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La morfología de Palaeospondylus muestra afinidad con los antepasados tetrápodos

Tatsuya Hirasawa^1,2, Yuzhi Hu³, Kentaro Uesugi⁴

¹Department of Earth and Planetary Science, Graduate School of Science, the University of Tokyo, Tokyo, Japan. hirasawa@eps.s.u-tokyo.ac.jp.

|May 25, 2022

Resumen

Palaeospondylus gunni, un fósil enigmático, se revela como un sarcopterygiano y probablemente un tetrápodo de tallo. Sus características únicas sugieren la evolución heterocrónica en la raíz de los tetrápodos, aclarando su posición evolutiva.

Área de la Ciencia:

Paleontología
Evolución de los vertebrados
Anatomía comparada

Sus antecedentes:

Palaeospondylus gunni, descubierto en 1890, es un fósil enigmático del período Devónico Medio.
Su posición filogenética ha permanecido incierta debido a características morfológicas inusuales.
La dificultad para comparar Palaeospondylus con los morfotipos conocidos de vertebrados ha obstaculizado la clasificación.

Objetivo del estudio:

Para aclarar la posición filogenética de Palaeospondylus gunni.
Para determinar las relaciones evolutivas de Palaeospondylus dentro de los vertebrados.
Investigar las implicaciones del desarrollo y la evolución de la morfología única de Palaeospondylus.

Principales métodos:

Para el análisis detallado del esqueleto se empleó la tomografía microcomputada de rayos X sincrotrón (SR-μCT).
Se realizaron análisis filogenéticos utilizando datos morfológicos, comparando a Palaeospondylus con tetrápodos conocidos.
Examen microscópico de elementos esqueléticos centrados en la histología ósea y las estructuras celulares.

Principales resultados:

Palaeospondylus es identificado como un sarcopterygian, muy probablemente un tetrápodo de tallo.
Su esqueleto comprende elementos endosqueléticos con lacunas de condrocitos hipertrofiados, osteoides y hueso pericondral limitado.
El neurocráneo, a pesar de carecer de dientes y huesos dérmicos, muestra un parecido con Eusthenopteron y Panderichthys, colocando a Palaeospondylus filogenéticamente entre ellos.

Conclusiones:

Palaeospondylus exhibe una combinación única de características, incluido un esqueleto cartilaginoso y apéndices emparejados ausentes.
Estos rasgos también se encuentran en las larvas de tetrápodos de corona, lo que sugiere plasticidad en el desarrollo.
El estudio revela una evolución heterocrónica inesperada en el origen de los tetrápodos, con Palaeospondylus proporcionando información clave.

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