Artiodactyla

“ The number of ribs varies from twelve (Camelus, Hydropotes) through thirteen (Cervus, Gazella) to fourteen in Dicotyles, Giraffa, etc.
The curious form of teeth known as "selenodont" is characteristic of the Artiodactyla, though only found well developed in the modern forms, and of those only in the Pecora. The more primitive forms had "bunodont" teeth with typically four tubercles (if we except the tritubercular and but little-known Pantolestes) ; and the intermediate "buno-selenodont" type characterises such groups as the Anthracotheriidae. ”

“ The only existing Perissodactyla of the western hemisphere are the tapirs (Tapirus) of Central and tropical South America, a very remarkable contrast to the ancient faunas, especially of the northern continent, as will be shown in the sequel. The Artiodactyla are more varied, though very scanty in comparison with those of the Old World; even North America, which has but a poor representation of these animals, is much richer than the southern continent, where, indeed, all the hoofed animals are the descendants of comparatively recent immigrants from the north and none are truly autochthonous. ”

“ Horses of primitive type, the feet having three functional toes instead of one, were relatively abundant. Very large llama-like animals were present, but nothing has been ascertained with regard to the deer and antelopes of the time, and the only other representative of the Artiodactyla yet recovered is a peccary, interesting as being a species of the genus (†Platygonus) which became so abundant and widespread in the Pleistocene. Scanty and incomplete as this fauna is, it suffices to show that the middle Pliocene mammals were much more primitive than those of the Pleistocene. ”

“ The bodies of the cervical vertebrae have flat articular surfaces, the bones of the two rows of the carpus alternate, and in the tarsus the navicular articulates with the calcaneum, which, as in the Artiodactyla, is articulated to the fibula, while the astragalus, which is slightly grooved above, is formed on the Perissodactyle plan. ”

“ Though, as has been pointed out, it is a fact that the hind-feet are often on a different plane of evolution from the fore-feet, it seems that this amount of difference does not characterise any Ungulate, not excepting the genus now under consideration.
The toes are very spreading. The pelvic girdle is of great strength and broadness. The femur, as in the Perissodactyles, has a well-developed third trochanter; but whereas in this particular the hind-limb is Perissodactyle, it is Artiodactyle in the fact that the tibia and the fibula articulate with the astragalus and calcaneum. ”

“ This type of astragalus is altogether peculiar to the artiodactyls, all of which possess it; it is unlike that of any other mammal whatever and may be recognized [360] at a glance. The calcaneum, or heel-bone, has a large convex facet, by means of which it articulates with the fibula, or external leg-bone; there is no such articulation in the perissodactyls. The lower end of the calcaneum is narrow and fits into a step cut in the cuboid, which is thus every whit as peculiar and characteristic as the calcaneum and astragalus. ”

“ The artiodactyls are and for a very long time have been a very much larger and more variegated group than the perissodactyls, and the Old World has been and still is their headquarters and area of special development, where they are represented in far greater number and variety than in the New; the perissodactyls, on the other hand, flourished especially in North America, as was shown in the preceding chapter. ”

“ A somewhat larger species—the Pterodactylus macronyx, or Long-clawed Pterodactyle—was subsequently discovered by the Rev. Dr. Buckland, in the lias formation of Lyme Regis: its wings, when expanded, must have been about four feet from tip to tip. The smallest known species—the Pterodactylus brevirostris, or Short-beaked Pterodactyle—was discovered in the lithographic slate at Solenhofen, Germany, and has been described by Professor Soemmering.
Remains of the largest known kinds of Pterodactyle have been discovered more recently in chalk-pits, at Burham, in Kent. ”

“ Had we to deal only with the still living genera of Artiodactyles, it would be easy to sort them into two groups on the characters of the teeth; for the Pigs and Hippopotamus are provided with tubercular molars; they are bunodont. The Deer, Camels, Oxen, Giraffes, etc., have selenodont molars. Besides, the latter are "Ruminants," and have a more complicated stomach. The existing Chevrotains forbid a more trenchant division, since they are, as will be pointed out in due course, somewhat intermediate in structure; the feet are more Pig-like, and the stomach is not so typically Ruminant. ”

“ The classification of the immense horde of living and extinct genera and species which are referable to the artiodactyls is an extremely difficult problem, which has found no thoroughly satisfactory solution and will not until much more is learned concerning the history of the order and conflicting opinions can be reconciled. ”

“ The forelimbs are always a pair of wings, the fifth digit or “little” finger being enormously elongated for the support of a smooth flying membrane (seen in specimens from the lithographic stone of Bavaria) . The wings are thus constructed on the same plan as those of a bat, but instead of four fingers, only one is elongated to bear the membrane. The hind-limbs are comparatively feeble, and must have been of very little use for walking.
The remains of pterodactyles are found chiefly in marine deposits, so that these reptiles must have frequented the coastlines. ”

“ This may be observed (among other examples) in the Penguin and the Swan. But here the parallel ends. The proximal end in Birds, we have already seen to be hidden by the anchylosed distal row of the carpus, and the distal end though often convex from side to side never presents the trochlear joint of « 56 » the Pterodactyle. Consequently so far as regards the form of the articular ends the resemblance is closer with Reptiles and clawed Mammals than with Birds. In Birds the small metacarpal is usually of similar length with the large one as is the case with Pterodactyles.
FIRST PHALANGE.
Pl. ”

“ The odontoid process of the axis vertebra is somewhat cheese-taster shaped, as in recent Artiodactyles. There are fourteen dorsal vertebrae and a very large number of caudals. The radius and the ulna are completely separated, as are the carpals. There are five digits to the fore-limbs. The fibula is complete and independent. The hind-foot is four-toed. Several species of the genus are known. ”

“ In length the metacarpus resembles that of the Ruminants, in which however it consists of but one bone; while in Pterodactyles there is a separate bone for each of the four fingers; they are closely united together without being blended. In some Pterodactyles the metacarpals of the short fingers are as fine as hairs, so that it is impossible that they should have articular facets on the carpus. In Ornithopterus the metacarpus has some resemblance with that of the bird, but the articulation with the phalanges of the finger for flight is stiff. ”

“ The major problem for students working with the Mexican leptodactylids has not been the separation of Engystomops or Leptodactylus from other genera but the separation and definition of the eleutherodactyline frogs currently placed in three genera, Eleutherodactylus, Syrrhophus, and Tomodactylus. As will be shown in this paper, these are more conveniently placed in four genera. Once a fourth genus is recognized, certain phylogenetic problems disappear and a reasonable zoogeographic interpretation is possible for Middle American leptodactylid distribution. ”

“ The artiodactyls are the even-toed hoofed mammals and include such familiar forms as pigs, camels, deer, goats, sheep, and hippopotamuses. This is a large and varied group of animals, but the basic anatomical structure of the limbs and teeth show well the relationship between the different forms. Artiodactyls are abundant fossils in rocks ranging from Eocene to Pleistocene in age and are common in rocks of this age in Texas. ”

“ But no Pterodactyle has the head of the humerus convex from the radial to the ulnar sides, and the bird is distinctive in having the ulnar crest developed on the inferior side of the head: a faint approximation to a similar development is seen in Crocodile, but there is no trace of such a process in Pterodactyle. The distal end is more Bird-like than Lacertian in form, but is twisted to a greater angle with the proximal end than in birds.
Altogether the bone is distinctive. The points in which it is unlike birds and reptiles are those in which Birds and Lizards resemble each other ”

“ The whole unicellular body consists, therefore, of three concentric spheres, and possesses neither skeleton nor alveoles, nor other differentiated parts. The innumerable fine pseudopodia, which issue from the central capsule through the evenly distributed pores in its membrane, radiate in all directions through the calymma and pass out over its surface. Actissa can, therefore, be directly derived phylogenetically from the simplest skeletonless Heliozoa (Actinophrys, Heterophrys, Actinosphærium, Sphærastrum) . ”

“ Rickettsiaare intracellular symbionts of eukaryotes that are best known for infecting and causing serious diseases in humans and other mammals. All known vertebrate-associated Rickettsiaare vectored by arthropods as part of their life-cycle, and many other Rickettsiaare found exclusively in arthropods with no known secondary host. However, little is known about the biology of these latter strains. Here, we have identified 20 new strains of Rickettsiafrom arthropods, and constructed a multi-gene phylogeny of the entire genus which includes these new strains. ”

“ It is therefore extremely probably that Actissa not only forms the common stem-form of the whole class in a phylogenetic sense, but is also its common ontogenetic or germinal form. Probably in all Radiolaria the Sphærastrum-stage develops immediately into the typical Actissa-stage, by the formation of a firm membrane between the protoplasmic body of the spherical Heliozoan cell and its jelly-veil. Thus arises the characteristic central capsule, which is wanting in the nearly related Heliozoa. ”

“ By mapping host species onto our phylogeny, we are able to make inferences about patterns of host-switching in the genus. It is clear from Figure 1 that Rickettsiabacteria have an extremely diverse host range, occurring in arthropods, vertebrates, plants, amoebas, ciliates, annelids and hydrozoa, and that there have been numerous shifts between these hosts. The earliest shift splits the genus into two major divisions: the hydra and torix groups and all other arthropod Rickettsia. As mentioned, the hydra group are symbionts of protists and undetermined hosts. ”

“ For those Rickettsiathat are vertebrate pathogens but vectored by arthropods, the effects of the bacteria on their arthropod hosts are generally poorly understood [57] .Rickettsia prowazekiiis clearly pathogenic to infected lice, and transmission through humans is essential to the maintenance of the bacteria in arthropod populations. In every other case, human infections are accidental, but transmission through other vertebrates may allow the bacteria to persist in populations. Many of the bacteria that can infect vertebrates are also transmitted vertically by the arthropod host [60] . ”

“ The feet are four-toed, the lateral toes not reaching the ground.
The principal genus is the Eocene and Miocene Caenotherium. Of this genus there were a considerable number of species all European in range, and of small size—not more than a foot or so in length. Their small size is suggestive of the Chevrotains. In the skull the orbital cavity is nearly or quite surrounded by bone, and the tympanic bulla is large and inflated. A common feature of Artiodactyles, a failure of the nasals and maxillae to meet at the side of the face, is to be seen in this ancient forerunner of the Pecora. ”

“ The hollow rods are very thin, either cylindrical or prismatic. As the ascending rods alternate regularly with the corner-spines of the basal ring, we may call the latter perradial, the former interradial. Ehrenberg has distinguished in his genus Dictyocha not less than fifty species, thirty-five living and twenty-five fossil (ten species both living and fossil) . The greater part of these cannot be retained, as they are only slight varieties or abnormalities of single pieces of the skeleton, such as very frequently occur associated with the common regular forms in one and the same individual. ”

“ Definition.—Phacodiscida with simple medullary shell, and with three radial spines on the margin of the disk, placed in the equatorial plane.
The genus Triactiscus exhibits on the margin of the lenticular phacoid shell three radial solid spines, the distance between which is sometimes equal, at other times unequal. Either all the three spines are of equal size and similar form, or one odd arm is smaller than the two paired arms. The triradial form of this genus is repeated in Tripodocyclia among the Coccodiscida, and in Tripodictya among the Porodiscida. ”

“ Within the genus, there have been three major transitions in life history: becoming sex ratio distorters, arthropod vectored vertebrate pathogens and, in one case, an arthropod vectored plant pathogen. Based on current data, infecting plants and parthenogenesis induction in the arthropod host has arisen only once, and male-killing twice. Until the effect of R. belliion vertebrates in the field has been properly defined, we cannot say for sure how many times vertebrate pathogenesis has evolved. ”