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Many dinosaurs were taller than thought, study concludes

Sept. 30, 2010
Courtesy of the University of Missouri-Columbia
and World Science staff

Many di­no­saurs were taller than tra­di­tion­al es­ti­mates in­di­cate, be­cause their joints con­tained thick lay­ers of car­ti­lage that haven’t been ac­counted for, a new study sug­gests.

“Di­nosaur bones mount­ed in mu­se­ums don’t ac­cu­rately re­flect what the an­i­mals ac­tu­ally had in their bod­ies,” said said anat­o­mist Law­rence Wit­mer of the Ohio Uni­vers­ity Col­lege of Os­te­o­path­ic Med­i­cine, a co-au­thor of the stu­dy, which ap­pears this week in the re­search jour­nal PLoS One.

This is be­cause “the car­ti­lage caps were lost along with the oth­er soft tis­sues,” he added.

Di­no­saur bones have round­ed ends with rough sur­faces that mark where blood ves­sels fed large amounts of car­ti­lage in the joint. The car­ti­lage could have added 10 per­cent or more to the height of a di­no­saur, a study in­di­cates. (Cred­it: Ca­sey Hol­l­i­day/U. of Mis­sourri)
“Our study of the limbs of modern-day rel­a­tives of di­no­saurs shows that di­no­saurs were sig­nif­i­cantly taller than orig­i­nal es­ti­mates,” ex­plained Ca­sey Hol­li­day, lead au­thor of the study and an anat­o­mist at the Uni­vers­ity of Mis­souri School of Med­i­cine. 

“The ends of many di­no­saurs’ long bones, which in­clude leg bones such as the fe­mur or tib­ia, are round­ed and rough and lack ma­jor ar­tic­u­lat­ing struc­tures like con­dyles, which are bony pro­jec­tions. This in­di­cat­ed that very thick car­ti­lages formed these struc­tures, and there­fore the joints them­selves, and would have added sig­nif­i­cant height to cer­tain di­no­saurs,” Hol­li­day added.

“This study of­fers new da­ta in­to how and why rep­tiles, and mam­mals, such as hu­mans, build their joints with such dif­fer­ent amounts of bone and car­ti­lage.”

Hol­li­day and Law­rence Wit­mer, an anat­o­mist at the Ohio Uni­vers­ity Col­lege of Os­te­o­path­ic Med­i­cine, stud­ied os­triches and al­li­ga­tors, thought to be di­no­saurs’ clos­est modern-day rel­a­tives. The in­ves­ti­ga­tors then stud­ied fos­sil­ized limbs of di­no­saurs in­clud­ing Ty­ran­no­saur­us rex, Al­lo­saur­us, Bra­chi­o­saur­us and Tri­cer­a­tops. The team de­ter­mined that the lengths of al­li­ga­tors’ and os­triches’ limbs in­cluded be­tween 6 and 10 per­cent car­ti­lage.

Ap­ply­ing the find­ings to di­no­saurs, Hol­li­day de­ter­mined that many mem­bers of the “the­ro­pod” line­age, which in­cluded T. rex, were only mod­estly taller than pre­vi­ous es­ti­mates. On the oth­er hand, so-called orn­this­chian and sau­ro­pod di­no­saurs, such as Tri­cer­a­tops and Bra­chi­o­saur­us, may have been 10 per­cent taller or more. 

For ex­am­ple, Bra­chi­o­saur­us, pre­vi­ously thought to be 42 feet tall, may ac­tu­ally have been more than a foot taller with the ad­di­tion­al joint car­ti­lage, Hol­li­day said.

Un­der­stand­ing the struc­tures of the soft tis­sues in di­no­saurs might al­so have im­plica­t­ions for their speed and pos­ture, the re­search­ers said. While an in­crease in limb length typ­ic­ally means a taller di­no­saur, it could al­so mean a faster or slower an­i­mal, de­pend­ing on how it af­fects the skel­e­ton. 

Di­no­saur bones dif­fer from those of mam­mals, in­clud­ing hu­mans, the in­ves­ti­ga­tors ex­plained. 

Mam­mals have small pro­tru­sions at the end of each bone that help it con­nect with anoth­er bone at a joint, like two puz­zle pieces. The bones are linked by a very thin car­ti­lage lay­er, which pro­vides pad­ding in the joint, but of­ten wears down, lead­ing to pain­ful con­di­tions like ar­thri­tis. Di­no­saur bones, on the oth­er hand, have round­ed ends and no ob­vi­ous way to con­nect one with anoth­er. Soft tis­sue struc­tures like car­ti­lage and mus­cles leave marks on bones, which en­a­ble pa­le­on­tol­ogists to make soph­is­t­icated de­ter­mina­t­ions about a di­no­saur’s phys­i­cal at­tributes.

Alliga­tors have smooth, round­ed bones while young os­triches have rough sur­faces on their bones that mark where blood ves­sels feed large car­ti­lag­i­nous struc­tures in the joints. Both char­ac­ter­is­tics are si­m­i­lar to di­no­saur bones, ac­cord­ing to the sci­en­tists.

Hol­li­day’s team dis­sect­ed the al­li­ga­tor and os­trich bones and made casts of the bones with car­ti­lage. The team then re­moved the car­ti­lage and com­pared the bones to the casts. The bones with­out car­ti­lage were 4 to 10 per­cent smaller.

In the fu­ture, Hol­li­day hopes to col­la­bo­rate with vet­eri­nar­i­ans to study how and why dif­fer­ent ver­te­brates build their joints with dif­fer­ent pro­por­tions of car­ti­lage and bone.

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Many dinosaurs were taller than traditional estimates show, because their joints contained thick layers of cartilage that haven’t been accounted for, a new study suggests. “Dinosaur bones mounted in museums don’t accurately reflect what the animals actually had in their bodies in life,” said said anatomist Lawrence Witmer of the Ohio University College of Osteopathic Medicine, a co-author of the study, which appears this week in the research journal PloS One. This is because “the cartilage caps were lost along with the other soft tissues,” he added. “Our study of the limbs of modern-day relatives of dinosaurs shows that dinosaurs were significantly taller than original estimates,” said Casey Holliday, lead author of the study and an anatomist at the University of Missouri School of Medicine. “The ends of many dinosaurs’ long bones, which include leg bones such as the femur or tibia, are rounded and rough and lack major articulating structures like condyles, which are bony projections. This indicated that very thick cartilages formed these structures, and therefore the joints themselves, and would have added significant height to certain dinosaurs,” Holliday added. “This study offers new data into how and why reptiles, and mammals, such as humans, build their joints with such different amounts of bone and cartilage.” Holliday and Lawrence Witmer, an anatomist at the Ohio University College of Osteopathic Medicine, researched on ostriches and alligators, thought to be dinosaurs’ closest, modern-day relatives. The investigators then studied fossilized limbs of dinosaurs including Tyrannosaurus rex, Allosaurus, Brachiosaurus and Triceratops. The team determined that the lengths of alligators’ and ostriches’ limbs included between 6 and 10 percent cartilage. Applying the findings to dinosaurs, Holliday determined that many members of the so-called theropod lineage, which included Tyrannosaurus, were only modestly taller than previous estimates. On the other hand, so-called ornthischian and sauropod dinosaurs, such as Triceratops and Brachiosaurus, may have been 10 percent taller or more. For example, Brachiosaurus, previously thought to be 42 feet tall, may actually have been more than a foot taller with the additional joint cartilages, Holliday said. Understanding the structures of the soft tissues in dinosaurs might also have implications for their speed and posture, the researchers said. While an increase in limb length typically means a taller dinosaur, it could also mean a faster or slower animal, depending on how it affects the skeleton. Dinosaur bones differ from those of mammals, including humans, the investigators explained. Mammals have small protrusions at the end of each bone that help it connect with another bone at a joint, like two puzzle pieces. The bones are linked by a very thin cartilage layer, which provides padding in the joint, but often wears down, leading to painful conditions like arthritis. Dinosaur bones, on the other hand, have rounded ends and no obvious way to connect one with another. Soft tissue structures like cartilage and muscles leave marks on bones, which enable paleontologists to make sophisticated determinations about a dinosaur’s physical attributes. Alligators have smooth, rounded bones while young ostriches have rough surfaces on their bones that mark where blood vessels feed large cartilaginous structures in the joints. Both characteristics are similar to dinosaur bones, according to the scientists. Holliday’s team dissected the alligator and ostrich bones and made casts of the bones with cartilage. The team then removed the cartilage and compared the bones to the casts. The bones without cartilage were 4 to 10 percent smaller. In the future, Holliday hopes to collaborate with veterinarians to study how and why different vertebrates build their joints with different proportions of cartilage and bone.