A vertebra of a small species of Pachycetus from the North Sea and its inner structure and vascularity compared with other basilosaurid vertebrae from the same site
article
In the Western Scheldt Estuary near the Belgian-Dutch border, middle to late Eocene
strata crop out at the current seafloor. Most vertebrae of large Eocene basilosaurid
taxa from this area were previously described in several papers. They represent three
morphotypes: elongated vertebrae of a large species of Pachycetus (Morphotype 1b),
a not-elongated vertebra of a large ‘dorudontid’ basilosaurid (Morphotype 2) and
‘shortened’ vertebrae of a new, unnamed taxon (Morphotype 3). This article deals with a
still undescribed, smaller vertebra, NMR-16642, from this site. Our first aim was to date
it by dinoflagellate cysts in adhering sediments. Yielding an age of about 38 Ma, it is one
of the very few remains of basilosaurids from Europe, of which the age could be assessed
with reasonable certainty. The vertebra, Morphotype 1a, is assigned to a small species
of Pachycetus. High-quality CT scans are used to differentiate between NMR-16642,
Morphotype 1a, and the large species of Pachycetus, Morphotype 1b. Another aim of
this paper is to investigate the inner structure and vascularity of the study vertebra
and that of the other morphotypes (1b, 2, 3) from this area by using high-quality CT
scans. Notwithstanding differences in size, shape and compactness, the vertebral inner
structure with a multi-layered cortex of periosteal bone, surrounding two cones of
endosteal bone appears to be basically similar in all morphotypes. Apparently, this
inner structure reflects the ontogenetic vertebral growth. An attempt to reconstruct
the vascularity of the vertebrae reveals a remarkable pattern of interconnected vascular
systems. From the dorsal and, if present, ventral foramina, vascular canals are running to
a central vascular node. From this node a system of vascular canals goes to the epiphyseal
ends, giving rise to separate systems for cortex and cones. It is the first time that the
vascularity of vertebrae of archaeocetes is investigated.
strata crop out at the current seafloor. Most vertebrae of large Eocene basilosaurid
taxa from this area were previously described in several papers. They represent three
morphotypes: elongated vertebrae of a large species of Pachycetus (Morphotype 1b),
a not-elongated vertebra of a large ‘dorudontid’ basilosaurid (Morphotype 2) and
‘shortened’ vertebrae of a new, unnamed taxon (Morphotype 3). This article deals with a
still undescribed, smaller vertebra, NMR-16642, from this site. Our first aim was to date
it by dinoflagellate cysts in adhering sediments. Yielding an age of about 38 Ma, it is one
of the very few remains of basilosaurids from Europe, of which the age could be assessed
with reasonable certainty. The vertebra, Morphotype 1a, is assigned to a small species
of Pachycetus. High-quality CT scans are used to differentiate between NMR-16642,
Morphotype 1a, and the large species of Pachycetus, Morphotype 1b. Another aim of
this paper is to investigate the inner structure and vascularity of the study vertebra
and that of the other morphotypes (1b, 2, 3) from this area by using high-quality CT
scans. Notwithstanding differences in size, shape and compactness, the vertebral inner
structure with a multi-layered cortex of periosteal bone, surrounding two cones of
endosteal bone appears to be basically similar in all morphotypes. Apparently, this
inner structure reflects the ontogenetic vertebral growth. An attempt to reconstruct
the vascularity of the vertebrae reveals a remarkable pattern of interconnected vascular
systems. From the dorsal and, if present, ventral foramina, vascular canals are running to
a central vascular node. From this node a system of vascular canals goes to the epiphyseal
ends, giving rise to separate systems for cortex and cones. It is the first time that the
vascularity of vertebrae of archaeocetes is investigated.
Topics
TNO Identifier
993095
Source
PeerJ, pp. 1-27.
Pages
1-27