Baurusuchidae

Baurusuchidae Temporal range: 90–66 Ma PreЄ Є O S D C P T J K Pg N Turonian - Maastrichtian
Skull of Baurusuchus salgadoensis
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	Crocodylomorpha
Branch:	†Sebecosuchia
Branch:	†Baurusuchia Warren, 1968
Family:	†Baurusuchidae Price, 1945
Subgroups
See text.

Baurusuchidae is a Gondwanan family of mesoeucrocodylians that lived during the Late Cretaceous. It is a group of terrestrial hypercarnivorous crocodilians from South America (Argentina and Brazil) and possibly Pakistan. Baurusuchidae has been defined as a clade containing the most recent common ancestor of Baurusuchus and Stratiotosuchus and all of its descendants. It may, however, be polyphyletic, as recent phylogenetic analyses have placed Baurusuchus within Notosuchia and other baurusuchids within the more distantly related clade Sebecia. A recent study of the family finds it monophyletic by including the South American genera Baurusuchus, Cynodontosuchus, Pissarrachampsa, Stratiotosuchus, and Wargosuchus. Other traditional baurusuchids like Pabwehshi are excluded. The recently named Campinasuchus is also included in the family. Baurusuchids have been placed in the suborder Baurusuchia, and two subfamilies have been proposed: Baurusuchinae and Pissarrachampsinae.

Genera

Several genera have been assigned to Baurusuchidae. Baurusuchus was the first, being the namesake of the family. Remains of Baurusuchus have been found from the Late Cretaceous Bauru Group of Brazil in deposits that are Turonian - Santonian in age.^[1] In addition to Baurusuchus, five other South American crocodyliforms have been assigned to Baurusuchidae: Campinasuchus, Cynodontosuchus, Pissarrachampsa, Stratiotosuchus, and Wargosuchus. Cynodontosuchus was the first known baurusuchid, named in 1896 by English paleontologist Arthur Smith Woodward, although it was only recently assigned to Baurusuchidae.^[2] Wargosuchus was described in 2008.^[3] Cynodontosuchus and Wargosuchus are known only from fragmentary remains. Both genera are from the Santonian of Argentina.

Skull of Pissarrachampsa.

A fourth genus, Stratiotosuchus, was assigned to Baurusuchidae in 2001. Fossils have been found from the Turonian - Santonian of Brazil.^[4] Pabwehshi is the youngest genus that has been assigned to Baurusuchidae, and is from the Maastrichtian of Pakistan.^[5] It was named in 2001 but has since been reassigned as a basal member of Sebecia.^[6]

A new genus, Campinasuchus, was assigned to the family in May, 2011. It is known from the Turonian-Santonian Adamantina Formation of the Bauru Basin of Brazil.^[7] Soon after, the new genus Pissarrachampsa was named from the Campanian–Maastrichtian Vale do Rio do Peixe Formation, also in the Bauru Basin.

Phylogeny

The family Baurusuchidae was named by Brazilian paleontologist Llewellyn Ivor Price in 1945 to include Baurusuchus.^[8] In 1946, American paleontologist Edwin Harris Colbert erected the group Sebecosuchia, which united Baurusuchidae with the family Sebecidae (represented by the genus Sebecus).^[9] Both Baurusuchus and Sebecus have deep snouts and ziphodont dentitions (teeth that are serrated and laterally compressed).^[10] Other forms were later found that had a close appearance to these two genera, among them Cynodontosuchus, Stratiotosuchus, and Wargosuchus. Several features were used to unite these groups: a deep snout, a ziphodont dentition, a curved tooth row, an enlarged canine-like dentary tooth that fits into a deep notch in the upper jaw, and a groove on the lower jaw.^[11]

Many phylogenetic analyses within the past decades have supported a close relationship between the two families.^[10] Baurusuchids and sebecosuchids are both early members of the clade Metasuchia, which includes the subgroups Notosuchia (mainly terrestrial crocodyliforms) and Neosuchia (larger, often semiaquatic crocodyliforms, including living crocodylians). Sebecosuchians, which include both baurusuchids and sebecosuchids, were found to be closely related to notosuchians in several studies.^[12] The new genera Iberosuchus and Eremosuchus were later assigned to Baurusuchidae, and phylogenetic analyses encompassing these taxa continued to find Baurusuchidae to be closely related to Sebecidae.^[13] Both families were allied with notosuchians in the larger group Ziphosuchia, composed of ziphodont crocodyliforms. More recently, sebecosuchians - including baurusuchids - have been placed within Notosuchia as derived members of the clade. Below is a modified cladogram from Ortega et al. (2000) placing baurusuchids within Notosuchia:^[14]

Notosuchia	Notosuchus Libycosuchus Baurusuchus Iberosuchus Sebecus Itaborai crocodile Bretesuchus     Baurusuchids

In 2004, the superfamily Baurusuchoidea was established to include baurusuchids and sebecids. Phylogenetically, Baurusuchoidea was defined as the most recent common ancestor of Baurusuchus and Sebecus and all of its descendants while Baurusuchidae was defined as the most recent common ancestor of Baurusuchus and Stratiotosuchus and all of its descendants.^[15]

In a 2005 analysis, Sebecidae was found to be a paraphyletic grouping, or a grouping that includes some descendants of a common ancestor but not all. Sebecids formed an assemblage of basal sebecosuchians, while baurusuchids remained a valid grouping of derived sebecosuchians. Below is a modified cladogram from Turner and Calvo (2005):^[16]

Metasuchia	Neosuchia Libycosaurus Notosuchia  Sebecosuchia  Pehuenchesuchus Eremosuchus Sebecus Iberosuchus Bretesuchus  Baurusuchidae  Baurusuchus Pabwehshi

Later studies noted many features that distinguished baurusuchids from sebecosuchids. Sebecosuchids were often considered to be more closely related to Neosuchia, a group that includes modern crocodylians, while baurusuchids were thought to be a more distantly related clade.^[17] In a 1999 phylogenetic analysis, Baurusuchus formed a clade with notosuchians to the exclusion of other ziphosuchians.^[18] This placement has been upheld by recent analyses, which place Baurusuchus within Notosuchia.^[19]

In 2007, a new clade called Sebecia was erected.^[6] Sebecia included sebecids and peirosaurids. Peirosauridae, a family of small terrestrial crocodyliforms, had often been placed in or near Neosuchia in previous studies. The assignment of sebecids to Sebecia placed the family closer to Neosuchia than Notosuchia. In this study, baurusuchids were split up, with Baurusuchus placed as a more basal metasuchian and the remaining baurusuchids (Bretesuchus and Pabwehshi) placed as sebecians. Therefore, the family Baurusuchidae was paraphyletic. Below is a modified cladogram from Larsson and Sues (2007):^[6]

Metasuchia	Notosuchia Notosuchus Malawisuchus Araripesuchus Baurusuchus Neosuchia  Sebecia  Pabwehshi  Sebecidae  Sebecus Bretesuchus Peirosauridae     Baurusuchids

More recent studies have nested Baurusuchus deep within Notosuchia, just as the larger group Sebecosuchia once was, while the remaining sebecosuchian genera have been placed more distantly in Metasuchia.^[19] A new baurusuchid called Pissarrachampsa was named in 2011, and a comprehensive phylogenetic analysis of baurusuchids was conducted along with its description. Montefeltro et al. (2011) found Baurusuchidae to be a monophyletic group with the genera Baurusuchus, Cynodontosuchus, Pissarrachampsa, Stratiotosuchus, and Wargosuchus. They adopted the name Baurusuchia in a phylogenetic sense to distinguish baurusuchids from related crocodyliforms. Baurusuchia was first erected as an infraorder in 1968, but in the 2011 analysis it was found to be in an identical position to Baurusuchidae in the final tree. The only difference between Baurusuchidae and Baurusuchia is that the former is a node-based taxon and the latter is a stem-based taxon. Baurusuchidae is defined as the least inclusive clade containing Baurusuchus, Cynodontosuchus, Pissarrachampsa, Stratiotosuchus, and Wargosuchus. As in all node-based clades, there is a most recent common ancestor; these genera are all of its known descendants. Baurusuchia is defined as Baurusuchus pricei and all Crocodyliformes that share a more recent common ancestor with B. pricei than with Notosuchus terrestris, Mariliasuchus amarali, Armadillosuchus arrudai, Araripesuchus gomesi, Sebecus icaeorhinus, Bretesuchus bonapartei, Peirosaurus torminni, or Crocodylus niloticus.^[11]

In contrast to the node-based Baurusuchidae, the stem-based Baurusuchia does not include a common ancestor and all its descendants, but rather all forms more closely related to a specific baurusuchid than a non-baurusuchid. As a stem-based taxon, Baurusuchia is more inclusive than Baurusuchidae; a new taxon could potentially be placed outside Baurusuchidae because it is not a descendant of the most recent common ancestor of baurusuchids, but would still be a baurusuchian because it is more closely related to baurusuchids than it is to other crocodyliforms. For now, however, Baurusuchidae and Baurusuchia are essentially identical in scope.^[11]

Montefeltro et al. (2011) also divided Baurusuchidae into two subfamilies, Pissarrachampsinae and Baurusuchinae. Pissarrachampsinae includes Pissarrachampsa and Wargosuchus while Baurusuchinae includes Stratiotosuchus and Baurusuchus. Cynodontosuchus is not a member of either of these subfamilies, but the most basal baurusuchid. Many of the unique features that separate Cynodontosuchus may also be associated with a juvenile individual. The material that Cynodontosuchus is based on has been suggested to be a juvenile form of Baurusuchus, and the two taxa may be synonymous.^[11]

Below is a cladogram from Montefeltro et al. (2011):^[11]

Notosuchia	Notosuchus Mariliasuchus Armadillosuchus  Baurusuchia/Baurusuchidae  Cynodontosuchus  Pissarrachampsinae  Pissarrachampsa Wargosuchus  Baurusuchinae  Stratiotosuchus Baurusuchus B. albertoi B. salgadoensis B. pachecoi

A sixth genus of baurusuchid, Campinasuchus, was named just a few months before Pissarrachampsa, and was not included in the analysis.^[20]

Paleobiology

In 2011, fossilized eggs were described from the Late Cretaceous Adamantina Formation of Brazil that may have been laid by a baurusuchid, most probably Baurusuchus. A new oospecies called Bauruoolithus fragilis was named on the basis of these remains. The eggs are about twice as long as they are wide and have blunt ends. At about a quarter of a millimeter in thickness, the shells are relatively thin. Some eggs may have already hatched by the time they were buried, but none show extensive degradation. In living crocodilians (the closest living relatives of baurusuchids), eggs undergo extrinsic degradation to allow hatchlings to easily break through their shells. The fossils indicate that baurusuchid hatchlings probably broke through thin egg shells rather than shells that had been degraded over their incubation period.^[21]

References

1. Candeiro, C.R.A.; Martinelli, A.G.; Avilla, L.S.; Rich, T.H. (2006). "Tetrapods from the Upper Cretaceous (Turonian-Maastrichtian) Bauru Group of Brazil: a reappraisal". Cretaceous Research. 27 (6): 923–946. doi:10.1016/j.cretres.2006.05.002.
2. Woodward, A.S. (1896). ". On two Mesozoic crocodilians, Notosuchus (genus novum) and Cynodontosuchus (genus novum) from the red sandstones of the Territory of Neuquén (Argentine Republic)". Anales del Museo de la Plata (Paleontología). 4: 1–20.
3. Martinelli, A.G.; Pais, D.F. (2008). "A new baurusuchid crocodyliform (Archosauria) from the Late Cretaceous of Patagonia (Argentina)". Comptes Rendus Palevol. 7 (6): 371–381. doi:10.1016/j.crpv.2008.05.002.
4. Campos, D.A.; Suarez, J.M.; Riff, D.; Kellner, A.W.A (2001). "Short note on a new Baurusuchidae (Crocodyliformes, Metasuchia) from the Upper Cretaceous of Brazil". Bol. do Museu Nacional, Geologia. 57: 1–7.
5. Wilson, J.A.; Malkane, M.S.; Gingerich, P.D. (2001). "New crocodyliform (Reptilia, Mesoeucrocodylia) from the Upper Cretaceous Pab Formation of Vitakri, Balochistan (Pakistan)". Contributions from the Museum of Paleontology, University of Michigan. 30 (12): 321–336.
6. Larsson, H. C. E.; Sues, H.-D. (2007). "Cranial osteology and phylogenetic relationships of Hamadasuchus rebouli (Crocodyliformes: Mesoeucrocodylia) from the Cretaceous of Morocco". Zoological Journal of the Linnean Society. 149: 533–567. doi:10.1111/j.1096-3642.2007.00271.x.
7. Carvalho, I.S.; et al. (2011). "Campinasuchus dinizi gen. et sp. nov., a new Late Cretaceous baurusuchid (Crocodyliformes) from the Bauru Basin, Brazil". Zootaxa (2871): 19–42. Preview PDF.
8. Price, L.I. (1945). "A new reptile from the Cretaceous of Brazil". Rio de Janeiro, Departamento Nacional da Produção Mineral, Notas preliminares e estudos. 25: 1–8.
9. Colbert, E.H. (1946). "Sebecus, representative of a peculiar suborder of fossil Crocodilia from Patagonia". Bulletin of the American Museum of Natural History. 87: 217–270.
10. Carvalho, I.S.; Campos, A.C.A.; Nobre, P.H. (2005). "Baurusuchus salgadoensis, a new Crocodylomorpha from the Bauru Basin (Cretaceous), Brazil" (PDF). Gondwana Research. 8 (1): 11–30. doi:10.1016/S1342-937X(05)70259-8. ISSN 1342-937X.
11. Montefeltro, F.C.; Larsson, H.C.E.; Langer, M.C. (2011). "A new baurusuchid (Crocodyliformes, Mesoeucrocodylia) from the Late Cretaceous of Brazil and the phylogeny of Baurusuchidae". PLoS ONE. 6 (7): e21916. doi:10.1371/journal.pone.0021916. PMC 3135595. PMID 21765925.
12. Gasparini, Z.B.; Chiappe, L.M.; Fernandez, M. (1991). "A new Senonian peirosaurid (Crocodylomorpha) from Argentina and a sinopsis of the South American Cretaceous crocodilians". Journal of Vertebrate Paleontology. 11 (3): 316–333. doi:10.1080/02724634.1991.10011401.
13. Ortega, F.; Buscaloni, A.D; Gasaparini, Z. (1996). "Reinterpretation and new denomination of Atacisaurus crassiproratus (Middle Eocene; Issel, France) as cf. Iberosuchus (Crocodylomorpha, Metasuchia)". Geobios. 29: 353–364. doi:10.1016/S0016-6995(96)80037-4.
14. Ortega, F. Z.; Buscalioni, A. D.; Calvo, J. O. (2000). "A new species of Araripesuchus (Crocodylomorpha, Mesoeucrocodylia) from the Lower Cretaceous of Patagonia (Argentina)". Journal of Vertebrate Paleontology. 20 (1): 57–76. doi:10.1671/0272-4634(2000)020[0057:ANSOAC]2.0.CO;2.
15. Carvalho, I.S.; Ribeiro, L.C.B.; Avilla, L.S. (2004). "Uberabasuchus terrificus sp. nov., a new Crocodylomorpha from the Bauru Basin (Upper Cretaceous), Brazil" (PDF). Gondwana Research. 7 (4): 975–1002. doi:10.1016/S1342-937X(05)71079-0. ISSN 1342-937X.
16. Turner, A.H.; Calvo, J.O. (2005). "A new sebecosuchian crocodyliform from the Late Cretaceous of Patagonia". Journal of Vertebrate Paleontology. 25 (1): 87–98. doi:10.1671/0272-4634(2005)025[0087:ANSCFT]2.0.CO;2.
17. Clark, J.M. (1997). "Patterns of evolution in Mesozoic Crocodyliformes". In Fraser, N.C.; Sues, H.-D. In the Shadow of the Dinosaurs: Early Mesozoic Tetrapods. Cambridge: Cambridge University Press. pp. 84–97.
18. Pol, D. (1999). "Basal Mesoeucrocodylian relationships: new clues to old conflicts". Journal of Vertebrate Paleontology. 19 (3, Supplement): 69A. doi:10.1080/02724634.1999.10011202.
19. Sereno, P. C.; Larsson, H. C. E. (2009). "Cretaceous crocodyliforms from the Sahara". ZooKeys. 28 (2009): 1–143. doi:10.3897/zookeys.28.325.
20. Ismar De Souza Carvalho; Vicente De Paula Antunes Teixeira; Mara Lúcia Da Fonseca Ferraz; Luiz Carlos Borges Ribeiro; Agustín Guillermo Martinelli; Francisco Macedo Neto; Joseph J. W. Sertich; Gabriel Cardoso Cunha; Isabella Cardoso Cunha & Patrícia Fonseca Ferraz (2011). "Campinasuchus dinizi gen. et sp. nov., a new Late Cretaceous baurusuchid (Crocodyliformes) from the Bauru Basin, Brazil" (PDF). Zootaxa. 2871: 19–42.
21. Oliveira, C.E.M.; Santucci, R.M.; Andrade, M.B.; Fulfaro, V.J.; Basílo, J.A.F.; Benton, M.J. (2011). "Crocodylomorph eggs and eggshells from the Adamantina Formation (Bauru Group), Upper Cretaceous of Brazil". Palaeontology. 54 (2): 309–321. doi:10.1111/j.1475-4983.2010.01028.x.