This time we don't stop in Patagonia, instead visiting three different landmasses to meet three smallish titanosaurs known primarily from bones between the middle of the neck and the base of the tail. If you feel like you need a hit of fresh Patagonian titanosaurs, if you have access to the Journal of Vertebrate Paleontology allow me to suggest Otero et al. (2020), right off the presses, on the appendicular anatomy of Patagotitan mayorum. Or perhaps freely available Kundrát et al. (2020), dealing with an embryonic Patagonian titanosaur with a blunt horn?
Sunday, September 20, 2020
Sunday, September 13, 2020
When I wrote about the NPS fossil proboscidean inventory, you may recall that I mentioned there was one Eastern record I wished I could have confirmed. I thought it was only fitting to shine a spotlight on it in conjunction with the anniversary of the event that made the park unit in question famous.
Sunday, August 30, 2020
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.|
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.
Sunday, August 23, 2020
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.)
Sunday, August 16, 2020
Sunday, August 2, 2020
|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.")
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.
Sunday, July 26, 2020
|One of these...|
Craniates, in brief, are brachiopods from the "inarticulate" structural wing but the "calcitic" compositional wing. At the Brickyard section, the two most abundant are Acanthocrania setigera and Petrocrania halli, which can be difficult to distinguish in practice (Rice 1987). The phosphatic inarticulate Schizocrania, which does a lot of the same things, is also present but much rarer. Other inarticulates at the Brickyard, from the phosphatic side, include Craniops minor, Pseudolingula eva, and Trematis sp. (Rice 1987). Other species are cited in museum collections; one which I've seen, "Crania" (now Acanthocrania) granulosa, looks suspiciously like the "raspberry cystoids" in this post.
Acanthocrania and Petrocrania have thin domed shells with concentric growth rings. Unlike most of the other Decorah brachs, they do not have strong ridges (and, of course, they don't look much like the other brachiopods in a lot of other ways, too). They seem to have been attractive to encrusters; all of the loose specimens I have are covered with bryozoans, and some of them have either tabulate corals or cornulitids growing on them as well. For their part, craniates are noted encrusters of other brachiopods; presumably the unattached specimens in the photos were also originally attached to other brachiopods, becoming dislodged (probably after the death of the craniate).
|What do the five rounded domed blobs of bryozoans have in common? If you turn them over, they all have the heart of a brachiopod.|
|This strophomenid has a craniate encrusting on the lower right, as well as several cornulitids.|
Rice, W. F. 1987. The systematics and biostratigraphy of the Brachiopoda of the Decorah Shale at St. Paul, Minnesota. Pages 136–166 in R. E. Sloan, editor. Middle and Late Ordovician lithostratigraphy and biostratigraphy of the Upper Mississippi Valley. Minnesota Geological Survey, St. Paul, Minnesota. Report of Investigations 35.