Introduction

The crocodylians (order Crocodylia, class Reptilia) are a crown group that comprises the alligators, caimans, crocodiles and gharials (Brochu et al, 2009). It consists of all modern crocodylians and all the extinct relatives that descended from the last common ancestor of all living crocodylian species. Note that the term Crocodylia is restricted to the crown group (Brochu, 2003). The phylogeny and phylogenetic context of the crown group are shown below:
The crown node of the Crocodylia is shown above as a black dot. The clade belongs to the Archosauria and forms a sister group to the Aves (birds). The crocodylian total group, known as the Pseudosuchia, contains all crown-group archosaurs that are more closely related to the Crocodylia than to the birds (Benton, 1999).
​
The above phylogenetic tree also shows the stem line of the Crocodylia (in red) together with the stem lines of the higher-order taxa to which the crocodylians belong: the Archosauria (in cyan), the Archelosauria (in purple), the Sauria (in blue) and the Amniota (in green). As there are no known stem-group Archelosauria fossils, and the stem-Sauria and stem-Amniota lines are examined in the page on Rhynchocephalia, we will consider here only the stem-Archosauria and the stem-Crocodylia.

 The stem group of the Archosauria

Many stem-group archosaurs have been identified and several phylogenetic trees of the stem group have been published. One of these is shown below:
The earliest known fossil representing stem-Archosauria is Eorasaurus olsoni, a member of the family Erythrosuchidae found in the North Dvina Horizon of Late Permian (Early Wuchiapingian - Capitanian) age at the Syomin Ovrag ravine near the village of Il’inskoe on the right bank of the Volga River (Sennikov, 1997; Ezcurra and Butler, 2018). Only fragmentary remains can be seen in the available public-domain images of this species, but many of the other species that appear in the above tree are illustrated below (to see larger versions, click on images):
Names in    red indicate   that the fossil is younger  than the oldest known crown-group fossil.
​* after name indicates that the image represents a life restoration.
The above images illustrate the ancestry of the archosaur crown group. Note that most of the stem species (represented by names in red) post-date the appearance of the crown group; these represent branches of the stem line that continued to evolve after the crown-group had appeared.

The species are numbered in order from the most basal to the most crownward in the phylogeny, and a general transition can be seen from lizard-like to crocodile-like forms. For a detailed discussion of the skeletal changes that occurred through the archosaur stem line, see Sookias (2016).

The oldest known crown-group archosaur fossil is the stem crocodylian Ctenosauriscus koeneni, a member of the clade Poposauroidea from the Early Triassic (latest Olenekian) Solling Formation at Bremketal, near Göttingen, Lower Saxony, Germany (Butler et al, 2011; Benton et al, 2015). This fossil is illustrated below (click on image for larger version):
* after name indicates that the image represents a life restoration.
The archosaurian stem group appeared in the Middle Permian (Guadalupian) and continued until the Late Triassic, with the crown group appearing in the Early Triassic:
The above tree indicates that the stem-to-crown transition for the Archosauria lasted only around 10 million years. The tree also illustrates a ghost lineage of 15 million years on the turtle stem line relative to the appearance of the stem-Archosauria.

​The stem group of the Crocodylia

The richness of the fossil record of the stem-Crocodylia has led to much research on their phylogeny over the past few years. The resulting trees are generally similar, and the following, which combines trees from the work of Ezcurra and Butler (2018) and Godoy et al (2019), is a representative example (note that it is divided into two panels):
The earliest-known fossils in the crocodylian stem line are Vytshegdosuchus zbeshartensis and Ctenosauriscus koeneni. They are of approximately the same (Late Olenekian) age, but given the lack of illustrations of the former species only Ctenosauriscus will be considered here. It is a member of the clade Poposauroidea from the Early Triassic (latest Olenekian) Solling Formation at Bremketal, near Göttingen, Lower Saxony, Germany (Butler et al, 2011; Benton et al, 2015). Note that the Poposauridae are by no means the most basal pseudosuchians in the above tree, even though Ctenosauriscus koeneni is the oldest pseudosuchian known. This fossil is illustrated below, together with other members of the stem-group. However, owing to the large number of images, we will consider them in groups that are progressively higher (more crownward) in the tree.

The most basal group comprises the clade Phytosauria. Some examples are shown below (as for all fossil illustrations on this website, click on image to see a larger version): 
​* after name indicates that the image represents a life restoration.
The above images show that the phytosaurs are superficially like crocodiles, but they do actually have several features that distinguish them from all other reptiles (Stocker et al, 2017).
​
The next group of images represent the clade comprising the Aetosauria, Ornithosuchidae and Erpetosuchidae:
​* after name indicates that the image represents a life restoration.
The aetosaurs (represented above by Aetosauroides scagliai, Stagonolepis robertsoni and Aetosaurus ferratus) were heavily armored and had relatively small heads. The Ornithosuchidae (Venaticosuchus rusconii and Riojasuchus tenuisceps above) appear more similar to modern crocodiles, but had a reversed ankle joint relative to crocodiles and might have been capable of walking on their hind legs (Von Baczko and Ezcurra, 2013). Finally, the Erpetosuchidae (Dyoplax arenaceus and Parringtonia gracilis above) appear to have been more slender and more heavily armored than modern crocodiles.
​
The images shown below are examples of the stem clades from the Gracilisuchidae to the Poposauroidea: 
​* after name indicates that the image represents a life restoration.
The Gracilisuchidae (illustrated above by Yonghesuchus sangbiensis, Gracilisuchus stipanicicorum and Turfanosuchus dabanensis) appear to be rather similar to erpetosuchids but lack their heavy armor. In between the Gracilisuchidae and the Poposauroidea there are several species, of which an image is shown above of Ticinosuchus ferox. The latter appears similar in shape to the Gracilisuchidae, but is much larger (up to 3 meters in length). Lastly, we show above some examples of the Poposauroidea clade (Qianosuchus mixtus, Lotosaurus adentus, Arizonasaurus babbitti and Ctenosauriscus koeneni). Some members of the clade (not shown above) were bipedal while others had a “sail” on their back formed by spines extending from the vertebrae. Qianosuchus mixtus appears to have been aquatic (Li et al, 2006). 

The following images represent a long section of the stem-group tree between the Poposauroidea and the Thalattosuchia clades:
​* after name indicates that the image represents a life restoration.
The above images are, as usual on this website, numbered in order from most basal to most crownward. They show a trend from large, thick-set animals to smaller species with longer legs.
​
The next set of images represent the Thalattosuchia clade:
​* after name indicates that the image represents a life restoration.
The images above depict slender animals that are believed to have occupied an aquatic environment (Pierce et al, 2017).
​
All of the stem-group crocodylian fossils that we have examined so far belong to the stem group of the clade Crocodyliformes (see phylogenetic tree above). We will now consider the remainder of the stem-Crocodylia. The following images represent the stem group up to and including the clade Notosuchia: 
Names in    red indicate   that the fossil is younger  than the oldest known crown-group fossil.
​* after name indicates that the image represents a life restoration.
The fossils basal to the Notosuchia (Protosuchus richardsoni, Gobiosuchus kielanae, Sichuanosuchus huidongensis, and Hsisosuchus chungkingensis) appear to be similar to modern crocodiles, but have a blunter snout and are generally quite small. The remainder of the images shown above belong to the Notosuchia, which are generally small (less than a meter in length) and pug-nosed. Apart from the most basal representative, Simosuchus clarki, they appear fairly similar to modern crocodiles, although they occupied predominantly terrestrial habitats (Wilberg et al, 2019). Note that a few of the species shown above (represented by names in red) post-date the appearance of the crown group; these represent branches of the stem line that continued to evolve after the crown-group had appeared.

​The next set of images represent the stem clades from the Tethysuchia to the Goniopholididae:
Names in    red indicate   that the fossil is younger  than the oldest known crown-group fossil.
​* after name indicates that the image represents a life restoration.
The Tethysuchidae are represented above by Pholidosaurus meyeri, Chenanisuchus lateroculi, Terminonaris robusta, Sarcosuchus imperator and Elosuchus cherifiensis. They resemble modern gharials. The Tethysuchidae occupied mainly freshwater environments  (Wilberg et al, 2019). The remaining images above, apart from Nannosuchus gracilidens (a member of the Goniopholididae), which is only pictured as a partial skull, show some resemblance to modern alligators.
​
The final set of images represents the most crownward members of the stem-Crocodylia:
​Names in    red indicate   that the fossil is younger  than the oldest known crown-group fossil.
​* after name indicates that the image represents a life restoration.
The fossils shown above appear similar to modern alligators.
​
The oldest known member of the crown-Crocodylia is Brachychampsa montana, a stem-Alligatoridae first described from the Late Cretaceous “Hell Creek Beds” of the Lance Formation at a location 25 miles southeast of Lismas, Dawson County, Montana (Gilmore, 1911) but later also described in more detail from the Late Cretaceous (Late Campanian) De-na-zin Member of the Kirtland Formation at Willow Wash in the Juan Basin, New Mexico (Sullivan and Lucas, 2003; Norell et al, 1994). A skeleton and a life restoration of this species are shown below (to see a larger image, click on image):
​* after name indicates that the image represents a life restoration.
​The stem-to-crown transition for the Crocodylia took place from late Triassic to Late Cretaceous time, as shown in the following time tree (divided into two panels):
​The duration of the stem-to-crown transition was very long: at least 169 million years. However, most of the evolutionary change occurred in two separate episodes, one in the Middle Triassic and the other in the Late Jurassic to Early Cretaceous:

References

​Benton, M. J. (1999). Scleromochlus taylori and the origin of dinosaurs and pterosaurs.Philosophical Transactions of the Royal Society of London B: Biological Sciences, 354(1388), 1423-1446.

Benton, M. J., Donoghue, P. C., Asher, R. J., Friedman, M., Near, T. J., & Vinther, J. (2015). Constraints on the timescale of animal evolutionary history. Palaeontologia Electronica, 18(1), 1-106.

Brochu, C. A. (2003). Phylogenetic approaches toward crocodylian history. Annual Review of Earth and Planetary Sciences, 31(1), 357-397.

Brochu, C. A., Wagner, J. R., Jouve, S., Sumrall, C. D., & Densmore, L. D. (2009). A correction corrected: consensus over the meaning of Crocodylia and why it matters. Systematic Biology, 58(5), 537-543.

Butler, R. J., Brusatte, S. L., Reich, M., Nesbitt, S. J., Schoch, R. R., & Hornung, J. J. (2011). The sail-backed reptile Ctenosauriscus from the latest Early Triassic of Germany and the timing and biogeography of the early archosaur radiation. PLoS One, 6(10), e25693.

Ezcurra, M. D., & Butler, R. J. (2018). The rise of the ruling reptiles and ecosystem recovery from the Permo-Triassic mass extinction. Proceedings of the Royal Society B, 285(1880), 20180361.

Gilmore, C. W. (1911). A new fossil alligator from the Hell Creek beds of Montana. Proceedings of the United States National Museum.

​Godoy, P. L., Benson, R. B., Bronzati, M., & Butler, R. J. (2019). The multi-peak adaptive landscape of crocodylomorph body size evolution. BMC evolutionary biology, 19(1), 1-29.

Li, C., Wu, X. C., Cheng, Y. N., Sato, T., & Wang, L. (2006). An unusual archosaurian from the marine Triassic of China. Naturwissenschaften, 93(4), 200-206.

Norell, M., Clark, J. M., & Hutchison, J. H. (1994). The Late Cretaceous alligatoroid Brachychampsa montana (Crocodylia): new material and putative relationships. American Museum novitates; no. 3116.

Pierce, S. E., Williams, M., & Benson, R. B. (2017). Virtual reconstruction of the endocranial anatomy of the early Jurassic marine crocodylomorph Pelagosaurus typus (Thalattosuchia). PeerJ, 5, e3225.

Sennikov, A. G. (1997). An enigmatic reptile from the Upper Permian of the Volga River Basin. Paleontological Journal C/C OF Paleontologicheskii  Zhurnal, 31, 94-101.

Sookias, R. B. (2016). The relationships of the Euparkeriidae and the rise of Archosauria. Royal Society open science, 3(3), 150674.

Stocker, M. R., Zhao, L. J., Nesbitt, S. J., Wu, X. C., & Li, C. (2017). A short-snouted, Middle Triassic phytosaur and its implications for the morphological evolution and biogeography of Phytosauria. Scientific Reports, 7(1), 1-9.

Sullivan, R. M., & Lucas, S. G. (2003). Brachychampsa montana Gilmore (Crocodylia, Alligatoroidea) from the Kirtland Formation (Upper Campanian), San Juan Basin, New Mexico. Journal of Vertebrate Paleontology, 23(4), 832-841.

Wilberg, E. W., Turner, A. H., & Brochu, C. A. (2019). Evolutionary structure and timing of major habitat shifts in Crocodylomorpha. Scientific Reports, 9(1), 1-10.

Von Baczko, M. B., & Ezcurra, M. D. (2013). Ornithosuchidae: a group of Triassic archosaurs with a unique ankle joint. Geological Society, London, Special Publications, 379(1), 187-202.
Image credits - Crocodylians
  • Header (American Alligator, Alligator mississippiensis)    By Tim Vickers [Public domain], from Wikimedia Commons​
  • Aenigmastropheus parringtoni: Martín D. Ezcurra, Torsten M. Scheyer, Richard J. Butler. Drawing by Emilio López-Rolandi., CC BY 2.5 <https://creativecommons.org/licenses/by/2.5>, via Wikimedia Commons
  • Protorosaurus speneri (2a): suvuk79, Copyrighted free use, via Wikimedia Commons
  • Protorosaurus speneri (2b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Dinocephalosaurus sp.: Jun Liu, Chris L. Organ, Michael J. Benton, Matthew C. Brandley & Jonathan C. Aitchison, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Dinocephalosaurus orientalis: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Tanystropheus longobardicus (4a): Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Tanystropheus longobardicus (4b): Nobu Tamura, licensed under Creative Commons Attribution- ShareAlike (CC BY-SA)
  • Skull of Macrocnemus bassanii: Vivien P. Jaquier, Nicholas C. Fraser, Heinz Furrer, and Torsten M. Scheyer, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Macrocnemus bassanii: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Macrocnemus obristi: Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Skull of Macrocnemus fuyuanensis: Vivien P. Jaquier, Nicholas C. Fraser, Heinz Furrer, and Torsten M. Scheyer, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Teraterpeton hrynewichorum: PrehistoryByLiam, Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
  • Trilophosaurus buettneri (9a): Daderot, CC0, via Wikimedia Commons
  • Trilophosaurus buettneri (9b): Nobu Tamura, licensed under Creative Commons Attribution- ShareAlike (CC BY-SA)
  • Pamelaria dolichotrachela: Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Shringasaurus indicus (11a): Saradee Sengupta, Martín D. Ezcurra, Saswati Bandyopadhyay, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Shringasaurus indicus (11b): Nobu Tamura, licensed under Creative Commons Attribution- ShareAlike (CC BY-SA)
  • Jawbone of Azendohsaurus madagaskarensis: Martin D. Ezcurra, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Noteosuchus colletti: Ezcurra, Martín D.; Montefeltro, Felipe; Butler, Richard J., CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Skull of Mesosuchus browni: From Open Access article Sobral, G., & Müller, J. (2019). The braincase of Mesosuchus browni (Reptilia, Archosauromorpha) with information on the inner ear and description of a pneumatic sinus. PeerJ, 7, e6798.
  • Mesosuchus browni: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Rhynchosaurus articeps: From Open Access article Ezcurra, M. D., Montefeltro, F., & Butler, R. J. (2016). The early evolution of rhynchosaurs. Frontiers in Ecology and Evolution, 3, 142.
  • Stenaulorhynchus stockleyi: Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Skull of Bentonyx sidensis: Foth et al., CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Skull of Langeronyx brodiei: From Open Access article Ezcurra, M. D., Montefeltro, F., & Butler, R. J. (2016). The early evolution of rhynchosaurs. Frontiers in Ecology and Evolution, 3, 142.
  • Skull of Fodonyx spenceri: British Geological Survey, licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
  • Isalorhynchus genovefae: Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Prolacerta broomi: From Open Access article Spiekman, S.N.F. A new specimen of Prolacerta broomi from the lower Fremouw Formation (Early Triassic) of Antarctica, its biogeographical implications and a taxonomic revision. Sci Rep 8, 17996 (2018). https://doi.org/10.1038/s41598-018-36499-6
  • Skull of Teyujagua paradoxa: Photographs by F. L. Pinheiro et al. Artwork by J. Anderson., CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Skull of Archosaurus rossicus: Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Skull of Proterosuchus fergusi: Foth et al., CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Proterosuchus fergusi: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • 'Chasmatosaurus' yuani: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Head of Sarmatosuchus otschevi: Dmitry Bogdanov, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
  • Jawbone of Guchengosuchus shiguaiensis: From Open Access article Butler, R. J., Ezcurra, M. D., Liu, J., Sookias, R. B., & Sullivan, C. (2019). The anatomy and phylogenetic position of the erythrosuchid archosauriform Guchengosuchus shiguaiensis from the earliest Middle Triassic of China. PeerJ, 7, e6435.
  • Chasmatosuchus rossicus: Dmitry Bogdanov, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Garjainia prima: Dmitry Bogdanov, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
  • Jawbone of Garjainia madiba: David J. Gower, P. John Hancox, Jennifer Botha-Brink, Andrey G. Sennikov, Richard J. Butler, CC BY 2.5 <https://creativecommons.org/licenses/by/2.5>, via Wikimedia Commons
  • Garjainia madiba: From Open Access article Gower, D. J., Hancox, P. J., Botha-Brink, J., Sennikov, A. G., & Butler, R. J. (2014). A new species of Garjainia Ochev, 1958 (Diapsida: Archosauriformes: Erythrosuchidae) from the Early Triassic of South Africa. PLoS One, 9(11), e111154.
  • Head of Uralosaurus magnus: Dmitry Bogdanov, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
  • Skull of Erythrosuchus africanus: Foth et al., CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Erythrosuchus africanus: Nobu Tamura, licensed under Creative Commons Attribution- ShareAlike (CC BY-SA)
  • Jawbone of Chalishevia cothurnata: Open Access article Butler, R. J., Sennikov, A. G., Ezcurra, M. D., & Gower, D. J. (2019). The last erythrosuchid—a revision of Chalishevia cothurnata from the late Middle Triassic of European Russia. Acta Palaeontologica Polonica, 64(4), 757-774.
  • Chalishevia cothurnata: Dmitry Bogdanov, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
  • Shansisuchus shansisuchus (34a): Jonathan Chen, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Shansisuchus shansisuchus (34b): DiBgd, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Euparkeria capensis (35a): Martin D. Ezcurra, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Euparkeria capensis (35b): Nobu Tamura, licensed under Creative Commons Attribution- ShareAlike (CC BY-SA)
  • Jawbones and tooth of Osmolskina czatkowicensis: Magdalena Borsuk-Białynicka and Susan E. Evans, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
  • Osmolskina czatkowicensis: Attribution 2.0 Generic (CC BY 2.0)
  • Skull of Vancleavea campi: Martin D. Ezcurra, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Vancleavea campi: Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Ribcage of Doswellia kaltenbachi: NMNH Paleobiology Department, CC0, via Wikimedia Commons
  • Doswellia kaltenbachi: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Proterochampsa nodosa: Martin D. Ezcurra, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Proterochampsa barrionuevoi: Nobu Tamura (http://spinops.blogspot.com), CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons
  • Pseudochampsa ischigualastensis (41a): M. Jimena Trotteyn, Martín D. Ezcurra, CC BY 2.5 <https://creativecommons.org/licenses/by/2.5>, via Wikimedia Commons
  • Pseudochampsa ischigualastensis (41b): Nobu Tamura, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Skull of Gualosuchus reigi: Foth et al., CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Chanaresuchus bonapartei: Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Ctenosauriscus koeneni (44a): From Open Access article Butler, R. J., Brusatte, S. L., Reich, M., Nesbitt, S. J., Schoch, R. R., & Hornung, J. J. (2011). The sail-backed reptile Ctenosauriscus from the latest Early Triassic of Germany and the timing and biogeography of the early archosaur radiation. PloS one, 6(10), e25693.
  • Ctenosauriscus koeneni (44b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Diandongosuchus fuyuanensis (45a): Michelle R. Stocker, Li-Jun Zhao, Sterling J. Nesbitt, Xiao-Chun Wu & Chun Li, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Diandongosuchus fuyuanensis (45b): Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Smilosuchus sp.: Yinan Chen, Public Domain, via Wikimedia Commons
  • Smilosuchus gregorii: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  •  Skull of Nicrosaurus kapffi: Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Skull of Parasuchus hislopi: Martin D. Ezcurra, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Skull of Parasuchus angustifrons: Stephan Lautenschlager, Richard J. Butler, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Skull of Aetosauroides scagliai: Ana Carolina Biacchi Brust, Julia Brenda Desojo, Cesar Leandro Schultz, Voltaire Dutra Paes-Neto, Átila Augusto Stock Da-Rosa, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Aetosauroides scagliai: Nobu Tamura, licensed under Creative Commons Attribution- ShareAlike (CC BY-SA)  license
  • Stagonolepis robertsoni: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skulls of Aetosaurus ferratus: Jaime Headden, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
  • Aetosaurus ferratus: Петр Меньшиков, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Venaticosuchus rusconii: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Riojasuchus tenuisceps: Maria Belen von Baczko, Julia Brenda Desojo, CC BY 2.5 <https://creativecommons.org/licenses/by/2.5>, via Wikimedia Commons
  • Riojasuchus tenuisceps: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Dyoplax arenaceus: O. Fraas., Public domain, via Wikimedia Commons
  • Parringtonia gracilis: Zissoudisctrucker, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Skull of Yonghesuchus sangbiensis: Richard J. Butler, Corwin Sullivan, Martín D. Ezcurra, Jun Liu, Agustina Lecuona and Roland B. Sookias, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Skull of Gracilisuchus stipanicicorum: Richard J. Butler, Corwin Sullivan, Martín D. Ezcurra, Jun Liu, Agustina Lecuona and Roland B. Sookias, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Gracilisuchus stipanicicorum: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Turfanosuchus dabanensis (59a): Captmondo, Copyrighted free use, via Wikimedia Commons
  • Turfanosuchus dabanensis (59b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Ticinosuchus ferox (60a): Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Ticinosuchus ferox (60b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Qianosuchus mixtus: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Lotosaurus adentus (62a): Jonathan Chen, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Lotosaurus adentus (62b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Arizonasaurus babbitti: Nobu Tamura, licensed under Creative Commons Attribution- ShareAlike (CC BY-SA)  license
  • Youngosuchus sinensis: Jonathan Chen, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Prestosuchus chiniquensis (66a): Vince Smith from London, United Kingdom, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons
  • Prestosuchus chiniquensis (66b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Rauisuchus tiradentes: Paleocolour, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Postosuchus sp.: Dallas Krentzel, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
  • Postosuchus kirkpatricki: Nobu Tamura, licensed under Creative Commons Attribution- ShareAlike (CC BY-SA)  license
  • Reconstructed skull of Carnufex carolinensis: Open Access article Zanno, L.E., Drymala, S., Nesbitt, S.J. & Schneider, V.P. Early crocodylomorph increases top tier predator diversity during rise of dinosaurs. Sci. Rep. 5, 9276; DOI:10.1038/srep09276 (2015), licensed under a Creative Commons Attribution 4.0 International License
  • Pseudhesperosuchus jachaleri: Tiouraren, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Saltoposuchus connectens: Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Litargosuchus leptorhynchus: Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Terrestrisuchus gracilis: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Hesperosuchus agilis: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Dibothrosuchus elaphros (75a): Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Dibothrosuchus elaphros (75b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Hallopus victor: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Platysuchus multiscrobiculatus: Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Steneosaurus bollensis (78a): Didier Descouens, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Steneosaurus bollensis (78b): Nobu Tamura, licensed under Creative Commons Attribution- ShareAlike (CC BY-SA)  license
  • Skull of Steneosaurus heberti: Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons 
  • Skulls of Steneosaurus megistorhynchus: G.Garitan, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Machimosaurus mosae: Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Pelagosaurus typus (82a): Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Pelagosaurus typus (82b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Teleidosaurus calvadosii: Société linnéenne de Normandie, No restrictions, via Wikimedia Commons
  • Protosuchus richardsoni (84a): Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Protosuchus richardsoni (84b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Gobiosuchus kielanae: Halszka Osmólska, Stephane Hua, and Eric Buffetaut, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
  • Sichuanosuchus huidongensis (86a): Zhangzhugang, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Sichuanosuchus huidongensis (86b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Hsisosuchus chungkingensis: Einar Fredriksen, CC BY-SA 2.0 <https://creativecommons.org/licenses/by-sa/2.0>, via Wikimedia Commons
  • Simosuchus clarki: D. Gordon E. Robertson, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Anatosuchus minor (89a): Sereno PC, Larsson HCE, licensed under the Creative Commons Attribution 3.0 Unported license.
  • Anatosuchus minor (89b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Araripesuchus wegeneri: Sereno PC, Larsson HCE, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
  • Araripesuchus wegeneri: Todd Marshall, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
  • Araripesuchus buitreraensis: Museo Provincial Carlos Ameghino, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Uruguaysuchus aznarezi: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Mahajangasuchus insignis: Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Mahajangasuchus insignis: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Kaprosuchus saharicus: Carol Abraczinskas, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
  • Kaprosuchus saharicus: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Montealtosuchus arrudacamposi: MARCO AURÉLIO ESPARZ…, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Uberabasuchus terrificus (96a): Andre Borges Lopes, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Uberabasuchus terrificus (96b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Pholidosaurus meyeri: FunkMonk, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Pholidosaurus meyeri: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Chenanisuchus lateroculi: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Terminonaris robusta: Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Sarcosuchus imperator (100a): Shadowgate from Novara, ITALY, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
  • Sarcosuchus imperator (100b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Elosuchus cherifiensis: Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Elosuchus cherifiensis: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Alligatorium meyeri: Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Alligatorellus beaumonti (103a): Ghedoghedo, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Alligatorellus beaumonti (103b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Atoposaurus oberndorferi: Ghedoghedo, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Theriosuchus pusillus (105a): C. L. Griesbach, Public domain, via Wikimedia Commons
  • Theriosuchus pusillus (105b): Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Knoetschkesuchus langenbergensis (106a): Daniela Schwarz, Maik Raddatz, Oliver Wings, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons
  • Knoetschkesuchus langenbergensis (106b): Hyrotrioskjan, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Skull of Nannosuchus gracilidens: The Trustees of the Natural History Museum, London, https://creativecommons.org/licenses/by/4.0/
  • Bernissartia fagessi: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Isisfordia duncani: Smokeybjb, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
  • Skull of Allodaposuchus precedens: Zoltan Csiki-Sava, Eric Buffetaut, Attila Ősi, Xabier Pereda-Suberbiola, Stephen L. Brusatte, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
  • Allodaposuchus precedens: Nobu Tamura under a Creative Commons 3.0 Unported (CC BY-NC-ND 3.0) license
  • Skull of Agaresuchus subjuniperus: Zoltan Csiki-Sava, Eric Buffetaut, Attila Ősi, Xabier Pereda-Suberbiola, Stephen L. Brusatte, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
  • Jaws of Lohuecosuchus megadontos: PePeEfe, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
  • Skull of Iharkutosuchus makadii: Zoltan Csiki-Sava, Eric Buffetaut, Attila Ősi, Xabier Pereda-Suberbiola, Stephen L. Brusatte, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
  • Brachychampsa sp.: Daderot, CC0, via Wikimedia Commons
  • Brachychampsa montana: Nobu Tamura, licensed under Creative Commons Attribution- ShareAlike (CC BY-SA)  license