This August 2018 video says about itself:
The Schomburgk’s Deer (Rucervus schomburgki) was a member of the family Cervidae.
Native to central Thailand, Schomburgk’s deer was described by Edward Blyth in 1863 and named after Sir Robert H. Schomburgk, who was the British consul in Bangkok from 1857–1864.
It is thought to have gone extinct by 1938, but there is speculation that the deer might still exist.
This graceful deer inhabited swampy plains with long grass, cane, and shrubs in central Thailand, particularly in the Chao Phraya River valley near Bangkok.
This deer avoided dense vegetation. They lived in herds that consisted of a single adult male, a few females, and their young.
The wild population of Schomburgk’s deer is thought to have died because of overhunting in 1932, with the last captive individual being killed in 1938.
The species was listed as extinct in the 2006 IUCN Red List of Threatened Species.
However, some scientists consider this species to be still extant.
In 1991, antlers were discovered in a Chinese medicine shop in Laos. Laurent Chazée, an agronomist with the United Nations, later identified the antlers from a photograph he took as coming from Schomburgk’s deer.
Only one mounted specimen is known to be in existence, which currently resides in Paris’s Muséum national d’Histoire naturelle after living in the zoo there until 1868.
From Northwestern University in the USA:
Rare deer likely lived 50 years beyond declaration of extinction
Fresh antlers from Schomburgk’s deer were photographed in Laos in 1991
September 6, 2019
A rare deer species that lived in central Thailand might have come back from the dead — without the help from sci-fi-like genetic engineering.
Schomburgk’s deer (Rucervus schomburgki) was added to the extinction list in 1938. But new evidence, gleaned from antlers obtained in late 1990 or early 1991, shows that it survived for at least an additional half-century and might still be around today.
The research was published last week (Aug. 30) in the Journal of the Bombay Natural History Society. Gary Galbreath, professor of biological sciences at Northwestern University’s Weinberg College of Arts and Sciences, was involved in the work.
After the wild population died out from overhunting in 1932, the last known Schomburgk’s deer died in captivity six years later. Or so we thought. A trucker in Laos found a set of antlers, seemingly in fresh condition, in the early 1990s. He then gave the antlers to a shop in the northern Laos province of Phongsali.
In February 1991, United Nations agronomist Laurent Chazée photographed the antlers. Galbreath and his collaborator G.B. Schroering recently analyzed the antlers’ physical condition in those photos. Based on the widely spreading, basket-shaped, hyper-branched structure of the antlers, the team determined the antlers belonged to a Schomburgk’s deer. (Other Asian deer’s antlers do not have the same signature basket shape.)
Galbreath also confirmed that the antlers were fresh when photographed in 1991. The antlers — spotted with dark red to reddish-brown dried blood — had been excised from the deer’s head. The color of the blood and condition of the exposed bone marrow offered clues into the antlers’ age.
“The relative antiquity of the antler specimens can be assessed by the materials, such as dried marrow, still adhering to them,” said Galbreath, an expert in Asian wildlife. “Even the blood was still reddish; it would become black with increased age. In the tropics, the antlers would not continue to look this way even within a matter of months.”
Before they were listed as “extinct,” the deer were well documented in Thailand. Galbreath believes a small population probably also lived in a remote area in central Laos, where they just might still be living today.