EXTINCT LEMUROIDEA.
On a former page (anteà, p. 13), attention was drawn to the interrupted distribution of the Lemurs, and to their present restricted range to the tropical and sub-tropical regions of Africa, of Madagascar, and of part of the mainland and of the islands of the Asiatic continent. In times geologically not very remote, they were inhabitants of both worlds.
The earliest appearance of the Primates in time is at the beginning of the Tertiary period. Lemuroids, some of them of a more or less primitive type, then lived in Europe in the Lower Eocene period. In the higher beds of the same epoch (to which the fresh-water deposits of the London clay of England, the Plastic clay of France, and the prolific Wasatch beds of Wyoming, Utah, and Colorado of America belong) undoubted Lemurs are represented by many genera, which in the Middle Eocene attained to a great development.
In the Upper Eocene of Europe many distinctively Lemuroid genera (Adapis, Microchærus, &c.) "formed," as Zittel remarks, "a very characteristic element of the fauna; they are connected with old Tertiary fore-runners, and combine features of the existing Lemurs and true Apes." The presence of these heat-loving animals in such northern latitudes undoubtedly indicates the existence there of a climate more genial at that epoch than now. In the corresponding period in North America remains have been less plentifully found; but for the most part the genera are representatives of those of the European beds.
In strata of Oligocene and older Miocene age no Lemuroid remains have come to light in Europe, and they are represented by only one or two doubtful forms in America. After that date they apparently vanished from the New World and from the northern portions of the Old.
Many of these extinct Lemuroids so combine the characters of the Insectivora and the Ungulata (or hoofed animals), with those of their own Sub-order, that it is often extremely difficult, even impossible, sometimes, to determine to which Order they really belong, owing to a blending of characters due to their common origin. The Upper Eocene forms present many affinities with the South American Capuchin Monkeys (Cebidæ). Dr. Forsyth Major is of opinion, however, that they are more highly, and not (as is generally believed) less specialised than those now living, which appear to have been the subject of retrogressive development.
The species to be noticed below are some of the more important of those which have been ascertained to belong to the present Sub-order.
No remains assignable with certainty to the families Chiromyidæ or Tarsiidæ, have as yet been discovered. The first form to be mentioned belongs to a family which has now no living representatives.
FAMILY MEGALADAPIDÆ.
This family has recently been established by Dr. Forsyth Major, for a fossil species represented by the greater portion of a large cranium and part of its lower jaw, found in a marsh at Amboulisatra, on the south-west coast of Madagascar. This species is the only representative of the single genus of the family.
GENUS MEGALADAPIS.
Megaladapis, Forsyth Major, Phil. Trans., vol. 185 B, p. 15 (1894).
The cranium, about 10 inches long, indicates an aged animal three or four times as long as the common Cat, which is an enormous size as compared with any living Lemur. Brain-case straight, narrow, short, low, and situated at a higher level than the facial region; an enormous lateral development of the region between the eyes; orbits small in diameter, communicating freely with the temporal fossa, protruding outwards and forwards, and surrounded by a thickened ring; facial region elongate and bent upward; palate convex downwards from front to back; ridges for attachment of the temporal muscles uniting in a great central crest; frontal bones constricted behind the orbits; maxillary bones behind the molar teeth greatly inflated by air-cavities; the two halves of the lower jaw ossified together. In the upper jaw the pre-molars have one outer and one inner cusp, and the molars one internal and two external cusps, the former being deeply separated from the hind outer cusp, and joined by a ridge to the front outer cusp. In the lower jaw, the posterior pre-molar has one outer cusp, a fore and hind inner cusp (each joined by a crescent to the outer cusp), and a central inner cusp; the three molars have two outer and three alternating inner cusps, and to the outer side a basal cingulum; the posterior molar has a strongly cusped heel.
Megaladapis madagascariensis, Forsyth Major, the only species of the genus, presents many marsupial and insectivorous characters and features which show some approach towards the South-American Howlers (Alouatta), a specialisation "not in the least," according to Dr. Major, "implying a near relationship, but probably only an adaptation to a corresponding function" implied in the "vocal organs of unusual size," which, he believes, Megaladapis to have possessed. Lemurine characters, however, predominate. In the shape of its molars it is related to Lepidolemur, and still more closely to Microcebus and Chirogale, while by the characters of its inter-orbital region it approaches to the Sifakas (Propithecus) and the extinct Adapis.
The small diameter of its orbits suggests, according to Dr. Major, that in habits this extinct giant Lemur was diurnal; and from the conformation of its lower jaw "there exists," continues the same distinguished investigator, "a strong assumption that, as in Alouatta, it was provided with vocal organs of unusual size."
The age of this Howling Lemur, estimated either geologically or by years, cannot be of very great antiquity. Its remains were found associated with those of the giant Moa-like bird, the Æpyornis, of Tortoises and Hippopotami, all now extinct, and of Crocodiles still living in the interior lakes of the island. Some of these animals were certainly contemporaneous with the now vanished Dodo and the large flightless Rail (Aphanapteryx), both of which were seen alive by Europeans little more than two centuries ago, and it is not improbable that Megaladapis may have been living in the Madagascar forests at the same period.
FAMILY LEMURIDÆ (anteà, p. 22).
In this family, and in its sub-family Lemurinæ (because of its affinities with Hapalemur), has to be included a large extinct species from Nossi Vey, in North-west Madagascar. Its fossil remains were recently described (P. Z. S., 1893, p. 532), but not named by Dr. Forsyth Major. They will prove, he believes, when more fully known, to be the type of a new genus. At present, however, owing to their incomplete state, it is not possible to describe the species fully. "The Lemuroid nature of the specimen is at once demonstrated by the great elevation and downward bending of the post-orbital processes ... showing that the osseous ring of the orbit was complete." Unusual for a Lemuroid is the very strong post-orbital constriction of the frontals, a character, however, seen in Adapis, an Eocene European form, and in Hapalemur. With the latter it agrees in the voluminous cranial and very short facial portion, and the "cuttingly sharp" inferior margin of its post-orbital process. Seen from the side, this fossil cranium is almost vertically truncated behind, as in the skull of Alouatta. The region between the eyes is vaulted by underlying air-chambers.
FAMILY ANAPTOMORPHIDÆ.
This family includes certain fossil forms of Lower Eocene age from the phosphatic deposits of Quercy in France, the Wasatch strata of Wyoming, and the Puerco beds in New Mexico. Their dental formula is the same as that of existing Lemurs, namely I 2(2-1), C 1(1-0), P (2-3)(2-3), M 33. In some of the genera there is a tendency to develop, as Cope has pointed out, large cutting teeth in the position of incisors, "thus approaching the Aye-Aye." The posterior pre-molars are more simple than the anterior true molar, a character which indicates some relationship to the Mouse-Lemurs (Chirogale). The mastoidal or posterior portion of the ear-capsules, and the neighbouring squamosal region of the cranium are swollen, as among the Galagos.
GENUS MICROCHÆRUS.
Microchærus, Wood, Lond. Geol. Journ., i., p. 5 (1846).
Heterohyus, Gerv., Zool. et Pal. Fr., p. 202, pl. 35, fig. 14.
Necrolemur, Filhol, C. R., lxxxvii., p. 1112 (1873); id. Ann. Sc. Geol., viii., p. 55, pl. iv., figs. 213-217 (1877).
This genus is distinguished from all other Lemurs by "the angle of the mandible being produced into a large hook-like flange." (Flower and Lydekker.) The orbits are large, indicating a nocturnal animal; the inter-orbital space is wide, and distinguishes it from Loris. The dental formula is I 21, C 11, P 33, M 33. The canine teeth are not prominent; the anterior lower pre-molar is only slightly developed; a gap separates the anterior and the median upper pre-molars.
This genus is represented by five species. Microchærus antiquus (Filhol) is of very small size, and has many affinities with Galago, as exhibited in the well-preserved cranium that has been recovered from the Phosphorites of Central France. The two lower molars have only one root. M. erinaceus, Wood, from the Upper Eocene of Hampshire; M. edwardsi (Filhol), from Central France, a species larger than M. antiquus, presents dental characters similar to the Galagos and the Mouse-Lemurs; M. parvulus (Filhol), and M. zitteli (Schlosser), are both from the Quercy Phosphorites of France; while M. armatus is from the Eocene of Alsace, and M. (Cryptopithecus) siderolithicus from the Bonerg of Frohnstellen.
GENUS MIXODECTES.
Mixodectes, Cope, Proc. Amer. Phil. Soc., p. 447 (1883); id., Rep. U. S. Geol. Surv., iii., p. 240, pl. xxiv. f, figs. 1 and 2.
The members of this genus, founded on fragmentary mandibles from the Puerco (Lower Eocene) strata of New Mexico, have a large front tooth "issuing from the ramus at the symphysis like a rodent incisor, the second tooth being similar but smaller and posterior and external to the first." The genus is represented by two species, M. pungens, Cope, and M. crassiusculus, Cope.
GENUS CYNODONTOMYS.
Cynodontomys, Cope, Palæont. Bull., p. 151 (1882); id., Rep. U. S. Geol. Surv., iii., p. 243, pl. xxiv., fig. 2.
This genus contains but one species, founded on several lower jaws disinterred from the Wasatch beds in the Big-Horn Bad-lands, in Northern Wyoming. The lower incisors, or perhaps, canines, are very large and close to the line of union of the two halves of the jaw; the molars have three cusps in front and a heel behind. The dental characters of the genus "resemble considerably those of Anaptomorphus and Necrolemur [Microchærus] but the large size of the inferior canine or incisor tooth distinguishes it from both." (Cope.) C. latidens, Cope, is the only species.
GENUS OMOMYS.
Omomys, Leidy, Journ. Acad. Nat. Sci. Philad., vii., p. 408 (1869).
This genus was established for the first Mammalian fossil—a lower jaw—described from the Bridger-beds as O. carteri. The posterior lower molar has cusps in opposing pairs; pre-molars, three in number, the two anterior one-cusped, the posterior two-cusped. The chin was longer and less rounded than in Anaptomorphus.
GENUS ANAPTOMORPHUS.
Anaptomorphus, Cope, Proc. Amer. Phil. Soc., 1872, p. 554; id., Rep. U. S. Geol. Surv., iii., p. 245, pl. xxiv. e, fig. 1; xxv., fig. 10.
This genus was founded by Cope on an almost entire cranium discovered in the Bridger (Eocene) beds of the upper Valley of Green river, and on other remains from what is known as the Wasatch formation of the Big-Horn Basin in Wyoming Territory, in North America. The external upper incisor is small and set close to the small canine; the pre-molars have each a large external and a smaller internal cusp; the true molars are wide and have one internal and two external cusps. In the lower jaw the two anterior molars are four-cusped, with a transverse ridge between the anterior pair, and an oblique ridge between the hind inner, and the front outer, cusp; the posterior is three-cusped and has a heel. The orbits are enclosed, as in typical Lemurs. Not less typical characters are the position of the lachrymal foramen, external to the orbit, and the unossified halves of the lower jaw. "Its dental formula (I 22, C 11, P 22, M 33) agrees only with the Indrisinæ. But no known Lemuridæ possess anterior lobes and cusps on all the pre-molars, so that in this respect, as in the number of its teeth, this genus resembles the higher Monkeys, the Simiidæ and Hominidæ, more than any existing member of the family.... It has ... a number of resemblances to Tarsius, which is, perhaps, its nearest ally among the Lemurs, although that genus has three pre-molars.... There is no doubt but that the genus Anaptomorphus is the most Simian Lemur yet discovered...." (Cope.)
The species included in this genus are A. æmulus (Cope), which did not exceed the size of a Marmoset or a Red Squirrel, and had short erect incisors; A. homunculus (Cope), a species founded on a cranium without a lower jaw, with the orbits not so large as in Tarsius, and the skull wide behind the eyes. "The A. homunculus was nocturnal in its habits," according to Professor Cope, "and its food was like that of the smaller Lemurs of Madagascar and the Malayan islands. Its size is a little less than that of the Tarsius tarsius."
Two other insufficiently characterised genera, both considered to be primitive Lemuroids, are Plesiadapis, Gervais, containing the species P. remensis, P. gervaisi, P. tournesarti, and P. daubrei, from the Lower Eocene strata of Rheims, which have five-cusped lower molars, and enlarged upper and lower incisors; and Protoadapis, Lemoine, with one or two high front cusps, and a low heel to its three pre-molars; the anterior molars with two pairs of opposite cusps, the posterior molar with a fifth cusp on the hind border. P. crassicuspidens, Lemoine, and P. recticuspidens, Lemoine, are its two species.
FAMILY ADAPIDÆ.
The different species associated together under this family are abundantly known from the Upper Eocene of France, England, and North America. They are remarkable in having an extra pre-molar in both jaws, the dental formula being I 22, C 11, P 44, M 33.
GENUS ADAPIS.
Adapis, Cuvier, Ossem. Foss. (2) iii., p. 265 (1822); Flower, Ann. and Mag. N. H., xvii., (1876), p. 323.
Palæolemur, Delfort., Act. de la Soc. Linn. Bord., xxix., pp. 87-95, pl. 5 (1873); id. C. R., lxxvii., p. 64 (1873).
Aphelotherium, Gervais, Zool. et Pal. Franç. (1), ii., Exp. 34 (1848-52).
Cænopithecus, Rütim, Denksch. Schw. Ges. Nat., xix., p. 88 (1862).
Notharctus, Leidy, Geol. Surv. Mont., p. 364 (1871).
? Thinolestes, Marsh, Am. Jour. Sci., 1872 (2), p. 205.
? Telmalestes, Marsh, op. cit., p. 206.
"The general form of the cranium," to quote Sir W. Flower, "the large size and anterior direction of the orbits, the small and narrow muzzle ... show its affinity to the Lemurine animals, and especially to the African forms. The whole skull, however, is more depressed than in the slow Lemurs and Galagos; the orbits are smaller, the brain cavity relatively smaller and more constricted behind the orbits, and the muscular ridges more developed."... The lower jaw is deep and stout. The posterior upper pre-molar is very similar to a true molar. "The upper molar teeth are nearly equal in size, and have nearly square crowns, with four distinct cusps, one at each angle, rather obliquely placed"; the hind inner cusp of the posterior molar inconspicuous. The lower molars have two pairs of obliquely placed cusps, connected by transverse ridges, anterior and posterior, with an oblique ridge running forwards and inwards from the outer hind cusp. The hindmost lower pre-molar has an internal cusp; the lower incisors have upright spatulate crowns like those of true Apes.
Several species of this genus have been described. Adapis Parisiensis (with the synonyms of Aphelotherium duvernoyi, Gervais, and Palæolemur betillei, Delfortrie) is one of the best known, and its remains have been found in Upper Eocene strata at Egerkingen, in Switzerland, at Sainte Néboule de Béduer, and in the Paris Gypsum, in France, as well as in England. It "more nearly resembles the Indo-African Lemurs, and not those of the island of Madagascar, or of the extreme east, having no near relationship with the Tarsius, the Aye-Aye, or the Indris, and not much with the true Lemurs." (Flower.) From the Eocene of Switzerland comes A. lemuroides. Adapis magna (Filhol) is larger than the preceding species, has a larger face, and a greater constriction between the cerebral and facial regions of the skull. It has been found in the phosphatic deposits at Raynal, in France. Adapis angustidens (Filhol), from the Quercy Phosphates of France, is distinguished by the structure of its molars, and by the great size of its two anterior pre-molars. A. tenebrosus (Leidy) has a large lower canine. A. minor (Filhol) is an additional species.
GENUS TOMITHERIUM.
Tomitherium, Cope, Vert. Bridg. Eoc. Wyom., p. 2, 1872.
Limnotherium, Marsh, Am. Journ. Sci., 1871, ii., p. 43 (in part).
This genus, which is allied to Adapis, is characterised by having its lower incisors with cutting edges; the first and second lower pre-molars with one root; the third with one cusp and a posterior heel, and the fourth an interior lateral cusp in addition. The lower true molars have two anterior cusps (the inner being double) and two posterior. The thigh is long and the knee free from the body as in the Anthropoidea, the hand capable of turning freely upwards at the wrist; the hind-limbs longer than the fore-, and "the details of the lower jaw, which is co-ossified in the centre, and teeth similar to that of the lower Monkeys." The remains of the only known species, T. rostratum (Cope), which was about the size of the Capuchin Monkey (Cebus capucinus) of Brazil, were found in the Bridger (Eocene) beds in an isolated spot on Blacks' fork, Wyoming.
GENUS MENOTHERIUM.
Menotherium, Cope, Bull. U. S. Geol. Surv. Territ., 1874, i., p. 22.
Laopithecus, Marsh, Am. Journ. Sei., 1875, i., p. 240.
This genus was established on an under jaw from the Lower Miocene White-river beds of Nebraska. Its molars are successively larger from anterior to posterior; the two pairs of cusps are obliquely opposite, the hinder pair longer than the front pair, and presenting a strong cingulum. Its discovery was the first indication of Lemurs in the Miocene of the United States. M. robustum, Marsh, was as large as a Coati; and M. lemurinum (Cope) about the size of a domestic Cat.
GENUS PELYCODUS.
Pelycodus, Cope, Cat. Verteb. Eoc. New Mex., p. 13 (1875).
Tomitherium, Cope, Rep. U. S. Geol. Surv. W. of 100° mer., ii., p. 135 (in part).
Lemuravus, Marsh, Amer. Journ. Sci., 1875, i., p. 239.
This genus is characterised by the second pre-molar having always two roots; the anterior has one root and the third three; the posterior has one external and one internal cusp. Of the true molars, all have two external cusps; the anterior and median have two internal cusps and the posterior has only one; of the lower teeth the posterior pre-molar has an internal cusp and a heel; the next one has no internal cusp; the molars often have the fore inner cusps double; the posterior molar has a strong heel. This genus contains three species, all described by Cope (P. jarrovii, P. tutus, P. frugivorus), with the hind inner cusp of the upper molars distinct from the heel; and P. angulatus, in which that cusp is small and is on the heel. Their remains have been found in the Lower Eocene (Wasatch) beds of New Mexico. P. helveticus has been described from the Upper Eocene of Egerkingen.
GENUS MICROSYOPS.
Microsyops, Leidy, Proc. Acad. Nat. Sci., Philad., 1872, p. 20.
Limnotherium, Marsh, Amer. Journ. Sci., 1871, ii., p. 43 (in part).
This genus is easily distinguished, as Cope points out in his sumptuously illustrated "Vertebrata of the Tertiary Formations of the West," by the absence of the first (anterior) inferior pre-molar, and probably of the superior first pre-molar also. The canine tooth of the lower jaw is very large. The posterior pre-molar has an internal cusp, and the molars two front inner cusps. There are three species, distinguished chiefly by size, M. spierianus (Cope), very small; M. elegans (Marsh), the largest, with seven teeth succeeding the canine in the lower jaw; and M. scottianus (Cope); all from the Eocene of Wyoming.
GENUS HYOPSODUS.
Hyopsodus, Leidy, Proc. Acad. Nat. Sci., Philad., 1870, p. 109.
The present genus is recognised by the front inner cusp of the lower molars being single, and their heel presenting a cusp at its inner hind angle (except in H. acolytus). Of the upper pre-molars, the median and posterior have an internal cusp; and the molars have two outer and two inner cusps with two small intermediate tubercles. There are six species known, from the Wasatch and Bridger beds of Wyoming and New Mexico, of which H. acolytus is distinguished by having the heel of the anterior and median lower molars without an inner hind cusp. Professor Cope remarks that though the species of this genus are not numerous, individuals of some of them are exceedingly common in the Eocene beds of Wyoming. H. paulus and H. minusculus, Leidy, H. vicarius and H. powellianus, Cope, with H. jurensis, Rutimeyer, from the Upper Eocene of Egerkingen, are the best known species.
The genera Indrodon, Cope, from the Lower Eocene Puerco formation of New Mexico, with three cusped upper and four cusped lower molars; Opisthotomus, Apheliscus, and Sarcolemur, Cope, from the Wasatch of Wyoming; Hipposyus, Leidy; Bathrodon, Mesacodon, and Stenacodon, Marsh, from the Middle Eocene Bridger beds; are of doubtful affinities.