Metrics details An Author Correction to this article was published on 05 August 2020 This article has been updated The Romualdo Formation (Araripe Basin) is worldwide known for the large number of well-preserved fossils but the dinosaur record is rather scarce which is the first tetrapod recovered from the basal layers of this stratigraphic unit that consist of dark shales is known by an incomplete but articulated right hind limb with the distal portion of the femur The new species differs from other coelurosaurs by a medial fossa in the tibia and digits II The phylogenetic analysis recovered Aratasaurus museunacionali closely related to Zuolong salleei The paleohistology indicate that the specimen is a juvenile with an estimated body length around 3.12 m The new taxon represents the first occurrence of basal coelurosaurians in the Araripe Basin and suggests a widespread distribution of this group during the Lower Cretaceous Location map of the Mina Pedra Branca, Ceará State. The crossed geologic hammers indicate where Aratasaurus museunacionali gen. et sp. nov. was found. Figure created by Renan Alfredo Machado Bantim on PS Adobe Photoshop CC, version 20.0.6. Outcrop of Mina Pedra Branca where Aratasaurus museunacionali gen was recovered with indication of the stratigraphy and where the dinosaur came from Figure created by Renan Alfredo Machado Bantim on PS Adobe Photoshop CC Composed stratigraphic section of Mina Pedra Branca quarry (Municipality of Santana do Cariri showing the fossiliferous calcareous nodule level (A) and the dark shale horizon (dinosaur) where Aratasaurus museunacionali gen were recovered from this layer such as fishes (e.g. the sole tetrapod known form this deposit is the dinosaur described here From the combination of “ara” and “atá” from the Tupi language meaning born and fire Incomplete but articulated right hind limb with the distal portion of the femur proximal half of the tibia and mid-distal regions of metatarsals I–IV The specimen (MPSC R 2089) is housed at the Museu de Paleontologia of the Universidade Regional do Cariri and a cast will be deposited at the Museu Nacional/UFRJ in a dark shale located about 2.5 m above the contact with Ipubi Formation Aratasaurus museunacionali differs from other basal coelurosaurs by the following combination of characters: tibia exhibiting a medial fossa; symmetric pes with digits II and IV subequal in total length; distal condyles of metatarsi II III and IV symmetric mediolaterally and with subequal width; width of metatarsi II and IV similar presenting the dorsal surface of the distal articulation bulbous The holotype (MPSC R 2089) of Aratasaurus museunacionali gen showing the femur and tibia before preparation Only a section of the distal portion of the femur is preserved (110 mm; Fig. 5). It is observable only from the medial view. The most distal region is in articulation with the proximal surface of the tibia, covering most of the posterior intercondylar fossa. A deep intercondylar fossa is observable. A marked groove separates the condyles. It is bulbous and exhibits a lateral ridge The fibular condyle forms a right angle with the anteroposterior axis of the articulation The medial surface of the tibia is marked by a fossa located close to the proximal articulation the fibular condyle is continuous with the fibular crest A deep fossa separates the lateral cnemial ridge from the fibular crest Part of the holotype (MPSC R 2089) of Aratasaurus museunacionali gen showing the (A) photo and (B) drawing of the right pes first to second phalanx of pedal digit II; pph1d3 first phalanx of pedal digit III; pph1-3d4 first to third phalanx of pedal digit IV; u1 it is reduced and has the same length as the first phalange of pedal digit I The proximal articulation is flattened and blade-like This bone contacts the mid-distal region of the medial surface of metatarsal II Metatarsals II and IV are morphologically and proportionally similar, being expanded mediolaterally. All exhibit collateral ligament pits. The longest is metatarsal III, which, based on the relation of the foot relative to the tibia, was about 243 mm long (Fig. 4) The dorsal surface of the distal articulation of metatarsals II and IV are bulbous The articulation of metatarsal III is markedly ginglymoid with an extensor pit on the dorsal surface The collateral ligament pits are present in all metatarsals being deeper in metatarsal III and shallower in metatarsal IV Digits II and IV are about the same length. The preserved pedal phalangeal formula is I-1, II-2, III-3 and IV-4 (Fig. 6) Although most of the phalanges are compressed some of the ones of digit III were preserved in their original shape and exhibit an ellipsoid cross-section with digit IV possessing the shortest phalanges compared to the remaining digits The collateral ligament pits of the phalanges of digits II and III are deep and symmetrical Although these pits are also deep in digit IV they exhibit a slight mediolateral asymmetry being deeper in the lateral side in digit III The dorsal surface of the proximal articulation of phalanges II-1 and III-1 is bulbous The distal articulation of phalanges II-1 and III-2 are marked by an extensor pit marks on the dorsal surface III-2 and III-3 and all of the digit IV show an asymmetric shaft with the proximal half of the ventral surface showing flexor processes The phalanges III-2 and III-3 also exhibit a concave ventral surface Unguals I, II and III are preserved (Fig. 7). Most of the dorsal surface of the ungual I is covered by rock matrix. The ventral surface of all unguals show a faint flexor tubercle. The lateral and medial surfaces of the unguals II and III exhibit ridges, especially in the ungual II. Pedal unguals (MPSC R 2089) of Aratasaurus museunacionali gen B) Photo and schematic drawing of the second pedal digit and (C D) photo and schematic drawing of the third pedal digit The rounded cnemial crest is also present in Zuolong sallei The lateral ridge on the cnemial crest is also observed in Zuolong sallei A rounded fibular condyle and an elongated fibular crest is shared with Aratasaurus museunacionali and Zuolong sallei This condyle in Australovenator wintonensis presents a ventral convexity which is different from the flattened surface of Aratasaurus museunacionali III and IV are about the same in Aratasaurus museunacionali while Zuolong sallei shows a metatarsal III twice the width of the metatarsals II and IV the distal articulation of metatarsals II and IV in Aratasaurus museunacionali are similar and differs from the condition of Aarun zhaoi in which metatarsals II is the widest and tallest among the other metatarsi of the pes The unguals of both Zuolong sallei and Aratasaurus museunacionali are also similar presenting flexor tubercles and symmetrical grooves in lateral facets the material known from the Aratasaurus museunacionali differs from derived coelurosaurian groups (e.g Ornithomimosauria) and Megaraptora mainly regarding by the cnemial crest and the disposition and morphology of metatarsals the new Brazilian theropod has a tibia similar to that of Zuolong salleei and the pes more similar with that of Aarun zhaoi and Tanycolagreus topwilsoni Osteohistological section of the second metatarsal of Aratasaurus museunacionali gen showing the four growth cycles (numbers 1–4) marked by two lines of arrested growth and one annulus po—primary osteons; LAG—lines of arrested growth Stratigraphic chart modified from Cohen et al based on the plesiomorphic characters and close relationships with Zuolong salleei Aratasaurus museunacionali integrates the most basal lineage of Coelurosauria Life reconstruction of Aratasaurus museunacionali gen secondary osteons and a high number of primary osteons implies on a juvenile/young adult ontogenetic stage for this animal The ontogenetic stage attributed to Aratasaurus museunacionali probably explains its reduced proportions because its asymptotic size was not reached indicating that this animal could have grown further traditional search tree bisection and reconnection (TBR) branch swapping with zero random seed 3,000 replicates and 10 saved trees per replication The obtained trees were reanalyzed in TBR with the parameter “stop when maxtrees hit” with additional coding for Santanaraptor placidus and Timimus hermani as follows: Two casts were also made to preserve external morphological data The bone was sectioned in previous existing breaking area A bone sample with approximately 1 cm of thickness was obtained It was embedded in clear epoxy resin Resapol T-208 catalyzed with Butanox M50 cut with a micro rectify (Dremel 4000 with extender cable 225) mounted to a diamond disk the mounting side was wet ground and polished using a metal polishing machine (AROPOL-E Abrasive sandpaper of different grits were used in this step (grit size 60 / P60 the section was examined and photographed under a transmitted light microscope (Zeiss Inc Spain) mounted to an AxioCam camera with Axio Imager The M2 imaging software was used in the examination procedure An amendment to this paper has been published and can be accessed via a link at the top of the paper First Early Cretaceous theropod dinosaur from Brazil with comments on Spinosauridae Brusatte, S. 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TNT version 1.5 including full implementation of phylogenetic morphometrics In Preparation and Sectioning of Specimens (eds Padian E.-T.) 55–160 (University of California Press Download references We would like to thank Plácido Cidade Nuvens (deceased in 2016) for obtaining the specimen studied here and Bruno C Vila Nova (UFPE) for preparing part of the material Diogenes de Almeida Campos (CPRM) and Francisco de Freitas Leite (URCA) are thanked for discussions regarding the name of the new species acknowledges Lucy Gomes de Souza (Museu Nacional/Universidade Federal do Rio de Janeiro) for helping with the TNT software The paleoartist Maurilio Oliveira is acknowledged for the life reconstruction of this new dinosaur This study was partially founded by the Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ #E-26/202.905/2018 to A.W.A.K.) the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq #420687/2016-5 and #313461/2018-0 to A.W.A.K.; #311715/2017-6 to J.M.S.; #305705/2019-9 to F.J.L.) the Fundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico (FUNCAP #BMD-0124-00302.01.01/19 to R.A.M.B. and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001 (CAPES #88887.162865/2018-00 to R.A.M.B.) acknowledges the doctoral fellowship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES - PROANTAR: 88887.336584/2019-00 and Finance code 001 CAPES #88887.162865/2019-00 to RAMB) Laboratório de Paleobiologia e Microestruturas Juliana Manso Sayão & Rafael Cesar Lima Pedroso de Andrade Laboratory of Systematics and Taphonomy of Fossil Vertebrates Museu Nacional/Universidade Federal do Rio de Janeiro organized the curation and preparation of the specimen performed the anatomical descriptive research preformed the phylogenetic analysis; J.M.S All authors contributed and reviewed the manuscript The authors declare no competing interests Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations Download citation DOI: https://doi.org/10.1038/s41598-020-67822-9 Anyone you share the following link with will be able to read this content: a shareable link is not currently available for this article Sign up for the Nature Briefing newsletter — what matters in science