Above: Possible extents of oviraptorid beaks, from Jansen's thesis.Recently, some of my adventures on Wikipedia have addressed the question of oviraptorid beaks. Now, contain yourselves, I know this sounds a little too exciting. But it's really a very rarely addressed topic. It's obvious that oviraptorids had beaks of some kind, with their strong, toothless, pointy jaws that don't quite close right when unsheathed by rhamphotheca (the keratinous covering that forms the beak). But just how these beaks looked and to what extent they covered the jaws hasn't been studied in a lot of detail.
I asked about this a few times back on the old version of dinoforum, and some commentors there (especially oviraptorer Jaime Headden) were very helpful in pulling educated guesses based on modern analogues. Jaime's conclusion, IIRC, was that most oviraptorids have been constructed with beaks that are too large or, more specifically, cover too much of the skull and jaws. You can see the difference in two versions of my own ovi profile drawings, old one here with extensive beaks, new one with corrected beak after Headden here. Note also the more subtle difference--the beaks on the newer version meet flush, without the upper beak overlapping the other (what use would that be?) and the beak does not incorporate the nostril, which is the exception, not the rule in modern beaked animals like birds and turtles.
The first real scientific work on this topic has not yet hit the official literature, but an unpublished phD thesis by Stig Jansen addresses this topic. Jansen also has a similar unpublished paper floating around for ornithomimid beaks, I'm sure you're Google-fu will turn it up.
Jansen's thesis comes to essentially the same conclusions as Headden did, and presents two potential extremes for the extent of oviraptorid beaks, illustrated by him above. Interestingly, one of the options has a keratin-less crest. Traditionally, crested oviraptorids or those with tall, pronounced skulls have been restored with horny, cassowary-like casques, though there was never any direct evidence for this, and they could just as well have been covered in skin or feathers.
Above: Skull reconstruction of Banji, note the striations on the crest. Fig. 2 from Xu & Han 2010.
I felt Jansen's approach was very weak. I'll be interested to see when it comes out, but it relies too much on superficial bone anatomy without considering microanatomical surfaces for the attachment of keratin and soft tissues, I would have liked to have seen a more aggressive study. This work doesn't really meet the bar for what should be standards of inferring nonbony skin structures in fossil sauropsids.
ReplyDeleteIt's great that he shows in turtles how the shape of the bony structure influences the shape of the beak, but it needed to be taken more aggressively.
Incidentally, the paper about beaks in ornithomimids and birds wasn't written by Jansen, it was written by Espen Knutsen. The final paragraph of that thesis reads:
"I suggest that future studies in this area should put a greater emphasis on histology to see whether the bone-structure in the area covered by ramphotheca shows any anomaly compared to the rest of the skull (especially in the junction from cover to non-cover). Histological examination of the foramina in birds with comparisons to ornithomimids (and other theropods) might also reveal if they are connected to keratin growth-zones, or if they can throw light on the type of sensory papillae present."
Neither thesis tackles the issue of what's going on at a less than superficial level. The methods used in both papers doesn't really help clarify the extent of the beak in either extinct taxa.
Until someone rolls up their sleaves and starts looking at the snouts of oviraptorosaurs and ornithomimids on a microanatomical level, either through high-res X-ray CT or histology, and compares the data collected to that of living birds, turtles and other beaked vertebrates, we're not going to even begin to really understand what's going on here.
Also, other workers have basically already started doing this-i.e. looking at microanatomy of dermal skull bones and finding ramifications for the extent/type of skin structures present over those bones. The bar is set high,if the work isn't done to meet a good understanding of what's really happening at the interface of hard and soft tissues, then any assumptions about the extent of keratins is just arm waving.
Can I just say that I only had a few hours to take pictures of the original skull, and my presumptions are based on the pictures. This was my Master thesis, and I had a year or so to study around the topic. More thorough studies should have been made, but I didn't have enough time, or money, to study the microanatomical surfaces for the attachment of keratin and soft tissue.
ReplyDeleteMy friend Espen M. Knutsen (Beak morphology in extant birds with implications on beak morphology in ornithomimids) and I are two of only a handful people that actually have compared the structures in jaw bones of oviraptorids, ornithomimids, birds and turtles, and the lack of original skulls did it difficult to simulate the accurate beak extension. But we did found out that only a few bones in the skull actually are covered with ramphotheca.
I know my conclusion is highly discussable, and my only goal was to get people thinking in a new direction.
Stig Olav
Hi Stig,
ReplyDeleteDon't get me wrong, I think it's great though that someone actually went in and started looking at this.
After all, a Master's thesis only opens the door on an idea usually.... can't wait to see what work comes in the future on this if you're going to keep going. :)
Nick