Researchers have described two beautifully preserved skulls of juvenile Gorgosaurus dinosaurs (G. libratus). The articulated specimens have enabled the scientists to build up a comprehensive picture of how these tyrannosaurids changed as they grew. Gorgosaurus and the much bigger, later tyrannosaurid T. rex exhibit similar changes in their skulls as they grow. This study will help palaeontologists to decipher tyrannosaur material and to determine the identity of previously misidentified specimens. It should also provide more evidence to help resolve the Nanotyrannus/T. rex debate.

Skulls of the two new juvenile Gorgosaurus libratus specimens in lateral view. A, TMP 2009.12.14; B, TMP 2016.14.1. Note scale bar equals 10 cm. Picture credit: Voris et al.

Picture credit: Voris et al

Gorgosaurus libratus

Named and described in 1914 (Lambe), Gorgosaurus is known from dozens of fossil specimens found in the upper Campanian Dinosaur Park Formation of Alberta and Judith River Formation of Montana. It is one of the best sampled and researched of all the Late Cretaceous tyrannosaurs, but juvenile material is rare. The recent discovery of additional juvenile Gorgosaurus libratus specimens from the Dinosaur Park Formation, including two well-preserved skeletons with articulated skulls, provided researchers which include Jared Voris and Darla Zelenitsky (University of Calgary), along with collaborators from the University of Ohio, the University of Alberta and the Royal Tyrrell Museum, an opportunity to develop a map outlining how this dinosaur changed as it grew and matured.

Illustrations of juvenile (left) and adult (right) skulls of Gorgosaurus in lateral (top) and dorsal views (bottom). Arrows and numbers indicate ontogenetically invariant autapomorphies of Albertosaurinae and Gorgosaurus as per emended diagnosis. Juvenile illustration based on TMP 2016.14.1 (lateral) and TMP 2009.12.14 (dorsal), adult illustration based on UALVP 10. Picture credit: Voris et al.

Picture credit: Voris et al

Sorting out Daspletosaurus Specimens

The research team, which also included Professor Phil Currie (University of Alberta), found that although the skulls of tyrannosaurs changed dramatically as they grew, several taxonomically informative traits remain present regardless of the age of the animal. This means that palaeontologists can use this information to determine which taxon is represented by juvenile fossil material.

Thanks to this research, two specimens previously identified as examples of immature Daspletosaurus individuals (coeval with Gorgosaurus) are instead confirmed as Gorgosaurus.

Left dentaries in lateral view of A, small juvenile (TMP 1994.12.155); B, juvenile (TMP 2016.14.1); C, subadult (TMP 1991.36.500); D, young adult (ROM 1247); and E, adult (TMP 1967.9.164) specimens of Gorgosaurus libratus. Note the development of the autapomorphic dorsoventral expansion in the posterior region of the bone through ontogeny. Scale bar equals 10 cm. Picture credit: Voris et al.

Picture credit: Voris et al

Comparisons with Tyrannosaurus rex

The team also found that both Gorgosaurus and T. rex underwent similar anatomical changes over their lifespans, but at different times. The changes started later in Tyrannosaurus rex and occurred over a longer time interval, resulting in a larger size and longer lifespan for T. rex when compared to Gorgosaurus.

Comparison of the growth series of Gorgosaurus libratus (top) and Tyrannosaurus rex (bottom), demonstrating similar ontogenetic stages (and morphologies) occurring at similar relative size (percent of largest specimen skull length) but different body sizes and biological ages. Picture credit: Voris et al.

Picture credit: Voris et al

Implications for Nanotyrannus

Having identified a series of anatomical traits that can be relied upon to permit palaeontologists to confidently assign juvenile tyrannosaur skull fossils to a specific taxon, this allows some specimens considered small or “dwarf” forms such as Nanotyrannus (N. lancensis) to be revisited. Some of these specimens may have been misidentified, since key characteristics may not have developed in young individuals before death, but this new data set would allow closer scrutiny of the fossil material.

The new for 2021 PNSO Nanotyrannus dinosaur model.

The picture (above) shows a model of a Nanotyrannus by PNSO.

To view the range of PNSO prehistoric animal figures in stock: PNSO Prehistoric Animal Models.

The scientific paper: “Two exceptionally preserved juvenile specimens of Gorgosaurus libratus (Tyrannosauridae, Albertosaurinae) provide new insight into the timing of ontogenetic changes in tyrannosaurids” by Jared T. Voris, Darla K. Zelenitsky, François Therrien, Ryan C. Ridgely, Philip J. Currie and Lawrence M. Witmer published in the Journal of Vertebrate Paleontology.

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An assessment of the Mill Canyon dinosaur track site north of Moab in Grand County, Utah by Bureau of Land Management regional palaeontologist Brent Breithaupt confirms that damage was caused to the Early Cretaceous tracks and trace fossils by a construction crew, but the damage is described as “minor”.

Trace fossils (dinosaur footprints) preserved at Moab (Utah). Picture credit: Bureau of Land Management.

Picture credit: Bureau of Land Management

Essential Repairs and Maintenance at an Important Fossil Site

The site, which covers approximately 2.3 acres contains over 200 tracks and other trace fossils recording activity around a body of water at an Early Cretaceous lake (approximately 112 million years ago). A construction crew had been employed to undertake repairs and improvements to the site including the replacement of boardwalks. Members of the public became aware of the maintenance work and reported possible damage to the fossils caused by the construction crew.

Everything Dinosaur published a blog article on reports of the damage caused by Bureau of Land Management contractors: Dinosaur Tracksite Damaged and having had concerns raised about damage to the site, it was decided to conduct an assessment of the area in order to find the best way to protect the fossils whilst still permitting public access.

This Damage to the Track Site Should Not Have Occurred

The assessment concluded that the overall damage was minor. Even so, Brent Breithaupt wrote in the report that:

“This damage should not have occurred”.

The regional palaeontologist added, that if the project had not been stopped:

“It is likely that much greater damage would have occurred with increased construction activities”.

As the Bureau of Land Management failed to consult palaeontologists on the maintenance plans, crews did not know which areas of the site to avoid. The incident was described in the report as “unfortunate” and the damage “could have been avoided”.

At least six different dinosaur tracks have been deciphered at Moab (Utah). Picture credit: Bureau of Land Management.

After the report was released, the Bureau of Land Management has confirmed that an additional environmental assessment would be undertaken, the public would be consulted and palaeontologists involved in future work at the location to supervise activities. The Bureau of Land Management reported that it “remains committed to protecting plant and animal fossils on our public lands”.

The Everything Dinosaur website: Dinosaur Toys.

Researchers from the Smithsonian Institute (Washington), the University of Oslo and the Ludwig Maximilian Universität (Munich), have published a paper that describes two ichthyosaur specimens from the famous Upper Jurassic Solnhofen deposits of southern Germany. The fossils, an almost complete Aegirosaurus (JME-SOS-08369) and a tail (JME-SOS183), reveal extensive soft tissue preservation, analysis of which indicates the presence of blubber in these marine reptiles.

Late Jurassic Aegirosaurus sp. (JME-SOS-08369) shown in (A) in normal light and (B) composite picture in UV light indicating location of further close-up images included in the scientific paper. Interpretative drawing (C). Note scale bar equals 20 cm. Picture credit: Delsett et al.

Picture credit: Delsett et al

These amazing fossil specimens representing marine reptiles that lived around 150 million years ago will help scientists to better understand how soft tissue can be preserved in the carcases of vertebrates deposited on the seafloor.

For models and replicas of ichthyosaurs and other prehistoric animals: Ichthyosaurs and Prehistoric Animal Models (CollectA).

Aegirosaurus

Aegirosaurus is a genus of ichthyosaur within the Ophthalmosauridae family. Its fossils are associated with the Upper Jurassic limestone deposits of Solnhofen in southern Germany. These deposits are famous for their vertebrate fossils, although ichthyosaur material is rare. Fossils ascribed to this genus have also been found in Lower Cretaceous strata in south-eastern France (Fischer et al, 2011). This discovery suggests that most Late Jurassic ichthyosaurs came through the end Jurassic extinction and continued to thrive in the Early Cretaceous.

Aegirosaurus was an active, nektonic pursuit predator, probably feeding on small fish and squid.

Picture credit: DPA

Evidence for Blubber

The nearly complete ichthyosaur skeleton (JME-SOS-08369) was excavated in 2009, whereas the second specimen involved in this study (the tail), was originally found in 1926, but not formally described. No genus has been assigned to the tail specimen, although the researchers confidently assign it to the Ophthalmosauridae.

The Late Jurassic ichthyosaur tail (specimen number JME-SOS2183) shown in (A) regular light, under ultraviolet light (B) with an interpretative line drawing (C). Note scale bar equals 10 cm. Picture credit: Delsett et al.

Picture credit: Delsett et al

Soft tissue samples were analysed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) analysis. The analyses confirm the presence of the phosphate mineral apatite, with phosphate most likely derived from the body itself. In addition, a yellow-coloured, amorphous substance was identified, the researchers postulate that this substance represents decomposed blubber.

Skull from Late Jurassic Aegirosaurus sp. (JME-SOS-08369) with (A) interpretative drawing and (B) photograph. Note scale bar equals 5 cm. Picture credit: Delsett et al.

Picture credit: Delsett et al

Identifying Adipocere

The researchers conclude that the detailed analysis of the yellowish, amorphous substance indicates that it is adipocere. This is late-stage post-mortem decomposing fatty acids produced by microorganisms under low oxygen conditions. As adipocere is a typical breakdown product of animal blubber, it is postulated that these ichthyosaurs had blubber to help insulate them, just as many extant marine mammals do. The paper does not address any endothermic implications for this conclusion.

Understanding Ichthyosaur Taphonomy

The two ichthyosaur specimens with their extensive soft tissue preservation will help scientists to interpret the taphonomy (how fossils are preserved) of Solnhofen Archipelago vertebrates. Future research will focus on microscopical and geochemical analysis of different parts of the specimens that have the potential to reveal more information about tissue types.

In addition, the beautifully preserved fossils hold the potential for investigations into the locomotion of ophthalmosaurids, helping scientists to better understand how these marine reptiles moved through the water.

The scientific paper: “The soft tissue and skeletal anatomy of two Late Jurassic ichthyosaur specimens from the Solnhofen archipelago” by Lene L. Delsett​, Henrik Friis, Martina Kölbl-Ebert and Jørn H. Hurum published in PeerJ.

The Everything Dinosaur website: Prehistoric Animal Figures.

Please note that following a study published in 2026, some of the fossil material previously assigned to Aegirosaurus was assigned to the newly erected ichthyosaur species Jabalisaurus tethyensis.

To read the blog post: A New Species of Jabalisaurus is Described.

Scientists have identified a trackway made by a large theropod dinosaur as it crossed shallow water, the tracks are exceptionally wide and reveal that this unfortunate predator probably had a dislocated toe.

Writing in the open access journal PLOS One, the researchers describe an exceptionally wide trackway (LH-Mg-10-16), made by a meat-eating dinosaur at a site at the Las Hoyas locality (La Huérguina Formation), in central Spain. The trackway consists of six prints (three left and three right prints) and has been interpreted as representing a large theropod dinosaur crossing shallow water, blanketed by a microbial mat.

Views of the LH-Mg-10-16 theropod trackway. Cartography done in the field (A), (B) scanned surface of the trackway, mounted from a set of colour photos. Colour ramp, showing the depths and the countours of the site (in cm). Note scale bar equals 1 metre. The cartography is reprinted from Las Hoyas a Cretaceous wetland, Gibert JM et al. under a Creative Commons BY licence, with permission from Dr. Friedrich Pfeil Verlag, original copyright 2016. Picture credit: Herrera-Castillo et al.

Lower Cretaceous (Barremian Faunal Stage)

The famous Las Hoyas site has been dated to around 129-127 million years ago (Barremian faunal stage of the Early Cretaceous). Although the Las Hoyas locality has yielded many amazing vertebrate fossils (birds, amphibians, fish), dinosaur fossils are relatively rare. Stride length calculations indicate that the theropod that produced this trackway had a hip height of around two metres. This would suggest a total body length of approximately eight metres. As far as Everything Dinosaur team members are aware, the only large theropod described from fossils associated with Las Hoyas is Concavenator (C. corcovatus).

It is not possible to determine the genus from these tracks, although the prints indicate a theropod that was either bigger than Concavenator or an exceptionally large Concavenator specimen. The known foot bones of Concavenator would have created a print, approximately half the size of the LH-Mg-10-16 tracks. This suggests that there may have been a much larger, as yet undescribed, theropod present in the Las Hoyas ecosystem.

The new for 2020 Wild Safari Prehistoric World Concavenator dinosaur model.

The picture (above) shows a Wild Safari Prehistoric World dinosaur model.

To view this model range: Wild Safari Prehistoric World Models and Figures.

Theropod Dinosaur Crossing Water

Sedimentary analysis indicate that the trackway was produced as the dinosaur traversed a microbial mat located on the bed of a watercourse. Marks on the surface of the substrate have been diagnosed as swimming traces of fish. The ichnospecies Undichna unisulca has been proposed, an ichnotaxon associated with the Las Hoyas site. The research team postulate that the trails were made by a type of deep-bodied bony fish (pycnodontiform), although body fossils of these fish are not common at Las Hoyas.

Undichna fish trails in Magenta LH-Mg-10-16. Fish trails (A and B) associated to the theropod footprints with interpretative line drawings (C) and (D). Lines in black trails and in red, wrinkles marks. Scale equals 10 cm. Picture credit: Herrera-Castillo et al.

A Damaged Left Foot

Detailed analysis of the trackway suggests that the “wide-steps” of the theropod are not unusual compared to other bipedal dinosaur tracks, but they do confirm that these trace fossils were made by a single individual animal.

The right footprints are more regular in shape compared to those made by the left foot. On the left foot the limited impressions made by digit II suggest that either this toe is missing or it is dislocated in some way. Birds suffer from “crooked toes”, a condition caused due to environmental factors, dietary deficits or genetics. In theropod dinosaurs it is often digit II that shows pathology including damage to the bones.

Taphonomic features of the theropod prints. Left footprints (A) and right footprints (B). The right footprints are more regular in shape whilst analysis of the left footprints suggest that this dinosaur had an injured foot. The scientists suggest that digit II of the left foot was either missing or dislocated. Picture credit: Herrera-Castillo et al.

Evidence of a Deformity or Injury

The research team concludes that despite a suspected toe injury/deformity the tracks reveal no signs of a limp. These remarkable trace fossils have captured a moment in time during the Early Cretaceous when a large, meat-eating dinosaur with a body length in excess of eight metres crossed a pool of water that was teaming with fish.

The scientific paper: “A theropod trackway providing evidence of a pathological foot from the exceptional locality of Las Hoyas (upper Barremian, Serranía de Cuenca, Spain)” by Carlos M. Herrera-Castillo, José J. Moratalla, Zain Belaústegui, Jesús Marugán-Lobón, Hugo Martín-Abad, Sergio M. Nebreda, Ana I. López-Archilla and Angela D. Buscalioni published in PLOS One.

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The debate continues as to when the first dinosaurs evolved. Some of the oldest specimens described to date come from the famous Ischigualasto Formation located in north-western Argentina. These sediments are estimated to be around 232 million years old. It is thought that the first true dinosaurs evolved in the Southern Hemisphere and many palaeontologists favour a South American origin whilst others consider the evolutionary cradle of the Dinosauria was Africa: Dinosaurs Out of Africa?

To compound this debate, the fossil record of the ancestors of dinosaurs is particularly sparse. Some older Argentinian deposits have provided evidence of the precursors to the “true dinosaurs”, with some of these fossils estimated to be around 236 million years of age. However, scientists from the Universidade Federal de Santa Maria (Rio Grande do Sul, Brazil), have reported the discovery of a single fossilised thigh bone from Middle Triassic sediments in Brazil that predates all the Argentinian dinosauromorph fossils.

A skeletal drawing showing the placement of the right femur bone (shown in white) and a photograph of the actual fossil. Skeletal drawing by Maurício Silva Garcia, photography by Rodrigo Temp Müller. Note scale bar = 50 cm.

Picture credit: Maurício Silva Garcia/Rodrigo Temp Müller

The Dinodontosaurus Assemblage Zone

The fossilised thigh bone (right femur) measures 11 cm in length and it comes from Middle Triassic sediments (Pinheiros-Chiniquá Sequence) from the famous Dinodontosaurus Assemblage Zone, so named because as well as archosaur fossils, the sediments have yielded an abundance of fossil material associated with the dicynodont Dinodontosaurus. The femur has a morphology similar to the thigh bones of other dinosauromorphs, but it comes from much older stratum, estimated to be at least 237 million years old (Ladinian faunal stage of the Middle Triassic).

This newly described specimen establishes that the Dinosauromorpha (dinosaurs and their close ancestors), were present in South America earlier than previously recorded and extends the fossil record of South American dinosauromorphs into the Ladinian stage of the Triassic.

The thigh bone might be small and no genus has been erected based on this single fossil, but it does represent the oldest dinosauromorph fossil found in South America to date.

A skeletal drawing of the Brazilian dinosauromorph (femur shown in white) with a comparison of fossil specimen stratigraphy from Argentina and Brazil which demonstrates the thigh bone represents the oldest evidence of Dinosauromorpha described to date in South America. Picture credit: Müller and Garcia.

Picture credit: Müller and Garcia

An Ecosystem Dominated by Other Reptiles

Based on comparisons with more complete fossil specimens the femur came from an animal around a metre in length, most of which was accounted for by its long, thin tail if this dinosauromorph possessed a similar body plan. It lived in a diverse ecosystem dominated by other types of reptile. For example, the giant pseudosuchian Prestosuchus was probably the apex predator and at nearly 7 metres in length, this giant member of the crocodile-line of the Archosauria would have dwarfed all the dinosauromorphs in the ecosystem.

A life reconstruction of the Brazilian dinosauromorph based on the 11 cm long femur. This ancestor of the Dinosauria would have been dwarfed by other archosaurs in the ancient environment (Prestosuchus). Picture credit: Caetano Soares.

Picture credit: Caetano Soares

For an update on the research into South American dinosauromorphs: A New Silesaurid from South America.

A scale drawing showing the relative sizes of the Brazilian dinosauromorph from the Pinheiros-Chiniquá Sequence compared to Prestosuchus chiniquensis. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The scientific paper: “Oldest dinosauromorph from South America and the early radiation of dinosaur precursors in Gondwana” by Rodrigo T. Müller and Maurício S. Garcia published in Gondwana Research.

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Scientists have identified the first confirmed dinosaur nesting site in Brazil. The fossilised eggs found suggest a colonial titanosaur nesting site and indicate individuals returning periodically to the same location to breed.  A paper has been published in the journal “Scientific Reports”.

The fossils consisting of preserved clutches and isolated egg fragments were excavated from sandy deposits in an abandoned limestone quarry (Lafarge Quarry) at Ponte Alta District, Uberaba Municipality in Minas Gerais State (south-eastern Brazil). The fossils were recovered from the Serra da Galga Formation (Upper Cretaceous) and although no fossilised embryos were found at the site, the shape of the eggs strongly suggest that they were laid by titanosaurs.

Images of selected titanosaurian eggs and egg-clutches collected from the Late Cretaceous Serra da Galga Formation (Bauru Group) at Ponto Alta nesting site, Uberaba Municipality, Minas Gerais State, Brazil. CPPLIP 1798, (a) the best-preserved recovered egg-clutch, bottom view. CPPLIP 1801, (b) isolated egg, with accompanying tomographic slice, showing thickness of the shell and its sedimentary fill. Specimen number CPPLIP 1799, (c) egg-clutch with accompanying tomographic slice, showing thickness of the shell, shells collapsed and its sedimentary fill. The specimen number CPPLIP 1800, (d and e) two eggs found associated. Specimen number CPPLIP 1804 (f) isolated partial egg. Note scale bars 5 cm. Picture credit: Fiorelli et al.

Picture credit: Fiorelli et al

Nesting in Colonies and Evidence of Breeding-site Fidelity

The Titanosauria were a highly successful clade of long-necked, long-tailed herbivores that were globally distributed during the Cretaceous and survived up until the very end of the Mesozoic. Some of the biggest terrestrial animals known to science are members of this clade, dinosaurs such as Patagotitan, Argentinosaurus and Notocolossus. All three of these titanosaurs lived millions of years before the Lafarge Quarry eggs were laid and they lived much further south (higher palaeolatitude).

A scale drawing of the giant titanosaur Patagotitan mayorum commissioned by Everything Dinosaur. This huge dinosaur was estimated to have measured around 35 metres when its fossil bones were initially examined. When Patagotitan was formally named and scientifically described its body size and weight was reduced slightly. However, a reconstructed, life-size skeleton was built measuring 37.2 metres in length. Titanosaurs are amongst the largest terrestrial animals known to science. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Numerous titanosaur nesting sites are known (Spain, Romania, France, India and most notably Argentina), writing in the academic journal “Scientific Reports”, the researchers report the first titanosaur nesting site from the Late Cretaceous of Brazil (Maastrichtian faunal stage). The fossil material consisting of several egg-clutches, partially preserved, isolated eggs and many eggshell fragments were found in two distinct levels, approximately two metres apart.

This discovery adds further support to the theory that these large herbivores nested in colonies and had preferred locations for their nesting sites, what is often referred to as breeding-site fidelity.

To read a related blog post about breeding-site fidelity (philopatry) identified in South American titanosaurs: Two New South American Titanosaurs Described.

The titanosaur egg fossils were found in two distinct layers (L1 and L2) approximately two metres apart. This suggests that this area was a preferred nesting site for titanosaurs. This is the first confirmed dinosaur nesting area found in Brazil. The eggs attributed to titanosaurs also represent the most northerly titanosaurian nesting site known from South America. The discovery of nests located at different levels indicates that titanosaurs returned regularly to preferred nesting areas. Picture credit: Fiorelli et al.

Picture credit: Fiorelli et al

Which Titanosaur Species?

Isolated and fragmentary remains of titanosaur eggs had previously been reported from Brazil, but the Lafarge Quarry specimens provide unambiguous proof of titanosaur nesting in Brazil. As no embryos have been found in association with the fossilised eggs, it is not possible to comment on the specific genus involved.

However, the researchers state that between the Santonian to the Maastrichtian faunal stages of the Late Cretaceous (86 to 66 million years ago) only derived titanosaurs such as saltasaurids and colossosaurians are recorded from South America. It is likely that the fossils associated with the nesting site represent an unknown genus.

Sue from Everything Dinosaur poses in front of the colossal Patagotitan skeleton which is being exhibited at the Natural History Museum (London). Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

During the Late Cretaceous the Ponte Alta District would have been located at around 26 degrees south of the Equator, putting it on a similar palaeolatitude of titanosaur nesting sites found in India. Previously, South American titanosaur nesting sites have been recorded between 33 to 47 degrees south of the Equator. This latitudinal difference could also influence the distribution of species on the Gondwana continent. The palaeoclimatic variation and geological characteristics could result in a difference in nesting time between titanosaurs living at different latitudes.

How Did Titanosaurs Build Nests?

The Lafarge Quarry site indicates colonial nesting which also suggests that these herbivorous dinosaurs moved around in herds. It is likely that Ponte Alta District titanosaurs scooped out pits in the soft sand using their back legs and then laid their eggs in clutches, before burying them and perhaps covering the nest with vegetation to help incubation.

To read an article about the naming of Austroposeidon magnificus the largest dinosaur from Brazil described to date: Brazil’s Biggest Dinosaur.

The scientific paper: “First titanosaur dinosaur nesting site from the Late Cretaceous of Brazil” by Lucas E. Fiorelli, Agustín G. Martinelli, João Ismael da Silva, E. Martín Hechenleitner, Marcus Vinícius Theodoro Soares, Julian C. G. Silva Junior, José Carlos da Silva, Élbia Messias Roteli Borges, Luiz Carlos Borges Ribeiro, André Marconato, Giorgio Basilici and Thiago da Silva Marinho published in Scientific Reports.

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