Coloradisaurus brevis was a small-to-medium early sauropodomorph from the Late Triassic of north-western Argentina. Its history includes a naming delay, a second incomplete skeleton and changes in its family placement. The fossils show a bipedal plant-eater from the Los Colorados Formation, but neither a full skeleton nor a direct body-mass measurement is available.
The type specimen preserves a skull and partial skeleton, while a second specimen lacks the skull and is assigned through diagnostic ankle anatomy and proportions. Estimates of length and mass therefore vary with reconstruction. The nearby fauna and red beds help describe a river-and-floodplain landscape, but they do not make every animal in the formation exactly contemporaneous.
Quick facts
| Scientific name | Coloradisaurus brevis (Bonaparte, 1978/1979) |
|---|---|
| Group | Sauropodomorpha; commonly placed in Massospondylidae |
| Age | Late Triassic, Norian; Los Colorados fauna broadly about 215–212.5 million years old |
| Location | La Esquina, La Rioja Province, Argentina |
| Length | Roughly 3–4.5 m in published reconstructions |
| Mass | Estimates range from about 70 kg to several hundred kilograms |
| Diet | Probably herbivorous |
| Locomotion | Mainly bipedal, inferred from the limb and body plan |
| Known species | One: C. brevis |
| Material | Type PVL 3967 and a second partial skeleton, PVL 5904 |
Separating specimens, growth and estimates
PVL 3967 preserves a partial skull and skeleton from the 1971 expedition. Missing regions mean body length and mass still depend on reconstruction.
PVL 5904 lacks a skull and is referred through ankle characters and proportions. It adds postcranial information but cannot be combined with the type as one individual.
Growth marks in a femur have been interpreted as cyclic deposition, and PVL 5904 as immature. These data inform development but do not calculate a precise adult mass.
The Los Colorados fauna is broadly Norian, while estimated length and mass vary with restored body volume. Neither a formation age nor a model estimate is a direct measurement of this specimen.
Discovery and naming
The fossils were collected at La Esquina in La Rioja Province, Argentina. In October 1971, an expedition from the Miguel Lillo Foundation recovered the type specimen PVL 3967. The field party included José Bonaparte, Martín Vince, Juan Carlos Leal and Tomás Fasola. The locality lies in the Los Colorados Formation, a succession known for a diverse Late Triassic vertebrate fauna.
Bonaparte first described the dinosaur as Coloradia brevis. The name appeared with a 1978 date in some contexts, including the cover, while the printed volume’s colophon indicates that it was issued in December 1979. This difference explains why both years appear in references. The species epithet brevis means short, reflecting the original comparison of its proportions.
The generic name Coloradia was already in use for an insect, creating a nomenclatural problem. Lambert proposed Coloradisaurus in 1983 as a replacement. The name’s availability and proper authorship were later treated formally by Galton in 1990, who supplied the diagnosis and type details required under zoological naming rules. Modern usage recognises Coloradisaurus brevis.
A second skeleton, PVL 5904, was later assigned to the genus. It is partially articulated but lacks a skull, so the referral depends on postcranial characters rather than direct comparison of the head. The two specimens provide complementary information, but they are distinct animals and should be reported separately.
Age and the Los Colorados landscape
The Los Colorados Formation is Norian in age, within the Late Triassic. The vertebrate fauna is commonly placed broadly around 215–212.5 million years ago, although precise dates and correlations vary through the sequence. An age assigned to the formation or its fossil assemblage is not necessarily a direct radiometric date on the Coloradisaurus bones.
Red mudstones and sandstones record continental rivers and floodplains. Channels carried sediment across the basin; overbank areas developed soils and preserved carcasses or isolated bones. Seasonal wet and dry periods are consistent with the geological record, but “red bed” does not mean that the animal lived in a featureless desert. Vegetation and water availability likely varied across habitats and time.
Other large sauropodomorphs, including Riojasaurus and Lessemsaurus, occur in comparable parts of the succession. Their presence helps illustrate the diversity of early large-bodied dinosaurs in the region. It does not prove that all named genera occupied precisely the same locality or lived together at the same moment. Stratigraphic position matters when reconstructing a community.
What the skeleton preserves
The holotype PVL 3967 preserves a partial skull and postcranial material. It is sufficient to diagnose the species but not a complete body. The second specimen PVL 5904 preserves portions of an articulated skeleton and offers further limb and vertebral information. Because it lacks a skull, its assignment relies on distinctive features of the ankle and proportions that match the genus.
Descriptions report as many as about 22 tooth positions in the maxilla and at least 18 in the dentary, though the preserved counts and missing portions must be distinguished from the number that a complete jaw may have carried. The premaxilla is not fully known, so its tooth complement cannot be confidently supplied. Tooth counts are anatomical observations only when the preserved and inferred positions are kept separate.
The teeth are compatible with plant processing, and the general sauropodomorph body plan supports herbivory. The skeleton lacks direct stomach contents or a securely associated coprolite that would show an actual meal. The skull and teeth make a plant-based diet a strong inference, not a catalogue of specific foods.
As in many early sauropodomorphs, the hind limbs support a primarily bipedal reconstruction. Forelimb anatomy and the centre of mass can be compared with better-known relatives, but incomplete bones limit calculations of speed and exact loading. There is no trackway confidently assigned to Coloradisaurus that records a particular walk or group movement.
Size, mass and growth
Published body-length estimates generally fall between about 3 and 4.5 metres. This range reflects alternative restorations of missing neck, tail and trunk regions as well as differences in which specimen is used. It does not mean researchers have measured a full skeleton of that length. PVL 3967 and PVL 5904 each preserve only part of the animal.
Mass estimates show an even wider spread. Older values around 70 kilograms contrast with reconstructions in the several-hundred-kilogram range, sometimes approaching 300–400 kilograms. These are model outputs, not weighing scales. A volumetric reconstruction changes when the torso is made deeper, the neck is lengthened, or the limbs and tail are restored with a different amount of muscle.
Bone histology provides evidence about growth. A study of femoral tissue identified cyclic growth patterns, which record changes in deposition through life. PVL 5904 was interpreted as an immature individual. Such samples can show that growth varied with age and conditions, but they cannot by themselves yield one adult mass. Histological growth marks may also be incomplete or remodelled, and one femur cannot represent every individual in a population.
The second skeleton’s immaturity further complicates comparisons with the type. A difference in proportions might reflect age, individual variation or taxonomic difference. The referred assignment is supported by shared diagnostic features, but it should not be used to claim that every bone represents a mature version of PVL 3967.
Classification and relatives
Coloradisaurus is a sauropodomorph. Earlier classifications sometimes placed it with Plateosauridae, a broad family of early forms. Many later studies recover it among Massospondylidae, a group that includes several Gondwanan and other early sauropodomorphs. The family tree is built from comparative characters, and different datasets can move genera between adjacent branches.
Family placement affects how researchers interpret its size, anatomy and relationship to other South American animals. It does not change the directly observed type bones. A responsible description identifies the commonly accepted placement and signals that detailed relationships may shift as taxa and anatomical scores are revised.
The dinosaur catalogue provides a contextual route from this profile to other named dinosaurs. It is an index rather than a claim that all early sauropodomorphs form one simple group.
Feeding, movement and possible pathology
Herbivory is inferred from the skull, tooth form and sauropodomorph relationships. The actual plants eaten are unknown. The region’s river plains could support varied vegetation, but the presence of plant fossils in a broad formation does not prove a specific meal. Nor do nearby carnivores establish that Coloradisaurus was routinely hunted in a way visible in its skeleton.
A scapular abnormality has been discussed in connection with the species. The interpretation is uncertain: a visible irregularity may reflect injury, disease, growth, preservation or a normal anatomical feature. Without diagnostic pathological structure, it should not be turned into a detailed story about a healed attack or disability. The bones do not preserve pain or the animal’s behaviour after the change.
No nest, eggs, skin impressions or direct social evidence are securely known for Coloradisaurus. Multiple specimens from a region do not establish a herd, and a river deposit may combine remains from different times. Calls, colour, display, courtship and exact speed remain unknown.
Reading the evidence carefully
Coloradisaurus brevis is a useful example of how nomenclature, specimen referral and body reconstruction interact. The 1978/1979 publication dates refer to different parts of the original issue; the replacement genus name solved a homonym problem; and the second skeleton adds information without becoming part of the type individual.
Its most reliable picture is an early sauropodomorph from Norian Argentina, known from two incomplete specimens and likely adapted to a plant-based diet. Length estimates of 3–4.5 metres and widely varying mass values communicate a plausible scale, not exact measurements. Its gait is mainly reconstructed as bipedal, while the family placement reflects current comparative analysis.
New diagnostic skull material from a securely dated horizon would test the referred specimen and clarify anatomy. Better associated adult material could constrain size and growth, while additional geological dates could refine its temporal place among South American sauropodomorphs. For now, the fossils are informative precisely when their separate contributions and gaps are kept visible.
Frequently asked questions
When did Coloradisaurus live?
It lived during the Norian Age of the Late Triassic. The Los Colorados fauna is broadly dated to about 215–212.5 million years ago.
How large was Coloradisaurus?
Published reconstructions range from about 3 to 4.5 metres long. Mass estimates vary from roughly 70 kilograms to several hundred kilograms.
Why was it first called Coloradia?
The original genus name was already used for an insect. Coloradisaurus was proposed as a replacement, with its availability formally addressed later.
What fossils are known?
The type PVL 3967 preserves a partial skull and skeleton. PVL 5904 is a separate partial skeleton without a skull, referred using ankle anatomy and proportions.