CHAPTER XI

HISTORY OF THE †AMBLYPODA AND †CONDYLARTHRA

These are two orders of hoofed animals which long ago vanished from the earth and no member of either is known to have survived later than the Eocene epoch; both were of great antiquity, dating back to the Paleocene, perhaps even to the Cretaceous. The last of the †Amblypoda are found in the lowest Uinta or highest Bridger, but they were relatively abundant in all the more ancient beds. The following table gives the more important American forms:

Order †AMBLYPODA. †Short-Footed Ungulates

Suborder †TALIGRADA

I. †PERIPTYCHIDÆ.

_†Periptychus_, Paleoc.

II. †PANTOLAMBDIDÆ.

† _Pantolambda_, Paleoc.

Suborder †PANTODONTA

III. †CORYPHODONTIDÆ.

_†Coryphodon_, Wasatch and Wind River.

Suborder †DINOCERATA

IV. †UINTATHERIIDÆ.

_Bathyopsis_, Wind River. _†Elachoceras_, Bridger. _†Uintatherium_, do. _†Eobasileus_, do.

As is shown in the table, the suborder †Taligrada is entirely Paleocene in distribution, the †Pantodonta are lower Eocene and the †Dinocerata chiefly middle Eocene, though persisting into the upper. The †Dinocerata were the most striking and characteristic of Bridger mammals, and two or three phyla of them may be distinguished, though for our purposes this is hardly necessary, for these strange and bizarre creatures were all very much alike. From the commonest and best-known genus (_†Uintatherium_) they are called †uintatheres. They were large and ponderous animals, the veritable giants of their time, far exceeding any of their contemporaries. In appearance they were among the most fantastic of the many curious beasts which the fossils have revealed.

The skull carried three pairs of bony protuberances, or horn-like outgrowths; one pair on the nasal bones suggest by their shape and character that they formed the support of dermal horns like those of the paired-horn rhinoceroses (_†Diceratherium_) of the Oligocene and lower Miocene. (See p. 239.) The second pair, which were moderately high and thick prominences, almost cylindrical in shape and tapering but slightly to their bluntly rounded ends, were chiefly outgrowths of the maxillaries, or upper jaw-bones. From their shape, it is likely that these were not sheathed in horn, but were merely covered with skin, as were also the third pair, which arose from the parietals. These were massive, club-shaped prominences, eight or ten inches high and broadening to the free ends, a shape which makes it impossible to suppose that these were true horn-cores covered with horny sheaths. A high crest of bone, representing the occipital crest, enclosed the top and back of the cranium, connecting the posterior pair of “horns” and dying away in front of them. The top of the cranium had thus a deep, basin-like character, such as is to be found in no mammal outside of this suborder and was one of the most peculiar features of this extraordinary skull. The brain-cavity was absurdly small, the growth of the brain not having kept pace with that of the body; the cavity is hidden away in the postero-inferior portion of the skull, the immense thickness of the cranial walls being somewhat lightened by the formation of sinuses, but these were much less extensive and pervasive than in other very large, horned or tusk-bearing mammals, such as elephants, rhinoceroses, etc. Probably, as in the case of the †titanotheres and †entelodonts, this deficiency of brain-development was at least one of the factors which led to the early extinction of the group. The premaxillaries were slender and rod-like bones, which did not meet in the middle line and carried no teeth. The long and massive nasal bones and the position of the nasal opening show that these animals cannot have had a proboscis of any kind. The lower jaw was remarkable for the great bony flange which, in the males, descended on each side from the lower border, near the anterior end, and served to protect the great canine tusks from fracture.

[Illustration: FIG. 230.—Skull of †uintathere (_†Uintatherium alticeps_), lower jaw supplied from another species. Princeton University Museum. For restoration, see Fig. 231, p. 447.]

The female skull differed in two respects from that of the male: (1) the horn-like protuberances were much more slender and less prominent; (2) as the upper canine did not form a tusk, the lower jaw had no flanges. The skull of the artiodactyl _†Protoceras_ (p. 406) was remarkably similar to that of the †uintatheres.

The dental formula was: _i_ 0/3, _c_ 1/1, _p_ 3/3, _m_ 3/3, × 2 = 34. The upper incisors were completely lost and the lower ones had the very unusual peculiarity of being bilobate, or having the crown separated into two well-defined cusps. The upper canines in the males were very large, relatively thin, recurved and sabre-like tusks, with acute points and sharp edges, which must have been terrible weapons, though it is difficult to see how they were used; probably the mouth was widely opened, so as to clear the points of the tusks, and the animal then struck with them, as a snake does with its fangs. The lower canine was very small and was included in the incisor series, the shape and function of which it had assumed. Thus, the †uintatheres, with their toothless premaxillaries and, to all appearances, eight lower incisors, formed a curious parallel to the true ruminants (Pecora), and, as in the latter, they must have had a firm elastic pad on the premaxillaries, against which the lower incisors could effectively bite, when cropping the soft plants which formed the diet of these great beasts. The grinding teeth were low-crowned and surprisingly small in comparison with the size of the skull. The premolars and molars were nearly alike and had two or more transverse crests.

Aside from the altogether exceptional character of the skull, the skeleton was quite strikingly elephantine in appearance, so much so, in fact, that these animals have repeatedly been referred to the Proboscidea and some writers are still of the opinion that the two orders were related. There is, however, no sufficient ground for this view; the undeniable likenesses are much more probably to be ascribed to the operation of convergent development.

[Illustration: FIG. 231.—One of the elephantine †amblypods (_†Uintatherium alticeps_) of the Bridger stage. Male in foreground, female behind. Restored from specimens in the museums of Yale and Princeton universities.]

The neck was of moderate length, sufficiently long to enable the animal to reach the ground with the lips, a necessity in the absence of a proboscis. The body was very long and, as is shown by the length and curvature of the ribs and the great breadth of the hip-bones, extremely bulky. The limbs were very massive, and the long bones had lost the marrow-cavities, being filled with spongy bone, as in the elephants, †titanotheres and most other very heavy mammals. The bones of the fore-arm and lower leg were separate. The hip- and thigh-bones and shin-bones were remarkably elephantine in character and, if found isolated, might readily be referred to some unknown proboscidean, but the bones of the fore limb were quite different from those of the elephants. The feet likewise had a very proboscidean appearance, notwithstanding important and significant deviations in structure; they had the same shortness and massiveness and a similar reduction in the size of the hoofs, and the presence of all five digits added to the resemblance. Undoubtedly, the feet had the same columnar shape and arrangement of elastic pads. The living animal must have had an appearance quite similar to that of a rather small elephant, not exceeding six or seven feet in height at the shoulders and therefore not surpassing the largest modern rhinoceroses, the broad-lipped species of Africa (_Opsiceros simus_). Of course, the head must be excepted from the comparison, as that was totally unlike the head of any existing creature; with its long and narrow shape, its fantastic protuberances and its lack of a proboscis, it had no suggestion of likeness to any proboscidean. Whether the great body was naked, or clothed with hair, it is of course impossible to determine with confidence, but, all things considered, it seems unlikely that the hair should have been completely lost in any terrestrial mammal at so early a period. As we have seen in the preceding chapters, hairy elephants and rhinoceroses continued into and through the Pleistocene, not only in the cold regions of the north, as is shown by the hair of the American †Mastodon. In the tropics conditions were different, and in that uniformly warm climate the loss of hair by the very large mammals probably took place long before the Pleistocene. At all events, it is a significant fact that no hairless land mammals are now known in any region which has severe winters. It is true that the middle Eocene climate over most of North America was warm-temperate or subtropical, and the †uintatheres may, in consequence, have been hairless, but there is no evidence of this.

[Illustration: FIG. 232.—Skull of _†Elachoceras parvum_ (lower jaw restored). Princeton University Museum.]

Within the limits of the †uintathere family, considerable modification and change may be traced, which, as in the case of the Proboscidea, principally affected the skull and the general stature. It is hardly worth while to deal separately with the two or more phyla which may be distinguished, for the differences between them are relatively unimportant. In the uppermost part of the Bridger stage almost the latest representatives of the family are found and the genus (_†Eobasileus_) was of the largest size. These animals had remarkably long and narrow heads and very large, shovel-shaped nasal protuberances; in the males the upper canine tusks were very long and curved back nearly in a semicircle. In the middle portion of the stage the species of _†Uintatherium_ were somewhat smaller and had shorter, wider and higher heads, the tusks, though well developed, were not quite so long, nor so strongly recurved; in some species they were nearly straight, with “hastate” or spear-head point. In the same horizon is found a third genus (_†Elachoceras_) which was probably a survival persisting from the lower Bridger, in which none of these animals and little of anything else has yet been found. _†Elachoceras_ was hardly half as large as the common species of _†Uintatherium_ and its skull might be described as a preliminary sketch for that of the latter; the nasal horns were extremely small, or, more probably, entirely absent; the median pair were mere low knobs, hardly an inch in height, and the posterior pair were simply thickenings of the crest which enclosed the top of the cranium on three sides, scarcely rising above it. This crest itself was much less prominent than in _†Uintatherium_ and the basin-like top of the skull, in consequence, very much shallower. The upper incisors and the first premolar had already been lost and the upper canine enlarged into a sabre-like tusk, which, however, was relatively smaller than in the succeeding genera. The grinding teeth were quite the same as in the latter. Unfortunately, the skull of _†Elachoceras_ is the only part of the animal which is known, but, so far as that is concerned, it is precisely what we should expect the forerunner of _†Uintatherium_ to be; an ancestor made to order could hardly be more diagrammatic. It might, of course, be objected that no such relation as that of ancestor and descendant could obtain between these two genera, because they were contemporaries, but the case is like that of the ancestral elephants described in the preceding chapter. _†Mœritherium_ and _†Palæomastodon_ are found together in the Egyptian Oligocene, the former surviving for a considerable time after it had given rise to the latter, and in the upper Eocene only _†Mœritherium_ occurs. Many similar instances might be given, just as grandfathers often live long with their grandchildren.

In the Wind River stage, or upper division of the lower Eocene, lived the still incompletely known _†Bathyopsis_, of which, however, sufficient material has been obtained to show that it was much less specialized than any of the Bridger genera. This genus comprised animals much smaller than its successor, _†Elachoceras_ of the middle Eocene, being smaller than a tapir; it stood in much the same relation to _†Elachoceras_ as the latter did to _†Uintatherium_. In the American Museum of Natural History is a highly interesting skull of _†Bathyopsis_, which will shortly be described by Professor Osborn. The premaxillaries have not been preserved, and it is therefore impossible to say whether the upper incisors had already been suppressed or not, and though the upper canine has not been found, there can be no reasonable doubt that it was a tusk. The lower canine had not yet gone over to the incisor series, but was a thin though large tusk. There was one more lower premolar, four in all, than _†Uintatherium_ possessed, and all the premolars were somewhat smaller and simpler than the molars. The small skull had a broad and somewhat concave cranial roof, with slightly raised enclosing crest, and the horn-like protuberances of the posterior and median pairs were present in an incipient stage. Whether those of the nasal pair were also indicated is not known, but probably they were not. The lower jaw was of very peculiar shape; the flange of the inferior border was not so well defined as in _†Uintatherium_, but had no hinder margin and rose very gradually backward.

The series of genera in descending order, _†Eobasileus_, _†Uintatherium_, _†Elachoceras_ and _†Bathyopsis_, immediately impresses the observer as being a natural phylogenetic series of successive ancestors and descendants. Unfortunately, only the skull is known in the two last named, but there is no ground for supposing that the discovery of the skeletons would require any alteration in the series as we now have it. No member of this series has yet been found in the Wasatch, but there can be no doubt that it was represented in that stage, for a recent expedition from the American Museum has collected teeth of a _†Bathyopsis_-like form in still older beds.

SUBORDER †PANTODONTA

During the older part of the lower Eocene the †uintatheres must have been a rare and unimportant element of the fauna, at least in those parts of the continent whose history we know. Their place was taken by another suborder, the †Pantodonta, which was not ancestral to them, but collaterally related and descended from a common ancestry. The largest and most dominating of Wasatch mammals was the genus _†Coryphodon_, which also occurred in the lower Eocene of Europe, and the species of which ranged in stature from a tapir to an ox, though of much heavier form than the latter. The latest surviving species lived in the Wind River stage as a contemporary of _†Bathyopsis_, but then the suborder gave way to the †uintatheres.

In _†Coryphodon_ (see Fig. 142, p. 279) the number of teeth was unreduced, a fact which is recorded in the name of the suborder, the dental formula typical of all the primitive ungulates being applicable to the genus. This formula was: _i_ 3/3, _c_ 1/1, _p_ 4/4, _m_ 3/3, × 2 = 44. The upper incisors were rather small, but functional, and the canines of both jaws were formidable tusks, though not rivalling in size the great sabres of the †uintatheres; the premolars had a simpler structure than the molars, which resembled those of the †uintatheres in a general way, but not closely. The skull differed greatly from that of the †uintatheres in having no horn-like protuberances, and was relatively large and heavy, the cranium having a broad, flat roof and no sagittal crest, and the lower jaw had no descending flange from the inferior border; in every way this skull was more normal and less bizarre-looking. The neck was proportionately longer than in the †uintatheres, the body long and the tail of medium length; the trunk-vertebræ had surprisingly small and weak spines, perhaps an indication of aquatic habits. The limbs were quite short and very heavy, and the bones, in comparison with those of the †uintatheres, were less proboscidean and more perissodactyl in character. For example, the femur retained the third trochanter and the long bones had marrow-cavities. The feet, on the contrary, were very like those of the †uintatheres, being extremely short and five-toed and with reduced, nodular hoof-bones; even in the details of the wrist and ankle joints there was no important difference between the two groups.

SUBORDER †TALIGRADA

None of the ungulate series considered in the foregoing chapters can be traced back to a time earlier than the Wasatch, and many of them not so far, but in the case of the †Amblypoda the line may be carried down through the Paleocene. In the upper stage of that epoch (Torrejon) the order was represented by _†Pantolambda_ (Fig. 143, p. 285), a member of the third suborder, †Taligrada. The best-known species of the genus was an animal with head and body somewhat smaller than those of a sheep and much shorter legs. The teeth were present in unreduced number, 44 in all; the canines were tusk-like, but very much smaller proportionately than those of _†Coryphodon_; the premolars were smaller and simpler than the molars, which closely represent the common starting point, whence the curious tooth-patterns found in the subsequent genera of the various families were derived. The skull was long and narrow and had a prominent sagittal crest; the neck was of ordinary length, about equal to that of the head; the body was long and the tail very long, much as in the great cats. The hip-bones were narrow and slender and not bent outward, having no such breadth as in _†Coryphodon_. The limbs were short and relatively heavy, and the various bones were of such primitive character that, if found isolated and not in association with teeth or foot-bones, one would hardly venture to consider them as belonging to any hoofed animal; the humerus had a very prominent deltoid crest and an epicondylar foramen, and the femur had the third trochanter. The five-toed feet were very short, and the digits were arranged in a spreading manner and were relatively much more slender than in _†Coryphodon_. Each digit terminated in a flat, pointed, well-developed hoof; evidently there was no elastic pad to bear the weight, such as recurs in nearly all very heavy ungulates. The gait of the animal was probably semi-plantigrade, the hoofs being the principal points of support.

While _†Pantolambda_ was an undoubted ungulate and a member of the †Amblypoda, there were many structural features in its skeleton which point to a relationship with the primitive flesh-eaters. In the lower stage of the Paleocene, the Puerco, the genus _†Periptychus_ would seem to be the most ancient known member of the order, but it is still very imperfectly understood.

* * * * *

In the mode of evolution of the †Amblypoda, so far as that is recorded by the fossils, there is much to recall the development of the Proboscidea, though the story began and ended at far earlier dates and may be traced back to a much more primitive stage.

(1) There was a rapid increase of stature, especially of bulk, in the †coryphodonts, but decidedly more gradual in the †uintatheres, which eventually attained a far larger size.

(2) The upper incisors were suppressed and the canines grew into formidable tusks, at first straight, then the superior one, enlarging still farther, acquired a curved, scimitar-like shape, while the inferior one dwindled and became functionally one of the incisors.

(3) The grinding teeth remained low-crowned throughout, but acquired a more complex pattern, and the premolars became almost like the molars.

(4) The skull underwent a most remarkable transformation. Beginning with a form that might have belonged to almost any of the ancient mammals, hoofed or clawed, having very prominent sagittal and occipital crests, long cranium and short face, it became in _†Coryphodon_ flat-roofed, with moderately elongated face, while in the †uintatheres the top of the cranium gradually took on a deeply concave basin-shape and, with equal gradualness, three pairs of horn-like protuberances; the lower jaw developed a great bony flange for the protection of the upper tusks. These peculiarities grew more and more exaggerated and were most striking in the terminal genus of the series, _†Eobasileus_.

(4) Unfortunately, nothing is yet known of the skeleton of _†Bathyopsis_ and _†Elachoceras_, so that it is not practicable to follow out all the stages of skeletal modification, though the general course of development is sufficiently plain. The neck did not change greatly, except to become very strong and heavy and to grow shorter proportionately as the skull was lengthened. The body remained long throughout the series, but gained greatly in bulk, as the stature of the animal increased.

(5) The limb-bones lost their primitive character, such as the epicondylar foramen of the humerus and the third trochanter of the femur, and then, with the great increase of the weight to be supported, the marrow-cavities were filled with spongy bone and the hip-bones increased enormously in width; the femur lost its cylindrical shape and was flattened antero-posteriorly, which gave it a very elephantine appearance. None of the limb-bones was suppressed or greatly reduced in size, nor was there any coössification between them.

(6) The feet early gained their definitive character; at no time was there any loss of digits, but the originally divided toes were, in the genera of the Wasatch and subsequent stages, united into the columnar foot, and the hoofs were reduced from their primitively pointed shape to nodular form.

As in the Proboscidea, therefore, there was comparatively little change in the skeleton after the massive and bulky proportions had been acquired, but great and continual modification of the skull. At the time when the †Amblypoda finally disappeared, no ungulate had acquired the hypsodont dentition. Had the group survived till the middle Miocene, a time when the spread of grassy plains so profoundly affected the feeding habits of many herbivorous mammals, the high-crowned teeth might have been developed in them also, and this, in turn, would have produced other changes in the skull, making closer the parallel with the Proboscidea.

In conclusion, a few words may be said concerning the geographical distribution of the †Amblypoda. In the Paleocene the only known representatives of the order were those of North America, but the †coryphodonts of the lower Eocene migrated to the Old World; indeed, the genus _†Coryphodon_ was first described and named from English specimens, but there were no such abundance and variety of these animals in Europe as there were in the western United States. The †uintatheres were strictly North American in distribution and no member of the suborder has ever been found outside of this continent. Animals referred to the †Amblypoda by some authorities have been obtained in the Oligocene and Miocene of South America, but the assignment has been made upon insufficient evidence. (See p. 508.)

ORDER †CONDYLARTHRA

The †Condylarthra were a group of exceedingly primitive ungulates, which served to connect the hoofed and clawed mammals in quite an intimate manner. So few indeed were the distinctively ungulate characters which they had acquired, that it is still premature to make any positive statements regarding their geographical distribution, because unusually well-preserved specimens are required to make sure of their presence in any particular region. Concerning North America there is no room for question, and there is hardly any doubt that they existed in the Paleocene of Europe. The South American remains which have been referred to this order may very well prove eventually to belong to it properly, but until both feet and skulls have been obtained in unequivocal association, the reference can be only tentative. In North America they ranged through the Paleocene and lower Eocene, but are not known from any subsequent formation, and even in the Wind River only a few stragglers survived.

The principal American families and genera are as follows:

I. †MENISCOTHERIIDÆ.

_†Meniscotherium_, Wasatch and Wind River.

II. †PHENACODONTIDÆ.

_†Protogonodon_, Puerco. _†Euprotogonia_, Torrejon. _†Phenacodus_, Wasatch and Wind River.

1. _†Phenacodontidæ_

The typical Wasatch genus _†Phenacodus_, which is very fully known from nearly complete skeletons, included species which varied in size from a fox to a small sheep; the same genus occurred in the Wind River, but not later. _†Phenacodus_ had the unreduced dental formula: _i_ 3/3, _c_ 1/1, _p_ 4/4, _m_ 3/3, × 2 = 44.

[Illustration: FIG. 233.—Skeleton of the Wasatch †condylarth, _†Phenacodus primævus_. American Museum. For restoration, see Fig. 141, p. 278.]

The incisors were small and simple, the canines tusk-like, but of no very great size, the premolars smaller and simpler than the molars. The latter were of the quadrituberculate pattern, of four simple, conical cusps arranged in two pairs, a pattern which is common to the earlier and less specialized members of many ungulate groups. The skull was long, narrow and low, with long and well-defined sagittal crest. As in primitive skulls generally, the cranial region was long and the face short, the eyes being very far forward; this does not imply large brain-capacity, indeed, the brain was very small, but merely that the portion of the skull behind the eyes was relatively long. The jaws were short and shallow, in accordance with the small and low-crowned teeth which they carried. The neck was of medium length, but the body was elongate and the tail was very long and stout. The hip-bones were narrow and slender, as in primitive ungulates generally. The limbs were short and stout and retained many very primitive characteristics. The humerus had a prominent deltoid crest and an epicondylar foramen; the fore-arm bones were separate and the ulna quite unreduced, being almost as stout as the radius. The femur had the third trochanter and the leg-bones were distinct, though the fibula was slender. The feet, which were short, had five digits each, but the third toe was enlarged, while the first and fifth were shortened, as though preparing to disappear and thus give rise to a three-toed perissodactyl foot. The ankle-bone (astragalus) had a rounded, convex lower end, fitting into the navicular, so that it might readily be taken for that of a clawed mammal.

2. _†Meniscotheriidæ_

A second family of Condylarthra was represented in the lower Eocene by the genus _†Meniscotherium_ and was in some respects considerably more advanced than the †phenacodonts. These were small animals, in which the molars had acquired a crescentic pattern, recalling that seen in the early horses and in the †titanotheres and †chalicotheres, and other perissodactyl families. In the upper molars the two external cusps had been so extended as to form a continuous outer wall, each of the cusps having a concave external face and the two uniting in a prominent median ridge. The lower molars had two crescents, one behind the other, as in several families of both perissodactyls and artiodactyls. The body and tail were long, the limbs relatively longer and lighter than those of _†Phenacodus_ and the five-toed feet were so like those of the modern conies, or klipdasses, of Africa and Asia Minor, that by some investigators the family has been referred to the same order, the Hyracoidea, but the suggestion is not a probable one. It is much more likely that these problematical little †meniscotheres were merely a short-lived branch of the †Condylarthra.

[Illustration: FIG. 234.—Lower Eocene †condylarth, _†Meniscotherium terræ-rubræ_. Restored from a skeleton in the American Museum.]

The †condylarths were quite abundantly represented in the Paleocene, where the genus _†Euprotogonia_ was the forerunner of the Wasatch _†Phenacodus_, but had an even more primitive type of dentition. The upper molars were not quadritubercular, but tritubercular, the three cusps arranged in a triangle, the two outer ones forming the base and the single inner one the apex. This type of upper molar was, or is still, common to the primitive and unspecialized members of a great many mammalian orders, marsupials, insectivores, rodents, carnivores, lemurs, artiodactyls, etc., and there is strong reason to believe that the tritubercular molar was the common starting point for almost all types of mammalian dentition. However that may be, _†Euprotogonia_ is of great interest as materially helping to close the gap between the clawed and the hoofed mammals, belonging, as it did, to the latter and yet retaining in dentition, limbs and feet so many characteristics of the former.

†Condylarthra were probably present in the lowest Paleocene (Puerco stage), but the material so far obtained is so fragmentary that there can be no certainty on this point.

It is not at all probable that any of the North American †Condylarthra should be regarded as ancestral to any of the more advanced ungulate groups; on the contrary, they would appear to have come to an end in the Wind River, leaving no descendants behind them. It is further true, as was mentioned above, that the presence of †Condylarthra in other continents, while very probable, cannot be positively asserted, because the evidence is incomplete. Yet it would be a great mistake to assume, for this reason, that these most primitive of ungulates were devoid of evolutionary importance and interest. As is so often the case, where, in the absence of the direct ancestry, the collateral relations afford very valuable information as to the course of descent and modification, the †Condylarthra throw useful light upon the origin of the ungulate groups. It is extremely probable that the †condylarths, or some very similar series of primitive hoofed mammals, had a very wide and perhaps cosmopolitan range at the end of the Cretaceous and beginning of the Tertiary period, and that, in the still unidentified region, where the artiodactyls and perissodactyls arose, it was from a condylarthrous ancestry. Possibly, all the other ungulate orders may yet be traced back to the same stock, but it is rather more likely that the ungulates include several series of quite independent origin. At all events, it is quite certain that the clawed mammals long antedated the hoofed types and that the latter arose, either once or at several separate times, from the former. The †Condylarthra show how one, at least, of these transitions was effected, and thus, in principle, how all were accomplished.