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doi: 10.1002/(SICI)1097-4687(199910)242:1<1::AID-JMOR2>3.0.CO;2-9pmid: 10493780
The morphology of 16 occipital spines of the xenacanthid Orthacanthus from Upper Carboniferous deposits of Robinson (Kansas, USA), Nýřan (Czech Republic) and Puertollano (Spain) is described. The nonreplaced spines reveal the growth pattern of the shark. Moreover, the relationship between growth and paleoenvironmental conditions can be used to determine paleoecological conditions. Both external and internal morphology indicate that the spine was superficially inserted in the skin. During growth, the spine moved from a deep position in the dermis, in which trabecular dentine is formed, to a more superficial location in which centrifugally growing lamellar dentine was formed. Centripetally growing lamellar dentine was deposited more slowly than the centrifugally growing dentine; it obliterated the pulp cavity. The denticles are independent dermal elements formed by a dermal papilla and secondarily attached by dentine to the spine proper. The number of denticles per annual cycle and the density of denticulation vary with the growth rate. Moreover, the ratio of length of denticulated region to total length of the spine changes throughout ontogeny. In consequence, those features cannot be used for systematic purposes without a careful analysis of the variability. Centrifugally growing lamellar dentine in spines from Robinson shows a regular alternation of layers, suggesting tidal conditions in the environment in which the sharks lived. Monthly and seasonal cycles also occur. Tidal (lunar) cyclicity is also observed in the denticles: size and distance between denticles increase and decrease gradually, forming waves that are considered seasonal and yearly cycles. The observed regularity could be related to the variation in calcium phosphate deposition following the cyclical changes in water temperature produced in the tidal zone. Monthly and seasonal cycles are the result of the interaction of the solar and tidal (lunar) cycles. The cyclical pattern of growth is used to determine the age and growth rates. Orthacanthus was a fast‐growing shark like the Recent sharks Isurus, Mustelus, and Negaprion. J. Morphol. 242:1–45, 1999. © 1999 Wiley‐Liss, Inc.
doi: 10.1002/(SICI)1097-4687(199910)242:1<47::AID-JMOR3>3.0.CO;2-Bpmid: 10493781
The acrosome of Platycleis albopunctata (Orthoptera: Tettigoniidae) is relatively large and complex, consisting of an apical vesicle and two large wing‐like extensions that give the spermatozoon the shape of an arrow. The wings have actin microfilaments and microtubules and are covered with a noticeable extracellular material. Actin filaments are present in the acrosome when it first appears in spermatid stages. The acrosome and the acrosomal attachment to the nucleus are more resistant than other structures to the reducing agents DTT and SDS. At the end of spermiogenesis, groups of spermatozoa juxtapose their sperm heads and become joined to form a spermatodesm encircled by an amorphous material. Treatment with the ionophore A23187 rapidly disrupted acrosomes of the free gametes, but acrosomes from spermatozoa contained in the spermatodesm were not disassembled. Packaging of sperm in a spermatodesm appears to protect the acrosome. J. Morphol. 242:47–56, 1999. © 1999 Wiley‐Liss, Inc.
doi: 10.1002/(SICI)1097-4687(199910)242:1<57::AID-JMOR4>3.0.CO;2-5pmid: 10493782
Most studies of sexual dimorphism in mammals focus on overall body size. However, relatively little is known about the differences in growth trajectories that produce dimorphism in organ and muscle size. We weighed six organs and four muscles in Rattus norvegicus to determine what heterochronic and allometric scaling differences exist between the sexes. This cross‐sectional growth study included 113 males and 109 females with ages ranging from birth to 200 days of age. All muscle and organ weights were ultimately greater in males than in females, because males grew for a longer period of time, had a greater maximum rate of growth, and spent more time near the maximum rate. No ontogenetic scaling differences existed between the sexes in organ weight except for lungs and gonads. During growth, organ weights were negatively allometric to body weight. No scaling differences relative to body weight existed between the sexes for muscles; however, there was variation in the allometric relations among muscles relative to body weight. Sexual dimorphism in muscles and organs appears to be a size difference resulting from differences in the duration and rates of growth. J. Morphol. 242:57–66, 1999. © 1999 Wiley‐Liss, Inc.
doi: 10.1002/(SICI)1097-4687(199910)242:1<67::AID-JMOR5>3.0.CO;2-#pmid: 10493783
The laryngeal apparatus of Caperea marginata is described for the first time and proves to be significantly different from that of any mysticete previously described. This difference is especially noticeable in the position of the laryngeal sac, which is separate from the tracheal rings and lies to the right of the animal. Massive ontogenetic development of the sac in adult males is demonstrated, far greater than that seen in most other mysticetes. Histological analysis of the laryngeal sac shows the walls to be very muscular, abundantly innervated, and vascularized, indicating an active organ. Coiled blood vessels and nerves support the hypothesis that the sac undergoes extensive expansion and contraction. A possible association with the unique thoracic development of the species is suggested. The roles of the laryngeal sac and arytenoid cartilages in mysticete sound production are also discussed. J. Morphol. 242:67–81, 1999. © 1999 Wiley‐Liss, Inc.
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