Aggregations and parental care in the Early Triassic basal cynodonts<i>Galesaurus planiceps</i>and<i>Thrinaxodon liorhinus</i>

Jasinoski, Sandra C.; Abdala, Fernando

doi:10.7717/peerj.2875

Cited by 31 publications

(30 citation statements)

References 47 publications

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“…Burrow complexes containing Galesaurus , Thrinaxodon and Langbergia in outcrops of the Lower-Middle Triassic of South Africa suggest that fossorial activities were a common behavior in these basal non-mammaliaform cynodonts [134–136]. Moreover, complex tetrapod burrows discovered in several Lower Triassic to Jurassic continental sequences of South America, Africa and Antarctica are considered as being produced by non-mammaliaform cynodonts [137–140].…”

Section: Discussionmentioning

confidence: 99%

The postcranial anatomy of Brasilodon quadrangularis and the acquisition of mammaliaform traits among non-mammaliaform cynodonts

2019

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Brasilodon quadrangularis (Cynodontia, Probainognathia) is an iconic non-mammaliaform cynodont from the Late Triassic of Brazil ( Riograndia Assemblage Zone, Candelária Sequence), being considered as the sister taxon of Mammaliaformes. Although its phylogenetic position is very important, several aspects of its postcranial anatomy remain unclear or unstudied. Here, we present a detailed description of the postcranial elements referred to Brasilodon , including previously mentioned specimens and new ones, which add relevant information about its postcranial morphology and provide a new insight into the anatomical transition between advanced non-mammaliaform cynodonts and early mammaliaforms. Functional and ecological implications are also investigated, based on the postcranial morphology and muscular reconstructions. The postcranium of Brasilodon differs from most non-mammaliaform cynodonts and presents similarities with tritylodontids, early mammaliaforms and extant therians, such as a ventrally oriented scapular glenoid facet, a distinct and ossified greater humeral tubercle, lack of ectepicondylar foramen, olecranon process, hemispherical humeral and femoral heads and a prominent intertrochanteric crest. The humeral torsion, the length of the deltopectoral crest, the large bicipital groove and the well-developed lesser tubercle, indicate that the forelimb of Brasilodon was hold in a semi-sprawling position, with well-developed adductor muscles to maintain the body off the ground. The short femoral neck and the strong medial projection of the femoral head indicate the femur was held in a more erect posture than in basal non-mammaliaform cynodonts. The anterodorsally projected iliac blade with reduced postacetabular process, reduction of the anterior part of the pubis, medially located lesser trochanter indicate a basically mammalian pattern of pelvic musculature, able to swing the femur in a nearly parasagittal plane.

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Section: Discussionmentioning

confidence: 99%

The postcranial anatomy of Brasilodon quadrangularis and the acquisition of mammaliaform traits among non-mammaliaform cynodonts

2019

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“…They studied 35 Galesaurus and 104 Thrinaxodon specimens and found two and seven aggregations, respectively. Given that only one of the seven Thrinaxodon aggregations contains juveniles, they proposed that Thrinaxodon subadults and adults formed social aggregations more often than did Galesaurus (Jasinoski & Abdala ). The discovery of Galesaurus NMQR 135 representing an aggregation brings the total of known aggregations to three amongst 35 specimens.…”

Section: Discussionmentioning

confidence: 99%

“…Galesaurus actually appears to have been better adapted to its environment by being a sturdy animal capable of excavating its own burrows and thus providing its own shelter. However, Jasinoski & Abdala (2017 a , b ) suggested that parental care lasted longer in Galesaurus and perhaps it was Thrinaxodon 's ability to reach independence at younger ontogenetic stages that resulted in it being relatively more successful.…”

Section: Discussionmentioning

confidence: 99%

“…Thrinaxodon specimens are conspicuously more abundant than those of Galesaurus and it has a notably longer biostratigraphical range, extending most of the way through the LAZ. Recent behavioural studies (Jasinoski & Abdala ) have hinted at possible reasons for the better success of Thrinaxodon , but this topic has yet to be fully explored. New data from this study may shed light on possible drives for the selective advantage of one taxon, which has important implications for the biology and ecology of the Early Triassic cynodonts living in a post‐extinction environment.…”

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confidence: 99%

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Postcranial morphology of the Early Triassic epicynodont Galesaurus planiceps (Owen) from the Karoo Basin, South Africa

Butler

Abdala

Botha‐Brink

2018

Papers in Palaeontology

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The Early Triassic non‐mammaliaform epicynodont Galesaurus planiceps formed an important part of ecosystems following the Permo‐Triassic Mass Extinction, the greatest mass extinction in Phanerozoic history. Here, we re‐examine the postcranial skeleton of Galesaurus and present data which sheds light on the biology, ecology and possible survival strategies of this species. We find evidence for two distinct morphotypes, a gracile and a robust morph, which we interpret as stages in an ontogenetic series. The primary differences between the morphs manifest in the girdles, with further subtle differences in the fore and hind limbs. Our study also reveals postcranial differences between Galesaurus and the contemporaneous taxon Thrinaxodon liorhinus, allowing these taxa to be distinguished in the absence of cranial material. We also report the first evidence of intraspecific variation in the presence and distribution of disc‐like phalanges in a non‐mammaliaform cynodont. An analysis of the osteohistology of Galesaurus reveals rapid growth to skeletal maturity within one year, thereafter transitioning to slow intermittent growth. This growth pattern is similar to that of Thrinaxodon, which also grew rapidly and continuously to skeletal, and possibly reproductive, maturity within its first year of life. Features such as a strong, reinforced pelvis, elongated ilium, thick, robust forelimbs and stout unguals indicate that Galesaurus was capable of actively excavating burrows. The combination of rapid maturation and fossoriality may have aided its survival in the harsh, unpredictable post‐extinction Early Triassic environment.

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“…Given their evolutionary success, it is not unreasonable to hypothesise that a certain degree of behavioural flexibility existed in NMT, which would have given them the ability to adapt their survival strategy to accommodate environmental variety [Laass et al, 2010]. In addition, NMT had a variety of complex behaviours also represented in mammals, such as headbutting, gregariousness, and parental care [Brink 1955[Brink , 1965Botha-Brink and Modesto 2007;Fiorelli et al 2013;Viglietti et al, 2013;Benoit et al, 2016b;Jasinoski and Abdala, 2017].…”

Section: Eq In Early Therapsidamentioning

confidence: 99%

Endocranial Casts of Pre-Mammalian Therapsids Reveal an Unexpected Neurological Diversity at the Deep Evolutionary Root of Mammals

Benoît

Fernández²,

Manger³

et al. 2017

Brain Behav Evol

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The origin and evolution of the mammalian brain has long been the focus of scientific enquiry. Conversely, little research has focused on the palaeoneurology of the stem group of Mammaliaformes, the Permian and Triassic non-mammaliaform Therapsida (NMT). This is because the majority of the NMT have a non-ossified braincase, making the study of their endocranial cast (sometimes called the “fossil brain”) problematic. Thus, descriptions of the morphology and size of NMT endocranial casts have been based largely on approximations rather than reliable determination. Accordingly, here we use micro-CT scans of the skulls of 1 Dinocephalia and 3 Biarmosuchia, which are NMT with a fully ossified braincase and thus a complete endocast. For the first time, our work enables the accurate determination of endocranial shape and size in NMT. This study suggests that NMT brain size falls in the upper range of the reptilian and amphibian variation. Brain size in the dicynodont Kawingasaurus is equivalent to that of early Mammaliaformes, whereas the Dinocephalia show evidence of a secondary reduction of brain size. In addition, unlike other NMT in which the endocast has a tubular shape and its parts are arranged in a linear manner, the biarmosuchian endocast is strongly flexed at the level of the midbrain, creating a near right angle between the fore- and hindbrain. These data highlight an unexpected diversity of endocranial size and morphology in NMT, features that are usually considered conservative in this group.

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Aggregations and parental care in the Early Triassic basal cynodontsGalesaurus planicepsandThrinaxodon liorhinus

Cited by 31 publications

References 47 publications

The postcranial anatomy of Brasilodon quadrangularis and the acquisition of mammaliaform traits among non-mammaliaform cynodonts

The postcranial anatomy of Brasilodon quadrangularis and the acquisition of mammaliaform traits among non-mammaliaform cynodonts

Postcranial morphology of the Early Triassic epicynodont Galesaurus planiceps (Owen) from the Karoo Basin, South Africa

Endocranial Casts of Pre-Mammalian Therapsids Reveal an Unexpected Neurological Diversity at the Deep Evolutionary Root of Mammals

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