Limits...
Transition of Eocene whales from land to sea: evidence from bone microstructure.

Houssaye A, Tafforeau P, de Muizon C, Gingerich PD - PLoS ONE (2015)

Bottom Line: Conversely, hind-limbs in basilosaurids became strongly reduced with no involvement in locomotion but display strong osteosclerosis in the femora.Our study confirms that Remingtonocetidae and Protocetidae were almost exclusively aquatic in locomotion for the taxa sampled, which probably were shallow water suspended swimmers.Basilosaurids display osseous specializations similar to those of modern cetaceans and are considered more active open-sea swimmers.

View Article: PubMed Central - PubMed

Affiliation: UMR 7179 CNRS/Muséum National d'Histoire Naturelle, Département Ecologie et Gestion de la Biodiversité, Paris, France; Steinmann Institut für Geologie, Paläontologie und Mineralogie, Universität Bonn, Bonn, Germany.

ABSTRACT
Cetacea are secondarily aquatic amniotes that underwent their land-to-sea transition during the Eocene. Primitive forms, called archaeocetes, include five families with distinct degrees of adaptation to an aquatic life, swimming mode and abilities that remain difficult to estimate. The lifestyle of early cetaceans is investigated by analysis of microanatomical features in postcranial elements of archaeocetes. We document the internal structure of long bones, ribs and vertebrae in fifteen specimens belonging to the three more derived archaeocete families--Remingtonocetidae, Protocetidae, and Basilosauridae--using microtomography and virtual thin-sectioning. This enables us to discuss the osseous specializations observed in these taxa and to comment on their possible swimming behavior. All these taxa display bone mass increase (BMI) in their ribs, which lack an open medullary cavity, and in their femora, whereas their vertebrae are essentially spongious. Humeri and femora show opposite trends in microanatomical specialization in the progressive independence of cetaceans from a terrestrial environment. Humeri change from very compact to spongious, which is in accordance with the progressive loss of propulsive role for the forelimbs, which were used instead for steering and stabilizing. Conversely, hind-limbs in basilosaurids became strongly reduced with no involvement in locomotion but display strong osteosclerosis in the femora. Our study confirms that Remingtonocetidae and Protocetidae were almost exclusively aquatic in locomotion for the taxa sampled, which probably were shallow water suspended swimmers. Basilosaurids display osseous specializations similar to those of modern cetaceans and are considered more active open-sea swimmers. This study highlights the strong need for homologous sections in comparative microanatomical studies, and the importance of combining information from several bones of the same taxon for improved functional interpretation.

Show MeSH

Related in: MedlinePlus

Phylogenetic relationships of early cetaceans showing the temporal ranges and general relationships of Pakicetidae, Ambulocetidae, Remingtonocetidae, Protocetidae, and Basilosauridae discussed here.Modified from [75,76].
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4340927&req=5

pone.0118409.g001: Phylogenetic relationships of early cetaceans showing the temporal ranges and general relationships of Pakicetidae, Ambulocetidae, Remingtonocetidae, Protocetidae, and Basilosauridae discussed here.Modified from [75,76].

Mentions: Here we focus on the transition of cetaceans from land to sea. Cetaceans arose in the early Eocene (about 50 Myr ago), when the earliest fossils are known in Indo-Pakistan. ‘Archaic’ or ‘primitive’ cetaceans, called archaeocetes, include five families illustrating various modes of adaptation to an aquatic life (Fig. 1). The degree of aquatic adaptation and swimming modes of these taxa are debated (e.g. [1–11]). Here we address the lifestyle of early cetaceans by analysis of microanatomical features in postcranial elements of the three more derived archaeocete families, Remingtonocetidae, Protocetidae, and Basilosauridae, extending research by Buffrénil et al. [12], Madar [13,14] and Gray et al. [15].


Transition of Eocene whales from land to sea: evidence from bone microstructure.

Houssaye A, Tafforeau P, de Muizon C, Gingerich PD - PLoS ONE (2015)

Phylogenetic relationships of early cetaceans showing the temporal ranges and general relationships of Pakicetidae, Ambulocetidae, Remingtonocetidae, Protocetidae, and Basilosauridae discussed here.Modified from [75,76].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4340927&req=5

pone.0118409.g001: Phylogenetic relationships of early cetaceans showing the temporal ranges and general relationships of Pakicetidae, Ambulocetidae, Remingtonocetidae, Protocetidae, and Basilosauridae discussed here.Modified from [75,76].
Mentions: Here we focus on the transition of cetaceans from land to sea. Cetaceans arose in the early Eocene (about 50 Myr ago), when the earliest fossils are known in Indo-Pakistan. ‘Archaic’ or ‘primitive’ cetaceans, called archaeocetes, include five families illustrating various modes of adaptation to an aquatic life (Fig. 1). The degree of aquatic adaptation and swimming modes of these taxa are debated (e.g. [1–11]). Here we address the lifestyle of early cetaceans by analysis of microanatomical features in postcranial elements of the three more derived archaeocete families, Remingtonocetidae, Protocetidae, and Basilosauridae, extending research by Buffrénil et al. [12], Madar [13,14] and Gray et al. [15].

Bottom Line: Conversely, hind-limbs in basilosaurids became strongly reduced with no involvement in locomotion but display strong osteosclerosis in the femora.Our study confirms that Remingtonocetidae and Protocetidae were almost exclusively aquatic in locomotion for the taxa sampled, which probably were shallow water suspended swimmers.Basilosaurids display osseous specializations similar to those of modern cetaceans and are considered more active open-sea swimmers.

View Article: PubMed Central - PubMed

Affiliation: UMR 7179 CNRS/Muséum National d'Histoire Naturelle, Département Ecologie et Gestion de la Biodiversité, Paris, France; Steinmann Institut für Geologie, Paläontologie und Mineralogie, Universität Bonn, Bonn, Germany.

ABSTRACT
Cetacea are secondarily aquatic amniotes that underwent their land-to-sea transition during the Eocene. Primitive forms, called archaeocetes, include five families with distinct degrees of adaptation to an aquatic life, swimming mode and abilities that remain difficult to estimate. The lifestyle of early cetaceans is investigated by analysis of microanatomical features in postcranial elements of archaeocetes. We document the internal structure of long bones, ribs and vertebrae in fifteen specimens belonging to the three more derived archaeocete families--Remingtonocetidae, Protocetidae, and Basilosauridae--using microtomography and virtual thin-sectioning. This enables us to discuss the osseous specializations observed in these taxa and to comment on their possible swimming behavior. All these taxa display bone mass increase (BMI) in their ribs, which lack an open medullary cavity, and in their femora, whereas their vertebrae are essentially spongious. Humeri and femora show opposite trends in microanatomical specialization in the progressive independence of cetaceans from a terrestrial environment. Humeri change from very compact to spongious, which is in accordance with the progressive loss of propulsive role for the forelimbs, which were used instead for steering and stabilizing. Conversely, hind-limbs in basilosaurids became strongly reduced with no involvement in locomotion but display strong osteosclerosis in the femora. Our study confirms that Remingtonocetidae and Protocetidae were almost exclusively aquatic in locomotion for the taxa sampled, which probably were shallow water suspended swimmers. Basilosaurids display osseous specializations similar to those of modern cetaceans and are considered more active open-sea swimmers. This study highlights the strong need for homologous sections in comparative microanatomical studies, and the importance of combining information from several bones of the same taxon for improved functional interpretation.

Show MeSH
Related in: MedlinePlus