Two Reviews of The Origin of Birds (1926-7)

I. From: The Auk, vol. XLIII, July 1926, pp. 390-1.

Heilmann on ‘ The Origin of Birds.’

This important work consists of a compilation of all the data so far presented bearing upon the ancestry of birds with much discussion of their reptilian relationships, and the author’s conclusions on the subject. His researches have been exhaustive and his success in digesting and presenting in readable form a resumé of such varied publications is remarkable, especially when we realize that Dr. Heilmann is a Dane writing his treatise in English.

He divides his work into four parts: In Part I he considers “Some Fossil Birds,” first Archaeornis and Archaeopteryx and then Ichthyornis and Hesperornis. He has studied exhaustively the specimen of Archaeornis in the Berlin Museum and given us a colored restoration of it as a frontispiece to his book as well as one of the Loon-like Hesperornis, and his graphic pen pictures of the life of these birds respectively in the tree fern forests of the Jurassic and in the Cretaceous seas, and their conflicts with their reptilian contemporaries is vivid indeed. He also by means of numerous original drawings and photographs shows us the close correspondence in the skeletal structures of reptiles and birds. Part 11 discusses the embryonic stages of birds and reptiles and sketches the development of the skeleton in the two groups.

Part III consists of “Some Anatomical and Biological Data” in which are considered the supra-temporal fenestra, digital claws, cerebrum and cerebellum, organs of sense, sexual organs and secondary sexual characters in birds and reptiles.

Taken together the data presented in these three parts serve to demonstrate the close relationship between birds and reptiles and the certainty of their common ancestry, preparing us for Part IV in which Dr. Heilmann seeks for the group of reptiles from which the birds probably sprung, i.e., the “Proavian.” This he considers is found in the Pseudosuchia a group of fossil reptiles less specialized than the Dinosaurs. Some of these had evidently developed into terrestrial runners with the fore part of the body elevated from the ground and from these arose arboreal climbers from which was evolved the Archaeornis and eventually the modern birds.

The resemblances of the Pterodactyls to birds he considers merely superficial and the claims advanced for Iguanodon and certain other types as the direct avian ancestor are disposed of. The many sketches of restorations give the reader a much clearer idea of these various early types than is possible in a description, and for those who wish to follow the subject further the excellent bibliographies, often accompanied by synopses, are a great help.

Dr. Heilmann is to be congratulated upon producing a book at once interesting to the scientific investigator and yet understandable by the layman desirous if getting some knowledge of this interesting problem. W. S. [William Shufeldt]

II. From: Ibis, series 2, vol. 12 (1926), pp. 602-604.

Heilmann on the Origin of Birds.

[The Origin of Birds. By Gerhard Heilmann. Pp. iv+208; 2 plate& and 141 figs. London (11. F. & 0. Witherby), 1926.]

The origin of flight and the origin of birds are subjects so interesting that any further light on either problem cannot fail to be welcomed. In the present work, Mr. Heilmann, has marshalled such an army of facts and observations on both recent and fossil birds and reptiles, and has illustrated his theories and observations with such a facile pen that ornithologists and palaeontologists alike must be interested. He approaches his subject in a highly scientific way. The book is divided into four parts, dealing respectively with birds from the palaeontological, embryological, and morphological standpoints, with a final section on the Proavian and a general summary of results. Naturally it is impossible to fully understand the author’s remarks and contentious”, without some knowledge of osteology and embryology, but each point, as a rule, is well illustrated and should be followed with little difficulty even by the unscientific reader.

The first-or palaeontological – section of the book deals at length with the most important fossil birds, Archaeopteryx, Archaeornis, Hesperornis, and Ichthyornis. Each of these, especially Archaeornis, is treated in some detail and its affinities traced. The author had the advantage of personally studying the Berlin specimen of Archaeopteryx -which, chiefly on account of the structure of its shoulder. girdle, Petronlevics has lately referred to a new genus Archaeornis – as well as casts of the London Archaeopteryx. It is well known that close resemblances exist between the” early birds and the reptiles, and the main conclusion estab- lished in the first part of the book is that, on osteological characters, these birds are much more closely allied to the reptiles than to modern birds. In Heilmann’s words: “From its remains Archaeornis might be characterized as a reptile in the disguise of a bird.”

Osteological considerations alone, however, cannot settle the question, and part ii. deals with the embryonic stages of reptiles and birds. This is an extraordinarily interesting part and is well illustrated. The subject is treated simply and at fair length. The conclusions reached, as might be expected, simply show that in ontogeny the bird embryo passes through a stage reminiscent of the Jurassic and Cretaceous birds.

The third part of the book is devoted to certain anatomical and biological considerations with regard to the birds and reptiles, special reference being made to the supratemporal fossa, the brain, sense organs, and secondary sexual characters. These considerations simply serve to strengthen the resemblances between the reptiles and the birds and the descent of the latter from the former.

The final section is devoted to the Proavian. Heilmann thinks the birds arose in the following way. From the reptiles, probably among the Pseudosuchia – the group of Dinosaurs to which Ornithosuchus and other Triassic forms belong – there arose a form with bipedal gait. This form eventually gave rise to terrestrial runners, which in turn developed into arboreal climbers. The terrestrial running phase caused the hind limbs to assume a more bird-like position. The fore-arms in the running creature were held close to th e body and, with the tail, developed a parachutal plane consisting of longish scales developed along the posterior side of the fore-arm and the sides of the flattened tail. Ultimately, by the continued friction of the air, the scales became gradually modified until the perfect feather was produced. Subsequently the whole body became feathered. The lengthening of the penultimate phalanges of the fingers, the strengthening of the arms, and the coalescence and ossification of the two halves of the breast bone are due to the intensive use of the arms during the arboreal phase.

The ultimate attainment of warm, blood, the expansion of the air-sacs of the lungs spreading through the whole body, and into the bones, coupled with the resulting refinement enlargement of the brain, weigh the scale, and the reptile has become a bird.

The book, written as it is by a distinguished artist, is excellently illustrated. In addition, each part contains valuable list of literature and there is a good index. To all. students of fossil or living birds or reptiles, it may be confidently recommended.

W. E. Swinton.