6o8 



NA TURE 



[April 28, 1892 



character ; they are strong and easily reversed, and in 

 all of them the first doublet is situated on the less refran- 

 gible side of the spectrum, and all the others in the violet 

 and ultra-violet. The series shift towards the less re- 

 frangible side with increasing atomic weight. 



For further details the reader is referred to the follow- 

 ing memoirs :— Kayser and Runge, " Ueber die Spectren 

 der Elemente," Abhandl. der Berl. Akademte, 1890-92; 

 Rydberg, " Recherches sur la constitution des spectres 

 d'dmission des elements chimiques," Kongl. Svenska 

 Vetenskaps-Akademiens Handlingar, Bandet 23, No. 11, 

 1890. C. RUNGE. 



ABERRANT FOSSIL UNGULATES OF 

 SO UTH AMERICA. 



TILL within the last few years palaeontologists and 

 zoologists were being continually startled by the 

 discovery of strange forms of extinct Ungulates which 

 rewarded the researches conducted in the Tertiary rocks 

 of the United States. The animals thus brought to the 

 notice of the scientific world have, to a very large extent, 

 modified our conceptions of the relationships of the 

 various groups of hoofed or Ungulate Mammals to one 

 another ; and have led to the very general adoption of 

 the view of the ordinal unity of all these multifarious 

 types. Several of them, indeed, so far as we may judge 

 from their mere skeletons, indicate signs of a transition 

 between the Perissodactyle and Proboscidean modifica- 

 tions of Ungulate structure ; but none of them tend in 

 the least degree to break down the hard and fast line of 

 demarcation between the Perissodactyle (odd-toed) and 

 Artiodactyle (even-toed) modifications, which is main- 

 tained throughout all the known Tertiary deposits of the 

 Old World. Moreover, after a little " shaking down," 

 the whole of these North American Ungulates, with the 

 exception of the curious Rodent-like Tillotherium, fall 

 fairly well into their places in the Ungulate order ; 

 although some of the earlier and smaller types pre«;ent 

 indications of close affinity with the common stock from 

 which we may presume both Ungulates and Carnivores 

 to have taken origin. 



At the present time the wave of discovery of new forms 

 appears to be passing from the northern to the southern 

 half of the New World ; so that while the palaeontologists 

 of the United States are to a great extent engaged in the 

 important task of revising and completing the preliminary 

 work of the last twenty years, their confreres in Argentina 

 are almost flooding scientific literature with descriptions — 

 sometimes, it is to be feared, rather crude and hasty ones 

 — of a number of new or hitherto imperfectly known forms 

 of extinct mammals. This descriptive work has been 

 mainly undertaken by Messrs. Ameghino, Burmeister, 

 and Moreno. Unfortunately, however, the greater part 

 of it is still in the form of preliminary notices, unaccom- 

 panied by illustrations ; while on several points the three 

 describers above mentioned are by no means in accord, and 

 it is quite clear that unnecessary names have frequently 

 been published. There is. indeed, one large illustrated 

 work published by Dr. Ameghino ; but since, so far 

 as we are aware, there is only a single copy (in the 

 Natural History Museum) in England, palaeontologists 

 have not the opportunity of paying it that attention in 

 private study which its importance demands. 



In spite, however, of these drawbacks, the information 

 at present before us — imperfect though it be — introduces 

 us to several groups of extinct Ungulates totally unlike 

 any found in all the rest of the world put together, and 

 which are of especial interest as tending to a certain ex- 

 tent to break down the distinction between Perissodactyles 

 and Artiodactyles. It should be observed, before pro- 

 ceeding further, that the explorations conducted in 

 NO. II 74, VOL. 45] 



Patagonia and various parts of Argentina have shown 

 that the deposits containing mammalian remains, instead 

 of being exclusively of Pleistocene age, comprise a large 

 portion of the Tertiary period, probably extending down 

 at least as far as the Oligocene ; although the exact 

 correlation of the difi'erent beds with European deposits 

 is probably premature. 



With these preliminary observations,' and asking our 

 readers at the same time to bear in mind that a consider- 

 able part of our knowledge is still in a very imperfect and 

 crude condition, we propose to glance at some of the 

 peculiarities presented by the more remarkable forms 

 of Ungulates described from the deposits in question. 



Since the date of the publication of the results of 

 Darwin's voyage in the Beagle, we have been gradually 

 acquiring a knowledge of the structure of that remark- 

 able South American Ungulate known as Macrauchenia, 

 of which the complete osteology has been described by 

 Burmeister. This animal, which had the general propor- 

 tions and size of a horse, conforms in several respects — 

 more especially in having three-toed feet, in which the 

 middle (third) digit is symmetrical in itself— so markedly 

 with the Perissodactyles, that by common consent it has 

 been generally regarded as an extremely aberrant mem- 

 ber of that group. The molar teeth are, indeed, more 

 like those of the Rhinoceros and Palaeotherium than of 

 any other Old World Ungulates, while the infoldmg of 

 the enamel of the crowns of the incisors is a character 

 known elsewhere only in the horses. The absence of 

 any gap in the dental series, and the nearly even height 

 of the teeth, are characters in which Macrauchenia agrees 

 with the 0\(\\N orXd Anoplotherium. Perissodactyle affini- 

 ties are indicated by the presence of a third trochanter 

 on the femur ; but in certain peculiarities in the ankle- 

 joint this animal differs from all typical Perissodactyles, 

 and agrees with the Artiodactyles. Moreover, a certain 

 peculiarity of structure in the vertebras of the neck is 

 repeated elsewhere only in the camels and llamas, which 

 form an isolated group of Artiodactyles. In the complete 

 closure of the orbit by bone, Macrauchenia resembles 

 the horses and many Artiodactyles ; but in the narial 

 aperture being situated on the top of the skull between 

 the orbits (whence the nostrils were probably produced 

 in the form of a proboscis), it is absolutely pecuHar. 



There are thus many indications that, while Macrauche- 

 nia is a specialized form that can in no sense be regarded 

 as the ancestral type from which Perissodactyles and 

 Artiodactyles have originated, it retains certain generalized 

 features which were probably directly derived from such 

 ancestral stock. 



Among the Ungulates discovered in Patagonia is 

 one named Proterotheriuni, which was at one time re- 

 ferred to the Artiodactyles, but subsequently placed among 

 the Perissodactyles. In the skull, so far as can be 

 gathered from Ameghino's description, the orbit is closed, 

 as in Macrauchenia, but the narial aperture appears to 

 have had the normal position. The molar teeth are so 

 like those of true Perissodactyles that they were origin- 

 ally described under the name oi Anchitherium ; but the 

 rest of the dentition is very peculiar. Thus, in the upper 

 jaw there appears to have been only a single pair of in- 

 cisors in the premaxillas, these being pyramidal and 

 obliquely truncated like the canines of the pigs ; and as 

 there were no canines, it may be inferred that there was 

 a long toothless interval in the jaw. In the lower jaw 

 there were two pairs of incisors, and no canines. The 

 lower molar teeth were inserted by four distinct roots— a 

 feature unknown in any existing Perissodactyle, although 

 occurring in the pig. In the limbs, both the front and 

 hind feet were furnished with three complete toes, much 

 resembling those of Hipparion; the ankle-joint is, how- 

 ever, said to resemble that of the Artiodactyles. We 

 have no information as to the third trochanter of the 

 femur. On the whole, this genus appears to indicate a 



