A pelvis at the front – the notarium

Time to continue the general lesson in odd bits of pterosaurian anatomy and here we have a real specialisation: the notarium. This is unique to larger pterodactyloids and is essentially a fusion of the vertebrae that make up the spine where the shoulder articulates with the back to produce something that looks rather like a pelvis at the front. It has some interesting connotations for pterosaur evolution and ecology, and that of the development of bone in general.

The notarium turns up in all the pterodactyloid lineages except the basal ctenochasmatids (which include Pterodactylus) or any of the rhamphorhynchoids. It does therefore appear to have evolved early on in pterodactyloid evolution and been present in all but the most basal clade (and several other individual taxa from around the pterodactyloid tree it should be added), and probably not coincidentally appears just as pterodactyloids (and by extension pterosaurs as a whole given the relatively small size of the rhamphorhynchoids) started to get big.


A pterodactyloid notarium (the head would be towards the left). The articulation point for the shoulder is indicated by the rough patch of bone on the right hand end. This specimen is from a young animal hence the general lack of fusion of the various bones though the general pattern is clear.

The notarium consists of a number of dorsal vertebrae fused together into a single functional unit with both the actual centra (the big bit at the base of a vertebra) and the neural spines (the tall bits on top that you can feel on your own back when you bend forwards) being fused. The neural spines don’t always ‘fill in the gaps’ though in the way that the pelvis generally does, so you do see spaces remaining between them.

Having taken a very brief glance at the pterosaur literature, no one seems to have bothered cataloguing how may vertebrae make up the notarium except in a few specific species but in my experience it’s typically over five.

Apart from the basic morphology of a notarium being just a bunch of vertebrae welded together they typically have a socket sunk into the neural spines for the scapula (shoulder blade) to fit into. This is because the basic function of the notarium is to provide a strong platform for flight. With big pterosaurs (and as noted, only the big pterodactyloids have a notarium) they need a secure base for anchoring the flight muscles to power the flight stroke (and pterosaurs, unlike birds have a quite a lot of muscles mass on their shoulders for the upstroke) and to anchor the scapula itself. It might also serve to support forces going through it with the kind of quadrupedal launch hypothesised by Mike Habib. The notarium then as essentially an anterior pelvis makes a lot of sense mechanically.

The interrelationships of the various pterosaur clades are somewhere between complex and controversial depending on exactly your view, and even while some clades remain pretty fixed, different species can flit between groups causing problems. While all pterodactyloid clades apart from the ctenochasmatids (assuming you even think they are a true clade) have taxa in them with notaria, several species definitively do not have them (we have a good skeleton and there’s no notarium) and others may not (we just don’t know as we don’t have a complete enough skeleton). The short version is that it tends to be absent (or apparently absent) in relatively small taxa (like Tapejara and Germanodactylus) and then present on the big ones. It’s not present in juveniles either, or of course in the relatively small rhamphorhynchoids.

The obvious conclusion then is that this has evolved multiple times in multiple clades because it is a functional necessity of large size in pterosaurs (or perhaps flying animals in general since we don’t have any really giant birds or bats to compare to them). The notarium provided a stable base for the attachment of flight muscles and to anchor the scapula for both flying and launching into the air.

10 Responses to “A pelvis at the front – the notarium”

  1. 1 Mike Taylor 05/06/2009 at 8:06 pm

    Thanks, Dave, interesting stuff. Except: shouldn’t the notarium be described as a SACRUM at the front? We already have a perfectly good pelvis at the front, namely the pectoral girdle.

    The first ever skeletal reconstruction of a sauropod — John A. Ryder’s (1877) Camarasaurus — was given a notarium. See http://www.miketaylor.org.uk/dino/pubs/dahp2008/abstract.html

    I would LOVE to know what was going through his (or more likely) Cope’s mind when they made that decision. Is it possible that the pneumatic vertebrae of Camarasaurus were put Cope so strongly in mind of birds that he reconstructed the anterior dorsals as birdlike in this way?

  2. 2 David Hone 05/06/2009 at 8:30 pm

    Hi Mike, yes probably, but I wanted to draw th audience in and with lots of people of varying levels of interest / knoweldge in palaeo, I didn’t want to use a word they migth to recognise (sacrum) to describe another they might not recognise. I have still not got around to doing any really proper anatomical posts or I could jsut link to myself to cover for it, so till then I’m keeping things loose.
    As for the Cope mount, maybe he felt it was so heavy it would need the extra support to mount the muscles / forces of transporting such a body. Even now I look at something like Brachiosaurus and wonder how te hell the humerus didn;’t just slide out when it put it’s full weight forwards.

  3. 3 Andrew R. C. Milner 06/06/2009 at 12:16 am

    You mention in your experience five or over fused vertebrae in the notarium. What’s the maximum number of vertebrae you, or anyone else, have seen fused?

  4. 4 David Hone 06/06/2009 at 7:40 am

    Unwin (2003) has a drawing of a Pteranodon notarium with 9 in in (7 main ones and then two more fused at the centra, and with their neural spines fused as a pair, but those neural spines NOT fused to the other 7, but I think it’s still a single functional structure). The truth is we don’t have that many of them as despite being big and robust structures, we don’t have many good large pterodactyloid specimens. It would not surprise me if we found one with a notarium and a sacrum and possibly nothing in between (i.e. all the dorsals are fused to one or the other) and a couple of taxa only have two or three free dorsals. There’s been no systematic review of them that I know of and I’ve not seen many, so I can’t be more precise, sorry.

  5. 5 David Marjanović 09/06/2009 at 2:35 am

    It would not surprise me if we found one with a notarium and a sacrum and possibly nothing in between (i.e. all the dorsals are fused to one or the other) and a couple of taxa only have two or three free dorsals.

    That’s what some birds look like – except that bird notaria never articulate with the shoulder girdle.

    • 6 David Hone 23/06/2009 at 2:27 pm

      Quite, and given the size of the notarium and pelvis in say Pteranodon (in terms of the numbers of vertebrae involved) it’s certainly plausible if not likely. I’d love to see a complete series from a big azdarchid.

  6. 7 Nick Gardner 09/06/2009 at 11:04 pm

    Where did you get that scale bar? I think I have two like that.

    • 8 Nick Gardner 09/06/2009 at 11:07 pm

      … which sounds curiously like I don’t know where I got my own scale bars from. Which isn’t the case, since I picked up both at SVP last year, I was just curious if we got them from the same vendor. I never seem to be able to have scale bars at my disposal when I go to snap photos for personal use, I find myself using ad hoc alternatives, like gel pens and measuring tape (the latter being obviously better).

  1. 1 Pterosaur ontogeny « Dave Hone's Archosaur Musings Trackback on 14/05/2012 at 8:30 am
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