Therizinosaurs From Upper Cretaceous Uzbekistan

Therizinosauroidea (Dinosauria: Theropoda) from the Upper Cretaceous of Uzbekistan

Authors:

Sues et al

Abstract:

Skeletal remains of indeterminate therizinosauroid dinosaurs are present in the Cenomanian Khodzhakul Formation and common in the Turonian Bissekty Formation of Uzbekistan. At least two taxa are present in the Bissekty Formation based on different frontal and humerus morphotypes. Phylogenetic analysis based on a dataset with 348 morphological characters and including all known therizinosaurian taxa places the Bissekty taxa as derived non-therizinosaurid therizinosauroids. The Bissekty therizinosauroids are more derived than Alxasaurus elesitaiensis in the extensive pneumatization of the postcranial axial skeleton, the absence of teeth in the anterior portion of the dentary, the weak development or even absence of pits for the collateral ligaments on the manual phalanges, and the subtriangular medial aspect of the distal end of the humerus, with the entepicondyle positioned well medial to the ulnar condyle. They are less derived than Therizinosauridae in the presence of a basisphenoid recess, the absence of pneumatic openings on the anterior caudal vertebrae, the distal end of metacarpal III not being ginglymoid in dorsal view, and the separation of the femoral head from the neck of that bone by a raised ventral rim.

Therizinosaur Nesting Site Discovered From Maastrichtian Cretaceous Mongolia

A nursery of bizarre-looking dinosaurs known as therizinosaurs has been found in the Gobi Desert in Mongolia.

The nesting colony contained at least 17 clutches of eggs

"Not only is this the largest colony of nonavian theropods, but this is the best documented site," said study co-author Yoshitsugu Kobayashi, a vertebrate paleontologist at Hokkaido University in Japan, who presented the findings here at the 73rd annual Society of Vertebrate Paleontology conference.

link.

Diet and Size Does Not Always Correlate in Dinosaur Lineages

Every kid knows that giant carnivores like Tyrannosaurus rex dominated the Cretaceous period, but they weren't the only big guys in town. Giant plant-eating theropods – close relatives of both T. rex and today's birds – also lived and thrived alongside their meat-eating cousins. Now researchers have started looking at why dinosaurs that abandoned meat in favor of vegetarian diets got so big, and their results may call conventional wisdom about plant-eaters and body size into question.

Scientists have theorized that bigger was better when it came to plant eaters, because larger digestive tracts would allow dinosaurs to maximize the nutrition they could extract from high-fiber, low-calorie food. Therefore, natural selection may have favored increasing body sizes in groups of animals that went meatless.

Three groups of giant feathered theropods from the Cretaceous period seemed to follow that rule of thumb – the biggest specimens were also the plant-eaters. Lindsay Zanno, research assistant professor of biology at North Carolina State University and director of the Paleontology; Geology Research Lab at the North Carolina Museum of Natural Sciences, and Peter Makovicky, associate curator of paleontology at the Field Museum in Chicago, decided to see if diet was the determining factor when it came to size. Makovicky notes that "Having three closely related lineages of dinosaurs adapting to herbivory over the same geological time span and showing evidence of increasing size provided a near perfect test case."

Zanno and Makovicky estimated body mass for 47 extinct species of feathered dinosaur, representing three major groups that abandoned a strictly meat-eating diet – ornithomimosaurs ("bird-mimics"), oviraptorosaurs ("egg-thieves"), and the bizarre therizinosaurs ("scythe-lizards"). Most species in these lineages also possessed a toothless beak, three-toed feet, and shorter tails than your average dinosaur, making them look a lot like modern birds.

All three groups evolved gigantic proportions: the largest oviraptorosaur weighed over 7,000 pounds, and the biggest ornithomimosaurs and therizinosaurs topped out at over 13,000 pounds. "The largest feathered dinosaurs were more than 100 times more massive than your average person," says Zanno. "The reality is that for most of us, it is downright difficult to imagine a feathered animal of gigantic proportions."

The researchers also found that average body mass did increase in these groups over time (on average, the earliest members were smallest and the last species to evolve were among the largest). But this simple correlation didn't indicate whether large size was an evolutionary advantage.

To test whether these groups were being driven to get bigger by natural selection, Zanno and Makovicky fitted different evolutionary models to the data, looking to see which model best described the patterns of body mass from ancestor species to descendant species. They found that these theropod groups were experimenting with different body masses as they evolved, with some getting bigger, while others were getting smaller. In short, there was no clear-cut drive to get big – size seemed to provide no overwhelming advantage during the evolution of these animals.

The researchers' results appear in Proceedings of the Royal Society B.

"Results of our study don't rule out diet as affecting body mass, but do seem to indicate that fluctuating environmental conditions over time were trumping the benefit of becoming a giant," Zanno says. "The long and short of it is that for plant-eating theropods, bigger wasn't always better."

A New North American Therizinosaur

A new North American therizinosaurid and the role of herbivory in ‘predatory’ dinosaur evolution



1. Lindsay E. Zanno (1,*)
2. David D. Gillette (2)
3. L. Barry Albright (3)
4. Alan L. Titus (4)

-Author Affiliations

1. Department of Geology, The Field Museum

2. Museum of Northern Arizona,

3. Department of Chemistry and Physics, University of North Florida

4. Grand Staircase-Escalante National Monument

* Author for correspondence (lzanno@fieldmuseum.org).


Abstract

Historically, ecomorphological inferences regarding theropod (i.e. ‘predatory’) dinosaurs were guided by an assumption that they were singularly hypercarnivorous. A recent plethora of maniraptoran discoveries has produced evidence challenging this notion. Here, we report on a new species of maniraptoran theropod, Nothronychus graffami sp. nov. Relative completeness of this specimen permits a phylogenetic reassessment of Therizinosauria—the theropod clade exhibiting the most substantial anatomical evidence of herbivory. In the most comprehensive phylogenetic study of the clade conducted to date, we recover Therizinosauria as the basalmost maniraptoran lineage. Using concentrated changes tests, we present evidence for correlated character evolution among herbivorous and hypercarnivorous taxa and propose ecomorphological indicators for future interpretations of diet among maniraptoran clades. Maximum parsimony optimizations of character evolution within our study indicate an ancestral origin for dietary plasticity and facultative herbivory (omnivory) within the clade. These findings suggest that hypercarnivory in paravian dinosaurs is a secondarily derived dietary specialization and provide a potential mechanism for the invasion of novel morpho- and ecospace early in coelurosaurian evolution—the loss of obligate carnivory and origin of dietary opportunism.

Hat tip to Bill Parker of Chinleana.