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. 2021 Jul 22;11(1):14960.
doi: 10.1038/s41598-021-93994-z.

New transitional fossil from late Jurassic of Chile sheds light on the origin of modern crocodiles

Fernando E Novas  1   2 , Federico L Agnolin  3   4   5 , Gabriel L Lio  1 , Sebastián Rozadilla  1   2 , Manuel Suárez  6 , Rita de la Cruz  7 , Ismar de Souza Carvalho  8   9 , David Rubilar-Rogers  10 , Marcelo P Isasi  1   2
Affiliations

New transitional fossil from late Jurassic of Chile sheds light on the origin of modern crocodiles

Fernando E Novas et al. Sci Rep. .

Abstract

We describe the basal mesoeucrocodylian Burkesuchus mallingrandensis nov. gen. et sp., from the Upper Jurassic (Tithonian) Toqui Formation of southern Chile. The new taxon constitutes one of the few records of non-pelagic Jurassic crocodyliforms for the entire South American continent. Burkesuchus was found on the same levels that yielded titanosauriform and diplodocoid sauropods and the herbivore theropod Chilesaurus diegosuarezi, thus expanding the taxonomic composition of currently poorly known Jurassic reptilian faunas from Patagonia. Burkesuchus was a small-sized crocodyliform (estimated length 70 cm), with a cranium that is dorsoventrally depressed and transversely wide posteriorly and distinguished by a posteroventrally flexed wing-like squamosal. A well-defined longitudinal groove runs along the lateral edge of the postorbital and squamosal, indicative of a anteroposteriorly extensive upper earlid. Phylogenetic analysis supports Burkesuchus as a basal member of Mesoeucrocodylia. This new discovery expands the meagre record of non-pelagic representatives of this clade for the Jurassic Period, and together with Batrachomimus, from Upper Jurassic beds of Brazil, supports the idea that South America represented a cradle for the evolution of derived crocodyliforms during the Late Jurassic.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Locality map, geological context, and skeletal reconstruction of Burkesuchus mallingrandensis. Skeletal reconstruction based on holotype and paratype specimens.
Figure 2
Figure 2
Photographs and line drawings of the cranium (SGO.PV 17700) of Burkesuchus mallingrandensis in (A, B) dorsal; (C,D) posterior; and (E,F) left lateral views. ae, foramen aereum; an, surface for articulation with nasal; ap, surface for articulation with prefrontal; cq, cranioquadrate passage; dp, descending process of the postorbital; eam, external auditory meatus; for, foramen magnum; fos, blind fossae; fr, frontal; gr, longitudinal groove for the upper earlid; ot, otoccipital; par, parietal; q, quadrate; qj, quadratojugal; par, parietal; po, postorbital; poc, paraoccipital process; sf, supratemporal fenestra; sfor, supratemporal foramen; soc, supraoccipital; sq, squamosal; suf, subtympanic foramen; tub, ventral tubercle of paraoccipital process; va, vagi foramen; vlw, ventrolateral wing of the squamosal; XII, exit foramina for the hypoglossal nerve. Scale bar: 1 cm.
Figure 3
Figure 3
Photographs of vertebrae and osteoderm of Burkesuchus mallingrandensis (SGO.PV 17700). (A) cervical vertebra in left lateral view; (B–D) dorsal vertebra in (B) dorsal, (C) anterior, and (D) left lateral views; (E–F), dorsal osteoderm in (E), dorsal and (F), ventral views. ap, articular facet for the preceding osteoderm; di, diapophysis; nc, neural canal; ns, neural spine; pl, centroprezygapophyseal lamina; poz, postzygapophysis; prz, prezygapophysis; tp, transverse process. Scale bar: 1 cm.
Figure 4
Figure 4
Photographs of pectoral girdle and forelimb bones of Burkesuchus mallingrandensis (SGO.PV 17700). (A) Left scapula and coracoid in lateral view; (B–E), left humerus in (B) anterior, (C) lateral, (D) medial, and (E) posterior views; (F–I) left ulna in (F) anterior, (G) lateral, (H) medial, and (I) posterior views. ac, acromion; avp, anteroventral process; cf, coracoid foramen; cl, lateral cotyle; cm, medial cotyle; dpc, deltopectoral crest; hh, humeral head; gf, glenoid facets; lc, lateral condyle; ld, lateral depression; mc, medial condyle; ol, olecranon; pvp, posteroventral process; sb, scapular blade. Scale bar: 2 cm.
Figure 5
Figure 5
Photographs of right femur of Burkesuchus mallingrandensis (SGO.PV 17701) in (A) anterior, (B) lateral, (C) medial, and (D) posterior views. bf, basitrochanteric fossa; ft, fourth trochanter; gt, greater trochanter; fh, femoral head; lc, lateral condyle; mc, medial condyle. Scale bar: 2 cm.
Figure 6
Figure 6
Cladogram showing the phylogenetic position of Burkesuchus mallingrandensis. See details in Supplementary Information.
Figure 7
Figure 7
Occipital view of cranium of selected crocodyliforms. (A) Sphenosuchus (Sphenosuchia); (B) Protosuchus (“Protosuchia”); (C) Pelagosaurus (Thalattosuchia); (D) Notosuchus (Mesoeucrocodylia, Notosuchia); (E) Burkesuchus (Mesoeucrocodylia); (F) Allodaposuchus (Mesoeucrocodylia, Eusuchia); and (G) Osteolaemus (Mesoeucrocodylia, Neosuchia). bo, basioccipital; car, carotid foramen; co, occipital condyle; cq, cranioquadrate canal or foramen; fa, foramen aereum; fm, foramen magnum; ot, otoccipital; par, parietal; ptf, post-temporal fenestra; q, quadrate; qj, quadratojugal; soc, supraoccipital; sq, squamosal; tu, ventral tubercle of the paraoccipital process of otoccipital; va, vagus foramen; XII, foramen for cranial nerve XII. (A) modified from; (B,C) modified from; (D), modified from; (F), modified and reconstructed from,; (G), modified from. Not to scale.
See this image and copyright information in PMC

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