,
53 although much of this material has unclear taxonomic affinities due to its fragmentary nature
54 (Brodkorb 1963; Longrich 2009; Longrich et al. 2011). The Ornithurae include crown birds, or
55 Neornithes, as well as an array of morphologically similar non-neornithine birds from the
56 Cretaceous. The definition of Ornithurae has recently undergone significant and frequent
57 changes in the literature (Gauthier and de Queiroz 2001; Chiappe 2002; O’Connor and Zhou
58 2012). Cretaceous Ornithurines identified in Alberta include members of Hesperornithes,
59 Ichthyornithiformes, and Palintropiformes (Fox 1974; Fox, 1983; Hope 2002; Currie 2005;
60 Longrich 2006; Longrich 2009; Aotsuka and Sato 2016). Additionally, Hope (2002) briefly
61 described a specimen from the Dinosaur Park Formation and assigned it to the ornithurine family
62 Cimolopterygidae, making this the first purported cimolopterygid from the Campanian. All other
63 specimens assigned to this family are Maastrichtian in age. However, Longrich (2009)
64 questioned the identification of the specimen described by Hope (2002) due to a lack of shared
65 derived diagnostic characters for Cimolopterygidae, in spite of overall similarity to the
66 Maastrichtian specimens. The family Cimolopterygidae Brodkorb 1963 originally included
67 Cimolopteryx rara, Marsh 1892, and Ceramornis major Brodkorb 1963, Cimolopteryx maxima
68 Brodkorb 1963, and Cimolopteryx minima Brodkorb 1963 were added later. Recent additions
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69 include Cimolopteryx petra Hope 2002, Lamarqueavis australis Agnolin 2010, and
70 Lamarqueavis sp. (Agnolin 2010). Agnolin (2010) also renamed Cimolopteryx minima and
71 Cimolopteryx petra as Lamarqueavis petra and Lamarqueavis minima. Tokaryk and James
72 (1989) described a partial coracoid from the Maastrichtian of Saskatchewan as Cimolopteryx sp.
73 (SMNH P1927.936). These specimens, plus the partial coracoid described here (UALVP 55089),
74 and numerous indeterminate ornithurine bone fragments described by Longrich (2006, 2009),
75 form the entirety of avian specimens derived from non-marine Cretaceous sediments in Alberta.
76 UALVP 54089 is also roughly one to two million years older than the purported cimolopterygid
77 described by Hope (2002) and Longrich (2009) (Eberth, 1996). Due to its age and the fact that
78 fossil birds are poorly represented in the province, the specimen (UALVP 55089) warrants
79 consideration in order to add to the current understanding of avian diversity in the province and
80 its relationships to other birds in North America.
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82 Institutional Abbreviations
83 AMNH, American Museum of Natural History, New York, BMNH, British Museum of
84 Natural History, London, SDSM, South Dakota School of Mines, Rapid City, South Dakota,
85 SMNH, Saskatchewan Museum of Natural History, Regina, Saskatchewan, RTMP, Royal
86 Tyrrell Museum of Palaeontology, Drumheller, Alberta, UALVP, University of Alberta
87 Laboratory for Vertebrate Palaeontology, Edmonton, Alberta, UCMP, University of California
88 Museum of Paleontology, Berkeley, California.
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90 Materials and Methods
91 UALVP 55089 is a partial left coracoid, in the collections of University of Alberta
92 Laboratory of Vertebrate Paleontology, Department of Biological Sciences.
93 Osteological nomenclature is derived from Baumel and Witmer (1993), with English
94 equivalents for Latin terms when possible. The specimen was examined using a Wild M3
95 stereomicroscope, and photographed with a Nikon D500 camera and Nikkor 60mm Micro AF-D
96 f. 2.8 lens. Micro-CT scans of UALVP 55089 were acquired using a Skyscan1174 at 50 kV, 800
97 μA, 40 W, 35 μm image size, 2500 ms exposure, and 360° rotation at 0.2° per step. A coracoid
98 of Grus canadensis was Micro-CT scanned with an aluminum filter at 50 kV, 800 μA, 40 W, 35
99 μm image size, 2500 ms exposure and 180° rotation at 1° per step. A scapulocoracoid of Ardea
100 herodias was CT scanned for comparison, using a Siemens Sensation 64 at 80 KV, 90.00 mAs, a
101 pixel size of 0.502 mm and slice increment of 1.00 mm. Images were processed with Mimics
102 14.0.
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104 Results
105 Systematic Paleontology
106 Aves Linnaeus, 1758
107 Ornithurae Haeckel, 1866
108 Ornithurine G (cf. Cimolopteryx)
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110 Locality
111 RTMP BB010 (BB = Bonebed), 12U 465507: 5621617 (50.74531°N 111.488896°W),
112 Dinosaur Park Formation, Belly River Group (Campanian), Dinosaur Provincial Park, Alberta,
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113 Canada. Detailed locality and stratigraphic information on the site is registered at the Royal
114 Tyrrell Museum. BB010 is a vertebrate microfossil site in the middle to upper Dinosaur Park
115 Formation, below the Lethbridge Coal Zone (Eberth 1990; Tanke 1999). Based on revised
116 stratigraphic correlations from Fowler (2017), the age of the site can be estimated as between
117 76.6–76.1 Ma.
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119 Description
120 UALVP 55089 (Fig. 1) consists of the omal end of an avian left coracoid. The fragment is
121 24.7 mm in length. The scapular cotyle is 4.4 mm in diameter, strongly concave and circular in
122 outline, and slightly flattened along the circumference near the sulcus supracoracoideus. The
123 cotylar rim has been largely worn away, partially exposing internal structures within the bone.
124 The coracoid shaft is slender, dorsoventrally compressed, and elliptical in cross-section. The
125 supracoracoideus nerve foramen is positioned caudomedial to, and roughly half the diameter of
126 the cotyle away from, the scapular cotyle. In dorsal view, the foramen is positioned midway
127 within an elongate groove running along the medial edge of the cotyle and directed towards the
128 apex of the procoracoid process. The maximum craniocaudal length of the humeral articular
129 facet is 9.7 mm. Field et al. (2013) showed that this measurement is strongly correlated with
130 body mass, and following comparison to similar-sized examples, UALVP 55089 is estimated to
131 have been roughly equivalent in mass to a large gull, e.g. Larus marinus (Charadriiformes:
132 Laridae). The humeral articular facet is positioned cranial to the scapular cotyle. A distinct lateral
133 apex projects from the caudal-most edge of the humeral articular facet (Fig. 1). A portion of the
134 facet also extends caudomedially to envelope the scapular cotyle, forming a ridge that is concave
135 in profile and extends to the lateral edge of the scapular cotyle (Fig. 1,C). In dorsal view, the tip
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136 of the procoracoid process projects craniomedially and forms a slight hook. In medial view, the
137 procoracoid process is also slightly deflected ventrally. The dorsal portion of the sulcus
138 supracoracoideus extends farther cranially than the ventral portion. The surface of the sulcus
139 supracoracoideus is largely flat, although the dorsal surface directly caudal to the base of the
140 acrocoracoid process is weakly concave. Only the base of the acrocoracoid process is preserved,
141 although it may have extended ventrally beyond the coracoid shaft. The base also has a slight
142 medial curvature and may have overhung the sulcus supracoracoideus. The caudal portion of the
143 acrocoracohumeral ligament scar is visible along the dorsocranial edge of the humeral articular
144 facet.
145 The internal structure of the coracoid of UALVP 55089 is visible within breaks and some
146 worn areas, particularly a break on the acrocoracoid process (Fig. 1,D). This break reveals
147 extensive endosteal struts forming small chambers throughout the coracoid body. A micro-CT
148 scan of UALVP 55089 shows a large hollow chamber extending from just below the scapular
149 cotyle into the acrocoracoid process, in addition to further endosteal struts (Fig. 1). Many of the
150 chambers are connected, suggesting the coracoid was pneumatic, although an external pneumatic
151 foramen is not preserved. A small canal is present on the medial edge of the procoracoid process
152 (Fig. 1,D). This canal was likely exposed by wear of the bone surface, as it penetrates the bone
153 for a short distance and does not open into any larger internal chambers.
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155 Remarks
156 UALVP 55089 is diagnosed as an ornithurine bird on the basis of the cranially-shifted
157 humeral articular facet relative to the cotyle (Longrich 2009), well-developed acrocoracoid
158 process, distinct procoracoid process, and humeral articular facet angled relative to scapular
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159 cotyle (Dyke et al. 2011; McLachlan 2017). Longrich (2009) suggested that an intermuscular
160 ridge on the ventrolateral surface of the coracoid shaft is an additional ornithurine trait, but this
161 feature is not preserved on this specimen.
162 UALVP 55089 is similar in overall appearance to members of the Cimolopterygidae, with
163 the exception of Lamarqueavis (Agnolin, 2010). These include Ceramornis major, Cimolopteryx
164 maxima, Cimolopteryx minima, Cimolopteryx petra, and Cimolopteryx rara (Brodkorb 1963;
165 Hope 2002; Longrich et al. 2011). It also resembles a number of partial ornithurine coracoids
166 from other regions in North America, all of which are from the Maastrichtian. These include
167 SMNH P1927.936, referred to Cimolopteryx sp. by Tokaryk and James (1989); TMP
168 1993.019.0001, referred to “Ornithurine E” by Longrich (2009); TMP 1993.116.0001, referred to
169 Cimolopteryx sp. by Hope (2002) and to “Ornithurine F” by Longrich (2009)); UCMP 53963,
170 referred to “Ornithurine A”; and SDSM 64281, referred to “Ornithurine C” by Longrich et al.
171 (2011). The derived ornithurine Iaceornis marshi (YPM 1734) from the late Santonian/early
172 Campanian is also compared (Clarke 2004; Mayr 2016). Lastly, UALVP 55089 is compared to
173 the neornithine Anatalavis oxfordi Olson 1999, an Eocene anseriform from England, for which
174 largely complete coracoids are known, including BMNH A5922. Fossil birds that are not
175 included in this comparison share less in common with UALVP 55089, such as the Campanian-
176 Maastrichtian Palintropus, which lacks a procoracoid process in contrast to all other taxa
177 discussed here (Hope 2002; Longrich 2009; Longrich et al. 2011). UALVP 55089 is
178 distinguished from these other specimens by a particular set of features. It is larger than all other
179 Cimolopteryx coracoids, with Ceramornis major and Cimolopteryx maxima closest in size,
180 followed by Cimolopteryx rara, Cimolpteryx petra, and Cimolpteryx minima. It is also larger
181 than the coracoids of Iaceornis and of Ornithurines A, E, and F, and only slightly smaller than
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182 Anatalavis and Ornithurine C (Longrich et al. 2011). The omal end of the coracoid is only
183 slightly shorter than in Ornithurine C (SDSM 64281) from the late Maastrichtian of Montana.
184 The latter was tentatively assigned to Graculavus augustus, due to its large size (Longrich et al.
185 2011).
186 The coracoid shaft is more robust than those of Cimolopteryx petra, Cimolopteryx rara,
187 and Iaceornis, although less so than those of Anatalavis, Cimolopteryx minima and Ornithurine
188 A (UCMP 53963) (Hope 2002; Longrich et al. 2011). The shafts of Ornithurine E (TMP
189 1993.019.0001) and Ornithurine F (TMP 1993.116.0001) from Longrich (2009) are not well-
190 preserved and therefore not comparable. SMNH P1927.936 is incomplete, although the specimen
191 was described by Tokaryk and James (1989) as being most similar to Cimolopteryx rara, which
192 our comparisons support. Cimolopteryx petra was described by Hope (2002) and also closely
193 resembles SMNH P1927.936. Specimens of Cimolopteryx maxima do not preserve the coracoid
194 shaft and so cannot be compared.
195 The procoracoid process of UALVP 55089 is roughly similar to preserved examples of this
196 structure in other specimens, with minor variation in the degree to which the process hooks
197 medially and ventrally. In Anatalavis the procoracoid process is longer and the tip has a strong
198 ventral curvature (Olson 1996). The procoracoid process of Ceramornis appears to be less
199 developed than in Cimolopteryx and UALVP 55089, although this could also be due to wear. In
200 Iaceornis the procoracoid process is markedly smaller than the other examples compared here
201 (Clark 2004; Bell and Everhart 2011). Unlike Cimolopteryx rara, UALVP 55089 lacks the
202 distinct ridge or strut extending from the procoracoid into the sulcus supracoracoideus as
203 described by Longrich et al. (2011).
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204 The dorsal opening of the supracoracoid foramen in UALVP 55089 is situated in the center
205 of a conspicuous depression or groove that extends towards the procoracoid. This feature is
206 absent in most other specimens that preserve supracoracoid foramina, although Ceramornis
207 major, Cimolopteryx rara, Ichthyornis dispar, Ornithurine D (UCMP 187207) from Longrich et
208 al. (2011), which is otherwise dissimilar to UALVP 55089), and Ornithurine E (TMP
209 1993.019.0001) may show weakly-developed, less extensive grooves (Brodkorb 1963; Hope
210 2002; Clarke 2004; Longrich 2009; Longrich et al. 2011).
211 The scapular cotyle of UALVP 55089 is circular in outline, although as in many other
212 specimens the edge adjacent to the sulcus supracoideus is relatively straight. It is most similar in
213 shape to those of Ceramornis, Cimolopteryx maxima, Iaceornis, and Ornithurine A (UCMP
214 53963) (Longrich et al. 2011). The cotyla of Cimolpteryx minima, Cimolopteryx rara, and
215 Ornithurine C (SDSM 64281) are more slightly more sub-circular. The cotyle of Anatalavis
216 oxfordi is damaged but also appears to be sub-circular (Fig. 4). The cotyla of Ornithurine E
217 (TMP 1993.019.0001) and Ornithurine F (TMP 1993.116.0001) described in Longrich (2009)
218 are transversely elongate, and that of the former extends onto the procoracoid, which is absent in
219 UALVP 55089.
220 A distinct lateral apex projects from the caudal margin of UALVP 55089 (Fig. 1). This
221 feature is shared with Ornithurine A (UCMP 53963), C (SDSM 64281), Ornithurine E (TMP
222 1993.019.0001), and Ornithurine F (TMP 1993.116.0001) (Longrich 2009; Longrich et al. 2011),
223 and possibly Iaceornis as well, although the lateral margin of the humeral articular facet in
224 UALVP 55089 is less curved than in these taxa. The lateral apex is also less pronounced and
225 more rounded in Ornithurine A (UCMP 53963) and C (SDSM 64281). This lateral apex is absent
226 in Anatalavis, Ceramornis, Cimolopteryx maxima, Cimolopteryx minima, Cimolopteryx petra,
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227 and Cimolopteryx rara (Hope 2002; Longrich et al. 2011). The extension of the humeral articular
228 facet that forms a ridge and envelopes the scapular cotyle in UALVP 55089 is also present in
229 compared specimens, whereas the convave profile of the ridge is present in Ceramornis,
230 Ornithurine E (TMP 1993.019.0001), and Ornithurine F (TMP 1993.116.0001), and to a lesser
231 degree in Cimolopteryx minima and Cimolpteryx rara. The degree of deflection of the humeral
232 articular facet relative to the scapular cotyle is moderate in UALVP 55089; the deflection is less
233 than in Anatalavis, Cimolopteryx minima, Cimolopteryx rara, and Ornithurine A (UCMP 53963)
234 and Ornithurine C (SDSM 64281). The facet is more deflected than in Cimolopteryx petra, and
235 most similar to Ceramornis, Cimolopteryx maxima, Ornithurine E (TMP 1993.019.0001), and
236 Ornithurine F (TMP 1993.116.0001). Iaceornis is noted as having a concave surface of the
237 humeral articular facet (Clark 2004), possibly similar to Cimolopteryx maxima and Ceramornis,
238 whereas those of UALVP 55089 and other comparable Cretaceous ornithurines are largely flat to
239 weakly concave.
240 In medial view, the omal end of the coracoid is long and straight in UALVP 55089, giving
241 it a robust, pillar-like appearance. Ornithurine A (UCMP 53963) Cimolopteryx minima,
242 Cimolopteryx petra, and Cimolopteryx rara are similar, although the sulcus supracoracoideus is
243 shorter in Ornithurine A (UCMP 53963) and Cimolopteryx rara. The surface of the sulcus
244 supracoracoideus in these taxa is also flat to weakly concave as in UALVP 55089, whereas this
245 surface is more strongly concave in Anatalavis, Ceramornis, Cimolopteryx maxima, Iaceornis,
246 Ornithurine C (SDSM 64281), Ornithurine E (TMP 1993.019.0001), and Ornithurine F (TMP
247 1993.116.0001). Although the acrocoracoid process is not preserved, the slight ventral extension
248 of its base in UALVP 55089 is also present in Cimolopteryx rara and Cimolopteryx petra (Hope
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249 2002), as well as in Ornithurine A (UCMP 53963) and Ornithurine C (SDSM 64281). In
250 contrast, the acrocoracoid process in Iaceornis projects more medially (Bell and Everhart, 2011).
251 Micro-CT scans of UALVP 55089 show large, hollow cavities and extensive endosteal
252 strutting (Fig. 2). Although taken at a lower resolution, CT scans of the coracoid of Ardea
253 herodias show similar structures, including a large hollow chamber near the center of the
254 coracoid head (Fig. 2, E).
255
256 Discussion
257 Because of its age (76.6-76.1 Ma), its larger size, and its combination of morphological
258 characteristics, this specimen likely represents a new taxon. Additionally, Longrich et al. (2011)
259 suggested that coracoids are largely consistent in form within species, so that any variation can
260 be attributed to taxonomic differences. However, a single broken element does not warrant the
261 establishment of a generic name. UALVP 55089 is referred to here as Ornithurine G (cf.
262 Cimolopteryx) due to its close similarity to members of the genus Cimolopteryx following the
263 naming system of Longrich (2009) and Longrich et al. (2011). As the fossil record of Cretaceous
264 ornithurines is sparse and many remain unnamed, maintaining this consistency is practical and
265 will simplify the process of referring to these fragmentary elements. It is also recommended that
266 further use of this naming system to describe new fragmentary specimens should proceed
267 alphabetically, as was done here.
268
269 Pneumaticity of Ornithurine G (cf. Cimolopteryx)
270 Birds are well-known for their characteristic pneumatic skeleton, where pneumatic
271 diverticula pervade hollow spaces within the bone. The coracoids of the ornithurines Iaceornis
272 and Ichthyornis, however, are apneumatic (Clarke 2004). A pneumatic coracoid is a
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273 synapomorphy of neornithine birds, occurring in some members of Anseriformes, as well as
274 Paleognathae and Galliformes (Clarke 2004). The fossil record of neornithine birds in the
275 Cretaceous is sparse, often contested, and mostly based on fragmentary elements, with the best
276 example so far being the Maastrichtian fossil anseriform Vegavis from Antarctica, clearly
277 signifying a Mesozoic origin for Neornithes (Hope 2002; Clarke 2005; Mayr 2016).
278 Pneumaticity is unknown in Cimolopterygidae and Ornithurines A through F. Micro-CT scans of
279 Ornithurine G (cf. Cimolopteryx) show that the internal structure of the supracoracoideus nerve
280 foramen is a single canal with no accessory foramina. Large, hollow cavities and extensive
281 endosteal strutting consistent with pneumaticity are also observable (Fig. 2). This suggests that
282 Ornithurine G (cf. Cimolopteryx) should be placed within Neornithes; however, CT scans of the
283 apneumatic coracoid of Ardea herodias show similar structures, including a large hollow
284 chamber near the center of the coracoid head (Fig. 2, H, I) (Zelenkov 2011). Comparisons with
285 Micro-CT scans of the pneumatic coracoid of Grus canadensis likewise show similarities to
286 Ardea herodias and Ornithurine G (cf. Cimolopteryx), including hollow chambers located at the
287 omal end (Fig. 2, E, F, G) (Olson 1972). Similar examinations performed on the vertebrae of
288 extant taxa show that the most dependable parameter for identifying pneumaticity conclusively is
289 the occurrence of cortical openings or foramina connecting internally to large hollow chambers
290 in the bone (O’Connor 2006). The same may be true for avian coracoids; however, Ornithurine
291 G (cf. Cimolopteryx) is missing the sternal region and much of the coracoid shaft. It is therefore
292 unknown if a pneumatic foramen was present, preventing definitive placement within
293 Neornithes. Cimolopteryx rara (YPM 1805) preserves the sternal portion of the coracoid;
294 however, a pneumatic foramen is absent, and this may also have been the case for other members
295 of the genus and Ornithurine G (cf. Cimolopteryx).
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296
297 Cimolopteryx and Cimolopterygidae
298 Agnolin (2010) placed Lamarqueavis australis (MML 207) and Lamarqueavis sp.
299 (Ornithurine B; UALVP 47943, or the “Irvine Bird”) from Longrich (2009) in Cimolopterygidae
300 based on the following traits that unite the family: humeral articular facet ventrally oriented,
301 procoracoid process sternally-extended and developed as a thin lamina, and supracoracoid nerve
302 foramen large and positioned ventrally. However, many of these features are unique to
303 Lamarqueavis and not found in Cimolopteryx. Any difference in orientation of the humeral
304 articular facet between Lamarqueavis, Cimolopteryx, and other ornithurines is not evident in the
305 figures (Agnolin 2010). The thin lamina that comprises the procoracoid process in Lamarqueavis
306 extends farther sternally than in any other member of Cimolopterygidae and was described as
307 autapomorphic for the genus. As such, this particular trait cannot be used to diagnose the family
308 as a whole. The lamina also increases the width of the coracoid shaft in Lamarqueavis, extending
309 the distance between the tip of the procoracoid process and the scapular cotyle relative to other
310 cimolopterygid coracoids, and to Ornithurines A, C, E, F, and G cf. Cimolopteryx (Fig. 4;
311 Longrich 2009; Longrich et al. 2011). The ventrally positioned supracoracoid nerve foramen
312 may refer to the position of the foramen relative to the scapular cotyle. This trait is present in
313 other ornithurines including Iaceornis, Ichthyornis, Ornithurines A, C, D, E, F, and G cf.
314 Cimolopteryx, and is therefore not a synapomorphy of Lamarqueavis and Cimolopterygidae. The
315 supracoracoid nerve foramen in Lamarqueavis is also proportionately large compared to any
316 cimolopterygid. Likewise, the foramen is situated at a markedly greater distance sternally from
317 the scapular cotyle than in other members of Cimolopterygidae (Fig. 4 and Agnolin 2010).
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318 Agnolin (2010) also reassigned Cimolopteryx minima and Cimolopteryx petra to
319 Lamarqueavis based on a combination of unique traits that Cimolopteryx minima, Cimolopteryx
320 petra, Lamarqueavis australis, and Lamarqueavis sp. purportedly share, including: procoracoid
321 process large, caudally-extended, and straight or convex along its medial margin; humeral
322 articular facet subrectangular in shape, and scapular cotyle transversely elongate. However, these
323 are refuted here as not all members of Lamarqueavis share these features. The large, convex
324 medial margin of the procoracoid process is an autapomorphy of Lamarqueavis australis alone
325 (Agnolin 2010), and in Cimolopteryx minima and Cimolopteryx petra the procoracoid margins
326 are concave, not convex (Brodkorb 1963; Longrich et al. 2011). The procoracoid in
327 Lamarqueavis sp. appears to resemble that of Lamarqueavis australis, although its edge is
328 broken and its exact shape is difficult to discern (Longrich 2009). The shapes of the humeral
329 articular facets in Cimolopterygidae and the indeterminate Cretaceous ornithurines show a range
330 of subtle variation. The dorsal and ventral edges of the humeral articular facets of Cimolopteryx
331 minima, Cimolopteryx petra, and Lamarqueavis sp. are rounded rather than subrectangular
332 (Brodkorb 1963; Longrich 2009; Agnolin 2010; Longrich et al. 2011). As well, the scapular
333 cotyla of Cimolopteryx minima and Cimolopteryx petra are ovate to subtriangular, not
334 transversely elongate and strongly tear-drop shaped as in Lamarqueavis australis. The cotyle of
335 Lamarqueavis sp. is also circular, not elongate.
336 Additional characteristics of Lamarqueavis include a procoracoid process with a strong
337 ventral orientation towards the sulcus supracoracoideus in Lamarqueavis australis, a condition
338 also seen in Ichthyornis and Ornithurine D (Clarke 2004; Agnolin 2010; Longrich et al. 2011).
339 The humeral articular facet of Lamarqueavis australis is positioned cranial to the scapular cotyle
340 as in Ichthyornis and Ornithurine D (Clarke 2004; Longrich et al., 2011). In contrast, the humeral
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341 articular facet is positioned anterolateral to the cotyle in Cimolopterygidae, as well as in
342 Ornithurine G (cf. Cimolopteryx) (Fig. 3). It is not clear whether the acrocoracoid, typically
343 longer in other members of Cimolopterygidae, is complete or fragmentary. For these reasons,
344 Cimolopteryx minima and Cimolopteryx petra are not considered in this paper to be species of
345 Lamarqueavis. Mayr (2016) also noted that Lamarqueavis more closely resembles the
346 neornithines Psophiidae and Messelornithidae (Gruiformes) than Cimolopterygidae. As a result,
347 the precise relationships of Lamarqueavis remain unclear.
348 Brodkorb (1963) refers Cimolopterygidae to Charadriiformes, a conclusion cautiously
349 supported by Hope (2002). Furthermore, Brodkorb (1963) remarks that the coracoid of
350 Cimolopteryx rara appears most closely comparable to that of the Recurvirostridae
351 (Charadriiformes: Charadrii), although the details of this similarity are not presented. Instead, a
352 number of differences between Cimolopteryx rara and Recurvirostridae are listed, notably a
353 long, curved procoracoid process, which is present in other Charadriiformes, such as Larus
354 delawarensis (Charadriiformes: Laridae), Phalaropus tricolor (Charadriiformes: Scolopacidae),
355 and Uria aalge (Charadriiformes: Alcidae). The acrocoracoid process of Recurvirostra
356 americana (Recurvirostridae) is also proportionally larger, more robust, and much more medially
357 hooked than that of Cimolopteryx. Overall, Cimolopteryx rara resembles only members of its
358 genus as well as the unnamed Cretaceous ornithurine coracoids, including UALVP 55089, more
359 than members of Charadriiformes. Shufeldt (1914), after comparing Cimolopteryx rara with a
360 number of “water birds,” including members of Charadriiformes, determined that there were no
361 living representatives of the genus. However, he also suggested that Cimolopteryx rara was
362 likely a toothed bird closely related to Ichthyornis. This is an assertion not supported by
363 Longrich et al. (2011). Hope (2002) noted that Charadriiformes are particularly difficult to
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364 interpret, owing both to the presence of primitive features shared with many other neornithines,
365 and to the possession of derived traits that are also present in other semi-aquatic birds, such as
366 Pelecaniformes and Procellariiformes. Hope (2002) interpreted this mosaic-like pattern of
367 characters as indicating that Charadriiformes and other semi-aquatic birds maintained a host of
368 ancestral traits following an early, fast divergence. This may also be interpreted as convergence,
369 which could extend to other closely-related Cretaceous birds occupying similar aquatic and
370 shoreline habitats. The pes of the ornithurine Gansus was reported to show convergence with
371 neornithine diving birds, such as loons and diving ducks (Hope 2002), indicating that the
372 presence of homoplastic traits in neornithine and ornithurine birds was not unusual. Additionally,
373 traits linking cimolopterygids with modern forms, such as a deeply concave scapular cotyle, are
374 primitive for Ornithurae (Clarke 2004; Longrich 2009; Agnolin 2010). The lack of articulated
375 fossil material, the possibility of convergence or retention of plesiomorphic traits, and the
376 predominance of non-neornithine ornithurine birds in the Late Cretaceous (Fox 1974, 1983;
377 Tokaryk et al. 1997; Clarke 2004; Longrich 2006, 2009; Longrich et al. 2011; Aotsuko and Sato
378 2016; Bono et al. 2016), all suggests that there is little support for the placement of Cimolopteryx
379 or similar indeterminate coracoids within Neornithes. Thus, both the monophyly of
380 Cimolopterygidae and its inclusion within Charadriiformes lack discrete character support.
381 Cimolopterygidae is most parsimoniously considered a provisional taxon of non-neornithine
382 ornithurine birds that possess similar coracoids and may be closely related. Although Ornithurine
383 G (cf. Cimolopteryx) shares features with Cimolopteryx, the uncertainty regarding
384 Cimolopterygidae as a whole prevents a definitive referral to this group.
385
386
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387 Conclusions
388 UALVP 55089 represents a new ornithurine bird from the upper Campanian Dinosaur Park
389 formation of Alberta, larger than other similar ornithurines from the Cretaceous of North
390 America. It also represents the oldest example of a Cimolopteryx-like coracoid. UALVP 55089 is
391 therefore referred to as Ornithurine G (cf. Cimolopteryx) following the system of Longrich
392 (2009) and Longrich et al. (2011). The presence of pneumaticity cannot be established as a
393 pneumatic foramen is not preserved. Although fragmentary and difficult to assign with certainty,
394 it most closely resembles several unnamed non-neornithine ornithurines from North America,
395 many of which are similar to members of the enigmatic family Cimolopterygidae.
396
397 Acknowledgements
398 We would like to extend our gratitude to C. Scobey and J. Hudon of the Royal Alberta
399 Museum for access to coracoids of modern birds, as well as B. Strilisky of the Royal Tyrrell
400 Museum for access to fossil bird specimens. We would also like to thank Dr. A. Murray for
401 access to the Skyscan1174 Micro-CT scanner. We thank the two anonymous reviewers for their
402 comments and suggestions that helped to improve this manuscript. A special thank you to Dr.
403 Calvin R. Evans for his support. CT scans were performed by the Alberta Cardiovascular and
404 Stroke Research Centre (ABACUS) CT Facility at the University of Alberta Hospital’s
405 Mazankowski Centre. TNT 1.1 was provided by the Willi Hennig Society. S.R.M. was funded by
406 the Queen Elizabeth II Graduate Scholarship, the Dinosaur Research Institute, Alberta Lottery
407 Fund, and Alberta Historical Resources Foundation, and currently funded by NSERC. G.F.F was
408 funded by NSERC, Vanier Canada, and Alberta Innovates. P.J.C is supported by NSERC [Grant
409 # RGPIN-2017- 04715].
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410
411
412
413
414
415 References
416 Agnolin, F.L. 2010. An avian coracoid from the Upper Cretaceous of Patagonia,
417 Argentina. Studia Geologica Salmanticensia 46: 99–119.
418 Aotsuka, K., Sato, T. 2016. Hesperornithiformes (Aves: Ornithurae) from the Upper Cretaceous
419 Pierre Shale, Southern Manitoba, Canada. Cretaceous Research 63: 154-169.
420 Baumel, J.J., Witmer. L.M. 1993. Osteologia. In Handbook of avian anatomy: nomina anatomica
421 avium. Edited by J.J. Baumel, A.S. King, J.E. Breazile, H.E. Evans, and J.C. Vanden
422 Berge. 2nd ed. Publications of the Nuttall Ornithological Club 23 pp. 45–132.
423 Bell, A., Everhart, M.J. 2011. Remains of small ornithurine birds from a Late Cretaceous
424 (Cenomanian) microsite in Russell County, north-central Kansas. Kansas Academy of
425 Science, Transactions 114 (1-2):115-123.
426 Bono, R.K., Clarke, J., Tarduno, J.A., Brinkman, D. 2016. A Large Ornithurine Bird
427 (Tingmiatornis arctica) from the Turonian High Arctic: Climatic and Evolutionary
428 Implications. Scientific Reports 6.
429 Brodkorb, P. 1963. Birds from the Upper Cretaceous of Wyoming. International Ornithological
430 Congress Proceedings 19: 55–70.
431 Chiappe, L.M. 2002. Basal Bird Phylogeny: Problems and Solutions. In Mesozoic Birds Above
432 the Heads of Dinosaurs. Edited by L.M. Chiappe and L.M. Witmer. University of
433 California Press, Ltd., pp. 448–472.
Page 19 of 28
Can. J. Earth Sci.
Downloaded from www.nrcresearchpress.com by UNIVERSITY OF GLASGOW on 06/27/20. For personal use only.
20
434 Clarke, J.A., 2004. Morphology, phylogenetic taxonomy, and systematics of Ichthyornis and
435 Apatornis (Avialae: Ornithurae). Bulletin of the American Museum of Natural History
436 286: 1–179.
437 Clarke, J.A., Tambussi, C.P., Noriega, J.I., Erickson, G.M. and Ketcham, R.A. 2005. Definitive
438 fossil evidence for the extant avian radiation in the Cretaceous. Nature 433: 305–308.
439 Currie, P.J. 2005. Theropods, including birds. In Dinosaur Provincial Park: a spectacular ancient
440 ecosystem revealed. Edited by P.J. Currie and E.B. Koppelhus. Indiana University
441 Press, Bloomington and Indianapolis, pp. 367–397.
442 Dyke G., Wang X., Kaiser G. 2011. Large fossil birds from a Late Cretaceous marine turbidite
443 sequence on Hornby Island (British Columbia). Canadian Journal of Earth Sciences 48:
444 1489–1496.
445 Eberth, D.A. 1990. Stratigraphy and sedimentology of vertebrate microfossil sites in the
446 uppermost Judith River Formation (Campanian), Dinosaur Provincial Park, Alberta,
447 Canada. Palaeogeography, Paleoclimatology, Palaeoecology 78: 1–2, 1–36.
448 Eberth, D.A. 1996. Origin and significance of mudfilled incised valleys (Upper Cretaceous) in
449 southern Alberta, Canada. Journal of the International Association of Sedimentologists
450 43 (3): 459477.
451 Eberth, D.A. 2005. The geology. In Dinosaur Provincial Park: A Spectacular Ancient Ecosystem
452 Revealed. Edited by P.J. Currie and E.B. Koppelhus. Indiana University Press:
453 Bloomington and Indianapolis, pp. 54-82.
454 Field, D.J., Lynner, C., Brown, C., Darroch S.A.F. 2013. Skeletal Correlates for Body Mass
455 Estimation in Modern and Fossil Flying Birds. PLOS ONE 8 (11): e82000.
Page 20 of 28
Can. J. Earth Sci.
Downloaded from www.nrcresearchpress.com by UNIVERSITY OF GLASGOW on 06/27/20. For personal use only.
21
456 Fowler, D.W. 2017. Revised geochronology, correlation, and dinosaur stratigraphic ranges of the
457 Santonian-Maastrichtian (Late Cretaceous) formations of the Western Interior of North
458 America. PLOS ONE 12 (11): e0188426.
459 Fox, R. C. 1974. A Middle Campanian, nonmarine occurrence of the Cretaceous toothed
460 bird Hesperornis Marsh. Canadian Journal of Earth Sciences 11: 1335–1338.
461 Fox, R. C. 1984. Ichthyornis (Aves) from the early Turonian (Late Cretaceous) of Alberta.
462 Canadian Journal of Earth Sciences 21: 258–260.
463 Gauthier, J., de Queiroz, K. 2001. Feathered dinosaurs, flying dinosaurs, crown dinosaurs, and
464 the name 'Aves'. In New Perspective on the Origin and Evolution of Birds: Proceedings
465 of the International Symposium in Honor of John H. Ostrom. Edited by J. Gauthier and
466 L.F. Gall. Peabody Museum of Natural History, pp. 741.
467 Hope, S., 2002. The Mesozoic record of Neornithes (modern birds). In: Chiappe, L.M., Witmer,
468 L.M. (Eds.), Mesozoic Birds: Above the Heads of Dinosaurs. University of California
469 Press, pp. 339–388.
470 Longrich, N. 2006. An ornithurine bird from the Late Cretaceous of Alberta, Canada. Canadian
471 Journal of Earth Sciences 43: 1–7.
472 Longrich, N. 2009: An ornithurine-dominated avifauna from the Belly River Group
473 (Campanian, Upper Cretaceous) of Alberta, Canada. Cret. Res., 30: 161–177.
474 Longrich, N.R., Tokaryk, T. and Field, D.J. 2011. Mass extinction of birds at the Cretaceous–
475 Paleogene (K–Pg) boundary. Proceedings of the National Academy of Sciences, 108:
476 1525315257.
Page 21 of 28
Can. J. Earth Sci.
Downloaded from www.nrcresearchpress.com by UNIVERSITY OF GLASGOW on 06/27/20. For personal use only.
22
477 McLachlan, S.M. S., Kaiser, G.W.; Longrich, N.R. 2017. Maaqwi cascadensis: A large, marine
478 diving bird (Avialae: Ornithurae) from the Upper Cretaceous of British Columbia,
479 Canada. PLOS ONE 12 (12): e0189473.
480 Marsh, O.C., 1880. Odontornithes, a Monograph on the Extinct Birds of North America.
481 Government Printing Office, Washington.
482 Marsh, O.C., 1892. Notes on Mesozoic vertebrate fossils. American Journal of Science 55: 171–
483 175. 173 plates.
484 Mayr, G. 2016. Avian Evolution: The Fossil Record of Birds and its Paleobiological
485 Significance. John Wiley & Sons, Ltd, Chichester, UK.
486 O’Connor, P.M. 2006. Postcranial pneumaticity: an evaluation of soft-tissue influences on the
487 postcranial skeleton and the reconstruction of pulmonary anatomy in archosaurs.
488 Journal of Morphology 267: 1199 –1226.
489 O’Connor, J.K., Zhou Z. 2012. A redescription of Chaoyangia beishanensis (Aves) and a
490 comprehensive phylogeny of Mesozoic birds. Journal of Systematic Palaeontology 11
491 (7): 889-906.
492 Olson, S.J. 1972. Osteology for the Archaeologist, American Mastadon and the Woolly
493 Mammoth; North American Birds: Skulls and Mandibles; North American Birds:
494 Postcranial Skeletons. Peabody Museum Press, Cambridge, MA.
495 Olson, S. L. 1996. The anseriform relationships of Anatalavis Olson and Parris (Anseranatidae),
496 with a new species from the Lower Eocene London Clay. In Avian Paleontology at the
497 Close of the 20th Century: Proceedings of the 4th International Meeting of the Society
498 of Avian Paleontology and Evolution, Washington, D.C., 4-7 June 1996. Smithsonian
499 Contributions to Paleobiology 89.
Page 22 of 28
Can. J. Earth Sci.
Downloaded from www.nrcresearchpress.com by UNIVERSITY OF GLASGOW on 06/27/20. For personal use only.
23
500 Shufeldt, R.W.1915. Fossil Birds in the Marsh Collection of Yale University. Transactions
501 of the Connecticut Academy of Arts and Sciences 19:1–109.
502 Tanke, D., H. 1999. Relocating the lost quarries of Dinosaur Provincial Park, Alberta, Canada. In
503 Dinosaur Provincial Park: a spectacular ancient ecosystem revealed. Edited by P.J.
504 Currie and E.B. Koppelhus. Indiana University Press, Bloomington, IN. pp. 54–82.
505 Tokaryk, T. T., and P. C. James. 1989. Cimolopteryx sp. (Aves, Charadriiformes) from the
506 Frenchman Formation (Maastrichtian), Saskatchewan. Canadian Journal of Earth
507 Sciences 26: 2729–2730.
508 Tokaryk, T. T., S. L., Cumbaa, and J. E. Storer. 1997. Early late Cretaceous birds from
509 Saskatchewan, Canada: the oldest diverse avifauna known from North America. Journal
510 of Vertebrate Paleontology 17: 172-176.
511 Zelenkov, N.V. 2011. Ardea sytchevskayae sp.nov., a new heron species (Aves:Ardeidae) from
512 the Middle Miocene of Mongolia. Paleontological Journal 45: 572–579.
513 Zhou, Z., Clarke, J., Zhang, F. 2008. Insight into diversity, body size and morphological
514 evolution from the largest Early Cretaceous enantiornithine bird. Journal of Anatomy
515 212: 565–577.
516
517
518
519
520
521
522
523
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524
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526
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528
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530
531
532 Figure Captions
533 Figure 1. UALVP 55089, omal end of left coracoid. Dinosaur Park Formation. A, dorsal, B,
534 ventral, C, lateral, D, medial views. Abbreviations: acr, base of acrocoracoid process; als,
535 acrocoracohumeral ligament scar; g, groove; haf, humeral articular facet; la; lateral apex; pro,
536 procoracoid process; sc, scapular cotyle; snf, supracoracoid nerve foramen; ss, sulcus
537 supracoracoideus.
538
539 Figure 2. MicroCT scan of UALVP 55089, Grus canadensis, and Ardea herodias. A large
540 central chamber is present near the center of the coracoid head, connecting to a series of smaller
541 chambers that pervade the entirety of the bone. These vacuities are demarcated by a series of
542 endosteal struts. This is compared with the non-pneumatic coracoid of Ardea herodias, where
543 red indicates open space within the bone. Cross-sections of UALVP 55089 in A, longitudinal, B,
544 transverse, C, coronal, D, longitudinal views. Cross-sections of Grus canadensis in A,
545 transverse, F, coronal, G, sagittal views. Ghosting is a result of soft tissue remnants. 3D model of
546 Ardea herodias scapulocoracoid in H, lateral and I, medial views. Images not to scale.
547
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548 Figure 3. Comparison of UALVP 55089 (Ornithurine G (cf. Cimolopteryx)), Cimolopteryx rara,
549 Cimolopteryx petra, Anatalavis oxfordi, Lamarqueavis australis, and Lamarqueavis sp. A,
550 Dorsal view of UALVP 55089 (Ornithurine G (cf. Cimolopteryx)), B, Cimolopteryx rara (UCMP
551 53963); modified from Brodkorb (1963), C, Cimolopteryx petra (AMNH 21911); modified from
552 Longrich et al. (2011), D, Anatalavis oxfordi (BMNH A5922); modified from Olson (1999), E,
553 Lamarqueavis australis (MML 207); modified from Agnolin (2010), F, Lamarqueavis
554 sp.(UALVP 47493); modified from Longrich (2009).
555
556
557
558
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Figure 1. UALVP 55089, omal end of left coracoid. Dinosaur Park Formation. A, dorsal, B, ventral, C, lateral,
D, medial views. Abbreviations: acr, base of acrocoracoid process; als, acrocoracohumeral ligament scar; g,
groove; haf, humeral articular facet; la; lateral apex; pro, procoracoid process; sc, scapular cotyle; snf,
supracoracoid nerve foramen; ss, sulcus supracoracoideus.
234x227mm (300 x 300 DPI)
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Figure 2. MicroCT scan of UALVP 55089, Grus canadensis, and Ardea herodias. A large central chamber is
present near the center of the coracoid head, connecting to a series of smaller chambers that pervade the
entirety of the bone. These vacuities are demarcated by a series of endosteal struts. This is compared with
the non-pneumatic coracoid of Ardea herodias, where red indicates open space within the bone. Cross-
sections of UALVP 55089 in A, longitudinal, B, transverse, C, coronal, D, longitudinal views. Cross-sections
of Grus canadensis in A, transverse, F, coronal, G, sagittal views. Ghosting is a result of soft tissue
remnants. 3D model of Ardea herodias scapulocoracoid in H, lateral and I, medial views. Images not to
scale.
1200x935mm (72 x 72 DPI)
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Comparison of UALVP 55089 (Ornithurine G (cf. Cimolopteryx)), Cimolopteryx rara, Cimolopteryx petra,
Anatalavis oxfordi, Lamarqueavis australis, and Lamarqueavis sp. A, Dorsal view of UALVP 55089
(Ornithurine G (cf. Cimolopteryx)), B, Cimolopteryx rara (UCMP 53963); modified from Brodkorb (1963), C,
Cimolopteryx petra (AMNH 21911); modified from Longrich et al. (2011), D, Anatalavis oxfordi (BMNH
A5922); modified from Olson (1999), E, Lamarqueavis australis (MML 207); modified from Agnolin (2010),
F, Lamarqueavis sp.(UALVP 47493); modified from Longrich (2009).
399x119mm (300 x 300 DPI)
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... Total Cretaceous ornithurines such as Iaceornis or Cimolopteryx-like taxa known mostly from coracoids (Hope, Chiappe & Witmer, 2002;Agnolin, 2010;Longrich, Tokaryk & Field, 2011;Mohr et al., 2021), in which the glenoid is situated cranial to the scapular cotyle, a condition shared with most crown-group birds. ...
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Book
Knowledge of the evolutionary history of birds has much improved in recent decades. Fossils from critical time periods are being described at unprecedented rates and modern phylogenetic analyses have provided a framework for the interrelationships of the extant groups. This book gives an overview of the avian fossil record and its paleobiological significance, and it is the only up-to-date textbook that covers both Mesozoic and more modern-type Cenozoic birds in some detail. The reader is introduced to key features of basal avians and the morphological transformations that have occurred in the evolution towards modern birds. An account of the Cenozoic fossil record sheds light on the biogeographic history of the extant avian groups and discusses fossils in the context of current phylogenetic hypotheses. This review of the evolutionary history of birds not only addresses students and established researchers, but it may also be a useful source of information for anyone else with an interest in the evolution of birds and a moderate background in biology and geology.
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