Vascularised endosteal bone tissue in armoured sauropod dinosaurs.
The presence of well-vascularised, endosteal bone in the medullary region of long bones of nonavian dinosaurs has been invoked as being homologous to medullary bone, a specialised bone tissue formed during ovulation in birds. However, similar bone tissues can result as a pathological response in modern birds and in nonavian dinosaurs, and has also been reported in an immature nonavian dinosaur. Here we report on the occurrence of well-vascularised endosteally formed bone tissue in three skeletal elements of armoured titanosaur sauropods from the Upper Cretaceous of Argentina: i) within the medullary cavity of a metatarsal, ii) inside a pneumatic cavity of a posterior caudal vertebra, iii) in intra-trabecular spaces in an osteoderm. We show that considering the criteria of location, origin (or development), and histology, these endosteally derived tissues in the saltasaurine titanosaurs could be described as either medullary bone or pathological bone. Furthermore, we show that similar endosteally formed well-vascularised bone tissue is fairly widely distributed among nondinosaurian Archosauriformes, and are not restricted to long bones, but can occur in the axial, and dermal skeleton. We propose that independent evidence is required to verify whether vascularised endosteal bone tissues in extinct archosaurs are pathological or reproductive in nature.
University of Cape Town, Department of Biological Sciences, Private Bag X3, Rhodes Gift, 7700 South Africa.
Anusuya
A
Chinsamy
CONICET, Instituto de Investigación en Paleobiología y Geología, Universidad Nacional de Río Negro, Museo Carlos Ameghino, Belgrano 1700, Paraje Pichi Ruca (predio Marabunta) 8300, Cipolletti, Río Negro, Argentina.
Ignacio
I
Cerda
CONICET, Facultad de Ciencias Naturales Universidad Nacional de Tucumán, Miguel Lillo 205, (4000) Tucumán, Argentina.
Jaime
J
Powell
D000818:Animals; D001118:Argentina; D001808:Blood Vessels / Q000033:anatomy & histology*; D001842:Bone and Bones / Q000033:anatomy & histology*; D025061:Dinosaurs / Q000033:anatomy & histology*; D005580:Fossils