mammaliaformes

Morganucodon (“Glamorgan tooth”)

… is an early mammaliaform genus that lived during the late Triassic period. It first appeared about 205 million years ago. Unlike many other early mammals, Morganucodon is well represented by abundant and well preserved, though in the vast majority of cases disarticulated, material.

Morganucodon was a small, plantigrade animal. The tail was moderately long. According to Kemp (2005) “the skull was 2-3 cm in length and a presacral body length of about 10 cm [4 inches]. In general appearance it would have looked like a shrew or mouse”. There is evidence that it had specialized glands used for grooming, which may indicate that, like more advanced mammaliaformes, it had fur…

(read more: Wikipedia)

illustration by FunkMonk

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Lythronax’s news from the world of news, the first in the longest damn time!

There have been quite a few interesting critters from the last two months, and I’ll be posting them one by one. First off, we have two new docodonts, a clade of mammal relatives that are distinguished by their complex molars. This group has traditionally been known to be a highly diverse lineage - from ground-dwelling rodent-like animals to beaver-like swimmers (Castorocauda). But two new discoveries have expanded the ecological diversity of this group:

  • Agilodocodon scansorius looks like a squirrel or basal primate, and it certainly fulfilled a similar arboreal niche. Its hands and feet are adapted for climbing, and its teeth, with spade-like tips, are remarkably similar to New World monkeys like spider monkeys, howler monkeys, and marmosets. This suggests that Agilodocodon probably ate tree bark and sap. While docodonts have thus far been carnivorous-omnivorous or piscivorous (Castorocauda, that cheeky bugger), Agilodocodon is the first omnivorous docodont with a mainly herbivorous diet. It can’t resist the occasional insect, however, as it’s doing in the reconstruction up top that’s inspired by a large treeshrew. Image of the fossil from the Science paper here.
  • Docofossor brachydactylus has the claws of a mole, and it probably occupied a similar niche. Its entire body plan suggests a lifestyle of digging - its robust teeth are similar to golden moles and marsupial moles, its powerful limbs were kept abducted and sprawled, it has a reduction in the number of digits in the same way as golden moles, and its ribcage has become more barrel-like. Of course, the temptation to color Docofossor after a golden mole - the Cape golden mole - was just too strong. The Science paper can be found here.

I don’t believe that I’ve posted another pencil-colored design before; there will be a few more of them down the line.

Actualmente, los mamíferos son los tetrápodos (vertebrados con cuatro patas) dominantes. A pesar de que existen grupos con un mayor número de especies (como el de las aves), los mamíferos ostentan una mayor diversidad morfológica. Los hay en todos lados, en tierra, en el aire y en el agua. Los hay grandes como la ballena azul de hasta 30 metros y pequeños como el murciélago nariz de cerdo de Kitti de apenas 33 milímetros de longitud.

Los mamíferos verdaderos evolucionaron durante el Jurásico temprano. En muchos sitios encontraremos que aparecieron durante el Triásico tardío, pero eso no es del todo cierto. La evolución de los mamíferos fue gradual y sus características principales aparecieron como un mosaico en toda una variedad de pequeñas criaturas peludas desde el Triásico tardío. A estas formas transicionales las denominamos mammaliaformes (con forma de mamífero) y de ellas surgió el grupo principal de mamíferos que contiene a todos los ancestros que comparte un ornitorrinco y un humano.

Se asumía que los molares complejos habían sido una invención de los mamíferos verdaderos, pero se acaba de descubrir una especie de mammaliaforme que posee los molares más avanzados de su época. A esta nueva criatura se le denominó Megaconus mammaliaformis y aunque se le ha apodado la “ardilla jurásica”, en realidad su nicho ecológico era más semejante al de un armadillo o un damán que al de una ardilla. Este pequeñín se encontró completo y muestra una impresión del pelaje que cubrió su cuerpo. Si este bicho no es un mamífero, esto indica que el pelo evolucionó antes que los mamíferos y que no es una innovación evolutiva, sino un carácter heredado.

El estudio de este y otros mammaliaformes revelará más sobre el origen de nuestro grupo, el origen de los portadores de mamas.

FUENTE:
Zhou, C. F., Wu, S., Martin, T., & Luo, Z. X. (2013). A Jurassic mammaliaform and the earliest mammalian evolutionary adaptations. Nature, 500(7461), 163-167.