# Los Rastros Formation

The Los Rastros Formation is a mid-Carnian fossiliferous formation of the Agua de la Peña Group, in the Ischigualasto-Villa Unión Basin of northwestern Argentina. Fossil archosaur tracks, as well as many insects, fish, bivalves, crustaceans and plants have been reported from the formation.

## Geology

The formation overlies the Chañares Formation (and/or the Ischicuca Formation), and is overlain by the Ischigualasto Formation. The formation belongs to the Agua de la Peña Group of the Ischigualasto-Villa Unión Basin, where it is exposed in the Ischigualasto Provincial Park, a World Heritage Site in Argentina. The up to 1,000 metres (3,300 ft) thick formation of claystones, mudstones and sandstones was deposited in a deltaic to lacustrine environment during the first post-rift sequence in the basin.
A CA-TIMS U-Pb zircon age of 234.47 ± 0.44 Ma from the lower Los Rastros Formation was published in 2020. The acquired age demonstrates that most of the overlying lacustrine strata within the basin were deposited during or after the Carnian Pluvial Event (CPE).

## Paleobiota

The only tetrapod body fossil reported from the Los Rastros Formation is a poorly-preserved temnospondyl amphibian.

### Ichnofossils

Tetrapod footprints are a conspicuous type of ichnofossils (trace fossils) found in the Los Rastros Formation, particularly at the Quebrada de Ischichuca locality near Cerro Bola. Most of the trackways are symmetrical prints created by animals with a narrow bipedal stance, three toes contacting the ground, and a raised fourth toe. They were presumably early dinosaurs or dinosauromorphs, with a hip height exceeding 75 cm. These prints are found in deltaic sandbars, parallel to the lakeshore. While some sources tentatively interpret these as theropod footprints, the generalized nature of Triassic dinosaurs and their relatives prevent a precise referral. Some of the tridactyl trackways also preserve hand prints, with quadrupedal pseudosuchians or other archosaurs as likely trackmakers. Named reptile ichnotaxa from the Los Rastros Formation include Rhynchosauroides sp. (sphenodonts or other small reptiles) and Rigalites ischigualastianus (large quadrupedal pseudosuchians).
Another form of trackway consists of numerous non-overlapping sets of broad rounded depressions on a heavily trampled wackestone surface. They may have been left by a herd of dicynodonts walking down to the lakeshore. Palaeophycus tubularis invertebrate burrows are also abundant.

### Fish

Actinopterygians (ray-finned fish) of the Los Rastros Formation :
| Genus | Species | Locality | Material | Notes |
| Challaia | C. elongata | Agua de la Peña Creek (San Juan Province) | A very large (>70 cm) specimen which is mostly complete, missing the tail and the front of the skull. | A late-surviving acrolepid, also known from the Cuyo Basin. Previously referred to Myriolepis. |
| Gualolepis | G. carinaesquamosa | Cañón del Gualo (La Rioja Province) | Two specimens, each representing portions of the skull and anterior torso. | A probable chondrostean (distantly related to modern sturgeons and paddlefish) with similarities to the family Peipiaosteidae. |
| Rastrolepis | R. latipinnata | Cañón del Gualo (La Rioja Province) | A large (>39 cm) specimen which is mostly complete, missing the rear of the tail and the front of the skull. | An indeterminate actinopterygian similar to redfieldiiforms |
| Rastrolepis | R. riojaensis | Cañón del Gualo (La Rioja Province) | A large (>54 cm) specimen which is mostly complete. | An indeterminate actinopterygian similar to redfieldiiforms |

### Invertebrates

The Los Rastros Formation has produced many insect fossils, with most new species belonging to blattopterans (cockroaches and kin), coleopterans (beetles and kin), or hemipterans (true bugs). Among Triassic formations of South America, the Los Rastros Formation's insect diversity is only rivaled by the Potrerillos Formation in the Cuyo Basin. Other invertebrate fossils from the Los Rastros Formation include Lioestheria ("conchostracans" or clam shrimp) and Paleomutella (freshwater mussels).

#### Blattoptera

Blattoptera (cockroaches and relatives) of the Los Rastros Formation :
| Genus | Species | Locality |
| Argentinoblatta | A. herbsti | Río Gualo (La Rioja Province) |
| Argentinoblattula | A. revelata | Río Gualo (La Rioja Province) |
| Condorblatta | C. lutzae | Río Gualo, Los Chañares (La Rioja Province) |
| Hermosablatta | H. crassatella | Río Gualo, Picos Gemelos (La Rioja Province) |
| Hermosablatta | H. pectinata | Río Gualo (La Rioja Province) |
| Lariojablatta | L. chanarensis | Los Chañares (La Rioja Province) |
| Mancusoblatta | M. pulchella | Río Gualo (La Rioja Province) |
| Pulchellablatta | P. nana | Río Gualo (La Rioja Province) |
| Samaroblatta | S. corrientesina | Río Gualo (La Rioja Province) |
| Samaroblatta | S. gualoensis | Río Gualo (La Rioja Province) |
| Triassoblatta | T. argentina | Picos Gemelos (La Rioja Province) |

#### Coleoptera

Coleoptera (beetles and relatives) of the Los Rastros Formation :
| Genus | Species | Locality | Notes |
| Ademosyne | A. arcucciae | | An ademosynid |
| Ademosyne | A. elongatus | | An ademosynid |
| Ademosyne | A. hexacostata | | An ademosynid |
| Ademosyne | A. punctuada | | An ademosynid |
| Argentinocupes | A. abdalai | | A cupedid (reticulated beetle) |
| Argentinocupes | A. pulcher | Río Gualo, Los Chañares (La Rioja Province) | A cupedid (reticulated beetle) |
| Argentinosyne | A. bonapartei | Los Chañares (La Rioja Province) | A permosynid |
| Argentinosyne | A. frenguellii | | A permosynid |
| Argentinosyne | A. gonaldiae | | A permosynid |
| Argentinosyne | A. gualoensis | | A permosynid |
| Argentinosyne | A. losrastroensis | | A permosynid |
| Argentinosyne | A. rugosa | | A permosynid |
| Cardiosyne | C. elegans | | A possible elaterid (click beetle) |
| Cardiosyne | C. obesa | | A possible elaterid (click beetle) |
| Gemelina | G. triangularis | | A possible elaterid (click beetle) |

#### Hemiptera

Indeterminate corixids (water boatmen) are also known from the Gualo locality.
Hemipterans (true bugs) of the Los Rastros Formation :
| Genus | Species | Locality | Material | Notes |
| Apheloscyta | A. mayae | Gualo (La Rioja Province) | | A scytinopterid cicadomorph (a type of true bug related to leafhoppers and cicadas). Previously given the name Gualoscytina mayae. |
| Dysmorphoptiloides | D. losrastroensis | Gualo (La Rioja Province) | | A dysmorphoptilid auchenorrhynchan |
| Fulgobole | F. arcucciae | Gualo (La Rioja Province) | | A mesojabloniid cicadomorph. Previously given the name Australocicada arcucciae. |
| Gallegomorphoptila | G. acostai | Gualo (La Rioja Province) | | A dysmorphoptilid auchenorrhynchan, formerly referred to the genus Dysmorphoptiloides. |
| Gallegomorphoptila | G. breviptera | Gualo (La Rioja Province) | | A dysmorphoptilid auchenorrhynchan |
| Gallegomorphoptila | G. gigantea | Gualo (La Rioja Province) | | A dysmorphoptilid auchenorrhynchan, formerly referred to the genus Dysmorphoptiloides. |
| Gallegomorphoptila | G. pulcherrima | Gualo (La Rioja Province) | | A dysmorphoptilid auchenorrhynchan, formerly referred to the genus Dysmorphoptiloides. |
| Gualoscarta | G. obscura | Gualo (La Rioja Province) | | A dysmorphoptilid auchenorrhynchan |
| Mesoscytina | M. forsterae | Gualo (La Rioja Province) | | A scytinopterid cicadomorph. Previously given the name Argentinopheloscyta forsterae. |
| Popovigocimex | P. yurii | Gualo (La Rioja Province) | Forewing | A progonocimicid coleorrhynchan (moss bug) |
| Saaloscytina | S. carmonae | Los Chañares, Gualo (La Rioja Province) | | A saaloscytinid cicadomorph. Fossils of this species were formerly given the names Chanarelytrina nana and Chanarescytina carmonae. |
| Yurigocimex | Y. popovi | Gualo (La Rioja Province) | Forewing | A progonocimicid coleorrhynchan (moss bug) |

#### Other insects

Other insects of the Los Rastros Formation :
| Genus | Species | Locality | Material | Notes |
| Argentinoglosselytrina | A. pulchella | Gualo (La Rioja Province) | | A polycytellid glosselytrodean |
| Argentinoperlidium | A. rogersi | Gualo (La Rioja Province) | Forewing fragment | A gripopterigid plecopteran (stonefly). |
| Frenguelliphlebia | F. labandeirai | Gualo (La Rioja Province) | Forewing fragment | An indeterminate odonatopteran (a relative of dragonflies and damselfies) |
| Miomina | M. riojana | Los Chañares (La Rioja Province) | | A miomopteran |
| Notopamphagopsis | N. spp. | Gualo (La Rioja Province) | Wing fragments | Three unnamed species of haglid ensiferans (cricket-like insects) |

### Plants

A wide variety of plant fossils are known from the Los Rastros Formation, including both microfossils and macrofossils.
Most species from the formation have been listed by Lutz et al. (2011) and Pedernera et al. (2020).
* Calamitales
* Coniferales
* Cycadales
* Equisetales
* Osmundales
* Rhexoxilales

#### Seed ferns

"Seed fern" macrofossils of the Los Rastros Formation :
| Genus | Species | Locality | Material | Notes |
| Dejerseya | D. lobata | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | A possible peltasperm |
| Dejerseya | D. lunensis | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | A possible peltasperm |
| Dicroidium | D. argenteum | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | An umkomasialean (or corystosperm) |
| Dicroidium | D. crassum | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | An umkomasialean (or corystosperm) |
| Dicroidium | D. dubium | Ischigualasto Provincial Park (San Juan Province), Ischichuca Creek | Frond fragments | An umkomasialean (or corystosperm) |
| Dicroidium | D. lancifolium | Ischigualasto Provincial Park (San Juan Province), Ischichuca Creek | Frond fragments | An umkomasialean (or corystosperm) |
| Dicroidium | D. lineatum | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | An umkomasialean (or corystosperm) |
| Dicroidium | D. nondichotoma | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | An umkomasialean (or corystosperm) |
| Dicroidium | D. obtusifolium | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | An umkomasialean (or corystosperm) |
| Dicroidium | D. odontopteroides | Ischigualasto Provincial Park (San Juan Province), Gualo (La Rioja Province), Ischichuca Creek | Frond fragments | An umkomasialean (or corystosperm) |
| Dicroidium | D. pinnis-distantibus | Ischichuca Creek | | An umkomasialean (or corystosperm) |
| Johnstonia | J. coriacea | Agua de la Peña Creek, Ischichuca Creek | Frond fragments | An umkomasialean (or corystosperm) |
| Johnstonia | J. dutoitii | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | An umkomasialean (or corystosperm) |
| Johnstonia | J. stelzneriana | Ischigualasto Provincial Park (San Juan Province), Gualo (La Rioja Province) Ischichuca Creek | Frond fragments | An umkomasialean (or corystosperm) |
| Matatiella | M. roseta | | Seed cones | A seed fern of uncertain affinities, possibly a peltasperm or umkomasialean |
| Pachydermophyllum | P. papillosum | Agua de la Peña Creek. | Frond fragments | A peltasperm |
| Pachydermophyllum | P. praecordillerae | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | A peltasperm |
| Peltaspermum | P. monodiscum | Agua de la Peña Creek. | Seed cones | A peltasperm |
| Rhexoxylon | R. sp. | Ischichuca Creek | Fossil wood | An umkomasialean (or corystosperm) |
| Rochipteris | R. alexandriana | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | A possible petriellalean |
| Umkomasia | U. macleanii | | Strobili (seed cones) | An umkomasialean (or corystosperm) |
| Xylopteris | X. argentina | Ischigualasto Provincial Park (San Juan Province), Gualo (La Rioja Province), Ischichuca Creek | Frond fragments | An umkomasialean (or corystosperm) |
| Xylopteris | X. densifolia | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | An umkomasialean (or corystosperm) |
| Xylopteris | X. elongata | Ischigualasto Provincial Park (San Juan Province), Gualo (La Rioja Province), Ischichuca Creek | Frond fragments | An umkomasialean (or corystosperm) |
| Xylopteris | X. rigida | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | An umkomasialean (or corystosperm) |
| Zuberia | Z. brownii | Ischichuca Creek | | An umkomasialean (or corystosperm) |
| Zuberia | Z. feistmantelii | Gualo (La Rioja Province) | Frond fragments | An umkomasialean (or corystosperm) |
| Zuberia | Z. sahnii | Ischigualasto Provincial Park (San Juan Province), Ischichuca Creek | Frond fragments | An umkomasialean (or corystosperm) |
| Zuberia | Z. zuberi | Ischigualasto Provincial Park (San Juan Province), Ischichuca Creek | Frond fragments | An umkomasialean (or corystosperm) |

#### Other gymnosperms

Gymnosperm macrofossils of the Los Rastros Formation :
| Genus | Species | Locality | Material | Notes |
| Acevedoa | A. rastroensis | Ischigualasto Provincial Park (San Juan Province) | Female fructifications | Reproductive structures of a gymnosperm of uncertain affinities. Initially described under the (preoccupied) name Andersonia. |
| Baiera | B. africana | Ischigualasto Provincial Park (San Juan Province) | Leaf fragments | A ginkgoalean. |
| Baiera | B. pontifolia | Ischigualasto Provincial Park (San Juan Province), Gualo (La Rioja Province) | Leaf fragments | A ginkgoalean. |
| Baiera | B. schenkii | Ischigualasto Provincial Park (San Juan Province) | Leaf fragments | A ginkgoalean. |
| Cordaicarpus | C. sp. | Gualo (La Rioja Province) | Seeds | Cordaitalean conifer seeds. |
| Cycadocarpium | C. andium | Agua de la Peña Creek. | | |
| Czekanowskia | C. rigali | Agua de la Peña Creek. | | A czekanowskialean. |
| Desmiophyllum | D. sp. | Agua de la Peña Creek. | | |
| Dordrectites | D. elongatus | Ischichuca Creek | | |
| Harringtonia | H. argentinica | Agua de la Peña Creek. | | |
| Heidiphyllum | H. clarifolium | | | |
| Heidiphyllum | H. elongatum | Ischigualasto Provincial Park (San Juan Province), Gualo (La Rioja Province) | Leaf fragments | A voltzialean conifer. |
| Heidiphyllum | H. minutifolium | | | |
| Kurtziana | K. cachuetensis | Ischigualasto Provincial Park (San Juan Province) | Frond fragments | Possible cycads. |
| Pelourdea | P. polyphylla | Agua de la Peña Creek. | | |
| Pelourdea | P. problematica | Agua de la Peña Creek. | | |
| Phoenicopsis | P. sp. | Ischichuca Creek | | |
| Pterorrachis | P. ambigua | Agua de la Peña Creek. | | |
| Rissikia | R. media | Ischigualasto Provincial Park (San Juan Province), Gualo (La Rioja Province) | Leaf fragments | A podocarp conifer. |
| Samaropsis | S. sp. | Gualo (La Rioja Province) | Seeds | Cordaitalean conifer seeds. |
| Sphenobaiera | S. argentinae | Ischigualasto Provincial Park (San Juan Province) | Leaf fragments | A ginkgoalean. |
| Sphenobaiera | S. sp. cf. S. argentinae | Gualo (La Rioja Province) | Leaf fragments | A ginkgoalean. |
| Sphenobaiera | S. insecta | Ischigualasto Provincial Park (San Juan Province) | Leaf fragments | A ginkgoalean. |
| Sphenobaiera | S. sectina | Ischigualasto Provincial Park (San Juan Province) | Leaf fragments | A ginkgoalean. |
| Sphenopteris | S. sp. | Ischichuca Creek | | |
| Telemachus | T. elongatus | Ischichuca Creek | Seed cones. | A voltzialean conifer. |
| Yabeiella | Y. brackebuschiana | Ischigualasto Provincial Park (San Juan Province) | Leaf fragments | A gymnosperm of uncertain affinities. |
| Yabeiella | Y. mareyesiaca | | | A gymnosperm of uncertain affinities. |
| Yabeiella | Y. spathulata | | | A gymnosperm of uncertain affinities. |

#### Other plants

Non-gymnosperm plant macrofossils of the Los Rastros Formation :
| Genus | Species | Locality | Material | Notes |
| Cladophlebis | C. kurtzi | Agua de la Peña Creek. | | Osmundacean ferns |
| Cladophlebis | C. mendozaensis | Ischigualasto Provincial Park (San Juan Province), Agua de la Peña Creek. | Frond fragments | Osmundacean ferns |
| Cladophlebis | C. mesozoica | Agua de la Peña Creek. | | Osmundacean ferns |
| Cladophlebis | C. sp. cf. C. mesozoica | Gualo (La Rioja Province) | Frond fragments | Osmundacean ferns |
| Equisetites | E. fertilis | Agua de la Peña Creek. | | Small equisetales (horsetails) |
| Neocalamites | N. carrerei | Ischichuca Creek. | | Large equisetales (horsetails) |
| Neocalamites | N. ischigualasti | Agua de la Peña Creek. | | Large equisetales (horsetails) |
| Neocalamites | N. ramaccionii | Agua de la Peña Creek. | | Large equisetales (horsetails) |
| Neocalamites | N. sp. | Ischigualasto Provincial Park (San Juan Province), Gualo (La Rioja Province), Ischichuca Creek. | Stalk impressions | Large equisetales (horsetails) |
| Nododendron | N. sp. | Ischichuca Creek. | | Equisetales (horsetails) |
| Phyllotheca | P. australis | Agua de la Peña Creek. | | Small equisetales (horsetails) |
| Pleuromeia | P. sp. | Ischichuca Creek. | | Small lycopods. |