Susisuchus

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Susisuchus
Temporal range: Early Cretaceous
Susisuchus specimen.PNG
S. anatoceps specimen (A) and cross sectioned samples (B-C)
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauria
Clade: Pseudosuchia
Clade: Crocodylomorpha
Clade: Crocodyliformes
Clade: Neosuchia
Family: Susisuchidae
Salisbury et al., 2003
Genus: Susisuchus
Salisbury et al., 2003
Species
  • S. anatocepsSalisbury et al., 2003 (type)
  • S. jaguaribensisFortier and Schultz, 2009

Susisuchus is an extinct genus of neosuchian mesoeucrocodylian crocodyliform from the Early Cretaceous of Brazil. Fossils have been found from the Nova Olinda Member of the Aptian-age Crato Formation in the Araripe and Lima Campos Basins of northeastern Brazil. Named in 2003, Susisuchus is the sole member of the family Susisuchidae, and is closely related to the clade Eusuchia, which includes living crocodilians. The type species is S. anatoceps, known from a single partial articulated skeleton that preserves some soft tissue. A second species, S. jaguaribensis, was named in 2009 from fragmentary remains.

Discovery

Size of S. anatoceps and other Brazilian Cretaceous crocodylomorphs Size of Brazilian fossil crocodylomorphs.PNG
Size of S. anatoceps and other Brazilian Cretaceous crocodylomorphs

The genus Susisuchus was first erected with the description of the type species S. anatoceps in 2003. S. anatoceps was found in the Aptian-age Crato Formation in the Araripe Basin, and was the first crocodyliform to be described from the formation. The holotype skeleton is the most complete known specimen of Susisuchus, including most of the bones except for those of the hindlimbs, and even traces of soft tissue. The specimen is thought to have been a desiccated carcass before it was buried and later fossilized. A second species, S. jaguaribensis, was named in 2009 from the Lima Campos Basin about 115 kilometres (71 mi) from where the skeleton of S. anatoceps was uncovered. [1]

A new crocodyliform specimen from the Crato Formation was described in 2009. It can be distinguished from the two other crocodyliforms known from the formation, Araripesuchus and the trematochampsid Caririsuchus , on the basis of characteristics of the fibula and proportions of the femur and tibia. Since the limb elements differ from all other known crocodyliforms from the Araripe Basin, the specimen was tentatively classified as cf. Susisuchus sp. [2]

Description

The holotype specimen of Susisuchus anatoceps includes a skull and lower jaw, forelimbs, parts of the axial skeleton, and some osteoderms. There are traces of soft tissue around both forelimbs and the digits of the right hand. S. jaguaribensis is known from far less material, but the fragmentary remains are enough to diagnose the species. Both species have a contact between the squamosal and parietal bones that is situated on the posterior border of the supratemporal fenestra, a hole in the skull table. [1]

Osteoderms

Segmentation of dorsal osteoderms over time in advanced neosuchians (Susisuchus second from left). Neosuchian osteoderms.svg
Segmentation of dorsal osteoderms over time in advanced neosuchians (Susisuchus second from left).

Susisuchus has a dorsal shield of osteoderms that is similar to those of the more derived clade Eusuchia, which includes living crocodilians. Susisuchus was one of the first mesoeucrocodylians to have a tetraserial paravertebral shield, which is formed from the dorsal osteoderms to make the back more rigid. In a tetraserial paravertebral shield, there are four separate rows of paravertebral osteoderms (osteoderms near the midline of the back). Earlier mesoeucrocodylians such as Bernissartia have biserial paravertebral shields, in which there are only two rows of paravertebral osteoderms. These two rows of large osteoderms became segmented into four smaller rows in Susisuchus. [3] Susisuchus also has two rows of accessory osteoderms to either side of the paravertebral osteoderms which are not part of the shield. [4]

The segmentation of the paravertebral shield allowed for a greater degree of lateral flexibility in the trunk of Susisuchus. This flexibility would have enabled lateral undulation while swimming, resulting in greater efficiency in locomotion. Because the width of the paravertebral shield was not compromised by this segmentation, the back would remain rigid enough to overcome the forces encountered during high-walking, or walking semi-erect. However, the ability to high-walk would have restricted the size of Susisuchus. If Susisuchus grew any larger than 50 kilograms (110 lb), the forces encountered during high-walking would have been too great for the paravertebral shield to counteract. [3]

Classification

Possible resting postures of S. anatoceps at various depths Resting postures of Susisuchus.PNG
Possible resting postures of S. anatoceps at various depths

Susisuchus is closely related to Pachycheilosuchus from Glen Rose, Texas, United States, and Isisfordia from Winton, Queensland, Australia. All three genera are highly derived Early Cretaceous mesoeucrocodylians. [4] In the initial description of Susisuchidae, Isisfordia was considered a possible member of the family, although the genus had not yet been named. However, with its naming in 2006, Isisfordia was placed within Eusuchia as the most basal member of the clade, while Susisuchus was placed outside Eusuchia as its sister taxon. Below is a cladogram from Salisbury et al. (2006) showing the relationships of Susisuchus and Isisfordia within Mesoeucrocodylia: [3]

Mesoeucrocodylia' 

Susisuchus has amphicoelus thoracic, lumbar and caudal (tail) vertebrae, meaning that the ends of the centra of these vertebrae are concave. The presence of this feature in a crocodyliform with a tetraserial paravertebral shield is unusual, and has been used to erect the family Susisuchidae, of which Susisuchus is the only member. [4] Susisuchus can be considered a transitional form because it has a tetraserial paravertebral shield characteristic of eusuchians, but retains more primitive amphicoelus vertebrae characteristic of more basal crocodylomorphs.

With the description of S. jaguaribensis as a second species of Susisuchus, the genus has been phylogenetically redefined as a node-based taxon including the last common ancestor of Susisuchus anatoceps and Susisuchus jaguaribensis and all of its descendants. [1]

Related Research Articles

<span class="mw-page-title-main">Mesoeucrocodylia</span> Clade of reptiles

Mesoeucrocodylia is the clade that includes Eusuchia and crocodyliforms formerly placed in the paraphyletic group Mesosuchia. The group appeared during the Early Jurassic, and continues to the present day.

<i>Simosuchus</i> Extinct genus of reptiles

Simosuchus is an extinct genus of notosuchian crocodylomorphs from the Late Cretaceous of Madagascar. It is named for its unusually short skull. Fully grown individuals were about 0.75 metres (2.5 ft) in length. The type species is Simosuchus clarki, found from the Maevarano Formation in Mahajanga Province, although one isolated multicuspid tooth of this genus was discovered in Kallamedu Formation of India.

<i>Mariliasuchus</i> Extinct genus of reptiles

Mariliasuchus is an extinct genus of Late Cretaceous notosuchian mesoeucrocodylian found near Marilia, Brazil. The first bone remains were found and collected in 1995 by Brazilian paleontologist William Nava, in red rocks from the fossiliferous Adamantina Formation. Four years later, it was described as Mariliasuchus amarali, by Brazilian paleontologists Ismar de Souza Carvalho and Reinaldo J. Bertini.

Hyposaurus is a genus of extinct marine dyrosaurid crocodyliform. Fossils have been found in Paleocene aged rocks of the Iullemmeden Basin in West Africa, Campanian–Maastrichtian Shendi Formation of Sudan and Maastrichtian through Danian strata in New Jersey, Alabama and South Carolina. Isolated teeth comparable to Hyposaurus have also been found in Thanetian strata of Virginia. It was related to Dyrosaurus. The priority of the species H. rogersii has been debated, however there is no sound basis for the recognition of more than one species from North America. The other North American species are therefore considered nomina vanum.

Pachycheilosuchus is an extinct genus of neosuchian from the Early Cretaceous of Texas, United States. Previously known, in part, as the "Glen Rose form", this crocodylomorph is notable for its procoelous vertebrae, otherwise found only in derived eusuchian crocodilians, a thick margin on the maxillae, and a shield of armor on the neck formed by the fusion of six individual scutes.

Neuquensuchus is an extinct genus of crocodyliform from the Santonian-age Upper Cretaceous Bajo de la Carpa Formation of Neuquén Province, Argentina. The known remains were discovered on the campus of Universidad Nacional del Comahue in the city of Neuquén. Neuquensuchus was named by Lucas E. Fiorelli and Jorge O. Calvo in a publication dated to 2007, but which became available in 2008. The type species is N. universitas, in recognition of its discovery locality. Unlike the great majority of crocodyliforms, its shin was longer than its thigh, suggesting it had some running ability.

Rugosuchus is an extinct genus of neosuchian crocodyliform from the late Early Cretaceous of China. It is known from most of a skull, a partial postcranial skeleton, and a second partial skeleton including part of the hips. It was described by Xiao-Chun Wu and colleagues in 2001, with R. nonganensis as the type species. At the time of its description, it was the most complete crocodyliform from northeastern China, and only the second known.

<span class="mw-page-title-main">Eusuchia</span> Clade of reptiles

Eusuchia is a clade of neosuchian crocodylomorphs that first appeared in the Early Cretaceous, which includes modern crocodilians. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survived the K-Pg extinction.

Trematochampsidae is an extinct family of mesoeucrocodylian crocodylomorphs. Fossils are present from Madagascar, Morocco, Niger, Argentina, and Brazil. Possible trematochampsids have been found from Spain and France, but classification past the family level is indeterminant. The trematochampsids first appeared during the Barremian stage of the Early Cretaceous and became extinct during the late Maastrichtian stage of the Late Cretaceous.

<i>Eutretauranosuchus</i> Extinct genus of reptiles

Eutretauranosuchus is an extinct genus of goniopholidid crocodyliform. E. delfsi is the only known species within the genus.

<i>Armadillosuchus</i> Extinct genus of reptiles

Armadillosuchus is an extinct genus of sphagesaurid crocodylomorph. It was described in February 2009 from the late Campanian to early Maastrichtian Adamantina Formation of the Bauru Basin in Brazil, dating to approximately 70 Ma. Armadillosuchus was among the larger and more robust sphagesaurids, with a total length of approximately 2 metres (6.6 ft).

Gilchristosuchus is an extinct genus of neosuchian crocodyliform. Its fossils have been found in the upper Milk River Formation of Alberta, Canada, in rocks of either latest Santonian or earliest Campanian age. Gilchristosuchus was described in 1993 by Wu and Brinkman. The type species is G. palatinus, in reference to its distinctive palatine bones.

<i>Isisfordia</i> Extinct genus of reptiles

Isisfordia is an extinct genus of crocodyliform closely related to crocodilians that lived in Australia during the Middle Cretaceous (Albian–Cenomanian).

<i>Pholidosaurus</i> Extinct genus of reptiles

Pholidosaurus is an extinct genus of neosuchian crocodylomorph. It is the type genus of the family Pholidosauridae. Fossils have been found in northwestern Germany. The genus is known to have existed during the Berriasian-Albian stages of the Early Cretaceous. Fossil material found from the Annero and Jydegård Formations in Skåne, Sweden and on the island of Bornholm, Denmark, have been referred to as a mesoeucrocodylian, and possibly represent the genus Pholidosaurus.

Paluxysuchus is an extinct genus of neosuchian crocodyliform known from the Early Cretaceous Twin Mountains Formation of north-central Texas. It contains a single species, Paluxysuchus newmani. Paluxysuchus is one of three crocodyliforms known from the Early Cretaceous of Texas, the others being Pachycheilosuchus and an unnamed species referred to as the "Glen Rose Form". Paluxysuchus has a long, flat skull that is probably transitional between the long and narrow skulls of many early neosuchians and the short and flat skulls of later neosuchians.

Hulkepholis is an extinct genus of goniopholidid mesoeucrocodylian from the Early Cretaceous of southern England and eastern Spain. It contains two species, the type species, Hulkepholis willetti, and also H. plotos. Hulkepholis is most closely related to both species of Anteophthalmosuchus.

<span class="mw-page-title-main">Coelognathosuchia</span> Extinct clade of reptiles

Coelognathosuchia is an extinct clade of neosuchian crocodyliforms that includes all taxa more closely related to the family Pholidosauridae than to Bernissartia fagesii or Eusuchia. Martin et al. (2014) named the clade after finding goniopholidids and pholidosaurids to group together in their phylogenetic analysis of crocodyliform evolutionary relationships. In their analysis, Pholidosauridae was monophyletic and Goniopholididae was paraphyletic, being an assemblage of successively more basal taxa within Coelognathosuchia. Coelognathosuchia itself was positioned near the base of the larger clade Neosuchia as the sister group to a clade containing the Early Cretaceous neosuchian Bernissartia and Eusuchia, the group that includes all modern crocodilians and their closest extinct relatives.

<i>Confractosuchus</i> Extinct genus of eusuchian

Confractosuchus is a genus of extinct eusuchian crocodyliform from the Cretaceous Winton Formation of Australia. Described as a macro-generalist, Confractosuchus was found with the bones of a juvenile ornithopod dinosaur in its abdomen. It currently contains a single species, Confractosuchus sauroktonos, which literally means "broken dinosaur killer."

Titanochampsa is a genus of large mesoeucrocodylian from the Maastrichtian Marilia Formation of Brazil. Although only known from a single skull roof, the material shows that Titanochampsa was not a member of Notosuchia, which were previously believed to have been the only crocodyliforms present in the strata of the Bauru Group. Body size estimates vary greatly and range between 2.98–5.88 m due to the incomplete nature of the holotype fossil. The overall anatomy of the skull roof, alongside its size and possible affinities with Neosuchians, may suggest that it was a semi-aquatic ambush hunter similar to modern crocodilians.

Varanosuchus is an extinct genus of atoposaurid neosuchian from the Early Cretaceous Sao Khua Formation of Thailand. Varanosuchus is known from three individuals which preserve assorted postcranial material and a complete skull. The skull of Varanosuchus was altirostral, meaning it wasn't flattened like in modern crocodilians and instead much deeper, while the limbs were slender and straight, leading to it somewhat resembling a monitor lizard. Little is known about the ecology of atoposaurids, however, based on the slender, erect limbs, the altirostral skull and the well ornamented osteoderms it has been suggested that Varanosuchus was a terrestrial animal with some semi-aquatic affinities. Only a single species is recognized, Varanosuchus sakonnakhonensis.

References

  1. 1 2 3 Fortier, D.C.; Schultz, C.L. (2009). "A new neosuchian crocodylomorph (Crocodyliformes, Mesoeucrocodylia) from the Early Cretaceous of north-east Brazil" (PDF). Palaeontology. 52 (5): 991–1007. Bibcode:2009Palgy..52..991F. doi: 10.1111/j.1475-4983.2009.00894.x .
  2. Figueiredo, R.G.; Kellner, A.W.A. (2009). "A new crocodylomorph specimen from the Araripe Basin (Crato Member, Santana Formation), northeastern Brazil". Paläontologische Zeitschrift. 83 (2): 323–331. Bibcode:2009PalZ...83..323F. doi:10.1007/s12542-009-0016-6. S2CID   129166567.
  3. 1 2 3 Salisbury, S.W.; Molnar, R.E.; Frey, E.; Willis, P.M.A. (2006). "The origin of modern crocodyliforms: new evidence from the Cretaceous of Australia". Proceedings of the Royal Society B. 273 (1600): 2439–2448. doi:10.1098/rspb.2006.3613. PMC   1634899 . PMID   16959633.
  4. 1 2 3 Salisbury, S.W.; Frey, E.; Martill, D.M.; Buchy, M.C. (2003). "A new crocodilian from the Lower Cretaceous Crato Formation of north-eastern Brazil". Palaeontographica Abteilung A. 270 (1–3): 3–47. Bibcode:2003PalAA.270....3S. doi:10.1127/pala/270/2003/3. ISSN   0375-0442.