Allometry and body length of abelisauroid theropods: Pycnonemosaurus nevesi is the new king |
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| Affiliation: | 1. Museu Nacional/Universidade Federal do Rio de Janeiro, Departamento de Geologia e Paleontologia, 20940-040, Rio de Janeiro, RJ, Brazil;2. Museu de Zoologia da Universidade de São Paulo, Laboratório de Paleontologia, Avenida Nazaré, 48, Ipiranga, 04263-000, São Paulo, SP, Brazil;1. Department of Earth Sciences, Montana State University, Bozeman, MT, 59717, USA;2. Museum of the Rockies, Bozeman, MT, 59717, USA;1. CONICET, Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina;2. Museo Municipal “Ernesto Bachmann”, Dr. Natali S/N, Villa El Chocón, 8311, Neuquén, Argentina;3. Instituto de Investigación en Paleobiología y Geología, Universidad Nacional de Río Negro, Museo Carlos Ameghino, Belgrano 1700, Paraje Pichi Ruca (predio Marabunta), Cipolletti, 8300, Río Negro, Argentina;4. Laboratorio de Anatomía Comparada y Evolución de los Vertebrados, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Av. Ángel Gallardo 470, C1405DJR, Buenos Aires, Argentina;1. Museo Municipal Argentino Urquiza, Jujuy y Chaco s/n, 8319, Rincón de los Sauces, Neuquén, Argentina;2. CONICET, Instituto de Investigación en Paleobiología y Geología (CONICET-UNRN), Av. Roca 1242, 8332, General Roca, Río Negro, Argentina;3. Secretaría de Cultura de la Provincia de Río Negro, 8332, General Roca, Río Negro, Argentina;4. Museo Provincial de Ciencias Naturales Prof. Dr. Juan Olsacher, Dirección Provincial de Minería, Etcheluz y Ejército Argentino, 8340, Zapala, Neuquén, Argentina;1. CONICET – Área de Zoología, Departamento de Bioquímica y Ciencias Biológicas, Facultad de Química, Bioquímica y Farmacia, Universidad Nacional de San Luis, Chacabuco 917, 5700, San Luis, Argentina;2. CONICET – Fundación de Historia Natural ‘Félix de Azara’, CEBBAD, Universidad Maimónides, Hidalgo 775, 1405, Buenos Aires, Argentina;3. Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126, Pisa, Italy;4. Fondazione Museo Civico di Rovereto, Borgo Santa Caterina 41, 38068, Rovereto, TN, Italy;5. Secretaría de Cultura de la Provincia de Río Negro, Julio A. Roca 267, 8500, Viedma, Río Negro, Argentina;1. Laboratoire de Géologie de l’École Normale Supérieure (UMR CNRS 8538), 24, rue Lhomond, 75231 Paris cedex 5, France;2. Muséum d’Histoire Naturelle, Hôtel Boyer d’Eguilles, 6, rue Espariat, 13100 Aix-en-Provence, France |
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| Abstract: | Abelisauroid dinosaurs normally reached an average body length (BL) of 5–9 m, but there are controversies due to the incomplete or fragmentary nature of most specimens. For Ekrixinatosaurus, for example, BL was estimated as 10–11 m or 7–8 m; for Pycnonemosaurus it was proposed 7–8 m, however its preserved bones are larger than any other described abelisauroid. The lack of a consistent methodology complicates comparisons of estimated BL, so we reevaluated the estimative for the seven most complete specimens of abelisauroids and compared the values against 40 measurements from the skull, vertebrae and appendicular elements using bivariate equations. It allowed estimating the BL of other 30, less complete, specimens of abelisauroids and to evaluate the allometric scaling of the skeletal parts. Strong correlations (R2 > 0.96) were obtained for all vertebrae and hindlimb measurements, as well as skull height, and length of skull roof, lacrimal–squamosal, scapulocoracoid and humerus; other skull and forelimb measurements present weak correlation due to extreme morphological transformations observed in Abelisauridae and were not adequate for BL estimation. Abelisauroids gradually increased in size during evolution: the mean BL was 3.3 ± 2.5 m for basal abelisauroids and Noasauridae, 5.4 ± 1.8 m for basal Brachyrostra and Majungasauridae, and 7.1 ± 2.1 m for Furileusaura. Despite this variation, diversity of BL on each geographic region and stratigraphic epoch was relatively constant (BL usually varied from 4 to 8 m). The smallest noasaurid and abelisaurid are, respectively, Velocisaurus (1.5 ± 0.1 m) and Genusaurus (3.6 ± 0.0 m). The largest abelisaurids is Pycnonemosaurus nevesi (8.9 ± 0.3 m) followed by Carnotaurus (7.8 ± 0.3 m), Abelisaurus (7.4 ± 0.7 m) and Ekrixinatosaurus (7.4 ± 0.8 m). Skull measurement scale negatively at a similar rate but the height scales almost isometrically and the skull roof length scales more negatively; this probably caused a bending on the skull that may explain the upward orientation of the snout in large taxa. |
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| Keywords: | Abelisauroidea Abelisauridae Body length Allometry |
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