User:Armin Reindl/sandbox2

Armin Reindl/sandbox2 Temporal range: Priabonian =
Restoration
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Infraorder:	Cetacea
Family:	†Basilosauridae
Subfamily:	†Dorudontinae
Genus:	†Masracetus Gingerich 2007
Species
M. markgrafi (type) Gingerich, 2007

Masracetus (from Arabic Masr, "Egypt", and Greek ketos, "whale") is an extinct genus of basilosaurid ancient whale known from the Late Eocene (Priabonian, 37.2 to 33.9 million years ago) of Egypt.

History and naming

Fossils now assigned to Masracetus had been known for close to a hundred years prior to the animal's naming, with the holotype vertebrae and skull having been in the year 1905. The discovery, credited to fossil hunter Richard Markgraf was reportedly made near Dimê in the Fayum depression in strata that were later identified as those of the Birket Qarun Formation. The remains were subsequently described by German paleontologist Ernst Stromer, who frequently worked with Markgraf, and assigned to Zeuglodon isis (now known as Basilosaurus). Additional remains discovered by Markgraf in 1904 were also described by Stromer, namely a single posterior thoracic vertebra and two tail vertebrae (initially identified as Zeuglodon cf. brachyspondylus), before being redescribed by Everhard Johannes Slijper in 1936. Eventually, some weathered vertebral centra would come to be collected from Wadi Hitan some time prior to 2005, when they and the material discovered in 1905 were referred to the North American Cynthiacetus maxwelli. In the same study Mark D. Uhen further highlights the possibility that the type material may have come from the older Gehannam Formation, in contrast to Gingerich. Yet another specimen, consisting of much of the skeleton, was discovered in Wadi Hitan in early 2006.

While working on the cetacean chapter of the book "Cenozoic Mammals of Africa", Philip D. Gingerich came to regard this material as having belonged t a distinct taxon, a conclusion he later published as an addendum to his 2007 description of Stromerius nidensis. In this study, Gingerich provided a brief synopysis of the material's history, wrote a short section diagnosing and describing the animal and ultimately coining the name Masracetus markgrafi. Unlike Uhen, Gingerich follows Kellog in the belief that the fossil material originates in the strata of the Birket Qarun Formation. The same study also provides a neotype for Pontogeneus brachyspondylus (at the time "Zeuglodon" brachyspondylus), though it is mentioned that it might be synonymous with Masracetus.

Additional remains of Masracetus were discovered in subsequent years, with one particular field trip lead by Gingerich and the University of Michigan locating a badly weathered skeleton with well preserved teeth in 2010 at Qaret Umm Regl. This discovery, specifically the teeth, were described in 2013 by Gebely A. Abu El-kheir and colleagues, who make further mention of skeletons having been found both in the sediments of the Gehannam and Birket Qarun Formations (though they follow Gingerich and list Birket Qarun as the origin of the type material).

In 2017 Martínez-Cáceres and colleagues considered the possibility that Masracetus could be synonymous with Cynthiacetus, reasoning that unlike in other forms like Dorudon and Zygorhiza, the ratios of the lumbar vertebae measurements do not clearly set the two apart and could instead represent simple intraspecific variation between individuals. However, as the Masracetus skeleton discovered in 2006 had not yet been described, the team retains Masracetus as a distinct genus until the more complete material would be available for comparison. However, should this hypothesis proove to be correct, then Cynthiacetus would take priority over Masracetus, with the latter becoming a junior synonym.

The idea that Masracetus can be found in the sediments of both the Gehannam and Birket Qarun Formations is further supported by the work of El Anbaawy and colleagues published in 2018. Their study lists material of Masracetus being found from three horizons of the Gehannam Formation and four horizons of the Birket Qarun Formation north of Lake Qarun as well as two horizons of the Birket Qarun Formation in Wadi Hitan.

2022 saw the first mention of Masracetus remains from outside of Egypt, as Ayoub Amane and colleagues referred material from the western Saharah to this genus. The material includes multiple vertebrae from the Bartonian locality of Gueran (Aridal Formation) and a single vertebra from the Priabonian Ad-Dakhla locality.

The name Masracetus derives from the Arabic name for Egypt, Masr, and the Greek word "cetos" which means whale. The species name honours Richard Markgraf who collected the type specimen in 1905.

Description

The lumbar vertebrae are large but relatively short (anteroposteriorly) compared to those of other archaeocetes, with relatively greater width and height. This is especially noticable when compared with Basilosaurus, known for its extremly elongated vertebrae. While the diameter of the lumbar vertebrae in Masracetus is almost the same as for Basilosaurus isis, they are only half as long. Gingerich argued that the ratio between length and width in Masracetus was lower than that seen in Cynthiacetus, with the latter being more similarily proportioned to Dorudon. Gingerich further listed proportional differences between Masracetus and Pontogeneus brachyspondylus, however, Martínez-Cáceres and colleagues later determined that the single cervical vertebrae of that taxon could not be distinguished from the material of Masracetus or Cynthiacetus.

Masracetus is slightly larger than Cynthiacetus, itself regarded as one of the largest basilosaurids.

Paleobiology

Paleoenvironment

Masracetus is known from two geological formations, the older Gehannam Formation and the slightly younger Birket Qarun Formation, both of which crop out in the Fayum depression around Lake Qarun. The inferred environment of these formations matches the idea the kind of shallow marine environment close to the shore that basilosaurids are commonly found in, though some research has argued that this propensity for shallow water might be the result of carcasses floating closer to shore. The Gehannam Formation is Middle to Late Eocene in age and is rich in fossil whales and sea cows. Fossils were deposited in the outer neritic zone at a depth between 50 to 100 meters. Foramina collected from these sediments indicate normal salt levels of 32-35‰, which does not suggest any strong freshwater influence.

The Birket Qarun Formation was preserved following the Gehannam Formation and dates to the Late Eocene, specifically the Priabonian. It is interpreted as a offshore barrier sandbar complex, with the uppermost layers possibly representing an estuary.

Masracetus shared these biomes with at least two other basilosaurids, the smaller Dorudon atrox and the giant Basilosaurus isis, with the former having a more compact bauplan and the latter being well known for its highly elongated shape. Notably however, Masracetus is regarded as being much rarer than either of these in the environments they share.

Other animals to inhabit these environments include crocodilians, different sharks, sawfish, sea cows and turtles.

Paleoecology

Like other basilosaurids, Masracetus is thought to have been a predatory animal. However, as noted by Abu El-kheir and colleagues, the teeth of this animal are noticably less worn than those of its relatives, retaining sharp accessory denticles and main cusps. This could indicate that the teeth studied by this team belonged to a relatively young animal or that the prey that Masracetus fed on was less tough than what other basilosaurids preyed on.