Stangerochampsa

Stangerochampsa is an extinct genus of globidontan alligatoroid, possibly an alligatorine or a stem-caiman, from the Late Cretaceous of Alberta. It is based on RTMP.86.61.1, a skull, partial lower jaws, and partial postcranial skeleton discovered in the late Campanian–early Maastrichtian-age Horseshoe Canyon Formation. Stangerochampsa was described in 1996 by Wu and colleagues. The type species is S. mccabei. The generic name honors the Stanger family, the owners of the ranch where the specimen was found, and the species name honors James Ross McCabe, who discovered, collected, and prepared it. Stangerochampsa is described as "small to medium–sized"; the type skull is 20.0 centimetres (7.9 in) long from the tip of the snout to the occipital condyle, and is 13.0 centimetres (5.1 in) wide at its greatest, while the thigh bone is 14.2 centimetres (5.6 in) long. It had heterodont dentition, with large crushing teeth at the rear of the jaws.[2]

Stangerochampsa
Temporal range: Late Cretaceous,
Skeletal mount on display at the National Museum of Natural History
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Superfamily: Alligatoroidea
Clade: Globidonta
Genus: †Stangerochampsa
Wu et al., 1996
Type species
†Stangerochampsa mccabei
Wu et al., 1996

Classification

Wu and colleagues, using phylogenetic analyses, found their new genus to be closest to Brachychampsa, and then Albertochampsa and Hylaeochampsa successively, as part of a clade within Alligatorinae that also included Allognathosuchus, Ceratosuchus, and Wannaganosuchus. This arrangement also unites most Mesozoic and Paleogene alligatorines.[2] Brochu (1999), in an analysis of all alligatoroids, found Stangerochampsa and Brachychampsa to be just outside Alligatoridae, and suggested that Stangerochampsa and Albertochampsa were synonymous.[3] Brochu (2004)[4] and Hill and Lucas (2006)[5] also found Stangerochampsa to be outside of Alligatorinae; Hill and Lucas found Albertochampsa to its sister taxon.[5]

Below is a cladogram based on the results of a 2018 tip dating study by Lee & Yates that simultaneously used morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data, which shows Stangerochampsa's placement within Globidonta.[6]

Crocodylia
Alligatoroidea

Leidyosuchus†

Diplocynodontinae†

Diplocynodon†

Globidonta

Stangerochampsa†

Brachychampsa†

Navajosuchus†

Alligatoridae
Caimaninae

Caiman

Melanosuchus

Paleosuchus

Alligatorinae

Alligator

extinct basal Crocodilians† (including Mekosuchinae†)

Longirostres
Crocodyloidea

extinct basal crocodiles†

Crocodylidae

Gavialoidea

extinct basal Gavialoids†

Gavialidae

Gavialis

Tomistoma

On the other hand, in the phylogenetic analysis conducted by Bona et al. (2018) Stangerochampsa was recovered as an alligatorid, specifically as a stem-caiman, as shown in the cladogram below.[7]

Alligatoroidea

Leidyosuchus†

Diplocynodon†

Alligatoridae
Alligatorinae

Ceratosuchus†

Allognathosuchus†

Navajosuchus†

Arambourgia†

Procaimanoidea†

Wannaganosuchus†

Alligator prenasalis†

Alligator mcgrewi†

Alligator olseni†

Alligator sinensis Chinese alligator

Culebrasuchus†

Alligator mississippiensis American alligator

Alligator mefferdi†

Alligator thomsoni†

(stem-based group)
Caimaninae

Stangerochampsa†

Albertochampsa†

Brachychampsa†

Protocaiman†

Gnatusuchus†

Globidentosuchus†

Eocaiman†

Notocaiman†

Kuttanacaiman†

Purussaurus†

Mourasuchus†

Necrosuchus†

Tsoabichi†

Paleosuchus trigonatus Smooth-fronted caiman

Paleosuchus palpebrosus Cuvier's dwarf caiman

Centenariosuchus†

Caiman latirostris Broad-snouted caiman

Melanosuchus niger Black caiman

Caiman yacare Yacare caiman

Caiman crocodilus Spectacled caiman

Caiman brevirostris†

La Venta Caiman†

Caiman wannlangstoni†

(stem-based group)
(crown group)
(stem-based group)

References
  1. Rio, Jonathan P.; Mannion, Philip D. (6 September 2021). "Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem". PeerJ. 9: e12094. doi:10.7717/peerj.12094. PMC 8428266. PMID 34567843.
  2. Wu, Xiao-Chun; Brinkman, Donald B.; Russell, Anthony P. (1996). "A new alligator from the Upper Cretaceous of Canada and the relationships of early eusuchians" (PDF). Palaeontology. 39 (2): 351–375. Archived from the original (PDF) on 2011-09-28.
  3. Brochu, C. A. (1999). "Phylogenetics, taxonomy, and historical biogeography of Alligatoroidea". Society of Vertebrate Paleontology Memoir. 6: 9–100. doi:10.2307/3889340. JSTOR 3889340.
  4. Brochu, Christopher A. (2004). "Alligatorine phylogeny and the status of Allognathosuchus Mook, 1921". Journal of Vertebrate Paleontology. 24 (4): 857–873. doi:10.1671/0272-4634(2004)024[0857:APATSO]2.0.CO;2. JSTOR 4524781. S2CID 85050852.
  5. Hill, Robert V.; Lucas, Spencer G. (2006). "New data on the anatomy and relationships of the Paleocene crocodylian Akanthosuchus langstoni" (PDF). Acta Palaeontologica Polonica. 51 (3): 455–464.
  6. Michael S. Y. Lee; Adam M. Yates (27 June 2018). "Tip-dating and homoplasy: reconciling the shallow molecular divergences of modern gharials with their long fossil". Proceedings of the Royal Society B: Biological Sciences. 285 (1881). doi:10.1098/rspb.2018.1071. PMC 6030529. PMID 30051855.
  7. Paula Bona; Martín D. Ezcurra; Francisco Barrios; María V. Fernandez Blanco (2018). "A new Palaeocene crocodylian from southern Argentina sheds light on the early history of caimanines". Proceedings of the Royal Society B: Biological Sciences. 285 (1885): 20180843. doi:10.1098/rspb.2018.0843. PMC 6125902. PMID 30135152.
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