''Makaracetus'' is an extinct
protocetid
Protocetidae, the protocetids, form a diverse and heterogeneous group of extinct cetaceans known from Asia, Europe, Africa, South America, and North America.
Description
There were many genera, and some of these are very well known (e.g., ''R ...
early whale the remains of which were found in 2004 in
Lutetian
The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Midd ...
layers of the
Domanda Formation in the
Sulaiman Range
The Sulaiman Mountains, also known as Kōh-e Sulaymān ( Balochi/Urdu/ fa, ; "Mountains of Solomon") or Da Kasē Ghrūna ( ps, د كسې غرونه; "Mountains of Kasi"), are a north–south extension of the southern Hindu Kush mountain system i ...
of
Balochistan
Balochistan ( ; bal, بلۏچستان; also romanised as Baluchistan and Baluchestan) is a historical region in Western and South Asia, located in the Iranian plateau's far southeast and bordering the Indian Plate and the Arabian Sea coastline. ...
,
Pakistan
Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's List of countries and dependencies by population, fifth-most populous country, with a population of almost 24 ...
(, paleocoordinates ).
''Makaracetus'' is unique among archaeocetes in its feeding adaptations; its
proboscis
A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...
and the
hypertrophied
Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J. ...
facial muscles.
The generic epithet is a
portmanteau
A portmanteau word, or portmanteau (, ) is a blend of words[Makara
''Makara'' ( sa, मकर, translit=Makara) is a legendary sea-creature in Hindu mythology. In Hindu astrology, Makara is equivalent to the Zodiac sign Capricorn.
Makara appears as the vahana (vehicle) of the river goddess Ganga, Narmada, a ...](_blank)
, an elephant-headed sea monster from Hindu mythology, and ''cetus'', Greek for "whale". The species epithet, ''bidens'', is Greek for "two-teeth", in reference to the retention of only two incisors in each
premaxilla
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...
.
''Makaracetus''
' unique features even lead to propose a new classification of Protocidae based on the degree of their aquatic adaptation;
with ''Makarcetus'' alone in the subfamily Makaracetinae.
A combination of cranial features indicates that ''Makaracetus'' had a short, muscular proboscis similar to a tapir. There are broad and shallow
narial grooves on the dorsal side of the premaxilla extending the
nasal vestibule
The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal c ...
to the anterior end of the
rostrum
Rostrum may refer to:
* Any kind of a platform for a speaker:
**dais
**pulpit
* Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects
* Rostrum (ship), a form of bow on naval ships
* Ros ...
. These grooves are paralleled on the ventral side by extraordinary lateral
fossae, stretching from the anterior maxilla and over the premaxilla. The rostrum is angled downwards, like in a dugong, and has a reduced number of incisors. Enlarged
in front of the orbits indicate that the rostrum had a rich blood supply.
No living mammal displays this combination of characteristics. The expanded nasal is present in tapirs, but they are not aquatic animals. The morphology of sirenian rostra is similar, but sirenians are herbivorous, whereas ''Makaracetus''
' dentition clearly indicate that it was carnivorous. Walrus cranial morphology is different, but they are aquatic and use specialized buccal and facial muscles to feed on molluscs, fossils of which are abundant in the Domanda Formation. They probably provide the best ecological model among living mammals. More complete fossils must be recovered before ''Makaracetus'' can be adequately described.
Notes
References
*
Extinct mammals of Asia
Protocetidae
Fossil taxa described in 2005
Prehistoric cetacean genera
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