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15.1: Amphibians - Biology

15.1: Amphibians - Biology


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Characteristics of Amphibians

As tetrapods, most amphibians are characterized by four well-developed limbs. An important characteristic of extant amphibians is a moist, permeable skin that is achieved via mucus glands that keep the skin moist; thus, exchange of oxygen and carbon dioxide with the environment can take place through it (cutaneous respiration). Amphibians also have an auricular operculum, which is an extra bone in the ear that transmits sounds to the inner ear.

The fossil record provides evidence of amphibian species, now extinct, that arose over 400 million years ago as the first tetrapods. Amphibia can be divided into three clades: salamanders (Urodela), frogs (Anura), and caecilians (Apoda). The life cycle of frogs, like the majority of amphibians, consists of two distinct stages: the larval stage and metamorphosis to an adult stage. Some species in all orders bypass a free-living larval stage. All extant adult amphibians are carnivorous, and some terrestrial amphibians have a sticky tongue that is used to capture prey.

Evolution of Amphibians

The fossil record provides evidence of the first tetrapods: now-extinct amphibian species dating to nearly 400 million years ago. Evolution of tetrapods from fishes represented a significant change in body plan from one suited to organisms that respired and swam in water, to organisms that breathed air and moved onto land; these changes occurred over a span of 50 million years during the Devonian period.

One of the earliest known tetrapods is from the genus Acanthostega. Acanthostega was aquatic; fossils show that it had gills similar to fishes. However, it also had four limbs, with the skeletal structure of limbs found in present-day tetrapods, including amphibians. Therefore, it is thought that Acanthostega lived in shallow waters and was an intermediate form between lobe-finned fishes and early, fully terrestrial tetrapods. What preceded Acanthostega?

In 2006, researchers published news of their discovery of a fossil of a “tetrapod-like fish,” Tiktaalik roseae, which seems to be an intermediate form between fishes having fins and tetrapods having limbs (Figure 1). Tiktaalik likely lived in a shallow water environment about 375 million years ago.

The early tetrapods that moved onto land had access to new nutrient sources and relatively few predators. This led to the widespread distribution of tetrapods during the early Carboniferous period.

The Paleozoic Era and the Evolution of Vertebrates

The climate and geography of Earth was vastly different during the Paleozoic Era, when vertebrates arose, as compared to today. The Paleozoic spanned from approximately 542 to 251 million years ago. The landmasses on Earth were very different from those of today. Laurentia and Gondwana were continents located near the equator that subsumed much of the current day landmasses in a different configuration (Figure 2). At this time, sea levels were very high, probably at a level that hasn’t been reached since. As the Paleozoic progressed, glaciations created a cool global climate, but conditions warmed near the end of the first half of the Paleozoic. During the latter half of the Paleozoic, the landmasses began moving together, with the initial formation of a large northern block called Laurasia. This contained parts of what is now North America, along with Greenland, parts of Europe, and Siberia. Eventually, a single supercontinent, called Pangaea, was formed, starting in the latter third of the Paleozoic. Glaciations then began to affect Pangaea’s climate, affecting the distribution of vertebrate life.

During the early Paleozoic, the amount of carbon dioxide in the atmosphere was much greater than it is today. This may have begun to change later, as land plants became more common. As the roots of land plants began to infiltrate rock and soil began to form, carbon dioxide was drawn out of the atmosphere and became trapped in the rock. This reduced the levels of carbon dioxide and increased the levels of oxygen in the atmosphere, so that by the end of the Paleozoic, atmospheric conditions were similar to those of today.

As plants became more common through the latter half of the Paleozoic, microclimates began to emerge and ecosystems began to change. As plants and ecosystems continued to grow and become more complex, vertebrates moved from the water to land. The presence of shoreline vegetation may have contributed to the movement of vertebrates onto land. One hypothesis suggests that the fins of aquatic vertebrates were used to maneuver through this vegetation, providing a precursor to the movement of fins on land and the development of limbs. The late Paleozoic was a time of diversification of vertebrates, as amniotes emerged and became two different lines that gave rise, on one hand, to mammals, and, on the other hand, to reptiles and birds. Many marine vertebrates became extinct near the end of the Devonian period, which ended about 360 million years ago, and both marine and terrestrial vertebrates were decimated by a mass extinction in the early Permian period about 250 million years ago.

View Earth’s Paleogeography: Continental Movements Through Time to see changes in Earth as life evolved.


15.1.1 How Many Species are there on Earth and How Many in India?

Since there are published records of all the species discovered and named, we know how many species in all have been recorded so far, but it is not easy to answer the question of how many species there are on earth.

According to the IUCN (2004), the total number of plant and animal species described so far is slightly more than 1.5 million, but we have no clear idea of how many species are yet to be discovered and described. Estimates vary widely and many of them are only educated guesses.

For many taxonomic groups, species inventories are more complete in temperate than in tropical countries. Considering that an overwhelmingly large proportion of the species waiting to be discovered are in the tropics, biologists make a statistical comparison of the temperate-tropical species richness of an exhaustively studied group of insects and extrapolate this ratio to other groups of animals and plants to come up with a gross estimate of the total number of species on earth.

Some extreme estimates range from 20 to 50 million, but a more conservative and scientifically sound estimate made by Robert May places the global species diversity at about 7 million.

Let us look at some interesting aspects about earth’s biodiversity based on the currently available species inventories. More than 70 per cent of all the species recorded are animals, while plants (including algae, fungi, bryophytes, gymnosperms and angiosperms) comprise no more than 22 per cent of the total. Among animals, insects are the most species-rich taxonomic group, making up more than 70 per cent of the total.

That means, out of every 10 animals on this planet, 7 are insects. Again, how do we explain this enormous diversification of insects? The number of fungi species in the world is more than the combined total of the species of fishes, amphibians, reptiles and mammals. In Figure 15.1, biodiversity is depicted showing species number of major taxa.

It should be noted that these estimates do not give any figures for prokaryotes. Biologists are not sure about how many prokaryotic species there might be. The problem is that conventional taxonomic methods are not suitable for identifying microbial species and many species are simply not culturable under laboratory conditions. If we accept biochemical or molecular criteria for delineating species for this group, then their diversity alone might run into millions.

Although India has only 2.4 per cent of the world’s land area, its share of the global species diversity is an impressive 8.1 per cent. That is what makes our country one of the 12 mega diversity countries of the world. Nearly 45,000 species of plants and twice as many of animals have been recorded from India. How many living species are actually there waiting to be discovered and named?

If we accept May’s global estimates, only 22 per cent of the total species have been recorded so far. Applying this proportion to India’s diversity figures, we estimate that there are probably more than 1,00,000 plant species and more than 3,00, 000 animal species yet to be discovered and described. Would we ever be able to complete the inventory of the biological wealth of our country?

Consider the immense trained manpower (taxonomists) and the time required to complete the job. The situation appears more hopeless when we realise that a large fraction of these species faces the threat of becoming extinct even before we discover them. Nature’s biological library is burning even before we catalogued the titles of all the books stocked there.


Filling a gap in the distribution of Batrachochytrium dendrobatidis: evidence in amphibians from northern China

Chytridiomycosis caused by Batrachochytrium dendrobatidis (Bd) has been recognized as a major driver of amphibian declines worldwide. Central and northern Asia remain as the greatest gap in the knowledge of the global distribution of Bd. In China, Bd has recently been recorded from south and central regions, but areas in the north remain poorly surveyed. In addition, a recent increase in amphibian farming and trade has put this region at high risk for Bd introduction. To investigate this, we collected a total of 1284 non-invasive skin swabs from wild and captive anurans and caudates, including free-ranging, farmed, ornamental, and museum-preserved amphibians. Bd was detected at low prevalence (1.1%, 12 of 1073) in live wild amphibians, representing the first report of Bd infecting anurans from remote areas of northwestern China. We were unable to obtain evidence of the historical presence of Bd from museum amphibians (n = 72). Alarmingly, Bd was not detected in wild amphibians from the provinces of northeastern China (>700 individuals tested), but was widely present (15.1%, 21 of 139) in amphibians traded in this region. We suggest that urgent implementation of measures is required to reduce the possibility of further spread or inadvertent introduction of Bd to China. It is unknown whether Bd in northern China belongs to endemic and/or exotic genotypes, and this should be the focus of future research.


Amphibian Declines and Climate Disturbance: The Case of the Golden Toad and the Harlequin Frog

Current address: Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011, U.S.A. All reprint requests should be sent to this address.

Current address: Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011, U.S.A. All reprint requests should be sent to this address.

Abstract

The endemic golden toad (Bufo periglenes) was abundant in Costa Rica’s Monteverde Cloud Forest Preserve in April–May 1987 but afterwards disappeared, along with local populations of the harlequin frog (Atelopus varius). We examine the possible relationship between these sudden declines and unusually warm, dry conditions in 1987. For our analyses of local weather patterns, we define a 12-month (July–June) amphibian moisture-temperature cycle consisting of four periods: (1) late wet season (2) transition into dry season (3) dry season and (4) post-dry-season (early-wet-season) recovery. The 1986–1987 cycle was the only one on record (of 20 analyzed) with abnormally low rainfall in all four periods, and temperature anomalies in 1987 reached record highs. Flow in local aquifer-fed streams during the dry season and post-dry-season recovery period reached a record low. This climate disturbance, associated with the 1986–1987 El Niño/Southern Oscillation, was more severe than a similar event associated with the 1982–1983 El Niño, though this earlier oscillation was the strongest of the past century. Demographic data for one harlequin frog population, gathered during these two climatic events, support the hypothesis that in 1987, shortly before the population collapsed, the frogs underwent an unprecedented shift in distribution within the habitat in response to desiccating conditions. The juxtaposition of these rare demographic events suggests they were causally linked yet sheds little light on mechanisms underlying the sudden decline. While desiccation or direct temperature effects may have been factors leading to high adult mortality, moisture-temperature conditions may have interacted with some other, unidentifted agent. We discuss two hypotheses concerning possible synergistic effects: In the climate-linked epidemic hypothesis, microparasites are the additional agent. In the climate-linked contaminant pulse hypothesis, atmospheric contaminants scavenged by mist and cloud water in montane areas reach critical concentrations when conditions are abnormally warm and dry.

Abstract

El endémico sapo dorado (Bufo periglenes) era abundante en la Reserva del bosque nuboso de Monteverde en Costa Rica durante abril–mayo 1987 pero después desapareció al mismo tiempo que poblaciones locales de la rana harlequin (Atelopus varius). Se examinó la posible relación entre esta súbita disminución y las condiciones cálidas y secas de 1987. Para analizar los patrones locales de tiempo, se definió un ciclo de temperatura-humedad de 12 meses (julio–junio) que consiste de cuatro períodos: (1) últimos meses de la estación lluviosa (2) transición a la estación seca (3) estación seca y (4) recuperación después de la estación seca (principio de la estación lluviosa). El ciclo de 1986–1987 fue el único registrado (de 20 analizodos) que recibió precipitación anormalmente baja en todos los cuatro períodos, y las anomalías de temperaturas en 1987 fueron las más altas registradas. Los caudales en las quebradas locales que se alimentan de manantiales fueron los más bajos registrados durante la estación seca y el período de recuperación. Este trastorno del clima, asociado con El Niño/Oscilación del sur de 1986–1987, estuvo más severo que el evento parecido asociado con El Niño de 1982–1983, aunque esta oscilación anterior fue la más fuerte del último siglo. Datos para una población de ranas barlequines, recolectados durantes estos dos trastornos del clima, apoyan la hipótesis que en 1987, poco antes de que la población colapsara, las ranas cambiaron su distribución en el hábitat en respuesta a condiciones desecantes. La yuxtaposición de estos raros eventos demográficos sugieren que estuvieron ligados causalmente, pero dice poco de los mecanismos de la súbito disminución. Mientras que la desecación y los efectos directos de la temperatura pudieron haber causado mortalidad de adultos, también es posible que hubiera interacción entre las condiciones climáticas y otro factor. Se discuten dos hipótesis sobre una posible interacción: En la hipótesis de epidemia ligada al clima, los microparásitos son el factor adicional. En la hipótesis de contaminación ligada al clima, contaminantes atmosféricos removidos por la llovizna y niebla alcanzan concentraciones críticas cuando las condiciones son anormalmente cálidas y secas.


DEVELOPMENT THREE GRADES OF ONTOGENETIC INVOLVEMENT

1 INTRODUCTION

Viktor Hamburger [1980 ] famously claimed that developmental biology was left out of the modern synthesis from its inception in the early 20 th Century. He didn't mean that some anti-ontogeny conspiracy met in some smoke-filled room and decreed that developmental biology should be excluded. At the time, developmental biology was a discipline in good standing, and those who forged the synthesis were well aware of it. Developmental biology was ‘left out’ simply because it didn't seem to matter much one way or another it seemed to pose no threat, nor to offer any great enhancement to the emerging orthodoxy. In Hamburger's words, evolutionary biologists came to treat development as a ‘black box’, a process that played some contributory role in evolution, but whose details had little bearing on the correctness or otherwise of the synthesis theory. So for much of the 20 th Century developmental biology languished as a relative outsider among biological disciplines, an area of only marginal interest to evolutionists. It is only recently, now that more of the details of ontogeny are understood, that biologists have had cause to rethink the place of development in evolutionary biology. Developmental biology is now one of the most rapidly growing disciplines in biology. It has witnessed enormous advances in the understanding of the mechanics — genetic, epigenetic and environmental — of development in the last twenty years. It is clear now that an understanding of the processes of development is of cardinal importance to the project of explaining the mechanisms of evolution. Yet in spite of this flourishing — or perhaps because of it — there is little consensus on just how this newfound knowledge should impact our conception of evolutionary theory.

I attempt here to outline the space of possible roles for ontogeny in evolutionary biology. I don't intend to adjudicate — although I do have my preferences. It's an empirical issue which of the alternatives is most plausible. But I hope at least to help shed some light on just what that empirical issue is.

One coherent possibility is that an understanding of the processes of ontogeny should occasion no revision to the version of the modern synthesis theory we have grown so comfortable with [ Raff, 1996 ]. But there are others. I develop two other, increasingly central, possible roles for the process of development in evolution. These, by degrees, challenge the standard version of the modern synthesis. In developing the space of possibilities, it will help if we understand the rationale behind the original marginalization of ontogeny. The humble status of development more or less follows from the precepts of the modern synthesis, at least the version that was forged in the early 20 th Century, and which solidified in the latter half [ Gould, 1983 ]. The more we understand about these precepts, on the one hand, and the mechanisms of development, on the other, the more apparent it should become that the marginalization of development from the theory of evolution is no longer tenable, if it ever was.


Strengthening protected areas for biodiversity and ecosystem services in China

Recent expansion of the scale of human activities poses severe threats to Earth's life-support systems. Increasingly, protected areas (PAs) are expected to serve dual goals: protect biodiversity and secure ecosystem services. We report a nationwide assessment for China, quantifying the provision of threatened species habitat and four key regulating services-water retention, soil retention, sandstorm prevention, and carbon sequestration-in nature reserves (the primary category of PAs in China). We find that China's nature reserves serve moderately well for mammals and birds, but not for other major taxa, nor for these key regulating ecosystem services. China's nature reserves encompass 15.1% of the country's land surface. They capture 17.9% and 16.4% of the entire habitat area for threatened mammals and birds, but only 13.1% for plants, 10.0% for amphibians, and 8.5% for reptiles. Nature reserves encompass only 10.2-12.5% of the source areas for the four key regulating services. They are concentrated in western China, whereas much threatened species' habitat and regulating service source areas occur in eastern provinces. Our analysis illuminates a strategy for greatly strengthening PAs, through creating the first comprehensive national park system of China. This would encompass both nature reserves, in which human activities are highly restricted, and a new category of PAs for ecosystem services, in which human activities not impacting key services are permitted. This could close the gap in a politically feasible way. We also propose a new category of PAs globally, for sustaining the provision of ecosystems services and achieving sustainable development goals.

Keywords: conservation strategy ecosystem services protected areas sustainable development threatened species representation.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

The importance level of a…

The importance level of a site for threatened species in China, calculated by…

The importance of ecosystems service…

The importance of ecosystems service source areas in China, showing the spatial mismatch…

Distribution of nature reserves in…

Distribution of nature reserves in China’s four major regions (i.e., north region, south…

Comparison of habitat coverage (both…

Comparison of habitat coverage (both entire habitat and important habitat) for threatened species…

Comparison of habitat coverage of…

Comparison of habitat coverage of threatened species by nature reserves in China, in…

Priority areas for securing threatened…

Priority areas for securing threatened species habitat and source areas of key regulating…


Solving the Biodiversity and Conservation Multiple Choice Questions of Class 12 Biology Chapter 15 MCQ can be of extreme help as you will be aware of all the concepts. These MCQ Questions on Biodiversity and Conservation Class 12 with answers pave for a quick revision of the Chapter thereby helping you to enhance subject knowledge. Have a glance at the MCQ of Chapter 15 Biology Class 12 and cross-check your answers during preparation.

Select the correct answer:

Question 1.
Which of the following countries has the highest biodiversity?
(a) Brazil
(b) South Africa
(c) Russia
(d) India.

Question 2.
Which of the following is not a cause for loss of biodiversity?
(a) Destruction of habitat
(b) Invasion by alien species
(c) Keeping animals in zoological parks
(d) Over-exploitation of natural resources.

Answer: (c) Keeping animals in zoological parks

Question 3.
Which of the following is not an invasive alien species in the Indian context?
(a) Lantana
(b) Cynodon
(c) Parthenium
(d) Eichhornia.

Question 4.
Where among the following will you find pitcher plant?
(a) Rain forest of North-East India
(b) Sunderbans
(c) Thar Desert
(d) Western Ghats.

Answer: (a) Rain forest of North-East India

Question 5.
Which one of the following is not a major characteristic feature of biodiversity hotspots?
(a) Large number of species
(b) Abundance of endemic species
(c) Large number of exotic species
(d) Destruction of habitat.

Answer: (d) Destruction of habitat.

Question 6.
Match the animals given in column A with their location in column B:

Column I Column II
(i) Dodo (a) Africa
(ii) Quagga (b) Russia
(iii) Thylacine (c) Mauritius
(iv) Stellar’s sea cow (d) Australia

Choose the correct match from the following:
(a) i-a, ii-c, iii-b, iv-d
(b) i-d, ii-c, iii-a, iv-b
(c) i-c, ii-a, iii-b, iv-d
(d) i-c, ii-a, iii-d, iv-b.

Question 7.
What is common to the following plants: Nepenthes, Psilotum, Rauwolfia and Acontium?
(a) All are ornamental plants
(b) All are phylogenic link species
(c) All are prone to over-exploitation
(d) All are exclusively present in the Eastern Himalayas.

Answer: (c) All are prone to over-exploitation

Question 8.
The most important cause of biodiversity loss is:
(a) Over exploitation of economic species
(b) Habitat loss and fragmentation
(c) Invasive species
(d) Breakdown of plant-pollinator relationships

Answer: (b) Habitat loss and fragmentation

Question 9.
Amongst the animal groups given below, which one has the highest percentage of endangered species?
(a) Insects
(b) Mammals
(c) Amphibians
(d) Reptiles.

Question 10.
Which one of the following is an endangered plant species of India?
(a) Rauwolfia serpentina
(b) Santalum album (Sandal wood)
(c) Cycas beddonei
(d) All of the above.

Answer: (d) All of the above.

Question 11.
What is common to Lantana, Eichhornia and African catfish?
(a) All are endangered species of India
(b) All are key stone species
(c) All are mammals found in India
(d) All the species are neither threatened nor indigenous species of India.

Answer: (d) All the species are neither threatened nor indigenous species of India.

Question 12.
The extinction of passenger pigeon was due to:
(a) Increased number of predatory birds.
(b) Over-exploitation by humans
(c) Non-availability of the food
(d) Bird flu virus infection

Answer: (b) Over-exploitation by humans

Question 13.
Which of the following statements is correct?
(a) Parthenium is an endemic species of our country.
(b) African catfish is not a threat to indigenous catfishes.
(c) Steller’s sea cow is an extinct animal.
(d) Lantana is popularly known as carrot grass.

Answer: (b) African catfish is not a threat to indigenous catfishes.

Question 14.
Among the ecosystem mentioned below, where can one find maximum biodiversity?
(a) Mangroves
(b) Desert
(c) Coral reefs
(d) Alpine meadows

Question 15.
Which of the following forests is known as the ‘lungs of the planet Earth’?
(a) Tiaga forest
(b) Tundra forest
(c) Amazon rain forest
(d) Rain forests of North East India

Answer: (c) Amazon rain forest

Question 16.
The active chemical drug reserpine is obtained from:
(a) Datura
(b) Rauwolfia
(c) Atropa
(d) Papaver

Question 17.
Which of the following groups of plants exhibit more species diversity?
(a) Angiosperms
(b) Algae
(c) Bryophytes
(d) Fungi

Question 18.
Which of the below-mentioned regions exhibit less seasonal variations?
(a) Tropics
(b) Temperates
(c) Alpines
(d) Both (a) & (b).

Question 19.
The historic convention on Biological Diversity held in Rio Janeiro in 1992 is known as:
(a) CITES Convention
(b) The Earth Summit
(c) G-16 Summit
(d) AAAB Programme

Answer: (b) The Earth Summit

Question 20.
What is common to the techniques
(i) in-vitro fertilisation
(ii) cryopreservation and
(iii) tissue culture?
(a) All are in situ conservation methods.
(b) All are ex situ conservation methods
(c) All require ultra modern equipment and large space
(d) All are methods of conservation of extinct organisms

Answer: (b) All are ex situ conservation methods

Question 21.
Select the incorrect statement.
(a) Species diversity increases as we move away from the equator towards the poles.
(b) Stellar’s sea cow and passenger pigeon got extinct due to over-exploitation by man.
(c) Lantana and Eichhornia are invasive weed species in India.
(d) Among animals, insects are the most species-rich taxonomic group.

Answer: (a) Species diversity increases as we move away from the equator towards the poles.

Assertion and Reason Type Questions

In the following questions, a statement of Assertion (A) followed by statement of Reason(R) is given. Choose the correct option out of the choices given below each question.
(a) If both Assertion and Reason are true and Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are true but Reason is not a correct explanation of the Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.
Question 22.
Assertion: With few exceptions, tropics harbour more species than temperate or polar areas.
Reason: Species diversity decreases as we move away from the equator towards the poles.

Answer: (a) If both Assertion and Reason are true and Reason is a correct explanation of the Assertion.

Question 23.
Assertion: In wildlife conservation, micro-organisms are not considered to be conserved.
Reason: Micro-organisms are not of much importance to mankind.

Answer: (d) If both Assertion and Reason are false.

Question 24.
Assertion: Rate of extinction of wildlife has become rapid in the last one hundred years.
Reason: Unplanned human activities have destroyed the natural habitats of many species of wildlife.

Answer: (a) If both Assertion and Reason are true and Reason is a correct explanation of the Assertion.

Question 25.
Assertion: Golden langur is a vulnerable species.
Reason: Number of Golden langur has reduced and their natural habitat is also affected.

Answer: (b) If both Assertion and Reason are true but Reason is not a correct explanation of the Assertion.

Question 26.
Assertion: In India many national parks have been set up to protect wildlife.
Reason: Biosphere reserves have greater importance than the national parks.

Answer: (c) If Assertion is true but Reason is false.

Question 27.
Assertion: Cotton and jute are fibre-yielding plants.
Reason: Cotton is obtained from seed hair (lint) and jute fibres are obtained from stalks of retted jute.

Answer: (a) If both Assertion and Reason are true and Reason is a correct explanation of the Assertion.

Question 28.
Assertion: For the management of wildlife, environmental pollution must be checked.
Reason: Environment provides the life-supporting systems to wildlife.

Answer: (a) If both Assertion and Reason are true and Reason is a correct explanation of the Assertion.

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Issues

A collaboration between the Development and Disease Models & Mechanisms journal teams, this virtual Meeting will unite developmental biologists, human geneticists and clinical researchers to focus on building bridges from bench to clinic.

Development presents.

Our successful webinar series continues, with early-career researchers presenting their papers and a chance to virtually network with the developmental biology community afterwards. Here, Jessica Zuin discusses nonlinear control of transcription through enhancer-promoter interactions.

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Special issue: call for papers

The Immune System in Development and Regeneration
Guest editors: Florent Ginhoux and Paul Martin
Submission deadline: 1 September 2021
Publication: Spring 2022

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Contents

The name Reptiliomorpha was coined by Professor Gunnar Säve-Söderbergh in 1934 to designate amniotes and various types of late Paleozoic tetrapods that were more closely related to amniotes than to living amphibians. In his view, the amphibians had evolved from fish twice, with one group composed of the ancestors of modern salamanders and the other, which Säve-Söderbergh referred to as Eutetrapoda, consisting of anurans (frogs), amniotes, and their ancestors, with the origin of caecilians being uncertain. Säve-Söderbergh's Eutetrapoda consisted of two sister-groups: Batrachomorpha, containing anurans and their ancestors, and Reptiliomorpha, containing anthracosaurs and amniotes. [6] Säve-Söderbergh subsequently added Seymouriamorpha to his Reptiliomorpha as well. [7]

Alfred Sherwood Romer rejected Säve-Söderbergh's theory of a biphyletic amphibia and used the name Anthracosauria to describe the "labyrinthodont" lineage from which amniotes evolved. In 1970, the German paleontologist Alec Panchen took up Säve-Söderbergh's name for this group as having priority, [8] but Romer's terminology is still in use, e.g. by Carroll (1988 and 2002) and by Hildebrand & Goslow (2001). [9] [10] [11] Some writers preferring phylogenetic nomenclature use Anthracosauria. [12]

Michael Benton (2000, 2004) made it the sister-clade to Lepospondyli, containing "anthracosaurs" (in the strict sense, i.e. Embolomeri), seymouriamorphs, diadectomorphs and amniotes. [4] Subsequently, Benton included lepospondyls in Reptiliomorpha as well. [14] However, when considered in a Linnean framework, Reptiliomorpha is given the rank of superorder and includes only reptile-like amphibians, not their amniote descendants. [15]

Several phylogenetic studies indicate that amniotes and diadectomorphs share a more recent common ancestor with lepospondyls than with seymouriamorphs, Gephyrostegus and Embolomeri (e.g. Laurin and Reisz, 1997, [16] 1999 [5] Ruta, Coates and Quicke, 2003 [3] Vallin and Laurin, 2004 [2] Ruta and Coates, 2007 [17] ). Lepospondyls are one of the groups of tetrapods suggested to be ancestors of living amphibians as such, their potential close relationship to amniotes has important implications for the content of Reptiliomorpha. Assuming that lissamphibians aren't descended from lepospondyls but from a different group of tetrapods, e.g. from temnospondyls, [3] [17] [18] it would mean that Lepospondyli belonged to Reptiliomorpha sensu Laurin (2001), as it would make them more closely related to amniotes than to lissamphibians. On the other hand, if lissamphibians are descended from lepospondyls, [2] [16] [5] then not only Lepospondyli would have to be excluded from Reptiliomorpha, but seymouriamorphs, Gephyrostegus and Embolomeri would also have to be excluded from this group, as this would make them more distantly related to amniotes than living amphibians are. In that case, the clade Reptiliomorpha sensu Laurin would contain, apart from Amniota, only diadectomorphs and possibly also Solenodonsaurus. [2]

Gephyrostegids, seymouriamorphs and diadectomorphs were land-based, reptile-like amphibians, while embolomeres were aquatic amphibians with long body and short limbs. Their anatomy falls between the mainly aquatic Devonian labyrinthodonts and the first reptiles. University of Bristol paleontologist Professor Michael J. Benton gives the following characteristics for the Reptiliomorpha (in which he includes embolomeres, seymouriamorphs and diadectomorphs): [4]

  • narrow premaxillae (less than half the skull width) taper forward formulae (number of joints in each toe) of foot 2.3.4.5.4–5

Cranial morphology Edit

The groups traditionally assigned to Reptiliomorpha, i.e. embolomeres, seymouriamorphs and diadectomorphs, differed from their contemporaries, the non-reptiliomorph temnospondyls, in having a deeper and taller skull, but retained the primitive kinesis (loose attachment) between the skull roof and the cheek (with exception of some specialized taxa, such as Seymouria, in which the cheek was solidly attached to the skull roof [19] ). The deeper skull allowed for laterally placed eyes, contrary to the dorsally placed eyes commonly found in amphibians. The skulls of the group are usually found with fine radiating grooves. The quadrate bone in the back of the skull held a deep otic notch, likely holding a spiracle rather than a tympanum. [20] [21]

Postcranial skeleton Edit

The vertebrae showed the typical multi-element construction seen in labyrinthodonts. According to Benton, in the vertebrae of "anthracosaurs" (i.e. Embolomeri) the intercentrum and pleurocentrum may be of equal size, while in the vertebrae of seymouriamorphs the pleurocentrum is the dominant element and the intercentrum is reduced to a small wedge. The intercentrum gets further reduced in the vertebrae of amniotes, where it becomes a thin plate or disappears altogether. [22] Unlike most labyrinthodonts, the body was moderately deep rather than flat, and the limbs were well-developed and ossified, indicating a predominantly terrestrial lifestyle except in secondarily aquatic groups. Each foot held 5 digits, the pattern seen in their amniote descendants. [23] They did, however, lack the reptilian type of ankle bone that would have allowed the use of the feet as levers for propulsion rather than as holdfasts. [24]

Physiology Edit

The general build was heavy in all forms, though otherwise very similar to that of early reptiles. [25] The skin, at least in the more advanced forms probably had a water-tight epidermal horny overlay, similar to the one seen in today's reptiles, though they lacked horny claws. [26] [27] In chroniosuchians and some seymouriamorphs, like Discosauriscus, dermal scales are found in post-metamorphic specimens, indicating they may have had a "knobbly", if not scaly, appearance. [28]

Seymouriamorphs reproduced in amphibian fashion with aquatic eggs that hatched into larvae (tadpoles) with external gills [29] it is unknown how other tetrapods traditionally assigned to Reptiliomorpha reproduced.

Early reptiliomorphs Edit

During the Carboniferous and Permian periods, some tetrapods started to evolve towards a reptilian condition. Some of these tetrapods (e.g. Archeria, Eogyrinus) were elongate, eel-like aquatic forms with diminutive limbs, while others (e.g. Seymouria, Solenodonsaurus, Diadectes, Limnoscelis) were so reptile-like that until quite recently they actually had been considered to be true reptiles, and it is likely that to a modern observer they would have appeared as large to medium-sized, heavy-set lizards. Several groups however remained aquatic or semiaquatic. Some of the chroniosuchians show the build and presumably habits of modern crocodiles and were probably also similar to crocodylians in that they were river-side predators. While some other Chroniosuchians possessed elongated newt- or eel-like bodies. The two most terrestrially adapted groups were the medium-sized insectivorous or carnivorous Seymouriamorpha and the mainly herbivorous Diadectomorpha, with many large forms. The latter group has, in most analysis, the closest relatives of the Amniotes. [30]

From aquatic to terrestrial eggs Edit

Their terrestrial life style combined with the need to return to the water to lay eggs hatching to larvae (tadpoles) led to a drive to abandon the larval stage and aquatic eggs. A possible reason may have been competition for breeding ponds, to exploit drier environments with less access to open water, or to avoid predation on tadpoles by fish, a problem still plaguing modern amphibians. [31] Whatever the reason, the drive led to internal fertilization and direct development (completing the tadpole stage within the egg). A striking parallel can be seen in the frog family Leptodactylidae, which has a very diverse reproductive system, including foam nests, non-feeding terrestrial tadpoles and direct development. The Diadectomorphans generally being large animals would have had correspondingly large eggs, unable to survive on land. [32]

Fully terrestrial life was achieved with the development of the amniote egg, where a number of membranous sacks protect the embryo and facilitate gas exchange between the egg and the atmosphere. The first to evolve was probably the allantois, a sack that develops from the gut/yolk-sack. This sack contains the embryo's nitrogenous waste (urea) during development, stopping it from poisoning the embryo. A very small allantois is found in modern amphibians. Later came the amnion surrounding the fetus proper, and the chorion, encompassing the amnion, allantois, and yolk-sack.

Origin of amniotes Edit

Exactly where the border between reptile-like amphibians (non-amniote reptiliomorphs) and amniotes lies will probably never be known, as the reproductive structures involved fossilize poorly, but various small, advanced reptiliomorphs have been suggested as the first true amniotes, including Solenodonsaurus, Casineria and Westlothiana. Such small animals laid small eggs, 1 cm in diameter or less. Small eggs would have a small enough volume to surface ratio to be able to develop on land without the amnion and chorion actively effecting gas exchange, setting the stage for the evolution of true amniotic eggs. [32] Although the first true amniotes probably appeared as early as the Middle Mississippian sub-epoch, non-amniote (or amphibian) reptiliomorph lineages coexisted alongside their amniote descendants for many millions of years. By the middle Permian the non-amniote terrestrial forms had died out, but several aquatic non-amniote groups continued to the end of the Permian, and in the case of the chroniosuchians survived the end Permian mass extinction, only to die out prior to the end of the Triassic. Meanwhile, the single most successful daughter-clade of the reptiliomorphs, the amniotes, continued to flourish and evolve into a staggering diversity of tetrapods including mammals, reptiles, and birds.


In the Plethodon glutinosus group of Highton and Larson, 1979, Syst. Zool., 28: 579–599. See detailed accounts by Pope, 1965, Cat. Am. Amph. Rept., 15: 1–2, and Petranka, 1998, Salamand. U.S. Canada: 414–416. See Highton, 1972 "1971", Res. Div. Monogr. Virginia Polytech. Inst. State Univ., 4: 172. Beamer and Lannoo, 2005, in Lannoo (ed.), Amph. Declines: 856–858, provided a detailed account that summarized the biology and conservation literature. Wiens, Engstrom, and Chippindale, 2006, Evolution, 60: 2585–2603, recognized Plethodon longicrus, but Highton, Hastings, Palmer, Watts, Hass, Culver, and Arnold, 2012, Mol. Phylogenet. Evol., 63: 278–290, discussed the evidence and returned it to synonymy. Moskwik, 2014, J. Biogeograph., 41: 1957–1966, documented in this species significant elevational range changes since the 1940s. Raffaëlli, 2013, Urodeles du Monde, 2nd ed.: 395–396, provided a brief account, photograph, and range map.

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  • For additional sources of information from other sites search Google
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  • To search the NIH genetic sequence database, see GenBank
  • For additional information see AmphibiaWeb report
  • For information on conservation status and distribution see the IUCN Redlist
  • For related information on conservation and images as well as observation see iNaturalist for a quick link to their maps see iNaturalist KML
  • For access to available specimen data for this species, from over 350 scientific collections, go to Vertnet.

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