Massospondylus embryos and hatchlings show early sauropodomorph ontogeny (free pdf)
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Ben Creisler
Aug 4, 2025, 10:04:52 PM8/4/25
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Ben Creisler
A new paper:
Ethan D. Mooney, Tea Maho, Dylan C. T. Rowe, Diane Scott & Robert R. Reisz (2025)
Massospondylus embryos and hatchling provide new insights into early sauropodomorph ontogeny
Swiss Journal of Palaeontology 144: 44
DOI: https://doi.org/10.1186/s13358-025-00382-5
https://link.springer.com/article/10.1186/s13358-025-00382-5
Ontogeny and patterns of growth provide crucial insights into the evolution of dinosaurs and their biology, however, ontogenetic changes of the postcranial skeleton are generally poorly known and restricted to few species. Here, we report on the discovery of embryonic, eggshell, and hatchling material of the Early Jurassic sauropodomorph Massospondylus and provide new insights into the early life stages of early-diverging sauropodomorphs. The embryos described here represent a more advanced developmental stage than previously known embryonic materials and together show eggshells with progressive degrees of resorption correlating to embryonic development. The prominent “thumb” typical of early-diverging sauropodomorph dinosaurs also appears to be precociously ossified and ontogenetically variable. Together, these new Massospondylus embryos and hatchling indicate a quadrupedal posture and the resulting growth trajectory points to an important ontogenetically influenced ecological shift predicated on a continuum of locomotory dependent postural change, from obligate quadrupeds to obligate bipeds. Other Late Triassic and Early Jurassic sauropodomorph dinosaurs known from few ontogenetic stages also fit well on the extensive growth trajectory of Massospondylus with only modest variations in skull, neck, and limb proportions. This generally conservative body plan of early-diverging sauropodomorphs likely suggests a similar postural change for the early members of this large clade that preceded the obligate quadruped sauropods.
Free pdf:
Ethan D. Mooney, Tea Maho, Dylan C. T. Rowe, Diane Scott & Robert R. Reisz (2025)
Massospondylus embryos and hatchling provide new insights into early sauropodomorph ontogeny
Swiss Journal of Palaeontology 144: 44
DOI: https://doi.org/10.1186/s13358-025-00382-5
https://link.springer.com/article/10.1186/s13358-025-00382-5
Ontogeny and patterns of growth provide crucial insights into the evolution of dinosaurs and their biology, however, ontogenetic changes of the postcranial skeleton are generally poorly known and restricted to few species. Here, we report on the discovery of embryonic, eggshell, and hatchling material of the Early Jurassic sauropodomorph Massospondylus and provide new insights into the early life stages of early-diverging sauropodomorphs. The embryos described here represent a more advanced developmental stage than previously known embryonic materials and together show eggshells with progressive degrees of resorption correlating to embryonic development. The prominent “thumb” typical of early-diverging sauropodomorph dinosaurs also appears to be precociously ossified and ontogenetically variable. Together, these new Massospondylus embryos and hatchling indicate a quadrupedal posture and the resulting growth trajectory points to an important ontogenetically influenced ecological shift predicated on a continuum of locomotory dependent postural change, from obligate quadrupeds to obligate bipeds. Other Late Triassic and Early Jurassic sauropodomorph dinosaurs known from few ontogenetic stages also fit well on the extensive growth trajectory of Massospondylus with only modest variations in skull, neck, and limb proportions. This generally conservative body plan of early-diverging sauropodomorphs likely suggests a similar postural change for the early members of this large clade that preceded the obligate quadruped sauropods.
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