A remarkable new sauropod dinosaur discovery is the focus of a recent paper published in the open access journal “PeerJ”.  The study introduces Bicharracosaurus dionidei, fossils of which herald from Upper Jurassic deposits from the Cañadón Calcáreo Formation of southern Argentina. This research captures attention. Not only does it describe a new species, but it also reshapes how scientists understand sauropod evolution in the Southern Hemisphere.

Sauropod Evolution

Much of what we know about sauropod evolution comes from studying fossils from the Northern Hemisphere. Less is known about sauropod evolution and radiation in the Southern Hemisphere. Hence, the discovery of a new sauropod species from southern Argentina is especially significant. In March 2001, farmer Dionide Mesa reported the discovery of some dinosaur vertebrae.  Fieldwork commenced the following year and by 2011 much of the fossil material had been removed.  However, more neck bones (cervical vertebrae) were excavated in 2018.

In total, more than thirty vertebrae, ribs and parts of the pelvis were found.  The material dates from the Upper Jurassic (Oxfordian to Kimmeridgian faunal stages).  Palaeontologists estimate this sauropod fossil material to be approximately 155 million years old.  The fossils probably represent a mature, adult specimen.  Estimates suggest that this dinosaur measured between fifteen to twenty metres in length.

Bicharracosaurus dionidei life reconstruction and scale drawing. Picture credit: Everything Dinosaur (AI assisted).

Picture credit: Everything Dinosaur (AI assisted)

Bicharracosaurus dionidei

What makes Bicharracosaurus dionidei particularly interesting is its unusual mix of sauropod traits. For example, the dorsal vertebrae are similar to the dorsal vertebrae of diplodocids.  However, some fossil bones are reminiscent of the bones of brachiosaurids such as the giant Giraffatitan brancai from the Late Jurassic of Tanzania.  This combination of autapomorphies is unexpected.  Consequently, the research team conducted a detailed phylogenetic analysis.  The results were inconclusive. The overall evidence supports a position of Bicharracosaurus within Macronaria with several analyses and diagnostic characters suggesting brachiosaurid affinities. Bicharracosaurus sits in a somewhat uncertain evolutionary position.

Intriguingly, if the brachiosaurid affinity proves to be correct, then Bicharracosaurus dionidei would be the first member of the Brachiosauridae from the Jurassic of South America.

A Sauropod Puzzle

Several sauropods have been described from fossil material associated with the Cañadón Calcáreo Formation.  For instance, Tehuelchesaurus benitezii which was named and described in 1999 (Rich et al). Tehuelchesaurus is thought to be a macronarian like Bicharracosaurus.  However, whilst Bicharracosaurus shows a combination of sauropod characteristics (diplodocid and brachiosaurid), Tehuelchesaurus is thought to be a member of the Camarasauridae family.

Despite some similarities between Bicharracosaurus and Tehuelchesaurus benitezii fossil material, only in some of the phylogenetic results were these two species recovered as closely related. Whereas in most analyses, Tehuelchesaurus formed a clade with Janenschia robusta, a sauropod from the Late Jurassic of Tanzania. In addition, several diagnostic characters of Bicharracosaurus are absent in Tehuelchesaurus and vice versa. The results also show that other putative macronarian taxa have incongruent positions depending on the dataset.  These inconsistencies are hindering understanding of the early evolution of the Macronaria.

A model of a typical member of the Brachiosauridae family. The Wild Safari Prehistoric World Brachiosaurus dinosaur model. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The image (above) shows a model of a Brachiosaurus.

For models and replicas of sauropods, including brachiosaurids, diplodocids and other dinosaurs: Dinosaur Models and Dinosaur Toys.

The Naming of Bicharracosaurus dionidei

The taxonomic affinity of this new dinosaur species remains uncertain. It demonstrates that early macronarian evolution was more complicated than previously thought. Until now, scientists relied heavily on fossils from North America and Europe. In contrast, southern continents such as South America and Africa were underrepresented. As a result, evolutionary models may have been biased. Thanks to this newly described sauropod, palaeontologists have the opportunity to test existing ideas and refine theories.  However, it does suggest that sauropod diversity in Gondwana was greater than expected.

The genus name comes from a Spanish term meaning “big animal”. Meanwhile, the species name honours Dionide Mesa, in recognition of the original fossil discovery.

Overall, this study provides fresh insight into one of the most iconic dinosaur groups. It highlights the importance of Southern Hemisphere sauropod fossils. At the same time, it reveals how much there is still to learn. Each new discovery has the potential to challenge established ideas. In this case, Bicharracosaurus dionidei offers a fascinating glimpse into the complex early evolution of macronarian sauropods.

The scientific paper: “Bicharracosaurus dionidei, gen. et sp. nov., a new macronarian (Dinosauria, Sauropoda) from the Late Jurassic Cañadón Calcáreo Formation of Argentina and the problematic early evolution of macronarians” by Alexandra Reutter​, José Luis Carballido, Guillermo José Windholz, Diego Pol and Oliver W.M. Rauhut published in PeerJ.

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The discovery of a new titanosaur from Morocco is helping palaeontologists rethink dinosaur diversity at the end of the Mesozoic. Indeed, researchers conclude that Maastrichtian dinosaur diversity is underestimated.  Meet Phosphatotitan khouribgaensis the first definitive titanosaur described from the late Maastrichtian phosphates of Morocco. This exciting discovery provides fresh insights into African dinosaur faunas just before the mass extinction event.

A life reconstruction of the Late Cretaceous Moroccan titanosaur Phosphatotitan khouribgaensis. Picture credit: Everything Dinosaur (AI assisted).

Picture credit: Everything Dinosaur (AI assisted)

Learning About Late Cretaceous African Dinosaurs

The last few million years of the Cretaceous (Maastrichtian faunal stage), saw the final diversification of the Dinosauria prior to the K/Pg extinction event. Discussions of end-Cretaceous dinosaur diversity have focused on well-sampled faunas from Laurasia; far less is known about dinosaurian faunas of the Southern Hemisphere, especially Africa. Subsequently, African dinosaur faunas remain poorly understood.

Fortunately, the Maastrichtian-aged phosphate deposits of Morocco offer a rare window into this ancient palaeoecosystem. The fossils are found in the Khouribga Province (Sidi Chennane locality). They have yielded a variety of dinosaur fossils.  For example, abelisaurids and lambeosaurines.  Titanosaur fossils have been discovered, but no taxon had been erected.  However, the research team which included Dr Nicholas Longrich (University of Bath) were confident enough to describe a new species. Although incomplete, the remains are scientifically significant. The researchers identified dorsal, sacral, and caudal vertebrae, along with parts of the pelvis.  Importantly, the remains although fragmentary, preserve enough anatomical detail to confirm a new genus and species.

To learn more about the remarkable dinosaur biota associated with the Moroccan Maastrichtian phosphate deposits.

To read about Chenanisaurus barbaricus, a giant abelisaurid from North Africa: The Last African Dinosaur?

Two new abelisaurid theropods described: Two Abelisaurs Described from Fragmentary Remains.

Minqaria bata a new duck-billed dinosaur from the Late Cretaceous of Morocco: New Pony-sized Moroccan Lambeosaurine Dinosaur.

Links to South American Giants

Intriguingly, Phosphatotitan shows anatomical similarities with South American titanosaurs. In particular, it shares features with members of the Lognkosauria, a group that includes the enormous, Early Cretaceous Patagotitan (P. mayorum). For example, it possessed short dorsal and caudal centra, expanded dorsal and caudal neural spines, and a broad pubis. This new species differs from titanosaurs described from the Cretaceous of Africa and Europe.

This connection likely dates back to a time before Africa and South America fully separated. Around 100 million years ago, these landmasses split as the South Atlantic Ocean opened. Therefore, Phosphatotitan provides evidence of ancient biogeographic links across Gondwana.  The fossilised bones demonstrate that Phosphatotitan was much smaller than Patagotitan and other South American giants.  Scientists estimate that Phosphatotitan weighed between 3.5 and 4 tonnes. In contrast, Patagotitan is estimated to have weighed around 60 tonnes.

Sue from Everything Dinosaur poses in front of the colossal Patagotitan skeleton which is being exhibited at the Natural History Museum (London). The recently described Phosphatotitan khouribgaensis from the Late Cretaceous of Morocco could be closely related. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Why was Phosphatotitan khouribgaensis Small?

Despite its titanosaurian heritage and its close taxonomic relationship with Patagotitan, Phosphatotitan was surprisingly modest in size.  Body mass estimates of between three and a half to four tonnes have been proposed.  It was much smaller than most of its South American relatives. Its small size relative to other Lognkosauria suggests a lineage selected for small size. This could be a result of island dwarfism.  During the latest Cretaceous rising sea levels may have isolated parts of Morocco.  Consequently, the smaller landmasses and their limited resources could have favoured smaller dinosaurs.

Alternatively, environmental pressures may have played a key role. In some ecosystems, smaller herbivores outcompete larger ones. This pattern appears in South America, where smaller titanosaurs became more common. Similarly, Egyptian titanosaurs also tend to be small-bodied.  Therefore, Phosphatotitan may reflect a broader trend towards smaller sauropods in certain Late Cretaceous ecosystems.

Phosphatotitan khouribgaensis scale drawing. This titanosaur is thought to weigh around four tonnes and was around nine to ten metres long. Picture credit: Everything Dinosaur (AI assisted).

Picture credit: Everything Dinosaur (AI assisted)

Dinosaur Diversity in the Late Cretaceous May Have Been Underestimated

The discovery of Phosphatotitan khouribgaensis highlights the complexity of Late Cretaceous dinosaur dominated ecosystems. As continents drifted apart, dinosaur populations became increasingly isolated. This isolation led to high levels of endemism. At the same time, occasional dispersal events may have allowed some species to spread between landmasses. Consequently, dinosaur faunas in Gondwana were both diverse and regionally distinct.

The close relationships of Morocco’s titanosaurs and abelisaurids to South American species may reflect a wide distribution of these clades prior to the opening of the South Atlantic and the separation of Africa and South America around a hundred million years ago.  The high endemism seen in both the Northern and Southern Hemispheres suggests that Maastrichtian dinosaur diversity is underestimated.

The scientific paper: “A Titanosaurian Sauropod with South American Affinities (Lognkosauria: Argentinosauridae) from the Late Maastrichtian of Morocco and Evidence for Dinosaur Endemism in Africa” by Nicholas R. Longrich, Agustín Pérez-Moreno, Verónica Díez Díaz, Xabier Pereda-Suberbiola, Nathalie Bardet and Nour-Eddine Jalil published in Diversity.

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