Australia: The Land Where Time Began

A biography of the Australian continent 

Maniraptora 'Seizing Hands'

Maniraptora includes all dinosaurs that are closer to birds than to ornithomimids. This group of theropod dinosaurs are believed to have given rise to the birds at some time in the Jurassic, about 150 million years ago, making birds maniraptors. There appears to be a lot of convergent evolution in this group which, combined with the poor fossil record, has led to much disagreement as to which dinosaur is in and which is out. This a very diverse group, often with very dissimilar outward appearance, but internally there is a high degree of synapomorphy (shared traits). One structure that is common to the maniraptors is a unique wrist structure, the semilunate carpel. When other modifications of the forelimb are present it allows the movement necessary for the flight stoke of birds. It was apparently a preadaptation, being evolved to assist in grasping, then taking on a different function when other adaptations allowed the forelimb to be used as a wing.

Some other characteristics common to the members of the Maniraptora are, feathers, the neck, a fused clavicle, sternum, a downward pointing pubis instead of forwards (as in typical saurischians), a shortened tail that is stiffened distally, long arms with a hand (manus) that is larger than the foot (pes). There is evidence in the bones of large theropods that they had a respiratory system similar to birds, with air pockets in their bones, another feature that was predated in bird ancestors. There is evidence that at least some theropods slept with their heads under their arms as modern birds do. T. rex would have a problem with this feature. When birds are producing eggs they develop medullary bone in their limbs. This endosteally-derived bone tissue, that is calcium rich, lines the interior of the marrow cavity, and is used as a source of calcium for egg shell. Medullary bone has been found in the bones of the theropods T. rex and Allosaurus and the ornithopod Tenontasaurus. The theropods and ornithopods are on different lines, so it appears the medullary bone may have been a feature common to all dinosaurs.

There is evidence that at least some dinosaurs brooded and cared for their young. A number of specimens of Citipati have been found that were on top of eggs, as modern birds brood their eggs. Maiasaura, and many other dinosaurs have been found that were apparently moving in herds comprising the very young as well as the adults. A dinosaur embryo has been found that lacked the teeth of the adult, indicating that it needed to be fed for some time after hatching.

Gizard stones, gastroliths, are common to birds and dinosaurs.

An immature Scipionyx samniticus was found in Italy that retained parts of the intestine, colon, liver, muscles and trachea.

Analyses of Soft Tissue from Tyrannosaurus rex Suggest the Presence of Protein

Some major groups in the maniraptors are:

  • Aves - birds
  • Dromaeosaurs - 'raptor' dinosaurs
  • Troodontids - Suggested to be possibly the smartest dinosaurs.
  • Therizinisaurs - Bizarre herbivorous theropods?
  • Oviraptors - Strange maniraptorans that show evidence of a high degree of parental care.

Links

  1. Maniraptora
  2. Peter Schouten
  3. Closet veggie-lovers?: 'Predatory Dinos Ate Plants

Sources & Further reading

  1. John A. Long & Peter Schouten, Feathered Dinosaurs, the Origin of Birds, SCIRO Publishing, 2008
  2. Sloan, Christopher, 2000, feathered Dinosaurs, National Geographic Society, Washington
Author: M. H. Monroe
Email:  admin@austhrutime.com
Last updated 21/10/2016 




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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading