Ammonicrinus

Nothing too heavy today; I just wanted to draw your attention to a very unusual crinoid, Ammonicrinus from the Early and Middle Devonian of Europe and north Africa. While we're used to the idea that crinoids are either stalked things with spindly arms, or free-floating things with spindly arms, not all of them stuck to this body plan. Some of them evolved an enrolled body plan, such as Myelodactylus, which as a fossil looks a bit like a curled-up millipede. Some of them went even farther, like the subject of today's post (and see Bohatý 2011 for much more information).

Yes, this is a crinoid, just... different. Figure 1 in Bohatý (2011). CC-BY-4.0.

Ammonicrinus came in three great flavors: stalked and with a shielded but exposed crown ("exposed roller-type", seen only in the early history of the genus); stalked and with an entirely enrolled crown, most of the animal laying on the seafloor ("encased roller-type"); and barely stalked with an entirely enrolled crown, perched on a brachiopod shell ("settler type"). For the remarkable "encased roller-type", the base was a holdfast attached to something, which was followed by several large, bead-like columnals. Then the columnals began to widen and flatten into broad concave-convex structures, shaped something like brackets in cross-section. These bracket-shaped columnals then turned into a much narrower section which connected to a stocky crown. The crown and the thinner columnals were wrapped up within the broader bracket-shaped segments, with just enough space on either side to pass water through. For good measure, the segments were also decorated with long, articulated, echinoid-like spines (Bohatý 2011).

An early Ammonicrinus, of the "exposed roller-type". Figure 6 in Bohatý (2011). CC-BY-4.0.

What could have possessed the ammonicrinids to go in this direction? One possibility is that everything is tied to making an end-run around other crinoids. Typical crinoids would filter higher in the water column; Ammonicrinus could have the lower levels all to itself. The drawbacks are that the crinoid would be more exposed to predation from benthos (it's hard to believe that anything would willingly eat a crinoid, but there's no accounting for taste), and would be more vulnerable to fouling from the muddy bottom. Ammonicrinus addressed the issue of predation by protecting its crown via enrolling; the spines would have also offered protection. The spines would have also helped to brace the animal against the unstable bottom environment. To keep water flowing and to clear itself of sediment, it could rock the enrolled part of the skeleton, which would force water through the crown (Bohatý 2011).

An Ammonicrinus doing its thing, rocking to promote a current. Figure 14C in Bohatý (2011). CC-BY-4.0.

References

Bohatý, J. 2011. Revision of the flexible crinoid genus Ammonicrinus and a new hypothesis on its life mode. Acta Palaeontologica Polonica 56(3):615–639.

Your Friends The Titanosaurs, part 27: Ruyangosaurus, Saltasaurus, and Sarmientosaurus

Today on "Your Friends The Titanosaurs", it's a giant enigma (Ruyangosaurus giganteus), a much smaller and much better known titanosaur that also turns out to have its enigmatic side (Saltasaurus loricatus), and a good old-fashioned titanosaur skull taxon (Sarmientosaurus musacchioi), plus special guest stars Noasaurus and the Rincón de los Sauces titanosaur! (If anything seems odd, formatting-wise, it's because this is my first structurally complex post since Blogger changed to a new interface, and I'm dealing with a couple of things.)

Port Kennedy Bone Cave

I'd gotten to thinking about some things I'd written at other venues, including some pieces I'd done as National Fossil Day monthly features a few years back, at the moment only accessible through Internet Archive but potentially to come back one day. One of these I thought I'd scoop up, given I'd written a companion piece for it here back in the day: a description of Port Kennedy Bone Cave. (Also, it fits in with other Eastern caves covered so far, all sharing the common thread of being investigated by Henry Mercer near the end of the 19th century). So, here it is, with the text edited to be more like the blog style, and inline citations included.

Algoasaurus bauri

I'm going to go out on a limb and guess that most of you at best only know of Algoasaurus bauri as a name in a dinosaur genera list or a few lines of text in a comprehensive reference, unless you are from South Africa, are really into sauropods, or just keep track of dinosaur trivia. It had never spent much time in my thoughts until about a week ago, when I was paging through Dinosaurs: The Encyclopedia for some other reason, and I chanced upon the Algoasaurus entry. There, on page 103, was a reprint of the original line drawings from Broom (1904). In the center was a partial neural arch of a posterior dorsal vertebra, and as I glanced at it, it was whispering "Hey, buddy. Yeah, you. Don't I look kind of rebbachisaur-ish?"

From Broom (1904). The "x 1/7" business is not accurate outside of the original paper, but I will say the femur is estimated to have been 50 cm long (20 in) when complete, if that helps.

Normally I do not have 116-year-old line drawings whispering phylogenetic suggestions at me, so I thought I'd look into it a little more. What the heck, I like covering obscure dinosaurs of historic interest anyway.

Algoasaurus bauri was named by Robert Broom in 1904 for a partial skeleton discovered the year before during quarrying operations in Despatch, on the south coast of South Africa. It thus became the very first sauropod described from the continent of Africa. As Anchisaurus can tell you, what the quarry giveth, the quarry taketh away. The quarry workers were not especially interested in the find, and did not separate most of the bones from the clayey rock being used to make bricks, meaning to this day there may well still be bricks in the Nelson Mandela Bay Metropolitan Municipality that contain trace amounts of sauropod. Broom reported that the Port Elizabeth Museum collected "a few fragments of vertebrae and ribs", and that a separate attempt was made to recover more bones still at the site. The formation is now regarded as the Lower Cretaceous Kirkwood Formation (McPhee et al. 2016).

All told, Broom ended up with "a number of very imperfect fragments of vertebrae—cervical, dorsal, and caudal—a fairly good femur, an imperfect scapula, portions of many ribs, and an ungual phalanx". He most frequently compared the bones to Brontosaurus and Diplodocus, which isn't saying much in terms of classification, because at that time the only other reasonably complete sauropod he had to work with was Morosaurus (Camarasaurus). Due to the limited material and the equally limited opportunity for comparisons, Broom did not have much to say about the bones beyond generalities and measurements, although he did note that the femur had a small fourth trochanter and thus a less powerful caudofemoralis than the other known sauropods. He named the animal for Algoa Bay and the then-recently deceased paleontologist George Baur, producing something like "George Baur's Algoa Bay lizard".

From there, A. bauri was met with resounding shrugs, the fate of most sauropods until recent decades. Like some other taxa (Austrosaurus is particularly guilty of this), it made the rounds of the existing groups without finding a firm home; it was generalized enough to fit in almost anywhere, and sauropod classification was generalized enough to accommodate it almost anywhere. Broom gave material from his private collection to the American Museum of Natural History in 1913, including the A. bauri ungual phalanx he mentioned in Broom (1904), where it became AMNH 5631 (Broom 1915; now AMNH FR 5631 if you're searching their database).

A. bauri staged a minor resurgance in the early 2000s. Apparently I'm not the only person to have experienced the phenomenon of the chatty neural arch, because Canudo and Salgado (2003) brought up the apparent absence of a hyposphene as potentially indicating a rebbachisaurid affiliation. And why not? There's some intuitive appeal, after all; it's not a huge sauropod, and it comes from a reasonably appropriate time and place to be a rebbachisaur. The possibility of Algoasaurus being a rebbachisaur was mentioned into the early 2010s (e.g., Ibiricu et al. 2012), but received a solid dumping of cold water in McPhee et al. (2016). Not only could McPhee et al. not classify A. bauri beyond Eusauropoda indet., they couldn't find the type material, besides the AMNH claw and a caudal vertebra that potentially belonged to the type in the collections of the Iziko Museum in Cape Town (SAM-PK-K1500, if you're curious). It seems that Algoasaurus is not something you can set out to find; it just shows up whether you're prepared or not. (Why couldn't Broom have given the AMNH a more useful piece, like, say, that neural arch? Drat.)

So, pending discovery of a new specimen of A. bauri (and being able to make a convincing argument that it *is* A. bauri), or the rediscovery of more of the type, the neural arch of Algoasaurus will just have to whisper in vain. After all, while the neural arch whispers about rebbachisaurs, the scapula, at least as depicted, says "Are you sure about that? You know what a rebacchisaur scapula looks like." (The femur says "What are you looking at me for? I'm just a femoral shaft.")

References

Broom, R. 1904. On the occurrence of an opisthocoelian dinosaur (Algoasaurus Bauri) in the Cretaceous beds of South Africa. Geological Magazine, decade 5, 1(483):445–447.

Broom, R. 1915. Catalogue of types and figured specimens of fossil vertebrates in the American Museum of Natural History. II.–Permian, Triassic and Jurassic reptiles of South Africa. Bulletin of the American Museum of Natural History 25(2):105–164.

Canudo, J. I., and L. Salgado. 2003. Los dinosaurios del Neocomiense (Cretácico Inferior) de la Península Ibérica y Gondwana occidental: implicaciones biogeograficas. Pages 251–268 in F. Pérez-Lorente, editor. Dinosaurios y Otros Reptiles Mesozoicos de España. Instituto de Estudios Riojanos, Logroño, Spain.

Ibiricu, L. M., G. A. Casal, M. C. Lamanna, R. D. Martínez, J. D. Harris, and K. J. Lacovara. 2012. The southernmost records of Rebbachisauridae (Sauropoda: Diplodocoidea), from early Late Cretaceous deposits in central Patagonia. Cretaceous Research 34:220–232.

McPhee, B. W., P. D. Mannion, W. J. de Klerk, and J. N. Choiniere. 2016. High diversity in the sauropod dinosaur fauna of the Lower Cretaceous Kirkwood Formation of South Africa: implications for the Jurassic–Cretaceous transition. Cretaceous Research 59:228–248.