Prestosuchus

Prestosuchus Temporal range: Ma PreꞒ Ꞓ O S D C P T J K Pg N
AMNH 3856, a skeletal mount (cast) of Prestosuchus chiniquensis displayed at the American Museum of Natural History
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauria
Clade:	Pseudosuchia
Clade:	Loricata
Family:	†Prestosuchidae
Genus:	†Prestosuchus Huene, 1938
Type species
†Prestosuchus chiniquensis Huene, 1938
Other species
†P. nyassicus? (Huene, 1939)
Synonyms
"Karamuru vorax"? (nomen nudum) Kischlat, 2000 Huenesuchus Kischlat, 2023 Stagonosuchus? Huene, 1939

Prestosuchus (meaning "Prestes crocodile") is an

The first two specimens of Prestosuchus to be described were found at the Weg Sanga site near the town of

Huene described several more Prestosuchus-like reptiles shortly afterwards, although he did not consider them to be the same species as Prestosuchus chiniquensis. One specimen, with its fossils labelled as SNSB-BSPG AS XXV 131-139, was given its own genus and species: Procerosuchus celer. Another specimen, with its fossils labelled SNSB-BSPG AS XXV 13–24, 26–27, and 44–48, was designated as a second species of Prestosuchus, Prestosuchus loricatus.^[6] Some authors have considered both of these specimens to belong to P. chiniquensis, while others have gone as far as to consider not only Procerosuchus celer a separate genus, but also "Prestosuchus" loricatus.^[7]

Kischlat (2000) referred to "Prestosuchus" loricatus as "Abaporu" loricatus, but this name was never formalized and has not been used since. In the same paper, several Prestosuchus specimens, including the paralectotype of P. chiniquensis and the "Porto Alegre specimen" (i.e. UFRGS-PV-0156-T), were named as a different new genus, "Karamuru vorax".^[5] However, this name was also poorly defined and never formalized, so "Karamuru vorax" is considered a nomen nudum along with "Abaporu" loricatus.^[8][9][6] Kischlat (2023) later proposed the new genus name Huenesuchus for Prestosuchus chiniquensis. Although he admitted that Prestosuchus is a valid name, he preferred to replace that name under the argument that a type species was not explicitly established along ICZN guidelines.^[10] Other paleontologists have informally disagreed with this argument,^[11] and publications relevant to Prestosuchus have consistently treated P. chiniquensis as a valid type species.^[9][12][6]

Desojo & Rauhut (2024) redescribed the remains of "Prestosuchus" loricatus and determined that it was a valid species of poposauroid, not closely related to Prestosuchus chiniquensis. In accordance with this finding, "Prestosuchus" loricatus was placed into a new genus, Schultzsuchus, named after Cesar Schultz.^[7]

Porto Alegre specimens

Four specimens are stored at the Universidade Federal do Rio Grande do Sul (UFRGS) in Porto Alegre. The first to be described was UFRGS-PV-0156-T, a massive and well-preserved skull discovered along with most of a vertebral column at the Pascual Sanga outcrop in Candelária. It was originally described by Barberena (1978)^[13] and has experienced much discussion as to its relations to the original Munich specimens. A more complete partial skeleton from Vale Verde, UFRGS-PV-0152-T, was studied by Nesbitt (2011) along with the Munich lectotype and UFRGS-PV-0156-T. It is anatomically similar to the latter specimen but has yet to be fully described.^[1]

The most complete UFRGS specimen is UFRGS-PV-0629-T, a partial skeleton from Dona Francisca which was originally described in a thesis by Mastrantonio (2010).^[14] This specimen has been the subject of braincase (2013),^[15] skull (2019),^[16] and postcranial (2024)^[17] descriptions, as well as hip muscle reconstructions.^[18] The least complete UFRGS specimen is UFRGS-PV-0473-T, an isolated braincase which may be from the "Posto de Gasolina" outcrop in Dona Francisca.^[15] Porto Alegre has one additional Prestosuchus specimen unaffiliated with the UFRGS: MCP-146, a portion of the hip area stored at the Museu de Ciências e Tecnologia of Pontífícia Universidade do Rio Grande do Sul.^[19][9]

Other specimens

Various other museums have their own Prestosuchus specimens. One of the most spectacular specimens, ULBRA-PVT-281, consists of a very large and complete skull and partial skeleton discovered at "Posto de Gasolina" and now stored at the

Like its relatives, Prestosuchus had a deep skull and serrated teeth.

The premaxilla has a tall and boxy main body with four teeth. The premaxilla also has several slender branches: a bent anterodorsal process (front upper branch), a long maxillary process (outer rear branch), and well as a pronounced palatal process (inner rear branch). These define a triangular naris (nostril hole) similar to Saurosuchus but very distinct from that of Batrachotomus.^{[13][9][16][6]} The maxilla is deep and roughly textured, with a low, triangular antorbital fenestra and 11-13^[16] large teeth. Many specimens seemingly possessed a thin convex ridge ("roman nose") running along the midline of the elongated and narrow nasals, similar to Luperosuchus and Batrachotomus.^[13][12] However, some paleontologists have argued that this appearance is a result of distortion.^[9][16] Additional low, rough lateral ridges (similar to those of Rauisuchus) run along the upper edge of the snout from the nasal to the lacrimal and prefrontal. A palpebral bone is present above the orbit in the largest specimens^[22][12] but is absent in other skulls.^[16] Unlike Postosuchus and Luperosuchus, which have their palpebral forming the entire upper edge of their orbit, Prestosuchus has additional bones forming part of the upper edge; the postfrontal always participates in the orbit, and smaller specimens without a palpebral have the frontal contribute as well.^[12][16]

The orbit has an overall "keyhole" shape like many other loricatans, with its upper half having a smoother and wider border and its lower half being narrow and pointed. This shape is due to a slightly forward tilt of the lower branch of the

infratemporal fenestra. The tall and broad quadrate extends from a socket on the rear branch of the squamosal to below the level of the quadratojugal. It also sends forward two large plates of bone which connect with the pterygoid and quadratojugal.^{[13][9][12][16]}

The palate was solid, composed of flat and toothless bones. It incorporated long, slender vomers and rectangular palatines which extensively contact the rest of the skull. The pterygoids are standard for loricatans, with a long and plate-like front branch that curves upwards at its inner edge, a thicker laterally branch which curves down, and a two-pronged connection to the quadrate. The pterygoid was also connected to the jugal via a very thick, Y-shaped ectopterygoid.^[16] Curved, rod-like hyoid bones were present as well.^[12]

gastral basket.^[14][6][12]

There are two

chevrons are developed. Towards the tip of the tail the caudals become low, elongated, and simple. Osteoderms (bony plates) were present in two rows along the neck and back and one row along the tail. Individual osteoderms were wide, roughly heart-shaped, and more than one osteoderm per row was present above each vertebra.^[14][6][12]

Pectoral girdle and forelimbs

The

glenoid (shoulder socket) is a prominent roughened area for the triceps muscle. The lower front portion of the scapula has a large acromion, which is unusually hook-shaped in the type specimen of P. chiniquensis due to an oval notch on its upper edge.^[6] A low notch is also present at the front edge of the scapula-coracoid suture in most Prestosuchus specimens. This notch has not been reported in any other loricatan and some have considered it an autapomorphy (unique distinguishing feature) of Prestosuchus.^[1] The coracoid is low, about twice as long as it is high. Its rear edge has a large contribution to the glenoid, which is preceded by a coracoid foramen and then a horizontal ridge. The horizontal ridge may be an autapomorphy of P. chiniquensis,^[6] yet it has also been reported in Procerosuchus and Batrachotomus.^[12] The rod-like clavicles have a tall vertical portion which connects to the front of the scapula and a shorter horizontal portion at their base which connects to the tie-shaped interclavicle.^[14][12][6]

The humerus is thick and about two-thirds to three-fourths the length of the femur. It is flattened and very wide near the shoulder, as well as somewhat expanded near the elbow. Bony joints (such as the two distal condyles) and muscle scars (such as the deltopectoral crest) are well-developed. The ulna and radius are thinner but no less strongly developed, with the former having a large olecranon process and the latter having a conical medial process. The hand is a mostly unknown anatomical area in Prestosuchus; only a single metacarpal has been discovered and it is widest towards the wrist. The forelimbs as a whole are similar in structure (though not necessarily proportions) to those of other loricatans like Postosuchus.^[14][6]

Hip and hindlimbs

Several autapomorphies of Prestosuchus relate to the pelvis (hip). These traits are present in P. chiniquensis and P. nyassicus (Stagonosuchus), but notably absent in "P." loricatus, which is likely a different genus. The ilium has a deep bony acetabulum roofed by a horizontal supraacetabular crest. Unlike other loricatans, there is no vertical crest above the acetabular region. The postacetabular portion of the ilium has a distinctively concave upper edge and is markedly longer than the preacetabular portion. The pubis is straight, with a small contribution to the acetabulum above the obturator foramen. The tip of the shaft expands into a knob-like pubic boot like other loricatans, though it is much smaller than that of relatives such as Saurosuchus and Postosuchus.^[14][6]

Like the ilium, the ischium is another bone which is distinctive in Prestosuchus. It is thicker than the pubis and makes a larger contribution to the acetabulum. Prominent crests are developed along the dorsal (upper) and ventral (lower) edges of the ischium. A large midline ventral crest is only seen in P. chiniquensis, P. nyassicus, and Batrachotomus among loricatans. However, Batrachotomus's crest smoothly transitions from the base of the ischium to the shaft, whereas an abrupt angled incision is observed in this area for P. chiniquensis and P. nyassicus. The paired dorsal ridges are autapomorphies of Prestosuchus, though they extend further down the shaft in P. chiniquensis than P. nyassicus. They are edged by long depressions and separated by a shallow groove on the midline of the ischium, where the left and right ischia have fused. As with other loricatans, the tip of the ischial shaft is slightly expanded into an ischial boot.^[14][6]

The femur is very robust, without a clear

neck leading from the shaft of the bone to the head. The fourth trochanter manifests as a low, rough area rather than the pronounced knob or ridge present in most other archosaurs.^[14][12] With the exception of having a tapering (rather than rounded) medial condyle, Prestosuchus generally resembles other loricatans in the structure of the femoral head and distal condyles.^[6] The tibia is shorter than the femur but thick and expanded near the knee. A deep pit is present on the postero-medial portion of its upper expansion, as also observed in Procerosuchus and Batrachotomus. The fibula is much more slender, developing a large knob-like iliofibularis muscle scar as in various other pseudosuchians. Near the heel, a deep depression is present on the rear of the fibula. This depression is an autapomorphy of Prestosuchus, being lunate (crescent-shaped) in P. chiniquensis and elongated in P. nyassicus.^[14][6]

Prestosuchus has a "crocodile-normal"

astragalus and calcaneum. The astragalus has a large tibial facet and small fibular facet on its upper surface, a curved depression on its front surface, and facets for distal tarsal III and metatarsals I-II on its lower surface. The calcaneum is wide and has a convex fibular knob and calcaneal tuber, as with other crurotarsal archosaurs. The calcaneal tuber is wider than long and has a tall boxy expansion at its rear. The underside of the calcaneum has a large facet for distal tarsal IV and metatarsals III-IV, followed by a teardrop-shaped depression. The two distal tarsals (III and IV) were roughly triangular. Metatarsal III is the longest bone in the foot, while the thick and hooked metatarsal V is the shortest, followed by metatarsal I. All the metatarsals had strongly developed ginglymoidal joints. I-III and V are triangular in cross-section, while IV is hourglass shaped. The foot has a phalangeal formula of 2-3-4-3-X, indicating that the fourth toe was much smaller than the second and third, an unusual trait among early loricatans. The first toe had a large curved claw, the third toe was thick, and the second toe had both traits.^[6]

Classification

The cladogram below follows a simplified version of the strict reduced consensus tree by Desojo et al. (2020):[6]

Archosauria	Avemetatarsalia  Pseudosuchia  Ornithosuchidae  Suchia  Revueltosaurus Aetosauria Gracilisuchidae Ticinosuchus  Paracrocodylomorpha  Mandasuchus Poposauroidea  Loricata  Pagosvenator  Prestosuchidae  Saurosuchus Prestosuchus Batrachotomus Fasolasuchus Rauisuchidae Rauisuchus Polonosuchus Postosuchus Crocodylomorpha

Paleobiology

Musculature

In 2013, a study of the structure of its hind limb bones inferred that Prestosuchus chiniquensis had 13 leg muscle groups in common with both crocodilians and birds (which together make up the two living groups of archosaurs) but only two muscle groups in common with only crocodilians, indicating that the musculature of Prestosuchus better represents a

quadrupedal movement.^[18]

Growth

In a study on bone microstructure, Prestosuchus chiniquensis was found to have had a slower growth pattern compared to other "rauisuchians", more reminiscent of that of some notosuchians and crocodilians.^[23]

References

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2. ^ von Huene, F. (1938). Die fossilen Reptilien des südamerikanischen Gondwanalandes. Neues Jahrbuch für Mineralogie, Geologie und Paläontologie, 1938:142-151.
3. ^ "Prestosuchus". UFRGS. Archived from the original on February 7, 2012.
4. ^ Kischlat & Barberena (1999) Kischlat E-E, Barberena MC. Prestosuchus chiniquensis (Crurotarsi, Archosauria) does not need a neotype! Paleontologia em Destaque. 1999;14:53.
5. ^ ^{a b} Kischlat (2000) Kischlat E-E. Tecodôncios: a Aurora dos Arcossáurios no Triássico. In: Holz M, De Ros LF, editors. Paleontologia do Rio Grande do Sul. Porto Alegre: Editora da UFRGS; 2000. pp. 246–272.
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11. ^ Christian Kammerer [@Synapsida] (July 16, 2023). "Triassicists, please ignore this paper, which fundamentally misinterprets several aspects of the ICZN, and even if it didn't would be a case of citing the letter of the law to destroy its spirit: https://sbpbrasil.org/publications/index.php/rbp/article/view/300/170" (Tweet). Archived from the original on July 20, 2023. Retrieved July 20, 2023 – via Twitter.
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13. ^ ^{a b c d e} Barberena, Mario Costa (1978). "A huge thecodont skull from the Triassic of Brazil". Pesquisas, Institute de Geociências, Universidade Federal do Rio Grande do Sul, Porto Alegre. 9 (9): 62–75.
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