Mammal-like Reptiles Research Articles

Cognitive archaeology: in search of the earliest syntactic language-users in Himalaya

Recent scientific studies unfold that neural structures bearing on intonation of speech have a deep evolutionary history traced to mammal-like reptiles called therapsids found in the Triassic period (∼252.17 mya, million years ago). Therefore, these structures were already present in the primates. It goes to the credit of Homo sapiens who developed it to the extent that humans are defined as symbolling animals, for language is the most articulated symbolism. Cognitive archaeology makes it clear that it took hominins millions of years to develop a syntactic language. Stratigraphically controlled and securely established artefact-bearing sites of the Middle Palaeolithic Arjun complex in the Deokhuri Valley, West Nepal, provide firm dates for the presence of the earliest syntactic language speakers in Himalaya from 100 ka to 70 ka (thousand years ago).

Early shifts lead to big changes

Mammalian Evolution 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][1] [1]: /lookup/volpage/361/1249?iss=6408

Fossils reveal the complex evolutionary history of the mammalian regionalized spine.

A unique characteristic of mammals is a vertebral column with anatomically distinct regions, but when and how this trait evolved remains unknown. We reconstructed vertebral regions and their morphological disparity in the extinct forerunners of mammals, the nonmammalian synapsids, to elucidate the evolution of mammalian axial differentiation. Mapping patterns of regionalization and disparity (heterogeneity) across amniotes reveals that both traits increased during synapsid evolution. However, the onset of regionalization predates increased heterogeneity. On the basis of inferred homology patterns, we propose a "pectoral-first" hypothesis for region acquisition, whereby evolutionary shifts in forelimb function in nonmammalian therapsids drove increasing vertebral modularity prior to differentiation of the vertebral column for specialized functions in mammals.

Transcending human spondyloarthritis: Implications of the ecologic record from the Permian to the present

Spondyloarthropathy is recognized as far back as the Permian, 300 million years before present, increased in prevalence over geologic and modern time and is now essentially trans-mammalian in distribution. Four aspects allow spondyloarthropathy to be studied across phylogenetic lines and through time: Stability of disease characteristics and its spectrum, occurrence sufficiently early in life to for remains to be identified, absence of bias in skeletal preservation and lack of significant effect on organismal survival. Identified in mammal-like reptiles, dinosaurs and other more recent reptiles, it is with mammals that the disease became endemic. It strongly penetrated some early mammal lineages which were short-lived, in contrast to its geometric increase in population penetrance over geologic time. Prevalence increased seven fold in horses, rhinoceros and non-human primates and its current occurrence is independent of captive or free-ranging status. In addition to inflicting musculoskeletal morbidity, the disease is associated with behavior changes, some possibly related to interferon modulation. Spondyloarthropathy is considered a disease and rightly so, given its impact on mobility, health and behavior. However, it seems paradoxical that a phenomenon which has such negative effects would persist, let alone increase in population penetrance.

A Jugal in the Rough: The Evolutionary Importance of the Zygoma.

A Jugal in the Rough: The Evolutionary Importance of the Zygoma.

A caseian point for the evolution of a diaphragm homologue among the earliest synapsids.

The origin of the diaphragm remains a poorly understood yet crucial step in the evolution of terrestrial vertebrates, as this unique structure serves as the main respiratory motor for mammals. Here, we analyze the paleobiology and the respiratory apparatus of one of the oldest lineages of mammal-like reptiles: the Caseidae. Combining quantitative bone histology and functional morphological and physiological modeling approaches, we deduce a scenario in which an auxiliary ventilatory structure was present in these early synapsids. Crucial to this hypothesis are indications that at least the phylogenetically advanced caseids might not have been primarily terrestrial but rather were bound to a predominantly aquatic life. Such a lifestyle would have resulted in severe constraints on their ventilatory system, which consequently would have had to cope with diving-related problems. Our modeling of breathing parameters revealed that these caseids were capable of only limited costal breathing and, if aquatic, must have employed some auxiliary ventilatory mechanism to quickly meet their oxygen demand upon surfacing. Given caseids' phylogenetic position at the base of Synapsida and under this aquatic scenario, it would be most parsimonious to assume that a homologue of the mammalian diaphragm had already evolved about 50 Ma earlier than previously assumed.

The evolution of language and thought.

Language primarily evolved as a vocal medium that transmits the attributes of human culture and the necessities of daily communication. Human language has a long, complex evolutionary history. Language also serves as an instrument of thought since it has become evident that in the course of this process neural circuits that initially evolved to regulate motor control, motor responses to external events, and ultimately talking were recycled to serve tasks such as working memory, cognitive flexibility linguistic tasks such as comprehending distinctions in meaning conveyed by syntax. This precludes the human brain possessing an organ devoted exclusively to language, such as the Faculty of Language proposed by Chomsky (1972, 2012). In essence like Fodor's (1983) modular model, a restatement of archaic phrenological theories (Spurzheim, 1815). The subcortical basal ganglia can be traced back to early anurans. Although our knowledge of the neural circuits of the human brain is at a very early stage and incomplete, the findings of independent studies over the past 40 years, discussed here, have identified circuits linking the basal ganglia with various areas of prefrontal cortex, posterior cortical regions and other subcortical structures. These circuits are active in linguistic tasks such as lexical access, comprehending distinctions in meaning conferred by syntax and the range of higher cognitive tasks involving executive control and play a critical role in conferring cognitive flexibility. The cingulate cortex which appeared in Therapsids, transitional mammal-like reptiles who lived in age of the dinosaurs, most likely enhanced mother-infant interaction, contributing to success in the Darwinian (1859) "Struggle for Existence" - the survival of progeny. They continue to fill that role in present-day mammals as well as being involved in controlling laryngeal phonation during speech and directing attention (Newman & MacLean, 1983; Cummings, 1993". The cerebellum and hippocampus, archaic structures, play role in cognition. Natural selection acting on genetic and epigenetic events in the last 500,000 years enhanced human cognitive and linguistic capabilities. It is clear that human language did not suddenly come into being 70,000 to 100,000 years as Noam Chomsky (Bolhuis et al., 2014) and others claim. The archeological record and analyses of fossil and genetic evidence shows that Neanderthals, who diverged from the human line at least 500,000 years ago possessed some form of language. Nor did the human population suddenly acquire the capability to relate two seemingly unrelated concepts by means of associative learning 100,000 years ago, re-coined "Merge" by Chomsky and his adherents, Merge supposedly is the key to syntax but associative learning, one of the cognitive processes by which children learn languages and the myriad complexities of their cultures, is a capability present in dogs and virtually all animals.

Reconstructing the Auditory Apparatus of Therapsids by Means of Neutron Tomography

The internal cranial structure of mammalian ancestors, i.e. the therapsids or “mammal-like reptiles”, is crucial for understanding the early mammalian evolution. In the past therapsid skulls were investigated by mechanical sectioning or serial grinding, which was a very time-consuming and destructive process and could only be applied to non-valuable or poorly preserved specimens. As most therapsid skulls are embedded in terrestrial iron-rich sediments of Late Permian or Triassic age, i.e. so called “Red beds”, a successful investigation with X-Rays is often not possible.We successfully investigated therapsid skulls by means of neutron tomography at the facility ANTARES at FRM II in Munich using cold neutron radiation. This kind of radiation is able to penetrate iron-rich substances in the range between 5 and 15cm and produces a good contrast between matrix and bones, which enables segmentation of internal cranial structures such as bones, cavities and canals of nerves and blood vessels. In particular, neutron tomography combined with methods of 3D modeling was used here for the investigation and reconstruction of the auditory apparatus of therapsids.

Seasonal bone growth and physiology in endotherms shed light on dinosaur physiology

Cyclical growth leaves marks in bone tissue that are in the forefront of discussions about physiologies of extinct vertebrates. Ectotherms show pronounced annual cycles of growth arrest that correlate with a decrease in body temperature and metabolic rate; endotherms are assumed to grow continuously until they attain maturity because of their constant high body temperature and sustained metabolic rate. This apparent dichotomy has driven the argument that zonal bone denotes ectotherm-like physiologies, thus fuelling the controversy on dinosaur thermophysiology and the evolution of endothermy in birds and mammal-like reptiles. Here we show, from a comprehensive global study of wild ruminants from tropical to polar environments, that cyclical growth is a universal trait of homoeothermic endotherms. Growth is arrested during the unfavourable season concurrently with decreases in body temperature, metabolic rate and bone-growth-mediating plasma insulin-like growth factor-1 levels, forming part of a plesiomorphic thermometabolic strategy for energy conservation. Conversely, bouts of intense tissue growth coincide with peak metabolic rates and correlated hormonal changes at the beginning of the favourable season, indicating an increased efficiency in acquiring and using seasonal resources. Our study supplies the strongest evidence so far that homeothermic endotherms arrest growth seasonally, which precludes the use of lines of arrested growth as an argument in support of ectothermy. However, high growth rates are a distinctive trait of mammals, suggesting the capacity for endogenous heat generation. The ruminant annual cycle provides an extant model on which to base inferences regarding the thermophysiology of dinosaurs and other extinct taxa.

Sabretoothed Carnivores and the Killing of Large Prey

Sabre-like canines clearly have the potential to inflict grievous wounds leading to massive blood loss and rapid death. Hypotheses concerning sabretooth killing modes include attack to soft parts such as the belly or throat, where biting deep is essential to generate strikes reaching major blood vessels. Sabretoothed carnivorans are widely interpreted as hunters of larger and more powerful prey than that of their present-day nonsabretoothed relatives. However, the precise functional advantage of the sabretooth bite, particularly in relation to prey size, is unknown. Here, we present a new point-to-point bite model and show that, for sabretooths, depth of the killing bite decreases dramatically with increasing prey size. The extended gape of sabretooths only results in considerable increase in bite depth when biting into prey with a radius of less than ∼10 cm. For sabretooths, this size-reversed functional advantage suggests predation on species within a similar size range to those attacked by present-day carnivorans, rather than “megaherbivores” as previously believed. The development of the sabretooth condition appears to represent a shift in function and killing behaviour, rather than one in predator-prey relations. Furthermore, our results demonstrate how sabretoothed carnivorans are likely to have evolved along a functionally continuous trajectory: beginning as an extension of a jaw-powered killing bite, as adopted by present-day pantherine cats, followed by neck-powered biting and thereafter shifting to neck-powered shear-biting. We anticipate this new insight to be a starting point for detailed study of the evolution of pathways that encompass extreme specialisation, for example, understanding how neck-powered biting shifts into shear-biting and its significance for predator-prey interactions. We also expect that our model for point-to-point biting and bite depth estimations will yield new insights into the behaviours of a broad range of extinct predators including therocephalians (gorgonopsian + cynodont, sabretoothed mammal-like reptiles), sauropterygians (marine reptiles) and theropod dinosaurs.

Pathologies of non-marine bivalve shells from the Late Triassic of Poland

Gorzelak, P., Niedźwiedzki, G. & Skawina, A. 2010: Pathologies of non-marine bivalve shells from the Late Triassic of Poland. Lethaia, Vol. 43, pp. 285–289. Shells of Late Triassic non-marine bivalves from Lisowice (Lipie Śląskie clay pit, southern Poland), which co-occur with remains of several vertebrate taxa (mammal-like reptiles, carnivorous dinosaurs, pterosaurs, temnospondyl amphibians, hybodont sharks, dipnoan and ganoid fish), bear evidence of pathologies. Distribution, dimension and shape of some of these injuries (radiate tooth marks) closely match the dental morphology of lungfish (here probably represented by the genus Ceratodus). Thus, we interpret these pathologies as evidence of unsuccessful predatory attack on bivalves by this fish. This interpretation is also consistent with modern examples of such behaviour among lungfish. The feasibility that other culprits caused other pathologies (shell scarring and wedges) on the bivalves analysed is also discussed. Discovery of these traces constitutes important evidence of predator–prey interaction, which provides ‘fingerprints’ of trophic structure within this Late Triassic freshwater ecosystem. □Freshwater bivalves, lungfish, pathologies, predation, Triassic.

Dimetrodon Is Not a Dinosaur: Using Tree Thinking to Understand the Ancient Relatives of Mammals and their Evolution

The line of descent that includes all living mammals extends back in time over 300 million years. Many of the ancient relatives of mammals that fall along this line are very different in appearance from living mammals and are frequently mistaken for reptiles such as dinosaurs. This misconception is reinforced by the fact that these animals are often referred to as “mammal-like reptiles,” a term reflecting outdated methods for classifying organisms. In reality, these ancient mammal-relatives, known as synapsids, are more closely related to living mammals than they are to any reptiles. Evolutionary trees, which depict patterns of descent from common ancestors among organisms, are very useful for understanding why this is the case and for reconstructing the evolutionary histories of many of the unique characters found in mammals. Here, I provide an introduction to evolutionary trees and their implications for understanding the relationships between mammals, synapsids, and reptiles. This is followed by a review of synapsid diversity and a discussion of how evolutionary trees can be used to investigate when in synapsid history different mammalian characteristics first appeared.

About this title - Late Palaeozoic and Mesozoic Continental Ecosystems in SE Asia

Non-marine Late Palaeozoic and Mesozoic formations are widespread in mainland SE Asia. Although the first reports on fossils from some of these formations were published as early as the 1890s, it is only since 1980 that floras and faunas from the Permian, Triassic, Jurassic and Cretaceous of SE Asia have received the attention they deserve. Fieldwork in various parts of Thailand and Laos has revealed a succession of fossil assemblages that now allows a reconstruction of the evolution of continental ecosystems in that part of the world during the Late Palaeozoic and the Mesozoic. The first papers in this book present the geological background of these floral and faunal successions, as well as historical aspects of their discovery. Descriptions of new taxa and review papers deal with plants, sharks, bony fishes, turtles, crocodilians, dinosaurs and mammal-like reptiles. Papers about the Mesozoic palaeobiogeography, environments and climates of Asia conclude the volume.

The geological and palaeontological exploration of Laos; following in the footsteps of J. B. H. Counillon and A. Pavie

Abstract Historical studies on the exploration of SE Asia reveal interesting points concerning the geology and palaeontology of this part of the world: the first geological description of northern Laos was published in 1896 by the French geologist J. B. H. Counillon, a member of the famous Pavie Mission (1879–1895). Although scientific notes are rare in the literature about the Pavie Mission, which dealt with diplomacy and politics, Counillon's studies are very informative: they contain accurate observations on the geomorphology, hydrography, stratigraphy and palaeontology of the Mekong River and its banks. Counillon explored the dangerous region of Luang Prabang (northern Laos) with Captain Cupet. He discovered the first fossil tetrapods from Laos, and, with the help of Vasseur and Repelin, correctly referred them to dicynodont mammal-like reptiles.

Global Taxonomic Diversity of Anomodonts (Tetrapoda, Therapsida) and the Terrestrial Rock Record Across the Permian-Triassic Boundary

The end-Permian biotic crisis (∼252.5 Ma) represents the most severe extinction event in Earth's history. This paper investigates diversity patterns in Anomodontia, an extinct group of therapsid synapsids (‘mammal-like reptiles’), through time and in particular across this event. As herbivores and the dominant terrestrial tetrapods of their time, anomodonts play a central role in assessing the impact of the end-Permian extinction on terrestrial ecosystems. Taxonomic diversity analysis reveals that anomodonts experienced three distinct phases of diversification interrupted by the same number of extinctions, i.e. an end-Guadalupian, an end-Permian, and a mid-Triassic extinction. A positive correlation between the number of taxa and the number of formations per time interval shows that anomodont diversity is biased by the Permian-Triassic terrestrial rock record. Normalized diversity curves indicate that anomodont richness continuously declines from the Middle Permian to the Late Triassic, but also reveals all three extinction events. Taxonomic rates (origination and extinction) indicate that the end-Guadalupian and end-Permian extinctions were driven by increased rates of extinction as well as low origination rates. However, this pattern is not evident at the final decline of anomodont diversity during the Middle Triassic. Therefore, it remains unclear whether the Middle Triassic extinction represents a gradual or abrupt event that is unique to anomodonts or more common among terrestrial tetrapods. The end-Permian extinction represents the most distinct event in terms of decline in anomodont richness and turnover rates.

The playa environments of the Lodève Permian basin (Languedoc-France).

The Lodeve Permian synrift sequence is represented by thick stacked climate-controled playa cycles which have been constrained by structural, sedimentological, geochemical and paleontological processes. The present paper merges the different results in order to better constrain the dynamics and palaeoecologycal evolution of the playa system from Late Cisuralian to Early Lopingian time. In this depositional environment, thining upwards sheet-flood sequences represent flooding events; they are relayed by ephemeral ponding, suspension settling and limited carbonate precipitation accompanied by large amounts of shallow to subaerial sedimentary structures (current and wind ripples, desiccation cracks, rain drops, etc.). The aridity of the climate contrasts with the surprising abundance of the fauna encountered into carbonate-rich silty-clay playa-lake deposits. Ephemeral pools are colonized by numerous shellfish: Choncostraca, Triopsids, and Insects, which led to intense burrowing of the overbank deposits (Scoyenia facies). Tetrapods are common and dominated by several types of reptiles after footprints: Pelycosauria, Parareptilia and Lepidosauria in the Rabejac Fm, and Mammalian reptiles (Therapsida) on the top of the fluvial deposits of the Salagou Fm near La Lieude farm. In addition, elements of a weighty herbivorous Pelycosaurian and a small amphibian Tupilakosaurid, only described in the Triassic before, have been also found in the Upper part of the Permian series of this sector.

The Deep Roots of the Mammalian Tree

T. S. Kemp, the author of the much revered and useful Mammal-like Reptiles and the Origin of Mammals (1982), has produced a new book with the explicit aims of (1) updating the 1982 book with regard to new fossils and (2) elaborating “at a similar level the story of what happens next—the radiation of mammals after the end of the Cretaceous” (preface). The book addresses general topics and technical issues as well, dealing with the origin of mammals in the widest possible sense, that is, truly, the history of Synapsida. The readership targeted consists mostly of university students and paleontologists, but some of the broader topics will be of interest to evolutionary biologists and most scientists with a natural history background. The amateur or layperson attempting to tackle this book will face a steep learning curve, but if successfully completed much will be learned, and it will have proven the doggedness of his/her interest. The new book is graced by a clear prose, set at a fast pace, and profusely illustrated; the accomplished writing renders discussions vivid and makes progress through the lengthy and necessarily arid anatomical descriptions, if not enjoyable, at least an alleviated task. The similarities and differences between the two titles of Kemp’s books outline the substantial overlap between these works, as well as the subtle nuances in the topics covered. The 1982 book curtailed the history of Synapsida after a short chapter on Mesozoic Mammals. The new book consists of seven chapters. The first two (Introduction, and Time and Classification) are together just 11 pages long. The following five chapters form the core of the book. Chapters 3 (Evolution of the Mammal-like Reptiles) and 4 (Evolution of Mammalian Biology) are together about 120 pages long. The following three chapters—Chapter 5 (Mesozoic Mammals, 50 pages), Chapter 6 (Living and Fossil Marsupials, 25 pages) and Chapter 7 (Living and Fossil Placentals, 52 pages)—pertain to Mammalia as defined in this work (a traditional and conservative character-based definition highlighting the presence of a dentary condyle). Therefore, the book is organized along a phylogenetic axis with the exception of Chapter 4. This emphasis on phylogeny is reinforced assiduously by large and

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

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.

Phylogenetic and ontogenetic parallelisms on talo-calcaneal superposition

The process of talo-calcaneal superposition is one of the most important steps in the transformation of the reptilian foot (primitive) into the mammalian foot (modern). This change was developed in certain families of mammal-like reptiles and transitional mammals during the Mesozoic age and represents a different path in the morphological development of the foot to that of other dominant reptiles (Dinosaurs, etc.). The talo-calcaneal superposition takes place during the embryonic stage of human life and ends during the primary stages of the foetal period of the same. This study aims to demonstrate the similarities between the phylogenic and ontogenic development of the said morphological change.

Jaws of primitive mammals

Some of main osteological differences between mammals and reptiles are seen in the number of bones that constitute lower jaw and in jaw articulation. A lower jaw of mammals consists of only one bone, while in reptiles it consists of several bones (e.g., four to six in lizards and five in crocodiles). The jaw articulation in mammals is performed by squamosal of the skull and the mandible ( = dentary), while in reptiles it is done by quadrate of the skull and articular of the lower jaw. When mammals first appeared about 200 million years ago in the Mesozoic Era, the jaws of primitive mammals were morphologically intermediate between those of reptiles and typical mammals. Here, I briefly introduce the evolution of lower jaw morphology from the reptilian one to the mammalian one, showing lower jaw features of some mammal-like reptiles and primitive mammals.