Baurusuchidae

Baurusuchidae were a family of land-dwelling, hypercarnivorous crocodilians that thrived during the Late Cretaceous. Their fossils have been found across the ancient southern supercontinent of Gondwana, specifically in South America (Argentina and Brazil) and Asia (Pakistan). Under the rules of the PhyloCode, the family is officially defined as the smallest clade that includes Cynodontosuchus rothi, Pissarrachampsa sera, and Baurusuchus pachecoi. These animals are grouped within the suborder Baurusuchia, and scientists have proposed splitting them into two subfamilies: Baurusuchinae and Pissarrachampsinae.

Genera

Several genera make up the family. The first to be named was Baurusuchus, which also gave the family its name. Its remains come from the Turonian–Santonian deposits of Brazil’s Bauru Group. Besides Baurusuchus, five other South American crocodyliforms have been assigned here: Campinasuchus, Cynodontosuchus, Pissarrachampsa, Stratiotosuchus, and Wargosuchus.

The earliest known baurusuchid was Cynodontosuchus, described in 1896 by English paleontologist Arthur Smith Woodward, though it was only recently placed in this family. Wargosuchus was named in 2008. Both Cynodontosuchus and Wargosuchus are known only from fragmentary fossils, and both come from the Santonian of Argentina.

Stratiotosuchus was added to the family in 2001. The youngest genus once considered a baurusuchid is Pabwehshi, from the Maastrichtian of Pakistan; named in 2001, it has since been reclassified as a basal member of Sebecia. A new genus, Campinasuchus, was assigned to the family in May 2011, based on fossils from the Turonian–Santonian Adamantina Formation of Brazil’s Bauru Basin. Shortly after, Pissarrachampsa was named from the Campanian–Maastrichtian Vale do Rio do Peixe Formation, also in the Bauru Basin.

The family Baurusuchidae was first named in 1945 by Brazilian paleontologist Llewellyn Ivor Price, with Baurusuchus as its core. The following year, American paleontologist Edwin Harris Colbert created the group Sebecosuchia, which united Baurusuchidae with Sebecidae (whose main genus is Sebecus).

Phylogeny

Both Baurusuchus and Sebecus share deep snouts and ziphodont teeth—serrated and flattened sideways. Later discoveries, including Cynodontosuchus, Stratiotosuchus, and Wargosuchus, resembled these two genera closely. Several traits tied these groups together: a deep snout, ziphodont teeth, a curved tooth row, an enlarged canine-like tooth in the lower jaw that fit into a deep notch in the upper jaw, and a groove on the lower jaw.

For decades, many phylogenetic studies supported a close link between Baurusuchidae and Sebecidae. Both families are early members of Metasuchia, a clade that includes Notosuchia (mostly land-dwelling crocodyliforms) and Neosuchia (larger, often semiaquatic forms, including modern crocodilians). Several analyses found that sebecosuchians—which include both baurusuchids and sebecids—were closely related to notosuchians. Later, the genera Iberosuchus and Eremosuchus were added to Baurusuchidae, and further analyses still showed a close relationship with Sebecidae.

Both families were grouped with notosuchians in the larger clade Ziphosuchia, which contains all ziphodont crocodyliforms. More recently, sebecosuchians—including baurusuchids—have been placed within Notosuchia as derived members. A cladogram from Ortega et al. (2000) illustrates this placement.

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

A 2005 analysis found Sebecidae to be paraphyletic—meaning it included some, but not all, descendants of a common ancestor. In that view, sebecids formed a group of basal sebecosuchians, while baurusuchids remained a valid group of derived sebecosuchians. A cladogram from Turner and Calvo (2005) shows this.

Later studies highlighted many features that set baurusuchids apart from sebecosuchids. Sebecosuchids were often seen as more closely related to Neosuchia (which includes modern crocodilians), while baurusuchids were considered a more distant clade. In a 1999 analysis, Baurusuchus formed a clade with notosuchians, excluding other ziphosuchians. This placement has been upheld by recent work, which puts Baurusuchus within Notosuchia.

In 2007, a new clade called Sebecia was erected, including sebecids and peirosaurids. Peirosauridae, a family of small land-dwelling crocodyliforms, had often been placed near Neosuchia in earlier studies.

By assigning sebecids to Sebecia, the family was moved closer to Neosuchia than to Notosuchia. In that study, baurusuchids were split: Baurusuchus was placed as a more basal metasuchian, while the remaining baurusuchids (Bretesuchus and Pabwehshi) were placed as sebecians, making Baurusuchidae paraphyletic. A cladogram from Larsson and Sues (2007) illustrates this.

More recent studies have nested Baurusuchus deep within Notosuchia, much as the larger group Sebecosuchia once was, while other sebecosuchian genera have been placed more distantly in Metasuchia. A new baurusuchid, Pissarrachampsa, was named in 2011, and a comprehensive phylogenetic analysis of the family accompanied its description. Montefeltro et al. (2011) found Baurusuchidae to be a monophyletic group, including the genera Baurusuchus, Cynodontosuchus, Pissarrachampsa, Stratiotosuchus, and Campinasuchus.