No abstract

The fishes of t'he Order Crossopterygii arc characterized by a unique articulation within the braincase, by which the anterior division of the endocranium may be moved dorso-ventrally with respect to the posterior division. The st.ructure of the skull in both groups of crossopterygian fishes (the fossil Rhipidistia and the fossil and Recent Coelacanthini) is such that 'normal ' operation of the intracranial mc.chanisni involves lateral movements of the cheek region and palate corresponding to the dorso-vent,ral movements of the ethmoid portion of the braincase. The hyomandibular has a function of prime importance in integrating the movcinents of the various skull components relative to each other. There are important differences hetween the characteristic intracranial mechanisms of Rhipidistia and Coelacanthini which may be interpreted in adaptive as well as morphological terms. Analysis of the intracranial kinetics of the Rhipidistia rcveals a trend, in certain lines, for the amount of relative movement between the skull components to be tlrcrpased and this may be used to explain the loss of t,he intracranial joint in t,he Amphibia during their evolution from the Rhipidistia. The functional significance of the intracranial articulation has both a kinetic and a dynamic aspect and while in the Arnphibia the kinetic ability of the skull is almost wholly restricted, the dynamic features of the ancestral condition arc modified and developed as the basal articulation between the palate and endocranium is retained. INTHODUCTIONThe fishes of the Subclass Sarcoptervgii (Ronier, 1955) comprise three groups-the Dipnoi (fossil and Recent lungfishes), the Coelacanthini (including the Recent Latimeria)

Summary 1. Interpretation of structural evolution in a group such as the Sarcopterygii requires consideration of a combination of all possible functions, rather than single functions. 2. The Dipnoi are probably more closely related to the Crossopterygii than to other groups of fishes. The Sarcopterygii are a ‘natural’ group. Certain characters in common between the elasmobranchs and the Dipnoi or Coelacanthini seem to be the result of convergent evolution. 3. Evolution of the skull, in connexion with both respiratory and feeding mechanisms, has resulted in extreme specialization in all Sarcopterygii. The crossopterygian intracranial kinesis has evolved from an earlier mobility between the skull and neck and is adapted for increasing the power of the bite and for enclosing the prey from both above and below, in addition to other factors. Adaptive radiation is seen in the feeding mechanisms of all forms. The evolution of the Amphibia proceeded through elongation of the anterior division of the skull (which is not correlated with any changes in brain morphology) and loss of the kinetic mechanism in this sequence is at least partially associated with improved buccal pumping mechanisms for lung ventilation. 4. Adaptive radiation of the respiratory system in Dipnoi shows a progressive increase in the use of aerial respiration. The aquatic condition seen in Neoceratodus is probably secondary. Comparison of the three living genera shows a striking correlation between respiratory physiology and habit. There is little indication of reduction of the branchial respiratory system in known Rhipidistia, in which respiration was probably primarily aquatic. In Dipnoi and Rhipidistia, evolution of the lung allowed a partial control of the hydrostatic properties of the body. In coelacanths, aerial respiration was abandoned, except in certain secondarily freshwater forms, and the single lung is modified as an organ of hydrostatic balance. These changes are reflected in the over‐all body proportions. 5. Locomotion in Sarcopterygii (except the coelacanths Laugia and Piveteauia) is adapted for contact with the substrate in relatively shallow water in most cases. Adaptive radiation of the locomotor apparatus is seen with respect to the relative roles and functions of the paired and unpaired fins, over‐all body shape, caudal fin shape, and absolute size. An important function of the pectoral fins in advanced Rhipidistia was in supporting the body in shallow water and thus aiding lung ventilation. 6. Aestivation is an early feature of dipnoan biology, but was not evolved in Rhipidistia. The common faculty of urea production via the ornithine cycle and urea retention in coelacanths and dipnoans are adaptations to conditions in which the body tissues may become dehydrated (salt water and desiccation, respectively). The common pattern of nitrogen metabolism seems to have evolved during a marine phase in sarcopterygian evolution. 7. There is evidence that the earliest members of all sarcopterygian lines included marine forms. However, the sub...

An early tetrapod fossil from the Upper Devonian of Pennsylvania (Catskill Formation) extends the temporal range of tetrapods in North America and suggests that they attained a virtually global equatorial distribution by the end of the Devonian. Derived features of the shoulder girdle indicate that appendicular mechanisms of support and propulsion were well developed even in the earliest phases of tetrapod history. The specialized morphology of the pectoral skeleton implies that the diversity of early tetrapods was great and is suggestive of innovative locomotor patterns in the first tetrapods.

The hyomandibular of Eusthenopteron foordi Whiteaves is briefly described and an attempt is made to reconcile discrepancies between previous accounts. The course of the branches of the truncus hyoideo‐mandibularis (facial nerve VII) is discussed. The early evolution of the tetrapod stapes is considered in connection with the uncoupling of the head from the trunk and subsequent reduction in size ot the semicircular canals. The principal morphological character which distinguishes the stapes from the hyomandibular is found to be related to the course of the orbital (stapedial) artery and the truncus hyoideo‐mandibularis.

SynopsisThe Lower Carboniferous genus Prosagenodus Romer and Smith 1934 is re-examined. The type species Prosagenodus interruptus is re-assigned to the genus Ctenodus and a new genus Tranodis named for the American species, of which new material is described. The new species Ctenodus romeri is described, the new genus Straitonia is described, and the bearings of all these discoveries upon consideration of the phylogenies of Ctenodus and Sagenodus is discussed.

Living lungfish (Osteichthyes: Dipnoi) are known to have a very large cell size and unusually large quantitites of DNA per cell (up to 40 times the mammalian content). The pattern of evolution of cell size in fossil Dipnoi has been examined in order to see what light i t might possibly shed on the question of the origin and evolutionary significance of DNA multiplication in Dipnoi. In the Devonian, cell size was low and it increased only in the Carboniferous when the major dipnoan morphological and taxonomic diversifications were ebbing. If it can be shown that there is a functional relationship between cell size and DNA content, then the data suggest that increase in cellular DNA content have a retarding rather than stimulating effect on dip noan evolution. Since large cell size and (by inference) high cellular DNA content are not a primary feature of the dipnoan stock, i t is suggested that in those other vertebrates, such as certain amphibians, which show the same phenomenon, it is also a secondary feature. 363 J. EXP. ZOOL., 180: 363-372.

New data on the distribution of fossil fish together with floral and tetrapod evidence are used to develop an internal correlation of the strata of the early Mesozoic Newark Supergroup of eastern North America. Within the Newark, we recognize five informal biostratigraphic zones, each characterized by a particular fish fauna. These fish zones are then related to other Mesozoic freshwater deposits, augmented by palynologic and tetrapod data, to the European type area, and to important Early Mesozoic terrestrial sequences elsewhere. T h e oldest fish zones are the Dictyopyge zone found in the Middle Carnian age rocks of the Richmond, Taylorsville, and Scottsburg Basins and the Middle and Late Carnian Diplurns newarki zone represented in the-ham group, Dan River Group, Gettysburg Basin, and Newark Basin. These two zones correlate with the Chinle Formation and the Dockum Group of the southwestern United States as well as the Middle and Late Carnian rocks of the German basin. *The three youngest zones, early Jurassic in age, are characterized primarily by species groups of the holostean Semionotus. Fishes of the "Semionotus tenuiceps group" zone are known from the Hettangian Feltville and Towaco Formations of the Newark Basin and the Turners Falls Sandstone of the Deerfield Basin. T h e "Semionotus micropterus group" zone is found in the Late Hettangian-Early Sinemurian rocks of the Shuttle Meadow and East Berlin Formations of the Hartford Basin and the "Midland fish bed" of the Culpeper Basin. Youngest of these semionotid zones is the Sinemurian "Semionotus elegans group" representatives of which occur in the Sinemurian Portland Formation of the Hartford Basin and the Boonton Formation of the Newark Basin. Correlation by these fish zones suggests that all the coal-bearing Newark rocks are divisible into an older and younger sequence both dated palynologically (by others) as Middle Carnian. Further, while the time span over which extrusive basalts were deposited is limited to the Hettangian and Sinemurian of the Early Jurassic, the individual basalt flow formations are not correlative among basins in a simple one to one manner according to the biostratigraphic data. With respect to the rest of the world, the "Semionotus tenuiceps group," "S. micropterus group," and the "S. elegans group" zones correlate with the European Early Jurassic, the Glen Canyon Group of the southwestern United States, the upper- .