There are  x number of that, and x number of those, and only x numbers survive, and x numbers are
endemic, etc...
Read the
 Management plan for the Los Tuxtlas Biosphere Reserve in Spanish or Parkswatch in English to
get a feel for the living things of Los Tuxtlas!
draft
Fauna
Considering its small size, the Sierra de Los Tuxtlas, (app. 2000 square miles) has more bird
biodiversity than most places in the world. Almost 600 species have been registered, including more
than 200 migrants.
Birding is one of the Tuxtlas major tourist attractions, but with William Schaldach Jr´s recent death
To fully understand the avian richness of the area,  this part of the tuxtlas.com website is useful:

SCHALDACH Jr, W. J.  2003
A Partially Annotated and Taxonomic Checklist of The Birds of The State of Veracruz,
Mexico
Insects
There are oodles of insect studies of the Tuxtlas. Most concern themselves with beatles.

Insects are Los Tuxtlas most prevalent species. From microscopic blood sucking beasts to majestic
irridescent butterflies, it´s impossible to avoid these menaces. I realize one needs to be a little myopic
to see them, but there are hundreds of weird shaped and some absolutely beautiful crawling and
flying things around. And when I try to photograph them they show up as spots.
Because of  the diversity of endemic species of amphibians and reptiles, Los Tuxtlas it is one of the best known
neotropical regions in the world

45 species of amphibians and 117 reptiles have been reported, including  4 endemic reptiles and 11 endemic amphibians.
Around 15 percent of all  Mexican species are present in Los Tuxtlas.

Some of the more unusual  species that have been described for this region are:

Fan Lizard - Lagartija de abanico (Anolis sericeus),
Lesser Scaly Anole - lagartija de monte (Anolis uniformis),
Fer de Lance - nauyaca sorda (Bothrops asper),
Moreletti crocodile - lagarto (Crocodylus moreleti),
Tree Frog - rana arborícola (Hyla picta),
Green Iguana - iguana verde (Iguana iguana),
Pochitoque Turtle - tortuga pochitoque (Kinosternos leocostum),
Vaillant's Frog - rana acuática (Rana vaillanti),
Rosebelly Lizard - lagartija insectívora (Sceloporus variabilis),
Mexican Tree Frog - rana de lluvia (Smilisca baudini).
Reptiles
Mammals
Despite the Los Tuxtlas fame as a reservoir for mammalian species, I seem to miss their presence. Except for some
monkeys howling at me in Playa Escondida, a glimpse of a furtive otter, a tepezintle, lots of bats, some gorgeous
black squirrels and numerous captive species, i have no photos to prove their presence.

Of the 128 mammal species recorded in Los Tuxtlas 19 are almost extinct or highly endangered. Almost 30 percent
of Mexican species are present here.

Ocelot - ocelote  (Leopardus pardalis)
Margay - tigrillo  (Leopardus wiedii)
Collared Pecary - jabalí  (Pécari tajacu),
Brocket Deer - mazate  (Mazanma americana)
White Tail Deer - venado  (Odocoileus virgianus )
Spider Monkey - mono araña  (Ateles geoffroyi)
Howler Monkey - mono aullador  (Alovatta palliata)
Water Possum - tlacuaches  (Chironectes minimus)l
Tamandua - oso hormiguero  (Tamandua mexicana)
Mexican Tree Porcupine - puerco espín  (Sphiggurus mexicanus).
Fishes
The ichthyofauna of Lago Catemaco comprises 16 species, 44% of them endemic. The most
important families are the Cichlidae [6], the Poeciliidae [3] and the Characidae [2]...
The lake's endemic cichlid, an undescribed sister species of the widespread fluviatile _Theraps
fenestratus_, is characterized by color polymorphism.  In addition to the preponderant normally
pigmented individuals, both orange-pink and white oligomelanic morphs have
been reported ....

Five exotic species, among them _Oreochromis aureus_, the blue tilapia, are established in the lake
basin.. the principal threat to this ecosystem is anthropogenic eutrophication.  

The endemic Catemaco _Theraps_ species and the non-endemic cichlids found in the lake are
pond-bred in Florida for the ornamental fish trade and thus readily available through commercial
channels in North America, Europe and Japan.  One of the  three endemic poeciliid species,
_Xiphophorus milleri_, the Catemaco platyfish, is being maintained on a long-term basis by the
Aquarium for Wildlife Conservation in New York.  

http://www.peter.unmack.net/acn/as/3/vol3no2.txt
Fishes
Birds
Los Tuxtlas
Veracruz, Mexico