The genus was described in 2019 based on the fossil remains of at least 29 individuals and was key in establishing the clade Orientalosuchina, initially interpreted as a group of early alligatoroids endemic to Asia, although later studies have argued for them actually being crocodyloids instead.

During the Late Eocene it would have inhabited the tropical to warm-subtropical freshwater biomes of the Na Duong Formation, which featured ponds, an annoxic lake and swamp forests as some of the primary habitats.

The fossil remains of Orientalosuchus were discovered between 2009 and 2012 during systematic paleontological surveys of the Na Duong Basin in Northeastern Vietnam, near the Chinese border.

All fossils come from the Eocene (late Bartonian to Priabonian, 39 to 35 Ma) Na Duong Formation and appear to represent a minimum of 29 distinct individuals.

The holotype specimen, GPIT/RE/09761, consists of a partial skeleton featuring the skull, lower jaw and a plethora of postcranial bones including several vertebrae, ribs, various limb elements and over 50 osteoderms.

The description of Orientalosuchus was accompanied by the recognition of an entire clade of Cretaceous to Eocene crocodilians from east Asia, dubbed Orientalosuchina.

[1] The tip of the snout is formed by the premaxillae, whos contact with the maxillae coincides with a deep notch similar to that seen in true crocodiles and serves to receive an enlarged dentary tooth.

The small supratemporal fenestrae are located comparably close to the front of the skull table, with a longer stretch of bone separating them from the posterior edge and creating a long contact between parietal and the squamosals.

[1] The lower of the surface features a small, oval incisive foramen and two large suborbital fenestrae that extend from the notch between the 7th and 8th maxillary alveoli backwards, restraining the palatine bones between them.

The external mandibular fenestra of Orientalosuchus is noted as being very small, only slightly larger than the foramen intermandibularis caudalis that lies on the inner side of the jaw.

Phylogenetic analysis at the time found that they were all closely related and together formed a monophyletic clade the team dubbed Orientalosuchina, which they recovered at the base of Alligatoroidea.

[2] †Leidyosuchus †Deinosuchus †Diplocynodon †Krabisuchus siamogallicus †Protoalligator huiningensis †Orientalosuchus naduongenis †Dongnanosuchus hsui †Eurycephalosuchus gannanensis †Jiangxisuchus nankangensis †Eoalligator chunyii Alligatoridae However not all studies agree with the placement of Orientalosuchina at the base of Alligatoroidea.

Nils Chabrol et al. 2024 managed to recover both hypothesis, with Orientalosuchina composed of Orientalosuchus, Krabisuchus, Eurycephalosuchus and Dongnanosuchus, but lacking the remaining members included by Massonne and colleagues.

The results that recovered the clade closer to Crocodyloids, specifically as a basal branch of Longirostres outside of the crocodyloid-gavialoid split, places Orientalosuchus as the sister taxon to Dongnanosuchus.

This represents yet another notably different internal topology, retaining the close relationship between Jiangxisuchus and Eoalligator found by some with Orientalosuchus as their immediate sister taxon, Krabisuchus more basal and Dongnanosuchus closer to dwarf mekosuchines than any of the other traditional orientalosuchins.

However the remaining six analysis of the same study all recover more traditional results with Orientalosuchina absent from Mekosuchinae and support is generally regarded as weak, although worth of being researched further.

The main coal seam preserve abundant fossilized tree trunks, some of which measuring 1 m (3 ft 3 in) across, as well as the stems of royal ferns (Osmundaceae).

The diameter of the trunks, root system and the distance between the stumps (standing generally 3–5 m (9.8–16.4 ft) apart), suggest a density of about 600 trees per hectare, comparable to the peat swamp forests of modern Sumatra and Kalimantan.

However, this can be explained with the environment of the formation, with wet conditions favoring leaves with toothed margins and the flora is indeed indicative of a high water table.

Aquatic plants have been identified from slightly older layers of the Na Duong Formation and include lotus, which would have formed meadows at the same time that shallow ponds were present.

The basal rhino Epiaceratherium naduongense was an entirely terrestrial animal, but has been interpreted as an obligate browser who's long and slender bones and tapir-like hands fit it being a forest dweller.

All three localities also share the presence of orientalosuchins, Krabisuchus, Dongnanosuchus and Orientalosuchus respectively and similar parallels exist in other reptile groups, specifically pan-geoemydid turtles.

[7] In addition to the widespread Maomingosuchus, Böhme and colleagues furthermore mention the presence of a generalist longirostrine taxa similar in appearance to today's Crocodylus or the extinct Asiatosuchus which may have obtained lengths of up to 6 m (20 ft) and possessing heterodont dentition not dissimilar to that of Orientalosuchus.

[9] In a 2022 short communication, Kazim Halaclar and colleagues report numerous pieces of fossilized feces, better known as coprolites, from the Na Duong Formation.

Analysis of the overall morphology and composition of the coprolite itself confirms it stems from a carnivorous animal and the limited amount of bone fragments suggests that the producer had highly effective stomach acid.

Aspects of the preservation, such as the lack of deformation, can also be explained by the originator having been a semi-aquatic animal, another point in favor of the crocodilian hypothesis, before being rapidly buried by sediment, which can be explained through being positioned at the edge of a river or even seasonal flooding.The impressions are regarded as being too slender to have come from the feet of a squamate, but would be a good fit for the fourth and fifth fingers of a crocodilian, especially given the absence of claw marks of webbing.