A team of researchers has identified a new penguin-like diving dinosaur in Mongolia. The dinosaur was non-avian and had a streamlined body similar to those of modern diving birds such as penguins and auks. The study describing the findings was recently published in the journal Communications Biology. The research marks the first discovery of a non-avian theropod with a streamlined body. Theropods were a type of carnivorous dinosaur that walked on two legs.
Palaeontologist Yuong-Nam Lee from Seoul National University, South Korea, and his colleagues identified the new dinosaur species by examining the fossilised remains of a specimen from the Omnogovi Province, Mongolia. The researchers have named the dinosaur Natovenator polydontus which means "swimming hunter with many teeth". The specimen discovered in Mongolia is an almost complete skeleton and includes the skull, spinal column, one forelimb, and the remains of two hindlimbs of the penguin-like dinosaur.
Evolutionary advantages of streamlined bodies
Aquatic animals are known to have streamlined bodies. A streamlined body is a major adaptation for them because it allows them to move more efficiently in water. Diving birds are also known to have streamlined bodies. However, streamlined body shapes have not been documented in non-avian dinosaurs. This is primarily because most known non-avian theropods are terrestrial, except for a few, the authors noted in the new study.
There is also a lack of clear evidence of streamlined bodies in the semiaquatic groups. The new theropod reported in the study is from the Upper Cretaceous of Mongolia. The Upper Cretaceous period occurred 100.5 million to 66 million years ago.
What did Natovenator polydontus look like?
The new specimen is a well-preserved skeleton with several articulated dorsal ribs that are posterolaterally oriented to streamline the body as in diving birds, the study said. In other words, the configuration of the dinosaur's articulated dorsal ribs indicates that it had a dorsoventrally flattened and streamlined body.
The specimen suggests that the dinosaur's ribs pointed towards its tail, and it had a long neck similar to modern water birds such as geese, a statement released by Nature Publishing Group said. The advantage of these adaptations is that they may have reduced the drag that Natovenator polydontus would have been subjected to when swimming. This must have helped the dinosaur catch its prey.
The researchers stated that the dinosaur had a dorsoventrally compressed ribcage similar to aquatic reptiles. Streamlining of the body provides hydrodynamic advantages while swimming, the study said. Natovenator polydontus was a potentially capable swimming predator, and the streamlined body evolved independently in separate lineages of theropod dinosaurs, the body shape suggests.
The unusually high number of teeth that Natovenator had in relation to the size of its jaw could indicate that it consumed a fish- or insect-based diet, the study said.
Natovenator could have been closely related to halszkaraptorines, a group of non-avian theropods, according to the study. Previous research has suggested that halszkaraptorines may have been adapted for a semiaquatic lifestyle, similar to modern day waterfowl.
The discovery of the new dinosaur exemplifies the presence of diverse body forms among non-avian theropods, the authors noted.