Open Paleo

Lessemsaurus

Bonaparte, 1999 LES-uhm-SAWR-us

Named in honor of Don Lessem, a writer of popular science books about dinosaurs, combined with Greek 'sauros' meaning 'lizard'; the specific name sauropoides means 'sauropod-like', referencing its sauropodiform affinities.

227.3–205.7 million years ago Norian, Late Triassic
Late Triassic stages

Lessemsaurus is an extinct genus of sauropodiform dinosaur from the Late Triassic of what is now Argentina. Bonaparte erected it in 1999 on eight presacral neural arches, part of a disarticulated assemblage collected in 1971 that also yielded vertebrae, girdles and limb bones. Because nothing in the lot is articulated, a 2007 redescription restricted the type to those arches alone and referred the remaining elements, which come from at least three individuals, to the species separately. Most of what is known of the skeleton rests on that referred material.

Diagnosis

  1. Dorsal and middle to posterior cervical vertebrae with high neural arches
  2. Strong neural arch constriction below the postzygapophyses
  3. Deep postspinal fossa
  4. Dorsoventrally high infrapostzygapophyseal depression
  5. Middle and posterior dorsals with neural spines higher than long, the height to length ratio being 1.5 to 2
  6. Robust scapula with a markedly expanded blade
  7. Metacarpal I extremely short, its proximal end lateromedially wider than the length of the metacarpal
  8. Acute lateral process on the proximolateral corner of metacarpal II
  9. Pubic peduncle of the ilium with a medial flange forming a narrow, marginal medial wall of the acetabulum
  10. Brevis crest extending from the base of the ischial peduncle to the posterior tip of the postacetabular process
  11. Distal tibia subrectangular in cross-section, its major axis lateromedial and twice its anteroposterior extension

Species

Lessemsaurus sauropoides Bonaparte, 1999

Type species

From Ancient Greek '-oides' meaning 'resembling', combined with 'sauro-' (lizard/sauropod), meaning 'resembling a sauropod', in reference to its sauropod-like characteristics.

Holotype
PVL 4822-1 , Colección de Paleontologia de Vertebrados de la Fundación Instituto Miguel Lillo
Material
Eight presacral neural arches
Notes
Nothing in the assemblage is articulated, so Pol and Powell (2007) restricted the holotype to the eight arches Bonaparte described, individually numbered PVL 4822-1/1, /2, /3, /4, /5, /6, /7 and /10. They renumbered the rest of the lot as referred material from at least three individuals.
Horizon
upper Los Colorados Formation, Norian, Late Triassic , 227.3–205.7 million years ago
Locality
Paraje La Esquina, La Rioja, Argentina

References

  1. Bonaparte, J. F. (1999). Evolución de las vértebras presacras en Sauropodomorpha [Evolution of the presacral vertebrae in Sauropodomorpha]. Ameghiniana 36(2): 115-187. bonaparte1999d
  2. Pol, D.; Powell, J. E. (2007). New information on Lessemsaurus sauropoides (Dinosauria: Sauropodomorpha) from the Upper Triassic of Argentina. Special Papers in Palaeontology 77: 223-243.

    Describes the postcranial material and restricts the holotype to the eight presacral neural arches of the original description.

    pol2007a
  3. Paul, G. S. (2024). The Princeton Field Guide to Dinosaurs (3rd ed.). Princeton University Press.

    Source of the lower length and mass estimates.

    paul2024a
  4. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Sauropods. Princeton University Press.

    Source of the hip height, and of the upper length and mass estimates.

    jones2026b