Origins of Minmi paravertebra?

[triceratops83]

  Anyone care to guess how a predominantly Laurasian group of creatures managed to get one of their own into Australia? I know that Africa, for instance, had a similar fauna to the northern hemisphere in the Jurassic, so it probably had Nodosaurs like Gargoyleosaurus, and they could have spread to Australia - we have stegosaur footprints here, and likely had a similar set of animals to the rest of the world at that time. However, by the early Cretaceous, we had well and truly moved off and became isolated. Minmi is considered the basalmost member of Ankylosauridae, unlike Antarctopelta, (from late Cretaceous Antarctica) which is classed as a Nodosaurid, and makes more sense to be in the southern Hemisphere for the reason I just stated. Now, I never bought into that whole Serendipaceratops thing, I really can't see how a supposed Neoceratopsian got down here in the early Cretaceous, and it turns out that creature is something else anyway, but Minmi is Australia's most well preserved Dinosaur and can't be denied.
  So, does anyone else think it's weird that an Ankylosaur found its' way onto an isolated continent early in their evolution? If so, I'd like to hear your theories and thoughts on the subject. Maybe a Jurassic Ankylosaurid will be unearthed in Africa, but until then I think this is a novel subject for discussion. It certainly bugs me.

[Manatee]

This is an interesting topic. During the Early Jurassic the Americas, Australia, and Africa were all connected according to the ever-trustworthy Wikipedia, so it probably centers around the ancestors of Ankylosauria spreading out around that time. Finding a primitive ankylosaurian from Africa or South America would certainly clear things up, as you said. As of right now, there really is no thyreophorean giving insight into Minmi's ancestry; eventually there probably will be one found, and it should be interesting to see.

[triceratops83]

Someone could argue for an ancestor like Scelidosaurus, but then the cladistics would need to be overhauled. I'd like to know how Minmi was placed specifically in Ankylosauridae, rather than just the suborder Ankylosauria, which might make this easier to understand. As it is now, Minmi seems as unlikely to be found where it is as a Ceratopsian would be, whereas the isolation of Australia would more believably produce a remnant group of Cretaceous Stegosaurs.

[Dinoguy2]

Unfortunately, answers to many of these questions are probably to (never be) found in Antarctica, which served as the connection between Australia and the other continents for most of the Mesozoic.

[triceratops83]

More needs to happen in Antarctica, but I sympathise if it doesn't (I hate the cold.) I suspect there's a lot of interesting things buried down there.

[Lusotitan]

I know that Africa, for instance, had a similar fauna to the northern hemisphere in the Jurassic, so it probably had Nodosaurs like Gargoyleosaurus, and they could have spread to Australia - we have stegosaur footprints here, and likely had a similar set of animals to the rest of the world at that time.

Interestingly, there are no known ankylosaurids or nodosaurs known from Tendaguru or Lourinha. Only in the Morrison. Now, given that the Morisson is quite possibly the most well studied mesozoic formation period, certainly more well sampled then Tendaguru or Lourinha, this could be an artifact, but it might be notable none the less. Most other groups are known from at least two of these formations (Dryosaurids, Allosaurids, Ceratosaurids, Diplodocids, Brachiosaurs, Camptosaurids, Stegosaurids, Camarasaurids, Megalosaurids, etc), so it does seem odd that they're only found in North America.

[triceratops83]

I'm willing to hold my breath, Gargoyleosaurus and Mymoorapelta were only discovered relatively recently, and like you said, the Morrison has been worked more than the Tanzania and Portugal. One might turn up eventually. I just hope it's something that ties the sub-order together in a way that makes sense.

[DinoLord]

I think there's definitely potential for more Jurassic ankylosaur discoveries. Despite the extensive collection of the Morrison, Morrison ankylosaurs are quite rare compared to other Morrison fauna. I think that there are definitely some Portugese & Tanzanian ankylosaurs (and Minmi ancestors) waiting to be dug up.

[triceratops83]

On a similar note, I've seen some cladograms which place Muttaburrasaurus in the same family as Rhabdodon. For my Jurassic fauna argument it made more sense when Muttaburrasaurus was thought of as being a descendant of Camptosaurus, but now it belongs to a group of Late Cretaceous European Iguanodonts. I'm no cladistics expert but sometimes I think they rush these things.

[Lusotitan]

On a similar note, I've seen some cladograms which place Muttaburrasaurus in the same family as Rhabdodon. For my Jurassic fauna argument it made more sense when Muttaburrasaurus was thought of as being a descendant of Camptosaurus, but now it belongs to a group of Late Cretaceous European Iguanodonts. I'm no cladistics expert but sometimes I think they rush these things.

Yes, Muttaburasaurus has been consistently found to be a rhabodont these days. The fact that they also exist in Australia might be a bit surprising, but given a 90 million year ghost lineage before it was placed there, I wouldn't call it that extraordinary.

In summary, rhabdodonts appeared somewhere, around the J-K boundry, spread some direction, were doing stuff for 90 million years, in the mean time getting gigantic in the south, before becoming dwarfs at the end, then gigantizing again.

It's frankly seems surprising I'm the only person I've heard of who's favorite dinosaurs are rhabdodonts.

And if this wasn't enough, I saw an abstract in the SVP abstract book online this year saying they found Tenontosaurus to be a rhabodont. I'm not kidding. Incidentally, they also found Trinisaura, Macrogryphosaurus, and Anabisetia to be dryosaurids, and Ouranosaurus to fall in the middle of Hadrosauroidea. God hope this is Open Access.

[triceratops83]

In summary, rhabdodonts appeared somewhere, around the J-K boundry, spread some direction, were doing stuff for 90 million years, in the mean time getting gigantic in the south, before becoming dwarfs at the end, then gigantizing again.

Love the ambiguity.

[Brontozaurus]

Not exactly related, but does anyone ever consider island hopping as a means of dinosaur dispersion? I know we've got the continents all mapped out, but it seems likely to me that there might be islands that existed but never left a trace.

[Lusotitan]

Yes. It's likely this allowed North American taxa to get into Europe in the Jurassic (thought there was also a land bridge at some point, Asian taxa to get into North America throughout the Cretaceous, and allow American interchanges in the Late Cretaceous. There might have also been interchange from Europe to Appalachia (to Laramidia?) in this way.

[triceratops83]

Even during the early cretaceous I think that land bridges between South America and Antarctica are quite possible.