Early Synapsids (all clades)

[arctozilla]

This thread will show info about our unpopular ancestors and extinct relatives.

[arctozilla]

A Carboniferous synapsid with caniniform teeth and a reappraisal of mandibular size-shape heterodonty in the origin of mammals
The Royal Society

Heterodonty is a hallmark of early mammal evolution that originated among the non-mammalian therapsids by the Middle Permian. Nonetheless, the early evolution of heterodonty in basal synapsids is poorly understood, especially in the mandibular dentition. Here, we describe a new synapsid, Shashajaia bermani gen. et sp. nov., based on a well-preserved dentary and jaw fragments from the Carboniferous–Permian Halgaito Formation of southern Utah. Shashajaia shares with some sphenacodontids enlarged (canine-like) anterior dentary teeth, a dorsoventrally deep symphysis and low-crowned, subthecodont postcanines having festooned plicidentine. A phylogenetic analysis of 20 taxa and 154 characters places Shashajaia near the evolutionary divergence of Sphenacodontidae and Therapsida (Sphenacodontoidea). To investigate the ecomorphological context of Palaeozoic sphenacodontoid dentitions, we performed a principal component analysis based on two-dimensional geometric morphometrics of the mandibular dentition in 65 synapsids. Results emphasize the increasing terrestrialization of predator–prey interactions as a driver of synapsid heterodonty; enhanced raptorial biting (puncture/gripping) aided prey capture, but this behaviour was probably an evolutionary antecedent to more complex processing (shearing/tearing) of larger herbivore prey by the late Early to Middle Permian. The record of Shashajaia supports the notion that the predatory feeding ecology of sphenacodontoids emerged in palaeotropical western Pangea by late Carboniferous times.

www.researchgate.net/publication/357052977_A_Carboniferous_synapsid_with_caniniform_teeth_and_a_reappraisal_of_mandibular_size-shape_heterodonty_in_the_origin_of_mammals

[arctozilla]

From sprawling to parasagittal locomotion in Therapsida: A preliminary study of historically collected museum specimens

Abstract

Therapsids covered the entire spectrum of terrestrial locomotion from sprawling to parasagittal. Switching between sprawling and more erect locomotion may have been possible in earlier taxa. First, the axial skeleton shows little regionalization and allows lateral undulation, evolving then increasingly towards regionalization enabling dorsoventral swinging. During terrestrial locomotion, every step invokes a ground reaction force and functional loadings which the musculoskeletal system needs to accomodate. First insights into the functional loading regime of the fore- and hindlimb skeleton and the body stem of therapsids presented herein are based on the assessment and preliminary measurements of the historical collection of therapsids exhibited in the Paleontological Collection of Eberhard Karls Universität Tübingen, Germany. The specimens included are the archosaur Hyperodapedon sanjuanensis, the early synapsid Dimetrodon limbatus for comparison, and the therapsids Keratocephalus moloch, Sauroctonus parringtoni, Tetragonias njalilus, and Belesodon magnificus. The vertebral columns and ribs of the mounts were carefully assessed for original fossil material and, when preserved, ribs, sacral, and anterior caudal vertebrae were measured. The body of a tetrapod is exposed to forces as well as bending and torsional moments. To resist these functional stresses, certain musculoskeletal specializations evolved. These include: 1) compression resistant plate-like pectoral and pelvic girdle bones, 2) a vertebral column combined with tendinous and muscular structures to withstand compressive and tensile forces and moments, and 3) ribs and intercostal muscles to resist the transverse forces and torsional moments. The legs are compressive stress-resistant, carry the body weight, and support the body against gravity. Tail reduction leads to restructuring of the musculoskeletal system of the pelvic girdle.

vertebrate-zoology.arphahub.com/article/85989/

[arctozilla]

Study Sheds New Light on Origin of Whole-Body Endothermy

The whole-body endothermy seen in modern birds and mammals is long held to have evolved independently in each group, a reasonable assumption when it was believed that its earliest appearances in birds and mammals arose many millions of years apart. According to the new research, the evolutionary origin of endothermy could have occurred nearly 300 million years ago.

www.sci.news/paleontology/whole-body-endothermy-origin-10364.html

[arctozilla]

Here's Scott Hartmann's look on Dimetrodon posture.

www.google.com/amp/s/www.skeletaldrawing.com/home/21stcenturydimetrodon%3fformat=amp

[arctozilla]

Hypothesis on the function of Edaphosaurus' and Dimetrodon's sail.

eartharchives.org/articles/dimetrodon-and-its-sail/index.html

[Gorilla king]

Inostrancevia

Inostrancevia (†Inostrancevia alexandri (Amalitsky, 1922))

Order: Therapsida

Family: †Gorgonopsidae

Dimensions: total body lengths reaching up to 3.5 m and long, narrow skulls up to 60 cm long, weight ~250 kg

Temporal range: Wuchiapingian (Late Permian period), 260–254 Ma

A largest representative: Inostrancevia latifrons (Pravoslavlev, 1927)

Inostrancevia is an extinct genus of carnivorous therapsids, containing the largest members of the family Gorgonopsidae, predators characterized by long, saber-tooth-like canines. The various species inhabited northern Russia during the Upper Tatarian (Vyatskian), a Russian regional stage equivalent to the Wuchiapingian stage of the Late Permian period, dating from approximately 260 to 254 million years ago. It is known from several skulls and two almost-complete skeletons. The species in Inostrancevia were the largest gorgonopsids known; known individuals have total body lengths reaching up to 3.5 m and long, narrow skulls up to 60 cm long. Like several other gorgonopsids, Inostrancevia was characterized by strongly developed canine teeth, with those of the upper jaw up to 15 cm long, the root corresponding to half its length. Their bodies were slender, with rather short legs. Inostrancevia shared its habitat with Scutosaurus which it likely preyed upon.


prehistoric-fauna.com/Inostrancevia

[arctozilla]

Antiquity of forelimb ecomorphological diversity in the mammalian stem lineage (Synapsida)

Significance

Mammals and their closest fossil relatives use their shoulders and forelimbs for many functions, which is reflected by the great range of mammalian forelimb shapes. We found that forelimb shape diversity in the early mammalian lineage (Synapsida) began to increase about 270 million years ago, with the emergence of a group called Therapsida, and is accompanied by new forelimb functions. The functional diversification of therapsid forelimbs was curtailed by the Permo-Triassic mass extinction, but eventually continued as more mammal-like therapsids evolved new ecologies. Our analyses characterize the deep time origin of a quintessential part of the mammalian body plan: evolutionarily labile forelimbs that can be deployed in a wide range of functional and ecological roles.

www.pnas.org/doi/10.1073/pnas.1802543116

[oldindigosilverback]

Good thread. Somebody needs to post some info about the unpopular living organisms.

[arctozilla]

New study reveals the secrets of an ancient, extinct super predator

We were then able to investigate its internal structures. Anteosaurus’s organ of balance, its inner ear, was found to be relatively larger than that of its closest relatives and other predators living contemporaneously. This indicates that Anteosaurus was capable of moving much faster than its prey and competitors. We also found that the part of the brain responsible for coordinating the movements of the eyes with the head was exceptionally large. This would have been a crucial trait to ensure the animal’s tracking abilities. Its agility, as we pointed out in the paper, could be compared to that of the North American mountain lion, or cougar.

Taken together, all of these findings show that Anteosaurus’s nervous system was specialised and optimised so the animal could hunt swiftly and strike fast. Its prey would have included large herbivores like Moschognathus, small lizard-like animals, large amphibians or even other carnivores.

theconversation.com/new-study-reveals-the-secrets-of-an-ancient-extinct-super-predator-156588

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[arctozilla]

Here's a take on mammalian endothermy's origin. It seems like synapsids evolved endothermy during Late Triassic.

www.euronews.com/next/2022/07/20/us-science-mammals

[arctozilla]

Here's info about Permian synapsids from NHK Leaps in Evolution.

[arctozilla]

BBC Walking With Monsters: Life Before Dinosaurs also has info about synapsids from episode 2-3.

[arctozilla]

Evolution of synapsid skin.

blogs.scientificamerican.com/laelaps/getting-to-the-root-of-fur/

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[arctozilla]

History of synapsids in the Permian Period.

Synapsids dominated the terrestrial realm between the late Pennsylvanian and the Triassic. Their early evolution includes some of the first amniotes to evolve large size, herbivory, and macro-predators. However, little research has focused on the changes in diversity occurring during this early phase in their evolutionary history, with more effort concentrating on later events such the Permo-Triassic extinction. Here we assess synapsid diversity, at both the species and genus levels, between the Carboniferous (Moscovian) and the Middle Permian (Capitanian). A raw, taxic diversity (richness) estimate is generated, and we use two separate methods to correct for sampling biases in this curve. To remove the effect of anthropogenic sampling bias, we apply a recently published modification of the residual diversity method, and then generate a supertree, using matrix representation with parsimony to infer ghost lineages and obtain a phylogenetic diversity estimate. The general diversity pattern reflects the initial diversification of synapsids in the late Pennsylvanian and early Cisuralian, which was followed by an extinction event during the Sakmarian. Diversity recovered during the Artinskian and Kungurian, coinciding with the radiation of Caseidae, although other families begin to decline. A second extinction event occurred across the Kungurian/Roadian boundary, in which Edaphosauridae and Ophiacodontidae died out although Caseidae and Therapsida diversified. The sampling-corrected curves reveal further extinction during the Roadian, although therapsids were again unaffected. Pelycosaurian-grade synapsids survived during the Wordian and Capitanian, but were a minor part of an otherwise therapsid-dominated fauna. Evidence of significant anthropogenic sampling bias calls into question previous diversity studies that have not employed sampling correction.

www.cambridge.org/core/journals/paleobiology/article/abs/early-evolution-of-synapsids-and-the-influence-of-sampling-on-their-fossil-record/F954EFC9ABBCEF36ED469C715C3B16A3

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[arctozilla]

Apr 28, 2023 22:23:14 GMT -5 oldindigosilverback said:

Good thread. Somebody needs to post some info about the unpopular living organisms.

The thread is actually more than simply informative. It's also important because it concerns the history of us all. Considering we're synapsids as well.

[arctozilla]

The early evolution of synapsids, and the influence of sampling on their fossil record



The evolution of the mammalian jaw during the transition from non-mammalian synapsids to crown mammals is a key event in vertebrate history and characterised by the gradual reduction of its individual bones into a single element and the concomitant transformation of the jaw joint and its incorporation into the middle ear complex. This osteological transformation is accompanied by a rearrangement and modification of the jaw adductor musculature, which is thought to have allowed the evolution of a more-efficient masticatory system in comparison to the plesiomorphic synapsid condition. While osteological characters relating to this transition are well documented in the fossil record, the exact arrangement and modifications of the individual adductor muscles during the cynodont–mammaliaform transition have been debated for nearly a century.

We review the existing knowledge about the musculoskeletal evolution of the mammalian jaw adductor complex and evaluate previous hypotheses in the light of recently documented fossils that represent new specimens of existing species, which are of central importance to the mammalian origins debate. By employing computed tomography (CT) and digital reconstruction techniques to create three-dimensional models of the jaw adductor musculature in a number of representative non-mammalian cynodonts and mammaliaforms, we provide an updated perspective on mammalian jaw muscle evolution.

As an emerging consensus, current evidence suggests that the mammal-like division of the jaw adductor musculature (into deep and superficial components of the m. masseter, the m. temporalis and the m. pterygoideus) was completed in Eucynodontia. The arrangement of the jaw adductor musculature in a mammalian fashion, with the m. pterygoideus group inserting on the dentary was completed in basal Mammaliaformes as suggested by the muscle reconstruction of Morganucodon oehleri. Consequently, transformation of the jaw adductor musculature from the ancestral (‘reptilian’) to the mammalian condition must have preceded the emergence of Mammalia and the full formation of the mammalian jaw joint. This suggests that the modification of the jaw adductor system played a pivotal role in the functional morphology and biomechanical stability of the jaw joint.

onlinelibrary.wiley.com/doi/full/10.1111/brv.12314

[arctozilla]

Phylogeny of major clades of early amniotes showing wholesale turnover of the mammalian total group (Synapsida) during the Early–Middle Permian transition The duration of coexistence between eupelycosaurs and therapsids is reduced by the finding that varanopids are reptiles and not synapsids. Synapsid lineages are shown in green and diapsids in magenta. Miss., Mississippian; Guadal., Guadalupian; Lop., Lopingian; Low., Lower.

www.researchgate.net/figure/Phylogeny-of-major-clades-of-early-amniotes-showing-wholesale-turnover-of-the-mammalian_fig7_338376433

[Gorilla king]

SIMPLIFICATION AS A TREND IN SYNAPSID CRANIAL EVOLUTION


Abstract

The prevalence and meaning of morphological trends in the fossil record have undergone renewed scrutiny in recent years. Studies have typically focused on trends in body size evolution, which have yielded conflicting results, and have only rarely addressed the question as to whether other morphological characteristics show persistent directionality over long time scales. I investigated reduction in number of skull and lower jaw bones (through loss or fusion) over approximately 150 million years of premammalian synapsid history. The results of a new skull simplification metric (SSM), which is defined as a function of the number of distinct elements, show that pronounced simplification is evident on both temporal (i.e., stratigraphic) and phylogenetic scales. Postcranial evolution exhibits a similar pattern. Skull size, in contrast, bears little relationship with the number of distinct skull bones present.

Synapsid skulls carried close to their observed maximum number of elements for most of the Late Carboniferous and Early Permian. The SSM decreased in the Late Permian but, coincident with the radiation of early therapsids, the range of observed SSM values widened during this interval. From derived nonmammalian cynodonts in the Early Triassic through the earliest mammals in the Early Jurassic, both the minimum and maximum SSM decreased. Data from three representative modern mammals (platypus, opossum, and human) suggest that this trend continues through the Cenozoic.

In a phylogenetic context, the number of skull elements present in a taxon shows a significant negative relationship with the number of branching events passed from the root of the tree; more deeply embedded taxa have smaller SSM scores. This relationship holds for various synapsid subgroups as well. Although commonly ascribed to the effects of long-term selection, evolutionary trends can alternatively reflect an underlying intrinsic bias in morphological change. In the case of synapsid skull bones (and those of some other tetrapods lineages), the rare production of novel, or neomorphic, elements may have contributed to the observed trend toward skeletal simplification.







bioone.org/journals/evolution/volume-55/issue-7/0014-3820_2001_055_1419_SAATIS_2.0.CO_2/SIMPLIFICATION-AS-A-TREND-IN-SYNAPSID-CRANIAL-EVOLUTION/10.1554/0014-3820(2001)055[1419:SAATIS]2.0.CO;2.short

[arctozilla]

The origin and early radiation of the therapsid mammal-like reptiles: a palaeobiological hypothesis

Abstract

The replacement of the basal synapsid pelycosaurs by the more ‘mammal-like’ therapsids in the Permian was an important event in the history of tetrapods because it initiated the eventual transition to the mammals. It is also an example of taxon replacement in the fossil record that is unusually amenable to explanation, based on a combination of analysis of the biological significance of the inferred character changes, with the stratigraphic, palaeogeographic and palaeoecological circumstances of the time. An hypothesis is presented in which the origin of the therapsids resulted from a correlated progression of character evolution leading to higher levels of metabolic activity and homeostatic regulation of the body. It was a response to the availability of a seasonally arid, savanna-like biome. The subsequent explosive radiation of therapsids was associated with habitat expansion made possible by the Mid-Permian development of geographical continuity between that biome and the temperate biomes. The final extinction of the pelycosaurs was a case of incumbent replacement by the new therapsid lineages.

onlinelibrary.wiley.com/doi/10.1111/j.1420-9101.2005.01076.x

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