T. rex Size, Speed, and Development of the Young

T. rex Mother Hunting with Chick

(If you read the text, something is wrong with this picture...what is it?)

(See answer at bottom of blog.)

   

Newer evidence is mounting that T. rex may have been heavier than previously thought.  It was once thought that T. rex weighed between 4.5 to 6.5  tons, (4.08 to 5.44 metric tons).  However, newer estimates are are that T. rex or Tyrannosaurus rex weighed 9 tons, (8.16 metric tons).  That is 18,000 pounds!  So a Tyrannosaurus rex weighed as much as 100 adult men.

A T. rex egg has never been found but other Theropod eggs HAVE been found.  We think that a young newly hatched T.rex chick probably weighed between 5-10 lbs. (2.3-4.5 kg).  It is estimated that a young T. rex grew 3950 lbs. (1790 kg.) in one year.  So that is equal to the weight of 22 men.  So a young newly hatched T. rex grew in one year to be the size of 22 men.

To determine the size and weight of an adult T. rex the scientists called in help from the forensic detectives from the Chicago Police Department to scan the skeleton of Sue, the largest and most complete T. rex ever found.  The fossilized skull of Sue is so large that they took it and the larger fossilized bones to a Ford Motor Company site where they had a huge scanner.  They then digitally added muscle and skin etc. and the weight estimate went up 30%.  .   .  to 9 tons (or 8.16 metric tonnes).  So, if you think about it, paleontology is often like police forensics...trying to solve a mystery from limited evidence.

The above adult T. rex in the drawing is a drawing of a hefty 18,000 lb. T. rex.

T. rex, as an adult, was probably rather slow.  They were way too heavy to run 35 mph like in the movie Jurassic Park.  However, new discoveries of teen T. rex fossils has many paleontologists thinking that the young were the chase predators in a T. rex pack.  First you need to know that other Tyrnannosaurs, like Albertosaurus have been found to have died together.  So we can infer that they also lived and hunted together.  Bones of the Theropod carnivore Giganotosaurus were also found in a group.  Even the above mentioned Sue had a healed  broken leg.  This led paleontologists to infer that she must have been fed by a mate or a pack as her injury healed.  It would have taken around 6 weeks for her broken leg to heal.  And it HAD healed well before she died.  She had walked on it again.

So, getting back to the youthful T. rex.  They would have been much more lightly built than the full grown adults.  These youthful Tyrannosaurs would have been the ones to chase prey animals into an ambush where the huge 9 ton mom and dad would be waiting to crush the neck or bite of the head of the plant eating dinosaurs that got chased into the ambush.

Young (16 yrs. old) T. rex Hunts for Prey

Notice the above young T. rex is about 2 years shy of adulthood.  They reached maturity about as fast as we humans do.  We are adults at age 18, and so was a T. rex.

Younger still, adolescent T. rex (14 yrs old) Hunting for Prey

Younger still, this T.rex is more lightly built.  He would be able to run even faster than his 16 year old sister.  He was perhaps almost as long as his sister, but not as heavy.  This would have made him the chase dinosaur of his T. rex pack.  Notice that there are a few feathers.  Most paleontologist think that very young T. rex had feathers, to keep them warm.  When you live in a warm climate...and you get big, that is when you need to get rid of excess heat, not keep heat in. (Think of elephants in Africa.)  

Notice that there are more spots on the younger T. rex.  Some modern prey animals like cougars and leopards have spots, different spots, or more spots when they are young.  The feathers and spots were lost as the T. rex grew up.

Remember the first picture on today's blog entry?  I mentioned in the text that the young T. rex chicks were feathered to keep warm.  I also mentioned that often in predators the young have more spots or markings for camouflage from other predators.   So, I recognized my mistake and altered the first picture of the chick with more spots or stripes and feathers for keeping warm.  Notice that both chicks I drew have the larger head in proportion to body size.  This is called the "cuteness factor."  The cuteness factor in our day can be seen in many of our young.  It is seen in puppies, kittens, and even humans.

Large Adult Mother T. rex Hunting with Feathered and Spotted Chick

For more info look up these sites:  "Old Thunder Thighs:  T. rex's weight topped 9 tons" and... "Dinosaur Home, Size of a T-Rex Egg" and "Dinosaur World".