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Dinosaur "Arthritis" Revisited.



 On Feb. 2' 97 Joe Daniel took me to task for my use of supposed negative
evidence to state that dinosaurs either did not, or rarely suffered from,
osteoarthritis. I have spent some time considering and researching my
response and have subsequently been in contact with Dr. Bruce Rothschild
(American paleopatholgist and arthritis expert) about this particular
troubling and ongoing issue. Simply put, most "dinosaur arthritis" is either
a misdiagnosis or misinterpretation of the actual evidence- it is largely a
problem of semantics. Hopefully, this long and detailed posting (with
bibliography) will put the matter to rest and not spawn a "war of words"
which have unfortunately occurred on this list in the past. One disadvantage
of the Internet and mailing lists like this is that I don't know if my
specific response is a reply to a 9 year old kid or a 50 year old
veterinarian who specializes in arthritic conditions. Hey, I work mostly on
dinosaur bone fractures. But here goes:

 Daniel states that arthritis is found mostly in older animals and that most
wild animals don't reach advanced age. Both are not necessarily true.
Juvenile HOMO can get rheumatoid arthritis. Clausen, 1981 and Clausen, et
al., 1980 reported numerous cases (10-30% of population affected) of
free-ranging Caribou RANGIFER TARANDUS calves in Greenland aged only 3-8
weeks and affected with crippling (and ultimately fatal) polyarthritis of
the limb joints. 
 How does one scientifically define advanced age in dinosaurs? Daniel
states: "Perhaps I should clarify this to mean middleaged and beyond, not
just an absolute thing, just for the nitpickers out there." What is
middleaged and beyond? 10 years, 20, 50?? Can we ever really know? A more
detailed examination is necessary. 

 With the extensive material I've worked with from Dinosaur Provicial Park
(DPP) here in Alberta, Canada one can determine relative age (broken down in
the rough categories of hatchling, juvenile, subadult, adult, old adult) by
the following methods. This is simplified but not rocket science:

 1. Relative size of the bone/skeleton (very small-hatchling;
small-juvenile; medium-subadult; large-adult/old adult).
 2. Degree of vertebral neural arch to centrum fusion (unfused in
hatchlings/juveniles; partial fusion in subadults; complete fusion in
adults/old adults).
 3. Bone surface texture (very porous in hatchlings; porous in juveniles;
less so in subadults; and not in adults/old adults).
 4. Full development of secondary sexual and/or sexually dimorphic features
(ie. hadrosaur crests, ceratopsian frill ornamentation). Undeveloped in
hatchlings/juveniles; partially or poorly developed in subadults; fully
developed in adults and fully developed/atrophied [some ceratopsians only]
in old adults- see below.
 5. Development of pathological and "pathological" conditions in some
affected older individuals; ie: spondylosis deformans and "DISH"- diffuse
idiopathic skeletal hyperostosis, etc. Spondylosis deformans and DISH occurs
in extant adult and older animals of wide taxonomic backgrounds, not in
younger animals. Dinosaurs were similarly demographically affected. 
 6. Fusion of some cranial elements with advancing age.
 7. Tooth battery compliment (fewer rows of teeth in younger animals; more
rows in adults [and with more vertically stacked teeth per row in the latter]).
 8. A combination of any or all of the above. 
 
 Ceratopsians and hadrosaurs (animals I've worked on the most since starting
with Tyrrell in 1979) from DPP appear to have grown fast (egg to adult in
perhaps as little as 4-5 years- research in progress for ceratopsians) and
had determinate growth. An adult ceratopsian from DPP would be about 18 feet
long, a hadrosaur about 31-32 feet long. I have not seen any evidence of 20+
foot ceratopsians, or 40+ foot hadrosaurs in DPP. Once hadrosaurs reach a
length of 31-32 feet, and ceratopsians 18 feet, they show all the
manifestations of being a full sexually mature adult as described in 1-8
above and growth either stops or is thereafter so slow as to be negligable.
I'm told sauropods (a group I'm not familiar with at all) had indeterminate
growth, if so the really big examples should also be old animals. But begs
the question, how old (in years) was an old dinosaur? This question would be
in the "Top 5" questions we get from the public about dinosaurs. How old (in
years) was an old dinosaur? I suspect it varied greatly. We'll likely never
know. And how do you know when you have found the skeleton of an "old"
dinosaur? I think rings in dinosaur teeth or bone have little value with
this particular problem because of regular tooth replacement and continuous
bone remodelling throughout life. Bonebed evidence indicates that hadrosaurs
and ceratopsians grew quickly, but once attaining sexual maturity, how long
did they live after that to go on and develop supposed "arthritis" (Oh how I
hate that word when regularly used in conjuction with dinosaur pathology!!)?
This is more problematic but not an impossible situation in regards to the
dinosaur arthritis debate. 
 Daniel states: "Very few animals in the wild get old enough to show
senescent phenomenon."  I assume by this statement that he means that
predators kill off the injured, diseased and sick ones. Not always true.
Well, I can say that since I started compiling my ongoing bibliography
project in April, 1990, I'm continuously amazed at how imperfect natural
selection can be at times and how many animals can survive to advanced age
and despite severe and crippling injuries (including osteoarthritis),
especially those animals who live in large herds. Apparently, even when
sick, injured or diseased one can gain some degree of anonymity and live
longer by living within large herds.

 Peterson, et al., 1982 described osteoarthritis in aged Moose ALCES ALCES
from the Kenai Peninsula, Alaska, USA and Isle Royale, Michigan, USA. The
Kenai material was collected over a 9 year period and Isle Royale material
over a 4 year period. In Moose over 10 years of age (which would nicely fit
the requirements of Daniel's "middleaged and beyond" category), 31% (N=74)
of Kenai Moose and 30% (N=145) of Isle Royale Moose (the latter a protected
and unhunted population) were variously affected by osteoarthritis in the
lumbrosacral and coxofemoral joints. Moose lead mostly solitary lives and
are preyed on by pack-hunting Wolves CANIS LUPUS, so one would think animals
so crippled up with arthritis would fall prey much sooner than Peterson et
al.'s sample indicates and not show the high arthritis levels demonstrated
from the 2 widely seperated localites. These animals were ultimately taken
by Wolves and probably due to the advanced osteoarthritis. What ratio of
younger Moose died vs. those that survived into advanced age (and then
development of osteoarthritis) is unstated. No doubt a percentage of Moose
are killed in their first year or two, but I remember reading that once the
first year was survived, long-term survival was typical. My point here is to
demonstrate that it is entirely possible for solitary prey animals to reach
an advanced age and develop readily recognizable crippling advanced
osteoarthritic lesions while living with contemporaneous top predators.
Moose from both populations also suffered from periodontitis and advanced
tooth wear.

 But I digress. Moose are not dinosaurs, so we are back to the question of
how can one have a chance of preserving dinosaurs of advanced age. If the
dinosaur predators kill off their sick, diseased and injured dinosaur prey,
how can we ever have a chance of finding a truly "aged dinosaur" and finding
said "arthritis"? The chances would seem remote indeed. Chin up. Good news.
There is one way- monospecific or "low diversity" bonebeds. These are mass
mortality events. No selective filters here, no predator feeding biases, no-
an unbiased Mother Nature killing off large numbers of
herding/flocking/schooling animals simultaneously (as demonstrated time and
time again, one disadvantage of living in large herds/flocks/schools).
Monospecific mass mortality events can occur under a wide variety of
conditions: bad weather (flooding, lightning, storms); disease; fire;
drowning, poisoning; asphyxiation, etc. Mother Nature is not selective when
these events occur. Herding animals of all ages are affected and killed-
juveniles, subadults, adults and old adults. While the remains of the dead
dinosaurs are often disarticulated prior to burial, one can see evidence
that old (aged) animals are also represented in the bonebed deposit- lesions
of spondylosis deformans and DISH are present, there is nonpathological
fusion of some cranial elements, and in centrosaurine ceratopsians the
presence of resorption of orbital horncores/orbital boss (the latter
Sampson, Ryan and Tanke, in press) can be seen. Like herding animals today,
some seriously injured ceratopsians could remain anonymous within the large
herd (witness the PACHYRHINOSAURUS with the dinner plate-sized hole in the
side of its face- presented by B. Rothschild at Dinofest'96; Rothschild and
Tanke, in press; and a cast of which is in Jim Kirkland's travelling
ceratopsian dinosaur exhibit). Most of these ceratopsian bonebeds I've
extensively excavated/witnessed show little to no bias against limb bone
elements (phalanges excepted, but isolated ceratopsian phalanges are common
in DPP and while some are pathologic [see Rothschild, 1988], none show
arthritis) and these are the bones you would expect to see osteoarthritis.
But no. The pathologic lesions are conspicuous in their absence. Same for
museum collections. What am I to do with these overpowering field and museum
observations? Pretend they don't exist? Ignore them because it is negative
evidence? I might say there are no Late Cretaceous sauropods here in Alberta
because we have found no bones. I could be right or wrong in that instance.
If I say no sauropods in Alberta because of no bones, that is truly is
negative evidence. What about ceratopsian arthritis? Or hadrosaur arthritis?
Its not like I have no ceratopsian or hadrosaur bones to test my hypothesis.
I have hadrosaur and ceratopsian bones to look at and not just a few. I can
honestly say I've seen tens of thousands of ceratopsian and hadrosaur bones
in Alberta, collected most of the pathologic ones and none were with
arthritis. I will not go on through my career blind to the idea that Alberta
ceratopsians and hadrosaurs did not suffer from arthritis, I'll keep
looking- but I already know what the answer is and I'm free to pursue other
problems. If ultimately I'm proven wrong, hey that's great. We are one step
closer to the truth and science marches on. I would not say that because we
only have 2 confirmed examples of dinosaur arthritis that this is negative
evidence. It is evidence- only 2 specimens out of many hundreds of thousands
of dinosaur bones examined or collected in the past worldwide. The rare
arthritis phenomenon in dinosaurs is real. Dr. Rothschild summarizes the
situation so: As spondylosis deformans, a manifestation of aging, is not
rare in dinosaurs, they clearly lived long enough to develop arthritis, if
this were their "nature".  

 Having said all this, if any authors out there ever want to address or
discuss dinosaur pathology in their writings, I would strongly urge caution
in the use of the descriptive term "arthritis" or "osteoarthritis". Whoever
you choose to believe in this debate (or neither), one thing is clear-
dinosaur arthritis was rare. Either it was rarely preserved, rarely
happened, or both. What previous researchers/authors of popular articles or
books have called arthritis is really a misinterpretation of other
pathological vertebral fusions (congenital, spondylosis deformans and
trauma-related) and more common non-pathological (DISH) conditions also
involving fusion of the vertebrae. This continuance of published
misinformation (even up to the present day) is most unfortunate, given Dr.
Rothschild's exhaustive research and collaborative efforts into this
intriguing topic (Rothschild, 1985; 1987; 1990; Rothschild and Berman, 1991;
Rothschild and Martin, 1993; Rothschild and Tanke, 1992, Tanke and
Rothschild, 1997).  

 On Feb. 7th, Bonny Blackwell asked about possible taphonomic aspects of
pathologic dinosaur bones. Here in Alberta most of the material has not
travelled far from where the animal died, so abrasion of pathological
features on bone is largely not a problem. However, in the few abraded
examples I have seen, enough was present to still indicate their
pathological nature. I too would be interested in any publications dealing
with this topic.

 No doubt my comments here will result in some "flames". But I am one of
those lucky ones who is paid to do his hobby and I work with dinosaur bones
every day and feel I have a good sense about what is and what is not going
on with them. To professional and layman alike, paleopathology is a cryptic,
mysterious and often misunderstood field. The research applications and
contributions the study of paleopathology can make to better understanding
dinosaur behavior, physiology and lifestyle is enormous.

 Literature cited:

 Clausen, B. 1981. Summer Mortality Among Caribou Calves in West Greenland.
pp. 205-206. In: Wildlife Diseases of the Pacific Basin and Other Countries.
Edited by M.E. Fowler. Proc. 4th Inter. Conf. Wildl. Dis. Assoc., Aug.
25-28, 1981. Sydney, Australia.

 ____, Dam, A., Elvestad, K., Krough, H.V. and Thing, H. 1980. Summer
Mortality Among Caribou Calves in West Greenland. Nord. Vet.-Med., 32:291-300.

 Peterson, R.O., Scheidler, J.M. and Stephens, P.W. 1982. Selected Skeletal
Morphology and Pathology of Moose from the Kenai Peninsula, Alaska, and Isle
Royale, Michigan. Can. Jour. Zool., 60:2812-2817.

 Rothschild, B.M. 1985. Diffuse Idiopathic Skeletal Hyperostosis:
Misconceptions and Reality. Clinical Rheumatology in Practice, Sept./Oct.,
1985:3207-211. 

 ____ 1987. Diffuse Idiopathic Skeletal Hyperostosis as Reflected in the
Paleontologic Record: Dinosaurs and Early Mammals. Seminars in Arthritis and
Rheumatism, 17(2):119-125.

 ____ 1988. Stress Fracture in a Ceratopsian Phalanx. Jour. Paleo.,
62(2):302-303. 

 ____ 1990. Radiologic Assessment of Osteoarthritis in Dinosaurs. Ann. Carn.
Mus., 59(4):295-301.

 ____ and Berman, 1991. Fusion of Caudal Vertebre in Late Jurassic
Sauropods. Jour. Vert. Paleo., 11(1):29-36.

 ____ and Martin, L.D. 1993. Paleopathology- Disease in the Fossil Record.
CRC Press, Boca Raton, Florida. x + 365 pp. 

 ____ and Tanke, D.H. 1992. Paleopathology of Vertebrates: Insights to
Lifestyle and Health in the Geological Record. Geoscince Canada, 19(2):73-82.

 Tanke, D.H. and Rothschild, B.M. 1997 (in press). Paleopathology. pp.
___-___. In: Encyclopedia of Dinosaurs. Edited by P.J. Currie and K. Padian.
Academic Press, London.

 
Darren Tanke
Technician I, Dinosaur Research Program
Royal Tyrrell Museum of Palaeontology, Box 7500
Drumheller, Alberta, Canada. T0J 0Y0
             and
Senior Editor on the:
Annotated Bibliography of Paleopathology, Dento-Osteopathy and Related Topics
11,162 citations as of February 8, 1997.
Visit our bibliography homepage at: http://dns.magtech.ab.ca/dtanke
Can you help with this ongoing project? Email me at: dtanke@dns.magtech.ab.ca