Crocodylomorpha

Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction.

Crocodylomorphs Temporal range: Late Triassic–Present, 235–0 Ma^[1] PreꞒ Ꞓ O S D C P T J K Pg N
Skeleton of Terrestrisuchus, an early saltoposuchid crocodylomorph
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauria
Clade:	Pseudosuchia
Clade:	Paracrocodylomorpha
Clade:	Loricata
Clade:	Crocodylomorpha Hay, 1930
Subgroups
†Artzosuchus? †Carnufex †Dianchungosaurus †Dibothrosuchus †Dromicosuchus †Hesperosuchus †Kayentasuchus †Parrishia? †Pseudhesperosuchus †Redondavenator †Sphenosuchus †Syntomiprosopus? †Trialestes Saltoposuchidae Crush, 1984^[2] †Litargosuchus †Saltoposuchus †Terrestrisuchus Solidocrania Ruebenstahl et al., 2022^[3] †Junggarsuchus †Phyllodontosuchus? †Hallopodidae †Thalattosuchia Crocodyliformes

During Mesozoic and early Cenozoic times, crocodylomorphs were far more diverse than at Present. Triassic forms were small, lightly built, active terrestrial animals. The earliest and most primitive crocodylomorphs are represented by "sphenosuchians", a paraphyletic assemblage containing small-bodied forms with elongated limbs that walked upright, which represents the ancestral morphology of Crocodylomorpha. These forms persisted until the end of the Jurassic.^[4] During the Jurassic, Crocodylomorphs morphologically diversified into numerous niches, with the subgroups Neosuchia (which includes modern crocodilians) and the extinct Thalattosuchia adapting to aquatic life.

Evolutionary history

 

Life restoration of Hesperosuchus

When their extinct species and stem group are examined, the crocodylian lineage (clade Pseudosuchia, formerly Crurotarsi) proves to have been a very diverse and adaptive group of reptiles. Not only are they an ancient group of animals – at least as old as the dinosaurs – they also evolved into a great variety of forms and sizes. Some terrestrial notosuchians were noticeably small animals, less than 1.2 m (3 ft 11 in) in length, while aquatic or semiaquatic crocodylomorphs, especially tethysuchians, thalattosuchians, and some crocodilians reached around 8 m (26 ft) in length.^[5]

The earliest forms, the sphenosuchians, evolved during the Late Triassic, and were highly gracile terrestrial forms built like greyhounds. During the Jurassic and the Cretaceous, marine forms in the family Metriorhynchidae, such as Metriorhynchus, evolved forelimbs that were paddle-like and had a tail similar to modern fish. Dakosaurus andiniensis, a species closely related to Metriorhynchus, had a skull that was adapted to eat large marine reptiles. Several terrestrial species during the Cretaceous were herbivorous, such as Simosuchus clarki and Chimaerasuchus paradoxus. A number of lineages during the Cenozoic became wholly terrestrial predators.

Taxonomy and phylogeny

Historically, all known living and extinct crocodiles were indiscriminately lumped into the order Crocodilia. However, beginning in the late 1980s, many scientists began restricting the order Crocodilia to the living species and close extinct relatives such as Mekosuchus. The various other groups that had previously been known as Crocodilia were moved to Crocodylomorpha and the slightly more restrictive Crocodyliformes.^[6] Crocodylomorpha has been given the rank of superorder in some 20th and 21st century studies.^[7]

The old Crocodilia was subdivided into the suborders:

• Eusuchia: true crocodiles (which includes crown-group Crocodylia)
• Mesosuchia: 'middle' crocodiles
• Thalattosuchia: sea crocodiles
• Protosuchia: first crocodiles
• Sphenosuchia: wedge crocodiles
• Sebecosuchia: Sebecus crocodiles

Mesosuchia is a paraphyletic group as it does not include eusuchians (which nest within Mesosuchia). Mesoeucrocodylia was the name given to the clade that contains mesosuchians and eusuchians (Whetstone and Whybrow, 1983).

Phylogeny

Below is a cladogram modified from Nesbitt (2011)^[8] and Bronzati (2012).^[9]

Crocodylomorpha	CM 73372 Hesperosuchus  Dromicosuchus Sphenosuchus Dibothrosuchus Terrestrisuchus Litargosuchus Kayentasuchus  Crocodyliformes  Protosuchia    Metasuchia  Notosuchia   Neosuchia

The previous definitions of Crocodilia and Eusuchia did not accurately convey evolutionary relationships within the group. The only order-level taxon that is currently considered valid is Crocodilia in its present definition. Prehistoric crocodiles are represented by many taxa, but since few major groups of the ancient forms are distinguishable, a conclusion on how to define new order-level clades is not yet possible. (Benson & Clark, 1988).

Biology

The Crocodylomorpha comprise a variety of forms, shapes, and sizes, which occupied a range of habitats. As with most amniotes, Crocodylomorphs were and are oviparous, laying eggs in a nest or mound, known from strata as old as the Late Jurassic.^[10] Adult size varies widely, from about 55 cm long in Knoetschkesuchus to much larger dimensions, as in Sarcosuchus. Most crocodylomorphs were carnivores, but many lineages evolved to be obligate piscivores, such as the extant gharials.

References

1. Irmis, R. B.; Nesbitt, S. J.; Sues, H. -D. (2013). "Early Crocodylomorpha". Geological Society, London, Special Publications. 379 (1): 275–302. Bibcode:2013GSLSP.379..275I. doi:10.1144/SP379.24. S2CID 219190410.
2. Spiekman, S. N. F. (2023). "A revision and histological investigation of Saltoposuchus connectens (Archosauria: Crocodylomorpha) from the Norian (Late Triassic) of south-western Germany". Zoological Journal of the Linnean Society. 199 (2): 354–391. doi:10.1093/zoolinnean/zlad035.
3. Ruebenstahl, A. A.; Klein, M. D.; Yi, H.; Xu, X.; Clark, J. M. (2022). "Anatomy and relationships of the early diverging Crocodylomorphs Junggarsuchus sloani and Dibothrosuchus elaphros". The Anatomical Record. 305 (10): 2463–2556. doi:10.1002/ar.24949. PMC 9541040. PMID 35699105.
4. Ruebenstahl, Alexander A.; Klein, Michael D.; Yi, Hongyu; Xu, Xing; Clark, James M. (14 June 2022). "Anatomy and relationships of the early diverging Crocodylomorphs Junggarsuchus sloani and Dibothrosuchus elaphros". The Anatomical Record. 305 (10): 2463–2556. doi:10.1002/ar.24949. ISSN 1932-8486. PMC 9541040. PMID 35699105.
5. Godoy, P. L.; Benson, R. B. J.; Bronzati, M.; Butler, R. J. (2019). "The multi-peak adaptive landscape of crocodylomorph body size evolution" (PDF). BMC Evolutionary Biology. 19 (167): 167. doi:10.1186/s12862-019-1466-4. PMC 6686447. PMID 31390981.
6. Martin, J.E.; Benton, M.J. (2008). "Crown Clades in Vertebrate Nomenclature: Correcting the Definition of Crocodylia". Systematic Biology. 57 (1): 173–181. doi:10.1080/10635150801910469. PMID 18300130.
7. Parrilla-Bel, J.; Young, M. T.; Moreno-Azanza, M.; Canudo, J. I. (2013). Butler, Richard J (ed.). "The First Metriorhynchid Crocodylomorph from the Middle Jurassic of Spain, with Implications for Evolution of the Subclade Rhacheosaurini". PLOS ONE. 8 (1): e54275. Bibcode:2013PLoSO...854275P. doi:10.1371/journal.pone.0054275. PMC 3553084. PMID 23372699.
8. Nesbitt, S.J. (2011). "The early evolution of archosaurs: relationships and the origin of major clades". Bulletin of the American Museum of Natural History. 352: 1–292. doi:10.1206/352.1. hdl:2246/6112. S2CID 83493714.
9. Bronzati, M.; Montefeltro, F. C.; Langer, M. C. (2012). "A species-level supertree of Crocodyliformes". Historical Biology. 24 (6): 598–606. doi:10.1080/08912963.2012.662680. S2CID 53412111.
10. Russo, J.; Mateus, O.; Marzola, M.; Balbino, A. (2017). "Two new ootaxa from the late Jurassic: The oldest record of crocodylomorph eggs, from the Lourinhã Formation, Portugal". PLOS One. 12 (3): 1–23. Bibcode:2017PLoSO..1271919R. doi:10.1371/journal.pone.0171919. PMC 5342183. PMID 28273086.

Sources

• Benton, M. J. (2004), Vertebrate Palaeontology, 3rd ed. Blackwell Science Ltd
• Hay, O. P. 1930 (1929–1930). Second Bibliography and Catalogue of the Fossil Vertebrata of North America. Carnegie Institution Publications, Washington, 1, 990 pp.

External links

• - webpages by Ross Elgin on the University of Bristol server
  • classification (used here)
• from Palaeos