Symmetrodonta

Symmetrodonta is a group of Mesozoic mammals and mammal-like synapsids characterized by the triangular aspect of the molars when viewed from above, and the absence of a well-developed talonid. The traditional group of 'symmetrodonts' ranges in age from the latest Triassic to the Late Cretaceous, but most research in the last 20-30 years has concluded that they are not a true taxonomic group, but include several unrelated branches of the mammal tree. Despite this, the name is still used informally by some researchers for convenience, usually restricted to the spalacotheriids and zhangheotheriids.

Symmetrodonta

Laikayiu · CC BY-SA 3.0 · via Wikipedia/Commons. May be a photograph of a specimen, or an artist’s reconstruction — an interpretation of a skeleton, since colour and soft tissue are almost never preserved.

On record

Recorded, not inferred
Also called
symmetrodontPBDB
Sits inside
AllotheriaPBDB
Diet
insectivorePBDB, for Mammaliaformes
Life habit
scansorialPBDB, for Mammaliaformes
Motility
actively mobilePBDB, for Osteichthyes
Environment
terrestrialPBDB, for Mammalia

Time the record covers

At least 129 million years on record.

The record covers at least 201.4 Mya to 72.2 Mya. No occurrence read is dated outside 205.7 Mya to 66 Mya.

Late Triassic — about 3 of 28 occurrencesEarly Jurassic — about 2 of 28 occurrencesEarly JurassicMiddle Jurassic — about 1 of 28 occurrencesMiddle JurassicLate Jurassic — about 9 of 28 occurrencesLate JurassicEarly Cretaceous — about 8 of 28 occurrencesEarly CretaceousLate Cretaceous — about 5 of 28 occurrencesLate CretaceousPaleocene — about 0 of 28 occurrences208–204 Mya — about 1 occurrence204–199 Mya — about 2 occurrences199–194 Mya — about 0.6 occurrences194–189 Mya — about 0.1 occurrences184–179 Mya — about 0.7 occurrences179–175 Mya — about 0.7 occurrences175–170 Mya — about 0.6 occurrences155–150 Mya — about 2 occurrences150–146 Mya — about 4 occurrences146–141 Mya — about 5 occurrences126–121 Mya — about 3 occurrences121–116 Mya — about 2 occurrences116–112 Mya — about 1 occurrence97–92 Mya — about 0.8 occurrences92–87 Mya — about 1 occurrence87–83 Mya — about 0.1 occurrences83–78 Mya — about 0.4 occurrences78–73 Mya — about 0.4 occurrences73–68 Mya — about 1 occurrence68–63 Mya — about 0.7 occurrences201.4 Mya72.2 Mya208 Mya63 Mya

28 occurrences of Symmetrodonta on record, most of them in the Late Jurassic. Bar height is expected occurrences, not a count: each fossil is spread across the span it is dated to, so a tall narrow bar means tight dating and a low wide one means loose.

When

28 occurrences

These are dates about fossils, not the animal: the record can only begin after it arose and end before it died out, so either end may reach further. Shares are expected occurrences: a fossil dated to a span is counted partly in each period it straddles. More on what this infers.

Found in

11 formations

Morrison — 44.49°N, 107.88°WMorrison — 39.15°N, 108.77°WMorrison — 41.89°N, 106.00°WMorrison — 40.50°N, 109.17°WIlek — 55.88°N, 88.00°EIlek — 56.64°N, 91.99°EKsar Metlili — 32.70°N, 3.22°WStraight Cliffs — 37.64°N, 112.06°WStraight Cliffs — 37.60°N, 111.97°WLourinhã — 39.22°N, 9.34°WKota — 19.27°N, 79.52°EGrès à Avicula contorta — 48.62°N, 6.33°EArtoles — 40.82°N, 0.28°WWahweap — 37.60°N, 111.35°WTakli — 21.15°N, 79.10°EArgilas de Aveiro — 40.20°N, 8.50°W

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The named rock units Symmetrodonta has been recovered from, largest first. Drawn where the rock is now, not where it formed. 3 occurrences have no formation on record, which is common for older literature.

Symmetrodonta and its relatives

Late Jurassic

Where Symmetrodonta and its relatives were recorded in the Late Jurassic.

Found in the same rock

429 taxa

The Paleobiology Database records 25 sites for Symmetrodonta, and this reads all of them. The number is how many of those sites it was catalogued from too. The 24 sharing the most are listed.

This is not a list of everything alive at the time. It is only what has come out of the same ground as this animal and been written down.

Entered from

20 references

Each of the 28 occurrences read was entered from one of these publications, ordered by how many each accounts for. This is not a search for papers mentioning the name. 8 further references are not listed. Entries link to doi.org where the Paleobiology Database holds an identifier, and to its own record where it does not. Relayed as the Paleobiology Database holds them, not checked against what they resolve to.

Media and terms

Media content1

Picture of Symmetrodonta

Credit
Laikayiu
Licence
CC BY-SA 3.0
Commercial use
the licence allows it

No 3D scan of Symmetrodonta was found in MorphoSource and Sketchfab.

Smithsonian Open Access was not reached for this taxon, so this list is what the others held rather than everything there is.

The description on this site

Licence
CC BY-SA 4.0

This is what the site found, which is not the same as what exists.

Keep going

What may have been alongside itAllotheria through timeFormations of the Late JurassicThe world it lived on

Occurrence data from the Paleobiology Database, CC BY 4.0. (Simpson 1925)