Menadon besairiei: a Gomphodontosuchinae Traversodont Previously Only Found in Madagascar now Found in Middle-Upper Triassic Brazil

The Malagasy cynodont Menadon besairiei (Cynodontia; Traversodontidae) in the Middle–Upper Triassic of Brazil

Authors:

Melo et al

Abstract:

The traversodontid cynodont Menadon besairiei, previously known from the ‘Isalo II’ group of Madagascar, is reported for the first time from the Triassic of southern Brazil. New material referable to M. besairiei was collected in the Schoenstatt outcrop (Santa Cruz do Sul municipality), which belongs to the Santacruzodon Assemblage Zone (Carnian) in the Santa Maria Supersequence. Their attribution to the Malagasy taxon is based on the presence of a deep snout; four upper incisors, with procumbent first and second incisors, and three lower, procumbent incisors; five upper postcanines, the first one ‘peg-like’; six lower postcanines, the two most anterior and the most posterior being reduced; the quadrangular form of the postcanines; a pterygoid reaching the jugal and excluding the maxilla from the suborbital fenestra; a mandible with a tall coronoid process covering the last lower postcanine laterally; and a posteriorly projected angular process. A cladistic analysis of traversodontid cynodonts was performed based on a matrix composed of 30 taxa and 78 characters. In the resulting trees, M. besairiei nested within the clade Gomphodontosuchinae, the only traversodontid subclade reasonably well supported. Thus, the presence of M. besairiei is established in the Santa Cruz do Sul fauna, constituting the first record for South America and confirming the previously proposed biostratigraphic correlation between the ‘Isalo II’ and the Santacruzodon Assemblage Zone.

Massetognathus ochagaviae: a new Middle Triassic Traversodontid Cynodont From Brazil

New information on the postcranial skeleton of Massetognathus ochagaviae Barberena, 1981 (Eucynodontia, Traversodontidae), from the Middle Triassic of Southern Brazil

Authors:

Branco Pavanatto et al

Abstract:

New postcranial remains of Massetognathus ochagaviae are described based on a new specimen collected at the Dinodontosaurus Assemblage Zone from the Middle Triassic of Southern Brazil. Several isolated teeth collected together with the postcranial skeleton allowed a taxonomic assignation of the specimen to M. ochagaviae. Its postcranial morphology is quite similar to Massetognathus pascuali, especially regarding the morphology of the transverse process of presacral vertebrae (i.e. laminar in the anterior most and rounded in the posterior most presacral vertebrae); humerus (i.e. the head is dorsally deflected with a ‘fan-shaped’ distal end a deltopectoral crest abruptly ending at the middle of shaft); and femur (with a bulbous and dorsomedially inclined femoral head, lesser trochanter which abruptly begins near the intertrochanteric fossa and extending up to the middle of the femoral shaft and the medial condyle more pronounced and ventrally projected than the lateral one). On the other hand, the clavicle of M. ochagaviae is less lateromedially elongated than in M. pascuali.

Evidence Late Triassic Traversodontid Exaeretodons Were Scavenged

Biogenic control on the origin of a vertebrate monotypic accumulation from the Late Triassic of southern Brazil

Authors:

Müller et al

Abstract:

This study is a taphonomic investigation of a new Late Triassic monotypic association from the Hyperodapedon Assemblage Zone (Santa Maria Formation, southern Brazil). All skeletal elements belong to the traversodontid cynodont Exaeretodon, representing a minimum of four individuals from different ontogenetic stages. Biogenic traces are identifiable on some elements, such as invertebrate scavenging traces, vertebrate bite marks, and evidence of trampling which was probably responsible for accelerating the disarticulation of upper postcanine teeth and for fracturing a skull and a lower jaw. We classify this accumulation as generated by extrinsic biogenic action (predation/necrophagy and possibly trampling) due to the following reasons: (i) random spatial orientation of the elements enclosed into the matrix; (ii) absence of hydraulic equivalence among the specimens and presence of mudstone lenses in close association with the fossils; (iii) presence of nearly all Voorhies’ groups; (iv) association of a large number of cranial elements presenting different stages of disarticulation; and (v) presence of biogenic traces. Both disarticulation patterns and invertebrate scavenging traces indicate that the bones remained exposed for some time before burial. During this time of exposure, carnivore vertebrates also scavenged on some nutritive and transportable postcranial elements. We suggest an ecteniniid cynodont as a potential modifier agent (predation/necrophagy) of this particular monotypic accumulation of synapsids.

Ruberodon roychowdhurii: a new Carnian Triassic Traversodontid Cynodont From India

A new Late Triassic traversodontid cynodont (Therapsida, Eucynodontia) from India

Author:

Ray

Abstract:

A large traversodontid cynodont Ruberodon roychowdhurii, gen et. sp. nov., is described from the Late Triassic Tiki Formation of the Rewa Gondwana Basin, India, based on an ontogenetic series of five partial lower jaws. Ruberodon is characterized by a robust and deep dentary symphysis, lower dental formula of i3-c1-pc9, procumbent and hypertrophied first lower incisor, a large canine, long diastema between the lower canine and first postcanine, and a high coronoid process at 60° to the horizontal tooth row. With growth, the symphyseal region became relatively more slender with lengthening of the diastema. Phylogenetic analysis based on 19 taxa and 35 craniodental characters places Ruberodon within the clade containing Gomphodontosuchus, Menadon, Protuberum, Scalenodontoides, and the multispecific Exaeretodon. The new genus forms a sister taxon to E. statisticae and is more advanced than E. riograndensis and E. argentinus based on the presence of a strong coronoid ridge anterior to the masseteric fossa. Based on its tetrapod assemblage, the Tiki Formation may be globally correlated with other formations such as the lower part of the Maleri Formation of India, the Isalo II Beds of Madagascar, and the upper part of the Santa Maria Formation of Brazil. An early Carnian age is proposed for the Tiki Formation.

Mandagomphodon hirschsoni: a Traversodont Cynodont From Anisian Triassic Tanzania

The Traversodontid Cynodont Mandagomphodon hirschsoni from the Middle Triassic of the Ruhuhu Valley, Tanzania

Author:

James Hopson

Abstract:

Mandagomphodon hirschsoni (gen. nov., comb. nov.) is one of three species of traversodontid cynodont placed in Scalenodon [type species S. angustifrons (Parrington, 1946)] by Crompton (1972). It is based on a partial skull and lower jaws from the Middle Triassic of the Ruhuhu Valley, southwestern Tanzania. The upper postcanine teeth were used to diagnose species of Scalenodon, but newer traversodontid material indicates that the three species represent distinct genera. Material of “S.” hirschsoni, except for the postcanines, has not been described. It is unusual among traversodontids in having only three upper incisors, which are enlarged and procumbent. Three enlarged, procumbent anterior lower teeth are interpreted as two incisors and a canine. Analysis of postcanine wear facets indicates that the power stroke of the lower teeth was entirely in a posterior direction, including a slightly downward and backward grinding movement at the end of the stroke.

Exaeretodon riograndensis from Brazil's Santa Maria (2) Formation Triassic

The lower jaw and dentition of the traversodontid Exaeretodon riograndensis Abdala, Barberena & Dornelles, from the Brazilian Triassic (Santa Maria 2 Sequence, Hyperodapedon Assemblage Zone)

Authors:

1. Alexandre Liparini (a)
2. Téo V. Oliveira (b)
3. Flávio A. Pretto (c)
4. Marina B. Soares (c)
5. Cesar L. Schultz (c)

Affiliations:

a. Departamento de Biologia, Centro de Ciências Biológicas e da Saúde, Universidade Federal de Sergipe, Av. Marechal Rondon s/n, CEP 49100-000, São Cristóvão, SE, Brazil

b. Universidade Estadual de Feira de Santana, Departamento de Ciências Biológicas, Av. Transnordestina s/n, Bairro Novo Horizonte, CEP 44036-900, Feira de Santana, BA, Brazil

c. Departamento de Paleontologia e Estratigrafia, Instituto de Geociências, Universidade Federal do Rio Grande do Sul, Cx.P. 15001, Av. Bento Gonçalves, Bairro Agronomia, CEP 91540-970, Porto Alegre, RS, Brazil

Abstract:

Exaeretodon riograndensis Abdala, Barberena, & Dornelles, 2002 is the most abundant traversodontid preserved in the basal Santa Maria 2 Sequence (Hyperodapedon Assemblage Zone), southern Brazil and is closely related to Exaeretodon argentinus Cabrera, 1943 from the Ischigualasto Formation, Argentina. Previous anatomical studies of E. riograndensis have focused mainly on cranial material and little is known about the morphology of its lower dentition or postdentary bones. We describe the first fairly complete postdentary series of the mandible of E. riograndensis and provide additional information on its lower dentition. The postdentary bones of E. riograndensis include a complex coronoid, an angular with a delicate reflected lamina and a stout retroarticular process of the articular, contrasting with the morphology reconstructed for Argentinean specimens, which possess a small retroarticular process. Apart from that, the postdentary bones do not differ significantly from those known for E. argentinus, a fact expected due to the great similarity between other skeletal features of these species. Furthermore, the lower postcanines of E. riograndensis have virtually the same structure as those of E. argentinus, with an approximate quadrangular shape in occlusal view. Moreover, the transverse cusp row is placed anteriorly and comprises a lingual and a buccal cusp, and the occlusal basin delimited by the four main cusps is relatively deep. The new material does not add any taxonomically diagnostic features to E. riograndensis. However, the fossils greatly improve our understanding of the anatomy of the Brazilian species.