Thursday, February 08, 2024

The Last Stegosaur

Yanbeilong ultimus is too poorly known to be restored. The above restoration is based on late Jurassic taxa and is probably inaccurate

The latest stegosaur to be named, Yanbeilong ultimus, is more important for what it tells us about stratigraphy and extinction than morphology and relationships of Cretaceous stegosaurs.

Like stegosaurs from the Louhandong and Kukhtekian beds,Yanbeilong is based on just pelvic and vertebral elements. Discovered in the Zuoyun formation of Shanxi province, China, it consists of a sacrum, both ilia, the left ischium, the right pubis, seven dorsal verebrae and one caudal. The holotype lacks cranial or limb bones. Unlike the Hebei material, Yanbeilong is of limited value to taxonomists.

The new taxon can, however, shed much light on the demise of Stegosauria--both the timing and cause of that event. With the possible exception of Dravidosaurus, Yanbeilong is the geologically youngest stegosaur known. Unlike Mongolostegus, Wuerhosaurus and the Louhandong specimen, which are not precisely dated ("Aptian-Albian" or in the case of Wuerhosaurus "Valanginian-Albian") Yanbeilong is unambiguously dated. The Zuoyon is of Albian age. This places Yanbeilong at the end of the early Cretaceous. No other stegosaur definitely occurs as late as the last stage of the EK.

An Albian age is interesting inasmuch as no stegosaur is known from the subsequent Cenomanian stage. The Baynshiree formation, for example, never yielded a stegosaur and nor did Iren Dabasu. It seems reasonable to infer that Stegosauria essentially went out with the EK or Albian. Realizing Yanbeilong was the denouement of Stegosauria, Chinese researchers gave it the species name "ultimus"--the last.

Why did stegosaurs vanish in the Albian, or by the end of that stage? Studies have noted evidence for drastic climatic change in Asia, accompanided by floral change, around the end of that period.

Krassilov et al. note the appearance of Sequoiain Mongolia "indicates a radical change from subtropical redbed climate of pronounced seasonal dryness towards more humid and equable conditions. A climate change like this must have inflicted a major restructuring of terrestrial ecosystems at about the Albian-Cenomanian boundary."

Golozoubov et al. report similar findings. In the Partizansky basin of far eastern Russia, "The late Albian saw a sharp change of vegetation...Diversity markedly decreased...numerous warmth-requiring species became extinct...the released niches occupied by angiosperms." In the Razdolnensky basin "..diversity sharply decreased in the Albian...Many of the cycadophytes, conifers and ferns became extinct."

Loss of cycadophytes and bennetitales, in particular, likely proved fatal to stegosaurs. Their niches taken by angiosperms, the cycadophytes never revived, and nor did the stegosaurs requiring them. Drastic climate change, specifically wetter habitats, spurred the change.

Climate/floral transition, the root of the stegosaur demise, did not occur everywhere at once. There is evidence for it at the start of the Cretaceous as well as its end. In western North Ameria, the Jurassic-Cretaceous boundary saw a wetter climate. Stegosaurs, notably the iconic Stegosaurus, thrived in the late Jurassic of America, in dry, upper Morrison habitats. But they are unknown after the wetter Jurassic-Cretaceous transition. None have been found in the lower Yellow Cat sediments. Since increased rainfall proved inimical to American stegosaurs by the start of the Cretaceous, it isn't surprising that the same conditions were their nemesis in Asia. Dry habitats apparently persisted longest in Asia, but the late Albian finally witnessed the fatal change. Wetter conditions, probably resulting from a severe highstand, extirpated the last stegosaur.

References

Krassilov et al. New Fossil Plant and Insect Records Bearing on Cretaceous Climate of Western Gobi, Mongolia. American Journal of Plant Biology Vol. 2, No. 2, 2017 pp 43-48.

V. Golozoubov et al. Early Cretaceous change of Vegetation and Environment in East Asia Paleogeography, Paleoclimatolgy, Paleoecology 153, 1999 pp 139-146

Addendum

Dorsal vertebrae of Yanbeilong ultimus

The vertebrae have higher neural arches than those of other stegosaurs, and their neural canals are smaller. Yanbeilong is also distinguished by incomplete fusion of the sacrals (possible evidence for immaturity?). I'm not sure of the functional significance of high neural arches and small neural canals. Not surprisingly, Yanbeilong is considered most closely related to Wuerhosaurus and Stegosaurus but differs from them.

Friday, February 02, 2024

Old Teachers

Above, a pic of second grade teacher Mrs. Lucy Sweeney (formerly Miss Shea) the most recently deceased of the teachers I had.

Not surprisingly, as a person grows older, he outlives many of the adults he once knew, including teachers. Below, I summarize the fates of those I've had.

Bentley elementary school Manchester CT (torn down in 2008):

Kindergarten teacher: Mrs. Kirby died around 1995.

First grade teacher (1964-65): Miss Lillian Curtis whereabouts and fate unknown.

Second grade teacher(1965-66): Miss Lucy Shea, died January 6, 2024.

Third grade teacher: Miss Freeman, still alive.

Fourth grade teacher Mrs Lillian Simmers died September 2007. Another 4rth grade teacher, Miriam Thayer, also passed.

Fifth grade teacher Mr. Gessay still alive at this writing.

Sixth grade teacher Mrs Saunders passed in December 1994. Another teacher I had in 6th grade, Mr. Ewald, died in 1992.

Illing Junior High (1970-72):

Homeroom teacher Mr. Cox deceased for several years.

Science teacher Mr. von Deck died in 1981

Gym teacher Mr. Kelly, passed a few years ago.

Mrs. Norling social studies teacher died around 2010.

Mrs. Segar english teacher died c 1996.

Mr. Hadigian math teacher died around 2015.

Mrs Parks music teacher died several years ago.

East Catholic High School 1972-73:

Mrs. Farrell math teacher died 1992

Mr. Adamchak science teacher died 2022.

Mr. Richard history teacher deceased for a few years.

Manchester High School 1973-76:

Mr. Glaeser history teacher died 2001.

Mr. Perry science teacher died 2002.

Mrs. Yuska english teacher died 2005.

Mr. Burnet math teacher died 2005.

Mr. Sines science teacher died 2006.

Mr. Zatursky history teacher died 2007.

Mr. Stearns english teacher died 2007.

Mr. Vincenzo science teacher died 2008.

Mr. Hyde math teacher died 2010.

Mrs. Don english teacher died 2016.

In the "ancientfaces" site I wrote voluminously on some of these people notably Mr. Glaeser, Mrs. Don and Mrs. Yuska.

Lucy Sweeney (nee Shea) with husband Joe and others at a reunion.

Tuesday, November 14, 2023

Big Tarbosaurus Specimens

The largest known skull of T. bataar compared to a human.

In the Nemegt formation, Tarbosaurus is abundantly preserved. Researchers have found over 100 specimens. Knowledge of Tarbosaurus, however, is hampered by the paucity of described, adult material. The type, PIN 551-1, is thought to represent a mature individual but is an exception. Generally, only immature individuals have been published.

In part, the scarcity of adult specimens may be due to taphonomy. Nemegt tyrannosaurs often faced droughts. Juveniles, which heated up more quickly, may have suffered the highest mortality. But much of the reason may be economic.

Compared to western institutions, the paleontological museums and universities of Poland, Mongolia and Russia have limited resources. Cleaning and preparing a specimen, especially a large dinosaur, is costly. Often, it is beyond the means of researchers in Warsaw, Ulaanbataar and Moscow. With little funding, they can not afford to prepare, and hence publish, many of their bigger specimens. PIN 551-1 was an exception because it consists of just an incomplete skull. The postcrania was either absent, or not collected.

Despite lack of formal description, there have been reports of large Tarbosaurus individuals. One, nicknamed "teresa," is said to be complete, 12m long and with a 1.5 meter skull.

A large Tarbosaurus skull, photographed in situ.

A skull of 1.5 meters suggests a fully grown Tarbosaurus was as large as T. rex. It may have equalled the tyrant king in other ways, such as expansion of the posterior part of the skull and the degree to which its eyes faced forward, possibly conferring stereopsis. An adult Tarbosaurus might resemble Tyrannosaurus sufficiently to be put in the same genus, vindicating the view of Rozhdestvensky and Greg Paul (the latter in PDW). In addition, a larger Nemegt predator may have been able to overcome the more dangerous potential prey of its paleoenvironment such as Nemegtosaurus, Therizinosaurus and Deinocheirus.

Considering the potential value of the larger, unprepared T. bataar specimens, in clarifying taphonomic, paleoecological and taxonomic questions, more funding should be made available to institutions possessing such specimens.

Teeth of the top Nemegt predator, exposed during excavation.

Monday, September 11, 2023

Great Discovery!

The Hebei stegosaur

Plated dinosaurs survived past their Jurassic heyday, into the Cretaceous. The latter members of this group, however, are poorly known. Whereas Jurassic stegosaurs are represented by an abundance of material, from the Morrison, Shaximiao, Tendaguru, Villar del Arzobispo etc, Cretaceous remains tend to be rare and fragmentary. Only a few bones and teeth have been found in the La Amarga, Khuktekskayasvita, Kirkwood and other units. Fortunately a great discovery promises to enhance our knowledge. As if to compensate for the paucity of EK material previously known, a new specimen is almost complete, in natural articulation and with preserved skin.

Found in Fengning Man autonomous county, Jiecaigou village, Hebei province, China, the specimen is from the lower Jehol biota, c 130 Ma (Dabeigou formation, Valanginian-Hauterivian boundary). It is 5m long and essentially complete although lacking most of the dorsal osteoderms characteristic of stegosaurs. There may be a taphonomic bias against preservation of plates in Asia, accounting for the truncated ones of Wuerhosaurus and their near-absence in this specimen.

The Hebei stegosaur probably died in a drought. As Kenneth Carpenter once wrote, "so many animals die (in a drought) the predators can't keep up." That explains the pristine, unscavenged condition of some specimens. But when "compensatory" flooding occurred, the dorsal osteoderms (originally embedded in the skin but loosened by decomposition) were swept away and not buried with the rest of the skeleton.

A length of only five meters may indicate a immature individual. Stegosaurus and other taxa were considerably larger. Yet the Hebei stegosaur has a prodigious thagomizer. Still immature but too large to hide, it needed adult-sized weaponry. Clearly, caudal spikes were still effective as they lasted into the Cretaceous. What theropod attempted to prey on it?

The Dabeigou also yielded a theropod. Identified as a ceratosaur, it suggests persistence of a relict Jurassic fauna to Hauterivian time. It's noteworthy, though, that Kelmayisaurus petrolicus was originally identified as a ceratosaur, until its carcharodontosaurid affinities became clear. The Hebei stegosaur may be too early to be Wuerhosaurus, known from a Psittacosaurus bearing unit of probable Aptian age. But carcharodontosaurs ranged far and wide throughout much of the EK, so the Dabeigo beast could've faced a relative of K. petrolicus.

Whereas previouly known EK stegosaurs told us little, the Hebei stegosaur will tell us much. Ample fossilized skin, similiar to that of snakes and lizards, is "incredibly distinct and clear." We are very fortunate to have a late surviving stegosaur in this condition, and can now learn a lot about it.

The affinities of the new stegosaur have yet to be assessed. With the possible exception of the skull, it looks conservative, not much different from Jurassic taxa. Temporally the stegosaur is intermediate between Stegosaurus and Mongolostegus. Phylogenetically, it might be closer to the former. It would be interesting to compare its jaws and dentition with those of contemporary taxa such as Paranthodon, and the Siberian stegosaur. Does the Dabeigou stegosaur also show signs of adaptation to tough vegetation? Soon, studies will clarify its phylogenetic position and shed light on the paleoecology and evolution of Cretaceous stegosaurs.

Another view of the specimen showing the thagomizer. Dorsal osteoderms might've changed since the Jurassic but not means of active defense.

Thursday, August 24, 2023

A Secret Deal

According to a recent report, Iran's oil output, which has been steadily increasing this year, is poised to reach 3.4 million barrels a day by the end of the summer. Essentially, Iran will be producing at peak capacity. In view of US sanctions, that's odd, and suspicious. But it mirrors a harsh dilemma facing the US.

Lately OPEC states, led by Saudi Arabia, have cut production to maximize prices. This move alarmed the US, as it raised the specter of worse inflation. Knowing higher prices at the pump would spark a general round of price hikes, Biden was desperate to prevent this. For him, the economic and political consequences could be ruinous. More inflation would mean higher interest rates and that would lead to recession. A major economic downturn by 2024 could not be more poorly timed...Inevitably, Biden would lose support, enabling Trump to reenter the White House. To avert this disaster, Biden needed more oil on the market, a bigger supply to hold down prices. Where could he get it? OPEC states wouldn't break ranks and the Strategic Petroleum Reserve has already been depleted too much. There was only one source of real help. Ironically it is the very state the US has strongly opposed for decades.

Suddenly, Iran found itself in a strong position. For years the US severely curtailed its oil output. Now Washington did an about face... Considering the degree to which Iran has been "quietly flooding the markets with oil" in recent months, despite official sanctions, there must have been a secret deal. Biden realized he had to get Iranian oil flowing again even if Tehran made no concessions. He needed Iranian oil sales as much as Tehran did. Sanctions were de facto lifted. Iran won the waiting game. Why negotiate for a revival of the JCPOA, or curtail its nuclear program, if it has regained the economic fruit already? Iran again has substantial revenues to use in ways the US dislikes, like building its military and backing Assad. This is a humiliation for the US, but there was no alternative. It was either give in to Tehran or see the mercurial Trump back in power. America's economic vulnerability put Iran in the driver's seat.

Of course for political reasons the deal has to be secret. Biden can't be seen as "appeasing Iran." Hence, both sides maintain the facade of hostility with rhetoric and occasional action.

Wednesday, August 02, 2023

Helianthus flowers again

This past July was the wettest on record. We got 13.93 inches of rain, over treble the normal amount (4.17 inches). The start of August, however, has been dry and pleasant. Good weather coincided with the appearance of sunflowers. These bloomed some weeks later in Vernon CT:

This year's Vernon crop is comparable to last year's show there. The former Manchester garden was also good:

Adddendum, August 12. I just saw a nice Velvet Queen:

Monday, May 01, 2023

No Stegosaur Comeback

Some researchers believe a stegosaur will be found at Doellings Bowl, an early Cretaceous site in Utah. Forming the base of the Yellow Cat, the lowest member of the Cedar Mountain formation, Doellings Bowl has yielded iguanodonts, dromaeosaurs, polacanthid ankylosaurs, sauropods, therizinosaurs and an allosauroid. Currently, no stegosaurs are known from the site. Their presence is thought probable, however, because Doellings Bowl formed only about a stage after the stegosaur heyday of the late Jurassic. In addition, stegosaurs persisted into the early Cretaceous on other continents. Inasmuch as Morrison sauropods appear to have vanished by the Cretaceous, replaced by European forms, Stegosaurus could have suffered the same fate. Perhaps its niche was taken by European taxa such as Dacentrurus or Miragaia. The latter, in fact, was already present in the late Jurassic (Morrison formation) of America.

Survival of Stegosauria into Yellow Cat times is not likely, however. The Jurassic-Cretaceous transition witnessed a wetter climate, which proved inimical to plated dinosaurs. With the exception of Hesperosaurus mjosi from the base of the Morrison, local stegosaurs were adapted to a dry climate. This appears to have been true of Stegosaurus. Occuring higher in the Morrison (or later) than Hesperosaurus, Stegosaurus would've been vulnerable to wetter conditions. It wouldn't be surprising if the iconic stegosaur, like coeval sauropods (also dry-adapted) vanished at the end of the Jurassic.

Based on the record of the Yellow Cat, no stegosaur, local or European, persisted into the Berriasian stage. Doellings Bowl taxa are essentially the same as higher (Valanginian) taxa. Thriving under humid conditions, therizinosaurs, iguandonts and polacanthids predominated. Inasmuch as no stegosaur was ever found in the Valanginian aged deposits, they seem equally unlikely at Doellings Bowl, where similar taxa suggest a similar environment. And this environment excluded plated dinosaurs.

Even in Cretaceous environments highly reminiscent of the Jurassic, stegosaurs apparently never returned to regions where they had vanished. Africa was one example.

The Cenomanian Baharije environment had big sauropods, carcharodontosaurs and spinosaurs. The much older (late Jurassic) Tendaguru had a similar fauna suggestive of similar habitats. The Baharije looks like the Tendaguru revived, but with an important difference. Stegosaurs had vanished. Not only had they disappeared, for some reason they couldn't reappear despite prima facie evidence for a favorable environment.

The same appears true in the middle Cretaceous of America. At the time there was faunal exchange between Asia and America. Caenagnathids, hadrosauroids, ceratopsians, tyrannosauroids etc radiated across beringia and entered both continents. Surprisingly, though, stegosaurs--still present in Asia down to at least Aptian--did not recolonize America. There is no sign of a stegosaur in the Antlers formation or the middle Cedar Mountain (Ruby ranch) member. Both have yielded big allosauroids and sauropod giants, yet even in habitats which seem to mimic the Morrison to a considerable degree, plated dinosaurs remained defunct. Although allosauroid and sauropod remains in the Doellings Bowl suggest persistence of some favorable habitat, hence the possibility of a stegosaur, the record elsewhere argues this is illusory.

Why were stegosaur habitats ruined permanently, in one region after another? Wetter conditions probably undermined the key vegetation of stegosaurs--cycadopohytes and bennitatales. Stomach contents of Isaberrysaura confirm that stegosaurs required such plants, yet they became increasingly rare in the Cretaceous. Angiosperms proliferated at their expense. As narrow-snouted, selective feeders, stegosaurs could not easily adapt to other plants, or if they could they faced too much competition from ankylosaurs and iguanodonts which could more efficiently process it.