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  • A peer-reviewed version of this preprint was published in PeerJ on 26March 2018.

    View the peer-reviewed version (peerj.com/articles/4558), which is thepreferred citable publication unless you specifically need to cite this preprint.

    Gianechini FA, Makovicky PJ, Apestegua S, Cerda I. (2018) Postcranialskeletal anatomy of the holotype and referred specimens of Buitreraptorgonzalezorum Makovicky, Apestegua and Agnoln 2005 (Theropoda,Dromaeosauridae), from the Late Cretaceous of Patagonia. PeerJ 6:e4558https://doi.org/10.7717/peerj.4558

    https://doi.org/10.7717/peerj.4558https://doi.org/10.7717/peerj.4558

  • Postcranial skeletal anatomy of the holotype and referred

    specimens of Buitreraptor gonzalezorum Makovicky,

    Apestegua and Agnoln 2005 (Theropoda, Dromaeosauridae),

    from the Late Cretaceous of Patagonia

    Federico A Gianechini Corresp., 1 , Peter J Makovicky 2 , Sebastin Apestegua 3 , Ignacio Cerda 4

    1 Instituto Multidisciplinario de Investigaciones Biolgicas (IMIBIO-SL), CONICET-Universidad Nacional de San Luis., San Luis, Argentina2 Field Museum of Natural History, Chicago, Illinois, United States3 CONICET. Fundacin de Historia Natural Flix de Azara, CEBBAD, Universidad Maimnides., Buenos Aires, Argentina4 CONICET. Instituto de Investigacin en Paleobiologa y Geologa, Universidad Nacional de Ro Negro, General Roca, Ro Negro, Argentina

    Corresponding Author: Federico A Gianechini

    Email address: fgianechini@conicet.gov.ar

    Here we provide a detailed description of the postcranial skeleton of the holotype and

    referred specimens of Buitreraptor gonzalezorum. This taxon was recovered as a

    unenlagiine dromaeosaurid in several recent phylogenetic studies and is the best

    represented Gondwanan dromaeosaurid discovered to date. It was preliminarily described

    in a brief article, but a detailed account of its osteology is becoming known for recent

    work. Hitherto, the holotype is the most complete specimen found, so its exhaustive

    description provides much valuable anatomical information. The holotype and referred

    specimens preserve the axial skeleton, pectoral and pelvic girdles, and both fore- and

    hindlimbs. Diagnostic postcranial characters of this taxon include: anterior cervical centra

    exceeding the posterior limit of neural arch; antepenultimate and penultimate cervical

    vertebral centra with lateroventral tubercles; pneumatic foramina only in anteriormost

    dorsals; medial and distal caudal centra with a complex of ridges on lateral surfaces;

    pneumatic furcula with two pneumatic foramina on the ventral surface; scapular blade

    transversely expanded at mid-length; well-projected flexor process on distal humerus;

    dorsal rim of the ilium laterally everted; and concave dorsal rim of the postacetabular iliac

    blade. A paleohistological study of limb bones shows that the holotype represents a

    younger ontogenetic stage than one of the referred specimens (MPCA 238), which

    correlates with the fusion of the last sacral vertebra to the rest of the sacrum in MPCA 238.

    A revised phylogenetic analysis recovered Buitreraptor as a unenlagiine dromaeosaurid, in

    agreement with previous works. The phylogenetic implications of the unenlagiine

    synapomorphies and other characters, such as the specialized pedal digit II and the distal

    ginglymus on metatarsal II, are discussed within the evolutionary framework of Paraves.

    PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.26450v1 | CC BY 4.0 Open Access | rec: 22 Jan 2018, publ: 22 Jan 2018

  • 1 Postcranial skeletal anatomy of the holotype and referred

    2 specimens of Buitreraptor gonzalezorum Makovicky,

    3 Apestegua and Agnoln 2005 (Theropoda, Dromaeosauridae),

    4 from the Late Cretaceous of Patagonia

    5 Federico A. Gianechini1, Peter J. Makovicky2, Sebastin Apestegua3 and Ignacio Cerda4

    6 1 Instituto Multidisciplinario de Investigaciones Biolgicas (IMIBIO-SL), CONICET-Universidad Nacional de 7 San Luis. rea de Zoologa, Facultad de Qumica, Bioqumica y Farmacia, UNSL, Ciudad de San Luis, San 8 Luis, Argentina.

    9 2 Field Museum of Natural History, Chicago, Illinois, U.S.A.

    10 3 CONICET. Fundacin de Historia Natural Flix de Azara, CEBBAD, Universidad Maimnides, Buenos 11 Aires, Argentina.

    12 4 Instituto de Investigacin en Paleobiologa y Geologa, CONICET-Universidad Nacional de Ro Negro, 13 General Roca, Ro Negro, Argentina.

    14

    15 Corresponding Author:

    16 Federico A. Gianechini1

    17 Ejrcito de los Andes 950, Ciudad de San Luis, San Luis, D5700HHV, Argentina

    18 Email address: fgianechini@conicet.gov.ar

    19

    2021222324252627282930313233343536

    PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.26450v1 | CC BY 4.0 Open Access | rec: 22 Jan 2018, publ: 22 Jan 2018

  • 37 Abstract

    38

    39 Here we provide a detailed description of the postcranial skeleton of the holotype and referred

    40 specimens of Buitreraptor gonzalezorum. This taxon was recovered as a unenlagiine

    41 dromaeosaurid in several recent phylogenetic studies and is the best represented Gondwanan

    42 dromaeosaurid discovered to date. It was preliminarily described in a brief article, but a detailed

    43 account of its osteology is becoming known for recent work. Hitherto, the holotype is the most

    44 complete specimen found, so its exhaustive description provides much valuable anatomical

    45 information. The holotype and referred specimens preserve the axial skeleton, pectoral and

    46 pelvic girdles, and both fore- and hindlimbs. Diagnostic postcranial characters of this taxon

    47 include: anterior cervical centra exceeding the posterior limit of neural arch; antepenultimate and

    48 penultimate cervical vertebral centra with lateroventral tubercles; pneumatic foramina only in

    49 anteriormost dorsals; medial and distal caudal centra with a complex of ridges on lateral

    50 surfaces; pneumatic furcula with two pneumatic foramina on the ventral surface; scapular blade

    51 transversely expanded at mid-length; well-projected flexor process on distal humerus; dorsal rim

    52 of the ilium laterally everted; and concave dorsal rim of the postacetabular iliac blade. A

    53 paleohistological study of limb bones shows that the holotype represents a younger ontogenetic

    54 stage than one of the referred specimens (MPCA 238), which correlates with the fusion of the

    55 last sacral vertebra to the rest of the sacrum in MPCA 238. A revised phylogenetic analysis

    56 recovered Buitreraptor as a unenlagiine dromaeosaurid, in agreement with previous works. The

    57 phylogenetic implications of the unenlagiine synapomorphies and other characters, such as the

    58 specialized pedal digit II and the distal ginglymus on metatarsal II, are discussed within the

    59 evolutionary framework of Paraves.

    PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.26450v1 | CC BY 4.0 Open Access | rec: 22 Jan 2018, publ: 22 Jan 2018

  • 60 1. Introduction

    61

    62 Buitreraptor gonzalezorum is a paravian theropod whose remains were found in Late Cretaceous

    63 outcrops of the Candeleros Formation in the La Buitrera fossiliferous area, in Patagonia,

    64 Argentina. The paleontological significance of the many transformative discoveries made in this

    65 site were already enumerated in our previous papers (e.g., Apestegua & Zaher, 2006;

    66 Gianechini, Makovicky & Apestegua, 2011; Rougier, Apestegua & Gaetano, 2011; Makovicky,

    67 Apestegua & Gianechini, 2012; Gianechini & de Valais, 2016).

    68 Most phylogenetic analyses performed on coelurosaurian theropods recover Buitreraptor

    69 as member of a monophyletic Dromaeosauridae, within the subfamily Unenlagiinae, although

    70 some recent analyses recover Buitreraptor and other unenlagiines as stem avialans (Agnoln &

    71 Novas, 2011, 2013). Dromaeosauridae has experienced a remarkable increase in diversity since

    72 the 2000s, including species with both small and large body sizes, some of them represented by

    73 almost complete skeletons preserving plumage (e.g., Currie & Varricchio 2004; Norell et al.,

    74 2006; Turner, Hwang & Norell, 2007; Turner et al., 2007; Longrich & Currie, 2009; Xu et al.,

    75 2010; Zheng et al., 2010; Evans, Larson & Currie, 2013; Han et al., 2014; DePalma et al., 2015;

    76 L & Brusatte, 2015). Unfortunately, the Gondwanan record of these theropods remains sparse.

    77 Hitherto, the most significant Gondwanan specimens were found in Patagonia and Madagascar.

    78 The Patagonian record of unenlagiines currently includes five taxa, three of which preserve only

    79 post-cranial remains: Unenlagia comahuensis, Unenlagia paynemili and Neuquenraptor

    80 argentinus and two species with cranial remains, i.e., Buitreraptor gonzalezorum and

    81 Austroraptor cabazai. Recently, a fragmentary coelurosaurian represented only by hindlimb

    82 remains, but with possible deinonychosaurian affinities was described as Pamparaptor micros

    PeerJ Preprints | https://doi.org/10.7287/peerj.preprints.26450v1 | CC BY 4.0 Open Access | rec: 22 Jan 2018, publ: 22 Jan 2018

  • 83 (Porfiri, Calvo & Dos Santos, 2011). Its potential relationships with unenlagiines have not been

    84 thoroughly evaluated yet.

    85 Buitreraptor is the best represented unenlagiine to date. Its holotype consists of an

    86 almost complete, semi-articulated, and very well-preserved skeleton and at least five referred

    87 specimens are known. This taxon wa