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Giant dinosaurs hatched with adult-like proportions

Analysis of a new dinosaur fossil suggests that the largest species ever known to walk the Earth was born with adult-like proportions, perhaps allowing it to be more independent than some other species of dinosaur.

Giant dinosaurs hatched with adult-like proportions
Baby Rapetosaurus is compared to neonatal mammals. Rapetosaurus was only 35 cm tall at the hip, 
and weighed around 40 kg when it died a few weeks after hatching. This body size is similar to
 that of some large-bodied mammalian newborns: Black rhinoceros calves are ~ 35?45 kg
 at birth and stand a little taller at the shoulder than UA 9998 at ~ 65 cm. African elephants are
 close to a meter high at the hip and weigh between 90 and 120 kg at birth. Hippo newborns 
are the closest in both height and mass to UA 9998, checking in between 24?45 kg
 at birth with a shoulder height of 37 cm [Credit: D. Vital]
While several fossils of the ginormous Rapetosaurus krausei have been analyzed to date, very little is known about this species around the time of hatching. R. krausei is a type of titanosaur, the largest land vertebrates to have evolved. It is estimated to have reached lengths of about 15 meters (49 feet), but even these giants had to start small.

Analysis of the new fossil by Kristina Curry-Rogers et al. suggests that the youngster they studied, who died (likely from starvation) between the age of 39 and 77 days, weighed roughly 3.4 kilograms (kg) when it hatched.

Giant dinosaurs hatched with adult-like proportions
UA 9998, a Rapetosaurus perinate, would have stood only knee-high. In comparison, 
an adult Rapetosaurus femur is about the same length as an averaged-sized woman 
[Credit: Raul Martin and Kristina Curry Rogers]
By the end of its brief life, it had reached a mass of roughly 40 kg and was 35 centimeters tall at the hip.

The researchers used bone histology and x-ray computed tomography to understand its growth pattern. Based on the compactness of its bones, the authors say that this dinosaur's limbs likely remained similar in shape throughout its life.

Giant dinosaurs hatched with adult-like proportions
Thin-sections of limb bones reveal patterns of blood supply, degree of remodeling, 
and calcified cartilage growth plates that signal fast-growth and precocity 
for baby Rapetosaurus [Credit: K. Curry Rogers, M. Whitney, 
M. D'Emic, and B. Bagley]
This is in contrast to other dinosaur groups, such as theropods and ornithischians, whose limb proportions are different at birth than adulthood; evidence suggests that, in these latter cases, parental care was important.

Therefore, the authors propose that R. krausei infants may have been relatively independent after birth, compared to other species.

The study has been published in the journal Science.

Source: American Association for the Advancement of Science [April 21, 2016]

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