Detailed anatomy of the braincase of Macelognathus vagans Marsh, 1884 (Archosauria, Crocodylomorpha) using high resolution tomography and new insights on basal crocodylomorph phylogeny
Background Macelognathus vagans Marsh, 1884 from the Late Jurassic Morrison Fm. of Wyoming was originally described as a dinosaur by Marsh and in 1971 Ostrom suggested crocodilian affinities. In 2005, Göhlich and collaborators identified new material of this species from Colorado as a basal crocodyl...
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PeerJ Inc.
2017-01-01
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| author | Juan Martin Leardi Diego Pol James Matthew Clark |
| author_facet | Juan Martin Leardi Diego Pol James Matthew Clark |
| author_sort | Juan Martin Leardi |
| collection | DOAJ |
| description | Background Macelognathus vagans Marsh, 1884 from the Late Jurassic Morrison Fm. of Wyoming was originally described as a dinosaur by Marsh and in 1971 Ostrom suggested crocodilian affinities. In 2005, Göhlich and collaborators identified new material of this species from Colorado as a basal crocodylomorph. However, a partial skull found in association with mandibular and postcranial remains was not described. Methods Due to the small size and delicate structures within the braincase, micro CT studies were performed on this specimen. The new anatomical information was incorporated in a phylogenetic dataset, expanding both character and taxon sampling. Results This new material reinforces the non-crocodyliform crocodylomorph affinities of Macelognathusas it bears a large otic aperture, unfused frontals and lacks ornamentation on the dorsal cranial bones. The internal structures also support these affinities as this specimen bears traits (i.e., heavily pneumatized and expanded basisphenoid; the presence of additional pneumatic features on the braincase; and the otoccipital-quadrate contact) not present in most basal crocodylomorphs. Furthermore, the presence of a wide supraoccipital and a cranioquadrate passage are traits shared with Almadasuchus from the early Late Jurassic of Argentina. Macelognathus was recovered as one of the closest relatives of crocodyliforms, forming a clade (Hallopodidae) with two other Late Jurassic taxa (Almadasuchus and Hallopus). Discussion The clade formed by Almadasuchus + Hallopus + Macelognathus, the Hallopodidae, is characterized by a higher degree of suturing of the braincase, posteriorly closed otic aperture (paralleled in mesoeucrocodylians) and cursorial adaptations. Also, the phylogenetic position of this lineage of derived crocodylomorphs as the sister group of Crocodyliformes implies a large amount of unsampled record (ghost lineage), at least 50 million years. |
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| language | English |
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| publishDate | 2017-01-01 |
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| spelling | doaj.art-2a95effbfbed4502b6b2f4290d5ab8912023-12-03T10:15:09ZengPeerJ Inc.PeerJ2167-83592017-01-015e280110.7717/peerj.2801Detailed anatomy of the braincase of Macelognathus vagans Marsh, 1884 (Archosauria, Crocodylomorpha) using high resolution tomography and new insights on basal crocodylomorph phylogenyJuan Martin Leardi0Diego Pol1James Matthew Clark2CONICET, Instituto de Estudios Andinos “Don Pablo Groeber” (IDEAN), Facultad de Ciencias Exactas y Naturales, Departamento de Ciencias Geológicas, Universidad de Buenos Aires, Buenos Aires, ArgentinaCONICET, Museo Paleontológico Egidio Feruglio, Trelew, Chubut, ArgentinaDepartment of Biological Sciences, George Washington University, Washington, D.C., United States of AmericaBackground Macelognathus vagans Marsh, 1884 from the Late Jurassic Morrison Fm. of Wyoming was originally described as a dinosaur by Marsh and in 1971 Ostrom suggested crocodilian affinities. In 2005, Göhlich and collaborators identified new material of this species from Colorado as a basal crocodylomorph. However, a partial skull found in association with mandibular and postcranial remains was not described. Methods Due to the small size and delicate structures within the braincase, micro CT studies were performed on this specimen. The new anatomical information was incorporated in a phylogenetic dataset, expanding both character and taxon sampling. Results This new material reinforces the non-crocodyliform crocodylomorph affinities of Macelognathusas it bears a large otic aperture, unfused frontals and lacks ornamentation on the dorsal cranial bones. The internal structures also support these affinities as this specimen bears traits (i.e., heavily pneumatized and expanded basisphenoid; the presence of additional pneumatic features on the braincase; and the otoccipital-quadrate contact) not present in most basal crocodylomorphs. Furthermore, the presence of a wide supraoccipital and a cranioquadrate passage are traits shared with Almadasuchus from the early Late Jurassic of Argentina. Macelognathus was recovered as one of the closest relatives of crocodyliforms, forming a clade (Hallopodidae) with two other Late Jurassic taxa (Almadasuchus and Hallopus). Discussion The clade formed by Almadasuchus + Hallopus + Macelognathus, the Hallopodidae, is characterized by a higher degree of suturing of the braincase, posteriorly closed otic aperture (paralleled in mesoeucrocodylians) and cursorial adaptations. Also, the phylogenetic position of this lineage of derived crocodylomorphs as the sister group of Crocodyliformes implies a large amount of unsampled record (ghost lineage), at least 50 million years.https://peerj.com/articles/2801.pdfBraincasePhylogenyLate jurassicMicro CTCrocodylomorpha |
| spellingShingle | Juan Martin Leardi Diego Pol James Matthew Clark Detailed anatomy of the braincase of Macelognathus vagans Marsh, 1884 (Archosauria, Crocodylomorpha) using high resolution tomography and new insights on basal crocodylomorph phylogeny PeerJ Braincase Phylogeny Late jurassic Micro CT Crocodylomorpha |
| title | Detailed anatomy of the braincase of Macelognathus vagans Marsh, 1884 (Archosauria, Crocodylomorpha) using high resolution tomography and new insights on basal crocodylomorph phylogeny |
| title_full | Detailed anatomy of the braincase of Macelognathus vagans Marsh, 1884 (Archosauria, Crocodylomorpha) using high resolution tomography and new insights on basal crocodylomorph phylogeny |
| title_fullStr | Detailed anatomy of the braincase of Macelognathus vagans Marsh, 1884 (Archosauria, Crocodylomorpha) using high resolution tomography and new insights on basal crocodylomorph phylogeny |
| title_full_unstemmed | Detailed anatomy of the braincase of Macelognathus vagans Marsh, 1884 (Archosauria, Crocodylomorpha) using high resolution tomography and new insights on basal crocodylomorph phylogeny |
| title_short | Detailed anatomy of the braincase of Macelognathus vagans Marsh, 1884 (Archosauria, Crocodylomorpha) using high resolution tomography and new insights on basal crocodylomorph phylogeny |
| title_sort | detailed anatomy of the braincase of macelognathus vagans marsh 1884 archosauria crocodylomorpha using high resolution tomography and new insights on basal crocodylomorph phylogeny |
| topic | Braincase Phylogeny Late jurassic Micro CT Crocodylomorpha |
| url | https://peerj.com/articles/2801.pdf |
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