Alfred Sherwood Romer

The vertebrate body

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The Vertebrate as a Dual Animal — Somatic and Visceral

In the study of vertebrate anatomy and embryology, one frequently encounters the terms “somatic” and “visceral.” Musculature is somatic or visceral; there is a somatic skeleton and a visceral skeleton; a somatic nervous system and a visceral nervous system. Are these terms merely descriptive, as regards external or internal position? I believe not. The anatomical and structural differences between the two elements in each organ system and, in great measure, the differences in embryological origin are so marked that the contrasts appear to be basic in the make-up of a vertebrate.

Edops, a Primitive Rhachitomous Amphibian from the Texas Red Beds

A description is given of the skull and such postcranial material as is known of Edops craigi, a large labyrinthodont amphibian from the Wichita Permo-Carboniferous beds of Texas. The structure of the Edops skull shows this form to be a very primitive member of the Rhachitomi, approaching the embolomerous stage in many structural features.

CORRELATION OF THE PERMIAN FORMATIONS OF NORTH AMERICA

The chart (PI. 1) indicates the present stratigraphic classification of the Permian rocks in each important area of outcrop in North America and the time relations of the deposits in the several areas as now understood. Annotations in the text suggest the evidence for many of the correlations and point out unsolved and controversial problems.

Cartilage an Embryonic Adaptation

IT has been universally believed and taught that cartilage is the most ancient of vertebrate skeletal structures, and that bone is a later clevelopuient which has replaced it during the evolution of the more advanced vertebrate groups. This belief has seemed firmly established on grounds both of phylogeny and ontogeny. The lowest of living vertebrates-cyclostomes and sharks-have purely cartilaginous skeletons, while bone is found only in the more advanced fishes and in land animals. In the embryos of bony vertebrates superficial bony elements may develop directly, but much of the internal skeleton is first formed in cartilage, which later is replaced by bone. Evolutionary and developmental histories thus seem to tell the same story; ontogeny appears to recapitulate phylogeny, and there is seemingly ample reason to justify current belief in the primitiveness of cartilage. It is, however, highly probable that this pretty picture is a delusion and the reverse of the true situation. Modern evidence suggests that bone, not cartilage, was the primitive skeletal material; that cartilage originally was not an adult tissue but a purely embryonic one, evolved in connection with the development of internal skeletal elements; and that the presence of cartilage in the adult is indicative not of a primitive condition but of paedogenesis, the retention in the adult of an embryonic stage of the skeletal development. It is true that the lowest of living vertebrates are boneless, cartilaginous forms. During the past two decades, however, much new evidence has accumulated concerning Paleozoic fossil vertebrates which shows the phylogenetic picture in a quite different light. It is now quite clear, and generally accepted by workers in the field, that bone is a very ancient tissue, for it was well developed and

Skin breathing — Primary or secondary?☆

Abstract Lungs, rare in fishes today, were apparently very common in early times as an adaptation to then widespread seasonal drought conditions. The development of terrestrial limbs was probably likewise an adaptation promoting aquatic life under such conditions; despite their limbs the earliest amphibians could not become land dwellers because of a dearth of suitable food on land. Skin breathing in modem amphibians is associated with an inefficient type of lung breathing and lack of a developed gill-system to aid in carbon dioxide elimination. But all early amphibians possessed a good rib basket, suggesting a more advanced breathing mechanism, and not improbably many early forms retained functional gills. Further, it is highly probable that all early amphibians were completely scalesheathed. The pedigree of the modern orders is uncertain, but they appear to be specialized forms and not primitive in any regard.

American Carboniferous Dipnoans

New Carboniferous lungfish material is described and Figured, including Prosageno-dus? castrensis sp. nov., founded on a tooth plate from the Chester; a skull roof from the Pennsylvanian of Illinois assigned to S. serratus; a tooth from the same period and region described as Proceratodus carlinvillensis, gen. et sp. nov.; and S. ciscoenis sp. nov., from the summit of the Cisco of Texas. Prosagenodus gen. nov. is proposed, with Ctenodus interruptus Barkas as genotype. The North American Pennsylvanian and Permian dipnoans are reviewed.

Early history of Texas redbeds vertebrates

INTRODUCTION The late Paleozoic “redbeds” vertebrate fauna, best known from the deposits in the Wichita region of north central Texas, was considered by its discoverer, Cope, to be of Permian nature, and this belief is still held by many writers. Case, in 1908, announced the discovery of reptilian remains in red sediments of Pennsylvania age, and rightly concluded that the redbeds fauna was to be regarded as Permo-Carboniferous, pertaining to both systems. Nevertheless, the fauna is still treated generally as typically Permian, and, in particular, the Texas beds containing the major part of known finds have been universally assumed to be entirely of Permian age. It was early seen that some difference existed between the vertebrate assemblages in the lower and those in the upper portions of the Texas deposits included in the Wichita and Clear Fork groups. In 1928[1][1] the writer, following an investigation of the vertical distribution of . . . [1]: #fn-1

Notes on the Permo-Carboniferous Reptile Dimetrodon

1. A nearly complete postcranial skeleton of the Permo-Carboniferous reptile Dimetrodon is described and figured. The structure and possible function of the spines are discussed, and a mechanical explanation for their origin is suggested. The specimen shows Dimetrodon to have been a long-tailed form. The skeleton is restored and a life-restoration given. 2. Models of the probable musculature of the limbs of Dimetrodon are presented.

Cynodont reptile with incipient mammalian jaw articulation.

A diagnostic mammalian character is jaw articulation between squamosal and dentary bones, replacing the quadrate-articular joint of reptiles. A newly discovered Argentinian Middle Triassic form shows, for the first time in an ancestral reptile, definite evidence of a squamosal-dentary articulation supplementary to the persistent primitive connection.