The Ornithopod Thread- Hadrosaurs, iguanodonts and kin

Yes, in fact you see this with ceratopsians too- the juveniles of different genera/species are almost impossible to tell apart until they grow their characteristic horns and ornated frills, and as you surely know, many small, hornless ceratopsian genera have turned out to be juveniles of better known, larger ones (for example, Brachyceratops is know believed to be a juvenile Rubeosaurus- what was formerly known as Styracosaurus ovatus).

The experiment had already been done with Parasaurolophus in the 90s.

https://asunow.asu.edu/20151021-discoveries-how-speak-dinosaur

Right, higher oxygen levels and all that... good question, I really have no idea

Indeed, if it had been for visual display only they probably would've had soft-tissue crests, akin to those of Edmontosaurus if new discoveries are to be trusted.
Such a complex structure as Parasaurolophus' or Corythosaurus' crest had to serve more than one purpose- kind of like with antelope horns today.

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0145904

https://phys.org/news/2017-04-headless-dinosaur-reunited-skull-century.html

Nice look at a Muttaburrasaurus

http://www.abc.net.au/news/2017-09-04/road-trip-for-a-muttaburrasaurus-from-castlemaine-to-canberra/8852078

https://www.tandfonline.com/doi/abs/10.1080/02724634.2017.1398168?journalCode=ujvp20
(Abstract). 
Suggests Edmontosaurus was capable of quadrupedal gait from the start, rather than starting as obligate bipeds and becoming quadrupeds later on as had been suggested. 
(Below, Maiasaura hatchling, probably similar to the new find)

Weewarrasaurus, a new ornithopod from Australia. Known from a piece of opalised jawbone.

https://www.nationalgeographic.com/science/2018/12/exclusive-sparkly-opal-filled-fossils-reveal-new-dinosaur-species-paleontology/?fbclid=IwAR1RSRXCdzgY-RbT4l85z6OmOans7rYR_Cj-PFf_GZywLQC_wmKKbBILJfk

Not really sure how it difers from other small Australian ornithopods like Laellynasaura and Fulgurotherium, known also from very fragmentary remains...

https://www.eurekalert.org/pub_releases/2019-03/pmon-foo032919.php?fbclid=IwAR3bzkBLWWm4YbJO61m-4PdEzvWA_ABZMY_k5m1DrrHGIbCinRkA_wOuKEg#.XJ44QiNcGz4.facebook

Fostoria, a new iguanodontian described from Australia.

Dinosaur finds consisting of more than one bone are very rare in Australia; in this case, several elements were found, belonging to several individuals.

http://www.sci-news.com/paleontology/fostoria-dhimbangunmal-07265.html

Aquilarhinus, a new hadrosaur

https://www.msn.com/en-us/news/technology/this-shovel-chinned-eagle-nose-dinosaur-lived-in-texas-80-million-years-ago/ar-AAEf8gM?ocid=sf

Fathom wrote: »

Hadrosaurs had great variety. Differential reproduction?

Actually what I find intriguing about them is that postcranially, most of them look VERY much alike, and the head/crest is about the only thing that allows one to tell them apart. Something similar happens with ceratopsians. In both hadrosaurs and ceratopsians it can be extremely difficult even for paleontologists to determine what genus or species they're looking at unless there's a skull, and juveniles (which are yet to develop their distinctive crests) are even more problematic.

Although I suppose the same would be true of say, many antelopes if all we had to go by were the bones...

Fathom wrote: »

Did one species have a snorkel on the top of its head? For breathing at waterline, with rest of animal below surface?

The snorkel idea was once suggested for Parasaurolophus, perhaps the most iconic of the hadrosaurs (although one relatively rare in the fossil record):



The idea has long been discarded due to several reasons:

1. One would expect a snorkel to project more vertically; instead, the crest grows backwards and downwards at the tip.

2. Not all Parasaurolophus specimens have a long crest; in fact, it has been suggested that only adult males did, whereas females and juveniles had much shorter crests. This strongly suggests a role in courtship and social interaction. If the crest was a snorkel we would expect all Parasaurolophus to have the same equipment.

3. Most importantly, there is no opening at the tip of the crest. The animal's nasal passages DO go into the crest but it's just a detour; it is currently believed that the crest functioned not just as a visual display but also as a trombone of sorts, amplifying the dinosaur's calls.

In the 90s, scientists used a computer simulation to calculate how much air a Parasaurolophus would've been able to blow from its lungs, and reconstructed its possible voice. Check it out, it's rather eerie:



Keep in mind that Parasaurolophus is believed to have prefered more forested areas than other hadrosaurs, so it makes sense that sound would've been an important part of its communication.

Also worth mentioning that hadrosaurs as a whole are no longer believed to have been semiaquatic, as was once proposed. The idea was that since they had duck-like beaks, they probably dived to feed on aquatic plants, but this has long been disproven; the beaks were only vaguely reminiscent of those of ducks; in life, they were covered by a rather hooked, sharp keratinous cover to crop vegetation, and they had batteries of thousands of tiny teeth to grind hard food. They weren´t feeding on soft water plants.

Another piece of supposed evidence for their aquatic lifestyle was the fact that a "mummified" hadrosaur was once found which showed what was interpreted to be webbing between its fingers. However, later it was found that this supposed membrane was actually a sort of "mitten" of skin that kept the three central fingers bound tightly together, an adaptation for supporting the animal's weight as it walked on four legs.

Their tail was also not flexible, but rigid and very heavy, and probably one of their main means of defense against predators (they could use it like a sledghammer to strike a predator ). It was not sinuous and crocodile-like as suggested by early paleontologists.

So in short, we have no evidence of aquatic or semiaquatic hadrosaurs as of this moment, and absolutely no evidence of any dinosaurs having snorkel-like crests.