Evolution Of Reptiles Research Articles

Effects of TRH on hormone release from pituitaries of the lizard, Anolis carolinensis

The ability of thyrotropin-releasing hormone (TRH) to stimulate thyrotropin (TSH) from pituitaries of adult male lizards, Anolis carolinensis, was tested in vivo and in vitro. TSH output by pituitaries in vitro was determined by bioassay of the incubation medium using in vitro T 4 output by thyroids from the same lizards. Pituitaries incubated without TRH had no detectable TSH secretion during two consecutive (2 or 3 hr) periods of incubation. Incubation in 10 or 100 ng/ml TRH for 2 or 3 hr significantly augmented release of TSH bioactivity in a dose-dependent manner. Pituitaries taken from goitrogen (100 μg methimazole/day for 10 days)-treated lizards had elevated basal TSH secretion but did not respond to TRH. TRH injection in vivo (5 μg/hr for 10 hr) appeared to stimulate acute release of MSH activity as judged by darkening of skin color after each injection, and plasma T 4 was significantly elevated at the end of treatment. These results provide additional evidence that the reptilian thyrotrope has functional TRH receptors and the TSH-stimulating activity of the tripeptide along with its effects on other pituitary cells was present at an early stage of reptilian evolution.

The Structure, Development and Evolution of Reptiles

The Structure, Development and Evolution of Reptiles

The Structure, Development and Evolution of Reptiles. A Festschrift in Honour of Professor A. d'A. Bellairs on the Occasion of His Retirement. The Proceedings of a Symposium Held at The Zoological Society of London on 26 and 27 May, 1983. Symposia of the Zoological Society of London, Number 52.Mark W. J. Ferguson

Previous articleNext article No AccessNew Biological BooksThe Structure, Development and Evolution of Reptiles. A Festschrift in Honour of Professor A. d'A. Bellairs on the Occasion of His Retirement. The Proceedings of a Symposium Held at The Zoological Society of London on 26 and 27 May, 1983. Symposia of the Zoological Society of London, Number 52. Mark W. J. FergusonJames A. HopsonJames A. Hopson Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Quarterly Review of Biology Volume 61, Number 1Mar., 1986 Published in association with Stony Brook University Article DOIhttps://doi.org/10.1086/414810 Copyright 1986 Stony Brook Foundation, Inc.PDF download Crossref reports no articles citing this article.

Insulin-like growth factors I and II of nonmammalian sera

We have compared the insulin-like growth factors (IGFs) of a number of mammalian and nonmammalian vertebrate sera. Sera were subjected to acid gel filtration through G-75 Sephadex and separate binding protein and free IGF fractions were pooled. The IGF pools were subjected to flatbed isoelectric focusing and the concentration of IGF I in the fractions was detected with an immunoassay using 125I-hIGF I and the somatomedin C antibody of Underwood and Van Wyk. IGF II in the fractions was detected with either the 125I-IGF rat placental membrane RRA or the 125I-IGF II serum binding protein assay. One or more basic peaks of IGF I immunoactivity were detected in all the mammalian sera studied (human, guinea pig, rat, bovine, kangaroo, and opossum) and all the nonmammalian species studied (chicken, turtle, toad, and trout). Neutral and slightly acidic peaks of IGGF II receptor reactivity were observed in human, cow, and guinea pig serum. No distinct peaks of IGF II were observed in adult rat, opossum, or kangaroo serum. Distinct peaks oof IGF II activity in the neutral to slightly acidic range were clearly recognized in chicken and turtle serum, no such peaks were recognized in toad and trout serum. All mammalian sera studied contained acid stable, binding proteins with high affinity, saturable binding of 125I-IGF II. None of the nonmammalian sera studied contained demonstrable specific 125I-IGF II binding. These observations document the presence of separate IGF I and IGF II peptides in chickens and turtles but only IGF I in amphibians and fish. These observations indicate that the gene duplication giving rise to two separate IGFs arose before reptilian evolution. The acquisition of a specific IGF binding protein is limited to mammals.

The structure, development and evolution of reptiles

The structure, development and evolution of reptiles

Genomic Composition of Reptiles: Evolutionary Perspectives

Genomic Composition of Reptiles: Evolutionary Perspectives

Triassic environments, climates and reptile evolution

A consideration of all the available data on Triassic vertebrate faunas, and their stratigraphic location reveals a relatively sudden extinction event among the last of the mammal-like reptiles and the herbivorous rhynchosaurs in the Norian of the Upper Triassic. This event was apparently quickly followed by the radiation of the dinosaurs, also in the Norian. This conclusion suggests that competition was not the main factor in the initial success of the dinosaurs, but opportunistic radiation following the extinction of major reptile groups. A global review of Triassic sedimentary facies shows that there were climatic and floral changes towards the end of the Triassic. It is envisaged that increasing aridity in the later Triassic, resulting from plate motions and particularly affecting Gondwanaland and southwestern Laurasia, brought about floral changes and then the reptile extinctions. With the rapid evolution of new floras of conifers and bennettitaleans, the dinosaurs came to dominate all terrestrial faunas within the space of only a few million years.

Early Evolution of Reptiles

exploitation of the terrestrial environment. Following the achievement of these features, the early amniotes underwent a major radia­ tion. The fossil record of early amniotes is complete enough to establish their relationships to the major groups living today. It also provides an opportunity to consider the evolutionary processes associated with a period of major radiation. Early amniotes may be viewed today as a phylogenetically heterogeneous assemblage (or paraphyletic group), for they include the ultimate ancestors of mammals and birds, as well as of the modem squamates, crocodiles and turtles. Yet, within the context of the Paleozoic, they were a monophyletic group, with a close common ancestry. To judge by the general similarity of their skeletal anatomy to that of modern lizards and crocodiles, they probably had a broadly similar physiology as well. Amniotes appear suddenly in the fossil record, without any recognized predecessors (9). They are first known from the early Pennsylvanian (West­ phalian B) deposits of Joggins, Nova Scotia, within the stumps of upright lycopods (11). This peculiar mode of burial favors the preservation oftruly terrestrial animals and explains the absence of either reptiles or plausible terrestrial ancestors in older fossil localities that were the result of more normal, subaqueous deposition.

Variations in repetitive DNA and evolution in reptiles

1. 1. Repetitive DNA evolution has been studied in various reptilian species by means of the reassociation kinetics technique. 2. 2. Quantitative variations in genome sizes depend on differences essentially in repetitive DNA, but also in single-copy DNA. 3. 3. The behaviour of the variations in repetitive DNA in relation to the various taxonomic relationships existing among the species assayed, leads us to think that the duplicated fractions are mostly free to evolve. 4. 4. Some difference in repetitive DNA evolution is observed in Chelonia on one side and in Squamata on the other.

Evolution of the tetrapod ear: an analysis and reinterpretation

The dominant view of tetrapod otic evolution–the “standard view”–holds that the tympanum developed very early in tetrapod history and is homologous in all tetrapods and that the opercular process of the rhipidistian hyomandibula is homologous to the tympanic process of the stapes in lower tetrapods. Under that view, the labyrinthodont amphibians of the Paleozoic are usually considered ancestral to reptiles, and thus the “otic notch” of labyrinthodonts and the tympanum it presumably contained form the starting-point for middle ear evolution in reptiles. Four problems have classically been identified with the standard view: the differing relationships of the internal mandibular branch of N. VII (chorda tympani) to the processes of the stapes in amniotes and anurans; the differing orientations of the stapes in key fossil and living groups; the location of the tympanum in early fossil reptiles; and the transferral of the tympanum, during the origin of mammals, from the stapes to the articular bone of the lower jaw. An examination of these problems and of the solutions proposed under the standard view reveals the ad hoc, and therefore unsatisfactory, nature of the proposed solutions. To organize and review alternative hypotheses of otic evolution an analytical table is constructed, using three characters (tympanic process, Nerve VII, tympanum), each with two possible states. A total of eight hypotheses about middle ear evolution are possible under this system, one of which is the standard view. The seven “non-standard” hypotheses, only five of which have been argued in the literature, are briefly examined. Six of the “non-standard” hypotheses appear unattractive for various reasons, including reliance on ad hoc arguments. The seventh was first proposed by Gaupp in 1898. It is today almost universally ignored but apparently largely for historical rather than scientific reasons. This hypothesis, her called the “alternative view”, appears to rest on assumptions equally as plausible as those of the standard view. Moreover, it offers a solution of the problems associated with the standard view without, apparently, raising any similarly serious problems. This paper compares the standard and alternative views of middle ear evolution in detail. Comparison proceeds on two levels. On one level, they are compared in terms of the hypotheses of phyletic tetrapod relationships each promotes and how strongly each supports its hypothesis. Both views promote the same hypothesis of tetrapod relationships. The alternative view is the more parsimonious, but the difference is not considered sufficient to provide a choice. On another level, the two views are compared in terms of their implications for: (1) the evolution of relative and absolute auditory perceptive ability; (2) the origin of reptiles; (3) the evolution of the suspensorium and cranial kinesis; and (4) the origin and evolution of recent amphibians. The nature of the data required for a test of the implications of the two views is specified in each case. Where data are available. the alternative view is consistent and the standard view is inconsistent with these data. We conclude that the alternative view is the preferable hypothesis of middle-ear evolution. This conclusion implies the following: the tympanic membranes and the tympanic processes of the stapes in recent mammals, reptiles + birds. and frogs. are not homologous; the evolution of “special periotic systems” in the ancestors of amphibians and amniotes were independent events and preceded the evolution of tympanic membranes; the amphibian tympanic membrane. probably including that of labyrinthodonts. is not ancestral to that of amniotes. and that labyiinthodonts with an otic notch are not suitable as amniote ancestors; the stapes of early reptiles functioned primarily as part of the jaw suspension rather than in hearing; the mechanisms and abilities of sound perception in recent tetrapods are likely to be diverse rather than forming parts of a cline; and the lack of a tympanum in Gymnophiona and Caudata may be a retention of a primitive condition.

UNORTHODOXIES IN REPTILIAN PHYLOGENY.

Thanks to the labors of numerous workers during the past half-century, the general pattern of reptilian evolution has become clear in most regards. Except for occasional problematica, most fossil and recent reptiles can be assigned to one or another of half a dozen or so evolutionary lines and arrayed, in orders and subclasses, in a reasonable system of classification, such as that which I recently outlined in this journal (Romer, 1967). But while I believe a majority of competent workers would agree to most features of such a pattern of phylogeny and classification, the situation is far from being in a set, solid state. Complacency is unwarranted, and suggestions of alternatives should be welcomed and carefully considered. I wish here to discuss two proposals for modification with which I do not agree but which are advocated by very competent workers and hence worthy of careful consideration. These are (1) Reig's suggestion that the great archosaur group has arisen from primitive members of the mammal-like synapsid stock, and (2) Kuhn-Schnyder's advocacy of the theory that the reptiles are not a natural group, but have arisen in a number of independent lines from amphibian ancestors.

Early Reptilian Evolution Re-Viewed

Early Reptilian Evolution Re-Viewed

Reptile evolution in relation to environment

Reptile evolution in relation to environment

Dr. Robert Broom, F.R.S

THE election of Dr. Robert Broom as an honorary fellow of the Royal Society of South Africa is a recognition of a long life devoted to scientific work. As a student of medicine in Glasgow, Dr. Broom became fascinated by the problem of the ancestry of mammals, and on qualification migrated to New South Wales in order to work on the comparative anatomy and embryology of monotremes and marsupials while earning his living as a general practitioner. The Australian scientific world discovered his existence when a paper on the Organ of Jacobson arrived at the Linnean Society from an unknown man in the bush, to be followed by others. But during a visit to England, Broom saw some of the fossil reptiles recently brought from South Africa by Prof. H. G. Seeley, and realizing immediately that they presented a novel and direct approach to his problem of mammalian ancestry, sailed for South Africa instead of returning to Australia. There in a very few years he revolutionized our knowledge of the fossil reptiles of the Karroo, showed in broad outline, how they were related to one another, and introduced a zonal subdivision of the rocks in which they were found which has proved to be applicable in Russia and China as in Central Africa. In 1910 Broom visited New York and there discovered that the Pelycosaurs from the Texan Permian were closely related to the Deinocephalia, the most primitive group of the African mammal-like reptiles. His paper on this subject established this point once for all, and has ever since formed a point of departure from which all more recent work on the classification and evolution of reptiles has proceeded.

The Mammal-Like Reptiles of South Africa: and the Origin of Mammals

FOR many years the fossil reptiles found in the Karroo rocks of South Africa have excited great interest because they seem to include the ancestors of mammals, or at least show how some of the early reptiles may have passed into mammals. They date back to the Permian and Triassic periods, when mammals and birds must have had their beginning; and many of them are in so remarkable a state of preservation as whole skeletons that they are most satisfactory for study. Nearly all, however, are described in small scattered papers, and some are so strange that they have been interpreted in different ways at different times by various authors, so that it is not easy to obtain a good idea of the interesting phase of reptilian evolution which they represent. Dr. Broom has thus done good service to science by preparing an authoritative summary of our present knowledge of the subject, to which he himself has contributed the greater share during the past thirty years. With the aid of a grant from the Carnegie Trust he has published a handsome volume, which will be eagerly studied by all who are interested in current biological problems. The Mammal-Like Reptiles of South Africa: and the Origin of Mammals. Dr. Robert Broom. (Issued under the auspices of the Carnegie Corporation of New York, and the Research Board, Union of South Africa.) Pp. xvi + 376. (London: H. F. and G. Witherby, 1932.) 25s. net.