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Bernissart Iguanodons and their significance (long)


I'm new to the list (although my posting of the Aucasaurus publication was
forwarded to the list by G. Olshevsky), and would already like to make a
relatively long contribution on the Bernissart Iguanodons. I noticed that
this discovery was being discussed on the list a few days ago; being
Belgian, and having visited the Brussels Museum and having seen the
skeletons on numerous occasions, I think that my comments may help to
clarify the discussion. You will notice in this posting (and all future
messages), that I tend to be a fanatic when it comes to correctly using
generic and species names, and when referring to clades. I'd like to commend
G. Olshevsky for the incredible work he has done to sort out the taxonomic
mess that often existed.

A total of some 30 skeletons were discovered at the Bernissart site in the
late 19th century, all but one belong to the large species Iguanodon
bernissartensis (Boulenger vide van Beneden, 1881), a single smaller
skeleton was referred to Iguanodon mantelli (von Meyer, 1832). The
differences (not only size) of the I. mantelli specimen have been explained
to be related to ontogeny or sexual variation, however, the specimen is
neither a juvenile, nor a female specimen of I. bernissartensis.

The display of the skeletons in the Brussels museum (10 mounted skeletons,
including I. mantelli, all in the now outdated kangaroo-like pose; and about
20 less complete skeletons as in situ mount) makes it easy to compare I.
mantelli to I. bernissartensis. It is obvious that both belong to different
species. I. bernissartensis has extremely robust and powerful arms that
almost certainly prove that this species was primarily quadrupedal (you can
also see that these skeletons were forced into a bipedal kangaroo-like pose,
the caudal vertebrae have been assembled in a way that the tail would simply
have broken when the animal was alive). The arms of I. mantelli are much
more slender, and the skeleton appears to be correctly displayed in a
bipedal pose.

This is just one (visible) argument to justify that there were two different
species present at  125 MYA Bernissart. So Dr. David Norman was correct when
he finally settled the debate in the 1980s, and concluded there were 2
species present. He also referred I. mantelli to I. atherfieldensis; I have
compared British Wealden specimens (when visiting UK museums) of I.
atherfieldensis to I. mantelli, and they look identical in every anatomical

This is my proposal to resolve the confusing taxonomy of several species of
the genus Iguanodon :

Iguanodon bernissartensis (Boulenger vide van Beneden, 1881): the ICZN
(2000) was wise to adopt this species as the type species

"Iguanodon atherfieldensis " (= "I." mantelli) (Hooley, 1925): because this
species differs significantly from the type species, it should be placed
into a separate genus; Heterosaurus (Cornuel, 1850), Vectisaurus (Hulke,
1879) and Sphenospondylus (Lydekker, 1888) are all senior synonyms, all
these also received separate species names, H. neocomiensis, V. valdensis
and S. gracilis respectively (cfr. Olshevsky's genera list), all these
should be formally suppressed to retain the species "I." atherfieldensis.
Eventually "I." atherfieldensis may thus become Heterosaurus atherfieldensis
or (preferably) receive an entirely new generic name.

"Iguanodon" anglicus (Holl, 1829) : while Mantell's famous Maidstone slab (a
partial Iguanodon skeleton) has often been referred to "I." anglicus, it can
be demonstrated to be a specimen of "I." atherfieldensis. Which leaves "I."
anglicus with only very fragmentary material (a few teeth and postcranial
scraps), this material almost certainly belongs to "I." atherfieldensis but
it will never be possible to establish this because of the fragmentary
nature. The only option is that "I." anglicus will forever remain a nomen
dubium (similar situation as the remains of the sauropod "Rebbachisaurus"
tamesnensis, which almost certainly belong to Jobaria tiguidensis).

Conclusion :
Iguanodon bernissartensis is more closely related to the massive
iguanodontids Altirhinus kurzanovi (Mongolia) and Lurdusaurus arenatus
(Niger), they probably form an (yet unnamed) iguanodontoidean clade that did
not make it into the late Cretaceous.
"Iguanodon" atherfieldensis is more closely related to the gracile
hadrosauroid Ouranosaurus nigeriensis (Niger), but appears more primitive
(retained a larger thumbspike, Iguanodon-like skull ...), and is part of the
lineage that led to the more advanced hadrosaurids.

More information on the significance of the Bernissart discovery :

Not only Iguanodon skeletons were found, an incredible amount of vertebrate
and plant fossils was also recovered :
1. numerous plant fossils including mostly ferns and other primitive plants
(which led some researchers to conclude that the ecosystem was late
2. thousands of fish fossils, including several new species, all non-marine.
3. fragmentary remains of a primitive amphibian and even insects
4. some 300 relatively small coprolites, analysis discovered muscle tissue,
so they were all referred to theropods (I believe that many, if not most,
belong to more primitive archosaurs and are in fact crocodilian)
5. a beautiful nearly-complete skeleton of a dwarf-crocodile, named
6. Iguanodon skin impressions were reported, but appear to have been lost
during the excavation, only drawings remain.
7. the only non-iguanodont dinosaur skeletal element that was found is a
theropod finger bone (manual phalanx) that was referred to "Megalosaurus"
dunkeri (= Altispinax dunkeri). The single bone definitely belongs to a 5-8
m (16-26 ft)long neotheropod, possibly another Wealden species like Baryonyx
walkeri or Neovenator salerii (manual elements of the latter are unknown).

The Bernissart discovery has often been used to support herding among
dinosaurs in general and ornithopods in particular. This may not be the case
however, the 30 skeletons were the result of at least 3 different
accumulations. Subsequently all skeletons probably simply drifted together
in a river bend. The herding theory of the Bernissart animals was never
really based on evidence, but more on the dramatic picture of a the complete
group falling from a cliff, when fleeing from a predator.

Not only did the discovery change the incorrect (with the spike mounted on
the nose instead of the thumb) reconstructions, that were until then based
on fragmentary remains from the Wealden of southern England. The skeletons
were so perfectly preserved that they revealed the typical caudal tendons of
large ornithopods.
The complex nature of the Iguanodon bernissartensis hand could also be
established; the three unguals of the middle fingers had evolved into robust
hoofs that were clearly designed to bear the weight of the animal when
walking quadrupedaly. Manual digit V was highly flexible and served like the
human thumb, for reaching and holding branches etc. The Iguanodon thumb
(manual digit I) was almost unmovable and its only function could have been
as a defensive weapon (against predators or other Iguanodons).

While Dollo was clearly ahead of his time when he studied the Bernissart
specimens, the research of the abundant fossils was reduced to nearly zero
after he left the Museum. Only the study of Dr. Norman (1980s) again
demonstrated the importance of the discovery.  I think that all fossil
remains (Iguanodons and others) should receive new complete revisions, and
particularly be compared to other Wealden fossils from France, Germany, and
especially England. This would help to really establish the early Cretaceous
Wealden as one of the best documented mesozoic ecosystems.

Re-opening of the Bernissart quarry is now quite impossible, the skeletons
were excavated in a coal mine no less than 300m (1000 ft) below the surface
of the earth. The mine shafts are completely flooded for almost 100 years.
After the initial discoveries of the 1880s, several attempts were made for
new excavations, but all failed due to financial or practical problems. Even
the Germans (when occupying Belgium during World War I) had plans but these
also never materialized. Who knows what treasures may still be waiting below
the surface of the old southwestern Belgian town ! (perhaps complete
skeletons of Eotyrannus lengi, Baryonyx walkeri, Neovenator salerii, the
Wealden ankylosaurs Hylaeosaurus and Polacanthus, and all those enigmatic
small coelurosaurus like Aristosuchus and Calamospondylus; and why not, a
complete early Cretaceous deinonychosaur that further supports their
relationship with modern Neornithes, the Wealden Ornithodesmus cluniculus
has recently been suggested as a dromaeosaur).

I could write more pages on the Bernissart discovery, but have to stop here.
If any of you have questions or comments on this topic, you are very welcome
to do so.


Gunter Van Acker

quote of the day; (Ian Malcolm) "Life finds a way"