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Post by arctozilla on Apr 30, 2023 4:48:07 GMT -5
Evolution of the mammalian jaw The ancestral synapsid (mammal-like reptile) jaw has four elements, with the articulation formed between the small Articular and Quadrate bones, which is therefore referred to as a Quadro-Articular jaw. In therapsids (the ancestors of mammals), the joint has been simplified to an articulation between the Dentary and Squamosal bones, which is called a Dentary-Squamosal jaw. The Articular and Quadrate bones have moved into the middle ear as the Malleus and Incus ("Hammer" and "Anvil" bones), respectively. The Squamosal also contributes to the Zygomatic Arch, which is the mammalian cheek bone. www.mun.ca/biology/scarr/QA_vs_DS_jaw.html
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Post by oldindigosilverback on Apr 30, 2023 5:29:07 GMT -5
/\ The reptilian seems to have the larger skull while the mammalian seems to have a narrow skull in the post above.
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Post by arctozilla on Apr 30, 2023 5:53:30 GMT -5
Nature’s early “rehearsals” of the sabertooth: Rubidgea Let us look at Rubidgea, one of the largest (brown bear sized) and latest gorgonopsians, which lived in South Africa some 250 million years ago. You would not call it a sabertooth, but it had many of the anatomical features that define those predators. The fearsome upper canines (1) were the primary killing weapon, while the protruding incisors (2) acted both to stabilize the bitten area (thus protecting the canines from some lateral strains) and to pull chunks of meat off the carcass when feeding. The complex shape of the cranio-mandibular joint (3) allowed the mandible to remain articulated with the skull even at gapes in excess of 90 degrees. Some ventral muscles of the neck (4) attaching in the base of the skull contributed to the downward motion neccesary to sink the canines into the flesh of prey. And once the gape was reduced through head depression, the jaw-closing musculature (5) acted to complete the bite. chasingsabretooths.wordpress.com/2014/12/03/natures-early-rehearsals-of-the-sabertooth-rubidgea/Inviato dal mio 21061119DG utilizzando Tapatalk
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Post by arctozilla on Apr 30, 2023 7:25:25 GMT -5
The earliest segmental sternum in a Permian synapsid and its implications for the evolution of mammalian locomotion and ventilation Abstract The sternum is a stabilizing element in the axial skeleton of most tetrapods, closely linked with the function of the pectoral girdle of the appendicular skeleton. Modern mammals have a distinctive sternum characterized by multiple ossified segments, the origins of which are poorly understood. Although the evolution of the pectoral girdle has been extensively studied in early members of the mammalian total group (Synapsida), only limited data exist for the sternum. Ancestrally, synapsids exhibit a single sternal element and previously the earliest report of a segmental sternum in non-mammalian synapsids was in the Middle Triassic cynodont Diademodon tetragonus. Here, we describe the well-preserved sternum of a gorgonopsian, a group of sabre-toothed synapsids from the Permian. It represents an ossified, multipartite element resembling the mammalian condition. This discovery pulls back the origin of the distinctive “mammalian” sternum to the base of Theriodontia, significantly extending the temporal range of this morphology. Through a review of sternal morphology across Synapsida, we reconstruct the evolutionary history of this structure. Furthermore, we explore its role in the evolution of mammalian posture, gait, and ventilation through progressive regionalization of the postcranium as well as the posteriorization of musculature associated with mammalian breathing. www.nature.com/articles/s41598-022-17492-6
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Post by arctozilla on Apr 30, 2023 12:40:16 GMT -5
A review of fighting adaptations in dinocephalians (Reptilia, Therapsida) Abstract The cranial structure of anteosaurid and many tapinocephalid dinocephalians became modified in a manner consistent with Geist's hypothesis that they used their heads for pushing and ramming during intraspecific combat. These modifications are most pronounced in certain tapinocephalids by the evolution of a strong dorsal head shield supported by a massive arch network suitable for receiving and supporting blows delivered to the dorsal surface of the head. The position of the occipital condyle reduced the torque created by such blows at the craniocervical joint. Evidence also indicates that the head was reoriented into a position suitable for butting. The cranial architecture displayed by dinocephalians suspected of headbutting differs from that of living mammalian rammers. The differences can be directly attributed to the modification, in the former, of a reptilian skull with its relatively unexpanded braincase into a ramming instrument. www.cambridge.org/core/journals/paleobiology/article/abs/review-of-fighting-adaptations-in-dinocephalians-reptilia-therapsida/BE3C6EC465C531197647A8BEFC1F35E0Inviato dal mio 21061119DG utilizzando Tapatalk
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Post by arctozilla on May 1, 2023 12:26:11 GMT -5
EVOLUTIONARY PATTERNS AMONG PERMO-TRIASSIC THERAPSIDS Abstract A rich fossil record documents nonmammalian evolution. In recent years, the application of cladistic methodology has shed valuable light on the relationships within the therapsid clades Biarmosuchia, Dinocephalia, Anomodontia, and Cynodontia. Recent discoveries from South Africa suggest that Gondwana, rather than Laurasia, was the center of origin and radiation for many early therapsids. Because of their relative abundance and global distribution, therapsids have enjoyed widespread use in biostratigraphy, basin analysis, and paleo-environmental and -continental reconstructions. Synapsids (including therapsids) form the bulk of tetrapod diversity (in terms of both number of species and abundance) from Early Permian to Middle Triassic times and thus can provide critical information on the nature of the Permo-Triassic extinction in the terrestrial realm. Quantitative techniques have produced headway into understanding the relative importance of homoplasy and convergent evolution in the origin of mammals. web.archive.org/web/20120321142923/http://www11.cac.washington.edu/burkemuseum/collections/paleontology/sidor/Rubidge_Sidor2001.pdf
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Post by arctozilla on May 1, 2023 13:57:05 GMT -5
Fossils reveal the complex evolutionary history of the mammalian regionalized spine Early shifts lead to big changes Mammals represent one of the most morphologically diverse taxonomic groups. One of the unique features underlying this diversity is variability of the spine, which facilitates everything from flexibility for speedy running and support for upright walking. Jones et al. studied a group ancestral to modern mammals—nonmammalian synapsids, or mammal-like reptiles. As forelimb function diversified, the spine developed distinct regions. These regions then differentiated further, leading to the highly varied mammalian forms we see today. Science , this issue p. 1249 www.researchgate.net/publication/327782194_Fossils_reveal_the_complex_evolutionary_history_of_the_mammalian_regionalized_spineInviato dal mio 21061119DG utilizzando Tapatalk
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Post by arctozilla on May 13, 2023 15:11:05 GMT -5
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Post by arctozilla on May 14, 2023 2:01:39 GMT -5
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Post by arctozilla on May 18, 2023 13:30:14 GMT -5
Palaeoneurological clues to the evolution of denning mammalian soft tissue traits A rich fossil record chronicles the distant origins of mammals, but the evolution of defyning soft tissue characters of extant mammals, such as mammary glands and hairs is difficult to interpret because soft tissue does not readily fossilize. As many soft tissue features are derived from dermic structures, their evolution is linked to that of the nervous system, and palaeoneurology offers opportunities to find bony correlates of these soft tissue features. Here, a CT scan study of 29 fossil skulls shows that non-mammaliaform Prozostrodontia display a retracted, fully ossiffied, and non-ramiffied infraorbital canal for the infraorbital nerve, unlike more basal therapsids. The presence of a true infraorbital canal in Prozostrodontia suggests that a motile rhinarium and maxillary vibrissae were present. Also the complete ossification of the parietal fontanelle (resulting in the loss of the parietal foramen) and the development of the cerebellum in Probainognathia may be pleiotropically linked to the appearance of mammary glands and having body hair coverage since these traits are all controlled by the same homeogene, Msx2, in mice. These suggest that defyning soft tissue characters of mammals were already present in their forerunners some 240 to 246 mya. www.researchgate.net/publication/302413151_Palaeoneurological_clues_to_the_evolution_of_defining_mammalian_soft_tissue_traits
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Post by arctozilla on May 18, 2023 13:33:04 GMT -5
The origin of endothermy in synapsids and archosaurs and arms races in the Triassic Highlights • Birds and mammals likely acquired endothermy (warm-bloodedness) at the same time • This time was the Early Triassic, as suggested by phylogenetic macroevolutionary studies of both archosaurs and synapsids • Life remodelled itself most significantly in the aftermath of the devastating end-Permian mass extinction • The switchover happened in parallel with a shift in posture from sprawling to parasagittal in both major lineages • Cynodonts and avemetatarsalian archosaurs engaged in arms races through the Triassic, as their metabolic rates speeded up www.sciencedirect.com/science/article/pii/S1342937X20302252
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Post by arctozilla on May 18, 2023 14:16:48 GMT -5
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Post by Gorilla king on May 18, 2023 14:24:54 GMT -5
Evolution and identity of synapsid carpal bones
Abstract
To date there is little information on carpal bone homology in late Palaeozoic and Mesozoic Synapsida. Crucial to the understanding of homology in synapsid carpal elements is the fact that different nomenclatures are used for the carpals of non-mammaliamorph Synapsida (Gegenbauer’s canonical nomenclature) and Mammaliaformes (mammalian nomencla- ture). The homologies of the carpals of non-mammaliamorph synapsids and mammals were established early last century and have not been reviewed since then. Here we provide a detailed study of the carpal bones of synapsids ranging in age from the early Permian to Late Cretaceous. The mammaliamorph lunate, previously considered the homologue of the intermedium of non-mammaliamorph synapsids, is interpreted here as homologous to their lateral centrale. We interpret the single mammaliamorph centrale as a homologue of the medial centrale of non-mammaliamorph synapsids. In some synapsid specimens, we found that one or two centralia are fused to the radiale (e.g., the gorgonopsian Arctognathus and tritylodontid Bienotheroides), supporting a digging habit. A third centrale is present in the therocephalian Theriognathus, very likely an abnormal duplication. An additional medial bone in a biarmosuchian was interpreted as a prepollex/ sesamoid. A cartilaginous prepollex/sesamoid may also have been present in several non-mammaliamorph synapsids, which have an open space proximal to distal carpal I. Distal carpal V is completely lost in dicynodonts and it is mainly fused to distal carpal IV in the adult stage of most other therapsid groups, but showed a delayed development in most non-mammaliamorph cynodonts. In mammaliamorphs, distal carpal V is not present. Our observations provide an up- dated revision of synapsid carpal homologies, mainly on the basis of position and anatomical contacts and also taking into account the results of embryological studies.
www.researchgate.net/publication/345681007_Evolution_and_identity_of_synapsid_carpal_bones
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Post by oldindigosilverback on May 27, 2023 1:23:30 GMT -5
Reply 22. That is probably the way the Sabre tooth cats eat their prey.
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Post by arctozilla on Jun 3, 2023 11:20:16 GMT -5
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