Sebecosuchia Simpson, 1937

Martin, Jeremy E., 2015, A sebecosuchian in a middle Eocene karst with comments on the dorsal shield in Crocodylomorpha, Acta Palaeontologica Polonica 60 (3), pp. 673-680 : 674-676

publication ID

https://doi.org/ 10.4202/app.00072.2014

persistent identifier

https://treatment.plazi.org/id/8F6F87B8-ED18-9E08-FFE1-FC42FDACFE92

treatment provided by

Felipe

scientific name

Sebecosuchia Simpson, 1937
status

 

Suborder Sebecosuchia Simpson, 1937

Family et genus indet.

Material.— UCBL-FSL 530863a–c, three isolated teeth; MHNL 341, a set of isolated osteoderms including 5 complete and 6 fragmentary dorsal elements. The label accompanying these specimens reports the date 1895. Material from MP 14 (Mammal Paleogene reference level, Biochro’M 1997) of Lissieu, Rhône, France. Information on this locality is presented in Rage and Augé (2010).

Description.—Three teeth including the apex of a crown and two complete crowns are preserved ( Fig. 1 View Fig ). They are of the ziphodont type, i.e., their mesiodistal carinae bearing denticles from the base of the crown to the tip of the apex. These denticles consist of plication of the enamel ( Fig. 1A View Fig 3, B 2, C 3). The two best-preserved teeth have different general morphologies that reflect a different position in the tooth row. The smallest tooth (apicobasal length is 11 mm) is subconical and its crown is curved. This type of morphology was described in the premaxillary dentition of Iberosuchus macrodon by Antunes (1975). The other complete crown is much larger (apicobasal length is 23 mm) and is labiolingually compressed with the tip of the apex bent in a posterior direction. The labial or lingual surface of that tooth has two ridges running from the apex to the base of the crown. Teeth attributed to a mesosuchian from La Livinière ( Buffetaut 1986) superficially resemble the teeth described here in being slightly labiolingually compressed. Nevertheless, the teeth from La Livinière do not show individualised denticles on the mesiodistal carinae, but as highlighted by Buffetaut 1986) present crenulations of the enamel.

Eleven unusual osteoderms are preserved, six of them being complete ( Fig. 2 View Fig ). The osteoderms are dorsoventrally thin and at least three times longer than wide with a roughly rectangular outline. Their ornamentation does not show the cupular pattern observed in aquatic forms. Instead, these osteoderms have a vermiculate ornamentation as observed in the skull elements of Iberosuchus macrodon Antunes, 1975 . All osteoderms reported here possess a tall longitudinal ridge surrounded by fine ridges radiating perpendicularly to it. In one specimen ( Fig. 2D View Fig 1 View Fig ), one of the perpendicular ridges is thick, giving to the osteoderm a cross-like shape in dorsal view. The longitudinal ridge runs for almost the entire length of the osteoderm and gradually merges with the anterior bor- der, but finishes abruptly with the posterior border. Although the margins of the largest specimen seem eroded ( Fig. 2A View Fig ), the long margins of the other specimens are finely indented. The anterior margin is smooth and convex. In all specimens, the ventral surface is nearly flat to slightly convex and bears an interwoven pattern produced by the attachment of the epaxial musculature.

Remarks.—The material described above is assigned to the Sebecosuchia (including Sebecidae + Baurusuchidae ; e.g., Pol et al. 2012) on the basis of the following synapomorphies: mediolaterally compressed teeth with mesiodistal carinae possessing denticles (the ziphodont condition of Langston 1975); anteroposteriorly elongated dorsal osteoderms possessing a central median prominent keel running for most of the length; rugose ornamentation devoid of pits and cupules; anterolateral process of osteoderms absent. Under an alternative hypothesis allying Sebecidae with Peirosauridae (the Sebecia of Larsson and Sues 2007), the synapomorphies highlighted here would not be valid anymore and would be considered as homoplasic. Moreover, the Peirosauridae do not share the characters mentioned above for Iberosuchus or Bergisuchus . Indeed, the postcranial skeleton of peirosaurids is largely unknown, but if ornamentation of their osteoderms

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reflects that of the skull, they should present pits and cupules. Moreover, the presence of serrations or true denticles in the dentition of all Peirosauridae remains unclear (compare for example Hamadasuchus [ Larsson and Sues 2007] and Pepesuchus [ Campos et al. 2011]).

MHNL

Musee Guimet d'Histoire Naturelle de Lyon

MP

Mohonk Preserve, Inc.

Kingdom

Animalia

Phylum

Chordata

Class

Reptilia

Order

Crocodilia

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