Periodic Reporting for period 2 - EvoSaurAf (The evolution of long-necked dinosaurs of Africa before the Cenomanian-Turonian extinction)
Période du rapport: 2024-06-01 au 2025-05-31
Résumé du contexte et des objectifs généraux du projet
Sauropods were 4-legged plant eating dinosaurs with long necks and tails that thrived for more than 160 million years during the Jurassic and Cretaceous until their extinction at the Cretaceous-Paleogene limit, 66 million years ago. By the beginning of Late Cretaceous (95 million years ago) only two groups remained: Titanosauria (which includes the largest land dwelling animals that ever existed) and Rebbachisauridae (smaller and short limbed sauropods with whip-like tails and shorter necks). At the end of the Cretaceous before the final extinction of dinosaurs with the exception of birds, titanosaurs were the only sauropods that remained. Both rebbachisaurids and titanosaurs had evolved independently air-borne skeletons (pneumaticity) and adaptations to feed on ground level vegetation. However, why rebbachisaurids went extinct 90 million years ago while titanosaurs thrived is unknown. How these terrestrial animals coped with an environment where sea surface temperature rose to 3 to 9 ºC higher than present-day tropical temperatures and with sea levels on the rise, eventually forming shallow seas that completely flooded Europe and divided North America and Africa into separate landmasses might have played a part.
The scarce knowledge on African sauropods from the Late Cretaceous in particular was a void for this time period. However, fieldwork throughout the last 25 years in Niger yielded abundant sauropod skeletons dating from 95 million year old beds. Among these finds were seven skeletons of sauropod dinosaurs, three of them rebbachisaurids and four of them titanosaur. These skeletons range from 90 to 50 percent in completion, which is extraordinary for sauropod dinosaurs in general, where most species are known from a handful of bones on average and complete individuals are exceptional.
These skeletons not only improve our knowledge on 95 million year old African dinosaur faunas but also to evaluate whether these animals fed on the same or different vegetation, whether their skeletons grew at similar or different rates or if their air sac system differed in meaningful ways in reducing their weight or the impact it had in heat exchange. Evaluation of these biological traits is a first step in understanding how the largest terrestrial animals that ever existed coped with the changing world they lived in.
The scarce knowledge on African sauropods from the Late Cretaceous in particular was a void for this time period. However, fieldwork throughout the last 25 years in Niger yielded abundant sauropod skeletons dating from 95 million year old beds. Among these finds were seven skeletons of sauropod dinosaurs, three of them rebbachisaurids and four of them titanosaur. These skeletons range from 90 to 50 percent in completion, which is extraordinary for sauropod dinosaurs in general, where most species are known from a handful of bones on average and complete individuals are exceptional.
These skeletons not only improve our knowledge on 95 million year old African dinosaur faunas but also to evaluate whether these animals fed on the same or different vegetation, whether their skeletons grew at similar or different rates or if their air sac system differed in meaningful ways in reducing their weight or the impact it had in heat exchange. Evaluation of these biological traits is a first step in understanding how the largest terrestrial animals that ever existed coped with the changing world they lived in.
Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent
- Fieldwordk: In late 2022 a major paleontological expedition organized by the University of Chicago (USA) and the Institut de Recherche en Sciences Humaines (Niger) to Niger took place to collect several fossils in areas that had never been explored by paleontologists. Exploration of these new 95 million year old (Cenomanian stage) outcrops Southeast of Agadez turned extremely succesful, with several specimens of fish, turtles and theropod and sauropod dinosaurs found and collected. On top of that, this new locality is unique as it is the only site with a similar representation of predatory and plant eating dinosaur remains while other north African localities tend to preserve more predators and northwestern Niger localities tend to have more herbivore remains. Among the sauropods, four titanosaurs and two rebbachisaurid specimens were found and collected.
- Five new sauropod dinosaurs: The anatomy of these sauropod fossil skeletons was studied in detail, comparing bones of the new saudopod species of Niger with the same bones of other species and identifying which traits are unique (these traits are called "autapomorphies"). Autapomorphies were documented by photographing, describing and 3D scanning the osteological elements. These analyses determined at least 5 sauropod species, two rebbachisaurids and three titanosaurs lived in Niger 95 million years ago. Their limb bones were sampled by cutting a piece that was embedded in resin, polished and observed with magnification to document the bone microstructure. Comparing how different the deposition of bone was between the titanosaur and rebbachisaurid (similar to counting the rings of growth in tree trunks) showed very different growth strategies for these two lineages of animals that lived in the same environment.
- Digital Dinosaurs: 3D models of the surface of all fossil bones was achieved by taking hundreds of overlapping high resolution pictures of each individual bone during and after preparation and processing them in a computer software that, by triangulating overlapping points in the images, creates a high resolution virtual model of each bone (a technique called "Structure from Motion photogrammetry”). Computed Tomography uses X-rays to obtain sections of selected fossils that reveal their internal anatomy, as if the bone had been evenly cut in sections like sliced bread. These slices (tomograms) were used to produce 3D models of those internal structures, specially focused on learning the configuration of the air sacs of vertebrae with detail.
The results of these scans is the most complete virtual collection of African dinosaur fossils at present, and in the most detailed survey of the air sacs of a sauropod dinosaur, allowing to perform highly accurate skeletal reconstructions of most of the taxa.
- Five new sauropod dinosaurs: The anatomy of these sauropod fossil skeletons was studied in detail, comparing bones of the new saudopod species of Niger with the same bones of other species and identifying which traits are unique (these traits are called "autapomorphies"). Autapomorphies were documented by photographing, describing and 3D scanning the osteological elements. These analyses determined at least 5 sauropod species, two rebbachisaurids and three titanosaurs lived in Niger 95 million years ago. Their limb bones were sampled by cutting a piece that was embedded in resin, polished and observed with magnification to document the bone microstructure. Comparing how different the deposition of bone was between the titanosaur and rebbachisaurid (similar to counting the rings of growth in tree trunks) showed very different growth strategies for these two lineages of animals that lived in the same environment.
- Digital Dinosaurs: 3D models of the surface of all fossil bones was achieved by taking hundreds of overlapping high resolution pictures of each individual bone during and after preparation and processing them in a computer software that, by triangulating overlapping points in the images, creates a high resolution virtual model of each bone (a technique called "Structure from Motion photogrammetry”). Computed Tomography uses X-rays to obtain sections of selected fossils that reveal their internal anatomy, as if the bone had been evenly cut in sections like sliced bread. These slices (tomograms) were used to produce 3D models of those internal structures, specially focused on learning the configuration of the air sacs of vertebrae with detail.
The results of these scans is the most complete virtual collection of African dinosaur fossils at present, and in the most detailed survey of the air sacs of a sauropod dinosaur, allowing to perform highly accurate skeletal reconstructions of most of the taxa.
Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)
OVERVIEW OF RESULTS: There were at least five different coetaneous sauropod species in Niger 95 million years ago: two rebbachisaurids and three titanosaurs. These coetaneous sauropods from different lineages fed on different plant material, grew at different rates, and had differences in their air sac system. These differences might have played a role in how they dwelved in the changing world they inhabited. This project has resulted in four published articles and three more in review process, seventeen dissemination and communication activies in three continents (North America, Europe and Africa), two popular articles published in National Geographic (with a third one in the works) and a documentary filmed in IMAX. The researcher received intensive training in phylogenetic analysis, computed tomography, fieldwork techniques, writing science in English as second language, diplomacy or funding securing.
1) 3D MAPPING TECHNIQUES: New 3D mapping protocols for paleontological quarries was developed and tested to document their extraction to the most minute detail possible, with a daily record on progress of the excavation.This new mapping protocol not only will help future researchers in verifying the ID of bones within a quarry, but also to understand how each skeleton was buried. As a sidenote, many observations done in taxa discovered in the 2022 expedition have only been possible from 3D models of the quarries.
2) CENOMANIAN SAUROPODS FROM NIGER: Five different species of sauropods have been discovered in Niger, named provisionally “Taxon” A to E:
REBBACHISAURIDAE:
- Taxon A: A small sized rebbachisaur known from at least two relatively well preserved skeletons. It is one of the smallest sauropods from Niger (Cenomanian and otherwise), with a femur less than half the length of that of Taxon D. It has a humerus to femur ratio of 0.65 and a relatively short neck. The feeding capabilities of this species are those of a low to ground level browser, with a maximum feeding height of less than 3 meters.
- Taxon B: A medium sized Rebbachisaur about 40% larger than Taxon A and has a sail in its back like the famous theropod Spinosaurus. Given its larger size and aslightly more elongate neck, it is likely that the feeding envelope of Taxon B exceeded 3 meters in height, although probably a part of this envelope overlapped with Taxon A, so it probably fed at medium to low heights.
TITANOSAURIA:
- Taxon C: A moderately large and slender titanosaur, one of the most completely known worldwide. It has a remarkably long neck about half the length of the animal. The tail is reduced in length and height, less than half the length of the neck. The forelimbs are relatively elongate and slender. With a shoulder height of "only" 250 cm, its extremely elongated neck allowed it to reach a height of almost 900 cm in osteologically neutral pose, exceeding the 10 meter mark with the neck completely extended. Its more robust teeth also suggest it fed on different vegetation than Taxa A and B. This makes it a high browser.
- Taxon D: A giant and robust titanosaur known from four partial skeletons. The most complete of those skeletons has a femur greater than 190 cm, in the size realm of giant titanosaurs like Dreadnoughtus but a smaller than the largest titanosaurs like Patagotitan or Argentinosaurus. The posterior limb bones are far more stout than Taxon C. Assuming it had proportions similar to its relatives, it probably had an elongate neck with at least 14 cervical vertebrae. Even if the neck was not as elongate relative to the trunk as in taxon C, its greater shoulder height and longer neck (in absolute terms) likely conferred it a slightly greater feeding height than taxon C.
- Taxon E: A medium sized titanosaur known so far from a relatively incomplete and partially prepared skeleton. The morphology of its vertebrae is very different from Taxon C or D, indicating a different species. It is not complete enough to assess its feeding height or overall appearance.
3) PNEUMATIC APPARATUS: The bones of sauropod dinosaurs were invaded by air sacs derived from the respiratory apparatus, and this bone is named "pneumatic".
Rebbachisaurids from Niger have the same type of pneumaticity, with large spaces inside their vertebrae supported by plate or strut like bone laminae, more similar to beams in cross-section (named "camerate" bone).
Titanosaurs from Niger have hundreds of smaller chambers inside of each vertebra, more similar to an irregular honeycomb in cross section (named "camellate" bone). Some differences between Taxon D and Taxon C could be observed, since the latter has completely solid anterior tail vertebrae while the former had camellate tissue in the base of the tail.
These differences in pneumatic bone might have had an impact in the efficiency of their heat exchange (with Titanosaurs having a greater surface/volume proportion than rebbachisaurids and being more efficient) as well as in lightening their skeletons
5) GROWTH OF NIGERIEN SAUROPODS : The analysis of the microstructure of their bones show the complete specimen of Taxon C was a relatively young adult while rebbachisaurid Taxon A specimens were adults but slightly younger than Taxon C that just reached sexual maturity. Coetaneous titanosaur and rebbachisaurids grew their skeletal system in slightly different fashion, with titanosaurids having a more aggresive remodelling of the structure of their limb skeleton when growing while rebbachisaurids had a growth rate similar to non titanosaur sauropods.
1) 3D MAPPING TECHNIQUES: New 3D mapping protocols for paleontological quarries was developed and tested to document their extraction to the most minute detail possible, with a daily record on progress of the excavation.This new mapping protocol not only will help future researchers in verifying the ID of bones within a quarry, but also to understand how each skeleton was buried. As a sidenote, many observations done in taxa discovered in the 2022 expedition have only been possible from 3D models of the quarries.
2) CENOMANIAN SAUROPODS FROM NIGER: Five different species of sauropods have been discovered in Niger, named provisionally “Taxon” A to E:
REBBACHISAURIDAE:
- Taxon A: A small sized rebbachisaur known from at least two relatively well preserved skeletons. It is one of the smallest sauropods from Niger (Cenomanian and otherwise), with a femur less than half the length of that of Taxon D. It has a humerus to femur ratio of 0.65 and a relatively short neck. The feeding capabilities of this species are those of a low to ground level browser, with a maximum feeding height of less than 3 meters.
- Taxon B: A medium sized Rebbachisaur about 40% larger than Taxon A and has a sail in its back like the famous theropod Spinosaurus. Given its larger size and aslightly more elongate neck, it is likely that the feeding envelope of Taxon B exceeded 3 meters in height, although probably a part of this envelope overlapped with Taxon A, so it probably fed at medium to low heights.
TITANOSAURIA:
- Taxon C: A moderately large and slender titanosaur, one of the most completely known worldwide. It has a remarkably long neck about half the length of the animal. The tail is reduced in length and height, less than half the length of the neck. The forelimbs are relatively elongate and slender. With a shoulder height of "only" 250 cm, its extremely elongated neck allowed it to reach a height of almost 900 cm in osteologically neutral pose, exceeding the 10 meter mark with the neck completely extended. Its more robust teeth also suggest it fed on different vegetation than Taxa A and B. This makes it a high browser.
- Taxon D: A giant and robust titanosaur known from four partial skeletons. The most complete of those skeletons has a femur greater than 190 cm, in the size realm of giant titanosaurs like Dreadnoughtus but a smaller than the largest titanosaurs like Patagotitan or Argentinosaurus. The posterior limb bones are far more stout than Taxon C. Assuming it had proportions similar to its relatives, it probably had an elongate neck with at least 14 cervical vertebrae. Even if the neck was not as elongate relative to the trunk as in taxon C, its greater shoulder height and longer neck (in absolute terms) likely conferred it a slightly greater feeding height than taxon C.
- Taxon E: A medium sized titanosaur known so far from a relatively incomplete and partially prepared skeleton. The morphology of its vertebrae is very different from Taxon C or D, indicating a different species. It is not complete enough to assess its feeding height or overall appearance.
3) PNEUMATIC APPARATUS: The bones of sauropod dinosaurs were invaded by air sacs derived from the respiratory apparatus, and this bone is named "pneumatic".
Rebbachisaurids from Niger have the same type of pneumaticity, with large spaces inside their vertebrae supported by plate or strut like bone laminae, more similar to beams in cross-section (named "camerate" bone).
Titanosaurs from Niger have hundreds of smaller chambers inside of each vertebra, more similar to an irregular honeycomb in cross section (named "camellate" bone). Some differences between Taxon D and Taxon C could be observed, since the latter has completely solid anterior tail vertebrae while the former had camellate tissue in the base of the tail.
These differences in pneumatic bone might have had an impact in the efficiency of their heat exchange (with Titanosaurs having a greater surface/volume proportion than rebbachisaurids and being more efficient) as well as in lightening their skeletons
5) GROWTH OF NIGERIEN SAUROPODS : The analysis of the microstructure of their bones show the complete specimen of Taxon C was a relatively young adult while rebbachisaurid Taxon A specimens were adults but slightly younger than Taxon C that just reached sexual maturity. Coetaneous titanosaur and rebbachisaurids grew their skeletal system in slightly different fashion, with titanosaurids having a more aggresive remodelling of the structure of their limb skeleton when growing while rebbachisaurids had a growth rate similar to non titanosaur sauropods.