Saturday, May 29, 2010

Palintropus is not a crown bird

When it comes to crown Aves, I'm less sure of my self than I am for other theropods.  This is because the vast majority of modern species are not described osteologically, and I'm still gathering references on the Tertiary species.  Mesozoic Aves are generally extremely fragmentary of course, with even the most complete specimens (Vegavis, Polarornis) being only partial skeletons.  With that caveat in mind, here are my thoughts on Palintropus...

Palintropus Brodkorb, 1970

Diagnosis- (after Longrich, 2009) acrocoracoid process massive and knob-like (also in Gansus and Ichthyornis); edge of humeral articular facet with a prominent lip in ventral view (also in Yixianornis); prominent scar inside supracoracoid sulcus (unknown in most non-avian euornithines).

Other diagnoses- Marsh (1892) first noted the absent procoracoid process as diagnostic, but this is shared with Apsaravis.
Here I interpret the very large, centrally and distally placed supracoracoid foramen noted as diagnostic by Hope (2002) as the proximal edge of a dorsal coracoid fossa as in Apsaravis. This same feature was described as "prominent dorsal groove in coracoid shaft" by Longrich (2009).
Longrich also included the supracoracoid foramen opening into a medial groove of the coracoid shaft, which is shared with Apsaravis.

Palintropus sp. nov. proximal coracoid RTMP 88.116.1, after Longrich (2009).

Comments- Marsh (1892) originally included retusus in Cimolopteryx, as C. retusa. Shufeldt (1915) noted it was not referrable to Cimolopteryx and probably not even closely related, though he felt it was too fragmentary for further evaluation. Brodkorb (1963) first removed it to Apatornis, which he viewed as an ichthyornithine. He then (1970) placed it in a new genus Palintropus, which he believed was a cimolopterygid charadriiform.

Palintropus a galliform? Hope (2002) questionably referred this taxon to Galliformes. This was based on the reduced procoracoid process, coracoid facet for scapula placed entirely distal to glenoid. Several other characters were listed in Hope's Galliformes diagnosis as being reasons why she placed "specimens below" (consisting solely of Palintropus) in that order, but are eithjer undescribed (coracoid neck with stout and triangular cross section) or unknown (elongate coracoid shaft; narrow sternal end of coracoid; rudimentary lateral process) in that genus. She also noted the acrocoracoid was similar in size to galliforms (larger than tinamiforms, smaller than anseriforms and most neoavians), the absence of a pneumatic foramen is unlike tinamiforms, and the laterally positioned coracoid tubercle which merges with the glenoid is similar to galliforms. However, the procoracoid process is also absent in Patagopteryx and (as noted by Longrich, 2009) Apsaravis, while it is still present though reduced in basal galliforms like Paraortygoides, Paraortyx and Ameripodius. I also note Apsaravis has a coracoid facet placed distal to the glenoid. Lack of coracoid pneumatization is present in all non-avians (except perhaps Jixiangornis and Jianchangornis). The laterally positioned coracoid tubercle that merges with the glenoid is also found in galliforms, tinamiforms, Lithornis, Patagopteryx, Yixianornis, Jianchangornis, Ichthyornis and Ambiortus, so seems symplesiomorphic for Aves. Gansus and Ichthyornis also have moderate sized acrocoracoid processes.

Hope referred it questionably to the basal galliform family Quercymegapodiidae based on the large free lateral flange on the coracoid glenoid, further reduced procoracoid process (only with Quercymegapodius and not Ameripodius), and scar within the supracoracoid sulcus (only verified in Ameripodius). Also she correctly noticed the deep cup-like scapular facet is unlike crown galliforms. Apsaravis, Ichthyornis, Gansus, Yixianornis, Patagopteryx and Archaeorhynchus also have a large lateral flange on the coracoid glenoid. Almost all non-avian euornithines also have scapular cotyla which are deeper than those of crown galliforms. The texture of the supracoracoid sulcus is generally indeterminable in non-avian euornithines, even when they expose the sulcus as in Yixianornis. Hope, Mayr (2009) and Longrich all noted that it was unlike Tertiary Galliformes in having a supracoracoid foramen, and Longrich stated it differed further in lacking a strongly hooked acrocoracoid.

Thus Palintropus does not share any characters with galliforms not seen in Apsaravis except for the larger acrocoracoid (which is also seen in some non-avian euornithines). As Palintropus has some characters which exclude it from Galliformes, and the only character shared with a quercymegapodiid (the supracoracoid sulcus scar) is indeterminate in Apsaravis and most other non-avian euornithines, it is near certainly not a member of Quercymegapodiidae.

Palintropus related to Apsaravis? Longrich (2009) suggested Palintropus was related to Apsaravis based on the absent procoracoid process and medial supracoracoid groove. They also seem to share a deep dorsal fossa in the coracoid. While these characters are also shared with most enantiornithines, the scapulocoracoid articulation is unlike that clade. The referred dorsal and femur also lack enantiornithine synapomorphies (e.g. they have anteriorly placed parapophyses and no posterior trochanter). When added to a modified version of Clarke's phylogenetic analysis of birds (with basal galliforms such as Paraortygoides, Quercymegapodius and Ameripodius also added), Palintropus emerges as sister to Apsaravis. Longrich's hypothesis is thus supported.

P. retusus (Marsh, 1892) Brodkorb, 1970
= Cimolopteryx retusa Marsh, 1892
= Apatornis retusus (Marsh, 1892) Brodkorb, 1963
Late Maastrichtian, Late Cretaceous
Lance Formation, Wyoming, US
Holotype- (YPM 513) proximal coracoid

Diagnosis- (after Longrich, 2009) smaller than both Campanian species; lacks kink in the ridge connecting the humeral articular facet and acrocoracoid; acrocoracoid process shorter and more expanded; humeral articular facet broader anteriorly than posteriorly; dorsal groove extends to level of scapular cotyle.

P. sp. nov. (Hope, 2002)
Late Campanian, Late Cretaceous
Dinosaur Park Formation, Alberta, Canada
Material- (RTMP 86.36.126) proximal coracoid (Hope, 2002)
?(RTMP 89.81.12) dorsal vertebra (Longrich, 2009)
?(RTMP 2001.12.150) distal femur (Longrich, 2009)

Diagnosis- (after Longrich, 2009) over twice as large as P. retusus, a third larger than the other Campanian species; kink in the ridge connecting the humeral articular facet and acrocoracoid; acrocoracoid process shorter and more expanded; humeral articular facet broader anteriorly than posteriorly; dorsal groove extends to level of scapular cotyle.

Comments- Hope (2002) referred RTMP 86.36.126 to a new species of Palintropus, along with RTMP 86.146.11, 88.116.1 and five other RTMP specimens. She noted some of these specimens were smaller, so might belong to another species, or that Palintropus may have been sexually dimorphic. Longrich referred RTMP 86.36.126 to his Palintropus species A, along with a dorsal vertebra and femur based on their size.

P. sp. nov. (Longrich, 2009)
Late Campanian, Late Cretaceous
Dinosaur Park Formation, Alberta, Canada
Material- (RTMP 83.36.70) coracoid fragment (Longrich, 2009)
(RTMP 88.116.1) proximal coracoid (Hope, 2002)
?(RTMP 89.50.53) dorsal vertebra, partial synsacrum (Longrich, 2009)
(RTMP 92.53.3) coracoid fragment (Longrich, 2009)
?(RTMP 96.12.336) femur (Longrich, 2009)
(RTMP 2005.12.190) partial coracoid (Longrich, 2009)
Late Campanian, Late Cretaceous
Foremost Formation, Alberta, Canada
?(RTMP 86.146.11) proximal scapula (Hope, 2002)

Diagnosis- (after Longrich, 2009) intermediate in size between other species; lacks kink in the ridge connecting the humeral articular facet and acrocoracoid; acrocoracoid process taller and less expanded; humeral articular facet strongly semicircular; dorsal groove does not extend to level of scapular cotyle.

Comments- Hope (2002) referred RTMP 86.146.11 and 88.116.1 to the same undetermined Palintropus species as RTMP 86.36.126, though she noted the latter might belong to a different species or sex. Longrich (2009) placed the former specimens in his new Palintropus species B, which he stated differed markedly in morphology from P. retusus or P. species A.

P. sp. (Hope, 2002)
Late Campanian, Late Cretaceous
Belly River Group, Alberta, Canada
Material- (RTMP coll.) three partial coracoids (Hope, 2002)

Comments- Hope (2002) referred five coracoids in the RTMP collections to her new Palintropus species, two of which are probably RTMP 83.36.70 and 92.53.3 that were later mentioned by Longrich (2009) and referred to his Palintropus species B. Whether the other three belong to P. species A or B is unknown.

References- Marsh, 1892. Notes on Mesozoic vertebrate fossils. American Journal of Science. 55, 171-175.

Shufeldt, 1915. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences. 19, 1-110.

Brodkorb, 1963. Birds from the Upper Cretaceous of Wyoming. in Sibley (ed.). Proceedings of the XIII International Ornithological Congress. 50-70.

Brodkorb, 1970. The generic position of a Cretaceous bird. Quarterly Journal of the Florida Academy of Science. 32(3), 239-240.

Hope, 2002. The Mesozoic radiation of Neornithes. In Chiappe and Witmer (eds). Mesozoic birds: Above the heads of dinosaurs. Berkeley: University of California Press. 339-388.

Longrich, 2009. An ornithurine-dominated avifauna from the Belly River Group (Campanian, Upper Cretaceous) of Alberta, Canada. Cretaceous Research. 30(1), 161-177.

Mayr, 2009. Paleogene Fossil Birds. Springer-Verlag, Heidelberg & New York. 262 pp.

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