Physiology of dinosaurs

Barosauras lentus rearing: mounted skeleton at AMNH
Photo by Greg CC BY 2.0 

In a previous post I discussed the increase in brain metabolic rate during hominin evolution. Roger Seymour, who co-authored that study, has used similar insights to analyse the cardiovascular physiology of sauropod dinosaurs (open access). 

One of his conclusions is that if Barosaurus reared its head (as in the exhibit above) its mean arterial blood pressure would have been 700 mmHg and the left ventricle of the heart would have weighed a metric ton. The heart would have filled the chest and its thick wall been so stiff as to consume a huge amount of energy.

Diplodocus carnegii in the hall of the Natural History Museum in
South Kensington (now removed). Photo by Drow male CC BY-SA 4.0

Seymour goes so far to suggest that long-necked sauropods like Diplodocus were aquatic, floating on the surface of the water and lowering their heads to browse on vegetation. Abdominal air sacs would have helped it to float.

Sauropods are generally regarded as terrestial because of skeletal features, but perhaps they retained these because they needed to go on land to lay their eggs!

Dinocephalosaurus a live-bearing archosauromorph
From Liu et al. 2017

Large reptiles that became fully aquatic were viviparous as shown in a recent paper by Liu et al. (open access). This particular example was an archosauromorph and thus in the lineage that gave rise to dinosaurs (including birds) and crocodilians.