The following is my translation of an article called: Das Ammonshorn und seine Verwandten von Dr E Dacqué. It appeared in a German popular science magazine, Kosmos Handweiser für Naturfreunde 1913, Heft 9, Seiten 332-337. The original article is accompanied by 11 thoroughly informative illustrations whereas this translation has over ten less. 'Nautilid' and other terms are used in a very loose and generalized manner.
I'm not aware of any previous translation.
Trevor Dykes.

The ammonite and its relatives by Dr E Dacqué
The number of fossilised remains of prehistoric animals known to us is unmissably large. Many systematic excavations, not only chance finds, of the rock layers of all lands have brought heaps of fossil forms to our eyes on a daily basis. But, despite the great quantities of material, much of which can only be sensibly examined and scientifically interpreted by specialists, it has still not been possible to produce an entirely comprehensive tree of descent for all groups in the animal and plant kingdoms. Presently, we know only the rough outline, but not the details, of the unclear and mysterious paths of the development of life that we try to track through the ages of the Earth.

It is especially difficult to scientifically construct a secure tree of development, because of the realisation that a straightforwardly branching 'tree' is much too naive and primitive a metaphor for the actual developmental process for lifeforms. External similarities, and sometimes the identical shapes in the animal world, are in no way always evidence for close blood relationships; similar forms can also arise from entirely different starting stages which develop towards each other across the course of time. This development of the same form, which one terms convergence, can lead to organisms initially being seen as representatives of the same natural group or family, as long as one does not know the precise developmental history involved. This can result in things being put together that do not, in terms of their origins, belong together.
Our 'natural' systematics of animals and plants is littered with unnatural genera and families which are based on external appearances and, therefore, no serious specialist of today views this purely systematic classification, and the diagnosis and naming of genera and species, as a scientific labour.

Furthermore, one has also experienced that developments and adaptation does not always proceed in a single line but rather, within the same group, a large number of its finer developmental lineages crystallize partly simultaneously and partly following one another, but in the same direction; rather as if the cultural development of humans occurred not within a single family or nation, but in a number of families, tribes and peoples, which do not all reach the same level of development at the same time.

However, in paleontology, one is not yet in a position to follow such fine parallel series of developments of a group through several, let alone all the ages of the Earth with satisfactory precision. Should one want to present the transformation of a type, one is unfortunately forced to summarize rather than show the complete evolutionary lines, and to call upon only the main developmental and transformational stages, to present them as a simplified series of transitions, and thus represent the descent only to a certain degree. Nevertheless, from such an abstraction one gains a clear appreciation of the main points of the group, and these would otherwise be obscured by the endlessly changing details, as the following example should show.

Of all known fossilized residents of the prehistoric seas, it is the ammonites, or horns of Ammon, that are the most characteristic petrifications (Illustration 1). The mostly flat lime house is rolled together as a spiral, and this is why ammonites are also called snails in the common tongue, eg. the Franconian Jura, where they sometimes occur as wonderful, gold-yellow, glimmering, sulphurized fossils and are known and prized with the name Goldschnecken ('gold snails'). One has termed them the horns of Ammon for centuries due to their similarity with the rolled horns of the Egyptian-Roman god, Jupiter-Ammon, symbolized by a goat.

There is not a single animal in the seas of today with a real ammonite shell; but there are close relatives that teach us that these peculiar fossilized houses do not belong to snails, but rather to a highly developed group of molluscs, the cephalopods ('head feet'), with the common unshelled squids as near relations. The two living closest relatives of the horns of Ammon are the nautilus and the argonautan, which is also called Papiernatuilus ('paper nautilus') due to its thin, parchment-like shell.

The nautilus (Ill 2) lives in the southern Pacific and Indian Oceans. Its chambered house is completely enclosed within its last chamber but, inside and excepting for the foremost part, is the air-filled so called Wohnkammer ('living chamber'). An Animal much like an ink squid sits in there and grows, and a thin string projects from the rear end, the sipho, which contains an artery, and runs through all the chambers to the heart of the shell. The growth of the house occurs in such a way that the animal builds forward from the shell opening while, simultaneously, shifting towards the front, so that the newly hollow space behind can be blocked off by a new wall of lime. This means that new air chambers are always being added until the animal is fully grown.

The animal has a specialized way of life. Its house holds it in the water exactly as a hydrogen balloon hangs in the air; as a consequence of its supply of gas and the unusually resultant lift generated, it can rise up to the surface of the sea. Obviously, the animal can control these ascents and descents through the water by pressing its body together in the living chamber, and changes to the gas pressure in the air by means of the siphos. This is why it is of the utmost importance for the existence of the nautilus, that its house remains undamaged and air-proofed.

The house of argonauts is differently built to that of the nautilus (Ill 3). It seems to be a relatively unimportant organ for the existence of its owner, as only the female possesses one, when sexually mature, for the purposes of caring for the babies, whereas the male remains a naked mollusc polyp. The argonaut shell has no chambers and the animal is also not anchored to it, but can rather leave it easily.

Should one think of the hollow chambers of the nautilus shell as being entirely filled with a rock hard mud from lime, and then imagine the disappearance of the external shell, what remains of the inside is a model of a 'stone core' (Ill 4). One sees wavy lines running up over both sides. These lines clearly mark the places where the internal walls of the chamber contacted the inner side of the external shell. One calls such a curve a suture line. This is significant for our later considerations.

Mostly, the strata from earlier ages of the Earth provide fossil species of nautilus only as stone cores, without the presence of the former outer shell. Right back at the start of the Mesozoic*, they generally had the form of the present animals, but with the difference that, the further back we go into previous periods from today, countless species shows always a greater number of spirals (Ill 5).

(* Paleozoic (Cambrian, Silurian, Devonian, Carboniferous, Permian); Mesozoic (Triassic, Jurassic, Cretaceous); Cenozoic (Tertiary, Ice Age, Holocene). The Paleozoic followed on from a monstrously long epoch known as the Precambrian, from which absolutely no fossilized lifeforms are known.)

That is a first general developmental law in the evolution of a group, the meaning of which will become immediately clear the further one goes back beyond the Mesozoic time and into the Paleozoic. One finds namely then, that the nautilus lineage is entirely represented by species, the spirals of which were mostly so open, that the single lines were only weakly, or entirely not discernable (Ill 6). Going further back through the episodes of time, we find, rather than this form, more and more with shells that are only moderately sickle-shaped and finally even completely straight (Ill 7). These latter ones are the archetypes for the nautilus lineage from which the whole developmental radiation originated.

If we could follow the lineage of the nautilus through the ages, as in the sense just mentioned, and photograph its countless representatives onto a long, long reel of film, and project these images one after another onto the screen of a cinema, then we would see the straight shells gradually curving, then spiralling more and more until they were finally completely rolled up -and it is this change of rolling which essentially is the evolutionary history of the nautilus lineage, that we would be watching unfold through the ages with incredible slowness.

Naturally, one must realise that the development was not as straightforward as a short summary of that nature suggests. Countless branches with many forms arose and then disappeared again; soon one and quickly another line would change, so that different areas of the same age would often have different developmental stages of this coiling. As well as typical representatives there were also 'abnormal' ones with narrow openings, and others with strongly coiled houses which, however, stretched out at the end; and still others with siphos so wide, that they filled a very large portions of the chambers; and there was a type with an at first normal, almost straight house with regularly placed air chambers, but which later threw those off and laid on new ones beside the living chamber.

If we were to talk about the point of these adaptations for the nautilus, then it could be that the more recent, rounder shaped houses, as a consequence of their shape and compacter form, were much less prone to breakage than the earlier, elongated models, and that could have been of very great significance for the particular mode of existence of the group. This is because the house, with its gas content, is only able to function in an undamaged condition; as soon as water seeps in the gas escapes, and the shell would then be too heavy for the ascents and descents of the animal, so its abilities to swim both at depth and near the surface would be disturbed or completely impaired. Every adaptation is a matter of utility.

The horn of Ammon itself is built almost identically to the normal, coiled house of nautilus, but it does have the difference that the walls of the chambers (suture lines) of the stone core are not simple, swinging lines, but they are rather at least kinked and serrate, and are even mostly richly branched and twigged like a plant (Ill 1).

One makes the rather general assumption that ammonites are descendants of the earliest nautilids, because the geologically oldest ammonites have much similarity with nautilids as far as the build of the shell and suture lines go. Furthermore, the evidence shows that when the properly coiled nautilids appeared from their long, straight predecessors (at the end of the Silurian and start of the Devonian), we encounter the first, simple horns of Ammon in the history of the Earth, and these were constructed in the style of Goniatites (Ill 8), which is characterized by its kinked, but otherwise nautilid-like chamber walls.

The evolution of ammonites carries on from Goniatites, from these simple and relatively regular suture lines to the first emergence of backwards directed waves (Ill 9); such types are particularly characteristic for the Permian and the Triassic. And along with those, during the Triassic, we also find forms which already have the entire suture lines with regular branching. This was followed by the typical horns of Ammon from the Jurassic and Cretaceous, with their strongly branched and irregularly built suture lines (Ill 1).

During the Mesozoic, when the ammonites had their greatest blossom and ruled all seas with their incredible diversity, we also find some 'side lines' with shells consisting of more open spirals, or which are completely uncoiled from originally closed ones (Ill 10), and indeed, occasionally even more tower-like ones as with the common sea snail. Such irregularly constructed forms are very rare for the Triassic and Jurassic, but they become quite frequent for the Cretaceous.

One has taken the appearance of such side lines as perhaps being a sign of decadence in the relevant ammonite groups, a sort of exhaustion of the normal construction process and this especially so because, towards the end of the Cretaceous, other forms appeared with suture lines that were just as simple as the older ones from the Permian and Triassic. That has been interpreted as an atavistic fall back, as a symptom of senility for the group. Be that as it may: the fact is that the ammonites disappeared rather rapidly in the strata at the end of the Cretaceous, leaving no signs of descendants, and this group, which had been so richly diverse a short while earlier, provides no surviving individuals from the Tertiary.

However, as also at the end of the Cretaceous, during the middle of the extinction of the horns of Ammon, there was also a very large number of entirely ordinary species from which no particular peculiarities are to be found but which, as with the others, nevertheless died out, a recognised researcher recently came to the fruitful thought that the 'extinction' may actually be an artefact appearance: perhaps -he thinks- ammonites at the start of the Tertiary did not produce shells -a process of regression for molluscs- and so there may have been soft-bodied animals which were unable to leave fossilized hard parts in the further layers of the Earth; then only the soft parts existed. There could be descendants of shell-less ammonites still living among the present mass of unshelled cephalopods, which have not yet been recognised as such.

The researcher mentioned assumes that the last remains of the ammonites are the argonauts discussed above (Ill 3), the houses of which do not have resemblances with a horn of Ammon. But that is only external and concerns the ornamentation. Its embryological development shows it to be something entirely different, as it partly develops from the arms of the animal and not from the pallium; furthermore, it has no dividing walls for the chambers, no sipho and only a single whorl. While it appears to look like a horn of Ammon from a quick glance at the outside, that does not make it one -this is a matter of convergence and not one of a blood relationship with the ammonites. Perhaps the external similarity simply reflects the inner details of the organisation of the cephalopod nature, which gives rise to either a nautilus or ammonite-like shell; that it is in their nature, that when a house is developed, it can do nothing other than construct a horn of Ammon-like one, and that is why they all have external similarity!

Little is yet known about the lifestyle of the ammonites in the prehistoric world. Earlier, it was believed to be a free swimming animal of the high seas, and many thought the shells must have been extremely thin and transparent like gelatine, and that would point to a lifestyle among plankton. But there were also surely bed dwellers among them which were tied to a limited locality.

There is also another particular abnormality among Mesozoic ammonites, and this consists of a bracing of the living chamber. This feature (Ill 11) has been brought into connection with care of the young, as it is assumed that the young brood of this particular genus was probably carried for a while in the shell of the mother, and the extended size of the living chamber would have been necessary for such an objective. According to this, such abnormalities would be nothing more than the female form of normal male types. However, this otherwise attractive interpretation is called into question by the circumstance, that these extended forms, held to be females, are extremely rare in comparison to the normal ones, so rare that there would have been, at most, one female for every 100 males. This is so absurd that such a theory is hardly credible, even less so since the discovery -albeit from a different genus- of a house, which appeared to have a brood assembled within its shell, but had no dimensionally increased living chamber, but rather an entirely normal one. We must presently accept that 'abnormal' forms continue to pose a puzzle.

From whence this whole swarm of previously mentioned shelled polyps came is something that we do not know, and it is doubtful this will ever be known. Then already, at the start of the first real fossilious formation (Cambrian), the straight, elongated nautilids were present. Undoubtedly, these are the oldest and simplest forms. Ammonites, as with belemnites (a further group of fossil squid-like polyps) first appear later; both, as stated, branched from the nautilid lineage which, although poor in species, still survives in the oceans of today, while the much richer and more varied ammonites had to leave the theatre of life again during the Mesozoic -assuming that unrecognized descendants are not among the now naked polyps. The first of the ancient forms of nautilids, which we meet in the Cambrian, are unusually small, and had horny shells with few chambers, and they had a narrow, slit-like opening at the front. Presumably, the whole group arose still earlier from forms with a simple chitin shield on the back of the body, to provide some protection. But here we get lost among the fog of unknown ages in the archaic world, which stand at the beginning of the history of the Earth, exceeds all succeeding ages of the world combined in terms of length, and we know nothing about its living world.

An index of more of my translations of old Kosmos articles can be found at:

Kosmos Translations Archive

A number of Mesozoic (and post-Mesozoic) location summaries can be found at Localities.