Protocetidae
Encyclopedia
The protocetids form a diverse and heterogeneous group of cetacea
ns known from Asia, Europe, Africa, and North America. There were many genera, and some of these are very well known (e.g., Rodhocetus
). Known protocetids had large fore- and hindlimbs that could support the body on land, and it is likely that they lived amphibiously: in the sea and on land. It is unclear at present whether protocetids had flukes (the horizontal tail fin of modern cetaceans). However, what is clear is that they are adapted even further to an aquatic life-style. In Rodhocetus, for example, the sacrum
– a bone that in land-mammals is a fusion of five vertebrae that connects the pelvis
with the rest of the vertebral column
– was divided into loose vertebrae. However, the pelvis was still connected to one of the sacral vertebrae. Furthermore, the nasal openings are now halfway up the snout; a first step towards the telescoped condition in modern whales.
Their supposed amphibious nature is supported by the discovery of a pregnant Maiacetus
, in which the fossilised fetus was positioned for a head-first delivery, suggesting that Maiacetus gave birth on land.
The ungulate ancestry of these early whales is still underlined by characteristics like the presence of hoofs at the ends of toes in Rodhocetus.
Cetacea
The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...
ns known from Asia, Europe, Africa, and North America. There were many genera, and some of these are very well known (e.g., Rodhocetus
Rodhocetus
Rodhocetus is one of several extinct whale genera that possess land mammal characteristics, thus demonstrating the evolutionary transition from land to sea.-Description:...
). Known protocetids had large fore- and hindlimbs that could support the body on land, and it is likely that they lived amphibiously: in the sea and on land. It is unclear at present whether protocetids had flukes (the horizontal tail fin of modern cetaceans). However, what is clear is that they are adapted even further to an aquatic life-style. In Rodhocetus, for example, the sacrum
Sacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...
– a bone that in land-mammals is a fusion of five vertebrae that connects the pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
with the rest of the vertebral column
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...
– was divided into loose vertebrae. However, the pelvis was still connected to one of the sacral vertebrae. Furthermore, the nasal openings are now halfway up the snout; a first step towards the telescoped condition in modern whales.
Their supposed amphibious nature is supported by the discovery of a pregnant Maiacetus
Maiacetus
Maiacetus is a genus of early middle Eocene cetacean from Pakistan.-Paleobiology:The genus contains a single species Maiacetus inuus, first described in 2009 on the basis of two specimens, including a specimen which has been interpreted as a pregnant female and its fetus...
, in which the fossilised fetus was positioned for a head-first delivery, suggesting that Maiacetus gave birth on land.
The ungulate ancestry of these early whales is still underlined by characteristics like the presence of hoofs at the ends of toes in Rodhocetus.