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A Carnian theropod with unexpectedly derived features during the first dinosaur radiation

Nature Ecology & Evolution (2025)Cite this article

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Abstract

The early diversification of dinosaurs produced a major ecological change in the terrestrial ecosystems, culminating with tetrapod assemblages dominated in abundance by dinosaurs by the Triassic/Jurassic boundary (~201 million years ago (Ma)). Therefore, studying the initial diversification of dinosaurs is crucial to understand the establishment of Mesozoic assemblages. However, the lack of stratigraphically continuous fossil data in the few geological units that preserve the oldest known dinosaurs (~233–227 Ma, Carnian age) obscures our understanding of this initial diversification. The Ischigualasto Formation in northwestern Argentina (231.4–225.9 Ma) yields a rich vertebrate assemblage and new studies resulted in an abundant and stratigraphically near-continuous fossil record, which offers new insights into the early diversification of dinosaurs. Among the discoveries, we report Anteavis crurilongus gen. et sp. nov., an early-diverging theropod, which supports the notable diversity of small- to medium-sized dinosaurs during the late Carnian. Anteavis is recovered outside Neotheropoda, but it has features previously thought to be exclusive to that group. We show that dinosaur diversity and abundance in the Ischigualasto Formation were higher than previously recognized, particularly among small herbivores (<30 kg) and medium-sized (30–200 kg) predators. This diversification occurred in Ischigualasto during a climatic shift to semi-arid conditions, but the return of more humid conditions resulted in a gap in the dinosaur record that started at 228.91 ± 0.14 Ma. Only 15 million years (Myr) later, in the middle Norian age, the dinosaur record recovered its abundance and diversity in the basin, but now it was characterized by larger-bodied species. Our findings demonstrate an early dinosaur diversification probably punctuated by a climate-driven faunal turnover in, at least, southwestern Pangaea.

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Fig. 1: Skeletal anatomy of the Carnian theropod A. crurilongus.
Fig. 2: Phylogenetic relationships of A. crurilongus among early dinosaurs.
Fig. 3: General stratigraphic profile across the continuous sedimentary sequence of the Chañares–Los Colorados formations in the Hoyada de Ischigualasto locality.

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Data availability

All data generated or analysed during this study are included in this article and its Supplementary Information. The datasets for phylogenetic and rarefaction analyses are available via figshare at https://doi.org/10.6084/m9.figshare.29539004 (ref.61).

Code availability

The custom codes used for the phylogenetic and rarefaction analyses are available via figshare at https://doi.org/10.6084/m9.figshare.29539004 (ref. 61).

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Acknowledgements

R.N.M. thanks Secretaría de Ciencia, Tecnología e Innovación of San Juan (SECITI) and IMCN of the Universidad Nacional de San Juan. This study used computational resources from Universidad Nacional de Córdoba (https://ccad.unc.edu.ar/), which are part of SNCAD–MinCyT, Argentina. We also thank the Willi Hennig Society for supporting the free use of TNT software.

Author information

Authors and Affiliations

  1. Instituto y Museo de Ciencias Naturales, Universidad Nacional de San Juan, San Juan, Argentina

    Ricardo N. Martínez, Carina E. Colombi, Diego O. Abelín & Oscar A. Alcober

  2. CIGEOBIO, CONICET, San Juan, Argentina

    Carina E. Colombi, Diego O. Abelín & Ignacio Cerda

  3. Sección Paleontología de Vertebrados, CONICET–Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’, Buenos Aires, Argentina

    Martín D. Ezcurra

  4. School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK

    Martín D. Ezcurra

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  1. Ricardo N. Martínez
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  2. Carina E. Colombi
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  3. Martín D. Ezcurra
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  4. Diego O. Abelín
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Contributions

R.N.M. led the project, conducted phylogenetic analyses, results, discussions and paper writing. C.E.C. conducted palaeoenvironmental and taphonomic studies. M.D.E. conducted phylogenetic and rarefaction analyses. I.C. conducted the histology analysis. R.N.M. and M.D.E. produced the figures. D.O.A. performed specimen preparation. O.A.A. contributed to logistics.

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Correspondence to Ricardo N. Martínez.

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Extended data

Extended Data Fig. 1 Location and geology of the Ischigualasto–Villa Unión Basin at Hoyada de Ischigualasto locality.

a, Location maps of the study area. b, Geological map of the southern area of the Ischigualasto Basin (Hoyada de Ischigualasto). c, Ischigualasto Formation stratigraphic section and detailed sedimentological log of the Hyperodapedon-Exaeretodon-Herrerasaurus biozone. The detailed sedimentologic section of the study area corresponds to a 55 metre-thick interval that includes lithofacies characterization (that is, texture, structure, colors, paleosol features) and the stratigraphic position of the holotype of Anteavis crurilongus. Black star indicates the type locality of Anteavis crurilongus (PVSJ 1085).

Extended Data Fig. 2 Dorsal rib histology and cranial anatomy of Anteavis crurilongus (PVSJ 1085).

Complete transverse sections of the rib (a,b); general view (c) and detail (d) of the cortical bone; left prefrontal in lateral (e) and medial (f) views; partial left maxilla in lateral (g, h), occlusal (i, j), and medial (k, l) views; palatine ramus of left pterygoid in dorsal (m), and ventral (n) views; medial portion of the right pterygoid in dorsal (o), and ventral (p) views; right ectopterygoid in dorsal (q), and ventral (r) views; anterior portion of the right dentary in medial (s) and lateral (t) views; fragments of the posterior portion of the right dentary in lateral (u, v), and medial (w, x) views; and posterior portion of the right dentary in occlusal view (y). White arrowheads indicate the position of the lines of arrested growth (LAGs). Due to differences in the degree of magnification of the photographs, LAGs formed in the external fundamental system are only indicated in d. Abbreviations: a, alveolus; af, antorbital fossa; ap, anterior process; bf, basipterygoid flank; dp, dorsal process; EFS, external fundamental system; jpe, jugal process of the ectopterygoid; ecter, ectopterygoid recess; f, foramen; mg, Meckelian groove; ml, medial lamina; mr, mandibular ramus; os, orbital surface; pf, pterygoid fold; pmf, promaxillary foramen; pr, palatine ramus; r, ridge; s, symphysis; sg, groove for the splenial; slb, secondary lamellar bone; so, secondary osteon; svc, simple vascular canal; t, tooth; vp, ventral process. Scale bars: a-b 1 mm, c 0.5 mm, d 0.2 mm, e-y 10 mm.

Extended Data Fig. 3 Vertebral anatomy of Anteavis crurilongus (PVSJ 1085).

Anterior cervical vertebra in right lateral (a), left lateral (b), dorsal (c), and ventral (d) views; mid-cervical vertebra in right lateral (e), left lateral (f), dorsal (g), and ventral (h) views; posterior cervical vertebra in right lateral (i), left lateral (j), dorsal (k), and ventral (l) views; anterior dorsal vertebra in right lateral (m), left lateral (n), dorsal (o), and ventral (p) views; mid-dorsal vertebra in right lateral (q), left lateral (r), dorsal (s), and ventral (t) views; distal anterior caudal vertebra in right lateral (u), left lateral (v), dorsal (w), and ventral (x) views; mid-caudal vertebra in right lateral (y), left lateral (z), dorsal (aa), and ventral (ab) views; posterior caudal vertebra in right lateral (ac), left lateral (ad), dorsal (ae), and ventral (af) views. Scale bar: 10 mm.

Extended Data Fig. 4 Shoulder girdle, forelimb, hindlimb anatomy of Anteavis crurilongus (PVSJ 1085).

Right scapula and coracoid in lateral (a), medial (b), and posterior (c) views; right humerus in anterior and slightly medial (d), posterior and slightly lateral (e), proximal (f), lateral (g), and medial (h) views; proximal end of the right ulna in lateral (i), medial (j), and proximal (k) views; distal end of the right ulna in lateral (l), medial (m), and proximal (n) views; right manual phalanx in dorsal (o), ventral (p), lateral (q), and medial (r) views; left femur in lateral (s), medial (t), anterior (u), posterior (v), proximal (w), and distal (x) views; right tibia in lateral (y), medial (z), anterior (aa), posterior (ab), proximal (ac), and distal (ad) views; left astragalus in proximal (ae), distal (af), anterior (ag), posterior (ah), medial (ai), and lateral (aj) views; detail of the groove in the left astragalus in proximal view (ak); left metatarsal I in dorsal (al) and medial (am) views; left metatarsal II in dorsal (an) and lateral (ao) views; left metatarsals III and IV and left phalanx 1 of digit I in dorsal (ap) and lateral (aq) views; left metatarsal V in dorsal (ar), ventral (as), and proximal (at) views; distal tarsal 3 in proximal (au), and distal (av) views; distal tarsal 4 in proximal (aw), and distal (ax) views. Abbreviations: aaf, surface for astragalar ascending process; ae, anterior expansion; afh, articular facet for the humerus; amc, anteromedial corner; amt, anteromedial tuber; alt, anterolateral tuber; ap, ascending process; at, anterior tuberosities; bt, biceps tuber; c, coracoid; cc, cnemial crest; cco, calcaneal concavity; cf, coracoid foramen; ct, crista tibiofibularis; dip, dorsal intercondylar process; dt, dorsal tuberosity; dvd, dorsoventral depression; dpc, deltopectoral crest; ect, ectepicondyle; ent, entepicondyle; f, foramen; fc, fibular crest; ff, fibular facet; ft, fourth trochanter; g, glenoid; gr, groove; gt, greater trochanter; hh, humeral head; lc, lateral condyle; lclp, lateral collateral ligament pit; lf, lateral flange; llp, lateral ligament pit; ls, ligament scar; lt, lesser trochanter; mc, medial condyle; mlp, medial ligament pit; mp, medial protuberance; mt, medial tuberosity; n, notch; pp, post-glenoid process; r, ridge; rc, radial condyle; rf, fossa for articulation with the radius; s, scapula; sr, glenoidal sharp rim; ol, olecranon; ot, ovoid tuberosity; plf, posterolateral flange; pf, posterior fossa; pt, posterior tuberosities; rf, radial fossa; t, tuberosity; tf, tibial facet; ts, trochanteric shelf; uaf, articular surface for the ulnare; uc, ulnar condyle; vip, ventral intercondylar process. Scale bars: a–e g–r 10 mm, e 20 mm, s-ad ak-as 50 mm, ae-aj al-ax 10 mm, ak 10 mm.

Extended Data Fig. 5 Pelvic and sacral anatomy of Anteavis crurilongus (PVSJ 1085).

Pelvis in right lateral (a), left lateral (b), anterior (c), posterior (d), dorsal (e), and ventral (f) views; dorsosacral vertebra in left lateral (g), dorsal (h), ventral (i), anterior (j), and posterior (k) views; caudosacral vertebra in left lateral (l), dorsal (m), ventral (n), anterior (o), and posterior (p) views; close-up of the preacetabular process in anteromedial view (q); close-up of the postacetabular process in posteroventral and slightly lateral view (r); close-up of the sacrum in posteroventral view (s). Abbreviations: at, antitrochanter; bf, brevis fossa; bo, bony overgrow; dt, dorsal tuberosity; fcs, caudosacral rib facet; fds, dorsosacral rib facet; fs, fused sacral primordial vertebrae; il, ilium; ip, ischial peduncle; is, ischium; n, notch; na, neural arch; nc, neural channel; ns, neural spine; lp, left pubis; lprp, left preacetabular process; lpup, left pubic peduncle; of, obturator foramen; pf, pubic fenestra; pfo, pubic foot; pop, postacetabular process; pp, puboischiadic plate; pup, pubic peduncle; rp, right pubis; rpup, right pubic peduncle; rprp, right preacetabular process; sac, supraacetabular crest; t, tuberosity; 2 Sv, second sacral vertebra; 2 Sv, third sacral vertebra. Scale bars: a–f 50 mm, g,p 10 mm, q-s 10 mm.

Extended Data Fig. 6 Phylogenetic relationships of Anteavis crurilongus gen. et sp. nov. in the data matrix focused on early theropods.

(a) Global strict consensus tree recovered in the parsimony analyses under implied weighting; absolute (left) and GC (group present/contradicted) (right) symmetric resampling frequencies are shown above each branch. (b) Majority rule consensus tree recovered from the Bayesian phylogenetic analysis; numbers at nodes indicate posterior probabilities and branch colours indicate character state transition rates (that is, evolutionary rates).

Extended Data Fig. 7 Phylogenetic relationships of Anteavis crurilongus gen. et sp. nov. in the data matrix focused on early dinosauromorphs.

(a) Global strict consensus tree recovered in the parsimony analyses under implied weighting; absolute (left) and GC (group present/contradicted) (right) symmetric resampling frequencies are shown above each branch. (b) Majority rule consensus tree recovered from the Bayesian phylogenetic analysis; numbers at nodes indicate posterior probabilities and branch colours indicate character state transition rates (that is, evolutionary rates).

Extended Data Table 1 Measurements (in mm) of postatlantal vertebrae, pes, pelvic and long bone lengths of several early dinosaurs
Full size table
Extended Data Table 2 Measurements (in mm) of the pectoral girdle, humerus, ulna, pelvic girdle, and hindlimb of Anteavis crurilongus (PVSJ 1085)
Full size table
Extended Data Table 3 Taxa from the Hyperodapedon-Exaeretodon-Herrerasaurus biozone of the Ischigualasto Formation and their abundance according to weight ranges
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Supplementary information

Supplementary Information

Geological and palaeontological settings; holotypic specimen of A. crurilongus; extended diagnosis of A. crurilongus; detailed description of A. crurilongus; maturity assessment of PVSJ 1085; comparisons between Anteavis and Eodromaeus; phylogenetic analyses; body mass optimizations; rarefaction diversity curves; and references.

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Martínez, R.N., Colombi, C.E., Ezcurra, M.D. et al. A Carnian theropod with unexpectedly derived features during the first dinosaur radiation. Nat Ecol Evol (2025). https://doi.org/10.1038/s41559-025-02868-4

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