development

Supernumerary teeth in Necromys lasiurus (Rodentia, Cricetidae): the first record in Sigmodontinae

There are several kinds of anomalies related to the teeth reported in mammals, and one of them is known as supernumerary teeth and is commonly noticed in the literature, being reported in nearly all orders of mammals. Here, we report the occurrence of supernumerary molars in the sigmodontine rodent Necromys lasiurus, a common and widespread small rodent of tribe Akodontini. In order to assess the patterns of morphometric variation of N. lasiurus in eastern South America, we examined the skulls of 1763 specimens. The supernumerary molars were found in 2 individuals, which represent a frequency of 0.11%. The origin of supernumerary teeth started a long discussion on tooth homology, whether this anomaly is a result of heredity, a mutation or an atavism. Based on the morphologies presented by the extra teeth encountered in N. lasiurus and on the evidences and hypotheses available in the literature, we consider that the presence of these supernumerary molars in one of the studied animals could be considered an atavism, and we also consider the extra molar presented by the other specimen is a malformation, due to some kind of random process occurred in later stages of the development of distal dental germ. To the best of our knowledge, this represents the first record of supernumerary molars in the subfamily Sigmodontinae and one of the few known cases in rodents.

Dentes supranumerários em Necromys lasiurus (Rodentia, Cricetidae): primeiro registro em Sigmodontinae. Diversos tipos de anomalias dentárias já foram descritas para mamíferos e uma delas é conhecida como dente supranumerário, comumente reportada na literatura para quase todas as ordens de mamíferos. No presente trabalho apresentamos a ocorrência de molares extras em Necromys lasiurus, uma espécie de pequeno roedor sigmodontíneo comum e amplamente distribuído, membro da tribo Akodontini. Durante o levantamento de dados para avaliação morfométrica da variação da espécie no leste da América do Sul, foram examinados os crânios de 1763 espécimes. Os dentes supranumerários foram encontrados em dois indivíduos, representando 0.11% da amostra investigada. A ocorrência dos dentes supranumerários há muito tempo levanta questões acerca da homologia dentária, das mutações e dos atavismos que podem estar relacionados à origem desta anomalia. Baseados na morfologia apresentada pelos molares extra numerários de N. lasiurus, nós consideramos que a presença dos mesmos em um dos espécimes é um atavismo, e no outro, trata-se de uma malformação devido a um processo de origem tardia no desenvolvimento das gemas dentárias. Com base em nosso conhecimento de outras espécies e em toda a revisão bibliográfica, a ocorrência dos dentes supranumerários em N. lasiurus trata-se dos primeiros registros da anomalia para a subfamília Sigmodontinae e um dos poucos já registrados para a ordem Rodentia.

Aproximación cualitativa y aspectos funcionales en la ontogenia craneana de Puma concolor (Felidae)

La variación ontogenética en félidos fue abordada principalmente desde la perspectiva de estimación de edades, en base a secuencia de desgaste y reemplazo dentario. Sin embargo, casi ninguna especie ha sido estudiada aún en un contexto morfológico-funcional en relación al cambio de dieta y comportamiento. En este trabajo analizamos la variación ontogenética de Puma concolor, tanto de las estructuras morfológicas como de los tipos y grado de fusión de las suturas, con el fin de relacionar cambios de forma con cambios de hábitos que ocurren durante el crecimiento. Nuestra muestra incluye especímenes de entre menos de 10 días a más de 10 años de edad. Si bien la mayor parte de las estructuras presentes en adultos están ya manifestadas en estadíos juveniles finales, casi todos los cambios tienden al crecimiento y reforzamiento de estas, apuntando al fortalecimiento funcional del cráneo, vía el aumento del área de origen e inserción de musculatura temporal, masetérica y pterigoidea, así como el aumento en volumen de la musculatura cervical. La mayoría de las modificaciones suturales se evidencian antes de alcanzar la dentición definitiva y están asociadas al aumento de la resistencia al estrés mecánico, siendo los cambios más frecuentes la adquisición de la sutura de tipo aserrada y su fusión final. La comparación de los patrones evidenciados en P. concolor con félidos relacionados de menor tamaño (e.g. P. yagouaroundi) resultan pendientes, ya que las diferencias probablemente impliquen patrones de crecimiento distintos, producto de exigencias relacionadas con el tamaño de las presas.

Qualitative approach and function in the cranial ontogeny of Puma concolor (Felidae). The ontogenetic variation in felids was studied mainly from the perspective of age estimation based on the sequence of tooth replacement and wear. However, almost no species has been still analyzed in a morpho-functional frame, relating changes on diet and behavior. In this work, we analyzed the ontogenetic variation of the skull of Puma concolor, both in its morphological structures, as well as in its suture types and stage of fusion, in order to associate changes of shape with changes of habits that occur during the growth. Our sample includes specimens younger than 10 days, to specimens of approximately 10 years old. Although most of the structures present in adults are already observed in terminal young stages, almost all changes point to the functional strengthening of the skull, via the increased area for the origin and insertion of temporal, masseteric, and pterygoid musculature, as well as the enlargement of cervical muscles. Most of the sutural changes occur before reaching the permanent dentition, and are associated to the improvement of the resistance to mechanical stress, being the commonest change the acquisition of serrated suture and its final fusion. The comparison of the patterns observed in P. concolor with related species of lesser body size (e.g., P. yagouaroundi) are pending, since some differences can be associated to different growth pattern, product of different mechanical demands related to the size of preys.

El oso hormiguero, Myrmecophaga tridactyla: crecimiento e independización de una cría

Sara del Valle Jerez, Monique Halloy

El oso hormiguero, Myrmecophaga tridactyla, es uno de los mamíferos más distintivos de la fauna neotropical, siendo una especie amenazada en algunas partes de su distribución. Sin embargo se conoce poco de la relación madre-cría, vínculo fundamental en la sobrevida de esta especie. En este trabajo estudiamos aspectos relacionados a la interacción entre una madre y su cría durante su primer año de vida, en condiciones de semi-cautiverio. Consideramos el crecimiento y desarrollo de la cría, su forma de amamantamiento y su frecuencia, cuidados de la madre a su cría (acicalamiento y transporte), expresiones de juego e independización de la cría. Ambos se encontraban en la Reserva Experimental Horco Molle en el noroeste argentino y tenían acceso a un predio de 20 hectáreas cercadas. Se realizaron más de 600 horas de observación, incluyendo filmaciones de video, desde el nacimiento de la cría hasta el año de edad. Los resultados muestran que la etapa comprendida entre el octavo y noveno mes de vida es crítica. Durante este período se observa que la cría deja de mamar, aumenta el consumo de alimento (acercándose a los niveles de consumo de la madre), la madre deja de transportar a su cría y deja de acicalarla, la madre deja de jugar con su cría aunque esta sigue jugando hasta el undécimo mes (observándose elementos característicos del juego locomotor, con objeto y social) y, finalmente, los niveles de exploración aumentan considerablemente en ambos. Tomados en su conjunto, estos factores indican que el corte aproximado del vínculo madre-cría se iniciaría en el octavo mes para completarse en el noveno. En condiciones naturales es probable que sería en esta época que la cría emprendería paulatinamente su vida solitaria.

The anteater, Myrmecophaga tridactyla: growth and independization of an infant. The anteater, Myrmecophaga tridactyla, is one of the most distinctive mammals of the Neotropical fauna, being a threatened species in some parts of its distribution. Yet, little is known of the relationship between mother and infant, a fundamental bond for the survival of this species. In this paper, we studied aspects related to the interaction between the mother and her infant during its first year of life in semi-captive conditions. We considered the growth and development of the infant, nursing method and frequency, care provided by the mother to her young (grooming and transportation), play behavior, and the independization of the infant. Both lived in the Reserva Experimental Horco Molle in northwestern Argentina and had access to a fenced 20-hectare terrain. We recorded more than 600 hours of observation, including videotaping, starting at the birth of the infant until one year of age. Results show that the period between the eighth and ninth month is critical. During this period, the infant stops nursing, increases food consumption (reaching consumption levels of the mother), the mother stops transporting her infant and stops grooming it, the mother stops playing with her young although it continues to play until its eleventh month (observing characteristic elements of locomotor, object and social play), and, finally, exploration levels increase considerably in both mother and infant. Taken together, these factors indicate that the approximate break in the mother-infant bond would begin during the eighth month to be completed by the ninth month. In natural conditions, it is possible that it would be at about this time that the infant would gradually start its solitary life.