Embryos of an Early Jurassic Prosauropod Dinosaur and Their Evolutionary Significance

Reisz, Robert R.; Scott, Diane; Sues, Hans‐Dieter; Evans, David C.; Raath, Michael A.

doi:10.1126/science.1114942

Cited by 103 publications

(122 citation statements)

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“…The negative forelimb allometry that evidently characterized the ontogeny of P. lujiatunensis is comparable to that previously reported in the sauropodomorph dinosaur Massospondylus, which is inferred based on patterns of skeletal allometry to have been quadrupedal as a hatchling but to have shifted to a bipedal posture later in ontogeny 2,24 . Even hatchlings of at least some therizinosaurian theropods may have been preferentially quadrupedal, given the existence of embryos whose forelimbs are nearly equal in length to their hindlimbs 25 , although in the absence of preserved hatchlings this inference must be considered uncertain.…”

Section: Discussionsupporting

confidence: 68%

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Histology and postural change during the growth of the ceratopsian dinosaur Psittacosaurus lujiatunensis

et al. 2013

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A few dinosaurs are inferred to have undergone an ontogenetic shift from quadrupedal-tobipedal posture, or vice versa, based on skeletal allometry. The basal ceratopsian Psittacosaurus lujiatunensis is considered to have been mainly bipedal as an adult. Here we infer a postural shift in this species based on a novel combination of limb measurements and histological data. The forelimb is strongly negatively allometric relative to the hindlimb, and patterns of vascular canal orientation provide evidence that growth of the hindlimb was particularly rapid during the middle part of ontogeny. Histology also makes it possible to determine the ontogenetic ages of individual specimens, showing that the forelimb-tohindlimb ratio changed rapidly during the first or second year of life and thereafter decreased gradually. Occurrence of an ontogenetic shift from quadrupedality to bipedality was evidently widespread in dinosaurs, and may even represent the ancestral condition for the entire group.

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Section: Discussionsupporting

confidence: 68%

“…As in previous work 24 , the slope of the regression line on a bivariate plot of the lengths of two bones or limbs was interpreted as the allometric coefficient of length for one bone or limb relative to the other. Linear regressions were carried out in R, using the lm command.…”

Section: Methodsmentioning

confidence: 99%

Histology and postural change during the growth of the ceratopsian dinosaur Psittacosaurus lujiatunensis

et al. 2013

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“…The quadrupedal to bipedal shift inferred for Psittacosaurus is predicated upon the differential allometry of the fore-and hind limbs, which results in forelimbs that are relatively longer in young juveniles and shorter in older juveniles and adults (Zhao et al 2013). A similar phenomenon has also been documented in a growth series of the sauropodomorph Massospondylus (Reisz et al 2005). However, although there is evidence to link differing fore-and hind limb proportions to stance (Galton 1970: Maidment andBarrett 2014), Psittacosaurus possesses no unambiguous osteological indictors of quadrupedality at any age-for example, the manus lacks hoof-like unguals and is held in a supinated pose, so it appears to have been unsuitable for weightbearing at any age (Senter 2007).…”

Section: Determining Stance In Ornithischiansmentioning

confidence: 68%

“…Carrano 2005;Sander et al 2011), but this group achieved quadrupedal stance at similar body masses to those attained by some bipedal basal sauropodomorphs (for example, Riojasaurus and Antetonitrus both have femoral lengths of approximately 780-790 mm, but the former is bipedal and the latter quadrupedal: see Bonaparte 1972;Yates and Kitching 2003). Moreover, at least one dinosaur taxon, the basal sauropodomorph Massospondylus, exhibits the contrary trend of abandoning quadrupedality as body mass increased (Reisz et al 2005). These observations imply that simplistic mechanistic explanations based on body mass alone are inadequate to explain ornithischian quadrupedality.…”

Section: Evolutionary Drivers Of Ornithischian Quadrupedalitymentioning

confidence: 99%

The evolution of ornithischian quadrupedality

Barrett

Maidment

2017

J Iber Geol

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Ornithischian dinosaurs were primitively bipedal, but reverted to quadrupedality on at least three (and potentially several more) occasions: in Ceratopsia, Thyreophora and Hadrosauriformes. Each of these reversals was accompanied by anatomical changes to the whole skeleton that enabled the forelimb to function in weight bearing and that also resulted in numerous changes to the hip and hind limb musculature. Each quadrupedal clade acquired a suite of similar biomechanical characters, although they varied in terms of function and in how these character complexes were assembled. Some similar changes occurred in parallel among sauropodomorph dinosaurs as they transitioned from bipedality to quadrupedality. It is unclear why bipedal ornithischians reverted to quadrupedalism, but neither increases in body size nor the acquisition of dermal armour seem to have played a significant role. Increased head size might have influenced the position of the centre of mass and stance in ceratopsians and it is plausible that the evolution of herbivory played an important role in both ornithischians and sauropods, but the latter hypothesis is difficult to test.Resumen Los dinosaurios Ornitísquios, bípedos en origen, revertieron a la condición cuadrúpeda en al menos tres (y potencialmente más) ocasiones: en Ceratopsia, Thyreophora y Hadrosauriformes. Cada una de estas reversiones vino acompañada de cambios anatómicos en el resto de esqueleto que permitieron a la extremidad anterior funcionar para soportar su peso y llevaron a cambios en la cadera y la musculatura dela extremidad posterior. Cada clado cuadrúpedo adquirió una serie de caracteres biomecánicos parecidos, aunque variaron en su función y en la manera en la que estos conjuntos de caracteres encajaban. Cambios parecidos aparecieron paralelamente entre los dinosaurios sauropodomorfos durante su transición de bípedos a cuadrúpedos. Aunque no queda claro por qué los ornitísquios revertieron al cuadrupedismo, ni el aumento de masa corporal ni la adquisición de armadura parecen haber jugado un papel significativo. Un mayor tamaño de la cabeza pudo haber repercutido en el cambio de posición del centro de masas y cambio en la postura en los ceratopsios, y es posible que la evolución de la fitofagia jugara un papel importante, tanto en ornitísquios como saurópodos, aunque sea una hipótesis difícilmente contrastable.Palabras clave Ornithischia Á Dinosauria Á Locomoción Á Cuadrupedismo Á Biomecánica Á Morfología funcional Á Evolución

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“…The remains of embryonic, neonate, and juvenile dinosaurs are emerging from the fossil record with increasing frequency (e.g., Norell et al, 1994;Mateus et al, 1997;Xu et al, 2001;Reisz et al, 2005;Goodwin et al, 2006;Schwarz et al, 2007;Balanoff and Rowe, 2007;Balanoff et al, 2008;Kundrá t et al, 2008). This generalized trend is less obvious within Theropoda, where the number of known specimens representing these relatively early stages of skeletal ontogeny-especially those with well-preserved cranial materialcontinues to be extremely limited (Rauhut and Fechner, 2005).…”

Section: Introductionmentioning

confidence: 96%

The Perinate Skull of Byronosaurus (Troodontidae) with Observations on the Cranial Ontogeny of Paravian Theropods

Bever¹,

Norell²

2009

American Museum Novitates

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The skulls of two perinate paravians from Ukhaa Tolgod, Djadoktha Formation, Mongolia, are described here. The skulls are nearly unique in their combination of ontogenetic age and preservational quality and provide us with the first look at the morphology of such important anatomical regions as the rostrum, palate, and braincase at or near the onset of postnatal development in a nonavian paravian coelurosaur. Based on a number of derived characters, the skulls are allocated to a derived position within Troodontidae that is outside the clade consisting of Saurornithoides mongoliensis, Saurornithoides junior, Troodon formosus, and probably Sinornithoides youngi. A single synapomorphy, presence of a lateral maxillary groove, supports the Ukhaa perinates as Byronosaurus. The comparative morphology of the Ukhaa perinates with adult troodontids indicates a number of significant postnatal transformations (e.g., elongation and flattening of the rostrum, increase in the number of maxillary and dentary teeth, restructuring of the occipital plate and paroccipital process). These comparisons demonstrate that many characters historically considered important for phylogenetic and taxonomic assessments of adult maniraptorans are present at a relatively early stage of ontogeny. Differences in the developmental timing of various cranial characters have important implications for interpreting the fossil record as well as for understanding the role heterochrony has played in the evolution of derived coleurosaurs, including birds. The ontogenetic information provided by the Ukhaa perinates also allow us to comment on the enigmatic paravian Archaeornithoides deinosauriscus, which has been considered both the sister taxon to Avialae and a juvenile specimen of the troodontids Saurornithoides mongoliensis and Byronosaurus jaffei. We found no unique characters that support a priviledged relationship of Archaeornithoides deinosauriscus with avialans and only weak character support for this taxon as a basal troodontid-there is no known character evidence supporting it as a juvenile of either Saurornithoides or Byronosaurus.

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Embryos of an Early Jurassic Prosauropod Dinosaur and Their Evolutionary Significance

Cited by 103 publications

References 9 publications

Histology and postural change during the growth of the ceratopsian dinosaur Psittacosaurus lujiatunensis

Histology and postural change during the growth of the ceratopsian dinosaur Psittacosaurus lujiatunensis

The evolution of ornithischian quadrupedality

The Perinate Skull of Byronosaurus (Troodontidae) with Observations on the Cranial Ontogeny of Paravian Theropods

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