Sunday, January 19, 2020

Your Friends The Titanosaurs, part 20: Neuquensaurus, Normanniasaurus, and Notocolossus

The entrants this week come with both notability and downsides. Normanniasaurus genceyi is one of the few well-established Early Cretaceous titanosaurs, and Notocolossus gonzalezparejasi is one of the largest known titanosaurs. However, both are known from rather limited material to date. Neuquensaurus, on the other hand, has had no shortage of material referred to it, but is a historical mess. So far it has escaped the fate of Argyrosaurus superbus, Laplatasaurus araukanicus, and Titanosaurus indicus, historically significant names that have been re-analyzed and cut down to just a type specimen. There are still questions surrounding Neuquensaurus, but at least there are multiple specimens that can be assigned to it.

Sunday, January 5, 2020

A Devonian reef

When I visited Delaware Water Gap National Recreation Area and the surrounding area back in 2017, one of the places I stopped was at a Lower Devonian sponge-coral bioherm. A bioherm is a geological term for a mound-like feature made up of fossils. The useful thing about "bioherm" is that it just refers to the shape, rather than making any conclusions about how that structure came about. (You see, there are reefs, and then there are things that are like reefs but aren't reefs, and there are also just plain old accumulations of skeletal fragments, and there's actually a lot of nuance involved that can tell you things about depositional environment and so forth.)

Looks like circular stromatoporoid colonies with tabulates between them—or are there also some corallites in the circles? Things get complicated in a reef, especially 400 million years and some weathering later.

Anyway, this particular bioherm is one of a group identified as "patch reefs", which is more or less what it sounds like: a relatively small discrete reef. There's a handful of these scattered throughout the area, found in the Shawnee Island Member of the Coeymans Formation. They are described as including a central core up to 160 x 70 m (525 x 230 ft) in area and 15 m (15 ft) thick, surrounded by flank beds of skeletal debris. They are primarily formed of stromatoporoid sponges and favositid tabulate corals, and grew on a marine carbonate shelf (Monteverde 2001; Precht 1988). The rugged modern topography was still in the future; the Acadian Orogeny hadn't even kicked in yet and the previous topography generated by the Taconic Orogeny had been well eroded by the early Devonian.

This one's a bit easier to tell as a Favosites chunk (even if the photo isn't that sharp).

There hasn't been much occasion to talk about stromatoporoids previously. The first thing to know about stromatoporoids is that despite the confusingly similar name, they have nothing to do with stromatolites. Stromatolites, like Cryptozoon rosemontensis from back in 2014, are layered sedimentary structures left by microbial colonies. Stromatoporoids also show a layered appearance in cross-section, but that's because of layered body tissues: they were sponges (even if this is not immediately apparent), and produced body fossils, not trace fossils. The body, mineralized as calcium carbonate, consists of horizontal laminae supported by vertical pillars. A basic stromatoporoid plan has been adopted several times, including by some modern sponges, but classic Stromatoporoidea had its heyday in the middle Paleozoic as a reef-forming group. I don't think anyone has attempted to identify the Coeymans Formation stromatoporoids to genus or species since White (1882) invoked Stromatopora, but I might have missed that reference.

Not sure what's going on here; maybe a branching-type stromatoporoid (e.g., Amphipora) has gotten into the act as well.

On the other hand, the common Coeymans patch reef tabulate has been identified to the genus level as Favosites (Weller 1903; Willard et al. 1939; Epstein et al. 1967). Swartz and Swartz (1941) put it in F. helderbergiae, which is appropriate for the time and place, but you wouldn't be able to tell just walking by (unless you carry your own thin-sectioning equipment and microscope with you when you're out for a walk). Favosites, the "honeycomb coral", is rather more impressive than most of the tabulates in the Ordovician of Minnesota, rare Foerstephyllum colonies excepted. The reason for "honeycomb coral" isn't obvious from these photos, but if you did have a loose colony sitting in front of you, you'd be able to see the logic: it's a coral colony that resembles a chunk of honeycomb. Each "cell" of the "honeycomb" is a corallite that held a polyp, much smaller than the polyps of horn corals and other rugose corals but still much larger than the tiny animals of a bryozoan colony.

Not dinosaur skin, just weathering across a favositid that's been more effective on the corallite walls than the fill, producing a pebbly-looking "negative".

This photo shows a clear demarcation between favositid on the left and not-favositid on the right.

References

Epstein, A. G., J. B. Epstein, W. J. Spink, and D. S. Jennings. 1967. Upper Silurian and Lower Devonian stratigraphy of northeastern Pennsylvania, New Jersey, and southeasternmost New York. U.S. Geological Survey, Washington, D.C. Bulletin 1243.

Monteverde, D. H., leader. 2001. Road log and stop descriptions; Day 1, Stop 5: Montague mini-mall fossil site; flank of a coralline bioherm in the Coeymans Formation. Pages 191–198 in J. D. Inners and G. M. Fleeger, editors. 2001: a Delaware River odyssey. Field Conference of Pennsylvania Geologists, Harrisburg, Pennsylvania. Guidebook for the Annual Field Conference of Pennsylvania Geologists 66.

Precht, W. F. 1988. Lower Devonian reefs of the Coeymans Formation in the northern Appalachian Basin. Pages 514–519 in H. H. J. Geldsetzer, N. P. James, and G. E. Tebbutt, editors. Reefs; Canada and adjacent areas. Canadian Society of Petroleum Geologists, Calgary, Alberta. Memoir 13.

Swartz, C. K., and F. M. Swartz. 1941. Early Devonian and Late Silurian formations of southeastern Pennsylvania. Bulletin of the Geological Society of America 52:1129–1192.

Weller, S. 1903. The Paleozoic faunas. New Jersey Geological Survey, Trenton, New Jersey. Report on Paleontology 3.

White, I. C. 1882. The geology of Pike and Monroe Counties. Geological Survey of Pennsylvania, Harrisburg, Pennsylvania. Report of Progress 9(6).

Willard, B., F. M. Swartz, and A. B. Cleaves. 1939. The Devonian of Pennsylvania. Pennsylvania Geological Survey, Harrisburg, Pennsylvania, 4th series. General Geology Report 19.

Sunday, December 29, 2019

2019 in Review

It was a fairly quiet year here at Equatorial Minnesota. Although I don't particularly trust the statistics because of the miracle of referrer spam, none of this year's entries were unusually popular or unpopular. The local topics continued to dwindle, something I plan to look at.

Not enough of these lately.

Saturday, December 21, 2019

Your Friends The Titanosaurs, part 19: Muyelensaurus, Narambuenatitan, and Nemegtosaurus

Since the previous titanosaur post, two more genera and species have been added: Nullotitan glaciaris (Novas et al. 2019) and Yamanasaurus lojaensis (Apesteguía et al. 2019). Nullosaurus is currently in line for the February "YFTT", but there will probably be another six or seven titanosaurs by the time I get around to Yamanasaurus. In the meantime, we have a definite rarity: three titanosaurs with skull material.

Sunday, December 8, 2019

St. Croix Cambrian trace fossils

Here's something simple: photos of Cambrian trace fossils in the St. Croix Valley. If you would like a refresher on the rocks in question, may I suggest this post? We've already seen some photos of Skolithos burrows in the Mazomanie, a sandstone unit. The finer-grained rocks have other kinds of trace fossils, which makes sense because they represent different environments than the Mazomanie. At the same places in Osceola where Skolithos are found in abundance in the Mazomanie, much different burrows are locally abundant in the overlying St. Lawrence Formation. In the upper part of this formation, where the beds are sandy and can be hard to tell from the Jordan Sandstone (Sardeson 1932), the burrows are much thicker and horizontal.

There are a few in these pieces of float, including just below the scale bar and in the block above and to the left of the central block. The squares in the bar are 1 cm, so the burrows are a bit larger, on the order of finger-sized.

Returning to the same area nearly two and a half years later, I came across these remnants of a disintegrated block. If you expand the photo, you'll see that the largest chunks are those with burrows.

Comparable burrows can be found lower in the formation, in more typical-looking gray-green blocks. I wasn't seeing body fossils, which are reputed to be there, but there were certainly plenty of trace fossils.

This is more like what the St. Lawrence is supposed to look like, and there's another horizontal burrow, a bit smaller than those in the photos above but pretty similar.

One of the finer-grained units intertonguing with the Mazomanie is the Tomah Member of the Lone Rock Formation, another part of the ex-Franconia Formation. The Tomah is the finest-grained part of the Lone Rock Formation and has a tendency to erode into angular chips, blocks, and chunks, usually hand-sized or smaller, often in pastel greens and oranges. Some of the beds are heavily marked by various kinds of trace fossils.

Several different sizes are apparent here.

This one's unusual for having eroded out as a substantial piece.

This chip has traces close to 1 mm in diameter near the top and a thicker trace several mm across near the center, with a "lobed" appearance that may be due to erosion.

The large straight burrow on this piece has a lumpy surface somewhat reminiscent of "corn cob" Ophiomorpha, but not as coarse.

A slice of pizza covered with grains of rice?

I could go on ad nauseum with trace fossil photos from the Tomah (you may already be there), so just one more for the road. As far as I know, nobody has published a detailed analysis of the trace fossils in the Tomah or St. Lawrence, although I can't rule out there being some dissertation or other piece of grey literature I haven't run across. There's certainly quite a lot of these fossils there, though!

This one is dominated by burrows a couple of mm in diameter. Note the long slender trace in the upper center

References

Sardeson, F. W. 1932. Fauna of the Jordan Sandstone. Pan-American Geologist 58(2):103–106.

Sunday, December 1, 2019

Mimodactylus libanensis

If you're just in this for the dinosaurs, you may have gotten the impression that there aren't any Mesozoic fossils between, say, Egypt and Pakistan. This is not true; the Middle East just happens to specialize in marine Mesozoic rocks and fossils, so dinosaurs are not well represented. (Of course, these include the inevitable titanosaurs.) They're there, although as bits and pieces so far; eventually someone will name one. Pterosaurs are somewhat better known; before 2019 there was the azhdarchid Arambourgiana philadelphiae from Jordan and the much smaller azhdarchoid Microtuban altivolans from Lebanon. Now, Mimodactylus libanensis makes a third named pterosaur from this region, and is by far the best represented.

The type specimen of Mimodactylus libanensis (Figure 2 in Kellner et al. 2019, which see for full caption). The scale bar for a is 50 mm (2.0 in), and 10 mm (0.39 in) for the three insets. CC-BY-4.0.

Genus and species: Mimodactylus libanensis. The "Mim-" part is a reference to the Mineral Museum (MIM) of Beirut, Lebanon, where the type specimen is housed, and the ptraditional pterosaur "dactylus" comes from the Greek "dactylos", usually given as "finger" where pterosaurs are concerned. The species name refers to Lebanon (Kellner et al. 2019). Together, we get something like "Mineral Museum finger of Lebanon".
Citation: Kellner, A. W. A., M. W. Caldwell, B. Holgado, F. M. Dalla Vecchia, R. Nohra, J. M. Sayão, and P. J. Currie. 2019. First complete pterosaur from the Afro-Arabian continent: insight into pterodactyloid diversity. Scientific Reports 9:17875. doi:10.1038/s41598-019-54042-z.
Stratigraphy and geography: The type and only known specimen is from the Hjoûla Lagerstätte of the Sannine Limestone, of late Cenomanian age (early Late Cretaceous). It was found near Hjoûla in the northern part of Mount Lebanon Governorate, west and a little north of central Lebanon (Kellner et al. 2019). You may already know that Arabia has only recently split away from the African continent, geologically speaking. Back in the mid-Cretaceous, the two landmasses were still firmly connected and moving north, shrinking the Tethys Sea. Lebanon and other nearby areas were shallow marine settings on the leading edge of the tectonic action.
Holotype: MIM F1, a mostly complete and articulated to semi-articulated skeleton (Kellner et al. 2019). The skeletal restoration shows a few parts to be absent, such as the ilium and the top of the head, but I would not be surprised if at least some of these parts are actually present in the block but inaccessible.

The type specimen of Mimodactylus libanensis was a little fellow; Kellner et al. (2019) estimated its wingspan at approximately 1.32 m (4.33 ft). If that's a little abstract for you, the lower jaws are 102 mm long (4.02 in), and the humerus is 52 mm long (2.0 in). Kellner et al. (2019) interpreted it as a young individual, because many of the bones that fuse in adult pterosaurs were still unfused; for instance, no notarium (fusion of several dorsal vertebrae to brace the shoulders). Despite its youth, it is clearly not an example of either of the previously known pterosaurs from Lebanon, contemporaneous Microtuban and an unnamed ornithocheiroid. Rather, it was more closely related to one of the lesser-known groups of mid-Cretaceous pterosaurs, the istiodactylids (Kellner et al. 2019).

The istiodactylids are noted for having a small number of short pointed teeth, crowded toward the anterior end of relatively blunt and broad jaws ("relatively" meaning it doesn't come to a point, more or less). The breadth of the business end of the skull is sometimes compared to a duck's bill, but that's an exaggeration. Istiodactylus itself has one of those quaint, frustrating histories involving an early specialist (Harry Govier Seeley) inexplicably assigning a specimen to a genus known from completely non-overlapping material: in this case, a partial skull of a pterosaur placed in Ornithodesmus, otherwise represented solely by the hip vertebrae of what turned out to a dromaeosaur. Kellner et al. (2019) found M. libanensis to be near but just outside of Istiodactylidae proper, paired with the Chinese pterosaur Haopterus gracilis. They created Istiodactyliforms for M. libanensis and the istiodactylids, and Mimodactylidae for M. libanensis's branch.

M. libanensis has the istiodacylid-type crowding of small conical pointed teeth at the front of relatively broad jaws. There are some proportional differences in the wing compared to istiodactylids (the humerus being relatively shorter than some other elements), and overall the wings are relatively long as pterosaurs go, but the foot is similar to istiodactylids in being proportionally small. The pteroid (the rod-like projecting bone in the pterosaur wrist) is articulated pointing toward the body, for those of you keeping track of this historically controversial bone (Kellner et al. 2019).

The jaws of M. libanensis (Figure 3 in Kellner et al. 2019, which see for full caption). The scale bar for a is 10 mm (0.39 in), and for b is 1 mm (0.04 in). CC-BY-4.0.

Istiodactylids are often interpreted as preferring terrestrial areas and having scavenging habits. M. libanensis, on the other hand, is only known from a marine formation, and although its teeth are similar to istiodactylids, they aren't exactly the same. Kellner et al. (2019) looked in detail at a couple of hypotheses that would fit with the short pointed teeth. They decided insectivory was possible but questionable, because of the long wings and absence of insects (so far) in the host sediments. Instead, they proposed M. libanensis was going after decapod crustaceans in the shallow waters. The Hjoûla Lagerstätte, as the "lagerstätte" makes clear, is already known for producing well-preserved fossils, primarily of fish and crustaceans.

References

Kellner, A. W. A., M. W. Caldwell, B. Holgado, F. M. Dalla Vecchia, R. Nohra, J. M. Sayão, and P. J. Currie. 2019. First complete pterosaur from the Afro-Arabian continent: insight into pterodactyloid diversity. Scientific Reports 9:17875. doi:10.1038/s41598-019-54042-z.

Sunday, November 24, 2019

Hunting the history of the Channel Islands mammoths

My visit to Santa Rosa Island back in June was just part of a larger project on Channel Islands National Park, for which I've been gathering information, researching, and writing for a number of months. Part of that work is summarizing the history of paleontological investigations, which go back well into the 19th century, and one of the most important parts of that is the history of mammoth finds on the islands. As often happens the story turned out to involve many more parts than I thought.