Modern Reptiles Research Articles

Apatosaurus as a Means of Understanding Dinosaur Respiration

Dinosaur activity has been the object of speculation since the first skeletal reconstructions were completed in the last century. Charles Knight, the famous artist, painted dinosaurs as active agile animals whereas researchers later portrayed them as slow moving and clumsy due to some similarities with modern reptiles. Modern research leans toward an active lifestyle for such enormous animals. This implies that dinosaurs needed a lot of oxygen to supply the necessary energy for these activities, but is it possible to estimate just how much this really was? Modern investigations confirm that the ability to supply oxygen to active tissues such as muscle is the factor most likely to set the limits of performance.

Thoroughly Modern Reptiles

Thoroughly Modern Reptiles

Japanese Support of U.S. Research

Japanese Support of U.S. Research

Thoroughly Modern Reptiles

Thoroughly Modern Reptiles

Herpetofauna of the Ipswichian Interglacial Bed (Late Pleistocene) of the Itteringham Gravel Pit, Norfolk, England

-At least four species of anurans, one tortoise and one snake were identified from the Ipswichian interglacial bed (Late Pleistocene) of the Itteringham Gravel Pit, Norfolk, England. A tree frog (Hyla sp.) is reported for the first time as a British fossil. The herpetofauna indicates that the major habitat was a lentic one. The occurrence of the tree frog (Hyla sp.), continental water frogs (Rana), and the European pond tortoise (Emys orbicularis) indicates a continental climate with warmer summers than occur in England today. The mammalian fauna of the British Pleistocene has been well-studied (Stuart, 1982), but the British Pleistocene herpetofauna has been largely neglected until recently. These recent works include reports of the European pond tortoise from interglacial sites (Stuart, 1979, 1982), and short herpetofaunal papers on Cromerian (Holman, 1987c; Holman et al., 1988), Hoxnian (Holman, 1987a), Ipswichian (Holman, 1987b), Devensian/Flandrian (Holman, 1988) and Flandrian (Holman, 1985, 1987a) localities. Studies of fossil herpetofaunas are important in making paleoecological interpretations, for modern amphibians and reptiles have specific ecological requirements and most Pleistocene species have modern equivalents that have been well-studied in Britain and on the continent. Moreover, certain species may be particularly important in indicating specific environmental conditions because of stringent climatic reproductive constraints (Stuart, 1979). The Ipswichian Interglacial Stage.-Except for the Flandrian, the Ipswichian is the best known of the British interglacials. The Ipswichian (ca. 120,000-110,000 years before present) occurs between the cold glacial times of the older Wolstonian stage and the younger Devensian stage. Stuart (1982) provides a general discussion of the most important Ipswichian sites and their vertebrate fauna. The presence of fossils of the African hippo (Hippopotamus amphibius) is generally accepted as diagnostic of the Ipswichian. Some other mammals which no longer are native to Britain but do appear in the Ipswichian are the horse (Equus ferus), spotted hyena (Crocuta crocuta) and the lion (Panthera leo). The Ipswichian has also yielded the European pond tortoise (Emys orbicularis) from many of its sites. The type site of the Ipswichian is Bobbitshole, Ipswich, England. The Itteringham Deposit.-The Itteringham Gravel Pit (National Grid Reference 139305) is located beside the River Bure in the parish of Oulton, 6 km west of Aylsham, Norfolk, England. Deposits belonging to four distinct climatic stages have been identified. The uppermost valley deposits (mostly peat) belong to the present (Flandrian) interglacial. Beneath these are gravels and clays with fossil and sedimentary indications of intense cold and these are assigned to the last (Devensian) glacial. Stratigraphically lower are detrital muds and organic sands which are fully interglacial in character. 33 This content downloaded from 207.46.13.167 on Thu, 21 Jul 2016 05:09:32 UTC All use subject to http://about.jstor.org/terms L. A. HALLOCK ET AL.

The pachypleurosaurids (Reptilia: Nothosauria) from the middle triassic of Monte San Giorgio (Switzerland) with the description of a new species.

The largest and most diverse collection of Pachypleurosauridae (Nothosauria, Reptilia) comes from Monte San Giorgio, Switzerland. Several hundred complete skeletons were collected from four distinct horizons of bituminous limestones and shales of Anisian-Ladinian boundary to early Ladinian age (Middle Triassic). Serpianosaurus mirigiolensis comes from the oldest strata, the Grenzbitumenzone Beds. The three younger strata, all in the Lower Meride Limestone, yield three species of Neusticosaurus. Neusticosaurus pusillus comes from the Cava Inferiore horizon, Neusticosaurus peyeri, new species, from the Cava Superiore horizon, and Neusticosaurus edwardsii, new combination, from the Alla Cascina horizon. Neusticosaurus pusillus is biostratigraphically important because it is one of the rare species reported from both the Germanic and the Alpine Triassic. Neusticosaurus pusillus and N. peyeri are small and very similar in their anatomy. Neusticosaurus species are easiest separated by their number of presacral vertebrae. Ornamentation of the bone surface is distinctive for all four pachypleurosaurids. Soft parts are rarely preserved, except for one partial squamation. The biological age of Neusticosaurus individuals can be determined by skeletochronology (aging by bone annuli). Small species of Neusticosaurus were sexually mature after three to four years and lived for six to nine years. Taphonomic analysis of the small species indicates attritional mortality and suggests weak bottom currents in the Monte San Giorgio basin during early Ladinian times. Morphometric comparison of all four pachypleurosaurids indicates that the changing vertebral numbers between species are largely due to a change in number of segments. All Monte San Giorgio pachypleurosaurids are sexually dimorphic in forelimb development. Sex x has poorly differentiated and relatively short humeri whereas sex y has well differentiated and relatively long humeri. The sexes are of about the same size and represented in roughly equal numbers. Identification of gender was not possible. Good growth series, especially of Neusticosaurus peyeri, from embryo to large adult permitted qualitative and quantitative study of ontogeny. The skull grows with negative allometry; the humerus grows isometrically or with positive allometry, depending on sex and species; the femur grows isometrically. The adult size range in N. peyeri is considerably larger than in modern reptiles. The Monte San Giorgio pachypleurosaurids are a monophyletic group. The phylogeny of this group is congruent with the stratigraphic distribution of its members.

A fossil reptile embryo from the Middle Triassic of the Alps.

The first nothosaur (Neusticosaurus sp.) embryo, one of the very few fossil embryos known, provides a rare glimpse at reproduction in extinct reptiles. The specimen from the southern Alpine Middle Triassic (about 230 million years ago) was recognized as an embryo in comparison with an exceptionally large and well-understood sample of juvenile and sexed adult Neusticosaurus sp. The skeleton shows many embryonic features and may well be the smallest fossil reptile known (body length 51 millimeters). It reached only 22% of mean adult length whereas modern reptiles of this size do not hatch before they reach about 30% of mean adult length. The question of ovipary versus vivipary in pachypleurosaurs is discussed in light of the embryo.

Somatostatin and neuropeptide Y are almost exclusively found in the same neurons in the telencephalon of turtles

In mammals, somatostatin and neuropeptide Y (NPY) are largely found in the same neurons of the telencephalon. To determine if this is a phylogenetically ancient feature of telencephalic organization, the brain of red-eared turtles was examined using immunofluorescence double-labeling procedures. The results showed that somatostatin and NPY are found almost exclusively in the same neurons in the telencephalon of turtles, but these neuropeptides rarely co-occur in neurons outside the telencephalon. Thus, the extensive co-occurrence of NPY and somatostatin appears to be a feature of telencephalic organization that was present in the reptilian common ancestors of mammals and modern reptiles.

Jaw growth and tooth replacement inCaptorhinus aguti(Reptilia: Captorhinomorpha): a morphological and histological analysis

ABSTRACT We here report the results of a primarily histological study of jaw growth and tooth replacement in the Early Permian captorhinomorph reptile Captorhinus aguti. Preliminary histological examination shows that “drift” of teeth from the lingual to the labial side of the jaw apparently occurred through a combination of bone growth + remodelling. Simple graphical analysis of proportional changes in the C. aguti skull and jaws over a threefold span of size increase demonstrates that growth was essentially isometric. This fact and our preliminary histological observations are combined into a model of jaw growth plus tooth replacement, in which the positions and relative ages of teeth are described in terms of the Zahnreihen of Edmund (1960). Detailed histological observations are then used to test the model, which is confirmed in all essentials but shown to be incomplete as first formulated. With incorporation of the fact that during growth the older, smaller parts of the dentary and maxilla were progressively relocated anteriorly, our Zahnreihen-based model appears to be an accurate representation of tooth replacement in C. aguti. The C. aguti replacement system may have been derived with little change from that of single-rowed ancestors. It is uncertain whether this is true also of later multiple-rowed captorhinids. The exact mechanism of tooth loss in C. aguti and in modern reptiles, including control of timing, is uncertain.

Elaborate CNS cooling structures in large dinosaurs.

DURING sustained activity, or when exposed to high ambient temperatures, terrestrial animals often experience periods of core hyperthermia. The central nervous system (CNS) is very sensitive to elevated temperatures1–3, and consequently, both bradymetabolic and tachymetabolic4 terrestrial vertebrates have evolved physiological mechanisms which effect localised cooling of the brain, and thereby reduce any thermal impairment of CNS functioning. In modern reptiles this temperature gradient is produced by evaporative cooling from the buccal cavity and upper respiratory tract5,6, conducting heat from the brain through the floor of the cranium7. Mammals dissipate heat, by evaporation, from the nasal mucosa to the air flowing through the nasal passages. The cooled venous blood draining from this highly vascularised mucosa flows into the cavernous sinus, where counter-current heat exchange with the carotid arteries, elaborated into a rete in many forms, results in brain cooling8,9 (Fig. 1a). Dinosaurs would have experienced similar thermal problems to those of modern vertebrates, and these would have been particularly acute in the larger forms whose low surface area to volume ratio would have restricted dissipation of the enormous amounts of heat generated by the skeletal muscles during activity. It is therefore proposed that they required and possessed comparable physiological mechanisms to protect the brain during core hyperthermia.

Speculations on the growth rate and reproduction of some dinosaurs

If the dinosaurs Protoceratops grangeri and Hypselosaurus sp. grew at rates predicted for their body size from extant reptiles, their expected ages at reproductive maturity would be about 20 and 62 yr respectively. This calculation assumes that dinosaurs grew at ectothermic rates which are about an order of magnitude slower than those of endothermic vertebrates of the same body size. Such delayed reproductive maturity may have set a premium on selection for high juvenile survivorship that is reflected in the relatively large eggs of these dinosaurs and in their only moderately large clutch sizes compared to modern reptiles.

The Evolution of Reptilian Social Behavior

Reptiles display a diversity of behavior that is reflective of their evolutionary heritage from fish and amphibians and their ancestral contribution to the diversity found in birds and mammals. Much of the behavior observed in reptiles seems specific to the ecological setting within which they live. As a result, a diversity of behavior is found in each of the groups of modern reptiles. Recent studies on the social behavior of lizards have proved them capable of a variety of behavioral postures, sequences, and sociality that exceeds that found in some mammals and birds. While many species of lizards are territorial, others are hierarchial and some have harems. For all those territorial species studied, crowding results in increased social interaction, increased aggression, and a switch to hierarchial behavior. While smell and sound may be important stimuli for social behavior in some reptiles, posture, actions, and especially color appear to be most important in diurnal lizards. Temperature and energy studies suggest that the large extinct dinosaurs probably fought considerably less than commonly portrayed in movies and stories, but were also probably much more brightly colored than commonly shown in reconstructions.

Pathological epipodials and tarsus in Stretosaurus macromerus from the Kimmeridge Clay, Stretham, Cambridgeshire

T he specimen discussed here (P1. 13a) is the left hind limb of a Stretosaurus macromerus (Phillips) which is now in the Sedgwick Museum, Cambridge, England (No. J.35, 990C–0). It has been described by Tarlo (1959, p. 51 and p1. ix, fig. 1; 1960, pp. 161–3, fig. 8). The specimen shows (Pl. 13b) extensive pathological changes that affect the tibia, tibiale, intermedium, first distal tarsal, and the (fused) second and third distal tarsal. The fibula and fibula are may also be slightly affected. The lesion appears chiefly to consist of an erosion of the distal surfaces of these bones together with a proliferative reaction on the margins of the eroded areas. Since the ‘clinical’ course of disease has never been observable in Stretosaurus we cannot with any confidence affirm that the final lesion results from any well-recognized succession of pathological changes. We cannot even observe morbid processes in modern reptiles and assume that their precursors, living under Jurassic conditions 150 million years ago, responded to adverse stimuli in an identical fashion. A considerable body of evidence suggests that pathological changes then closely resembled those of today but it is probable that significant nuances of difference elude our detection. This being so the study of an archaic lesion reduces us to a search for apparent resemblances, a groping for analogies, among recent forms of disease. We inevitably interpret this specimen in the light of what we know about osseous pathology. A glance at P1. 13b, however, shows that it is

THE PELYCOSAUR TYMPANUM AND EARLY EVOLUTION OF THE MIDDLE EAR

Two groups of primitive reptiles of early Permian age, the Pelycosauria and Captorhinomorpha, are characterized in part by a massive, firmly attached stapes, and by a flat or slightly convex posterior skull margin. The characteristics of the middle ear region contrast strongly with conditions in modern reptiles, in which the stapes is very slender, and the concave posterior margin of the skull supports a superficial tympanum that functions in detection of air-borne sound. The middle ear region of the fossil amphibians, ancestors of reptiles, also probably ftunctioned to detect air-borne sound by means of a tympanum, which presumably was housed in the otic notch on the dorso-posterior margin of the skull. The tympanum resembled that of moderi. reptiles in its superficial position, but the stapes was primitively more massive and more firmly attached. The peculiarities of the pelycosaur middle ear have led to conflicting interpretations of its function and of its position in the general evolution of the tetrapod ear. A radical approach to the matter is that of Tumarkin (1955), who denies that the pelycosaurs and captorhinomorphs were sensitive to air-borne sounds. Watson (1948 et seq.), while he accepts the probability that these forms had a middle ear cavity and could hear, believes that the tympanum was lost upon closure of the otic notch. A crucial question in the functional interpretation of the pelycosaur middle ear is the size of membrane necessary to actuate a stapes as massive as that found in some fossil forms. The experimental part of the present study is an attempt to provide an answer to this aspect of the problem. Another difficulty in interpreting the pelycosaur middle ear is placement of a tympanum. Watson's claim that a tympanum could not have been supported superficially on the back of the pelycosaur skull is countered by Romer and Price (1940), who suggest simply that it was placed in a deep position, where it lay behind the quadrate and terminal to the stapes as it does in modern reptiles. Morphological relationships of the pelycosaur stapes suggest a different mode of tympanum support, which is elucidated in the body of this paper. The course of early evolution of the tetrapod middle ear is interpreted in the light of function and support of the tympanum in the pelycosaurs.

II.—The so-called Coprolites of Ichthyosaurians and Labyrinthodonts

It appears to be still generally supposed that the Ichthyosaurians differed from all modern reptiles in having a short intestine with a spiral valve, like that of the more generalized fishes; and the supposition is rendered all the more plausible by the common belief that some at least of the Labyrinthodonts were similarly characterized. In each case, it is true, coprolites or masses of partially digested food, marked with the line of an intestinal spiral valve, are often found in the same strata as the skeletons; but, so far as I have been able to discover, no instance is known in which the spirally-marked coprolite actually occurs in its natural position in the fossilized animal.

XXIX.—On the Development and Morphology of the Marsupial Shoulder Girdle

The various structures in the marsupial shoulder girdle are so unquestionably homologous with similar structures in the girdle of the human subject and of the Eutheria generally, that there has never been any difficulty in interpreting the parts in terms of human anatomy; but when the elements are compared with those in what we may consider to have been the ancestral condition, such as is exemplified in the shoulder girdle of the Monotremes, or of the Anomodonts, or in the more distantly related conditions met with in modern Reptiles and Amphibians, we are confronted with quite a number of difficulties, to which the most varied solutions have been applied by different morphologists. The chief difficulty in the way of comparing the typical mammalian girdle with that of the lower forms, is that in the girdle of the higher mammals certain structures are rudimentary, and, further, that the forms that have hitherto been examined have been so far removed from the ancestral stock that even a study of the early developmental conditions fails to give any clues that are more satisfactory than those afforded by comparative anatomy. Though it has been suspected that further results would be obtained from the study of the early condition in Marsupials and Monotremes, the embryos of these groups that have hitherto been studied have been too old to yield much further evidence than that obtained by a study of the adult forms.

VIII. On the vertebral characters of the order pterosauria, as exemplified in the genera pterodactylus (cuvier) and dimorphodon (Owen)

Although the skeletons of the extinct Flying Saurians of the mezozoic strata have been discovered in a more complete condition than those of any other contemporary Reptiles, they have not, hitherto, owing to the delicate texture and commonly crushed state of the bones, afforded satisfactory observations of the structure of the vertebræ. Yet the vertebral characters of a saurian skeleton are of peculiar interest to the Palæontologist and Comparative Anatomist, on account of the many and strongly-marked differences which they present in the extinct members of the Reptilian class. In the existing species, the articular terminal surfaces of the centrum, with the exception of those of the Geckos, Rhynchocephalus, and of some single vertebrae in the column of other Reptiles, are concave in front and convex behind. But in extinct Reptiles some genera ( Streptosndylus ) show reverse positions of the cup and ball; others ( Ichthyosaurus ) show both surfaces concave; others show both surfaces slightly concave ( Teleosaurus ); others show both surfaces flat (some Plesiosauri ); others are subconcave behind and flat before ( Cetiosaurus ); with many minor modifications. It is only on arriving at the uppermost of the mezozoic series of rocks in an ascending survey, that we find Lacertian genera ( Mosasaurus and Leiodon of the Chalk) and crocodilians ( Crocodilus basifissus , from the Greensand of New Jersey) presenting the procœlian || type of vertebra which prevails in tertiary and modern reptiles.