AVES Linnaeus, 1758

Candeiro, Carlos Roberto A., Agnolin, Federico, Martinelli, Agustín G. & Buckup, Paulo Andreas, 2012, First bird remains from the Upper Cretaceous of the Peirópolis site, Minas Gerais state, Brazil, Geodiversitas 34 (3), pp. 617-624 : 619-620

Class AVES Linnaeus, 1758

Genus and species indet.

REFERRED MATERIAL. — CPP 481, isolated pedal ungual phalanx lacking its proximal end ( Fig. 1A ). — CPP 470, isolated pedal phalanx 1 of left digit II ( Fig. 1B ).

PROVENANCE. — “Ponto 1 do Price” (see Candeiro et al. 2008), Peirópolis locality, Uberaba, Minas Gerais State, Brazil. Serra da Galga Member; Marilia Formation; Bauru Group ( Fernandes & Coimbra 1996).

DESCRIPTION

CPP 481 is a small pedal ungual of unknown position on the pes ( Fig. 1A ). The ungual is laterally compressed and dorsoventrally deep. The lateral sulcus is notorious and well defined, and is both dorsally and plantarly delimited by thin bony rims; regrettably, the eroded nature of bone surface precludes a detailed description of lateral sulci. Close to the plantar margin of the ungual there are small nutrient foramina. The proximal articular surface is dorsoventrally deep and laterally compressed, with well defined articular cotylae that are separated by a vertical and well defined ridge. The flexor tubercle is a low, rounded protuberance.

CPP 470 consists of a complete, robust pedal phalanx 1 of left digit II ( Fig. 1B ). It is dorsoventrally flat and transversely wide, and lacks a marked constriction of the shaft. It bears a well developed proximomedial process. In medial view, the process has a broad, circular surface for ligament attachment. The proximal articular surface is round and bordered by a small, proximodorsal rim. The distal trochlea is prominent, with the trochlear edges diverging ventrally. The trochlear rings are acute and tall, especially in the medial portion. The distal articular sulcus is deep and has a “V”-shaped section. The distal flexor pits are deep and bordered caudodorsally by an osseous rim.

REMARKS

CPP 481 is identified as a possible pedal ungual because it shows a poorly curved blade, symmetrically arranged lateral sulci, and its proximal articular surface ellipsoidal with a well-defined median keel (see Agnolin & Martinelli 2009). Regrettably, the incomplete nature of CPP 481 does not allow to identify to which digit it belongs. CPP 481 may be identified as a bird because it differs from derived coelurosaurian dinosaurs (i.e. Dromaeosauridae Matthew & Brown, 1922 , Troodontidae Gilmore, 1924 , Rahonavis ; Paul 2002), and resembles basal Aves in having greatly reduced flexor tubercle, such as most members of the Enanthiornithes (e.g., Soroavisaurus australis Chiappe, 1993 , Neuquenornis volans Chiappe & Calvo, 1994 , Sinornis santensis Sereno & Rao, 1992 ; Chiappe 1993; Chiappe & Calvo 1994; Sereno et al. 2002), Archaeopteryx Meyer, 1861 ( Mayr et al. 2007), Zhongornis Gao et al., 2008 ( Gao et al. 2008), Jeholornis Zhou & Zhang, 2002 ( Zhou & Zhang 2003) and Zhongjianornis Zhou, Zhang & Li, 2010 ( Zhou et al. 2009), among others. Moreover, CPP 481 also resembles birds and differs from derived coelurosaurian dinosaurs in having a relatively un-curved ungual blade. In fact, in basal birds most pedal unguals (with the single exception of the second one) show a nearly straight blade, as can be observed in some Enantiornithes and basal ornithurines (e.g., Sinornis santensis Sereno & Rao, 1992 ; Sereno et al. 2002), Archaeopteryx ( Mayr et al. 2007) , Zhongornis ( Gao et al. 2008) , Jeholornis ( Zhou & Zhang 2002) , and Zhongjianornis ( Zhou et al. 2009). On the other hand, in derived deinonychosaurian coelurosaurian dinosaurs (e.g., Buitreraptor Makovicky, Apesteguía & Agnolín, 2005 , Rahonavis Forster, Sampson, Chiappe & Krause, 1998 , Deinonychus Ostrom, 1969 , Microraptor Xu, Zhou & Wang, 2000 , Troodontidae ; Ostrom 1969; Rauhut & Werner 1995; Xu 2002; Makovicky et al. 2005) the ungual blade is extremely curved ( Zheng et al. 2009). Both features in combination may be employed to assign CPP 481 to Aves. Within this clade, a more precise referral of the available specimen is not possible due to the poorly informative and incomplete nature of the available material. The specimen CPP 470 resembles basal birds, such as Enantiornithes , in having a subcircular distal trochlear ring, with dorsally displaced and small distal flexor pits that are ellipsoidal in contour, features that allow us to identify this element as pertaining to a bird ( Agnolin & Martinelli 2009). A similar, but larger, element (MACN-PV-RN 1107) was described by Agnolin & Martinelli (2009) from the Upper Cretaceous Los Alamitos Formation of Río Negro Province, Argentina. They noted that the well developed proximomedial process and laterally expanded and dorsoventrally compressed shaft are features present in MACN-PV-RN 1107 and reminiscent of derived neornithine predatorial birds, such as Falconiformes ( Agnolin & Martinelli 2009); these features are also present in CPP 470. Nevertheless, given the incomplete nature of CPP 470, we identify it only as Aves indet.

Clade ORNITHOTHORACES Chiappe, 1996 cf. Enantiornithes Walker, 1981

Figures

FIG. 1. — A, B, Aves genera and species indet.: A, CPP 481, isolated pedal ungual phalanx in lateral view; B, CPP 470, isolated pedal phalanx 1 of left digit II in dorsal (left), lateral (right) and proximal (top) views; C, cf. Enantiornithes indet. (CPP 482), incomplete left metatarsal III in dorsal (left), ventral (right), and distal (below) views. Grey areas indicate broken surfaces. Abbreviations: dfp, distal flexor pit; ft, flexor tubercle; lc, lateral crest; lg, lateral groove; ls, lateral sulcus; pmp, proximomedial process; tr, trochlear ridge. Scale bars: A, B, 1 mm; C, 2 mm.