Trilophosuchus

Genus of crocodiles
Automatic taxobox
| fossil range = Oligocene Miocene, fossilrange|25|12.9|

The name Trilophosuchus derives from Ancient Greek and translates to "triple crested crocodile", referring to the three parallel ridges that run along the animal's skull table. The species name meanwhile honors Alan Rackham Senior, a supporter of the excavations in the Riversleigh WHA. Mead et al. (2002) also recovered such a clade, but placed Trilophosuchus as the basalmost genus in it, outside of the group formed by Quinkana, Mekosuchus and Volia (which had not been named at that point in time). This marks a trend in coming phylogenies, which recover broadly the same results, but differ in the precise topology of these derived forms. One outlier to this is the phylogenetic tree recovered by Stein et al. (2018), which recovered it as a more basal form related to Ultrastenos. However, this result has been deemed irregular and was likely caused by the inclusion of problematic taxa like Harpacochampsa. Shown below are three different phylogenetic trees, the first two showing early trees that established the close relationship between Trilophosuchus and Mekosuchus while the third shows it as the sister taxon to Ultrastenos. Willis (1997)

Mead et al. (2002)

Stein et al. (2018)

Putting aside the results of Stein et al. and minor fluctuations between its closest relatives, Trilophosuchus maintained its relative stability throughout the 21st century, as evidenced by the work of Lee and Yates (2018). In their research, morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data once again showed support for Trilophosuchus being part of an altirostral clade including Volia, Mekosuchus and Quinkana, only differing slightly in the internal relationships of this grouping. A more recent phylogenetic analysis on mekosuchines was published by Ristevski and colleagues in 2023. While the relation between Trilophosuchus, Mekosuchus and Volia once again shifted slightly, the only major departure from prior studies was that Quinkana was no longer found to be a close relative of them, instead grouping with Paludirex and Baru. The re evaluation of Ultrastenos and "Baru" huberi eventually came to lend credence to the tree previously published by Stein et al. in 2016, as the results indicate that "Baru" huberi and Ultrastenos were the same taxon and the sister to the clade that includes Trilophosuchus, Mekosuchus and Volia while maintaining an overal topology similar to that of Ristevski et al. 2023.

In many aspects the jaw musculature of Trilophosuchus compares well with that of modern crocodilians, with one of the more notable departures being caused by the shape of the supratemporal fenestrae. Due to them being much narrower than in extant forms, Trilophosuchus would rely much more heavily on the musculature of the pterygoid. More substantial are the changes to the neck musculature. The inclination of the back of the skull causes a notable shift in orientation for the musculature that flexes the head ventrally (down) and further indicates that the spinal column would likewise be positioned further down relative to the head. One of the muscles responsible for moving the head side to side in modern crocodiles (the M. obliquus capitis magnus) appears to be relatively poorly developed in Trilophosuchus, with lateral movement instead being more prominently controlled by the longissimus capitis, pars transversalis capitis muscle. The M. spinalis capitis and M. rectus capitis posterior, two muscles responsible for lifting and rotating the head, are positioned higher above the occipital condyle, effectively allowing Trilophosuchus to lift the head with more power. The alternative explanation would be that Trilophosuchus and Mekosuchus may have differed significantly enough in parts of their anatomy that are not currently known, allowing them to exploit different niches.