A new species of tyrannosauroid described by scientists as a “missing link” sheds new light on the evolution of Late Cretaceous tyrannosaurs.  The dinosaur, named Khankhuuluu mongoliensis represents a transitional form between the small, gracile early tyrannosauroids and the giant, bone-crushing, apex predators such as Daspletosaurus and Tyrannosaurus rex.  The large tyrannosaurs from the end of the Cretaceous (Campanian and Maastrichtian) have been intensively studied.  However, the evolutionary origins of these super-sized theropods remains poorly understood.  It is known that these dinosaurs evolved from much smaller ancestors.  The discovery of Khankhuuluu (pronounced: khan-KOO-loo), helps palaeontologists to fill in a gap between these ancestral forms and the Late Cretaceous giants.

Khankhuuluu mongoliensis represents a transitional form between small tyrannosauroids of the early Late Cretaceous and the giants of Campanian and Maastrichtian. Yes, I know Maastrichtian is not correct in the diagram :). Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Khankhuuluu mongoliensis

A team of researchers led by scientists from the University of Calgary (Alberta) have described a new species of tyrannosauroid from the Upper Cretaceous Bayanshiree Formation of southeastern Mongolia. University of Calgary PhD student Jared Voris found unique autapomorphies in two fossil specimens that had been assigned to the tyrannosauroid Alectrosaurus. For example, an air cavity was identified in the nasal bone and the student found other traits that indicate this dinosaur was evolving the skull anatomy that would generate immense bite forces.

Phylogenetic analysis suggests that K. mongoliensis sits just outside the Eutyrannosauria. This is the clade which contains giant tyrannosaurs such as Gorgosaurus, Lythronax, Tarbosaurus and T. rex as well as, smaller more lightly built predators.

The Eutyrannosauria is split into two tribes:

• Alioramini (for example Qianzhousaurus and Alioramus): smaller, slender, shallow-skulled forms.
• Tyrannosaurini (for example Tyrannosaurus rex): massive, deep-skulled forms.

Khankhuuluu and the Alioramini both share certain traits. They are lightly built, have long hind limbs and shallow skulls.  These characteristics are seen in juvenile specimens of the giant tyrannosaurs such as Tarbosaurus and T. rex. These traits evolved due to heterochrony, meaning changes in the timing of growth during evolution.  Writing in the journal “Nature” the research team which included Professor Darla Zelenitsky (University of Calgary) suggest that accelerated growth led to the evolution of the giant forms of tyrannosaur (peramorphosis). In contrast, the Alioramini retained juvenile traits into adulthood (paedomorphosis).  This explains, their smaller size and gracile build.

It is postulated that the different body types of the Alioramini and Tyrannosaurini likely helped them live side by side in Asia by filling different ecological roles.

The Prince of Dragons

The fossils were discovered in the 1970s at the Baishin-Tsav locality (Bayanshiree Formation). The strata are believed to have been laid down in the Turonian to Santonian faunal stages of the Late Cretaceous. The fossils of Khankhuuluu mongoliensis are thought to be approximately 86 million years old. Khankhuuluu is estimated to have weighed around 750 kilograms and measured around four metres in length.

The dinosaur’s name translates as “Mongolia’s Prince of Dragons”.  It hints that this theropod was a prince that led to the evolution of the “tyrant kings”.

The Everything Dinosaur blog has documented numerous articles about new discoveries leading to the erection of new Tyrannosauroidea taxa.  Most of these dinosaurs were considerably smaller than Khankhuuluu.

To read about the discovery of a small-bodied tyrannosauroid from southern Laramidia: Suskityrannus – The Shape of Things to Come.

The contemporary Timurlengia from Uzbekistan: New Dinosaur Sheds Light on How Tyrannosaurs Got Big.

Moros intrepidus, a member of the Superfamily Tyrannosauroidea from Utah: Moros – A Diminutive Tyrannosauroid.

Alioramini Not a Basal Lineage

Previously, phylogenetic analysis had relied too much on immature specimens, and this led to the assumption that the Alioramini were a primitive, early diverging group. However, the researchers postulate that the Alioramini were not basal, but more derived representing theropods that retained immature features into adulthood.

Furthermore, the study reveals that Asian tyrannosauroids (similar to Khankhuuluu) dispersed to North America. They gave rise to the Eutyrannosauria. The Eutyrannosauria diversified and remained exclusively in North America until a single dispersal to Asia in the latest Cretaceous that established the Alioramini and Tyrannosaurini tribes.

The scientific paper: “A new Mongolian tyrannosauroid and the evolution of Eutyrannosauria” by Jared T. Voris, Darla K. Zelenitsky, Yoshitsugu Kobayashi, Sean P. Modesto, François Therrien, Hiroki Tsutsumi, Tsogtbaatar Chinzorig and Khishigjav Tsogtbaatar published in Nature.

The Everything Dinosaur website: Dinosaur Models and Toys.

A newly published paper postulates that ungulate evolution has been shaped by two major ecological shifts. Tectonic shifts and global climate change have been the drivers of major biota turnover amongst large herbivorous mammals.

Ungulates are hoofed mammals.  This extremely diverse clade is subdivided into two orders, the Artiodactyla (even-toed) mammals that walk on two of their five toes and the Perissodactyla (odd-toed) mammals that walk on one or three toes. Molecular data led to a reclassification at the turn of the century with the establishment of a larger clade the Euungulata.

• Typical artiodactyls – ruminants such as cattle, goats, sheep, llamas, camels, hippos, giraffes, deer, pigs.
• Typical perissodactyls – rhinos, horses, tapirs.

It should be noted that the odd-toed ungulates were much more diverse in the past.  Brontotheres and knuckle-walking chalicotheres are extinct members of the Perissodactyla.

A wonderful prehistoric animal model. A 1:20 scale replica of the chalicothere Moropus – an extinct perissodactyl.

The picture above shows a typical chalicothere.  It is a 1:20 scale replica of Moropus from CollectA.  To view the range of CollectA scale prehistoric animal models: CollectA Deluxe Prehistoric Life.

Large Herbivores Shaping the Landscape

Large herbivores have shaped the Earth’s landscapes for the last forty million years.  A new study led by researchers from the University of Gothenburg in collaboration with scientists from Spain and the Museum für Naturkunde Berlin examines how these animals reacted to dramatic environmental changes.  The study, published in “Nature Communications” demonstrates that ecosystems managed to remain stable despite the extinction of many families.

Ungulates and other large mammals such as elephants are key ecosystem engineers.  The decline of large herbivores threatens entire habitats.  These large herbivores shape landscapes and promote biodiversity.  Current extinction rates, often referred to as the sixth mass extinction could lead to a loss of key taxa.

Dr Fernando Blanco, a visiting scientist at the Museum für Naturkunde Berlin led the research.  The fossils of over three thousand large herbivores from the past sixty million years to more recent times were studied.

Dr Blanco commented:

“We found that these ecosystems have remained surprisingly stable over long periods of time, even though species were added and others became extinct. Twice in the last sixty million years, however, the environmental pressure was so great that the entire system was globally reorganised.”

The End of the Tethys

The team discovered that the first major reorganisation of ecosystems took place around twenty-one million years ago.  This was during the Miocene Epoch.  The Tethys Sea closed and this created a landbridge between Eurasia and Africa.  A mass migration of species occurred. The ancestors of many extant ungulates moved into new habitats.  This had a profound effect on ungulate evolution.

A second major reorganisation of ecosystems occurred approximately ten million years ago.  This was during the Tortonian stage of the Miocene. Global cooling led to a massive reduction in forests and the spread of grasslands.  This led to a dramatic increase in grazing species and a gradual disappearance of many forest-dwelling species.  The researchers postulate that this was the beginning of a sustained decline in the functional diversity of large, herbivorous mammals.  This has led to a decrease in their influence over the planet’s ecosystems. Despite the extinctions, the researchers found that the basic ecological structure of herbivore communities remained remarkably stable.  Ecosystems remained stable even when many iconic taxa died out such as mastodons, mammoths and giant rhinoceroses.

A typical artiodactyl – a Cape buffalo (Syncerus caffer) photographed in Tanzania. Scientists reflect on ungulate evolution and the impact of large herbivores on the Earth’s ecosystems. Picture credit: Juan López Cantalapiedra.

Picture credit: Juan López Cantalapiedra

Co-author of the study, Dr Ignacio A. Lazagabaster from CENIEH (Centro National de Investigacion Sobre la Evolucion Humana, Spain) commented:

“It’s like a football team changing players during a game without the line-up changing significantly. New species came into play and the communities changed, but the new players fulfilled similar ecological tasks – as a result, the overall structure remained stable.”

The Resilience of Large Herbivores is Not Guaranteed

The research team remarks on the resilience of large mammals to survive glaciation, global cooling and other environmental crises.  However, many large taxa are extremely vulnerable today.

Fellow co-author of the study Dr Juan L. Cantalapiedra from the Spanish MNCN (Museo Nacional de Ciencias Naturales) stated:

“Our results show how enormously adaptable ecosystems can be. But there are limits. If we continue to lose species and their ecological roles on such a massive scale as in the present, we could soon reach a third global tipping point – and we humans are actively contributing to this.”

Everything Dinosaur acknowledges the assistance of the Museum für Naturkunde Berlin in the compilation of this article.

The scientific paper: “Two major ecological shifts shaped 60 million years of ungulate faunal evolution” by Fernando Blanco, Ignacio A. Lazagabaster, Óscar Sanisidro, Faysal Bibi, Nicola S. Heckeberg, María Ríos, Bastien Mennecart, María Teresa Alberdi, Jose Luis Prado, Juha Saarinen, Daniele Silvestro, Johannes Müller, Joaquín Calatayud and Juan L. Cantalapiedra published in Nature Communications.

For models of extinct mammals and other prehistoric animals: Prehistoric Animal Models and Toys.

Researchers have discovered the earliest evidence known to science of birds nesting in the Arctic.  A newly published study in the journal “Science” indicates that birds were nesting in polar regions during the Late Cretaceous.  Ancient Arctic birds nested alongside dinosaurs.  Fossils collected from the famous Prince Creek Formation of Alaska push back the record of Arctic nesting birds by up to thirty million years.

An illustration of Cretaceous Period birds with other dinosaurs from the same time period in the background. A paper in the journal Science documents the earliest-known example of birds nesting in the polar regions. A dromaeosaur feeds whilst Pachyrhinosaurus congregate in the background. Picture credit: Gabriel Ugueto.

Picture credit: Gabriel Ugueto

Ancient Arctic Birds

The University of Alaska Fairbanks led the research team.  However, researchers from the University of Reading were involved.  The scientists identified dozens of tiny fossil bones and teeth from the Alaskan excavation site.  Multiple types of birds were breeding in the Arctic. For example, diving birds that resembled loons, gull-like birds, and several kinds of birds similar to modern ducks and geese.  Analysis of the structure of the fossil material demonstrated that the bones represented very young birds such as hatchlings.

A hatchling bird beak, top left, and three foot bones are pictured to scale on a penny. The bones’ spongy texture tells scientists that they come from hatchlings, rather than adult birds. Picture credit: Pat Druckenmiller.

Picture credit: Pat Druckenmiller

The sediments are approximately seventy-three million years old (late Campanian faunal stage of the Cretaceous).

To read a blog post about dinosaurs nesting in the Arctic: Dinosaurs Nested in the Arctic.

Lead author of the study, Lauren Wilson, a doctoral student at Princeton University commented:

“Birds have existed for 150 million years. For half of the time they have existed, they have been nesting in the Arctic. Finding bird bones from the Cretaceous is already very rare. To find baby bird bones is almost unheard of. That is why these fossils are significant.”

More than Fifty Bird Fossils Found

Birds are key components in modern polar ecosystems.  Many species breed in these regions and spend all year either in the Arctic or Antarctic.  Although the Cretaceous polar regions were much warmer than today, they were still extreme, harsh environments.  Cretaceous polar regions would have experienced months of near total darkness.  They were challenging environments to colonise even though they were not as cold as they are today.  The fossil assemblage from the Prince Creek Formation suggests that chicks and adults of multiple species lived in the Arctic.  This suggests that birds began breeding in the Arctic early on in their evolution.

Prior to this research, the earliest known evidence of birds breeding in the polar regions dates to approximately forty-seven million years ago.  This was during the Eocene Epoch. The fossil material used in this study was collected from Prince Creek Formation exposures along the Colville River. Rather than focusing on large bones, the scientists collected every bone and tooth they could find from screen washes. Screen washing involves taking tubs of sediment and screening the sediments using sieves.  Once the majority of the stones and pebbles have been removed the remaining material is examined under a microscope.  In this way, tiny fossils including those of hatchling birds can be identified.

Joe Keeney, Patrick Druckenmiller and Jim Baichtal excavate at a site on the Colville River. Picture credit: Lauren Wilson.

Picture credit: Lauren Wilson

Evidence of Neornithes

Some of the tiny bones have skeletal features only found in Neornithes, the group that includes all extant birds. Like extant birds, some of these ancient species had no true teeth.

Co-author of the study, Dr Jacob Gardner (University of Reading) commented:

“Determining the identity of fossils using separate individual bones is notoriously difficult. For the first time, we determined the identities of large numbers of fossils using high-resolution scans and the latest computer tools, revealing an enormous diversity of birds in this ancient Arctic ecosystem. Polar bird communities have deeper evolutionary roots than previously imagined.”

Everything Dinosaur acknowledges the assistance of a media release from the University of Reading in the compilation of this article.

The scientific paper: “Arctic bird nesting traces back to the Cretaceous” by Wilson, L. N., Ksepka, D. T., Wilson, J. P., Gardner, J. D., Erickson, G. M., Brinkman, D., Brown, C. M., Eberle, J. J., Organ, C. L. and Druckenmiller, P. S. published in the journal Science.

For models and replicas of prehistoric animals: Dinosaur and Prehistoric Animal Models.