Embryonic metabolism of the ornithischian dinosaurs Protoceratops andrewsi and Hypacrosaurus stebingeri and implications for calculations of dinosaur egg incubation times

The embryonic metabolisms of the ornithischian dinosaurs Protoceratops andrewsi and Hypacrosaurus stebingeri have been determined and are in the range observed in extant reptiles. The average value of the measured embryonic metabolic rates for P. andrewsi and H. stebingeri are then used to calculate the incubation times for 21 dinosaurs from both Sauischia and Ornithischia using a mass growth model based on conservation of energy. The calculated incubation times vary from about 70 days for Archaeopteryx lithographica to about 180 days for Alamosaurus sanjuanensis. Such long incubation times seem unlikely, particularly for the sauropods and large theropods. Incubation times are also predicted with the assumption that the saurischian dinosaurs had embryonic metabolisms in the range observed in extant birds.

Figure 1

Mass growth of dinosaurs I. Mass (in kilograms) as a function of age (in years). The data are shown by the open circles (o) and the theoretical fits via Eq. (3) are shown by the solid line. The scale bar beside each dinosaur is 1 m long except for Shuvuuia deserti and Archaeopteryx lithographica whose scale bar is 0.1 m long.

Figure 2

Mass growth of dinosaurs II. Mass (in kilograms) as a function of age (in years). The data are shown by the open circles (o) and the theoretical fits via Eq. (3) are shown by the solid line. The scale bar beside each dinosaur is 1 m long except for Apatosaurus, the mamenchisaurid, and Alamosaurus sanjuanensis for whom the scale bar is 5 m long and Psittacosaurus mongoliensis for whom the scale bar is 0.3 m long.

Figure 3

Cladogram of the dinosaurs of Table 3.

Figure 4

Embryonic metabolism of the animals of this study for $\alpha =3/4$. The embryonic metabolic prefactor $B_o$ is shown as a function of the adult mass $M$ of the animals. Birds are shown with the solid diamonds, members of Crocodylia are shown with the upward-pointing solid triangles, other reptiles by the upward-pointing open triangles and dinosaurs are shown with downward-pointing solid triangles. The results for the birds and reptiles were determined via Eq. (3) while the results for the dinosaurs (Protoceratops andrewsi and Hypacrosaurus stebingeri) were derived from the incubation times reported in Ref. [1].

Figure 5

Juvenile and embryonic metabolisms of the animals of this study for $\alpha =3/4$. The metabolic prefactor $B_o$ is shown as a function of the adult mass $M$ of the animals. In the top panel, the data for birds are shown with solid squares for the juveniles FIG. 5. (Continued) and upward-pointing triangles for the embryos. In the middle panel, the data for reptiles are shown with solid squares and solid upward-pointing triangles for juvenile and embryonic members of Crocodylia, respectively. For the other reptiles, the juveniles are shown with the open squares and the embryos are shown by the upward-pointing open triangles. In the bottom panel, the data for the dinosaurs is shown by the solid circles for juveniles and by downward-pointing triangles for the embryos. The data used to determine the embryonic metabolisms for the dinosaurs (Protoceratops andrewsi and Hypacrosaurus stebingeri) are from Ref. [1]

Figure 6

Juvenile and embryonic metabolisms of the crocodylians and dinosaurs of this study for $\alpha =0.83$. The metabolic prefactor $B_o$ is shown as a function of the adult mass $M$ of the animals. For crocodylians, the data for juvenile and embryos are shown are shown with solid squares and upward-pointing solid triangles, respectively. For the dinosaurs, the data for juveniles are shown with solid circles for the juveniles and downward-pointing triangles for the embryos. Recall that the results for the embryonic dinosaurs (Protoceratops andrewsi and Hypacrosaurus stebingeri) are derived from the data of Ref. [1]