Losillasaurus: the Spanish sauropod whose placement changed

Losillasaurus giganteus is a sauropod from eastern Spain whose place on the dinosaur family tree has changed as new material and broader comparisons became available. Its fossils include an associated partial skeleton with a distinctive tail, along with skull and postcranial material described later. The history of its classification shows why a name, a specimen and a phylogenetic position should be discussed separately.

Quick facts

Excavation in the Los Serranos Basin

The fossils were found at La Cañada near Losilla de Aras in Valencia. Excavations began after the discovery of a large bone in 1989 and continued through the early 1990s. The material comes from the Villar del Arzobispo Formation, a dinosaur-bearing unit in eastern Spain. Current studies commonly place the relevant layers in the Kimmeridgian of the Late Jurassic, while older discussions described a broader Jurassic–Cretaceous transition.

Maria Lourdes Casanovas-Cladellas, José Luis Santafé and José Vicente Sanz named Losillasaurus giganteus in 2001. The genus refers to Losilla de Aras, and the species name reflects the large size inferred for the animal. That adjective is part of the taxonomic name; it is not a measurement of body length.

The original collection included a partial skull and a substantial, though incomplete, skeleton. The name-bearing type is an anterior caudal vertebra housed in the Museo de Ciencias Naturales de Valencia. Two additional tail vertebrae were designated as paratypes. Other bones from the same associated specimen were included in the description. Later publications have described additional material and specimens, each with its own locality and evidential status.

A tail that first suggested a different branch

The first two tail vertebrae have strongly curved neural spines that create a cutlass-like profile in side view. Other caudal vertebrae preserve ridges, grooves and changes in the shape of their spines along the tail. These features contributed to the diagnosis and provide useful comparisons with other sauropods.

When the genus was first described, the available characters led researchers to consider a position among basal diplodocoids. Subsequent work argued that the evidence did not support that placement and instead treated Losillasaurus as a non-neosauropod eusauropod. Later phylogenetic studies recovered it within Turiasauria, a group of early branching sauropods known from Europe and other regions.

These changes reflect expanded data and revised character comparisons, not a change to the name-bearing vertebra. A phylogenetic result is a hypothesis built from scored anatomy. Its position can shift when new skull features are added, a fossil is referred to a taxon or the character matrix is revised.

New skull material and tooth variation

A later specimen from the Villar del Arzobispo Formation preserves a partial skull with teeth and additional skeletal elements. It gave researchers new information about the front of the skull, which had been poorly represented in the original material. The new bones also helped compare the shapes of teeth within Turiasauria.

Sauropod teeth can vary along the jaws and between individuals. If an isolated tooth is assigned to a genus based only on a superficial shape, that variation can be mistaken for a difference between species. Cranial material provides the positions that isolated teeth lack. In the modern redescription, tooth characters and other skull features were considered with the vertebral and limb evidence rather than treated as an isolated puzzle.

A separate anterior caudal vertebra from Portugal has also been referred to Losillasaurus in the literature. Its assignment extends the known distribution, but a referred bone is not part of the type specimen. It is useful only to the extent that its features can be compared with the diagnostic anatomy from Valencia.

What the associated skeleton can and cannot show

The original material preserves vertebrae from several regions, parts of the skull, limb bones, pelvic elements and other fragments. Its association makes the anatomy more informative than a collection of unrelated isolated bones. It still lacks many parts and does not yield a full, undistorted body outline from nose to tail.

The type tail shows joint surfaces, neural spines and changes in the vertebral series. Those features help identify a sauropod and compare it with other taxa. They do not directly measure neck length, total mass or the animal’s feeding height. The word giganteus and illustrations of a giant body should not substitute for a documented scaling method.

Turiasaurs were sauropods, and the herbivorous feeding category follows from that broad anatomy and relationship. No plant remains, stomach contents, nest, skin impression or trackway is securely tied to Losillasaurus. The full appearance, behaviour and colour in a life reconstruction therefore rely on comparison with better-preserved relatives.

Age and landscape

The Villar del Arzobispo Formation records terrestrial and coastal settings that changed over time. Its sandstones and mudstones preserve dinosaur remains alongside evidence of water and nearby environments. A fossil locality samples a particular depositional context, while the formation as a whole spans a wider geological record.

Other sauropods have been reported from the broader Iberian record, including Barosaurus-like diplodocids in wider comparisons and the turiasaur Turiasaurus from Spain. Their presence does not show that all these dinosaurs lived together at one site. Beds, ages and individual associations must be checked before constructing a shared community.

Age assignments have also been refined since the original naming. The commonly used Kimmeridgian age comes from later work on the stratigraphy of the formation. Older labels that span the latest Jurassic and earliest Cretaceous should be read in light of those revisions rather than repeated as exact dates for every bone.

Why classifications change

Early sauropod relationships are difficult to resolve because many taxa are represented by incomplete skeletons and share ancestral features. In Losillasaurus, the tail provided the original diagnostic basis, while later skull discoveries added characters that were not available in the first analysis. A classification based on the type alone can therefore differ from one that includes the associated and later referred material.

Researchers also have to decide whether a new fossil belongs to a known genus. That decision depends on overlapping anatomy, not merely on a similar age or nearby geography. A tail vertebra can be highly informative if it preserves distinctive features, yet still not identify every bone found in the same formation.

Recent analyses place Losillasaurus among turiasaurs, but the history of earlier placements remains useful. It shows how the interpretation responded to added fossils and improved sampling. It does not mean that every detail of the family tree is final or that all historic referrals remain secure.

A changing record, not a changing animal

The dinosaur itself did not change as its classification moved from a proposed diplodocoid position to Turiasauria. What changed was the evidence available to compare it. A caudal series, partial skull and associated limb bones now support a more developed diagnosis than the original type vertebra could provide alone.

For readers, that means the safest reconstruction is specific about its foundation: the name is anchored by a tail vertebra; the associated material broadens the skeleton; later skull-bearing fossils add important comparisons; and Turiasauria is the placement recovered by recent analyses. The dinosaur catalogue records Losillasaurus as a Spanish sauropod while preserving that evidence trail.