Nopsca (1926)

Ferenc Nopcsa, Remarks to Petronievics’ Work on Archaeopteryx lithographica, in: Annales Géologiques de la Péninsule Balkanique, Tome VIII, fasc. 2 (Sofia, 1926).

Remarks to Petronievics’ Work on Archaeopteryx lithographica

By dr. FRANZ BARON NOPCSA

[This is my translation from a German original that appeared under the title "Bemerkungen zu Petronievics seinen Arbeiten über Archaeopteryx", IN]

I. Skull

II. Ribs

III. Anterior extremity

IV. Shoulder girdle

V. Posterior extremity

VI. Pelvis

The name of Petronievics will always remain connected honourably with the history of research into the genus Archaeopteryx. It is exclusively thanks to the logical arguments of the Belgrade philosopher, that A.S. Woodward, then Keeper at the Natural History Museum in London, decided to have the English Archaeopteryx specimen newly prepared in 1916. This provided the incentive for further researches and preparations, which were carried out by Parson in an outstanding way. Because of this, the Archaeopteryx slate of the Natural History Museum is not only the most valuable, but also the best-prepared piece in this collection, which in itself is rich in such specimens. The publication, a joint effort by Petronievics and A.S. Woodward, of the results of that preparation in 1916 was of the utmost importance and caused quite a sensation. A later publication on the same subject, and another on the also newly-prepared Berlin Archaeornis by Petronievics, date from the years 1921 and 1923, respectively. Unfortunately, Petronievics, to whom we have to thank the great increase in our knowledge of both the ëUrvögelí, is not a palaeontologist by profession, and thusfar few fossils have gone through his hands. Consequently, he treats specimens that are damaged by the process of fossilisation, as though they were intact preparations. In this respect, one should specifically point to the well-known, crushed Mesopithecus skull, whose significance is certainly unknown to Petronievics. A second, and unfortunately similarly striking flaw in the education of the Belgrade philosopher, is his relatively weak zoological training. This defect leads to an incorrect estimation of those features, that can easily be explained from further or lesser stages of ossification. Both flaws together of course produce the result, that he strongly overestimates small differences. With his works on Archaeopteryx these flaws in his experience culminate in the surprising thesis, that the differences between the London and Berlin specimens merit a distinction on a super-generic level. The aim of this work is firstly to reduce the differences observed by Petronievics between both Archaeopteryx specimens to their proper proportions, and then shed light upon some bold hypotheses by this scholar. The best way to carry through the first part of this programme is to discuss the differences, in parts of the anatomy, between both Archaeopteryx specimens. The columns show what Petronievics says about the separate parts.

I. Skull

London Specimen > Berlin Specimen

a) Teeth elliptical in cross-section > Teeth circular in cross-section

These differences are real, but it is difficult to imagine that their significance could be more than specific.

II. Ribs

London Specimen > Berlin Specimen

a) unknown > single-headed

At this point it should be remarked that the notion that the Berlin Archaeornis had single-headed ribs, is almost certainly false. The London specimen shows well-preserved two-headed ribs in the trunk, that, although not being in the proximity of the capitulum, show an extremely well-developed tuberculum. Both specimens of Archaeopteryx are certainly not so different as to presume that one would have had single-headed rib heads, and the other double-headed ones. Because the London observation is well-founded, Petronievicsí notion is presumably false.

III. Anterior extremity

London Specimen > Berlin Specimen

a) Metacarpal III compressed > M. III cylindrical

b) Carpals in a single row > Carpals in two rows

The differences that are mentioned here, could well be real, although the significance of the first point is at its most specific, and that of the second not even that. Petronievics acknowledges himself, that the carpus of the Berlin Archaeopteryx is more embryonic than that of the London specimen. It is most likely, that the larger London Archaeopteryx simply shows a further stage of ossification than the smaller Berliner does.

IV. Shoulder

London Specimen > Berlin Specimen

a) Scapula and coracoid fused > Both bones separated

b) Sternum unknown > Carinate-like sternum

c) Wide coracoid > Narrow coracoid

As far as the fusion of the shoulder elements of the London specimen is concerned, this seems at least dubious, because the scapula, which was released in 1925, is separated from the coracoid. Therefore, this point is of limited significance. But even if this difference, found by Petronievics , was to exist, it would be easy to explain it as another consequence of the London specimenís progressed degree of ossification. Because the sternum is absent in the London specimen, the two sterna cannot be compared, even if Petronievics reconstruction of the Berlin sternum were correct. However, large differences in the respective coracoids do seem to exist, but unfortunately the furculae of the Berlin specimen, which are placed before the coracoid, are broken. Furthermore, the frontal edge of the coracoid itself has been damaged. These two circumstances should lead to some circumspection in assessing the shape of the coracoid. Without having researched the Berlin specimen in person, I can hardly pass definite judgement, but the shapes in Petronievicsí illustrations do not seem to indicate a degree of conservation of the coracoid that justifies these far-reaching conclusions on the basis of its form alone.

V. Posterior extremity

London Specimen > Berlin Specimen

a) Tarsus fused with tibia > Tarsus not fused with tibia

Again, these differences point toward a higher degree of ossification in the London specimen compared to the Berliner.

VI. Pelvis

London Specimen > Berlin Specimen

a) 14-degree inclination between pubis and ischium > the same 45 degrees

b) Spina iliaca and processus lateralis separated > perfect fusion of both

c) Pubis with symphysis > without symphysis

d) Pubis with foramen obturatorium > without foramen obturatorium

f) Pubis distally thin > distal thickening

g) Bent ischium > Straight ischium

h) smooth and distally well-ossified ischium > rough and once cartilaginous

Truly heterogeneous items are united in this long list. Most of the differences mentioned in the list do not exist at all. Then there are some that have their origin in coincidences in the fossilisation process, and finally there are some differences in age. Firstly, no difference in the inclination of the pubis can be observed, because the London specimen may show us the ischium from the side, but the pubis from the top. Because of this, the angle between both elements cannot be the same as it was in the living animal; the difference mentioned in a) does therefore not exist at all. Also, the separation between the spina iliaca and lateralis is not present in the London specimen, because these parts blend into one another. They are only separated in the Belgrade philosopherís drawing. The slenderness of the distal pubisí end in the London specimen is also a point that cannot be established, because the thickened, spoon-shaped end of the London specimen corresponds very well to the thickening of the pubis in the Berlin specimen. The straightness of the Berlin ischium can only be construed as a deformation that occurred during fossilisation. The pubic symphysis, as well as the the good degree of ossification of the distal end of the ischium in the London specimen should therefore be explained as marks of advanced ossification. What remain as actual distinctions are only the alleged differences in the upper part of the pubis. Unfortunately, exactly these parts are buried beneath the femur in the Berlin specimen. Even when supposing their existence, one does not need to postulate on a pre-jurassic diphyletic origin of carinates and ratites on their basis. Contrary to Petronievics, who emphasised the differences between both specimens of Archaeopteryx, I would like to point at a few common characteristics. Because Petronievics observes great differences in the build of the shoulder girdle, one should firstly point out the similarity in contour of the flight feathers and the similarities in the skeleton of the anterior extremities. These resemblances indicate, that the anterior extremities of both specimens must have performed in almost an identical manner, both in flying and in climbing. This points to a quite similar musculature. Because the great differences Petronievics assumes in the shoulder girdle preclude a similar musculature, very strong evidence for the distinctions supposed by Petronievics will have to be presented. Sofar, Petronievics has not presented evidence that would even go halfway to proving his point. Just as striking as the resemblances in the build of the forequarters is also the fork-shaped end of the ischium of both Archaeopteryx specimens. Once again, Petronievicsí claim that the fork-shaped ischium should appear on two pelvisí that are so different in every other respect, seems confusing and throws doubt on his other assumptions. Because the observations concerning the ribs appear to confirm the doubts regarding his powers of observation, one should also meet his other statements with scepticism. On the basis of this entire analysis of the differences between both Archaeopteryx specimens, only those differences that Seeley emphasised many years ago appear to remain; supplemented by those through which the Berlin specimen revealed itself to be an imperfectly ossified specimen of the London animal. To have discovered these differences after careful study, is a merit of the Belgrade philosopher that should not be underestimated. However, these differences do not suffice to bring about either a specific or a generic separation, and no far-reaching hypotheses should be based on them. If this analysis of the first part of both works of the Belgrade scholar seems to significantly diminish their importance, they are undermined even further after examining the parts that have not been discussed sofar. The conclusion of the 1925 work states several things: that Petronievics had been the first to prove avian descent from the reptiles, subsequently the statement that birds originated in the lacertilians, and not in the dinosaurs, and that consequently the resemblances between birds and dinosaurs were merely marks of convergence, and finally that the ancestors of birds were climbing animals. As his dissertation, published in 1921 in Geneva, clearly demonstrates, Petronievics bases his hypothesis of the relation between lacertilians and birds exclusively on the fact that, despite a general lack of similarity in other respects, the Archaeopteryx coracoid, shows two peripheral incisures. Whereas it is dangerous to suppose a kinship between two groups on animal on the basis of a single character (in that case one could take the monotremes for birds), this argument is further weakened when characters that preclude the postulated relation appear between the groups in question. The ribs of lacertilians, for instance, show single-headed ribs, while the birds and Archaeopteryx have retained the two-headed ribs that are typical of lower terrestrial vertebrates. Because Petronievics time and again emphasises the irreversibility of evolution, this argument in particular turns against him. Because of this character, even he would at its best consider the lacertilians to be degenerated descendants of birds, but he wouldnít be able to see the birds as descendants of the lacertilians. His remaining hypothesis, that the similarity between birds and dinosaurs were to rest exclusively on convergences, is also without foundation. In the Proc.Zool.Soc. from 1918, it was Petronievics of all people, who, again basing himself on coincidences of preservation, emphasised the likeness to mammals of Cynognathians. However, he overlooked the fact that the Cynognathians are less mammal-like in certain characters of their physique than certain other Theriodonts. These points concerns the appearance of a Foramen entepicondyloideum and ectepicondyloideum, and the separation between the frontal and the orbit. Petronievics therefore denies a relation between birds and dinosaurs, because the bird-like characters are divided between different groups of dinosaur, but he supports a close kinship between Theromorphs and mammals regardless of similar circumstances. In a work not taken into account by Petronievics, I treat the emergence of several traits in various groups that all point to another group, as evidence in favour of a relation between all these groups (latent homoplasy).

Initially, it seems surprising that so keen a thinker as Petronievics appears not to have discovered several contradictions in which he has got caught up. In his defence I have to say that his rejection of the relationship between birds and dinosaurs seems to have been inspired as a logic consequence of his rejection of the Proavis ab ovo. Because he does not take my arguments of 1923 into account when rejecting a running Proavis, I it is superfluous to argue against his remarks at this point. The last of several sentences that Petronievics risked in 1925, was the one in which he claimed that only through him the descent of birds from reptiles was proved. Long before Petronievics began his palaeontological work, the [sauropsid ] origin of birds has become widely accepted among zoologists. It was also generally acknowledged that the archosaurs were closely related to birds; so even the ancestral group of birds within the reptiles was considered to be well-known. Petronievics attempts to overthrow this well-founded assumption, and at the same time wishes to replace it by the unsustainable theory of kinship between birds and lacertilians. He also applies scepticism where positive knowledge should be used; one cannot claim that this is evidence in favour of any specific type of relation between birds and reptiles.