Peltocephalus maturin

Peltocephalus maturin Temporal range: Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
The holotype mandible of P. maturin seen from three different angles.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Testudines
Suborder:	Pleurodira
Family:	Podocnemididae
Genus:	Peltocephalus
Species:	†P. maturin
Binomial name
†Peltocephalus maturin Ferreira et al., 2024[1]

Peltocephalus maturin is an extinct species of

Peltocephalus maturin was described in 2024 on the basis of specimen MERO.PV.H 007, a partial lower jaw discovered by gold miners within the Taquaras Quarry of Rondônia, Brazil. Since the Rio Madeira Formation is the only geological unit exposed at this quarry, the fossil is subsequently assumed to be Late Pleistocene to Early Holocene in age.^[1]

The species name references Maturin, a recurring entity in the works of

In addition to size, Peltocephalus maturin can be differentiated from its modern relative by the fact that the labial ridge that stretches closer to the outer surface of the dentary is higher up than the lingual (inner) ridge. Also unlike its modern relative, the two triturating surfaces enclosed by these ridges do not meet in the middle, as they are separated by a symphyseal ridge that stretches along the midline of the dentary. Additionally, each triturating surface can be divided into an anterior and posterior section, divided by a secondary ridge that runs at a right angle to the triturating surface. Ferreira and colleagues note that these features except for the presence of a secondary ridge are also shared by the enormous Miocene Stupendemys. However, Stupendemys and Peltocephalus maturin differ in that the latter has a more upturned symphyseal hook, narrower triturating surfaces and by having lower lingual ridges that from a V-shape towards the tip of the mandible, rather than the protruding ridges in Stupendemys that form a U-shape.^[1]

One of the most notable things about Peltocephalus maturin is the size of the holotype mandible. The dentary measures 27.8 cm (10.9 in) in length, which is comparable to that of the Cretaceous marine turtle Archelon. Total length estimates were conducted through two approaches, both yielding similar results. Approach 1 suggests an estimated straight carapace length of approximately 1.70 m (5 ft 7 in) while approach 2 yielded a slightly longer 1.73 m (5 ft 8 in). The lower and upper bounds lie between approximately 1.40–2.16 m (4 ft 7 in – 7 ft 1 in). While this would put the total length of Peltocephalus maturin below those of giants like Archelon and Stupendemys, it would still be one of the largest freshwater turtles in terms of carapace length, matched only by Carbonemys (estimated straight carapace length 1.8 m (5 ft 11 in)). It also far exceeds any other freshwater turtle of the Quaternary such as the Asian narrow-headed softshell turtle (straight carapace length 1.40 m (4 ft 7 in)) and the Arrau turtle (straight carapace length 1.09 m (3 ft 7 in)).^[1][3]

Phylogeny

Phylogenetic analysis confirmed the relationship between Peltocephalus maturin and Peltocephalus dumerilianus, both of which forming a clade that is deeply nested within Podocnemididae. The levels of resolution do differ between the two analysis conducted, with the strict consensus being poorly resolved though still supporting the clade formed by the two Peltocephalus species. The Majority Rule Tree, depicted below, yielded better resolved results that are in line with the internal relationships that were recovered by previous studies. Within this tree, Peltocephalus species are the basalmost off-shoot of a branch that also includes Stupendemys and the various species of Bairdemys, together forming one of two distinct branches within Erymnochelyinae.^[1]

Paleobiology

Diet in turtles can generally be inferred based on the height of the skull as well as the proportions and complexity of the triturating surface, which is used to cut and grind food. In this regard, Peltocephalus maturin bears close resemblance to its modern relative. Overall, podocnemidids are omnivores that consume varying levels of plant material, with Peltocephalus dumerilianus incorporating the greatest amount of other animals into its diet including

Ferreira and colleagues speculate that the extinction of Peltocephalus maturin may have been tied to exploitation by humans. Part of their reasoning is based on the extinction of various island species such as the turtles of the Turks and Caicos Islands as well as the meiolanids of Vanuatu and New Caledonia which are often thought to have been driven to extinction by human overhunting. Some of the earliest evidence for humans arriving in South America dates to roughly 12.6 to 9.8 thousand years BP and thus overlap with the presence of Peltocephalus maturin. Furthermore, sites that show signs of human habitation also preserve the remains of both tortoises and podocnemidids, with even modern humans still hunting turtles for their meat. At the same time, there is no evidence that humans and Peltocephalus maturin ever actually met, meaning that the reason for this species' extinction remains uncertain until the discovery of better materials provides more clues.^[1]

References