Intraspecific facial bite marks in tyrannosaurids provide insight into sexual maturity and evolution of bird-like intersexual display

Intraspecific aggression, or agonism, is a widespread intrasexual selective behavior important to understanding animal behavioral ecology and reproductive systems. Such behavior can be studied either by direct observation or inferred from wound/scar frequency in extant species but is difficult to document in extinct taxa, limiting understanding of its evolution. Among extant archosaurs, crocodylians display extensive intrasexual aggression, whereas birds show extreme visual/vocal intersexual display. The evolutionary origin of this behavioral divergence, and pattern in non-avian dinosaurs, is unknown. Here we document the morphology, frequency, and ontogeny of intraspecific facial bite lesions (324 lesions) in a large sample of tyrannosaurids (202 specimens, 528 elements) to infer patterns of intraspecific aggression in non-avian theropods. Facial scars are consistent in position and orientation across tyrannosaurid species, suggesting bites were inflicted due to repeated/postured behavior. Facial scars are absent in young tyrannosaurids, first appear in immature animals (~50% adult skull length), are present in ~60% of the adult-sized specimens, and show aggressor:victim size isometry. The ontogenetic distribution of bite scars suggests agonistic behavior is associated with the onset of sexual maturity, and scar presence in approximately half the specimens may relate to a sexual pattern. Considered in a phylogenetic context, intraspecific bite marks are consistent and widely distributed in fossil and extant crocodyliforms and non-maniraptoriform theropods, suggesting a potential plesiomorphic behavior in archosaurs. Their absence in maniraptoriform theropods, including birds, may reflect a transition from boney cranial ornamentation and crocodylian-like intrasexual aggression to avian-like intersexual display with the evolution of pennaceous feathers.

Sexual reproduction in the Caribbean coral genusIsophyllia(Scleractinia: Mussidae)

The sexual pattern, reproductive mode, and timing of reproduction ofIsophyllia sinuosaandIsophyllia rigida, two Caribbean Mussids, were assessed by histological analysis of specimens collected monthly during 2000–2001. Both species are simultaneous hermaphroditic brooders characterized by a single annual gametogenetic cycle. Spermatocytes and oocytes of different stages were found to develop within the same mesentery indicating sequential maturation for extended planulation. Oogenesis took place during May through April inI. sinuosaand from August through June inI. rigida. Oocytes began development 7–8 months prior to spermaries but both sexes matured simultaneously. Zooxanthellate planulae were observed inI. sinuosaduring April and inI. rigidafrom June through September. Higher polyp and mesenterial fecundity were found inI. rigidacompared toI. sinuosa. Larger oocyte sizes were found inI. sinuosathan inI. rigida, however larger planula sizes were found inI. rigida. Hermaphroditism is the exclusive sexual pattern within the Mussidae while brooding has been documented within the related generaMussa,ScolymiaandMycetophyllia. This study represents the first description of the sexual characteristics ofI. rigidaand provides an updated description ofI. sinuosa.

Sexual reproduction in the Caribbean coral genus Isophyllia (Scleractinia: Mussidae) in Puerto Rico

The sexual pattern, reproductive mode, and timing of reproduction of Isophyllia sinuosa and Isophyllia rigida, two Caribbean Mussids, were assessed by histological analysis of specimens collected monthly during 2000-2001. Results indicate that both species are simultaneous hermaphroditic brooders, with a single annual gametogenetic cycle. Spermatocytes and oocytes of different stages were found within the same mesentery indicating sequential maturation for extended planulation. Oocytes begin development 7-8 months prior to spermaries; beginning in May in I. sinuosa and August in I. rigida. Gametes of both sexes matured simultaneously; May-June in I. rigida and March-April in I. sinuosa. Planulae were observed in I. sinuosa during April and in I. rigida from June through September. Significantly higher polyp and mesenterial fecundity were found in I. rigida compared to I. sinuosa. Significantly larger oocyte sizes were found in I. sinuosa than in I. rigida, however significantly larger planula sizes were I. rigida compared to I. sinuosa. Hermaphroditism is the exclusive sexual pattern within the Mussidae; brooding has also been documented within the related Mussid genera Mussa, Scolymia and Mycetophyllia. These results represent the first description of the sexual characteristics of I. rigida and refute the previous description for I. sinuosa.

Sexual reproduction in the Caribbean coral genus Isophyllia (Scleractinia: Mussidae) in Puerto Rico

The sexual pattern, reproductive mode, and timing of reproduction of Isophyllia sinuosa and Isophyllia rigida, two Caribbean Mussids, were assessed by histological analysis of specimens collected monthly during 2000-2001. Results indicate that both species are simultaneous hermaphroditic brooders, with a single annual gametogenetic cycle. Spermatocytes and oocytes of different stages were found within the same mesentery indicating sequential maturation for extended planulation. Oocytes begin development 7-8 months prior to spermaries; beginning in May in I. sinuosa and August in I. rigida. Gametes of both sexes matured simultaneously; May-June in I. rigida and March-April in I. sinuosa. Planulae were observed in I. sinuosa during April and in I. rigida from June through September. Significantly higher polyp and mesenterial fecundity were found in I. rigida compared to I. sinuosa. Significantly larger oocyte sizes were found in I. sinuosa than in I. rigida, however significantly larger planula sizes were I. rigida compared to I. sinuosa. Hermaphroditism is the exclusive sexual pattern within the Mussidae; brooding has also been documented within the related Mussid genera Mussa, Scolymia and Mycetophyllia. These results represent the first description of the sexual characteristics of I. rigida and refute the previous description for I. sinuosa.