Abditosaurus

Abditosaurus kuehnei was a large herbivorous titanosaur that lived in what is now Catalonia about 70.5 million years ago. Its only known skeleton was discovered in 1954, but repeated interruptions left part of it in the hillside. The last major bones were recovered six decades later, and the animal received its scientific name in 2022.

The skeleton is partly articulated and includes teeth, a long neck series, trunk vertebrae, ribs, shoulder-girdle elements and limb bones. It is among the most complete titanosaurs known from Europe. Published estimates of about 17.5 metres and 14 tonnes are modelled values rather than measurements of a complete body.

Quick facts

Walter Kühne’s discovery in 1954

German palaeontologist Walter Georg Kühne travelled to the southern Pyrenees to search for small Mesozoic mammals. On 25 September 1954, near the village of Orcau, he instead found bones from a large sauropod. The locality now called Orcau-1 lies about six kilometres east of Tremp in Pallars Jussà.

Kühne worked there for roughly two weeks. Some bones were jacketed in plaster and sent to the Lucas Mallada Institute in Madrid, while others were protected in the rock. He returned in 1955 with local workers and institute staff. His field sketches show that he recognised the articulated rear portion of the skeleton. For mid-century Europe, a partly connected titanosaur was exceptional.

Funding ended before extraction was complete. In 1956 Albert-Félix de Lapparent and Emiliano Aguirre mentioned the bones as a new but unnamed species of Hypselosaurus. That was not a formal description of a separate taxon, and Hypselosaurus later became taxonomically problematic. Much of the material remained unprepared, while other bones stayed in the slope.

Returns to Orcau-1

Teams returned in 1984 and 1986 under Josep Vicenç Santafé of the Sabadell palaeontological institute, with researchers from Lleida. They recovered a sternal plate and more vertebrae, but again could not finish the site.

A new campaign began in 2012. The Catalan Institute of Palaeontology Miquel Crusafont, the University of Zaragoza and the Museu de la Conca Dellà worked through several seasons ending in 2014. They found bones left by earlier excavations as well as teeth, ribs, limb elements and a long articulated sequence of cervical and dorsal vertebrae.

Comparison between new quarry maps and Kühne’s notebooks joined the material from the different decades. The bones occupied one stratigraphic level within an area about six by four metres. No duplicated left or right elements require a second animal, so the associated material is interpreted as one skeleton.

The “hidden lizard”

Bernat Vila and colleagues established Abditosaurus kuehnei in 2022. Latin abditus means hidden or concealed, while Greek sauros means lizard. The name recalls the nearly sixty years between the first and final excavations. The species honours Kühne.

Only one species and one holotype are recognised. No isolated material from another locality has been securely referred to the genus, so its confirmed range remains limited to Orcau-1.

What the skeleton preserves

The holotype includes isolated teeth, twelve articulated or partly preserved cervical vertebrae with cervical ribs, seven nearly complete or fragmentary anterior and middle dorsal vertebrae, six dorsal ribs and additional rib fragments. Three chevrons are the only identified elements from beneath the tail vertebrae.

The shoulder girdle contains a right scapula, the rear of the left scapula, a right coracoid and a left sternal plate, together with an ossified sternal rib. The forelimbs are represented by the upper half of the left humerus, lower half of the right humerus and part of the right radius.

From the pelvis and hind limbs come part of the left ilium, the upper region of a right femur, a right tibia, a right fibula and the lower half of a left fibula with an attached calcaneum. The ossified sternal rib and calcaneum are notable because these elements were long thought to be strongly reduced or absent in titanosaurs and are not always recognised confidently.

Almost the entire skull is absent. Teeth alone cannot restore head shape, and missing tail and limb regions prevent direct measurement of total length. Even so, the joined neck, trunk vertebrae and girdle bones make this skeleton far more informative than most fragmentary European titanosaur finds.

Diagnostic anatomy

The diagnosis does not rest on one spectacular feature. The describing team identified fourteen autapomorphies distributed among vertebrae, ribs, scapula and limbs.

Dorsal vertebrae are especially informative. Their laminae and fossae form a characteristic arrangement, while some regions contain many pneumatic openings left by air spaces that lightened the axial skeleton. In the middle dorsals, accessory laminae and the positions of these openings differ from related titanosaurs.

The anterior dorsal ribs had broad plate-like shafts with D-shaped cross-sections, and the lower ends of some ribs expanded like spoons. The scapula was powerful and strongly expanded at its front. Together, these details distinguish the animal despite the near absence of a skull.

Length, mass and maturity

The original description estimated about 17.5 metres and 14,053 kilograms. Researchers used limb dimensions and comparative relationships derived from other large quadrupeds. Those results should be rounded: incompleteness and the choice of comparative model rule out treating either number as an exact living measurement. The size comparison guide explains why such reconstructions need ranges.

Even with that caution, Abditosaurus was substantially larger than most Late Cretaceous titanosaurs of Ibero-Armorica. In the published comparison it exceeded the largest known Atsinganosaurus and Garrigatitan specimens by more than seventy per cent, more than doubled the largest Lirainosaurus and Lohuecotitan, and was about twenty per cent larger than the largest bone then assigned to Ampelosaurus.

Thin sections from humerus, femur and tibia record a very mature, probably old individual. The researchers did not find the modified laminar bone associated with slowed growth and body-size reduction in some island titanosaurs. This was not a dwarf that merely died before reaching full size: large dimensions coincide with deep skeletal maturity.

Southern relationships

Phylogenetic analyses placed Abditosaurus among saltasaurines near lineages best known from South America and Africa. Depending on the analysis, comparatively close taxa included Brazil’s Maxakalisaurus and Egypt’s Paralititan. It stood apart from many small Late Cretaceous European titanosaurs.

A slightly higher bed near the skeleton yielded eggshell assigned to Fusioolithus baghensis. Similar shells and titanosaur embryos occur in South America, India and Africa. The combination of a large titanosaur with southern affinities and a Gondwanan-style egg type strengthens a dispersal scenario, although the shell has not been demonstrated to belong to Abditosaurus itself.

How could a large titanosaur reach Europe?

Late Cretaceous Europe was an archipelago, and the Pyrenean region formed part of the Ibero-Armorican island. The describing authors proposed that ancestors of Abditosaurus arrived in a new dispersal pulse from Africa near the beginning of the Maastrichtian.

Around 70.6 million years ago, falling global and regional sea level may have exposed parts of carbonate platforms in the western Tethys. These need not have formed a broad continuous bridge. Chains of land and narrower sea gaps could still have made stepwise movement by large terrestrial animals more feasible.

The Orcau-1 age of about 70.5 million years fits the timing. Yet no continuous series of populations from Africa to Catalonia has been found. African origin and a particular route remain a scientific hypothesis supported by relationships, arrival time, large size and associated eggshell rather than a directly observed journey.

Orcau-1 and burial

The skeleton lay in the lower Conques Formation of the Tremp Group. These continental sediments formed among rivers and floodplains along the southern side of the Pyrenean Basin. Plant remains, moulds of terrestrial Lychnus snails and shed crocodylomorph teeth also occur at the locality.

Two isolated dromaeosaurid teeth and eggshell fragments came from a slightly higher level. They characterise the local fauna but do not prove that a predator encountered this particular carcass. No described bite evidence supports that scene.

Partial articulation shows that much of the body was not scattered completely before burial. Missing elements and the site’s long excavation history nevertheless prevent a precise account of death, decay and transport without additional taphonomic evidence.

Food and way of life

As a sauropod, Abditosaurus was herbivorous. Its small individual teeth could crop vegetation but performed little oral chewing; most processing probably occurred in a large digestive tract, as reconstructed for sauropods generally.

The actual plants are unknown. Plant fossils from the formation are not gut contents, and no stomach material belongs to the holotype. Feeding height depended on neck posture and available vegetation, but an incomplete skeleton cannot define a precise maximum head height.

One skeleton cannot reveal whether these animals formed herds, cared for young or moved seasonally. A population-level dispersal over geological time is not evidence that one animal made annual long-distance migrations.

What a reconstruction can show

The broad anatomy of a large titanosaur is secure: a long neck and tail, deep trunk and four columnar limbs. The preserved vertebral sequence, scapulae and leg bones refine the scale and placement of several regions.

Head shape, complete tail length, soft-tissue contours and colour remain unknown. No skin impression or osteoderm was found with the skeleton, so armour in this genus is not established. Any colour scheme or row of dermal plates is an artistic addition.

Why the find matters

Abditosaurus combines three unusual records: a partly articulated skeleton, an exceptionally old individual and a lineage strikingly different in size and relationships from many island titanosaurs of Europe. It shows that these faunas did not consist only of long-isolated dwarfs such as Magyarosaurus.

The discovery also demonstrates the value of returning to old localities. Kühne’s notes allowed bones from separate decades to be reunited, while the 2012–2014 campaigns supplied enough anatomy for diagnosis and evolutionary analysis.

Evidence, inference and reconstruction