Sunday, July 21, 2019

Your Friends The Titanosaurs, part 14: Kaijutitan, Karongasaurus, and Laplatasaurus

This time around there are two easy entries and one tougher entry. Kaijutitan maui was named this year, and Karongasaurus gittelmani seems to have been largely forgotten by researchers. On the other hand, Laplatasaurus araukanicus, one of von Huene's South American titanosaurs, is a (waste)basket case.

Sunday, July 14, 2019

Aquilarhinus palimentus

I get to knock another notable fossil park off my list today with a new basal hadrosaur from Big Bend National Park. The NPS doesn't have a park covering the classic Upper Great Plains terrestrial Upper Cretaceous rocks, but it does have Big Bend, one of the best southern North American Upper Cretaceous areas known (to say nothing of its Lower Cretaceous and Cenozoic records). Our visitor today is the arch-snouted trowel-jawed Aquilarhinus palimentus.

But first, a brief note which connects to the history of this blog: "Lori" the Morrison troodontid has been officially described, as Hesperornithoides miessleri (Hartman et al. 2019). There's really no point in my writing anything about it, because the two lead authors (Scott Hartman and Mickey Mortimer) have their own blogs where they are covering it and I certainly couldn't add anything to them, so check them out!

Sunday, July 7, 2019

What I Did While I Was Out, part 2

I was out of the office for work again last week. This time I was a bit farther afield than Wyoming and the Dakotas; on the weekend of June 29–30 I was on Santa Rosa Island, one of the five islands of Channel Islands National Park. Here's a few photos from Santa Rosa:

This is a pretty representative view from the central part of Santa Rosa Island, featuring grassy and brushy vegetation over a lot of up-and-down topography.

Sunday, June 23, 2019

Your Friends The Titanosaurs, part 13: Isisaurus, Jainosaurus, and Jiangshanosaurus

We take a brief break from South America and journey to India and China this time. Conveniently, two of the three most significant Lameta Formation titanosaurs have come up (the other is venerable Titanosaurus indicus, which isn't for a while yet). On the other hand, that does mean we're going to be spending a lot of time trying to figure out how many sauropods can dance on a hill named Bara Simla, in the company of Friedrich von Huene and Charles Matley.

Sunday, June 16, 2019

Titanosaur osteoderms: functions and conclusions

We come now to the last part of our exploration of titanosaur osteoderms. For reference, the other parts can be found as follows: introduction and history of study, characteristics, and distribution in time, space, and across Titanosauria. This final entry will cover the proposed functions and offer some parting thoughts about the armored sauropods.

Sunday, June 9, 2019

What I Did While I Was Out

I made no post last week because I was traveling for work. Generally, I don't have the time to work on a post while traveling, and this was no exception. In order to get the most bang for our buck on work travel, we try to schedule as many projects as possible, and this trip was no exception. I had four separate projects scheduled over eleven days.

Sunday, May 26, 2019

Your Friends The Titanosaurs, part 12: Futalognkosaurus, Gondwanatitan, and Hypselosaurus

For today's entry in the ongoing series, we have a big sauropod that used to be even bigger, a small sauropod that appears to have been lost in a fire, and a small sauropod of historical interest which is a bit of a humbug.

Sunday, May 19, 2019

Trilobites and strange fate

For reasons that will become abundantly clear in a few months, I've been immersed in the paleontology and geology of Grand Canyon National Park for work. We've been doing a lot of projects in that general area over the past few years (Glen Canyon National Recreation Area, Lake Mead National Recreation Area, Tule Springs Fossil Beds National Monument, Walnut Canyon National Monument [check out the public report], Wupatki National Monument, and Zion National Park), and it's only fitting that we take on Grand Canyon. This particular story includes both Grand Canyon and Lake Mead.

Boulder Dam Recreation Area, later renamed Lake Mead National Recreation Area, was established in the 1930s to administer the reservoir Lake Mead that was filling behind Hoover Dam, at the time known as Boulder Dam. As originally conceived, the recreation area extended quite a bit farther east, into what is now part of western Grand Canyon National Park. This is because at the time it was planned that another dam, the Bridge Canyon Dam, was going to be constructed in that area, and the recreation area was sized to accommodate the anticipated reservoir. Obviously, unless you are a reader who has stumbled in from another timeline, no such dam was ever built, and in 1975 the park boundaries were reconfigured, with most of eastern Lake Mead NRA (Grand Wash Cliffs and east) being transferred to Grand Canyon National Park.

This area, as a matter of fact, looking due south into the Grand Wash Cliffs (photo taken from small plane, hence the plane structures and the whole "up in the air" thing).

Anyway, we were still back in the 1930s. The NPS had a few people on staff in the 1930s who specialized in geology, such as H. Donald Curry at Death Valley and Edwin McKee at Grand Canyon. Working at Boulder Dam Recreation Area was Ed Schenk, who had the challenge of contending with a field area that was steadily shrinking by the day as the reservoir filled. A substantial portion of his work at Lake Mead remains unpublished, but his research on the Cambrian escaped that fate (Schenk and Wheeler 1942). His counterpart at Grand Canyon, McKee, was also working on the Cambrian, and published a rather more famous work a few years later (McKee and Resser 1945). You may not recognize the citation, but if you've studied geology at the college level you may well have run into material that's been derived from this publication, in which McKee described the facies changes of the Cambrian formations in terms of marine advances and retreats: very briefly (and simply), there's the nearshore Tapeats Sandstone, the shallow marine Bright Angel Shale, and the deeper marine Muav Limestone.

As part of his work, Schenk collected fossils from about four dozen localities in and around the recreation area. About a quarter of the collections were from Cambrian rocks, all in that area which is now in western Grand Canyon NP. These collections included a fairly typical assortment of mid-Cambrian life, such as trilobites, brachiopods, and hyoliths. Several of these collections were cited in Schenk and Wheeler (1942). It is not immediately obvious, but the same collections are also cited in McKee and Resser (1945), with a few re-identifications. I only realized it when I thought to check because Schenk was noted as a collector in McKee and Resser (1945). Charles Resser, whom we met briefly earlier, also provided identifications for Schenk's paper. Essentially, the two papers were being worked on contemporaneously with contact between the groups of authors, and Schenk's shorter publication beat McKee's work into press by a couple of years (M&R '45 would also have been affected by wartime circumstances and Resser's passing in 1943).

If you're super-curious about these things, the collections definitely mentioned in both S&W and M&R are as follows, using M&R's stratigraphy ("F-" collections are Schenk's):
Peach Springs Member, Muav Limestone: fauna 73 = F-40
Bright Angel Shale tongue: fauna 74 = F-47
Spencer Canyon Member, Muav
Bright Angel Shale tongue
Sanup Plateau Member, Muav
Bright Angel Shale tongue: fauna 75 = F-37
Rampart Cave Member, Muav: fauna 76 = F-39
Flour Sack Member, Bright Angel Shale: faunas 46, 47 = F-16, F-17
Bright Angel Shale tongue
Tincanebits Tongue, Muav
Bright Angel Shale upper slope units: fauna 48 = F-44; fauna 49 = F.C. 761
Bright Angel Shale red-brown cliff unit?
Bright Angel Shale lower slope units: fauna 8 = F-15

Resser named several taxa from the F-# collections, and the holotypes for these taxa were sent to the USNM. These include Albertella schenki from F-44 (McKee and Resser #48; holotype USNM 108583), Lingulella mckeei from F-17 (M&R #47; USNM 108561a), Acrocephalops? arizonaensis from F-16 (M&R #46; USNM 108624), Kootenia simplex from F-37 (M&R #75; USNM 108591a), Kootenia schenki from F-40 (M&R #73; USNM 108586a), and Solenopleurella porcata from F-40 (M&R #73; USNM 108586a and 108626a). If you check the online USNM database, specimens with photos have the F-numbers on their slabs, showing their origin.

We come now to strange fate. Around 1960, with Schenk having long since left the NPS, staff at Lake Mead sent his old collections to the USGS for taxonomic identification. The USGS used to have a system where field geologists could send material for identification, usually to determine the relative age of rock units for mapping and resource projects. The resulting files were called "Examine & Report" (E&R) files. I've seen the files for the Lake Mead project, which took a while to complete for various reasons. Trilobite specialist A.R. "Pete" Palmer was sent the Cambrian samples for identification. Naturally enough, given the rock units involved, he used McKee and Resser (1945) for reference, as he remarked in the memo. Given that most of the fossils in McKee and Resser (1945) were only mentioned in lists, and type and figured specimens that might have given away the tale were retained from the collections by the Smithsonian, there was very little way of knowing that this exercise was actually about using McKee and Resser (1945) to identify fossils from some of the collections in McKee and Resser (1945).

References

McKee, E. D., and C. E. Resser. 1945. Cambrian history of the Grand Canyon region. Carnegie Institution of Washington Publication 563.

Palmer, A. R. 1963/10/17. O-60-55. USGS internal memo to M. B. Ingham (E&R file).

Schenk, E. T., and H. E. Wheeler. 1942. Cambrian sequence in western Grand Canyon, Arizona. Journal of Geology 50(7):822–899.

Sunday, May 12, 2019

Stillwater tusk(s): Minnesota's first

Stillwater, Minnesota is not the kind of place that comes to mind when thinking about good elephant country. If you've never been there, there's a bit of a drop from the top of the St. Croix Valley to the river (the map coming up will make this clear). Furthermore, Stillwater is not noted for its broad floodplain, so a proboscidean wouldn't have much space if it did come down. However, the deep valley of the St. Croix itself is of geologically recent vintage, a parting gift of the most recent ice age sending meltwater through an area marked by billion-year-old faults. This is all a long-winded way of saying that compared to today, it would have been much easier to have mammoths and mastodons wandering around the future area of Stillwater right after the ice had cleared out, only where they were wandering wouldn't have looked very much like how it looks like today.

In fact, what appears to be the first documented find of mammoth or mastodon fossils in Minnesota was made in Stillwater in 1856 (Anonymous 1860; Stauffer "1945"). The find was briefly mentioned in a description of the Minnesota Historical Society ("Already we find it its museum the remains of the first mastodon found in the State, presented by A. [Abram or Abraham] J. Van Vorhes, esq., of Stillwater"; Anonymous 1860), but a fuller account would not be made until Newton Horace Winchell took an interest in it.

According to Winchell, who met with Van Vorhes, the find came from coarse river gravel (actually the base of a bed of fine sand 30–40 feet thick [9–12 m] according to the included stratigraphic section) "far above the present river, but within the main valley" and consisted of a single mastodon tusk (Winchell 1878). Obviously, as an isolated find there's really no way to be certain where the tusk was when its services were no longer required by its owner, but we take our tusks where we find them. (There are differences between mastodon and mammoth tusks, but I don't know if these were known in the mid-1800s, or if this is just a case of "mastodon = generic American proboscidean".) Van Vorhes also reported pottery fragments at the top of the sand bed. Eight feet (about 2.5 m) of the tusk went to the Academy of Sciences of St. Paul (Winchell 1878), and would have been lost in the 1881 fire (mentioned previously).

Winchell also included an extensive quotation from Van Vorhes, who reported multiple tusks "were found about eight or ten feet [about 3 m] above the base of the hill: the hill at this point rises at an angle of about 45°. After excavating in the base of the hill on the grade of Myrtle Street about 37 feet [11 m], the tusks were found, consequently 37 feet below the surface. At this point the hill was about 90 feet high [27 m].

The crockery I found some thirty feet [9 m] farther into the hill and some six or eight feet [about 2 m] higher in the strata. This hill is a continuous tongue of land lying between the Florence mill stream and a spring run. The two streams run parallel and some 350 feet [107 m] apart. The hill is so steep on the Florence mill side as to be inaccessible except by clinging to roots and brush growing on it. The material at the base is sand and small gravel. Where the tusks were found the strata were pure sand ten or twelve feet thick [about 3 m], exhibiting clearly the direction of the current in an eastward inclination one or two degrees."

Leaving aside the question of one tusk or multiple tusks, the location of the find can be reasonably well established from Van Vorhes’s recollections (refreshing for a mid-19th-century find!). The Florence flour mill is long gone, and was not built until 1872, so Van Vorhes was using the then-current geography to describe the 1856 situation. However, as mentioned in the linked article, "The water for the mill was brought down from a dam located where the Pitman House once stood, now the northern portion of Trinity Lutheran Church, and supplied by a brook from McKusick’s Lake." The church is adjacent to Myrtle Street between 3rd Street N and 4th Street N, and a valley can be traced from this area to the lake. The "spring run" seems most likely to be related to a valley to the south, but the present-day distance is much greater than 350 feet. Given that Van Vorhes was an experienced surveyor, it's unlikely he would have been off by hundreds of feet or more; it seems more likely to me that the critical area has been so heavily modified in later years that the 1856 watercourses have been obscured or obliterated. My guess is that the find was made within 500 feet (150 m) of the present location of the church.

This map (helps to click) shows several of the landmarks mentioned above. As I said, I think the find was made in the vicinity of the modern church. (Here's a plug: I've found the Earth Point topo map overlay for Google Earth invaluable!)

The location was retransmitted incorrectly in Hay (1924:44), who placed it in Browns Creek. I suspect this stems from a misreading of a later report by Winchell. Winchell (1888:397) stated "In the fall of 1872 the writer [Winchell] first visited Stillwater, and in company with Mr. Abram Van Vorhes examined the deposit of tripoli in the valley of Brown's Creek. At the same time Mr. Van Vorhes pointed out the drift bank in which he had found ancient pottery and the remains of the mastodon." It's not hard to see how a reader may have come to the conclusion that the "drift bank" was in Browns Creek. This creek, though, is on the north side of Stillwater; Highway 96 borrows part of its valley. It is approximately 1.4 miles (2.3 km) north of the actual area of the find.

The loss of the specimen relegated it to a paper curio. Winchell returned to it once more, in 1910, which is notable because he hedged on the mastodon identification, acknowledging it could have been an "elephant" (mammoth). Aside from Hay (1924), the only other place it seems to have appeared in the literature since Winchell is Stauffer's inventory of Minnesota's Pleistocene fossils (usually given as 1945, but at least 1948). Winchell’s report is #17 in this publication, and Stauffer classified it as "Elephas sp.", which translates as "some kind of proboscidean". Stauffer included another Stillwater find, #6, a tusk found in terrace gravels “in the edge of Stillwater” at an unspecified time. With such little information, it is impossible to say anything else about it.

[An unrelated closing note: I really ought to plug the Geological Society of Minnesota more frequently for local readers; for example, there was a talk this week on Cretaceous fossils in Minnesota. This would have been the normal closing session of the spring lecture series, but an opportunity arose for the GSM to co-sponsor a presentation by Peter Brannen on "The Ends of the World", his book about extinction events, Monday, May 20th (see flyer below for more details). The fall lecture series will start up in September. The GSM staffs a booth during the State Fair in the Education building if you'd like to stop by and chat in person. Lectures are free and open to the public.]

Here's a flyer for the upcoming talk. Note: "Blue Line" should be "Green Line".

References

Anonymous. 1860. Minnesota. The Historical Magazine 4(5):141–142.

Hay, O. P. 1924. The Pleistocene of the middle region of North America and its vertebrated animals. Carnegie Institute of Washington Publication 322A.

Stauffer, C. R. “1945” [at least 1948 based on dates in the article]. Some Pleistocene mammalian inhabitants of Minnesota. Minnesota Academy of Science Proceedings 13:20–43.

Winchell, N. H. 1878. Primitive man at Little Falls. Minnesota Geological and Natural History Survey Annual Report 6:53–65.

Winchell, N. H. 1888. The geology of Washington County. Pages 375–398 in N. H. Winchell and W. Upham. The geology of Minnesota. Minnesota Geological and Natural History Survey, Final Report 2. Johnson, Smith & Harrison, state printers, Minneapolis, Minnesota.

Winchell, N. H. 1910. Extinct Pleistocene mammals of Minnesota. Bulletin of the Minnesota Academy of Science 4:414–422.

Sunday, May 5, 2019

Titanosaur osteoderms: distribution

My plan had been to wrap up everything in this post. (Well, originally it was to do everything in one post. Ha.) However, again the contents were beginning to sprawl, and I felt guilty about the lengths of a couple of recent posts. After all, this isn't a peer-reviewed journal article, is it? There are different expectations for a blog post. Therefore, we'll just have distribution here, and one more post for the functions and conclusion. For the previous installments, go here (introduction) and here (characteristics).

Sunday, April 21, 2019

Your Friends The Titanosaurs, part 11: Drusilasaura, Elaltitan, and Epachthosaurus

It's an all-Argentina installment this time around, including two large titanosaurs that seem to have gotten lost in the flood of titanosaur taxa (Drusilasaura deseadensis and Elaltitan lilloi) and a more modestly sized stalwart of the clade (Epachthosaurus sciuttoi).

Sunday, April 7, 2019

Titanosaur osteoderms: characteristics

Now that we've had a look at the background and history of study for titanosaur osteoderms, we can get into the nitty-gritty of their anatomy and where they were positioned on the body. It turns out there's still quite a lot we don't know about these structures.

Sunday, March 31, 2019

The Pacific Mastodon

Mastodons have been in the news this week, thanks to a new paper by Alton Dooley et al. that makes a case for distinguishing a new Pleistocene species, Mammut pacificus, from the familiar Mammut americanum. The paper is freely available, so give it a look if you're interested in the technical side of fossil proboscideans (mammoths, mastodons, elephants, and friends). If you're interested but not quite up to speed on the details, there's also an in-depth interview with the lead author.

The skull of the type specimen of M. pacificus, Figure 1 in Dooley et al. 2019. From the caption: "Cranium in: (A) dorsal, (B) ventral, (C) left lateral, (D) right lateral, (E) posterior, (F) distal end of left tusk (I1), lateral, and (G) right tusk (I1), lateral view. Teeth include left and right M2–M3. (A–E) are images of a resin cast of the holotype cranium on exhibit at the Western Science Center. All images are orthographic views of photogrammetric models. Scale = 10 cm."

Although mastodons and mammoths are among the most familiar extinct animals, our understanding of their species is still fairly hazy. For those of you who are unfamiliar with the issue, the short answer is that paleontologists historically loved to name proboscidean species. The long answer is too long for a post, but there's a little 1,800-page two-volume monograph by Henry Fairfield Osborn that may provide some illumination. You can read and download the volumes from the Biodiversity Heritage Library (both) and Internet Archive (1, 2). Two caveats for the reader: both volumes are large files (88 and 103 mb, respectively), and Osborn had some* ideas about taxonomy and evolution that have not quite stood the test of time. The 1920s and 1930s were a splitting time, and Osborn could split with the best of them. Over the following decades researchers have gradually settled on a shortlist of a few species and genera, but there are still a lot of questions, and given the results from the original binge of species-naming there hasn't been much of an appetite for creating more.

*By "some" I mean "all of them".

Western North America appears to have been mammoth country; mastodons are not particularly abundant, with many finds only coming in the past couple of decades. Dooley et al.'s project started with a mastodon found at Diamond Valley Lake West Dam near Hemet, California. This mastodon, now on display at the Western Science Center and known familiarly as "Max", has small third molars for its size. (As the interview relates, this fact only became apparent when Dooley was working on exhibit text, and then the project grew from there.) The authors began making comparisons to other mastodon specimens. What they concluded, after several years of work, was that mastodons from California and southern Idaho shared a small suite of characteristics unlike the more familiar mastodons of eastern North America. Aside from the small third molars, these include six fused sacral vertebrae (usually five in M. americanum), femora with relatively thicker shafts, no mandibular tusks (M. americanum sometimes has tusks in the lower jaw), and males with relatively thinner tusks at the base.

Figure 33 from Dooley et al. 2019. The caption there reads "Red circles mark all known M. pacificus localities, while blue circles mark the M. americanum localities that produced teeth used in this study and represented in Table S2. Note that while there are many additional M. americanum localities that were not included in this study and that are not indicated on the map, there are no known M. americanum localities in California. The M. americanum locality in Oregon is a non-diagnostic specimen that was included as M. americanum in this study, but that could represent M. pacificus."

Dooley et al. found not only that all of the mastodons that could be studied from California shared these characteristics, but that the differences extended well into the Pleistocene, into the Irvingtonian land mammal stage. The mechanism for species separation would most likely be ecological: mastodon fossils are particularly rare in the mountain and desert country that intervenes between California and the rest of North America, and there may simply have not been enough suitable suitable mastodon environments in that region to keep the California population connected to the eastern population. In recognition of this distinct population, Dooley et al. coined the name M. pacificus, the Pacific mastodon. Moral of the story? Keep looking at your fossils, even if it's something seemingly well-known; you never know when something unusual might turn up.

References

Dooley, A. C., E. Scott, J. Green, K. B. Springer, B. S. Dooley, and G. J. Smith. 2019. Mammut pacificus sp. nov., a newly recognized species of mastodon from the Pleistocene of western North America. PeerJ 7:e6614. doi:10.7717/peerj.6614.

Sunday, March 24, 2019

Your Friends The Titanosaurs, part 10: Diamantinasaurus, Dongyangosaurus, and Dreadnoughtus

For this week's post, we have two of the best represented titanosaur species, plus Dongyangosaurus sinensis, which isn't quite so well-represented but has some unusual features going for it. Our other guests are Diamantinasaurus matildae, one of a small number of Australian titanosaurs and titanosaur-like sauropods which lived close in time to the Early–Late Cretaceous boundary, and Dreadnoughtus schrani, controversial contender for the heavyweight crown.

Sunday, March 17, 2019

The "Proctor Lake hypsilophodont": Convolosaurus marri

This week, the long-rumored "Proctor Lake hypsilophodont" was published as Convolosaurus marri (Andrzejewski et al. 2019). I could hardly turn down profiling a "hypsilophodont" of such long-standing mystery, so let's get started.

Sunday, March 10, 2019

Titanosaur osteoderms: introduction and history of study

One of the most notable aspects of titanosaurs is the presence of bony armor in at least some species. It's where we get Lithostrotia ("inlaid with stones"), after all. Armored titanosaurs have been hinted at since the 1890s and accepted since the 1980s, but despite forty years of publications and many finds across the world, there are still many things we do not know about titanosaur armor. Even the position on the body is mostly a matter of inference.

I'd had the idea of looking at titanosaur osteoderms and ossicles (the technical terms) in more detail since poster Ornithopsis commented on them following the very first "Your Friends The Titanosaurs" post. Originally I thought I could do it in one post, but after fourteen pages of notes and forty-plus references, this seemed perhaps overly ambitious. Therefore, this post will focus on the history of study (and a healthy bibliography, for those of you collecting papers), and a couple of future posts will cover more detailed descriptions, location on the body, distribution in time, space, and the titanosaur family tree, and functions. If you want spoilers...

Sunday, March 3, 2019

Tiny frogs of the Chinle

I am embarrassed to realize that after five full years of doing this, with a header mentioning "National Park Service paleontology" and "the Mesozoic", I had not done anything with the Chinle Formation or Petrified Forest National Park. This week offers a fine opportunity to correct this oversight, with the publication of the first frog fossils from the Chinle Formation.

The Chinle Formation is a terrestrial unit, with its colorful rocks deposited in various floodplain, river, lake, and other settings during the Late Triassic. The mosaic of settings led to a variety of rock types, from conglomerates to mudstones, with a healthy supply of volcanic ash from eruption centers to the west. Because we're talking about the Late Triassic, before the end-Triassic extinctions gave dinosaurs the opportunity to fill most of the empty terrestrial niches, the Chinle is full of fossils from all sorts of unusual and obscure animals. (And also petrified wood and freshwater mussels. Lots and lots of petrified wood and mussels!) It and its correlatives are usually good for at least one surprise every few years. Lurking among all of the phytosaurs and aetosaurs and so forth were representatives of lineages that would blossom later. Some of them we know from bones (dinosaurs, early croc relatives, pterosaurs, etc.), others can be suspected based on time and place but haven't yet been found. With this week's announcement, frogs move from the potential to the confirmed (Stocker et al. 2019).

The Chinle Formation is divisible into a number of members, depending on where you are. In ascending order, the units in the Petrified Forest NP area are the Mesa Redondo, Blue Mesa, Sonsela, Petrified Forest, and Owl Rock members. For the frogs, we're dealing with the Blue Mesa and Sonsela members, representing approximately 223 to 213 million years ago. (Following the stratigraphy of the Chinle Formation requires a certain amount of effort and dedication. Not only are different members found in different places, but usage has varied over time.) The three frog-producing localities are spread from the park to the famous Placerias Quarry near St. Johns, Arizona (Stocker et al. 2019).

An outcrop of the Sonsela Member, from the park website (NPS/Andrew V. Kearns).

Frogs, being small and delicate, are not exactly heavily represented in the fossil record. The frog lineage, Salientia, is known back to the Early Triassic, but if you were doing a Compact Thescelosaurus-like project on Mesozoic salientians you'd be finished pretty quickly. Salientia includes early stem-frogs plus the crown group Anura, which is the group consisting of all living frogs, their most recent common ancestor, and everything else that falls within that group. There are to date two Early Triassic stem-frogs, the well-known Triadobatrachus of Madagascar and the somewhat less famous Czatkobatrachus of Poland, with the next named salientian being a respectable frog's jump all the way into the Early Jurassic of Arizona, Prosalirus of the Kayenta Formation. The Kayenta has historically proven stubborn about this whole "absolute dating" thing, but an age in the first half of the Early Jurassic is the consensus, so that's a gap of something approaching 60 million years (approximately 250 to 190 million years). The unnamed Chinle salientian practically splits the difference (Stocker et al. 2019).

The Chinle salientian is known from five tiny fossils. Fortunately, four of them are ilia, which are very distinctive bones in frogs: there is a cup-like socket for the femur and a long thin blade directed anteriorly, lengthened by cartilage, part of the mechanism that gives frogs their spring. In the case of the Chinle form, they are also well into the microvert range: approximately 6.2 mm long, or about a quarter of an inch, the kind of stuff you find when you run sediment through screens as opposed to spotting while hiking around. The whole animal would have been less than about 25 mm long, or about an inch, in the realm of modern miniature frogs (Stocker et al. 2019). So, if you were thinking that ur-frogs might have been prehistoric giants, well... not so much in the Chinle. There *were* enormous amphibians in the Chinle, specifically the metoposaur Koskinonodon and its equally enormous taxonomic history, but it isn't closely related to anything living and it didn't look much like a frog.

The form of the hip joint and shaft suggest that the Chinle form was well on the way to modern frog jumping mechanics (Stocker et al. 2019). It may have been a true anuran, but only time and more fossils will tell. The presence of a stem-frog or true anuran in the Chinle also has some implications for frog distribution and paleoecology. The two Early Triassic stem-frogs lived outside of the tropics, whereas the Chinle form was more or less at the equator in western Pangea, showing that the frog lineage had spread across the supercontinent within the Triassic. Also of interest is the persistence of salientians from the Chinle into the Kayenta; over the length of the Chinle, the local climate became more and more arid (Stocker et al. 2019).

A Triassic frog clings to the snout of a phytosaur, used with permission by Andrey Atuchin (supplied by Adam Marsh/PEFO).

References

Stocker, M. R., S. J. Nesbitt, B. T. Kligman, D. J. Paluh, A. D. Marsh, D. C. Blackburn, and W. G. Parker. 2019. The earliest equatorial record of frogs from the Late Triassic of Arizona. Biology Letters 15:20180922. doi:10.1098/rsbl.2018.0922.

Sunday, February 24, 2019

The many moods of Rauffella

Earlier in February, I attended a Geological Society of Minnesota fossil lab hosted by Jeff Thole and Macalester College. At some point someone brought out a fossil that they weren't familiar with; it looked a lot like the final photo in this post, a light-colored object that resembled loops of cord. What this person had was one of the most characteristic but least scientifically appreciated fossils of the Decorah Shale: the trace fossil Rauffella (specifically R. palmipes, as we'll get to later).

Sunday, February 17, 2019

Your Friends The Titanosaurs, part 9: "Campylodon", Clasmodosaurus, Choconsaurus, and Daxiatitan

I've come up against some judgement calls at this point. There are two varieties for this exercise. The first includes a group of names based on poor material that have had little study but which are sometimes/often stuck into Titanosauria, usually from historical inertia or the "provenance argument". The provenance argument goes something like this: "the only described sauropods from this time and place are titanosaurs, ergo this is a titanosaur". The provenance argument is a seductive bit of taxonomic stereotyping, but I'm wary of it. For one thing, the implicit flip side is "therefore there cannot be anything else here than titanosaurs". When the provenance argument is correct, it's not because you put in any effort or had any kind of insight, and when it isn't, you look stupid for being lazy. When confronted with this dilemma and, say, a handful of teeth which have no particular characteristics that would put them in one group or another, I don't see what's wrong with "indeterminate sauropod". The other type of judgement call includes the frustrating taxa that sometimes end up in a clade and sometimes end up outside of it, generally because they are in that fuzzy transitional zone.

For this particular entry, I had cause to consider examples of both types: in the historical orphan bin are "Campylodon" ameghinoi (=Campylodoniscus) and Clasmodosaurus spatula, and in the fuzzy clade bin is Chubutisaurus insignis. I decided that the position of Chubutisaurus is too unstable to be confident it's a titanosaur at this point, and so left it out. We can always cover it later on, with some of its similarly ambivalent cronies. As of this writing, others in a similar equivocal position which I currently have outside of Titanosauria include Angolatitan adamastor, the two Huanghetitan species, Ligabuesaurus leanzai, Mongolosaurus haplodon, Phuwiangosaurus sirindhornae, Tastavinsaurus sanzi, Triunfosaurus leonardii, and Wintonotitan wattsi. Two things they almost all have in common: late Early Cretaceous age, and when they do show up in Titanosauria they're just barely over the line. The other two were more problematic because there's not much material and they've never attracted much interest. I decided to cover them here together as examples.

Sunday, February 10, 2019

Bajadasaurus pronuspinax

Like their cousins the rebbachisaurids, the dicraeosaurids have been on a roll over the past year. I featured the new oldest dicraeosaurid, Lingwulong shenqi, last year. This week saw the publication of another new dicraeosaurid, from a much more typical time and place (the Early Cretaceous of South America), but with a unique style all its own: Bajadasaurus pronuspinax.

Saturday, January 26, 2019

New Pages: Geologic Time Scale and Classification Diagrams

So far the year has been quiet (well, up until Friday), so I thought I'd address a couple of nagging things, which I've done by adding two pages. The first page is a geologic time scale figure, from one I worked up for National Park Service reports. It's the kind of thing I thought would be handy to have on hand here for reference, instead of having a link to an external site. It'll be updated from time to time as dates are refined. The Quaternary is rather cramped, although I don't feel particularly apologetic for shortchanging Homo sapiens.

The second page is a sort of "map" to the classifications used in the various sheets over at The Compact Thescelosaurus, made with classic ASCII cladograms. (I contemplated drafting them in other ways, but none of them were as amenable to updating.) I thought this would be useful for visualizing the mess of classification columns. The process also forced me to look at the positions of a few clades, as you may have noticed from the updates sheet.

It's not connected to either topic, but I've also added a paragraph of new information to the post on the "Kweichow sauropod" after coming across a mention of it in Averianov and Sues (2017).

Finally, so as not to leave the post without an image, here's one attached to a quick story:

Back in spring 2001 I was on a field trip to the Badlands/Black Hills area of southwestern South Dakota. We were stopped along a road near Deadwood for lunch. One of the professors said something to the effect that "there are fossils in this formation." I looked down at the chunks of rock at my feet and said "You mean like this?"

Yeah, like this.

From my notes the source is the Whitewood Formation (or Dolomite, or Limestone), fittingly enough an (surprise, surprise) Upper Ordovician unit. More on its cephalopods can be found in Miller and Furnish (1937).

References

Averianov, A., and H.-D. Sues. 2017. Review of Cretaceous sauropod dinosaurs from central Asia. Cretaceous Research 69:184–197. doi:10.1016/j.cretres.2016.09.006.

Miller, A. K., and W. M. Furnish. 1937. Ordovician cephalopods from the Black Hills, South Dakota. Journal of Paleontology 11(7):535–551.

Saturday, January 19, 2019

Your Friends The Titanosaurs, part 8: Bonitasaura, Borealosaurus, and Brasilotitan

And so we reach Part 8, otherwise to be known as "Bonitasaura and these other two." Bonitasaura is one of the best-known sauropods, even if it isn't quite a household word, and also has some unusual jaw features going for it. Brasilotitan has some of the same jaw features, but is not known from nearly as much material and came along several years later. Borealosaurus has an uncertain grip on Titanosauria, and gripping things takes some creativity when you have either no fingers or just nubs.

Sunday, January 6, 2019

Crystal Ball for 2019

So we've come to 2019. I didn't do so well last year trying to apply a system, so that's gone. I'm trying to mix it up beyond "X# of new taxa"; the problem is "X#" is so easy to define and score.

Will the coming year bring, for no obvious reason, a photo of Simosuchus? (yes)