Lalieudorhynchus is an extinct genus of caseid synapsids that lived during the Guadalupian (= Middle Permian) in what is now Southern France. The genus is only known by its type species, Lalieudorhynchus gandi, which was named in 2022 by Ralf Werneburg, Frederik Spindler, Jocelyn Falconnet, Jean-Sébastien Steyer, Monique Vianey-Liaud, and Joerg W. Schneider. Lalieudorhynchus is represented by a partial postcranial skeleton discovered in the Lodève basin in the central part of the Hérault department in the Occitanie region. It belongs to an individual measuring approximately 3.75 m (12.3 ft) in length. The degree of ossification of its bones, however, indicates that it was a late juvenile or still growing young adult. Based on the internal structure of its bones, the describing authors interpreted Lalieudorhynchus as a semiaquatic animal that may have had a lifestyle similar to that of hippopotamus, spending part of its time in water but returning to land for food, though the idea that caseids were semi-aquatic has been previously contested by other authors. It is geologically one of the youngest known representatives of the caseids. The phylogenetic analysis proposed by Werneburg and colleagues identified Lalieudorhynchus as a derived caseid closely related to the North American species "Cotylorhynchus" hancocki.
Etymology The genus name is a combination of La Lieude located near the type locality, and "rhynchus", the Latinized form of the Greek "rhynchos" (the nose) sometimes used in the names of caseids. The specific epithet honours Georges Gand who worked on the Lodève basin for decades, notably on the La Lieude footprint slab, and co-organized and promoted the excavation campaigns for this caseid.
Description
Lalieudorhynchus is represented by a partial and disarticulated but well-preserved post-cranial skeleton. The holotype, represented by a series of bones cataloged UM-LIE 02–37, UM-LIE 39–41, UM-LIE 45 and UM-LIE 47, consists of about ten vertebrae (dorsal, sacral and caudal), about fifteen ribs, a complete right scapulocoracoid 50 cm (20 in) long, the dorsal branch of the left ilium, the right and left femora measuring 35.5 cm (14.0 in) long, and several foot bones (an astragalus, two tarsal elements and five phalanges). The total body length of this specimen is estimated at 3.75 m (12.3 ft). The holotype of Lalieudorhynchus shows a mixture of mature and immature characters throughout its skeleton indicating that this specimen was a late juvenile or a still growing young adult at the time of its death. The skull is unknown, but like its closest relatives, it was probably very small compared to the size of the body, triangular-shaped in dorsal view, and terminating anteriorly in a forward-sloping snout with very large external nostrils. The shape of its ribs indicates that Lalieudorhynchus had a barrel-shaped rib cage like other derived caseids. This must have housed large digestive tract suggesting that the animal had to feed on a large quantity of plants with low nutritional value. Lalieudorhynchus is characterized by several apomorphies. The neural spines of the sacral and anterior caudal vertebrae have a cross section with a very thin keel-like process forwards, which starting above the prezygapophyses and running upwards along the entire vertical edge to the top of the neural spine. The neural spines of the dorsal and caudal vertebrae have their dorsal end slender instead of showing lateral thickening. The first sacral rib has a narrow distal end. The scapulocoracoid has a fossa on the triceps process of the metacoracoid (one of the three bones forming the scapulocoracoid with the procoracoid and the scapula). The foot is characterized by a very large distal tarsus 1 of the same width as the astragalus, with almost all sides slightly concave. Lalieudorhynchus is also distinguished by a unique combination of characters. Like other caseids, it differs from Ruthenosaurus by its straight neural spines instead of being angled forwards. The middle caudal vertebrae have relatively long centra, elongated below their postzygapophyses, but with low neural arches, unlike Alierasaurus. The three sacral vertebrae and the most anterior caudal vertebra have a short and transversely very wide centrum like in Ruthenosaurus, while these same centra are much narrower in Cotylorhynchus romeri. The neural spine of the first sacral and the first caudal vertebra is very elongated dorsally as in "Cotylorhynchus" hancocki, which is not the case in C. romeri and Ruthenosaurus. A hyposphene is present under the postzygapophyses of the dorsal and caudal vertebrae, a feature previously reported only in C. hancocki. A supraglenoid foramen is present, opening laterally in the supraglenoid fossa and medially in the dorsal part of the subscapular fossa as in "C." hancocki. The shaft of the scapular blade is much wider than that of Alierasaurus. The anteromedial border of the scapula is bulged by the presence of a slightly rounded scapular process, a feature shared with "C." hancocki, "C." bransoni and "Angelosaurus" romeri, but not with C. romeri and Alierasaurus. Two parts of the glenoid fossa have an angle of approximately 130° as in C. bransoni. The femur has a posterior condyle occupying a much more distal position than the anterior condyle, contrary to Ruthenosaurus. The popliteal area of the femur of Lalieudorhynchus is relatively wide with robust grooves, and is much larger and deeper than in C. romeri. The proximal head of the bone is more massive dorso-ventrally than in C. romeri. The femur also has a large pronounced internal trochanter and a little fourth trochanter in its distal half, a feature shared with "C." hancocki, Angelosaurus romeri and A. greeni, and which differs from C. romeri, Angelosaurus dolani, Casea broilii, and Ruthenosaurus. The intercondylar fossa of the femur is very wide, inferring a narrow postero-dorsal condyle, unlike C. romeri and Ruthenosaurus. The astragalus is nearly as broad as long in contrast to most other caseids, but is very similar to that of "C." hancocki. The metatarsal I is robust and enlarged like in Alierasaurus. The phalanges are short and wide. They are shorter than in Alierasaurus.
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